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  • Articles  (74)
  • dispersion  (38)
  • biocompatibility  (35)
  • Electronic structure and strongly correlated systems
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  • Technology  (74)
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  • Articles  (74)
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  • 1
    Electronic Resource
    Electronic Resource
    Multifunctional Biocompatible Membrane and Its Application to Fabricate A Miniaturized Glucose Sensor with Potential for Use In Vivo (1999)
    Springer
    Biomedical microdevices 1 (1999), S. 155-166 
    Details
    ISSN: 1572-8781
    Keywords: MPC ; BMA ; AMPS ; biocompatibility ; cellulose triacetate ; diffusion-limiting effect ; glucose sensor ; needle type ; glucose oxidase ; serum ; whole blood
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract A multifunctional membrane with biocompatibility, diffusion-limiting effect, and the ability to curtail the responses of an H2O2 electrode to ascorbate and urate was prepared. It was composed of MB, AB, and CTA, where MB is the copolymer of 2-methacryloyloxyethyl phosphorylcholine (MPC) and n-butylmethacrylate (BMA), AB is the copolymer of acrylamide-2-methylpropane sulfonic acid (AMPS) and BMA, CTA is cellulose triacetate. Investigation of the biocompatibility of this membrane showed that, compared with CTA, relatively few platelets bound to it. The membrane was coated onto the working electrode of a needle-type glucose sensor on which immobilized glucose oxidase membrane has been coated. The sensor did not respond to ascorbate and urate at their concentration normally encountered in blood. Its response was not inhibited by metal ions in blood at usual concentration. The sensor exhibited superior thermostability in addition to a rapid response (〈90 seconds in batch operation), good reproducibility (RE〈5%), good stability (more than 36 hours continuously in heparinized whole blood), and a wide dynamic range (5–650 mg/dl glucose). The sensor was used to determine glucose in serum. The data obtained from the sensor showed good agreement with that from a clinical autoanalyzer (R=0.973).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009952625595
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  • 2
    Electronic Resource
    Electronic Resource
    A computerized technique for measuringin-situ concentrations during miscible displacements in porous media (1992)
    Springer
    Transport in porous media 7 (1992), S. 127-145 
    Details
    ISSN: 1573-1634
    Keywords: Miscible displacement ; dispersion ; in-situ concentration measurement ; computerized data acquisition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract A technique for measurement of thein-situ concentration in an unconsolidated porous medium has been developed. The method involves measurement of electrical conductivityin-situ, under dynamic conditions, for flow involving brine of differing concentrations, at selected locations along the porous medium and relating it to the brine strength. Data acquisition and analysis is carried out using a Hewlett — Packard micro-computer and its interface. A user-friendly software was designed and developed for the system. The measurement technique was evaluated by studying the effect of brine concentration, brine flow rate, and by conducting miscible displacements experiment. The experimentally measured dispersion coefficients for the porous medium agreed closely with the value predicted by the correlation available in the literature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00647393
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  • 3
    Electronic Resource
    Electronic Resource
    Analytic Solution to a Problem of Seepage in a Chequer-Board Porous Massif (1997)
    Springer
    Transport in porous media 28 (1997), S. 109-124 
    Details
    ISSN: 1573-1634
    Keywords: seepage ; conductivity ; double-periodic structure ; advection ; dispersion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract A study is made of steady two-dimensional seepage in a porous massif composed by a double-periodic system of ‘white’ and ‘black’ chequers of arbitrary conductivity. Rigorous matching of Darcy's flows in zones of different conductivity is accomplished. Using the methods of complex analysis, explicit formulae for specific discharge are derived. Stream lines, travel times, and effective conductivity are evaluated. Deflection of marked particles from the ‘natural’ direction of imposed gradient and stretching of prescribed composition of these particles enables the elucidation of the phenomena of transversal and longitudinal dispersion. A model of pure advection is related with the classical one-dimensional vective dispersion equation by selection of dispersivity which minimizes the difference between the breakthrough curves calculated from the two models.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006505908858
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  • 4
    Electronic Resource
    Electronic Resource
    Waves in partially saturated porous media (1992)
    Springer
    Transport in porous media 9 (1992), S. 25-37 
    Details
    ISSN: 1573-1634
    Keywords: Waves ; dispersion ; shock tube ; gas bubbles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The propagation of compressional waves in a porous medium is investigated in case the pore liquid contains a small volume fraction of gas. The effect of oscillating gas bubbles is taken into account by introducing a frequency-dependent fluid bulk modulus, which is incorporated in the Biot theory. Using a shock tube technique, new experimental data are obtained for a porous column subjected to a pressure step wave. An oscillatory behaviour is observed, consisting of two distinct frequency bands, which is predicted by the theoretical analysis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01039623
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  • 5
    Electronic Resource
    Electronic Resource
    On the transient non-Fickian dispersion theory (1996)
    Springer
    Transport in porous media 23 (1996), S. 107-124 
    Details
    ISSN: 1573-1634
    Keywords: solute transport ; Fick's law ; dispersion ; dispersivity ; equation of motion ; non-Fickian dispersion equation ; scale effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The Fickian dispersion equation is the basic relationship used to describe the nonconvective mass flux of a solute in a porous medium. This equation prescribes a linear relationship between the dispersive mass flux and the concentration gradient. An important characteristic of the Fickian relationship is that it is independent of the history of dispersion (e.g. the time rate of change of the dispersion flux). Also, the dispersivities are supposed to be medium constants and invariant with temporal and spatial scales of observation. It is believed that in general these restrictions do not hold. A number of authors have proposed various alternative relationships. For example, differential equations have been employed that prescribe a relationship between the dispersion flux and its time and space derivatives. Also, stochastic theories result in integro-differential equations in which dispersion tensor grow asymptotically with time or distance. In this work, three different approaches, which lead to three different non-Fickian equations with a transient character, are discussed and their primary features and differences are highlighted. It is shown that an effective dispersion tensor defined in the framework of the transient non-Fickian theory, grows asymptotically with time and distance; a result which also follows from stochastic theories. Next, principles of continuum mechanics are employed to provide a solid theoretical basis for the non-Fickian transient dispersion theory. The equation of motion of a solute in a porous medium is used to provide a rigorous derivation of various dispersion relationships valid under different conditions. Under various simplifying assumptions, the generalized theory is found to agree with the conventional Fickian theory as well as several other non-Fickian relationships found in the literature. Moreover, it is shown that for nonconservative solutes, the traditional dispersion tensor is affected by the rate of mass exchange of the solute.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00145268
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  • 6
    Electronic Resource
    Electronic Resource
    Two-dimensional adaptive Eulerian-Lagrangian method for mass transport with spatial velocity distribution (1988)
    Springer
    Transport in porous media 3 (1988), S. 473-489 
    Details
    ISSN: 1573-1634
    Keywords: Advection ; dispersion ; particles ; characteristics ; finite-element ; continuous fluid velocity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract A Eulerian-Lagrangian scheme is used to solve the two-dimensional advection-dispersion equation. Concentration and its partial differential operator are decomposed into advection and dispersion terms. Thus, advection is formally decoupled from dispersion and solved by continuous forward particle tracking. Dispersion is handled by implicit finite elements on a fixed Eulerian grid. Translation of steep gradients of concentration in advection-dominated flow regimes, is done without numerical distortion. Continuous spatial distribution of velocities are evaluated by using Galerkin's approach in conjunction with Darcy's law based on hydraulic input data from each element. The method was implemented on coarse FE grid with linear shape functions, demonstrating no over/under shooting and practically no numerical dispersion. Simulations, covering a wide range of Peclet numbers, yield high agreement with analytic and practical results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00138612
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  • 7
    Electronic Resource
    Electronic Resource
    The effect of dispersion model on the linear stability of miscible displacement in porous media (1989)
    Springer
    Transport in porous media 4 (1989), S. 85-96 
    Details
    ISSN: 1573-1634
    Keywords: Stability ; linear stability analysis ; miscible displacement ; aspect ratio ; mobility control ; dispersion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Chang and Slattery (1986, 1988b) introduced a simplified model of dispersion that contains only two empirical parameters. The traditional model of dispersion (Nikolaevskii, 1959; Bear, 1961; Scheidegger, 1961; de Josselin de Jong and Bossen, 1961; Peaceman, 1966; Bear, 1972) has three empirical parameters, two of which can be measured in one-dimensional experiments while the third, the transverse dispersivity, must be measured in experiments in which a two-dimensional concentration profile develops. It is found that nearly the same linear stability behavior results from using either model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00134743
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  • 8
    Electronic Resource
    Electronic Resource
    The influence of free convection on soil salinization in arid regions (1996)
    Springer
    Transport in porous media 23 (1996), S. 275-301 
    Details
    ISSN: 1573-1634
    Keywords: free convection ; through flow ; vadoze zone ; salinization ; dispersion ; multigrid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Evaporation of groundwater in a region with a shallow water table and small natural replenishment causes accumulation of salts near the ground surface. Water in the upper soil layer becomes denser than in the depth. This is a potentially unstable situation which may result in convective currents. When free convection takes place, estimates of the salinity profile, salt precipitation rate, etc., obtained within the framework of a 1-D (vertical) model fail. Very simplified model of the process is proposed, in which the unsaturated zone is represented by a horizontal soil layer at a constant water saturation, and temperature changes are neglected. The purpose of the model is to obtain a rough estimate of the role of natural convection in the salinization process. A linear stability analysis of a uniform vertical flow is given, and the stability limit is determined numerically as a function of evaporation rate, salt concentration in groundwater, and porous medium dispersivity. The loss of stability corresponds to quite realistic Rayleigh numbers. The stability limit depends in nonmonotonic way on the evaporation rate. The developed convective regime was simulated numerically for a 2-D vertical domain, using finite volume element discretization and FAS multigrid solver. The dependence of the average salt concentration in the upper layer on the Rayleigh number was obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00167100
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  • 9
    Electronic Resource
    Electronic Resource
    Influence of capillary pressure, adsorption and dispersion on chemical flood transport phenomena (1996)
    Springer
    Transport in porous media 24 (1996), S. 275-296 
    Details
    ISSN: 1573-1634
    Keywords: chemical flooding ; ternary ; immiscible ; surfactant ; numerical simulation ; interfacial tension ; phase behavior ; miscibility ; capillarity ; numerical grid ; adsorption ; dispersion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract This is the second of two joint papers which study the influence of several physical properties on the transport phenomena in chemical flooding. To that aim, we use a previously reported ternary two-phase model into which representative physical properties have been incorporated as concentration-dependent functions. Physical properties such as phase behavior, interfacial tensions, residual saturations, relative permeabilities, phase viscosities and wettability have been analyzed in the first paper. In this paper, we discuss the influence of capillary pressure, adsorption of the chemical component onto the rock and dispersion. Although arising from different phenomenological sources, these transport mechanisms show some similar effects on concentration profiles and on oil recovery. They are studied for systems with different phase behavior. A numerical analysis is also presented in order to determine the relevance of the number of grid blocks taken in the discretization of the differential equations. This numerical analysis provides useful guidelines for the selection of the appropriate numerical grid in each type of displacement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00154094
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  • 10
    Electronic Resource
    Electronic Resource
    Saltwater transport in a heterogeneous formation: A case study (1988)
    Springer
    Transport in porous media 3 (1988), S. 217-256 
    Details
    ISSN: 1573-1634
    Keywords: Salinity ; advection ; dispersion ; aquifers ; flow model ; transport model ; simulation ; sea water ; connate water ; leakage
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Historical information of the hydraulic and salinity aspect, detailed geological information, and information on the physical characteristics of the different layers comprising the formation, are needed for simulating the saltwater transport process in aquifers. In most simulation studies of field situations, there is an inadequacy of data and the modeller has to make justifiable assumptions to analyze a particular situation in order to provide an insight into the problem. A quasi-three-dimensional solute transport model is used to analyze the saltwater encroachment phenomena in aquifers underlying the City of Bangkok; first by calibrating the model's performance with available historical data and then by assessing the extent of future saltwater encroachment with the implementation of the regulatory pumpage to be followed in order to restrict the alarming rate of land subsidence. Model simulation indicates a substantial reduction in the rate of encroachment of the saltwater front with a reduction of pumpage after 1987.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00235330
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  • 11
    Electronic Resource
    Electronic Resource
    An adaptive domain decomposition method for simulation of transport in porous media (1988)
    Springer
    Transport in porous media 3 (1988), S. 549-562 
    Details
    ISSN: 1573-1634
    Keywords: Adaptive mesh ; finite element method ; dispersion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract A Galerkin finite element method is used along with a self-adaptive strategy of domain discretisation to model dispersion in an axisymmetric cylindrical porous medium. A solution strategy is proposed based on the use of a Gear scheme for the time stepping and partial vectorisation of the code. The domain is highly discretised in the area of the sharp transient front, while the remainder is coarsely discretised. The area covered by the fine mesh is determined by the value of the local concentration gradients. Numerical results are presented for the one and two dimensional cases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00959102
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  • 12
    Electronic Resource
    Electronic Resource
    On the Influence of Pore-Scale Dispersion in Nonergodic Transport in Heterogeneous Formations (1998)
    Springer
    Transport in porous media 30 (1998), S. 57-73 
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    ISSN: 1573-1634
    Keywords: groundwater ; nonergodic transport ; dispersion ; heterogeneous formations ; hydrogeology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Flow of an inert solute in an heterogeneous aquifer is usually considered as dominated by large-scale advection. As a consequence, the pore-scale dispersion, i.e. the pore scale mechanism acting at scales lower than that characteristic of the heterogeneous field, is usually neglected in the computation of global quantities like the solute plume spatial moments. Here the effect of pore-scale dispersion is taken into account in order to find its influence on the longitudinal asymptotic dispersivity D11we examine both the two-dimensional and the three-dimensional flow cases. In the calculations, we consider the finite size of the solute initial plume, i.e. we analyze both the ergodic and the nonergodic cases. With Pe the Péclat number, defined as Pe=Uλ/D, where U, λ, D are the mean fluid velocity, the heterogeneity characteristic length and the pore-scale dispersion coefficient respectively, we show that the infinite Péclat approximation is in most cases quite adequate, at least in the range of Péclat number usually encountered in practice (Pe 〉 102). A noteworthy exception is when the formation log-conductivity field is highly anisotropic. In this case, pore-scale may have a significant impact on D11, especially when the solute plume initial dimensions are not much larger than the heterogeneities' lengthscale. In all cases, D11 appears to be more sensitive to the pore-scale dispersive mechanisms under nonergodic conditions, i.e. for plume initial size less than about 10 log-conductivity integral scales.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006548529015
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  • 13
    Electronic Resource
    Electronic Resource
    A Solute Transport in Stratified Media (1998)
    Springer
    Transport in porous media 31 (1998), S. 133-143 
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    ISSN: 1573-1634
    Keywords: transport ; solute ; flux-averaged concentration ; stratification ; conductivity ; distribution ; arrival time ; dispersion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Two-dimensional and steady solute transport in a stratified porous formation is analysed under assumption that the effect of pore-scale dispersion is negligible. The longitudinal dispersion produced as a result of the vertical variation of hydraulic conductivity is analysed by averaging the variability of a solute flux concentration and conductivity. The evolution of the solute flux concentration is expressed with respect to the correlated variable, that is the travel (arrival) time τ at a fixed location and the averaging procedure is constructed to satisfy the boundary condition where the inlet concentration is a known function of time. In such a statement, a velocity-averaged solute flux concentration is described by a conventional dispersion model (CDM) with a dispersion coefficient which is a function of the arrival time. It is demonstrated that such CDM satisfies the assumption that hydraulic conductivity of the layers is gamma distributed with the parameter of distribution which is chosen to represent a reasonable value of the field scale solute dispersion. The overall behaviour of the model is illustrated by several examples of two-dimensional mass transport.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006557032656
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  • 14
    Electronic Resource
    Electronic Resource
    Comment on ‘fractal and superdiffusive transport and hydrodynamic dispersion in heterogeneous porous media’, by Muhammad Sahimi (1995)
    Springer
    Transport in porous media 21 (1995), S. 175-188 
    Details
    ISSN: 1573-1634
    Keywords: diffusion ; dispersion ; percolation ; fractals ; scaling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Two fundamental questions regarding the application of percolation theory to transport in porous media are addressed. First, when ‘critical path’ arguments (based on a sufficiently wide spread of microscopic transition rates) are invoked (in analogy to the case of transport in disordered semiconductors) to justify the application of percolation theory to the determination of relevant transport properties, then for long time scales (compared to the inverse of the ‘critical’ percolation rate), the fractal structure of the ‘critical’ path is relevant to transport, but not at short time scales. These results have been demonstrated concretely in the case of disordered semiconductors, and are in direct contradiction to the claims of the review. Second, the relevance of deterministic or stochastic methods to transport has been treated heretofore by most authors as a question of practicality. But, at least under some conditions, concrete criteria distinguish between the two types of transport. Percolative (deterministic) transport is temporally reproducible and spatially inhomogeneous while diffusive (stochastic) transport is temporally irreproducible, but homogeneous, and a cross-over from stochastic to percolative transport occurs when the spread of microscopic transition rates exceeds 4–5 orders of magnitude. It is likely that such conditions are frequently encountered in soil transport. Moreover, clear evidence for deterministic transport (although not necessarily percolative) exists in such phenomena as preferential flow. On the other hand, the physical limitation of transport to (fractally connected) pore spaces within soils (analogously to transport in metal-insulator composites) can make transport diffusive on a fractal structure, rather than percolative.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00613755
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  • 15
    Electronic Resource
    Electronic Resource
    A Fickian diffusion model for the spreading of liquid plumes infiltrating in heterogeneous media (1996)
    Springer
    Transport in porous media 24 (1996), S. 1-33 
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    ISSN: 1573-1634
    Keywords: unsaturated flow ; large-scale averaging ; dispersion ; high-resolution numerical simulations ; NAPL spills
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Infiltration of water and non-aqueous phase liquids (NAPLs) in the vadose zone gives rise to complex two- and three-phase immiscible displacement processes. Physical and numerical experiments have shown that ever-present small-scale heterogeneities will cause a lateral broadening of the descending liquid plumes. This behavior of liquid plumes infiltrating in the vadose zone may be similar to the familiar transversal dispersion of solute plumes in single-phase flow. Noting this analogy we introduce a mathematical model for ‘phase dispersion’ in multiphase flow as a Fickian diffusion process. It is shown that the driving force for phase dispersion is the gradient of relative permeability, and that addition of a phase-dispersive term to the governing equations for multiphase flow is equivalent to an effective capillary pressure which is proportional to the logarithm of the relative permeability of the infiltrating liquid phase. The relationship between heterogeneity-induced phase dispersion and capillary and numerical dispersion effects is established. High-resolution numerical simulation experiments in heterogeneous media show that plume spreading tends to be diffusive, supporting the proposed convection-dispersion model. Finite difference discretization of the phase-dispersive flux is discussed, and an illustrative application to NAPL infiltration from a localized source is presented. It is found that a small amount of phase dispersion can completely alter the behavior of an infiltrating NAPL plume, and that neglect of phase-dispersive processes may lead to unrealistic predictions of NAPL behavior in the vadose zone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00175602
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  • 16
    Electronic Resource
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    A linear stability analysis for miscible displacements (1986)
    Springer
    Transport in porous media 1 (1986), S. 179-199 
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    ISSN: 1573-1634
    Keywords: Stability ; linear stability analysis ; miscible displacement ; dispersion ; mobility control
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract A linear stability analysis has been performed for a miscible displacement in a semi-infinite system of finite thickness and unbounded width. A more general description of dispersion has been adopted than those used by previous workers. It is shown that, when there is a step change in concentration and the mobility ratio is unfavorable, the displacement can be unstable at the injection boundary. But, if the concentration is changed sufficiently slowly with time at the entrance to the system, the displacement is stable to infinitesimal perturbations, no matter how unfavorable the mobility ratio. When the mobility ratio is favorable, the displacement is unconditionally stable.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00714691
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  • 17
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    Issues in flow and transport in heterogeneous porous media (1986)
    Springer
    Transport in porous media 1 (1986), S. 319-338 
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    ISSN: 1573-1634
    Keywords: heterogeneity ; dispersion ; saturated flow ; unsaturated flow
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract This invited lecture enumerates various categories of flow and transport in heterogeneous media with particular reference to this Symposium. Specific attention is given to five topics within these categories. (1) We explore the compounding of spatially variable local permeability K to produce an apparent permeability K * on a scale large compared with that of variation of K. An inverse method generates and analyzes flow systems with K spatially periodic in two and three dimensions. (2) Physical arguments indicate that apparent hydraulic properties of an unsaturated composite medium may not represent any conceivable mean of the properties of the component media. (3) Conventionally, buried holes are thought to stay empty during generally unsaturated soil-water flow. The hole, however, acts as an obstacle to flow so that water may seep through it. The larger the hole the more likely this will happen. (4) Dispersion in heterogeneous porous systems with no maximum scale of variation is explored using a Lagrangian mode of analysis. (5) Comments are offered on ‘geostatistics’ and its application to heterogeneous soils and aquifers.
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    URL: http://dx.doi.org/10.1007/BF00208041
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  • 18
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    Advective and dispersive mixing in stratified formations (1995)
    Springer
    Transport in porous media 18 (1995), S. 231-243 
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    ISSN: 1573-1634
    Keywords: Stratified formations ; kinematic mixing ; dispersion ; random fields
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The mixing process in fluid flow is presented as the bending and stretching of material lines or filaments. A mixing exponent, which quantifies their specific rate of stretching, is defined and analyzed for the case of groundwater flow though stratified formations characterized by a Gaussian autocovariance function. The analysis is performed for purely advective mixing as well as for advective-dispersive mixing. The mixing exponent was found to be proportional to the variance of hydraulic conductivity and inversely proportional to the correlation scale of hydraulic conductivity and to the pore-level dispersion coefficient.
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    URL: http://dx.doi.org/10.1007/BF00616933
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  • 19
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    Scaling mixing during miscible displacement in heterogeneous porous media (1991)
    Springer
    Transport in porous media 6 (1991), S. 607-626 
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    ISSN: 1573-1634
    Keywords: dispersion ; dispersivity ; heterogenity ; miscible ; porous media ; scaling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract This paper discusses scaling of mixing during miscible flow in heterogeneous porous media. In large field systems dispersivity appears to depend on system length due to heterogeneities. Three types of scaling are discussed to investigate the heterogeneous effects. Dimensional analysis of mixing during flow through geometerically scaled heterogeneous models is illustrated using measured dispersion. Fractal analysis of mixing in statistically scaled heterogeneous porous media is discussed. Analog scaling of pressure transients in heterogeneous porous media is suggested as an in-situ method of estimating dispersion.
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    URL: http://dx.doi.org/10.1007/BF00137852
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  • 20
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    Modelling fluid flow in cross-bedded sections (1993)
    Springer
    Transport in porous media 12 (1993), S. 143-159 
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    ISSN: 1573-1634
    Keywords: Heterogeneity ; layers ; displacement ; numerical simulation ; flow in porous media ; dispersion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Beadpack experiments and numerical simulations have been carried out to study flow displacements, effluent profiles and streamline patterns for layered systems with flow not parallel to the layers. The effects of layer thickness, permeability contrast, angle of layer to flow direction, mobility ratio and flood rate have been examined. Each of these parameters influence the displacement profiles, and disperse the flood front. Such real effects must be considered when subsuming reservoir heterogeneities in average reservoir parameters in simulation studies, or interpreting core tests.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00616977
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  • 21
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    Fractal and superdiffusive transport and hydrodynamic dispersion in heterogeneous porous media (1993)
    Springer
    Transport in porous media 13 (1993), S. 3-40 
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    ISSN: 1573-1634
    Keywords: Diffusion ; dispersion ; percolation ; fractals ; scaling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract We review and discuss diffusion and hydrodynamic dispersion in a heterogeneous porous medium. Two types of heterogeneities are considered. One is percolation disorder in which a fraction of the pores do not allow transport to take place at all. In the other type, the permeabilities of various regions of the pore space are fractally distributed with long-range correlations. Both systems give rise to unusual transport in which the mean square displacement 〈r 2(t)〉 of a particle grows nonlinearly with time. Depending on the heterogeneities and the mechanism of diffusion and disperison, we may havefractal transport in which 〈r 2〉 growsslower than linearly with time, orsuperdiffusive transport in which 〈r 2〉 growsfaster than linearly with time. We show that percolation models can give rise to both types of transport with scale-dependent transport coefficients such as diffusivity and dispersion coefficients, which are consistent with many experimental observations.
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    A theory of macrodispersion for the scale-up problem (1993)
    Springer
    Transport in porous media 13 (1993), S. 97-122 
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    ISSN: 1573-1634
    Keywords: Scale up ; dispersion ; porous media ; random field
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Dispersion is the result, observable on large length scales, of events which are random on small length scales. When the length scale on which the randomness operates is not small, relative to the observations, then classical dispersion theory fails. The scale up problem refers to situations in which randomness occurs on all length scales, and for which classical dispersion theory necessarily fails. The purpose of this article is to present non-Fickian, theories of dispersion, which do not assume a scale separation between the randomness and the observed consequences, and which do not assume a single length scale. Porous media flow properties are heterogeneous on all length scales. The geological variation on length scales below the observational length scale can be regarded as unknown and unknowable, and thus as a random variable. We develop a systematic theory relating scaling behavior of the geological heterogeneity to the scaling behavior of the fluid dispersivity. Three qualitatively distinct regimes (Fickian, non-Fickian and nonrenormalizable) are found. The theory gives consistent answers within several distinct analytic approximations, and with numerical simulation of the equations of porous media flow. Comparison to field data is made. The use of Kriging to generate constrained ensembles for conditional simulation is discussed.
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    An experimental investigation of dispersion in layered porous media (1994)
    Springer
    Transport in porous media 15 (1994), S. 15-30 
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    ISSN: 1573-1634
    Keywords: Experiment ; dispersion ; layered heterogeneity ; permeability ; averaging ; permutation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Experiments were run in three linear, homogeneous, nonuniform porous media constructed in lucite columns using spherical glass beads. The columns were also joined end to end to create an in series layered heterogeneous porous media. Each column, all combinations of columns and several permutations were studied with a factorial experimental design to determine the effects of porosity, permeability, velocity, length, and column order upon dispersion. Attempts to predict the heterogeneous results from the homogeneous results were made, and a statistical regression based on the factorial design was calculated. Results showed that no simple averaging procedure accurately predicted the heterogeneous results. The statistical regression showed permeability, velocity, viscosity, length and column order to be significant.
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    URL: http://dx.doi.org/10.1007/BF01046156
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    A LGA model for dispersion in heterogeneous porous media (1994)
    Springer
    Transport in porous media 17 (1994), S. 19-32 
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    ISSN: 1573-1634
    Keywords: LGA model ; heterogeneous porous media ; miscible displacement ; dispersion ; tracer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The lattice gas automaton (LGA) model proposed in the previous paper is applied to the problem of simulating dispersion and mixing in heterogeneous porous media. We demonstrate here that tracer breakthrough profiles and longitudinal dispersion coefficients can be computed for heterogeneous porous media.
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    A stream tube model for miscible flow (1995)
    Springer
    Transport in porous media 18 (1995), S. 245-261 
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    ISSN: 1573-1634
    Keywords: Porous media ; miscible flow ; tracer ; dispersion ; convective flow ; stochastic ; stream tube ; continuous time random walk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract A simple theoretical model is described for deriving a 1-dimensional equation for the spreading of a tracer in a steady flow at the field scale. The originality of the model is to use a stochastic appoach not in the 3-dimensional space but in the 1-D space of the stream tubes. The simplicity of calculation comes from the local relationship between permeability and velocity in a 1-D flow. The spreading of a tracer front is due to local variations in the cross-sectional area of the stream tubes, which induces randomness in travel time. The derived transport equation is averaged in the main flow direction. It differs from the standard dispersion equation. The roles of time and space variables are exchanged. This result can be explained by using the statistical theory of Continuous Time Random Walk instead of a standard Random Walk. However, the two equations are very close, since their solutions have the same first and second moments. Dispersivity is found to be equal to the product of the correlation length by the variance of the logarithm of permeability, a result similar to Gelhar's macrodispersion.
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    A stream tube model for miscible flow (1995)
    Springer
    Transport in porous media 18 (1995), S. 263-282 
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    ISSN: 1573-1634
    Keywords: Porous media ; dispersion ; miscible flow ; heterogeneities ; stochastic ; stream tube ; layered ; fractal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Large-scale dispersion in heterogeneous porous media is studied by using a simple model based on stochastic calculation of convective flow in a bundle of stream tubes. The advantage of this approach is that there is a local relationship between velocity and permeability in the 1-dimensional space of the stream tubes. Dispersion is due to the variation in stream tube cross-section, related to the permeability field. First, the arrival times of the tracer in the stream tubes are related to the stochastic properties of the permeability field (variance and covariance). Then, transport equations are derived from the moments of the arrival times. The results agree with more complicated studies. For a permeability field with long-range correlation, the transport equation is not unique. It depends on the assumptions involving moments higher than two. Assuming a Gaussian shape for the tracer flux leads to equations similar to the ones obtained in previous studies of time-dependent dispersivity. Without this approximation, the equation is non-local (integrodifferential) and leads to a memory effect. In the last part of this paper, the general results are illustrated with several correlation functions for the permeability field: purely random, exponential and power law covariance, and perfectly layered media.
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    Experimental investigation of solute transport in large, homogeneous and heterogeneous, saturated soil columns (1995)
    Springer
    Transport in porous media 18 (1995), S. 283-302 
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    ISSN: 1573-1634
    Keywords: Solute transport experiments ; heterogeneous media ; dispersion ; scale-dependency
    Source: Springer Online Journal Archives 1860-2000
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    Notes: Abstract Laboratory tracer experiments were conducted to investigate solute transport in 12.5-m long, horizontally placed soil columns during steady saturated water flow. Two columns having cross-sectional areas of 10×10cm2 were used: a uniformly packed homogeneous sandy column and a heterogeneous column containing layered, mixed, and lenticular formations of various shapes and sizes. The heterogeneous soil column gradually changed, on average, from coarse-textured at one end to fine-textured at the other end. NaCl breakthrough curves (BTC's) in the columns were measured with electrical conductivity probes inserted at 50- or 100-cm intervals. Observed BTC's in the homogeneous sandy column were relatively smooth and sigmoidal (S-shaped), while those in the heterogeneous column were very irregular, nonsigmoidal, and exhibited extensive tailing. Effective average pore-water velocities (v eff) and dispersion coefficients (D eff) were estimated simultaneously by fitting an analytical solution of the convection-dispersion equation to the observed BTC's. Velocity variations in the heterogeneous medium were found to be much larger than those in the homogeneous sand. Values of the dispersivity,α=D eff/v eff, for the homogeneous sandy column ranged from 0.1 to 5.0 cm, while those for the heterogeneous column were as high as 200cm. The dispersivity for transport in both columns increased with travel distance or travel time, thus exhibiting scale-dependency. The heterogeneous soil column also showed the effects of preferential flow, i.e., some locations in the column showed earlier solute breakthrough than several locations closer to the inlet boundary. Spatial fluctuations in the dispersivity could be explained qualitatively by the particular makeup of the heterogeneities in the column.
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    Dispersion in consolidated sandstone with radial flow (1995)
    Springer
    Transport in porous media 19 (1995), S. 37-66 
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    ISSN: 1573-1634
    Keywords: dispersion ; sandstone ; radial flow
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract This paper presents some experimental and theoretical results for dispersion processes occurring in consolidated Berea sandstone with radial flow geometry. A comprehensive review of the derivation and application of several analytical solutions is also presented. The Galerkin finite element method is applied to solve the advection-dispersion equation for unidimensional radial flow. Individual and combined effects of mechanical dispersion and molecular diffusion are examined using velocity-dependent dispersion models. Comparison of simulated results with experimental data is made. The effect of flow rates is examined. The results suggest that a linear dispersion model,D=αu, whereD is the dispersion coefficient,u the velocity andα a constant, is not a good approximation despite its wide acceptance in the literature. The most suitable mathematical formulation is given by an empirical form of $$D = D_0 + \mathop \alpha \limits^` u^m$$ , whereD ois the molecular diffusion coefficient. For the range of Péclet number (Pe=vd/D m,wherev is the characteristic velocity,d the characteristic length andD mthe molecular diffusion coefficient in porous media) examined (Pe=0.5 to 285), a power constant ofm=1.2 is obtained which agrees with the value reported by some other workers for the same regime. From the results of experiments and numerical modelling, the effect of mobility ratios (defined as the ration of viscosities of displaced and displacing fluids) on dispersion is found to be negligible, provided that the ratio is favourable.
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    Dispersion and Attenuation of Surface Waves in a Fluid-Saturated Porous Medium (1997)
    Springer
    Transport in porous media 29 (1997), S. 207-223 
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    ISSN: 1573-1634
    Keywords: dispersion ; attenuation ; surface waves ; Rayleigh wave ; Love wave
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract An investigation is conducted of propagation of surface waves in a porous medium consisting of a microscopically incompressible solid skeleton in which a microscopically incompressible liquid flows within the interconnected pores, and particularly the case where the solid skeleton deforms linear elastically. The frequency equations of Rayleigh- and Love-type waves are derived relating the dependence of wave numbers, being complex quantities, on frequency, as a result those waves are dispersive as well as inhomogeneous. Nevertheless, the amplitudes of both surface waves attenuate along the surface of the porous medium, whereas they decay exponentially receding from the surface of the medium.
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    URL: http://dx.doi.org/10.1023/A:1006590119031
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    Experiments on Solute Transport in Aggregated Porous Media: Are Diffusions Within Aggregates and Hydrodynamic Dispersion Independent? (1997)
    Springer
    Transport in porous media 29 (1997), S. 281-307 
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    ISSN: 1573-1634
    Keywords: solute transport ; nonequilibrium ; heterogeneous porous media ; dispersion ; diffusion ; experiments ; modelling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Two region models for solute transport in porous media assume that hydrodynamic dispersion in mobile water and solute diffusion within immobile water regions are independent. Experimental and theoretical results for transport through a macropore indicate that hydrodynamic dispersion and solute exchange are interdependent. Experiments were carried out to investigate this problem for a column packed with spherical porous aggregates. The effective diffusion coefficient of a tracer within the agreggates was determined from specific experiments. The dispersivity of the bed was determined from experiments carried out with a column filled with nonporous beads. We took advantage of the dependence of hydrodynamic dispersion on density ratios between the invading and displaced solutions to obtain a set of breakthrough curves corresponding to situations where the diffusion coefficient remains constant, whereas the dispersivity varies. Simulations reproduce correctly the experiments. Small discrepancies are noted that can be corrected either by increasing the dispersion coefficient or by fitting the external mass transfer coefficient. Increased dispersion coefficients probably reveal a modification of Taylor dispersion due to solute exchange. The fitted external mass transfer coefficients are close to the values obtained with classical correlations of the chemical engineering literature.
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    Stability of vertical miscible displacements with developing density and viscosity gradients (1988)
    Springer
    Transport in porous media 3 (1988), S. 277-297 
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    ISSN: 1573-1634
    Keywords: Stability ; linear stability analysis ; miscible displacement ; aspect ratio ; mobility control ; dispersion
    Source: Springer Online Journal Archives 1860-2000
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    Notes: Abstract Viscous fingering and gravity tonguing are the consequences of an unstable miscible displacement. Chang and Slattery (1986) performed a linear stability analysis for a miscible displacement considering only the effect of viscosity. Here the effect of gravity is included as well for either a step change or a graduated change in concentration at the injection face during a downward, vertical displacement. If both the mobility ratio and the density ratio are favorable (the viscosity of the displacing fluid is greater than the viscosity of the displaced fluid and, for a downward vertical displacement, the density of the displacing fluid is less than the density of the displaced fluid), the displacement will be stable. If either the mobility ratio or the density ratio is unfavorable, instabilities can form at the injection boundary as the result of infinitesimal perturbations. But if the concentration is changed sufficiently slowly with time at the entrance to the system, the displacement can be stabilized, even if both the mobility ratio and the density ratio are unfavorable. A displacement is more likely to be stable as the aspect ratio (ratio of thickness to width, which is assumed to be less than one) is increased. Commonly the laboratory tests supporting a field trial use nearly the same fluids, porous media, and displacement rates as the field trial they are intended to support. For the laboratory test, the aspect ratio may be the order of one; for the field trial, it may be two orders of magnitude smaller. This means that a laboratory test could indicate that a displacement was stable, while an unstable displacement may be observed in the field.
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    An analysis of the viability of polymer flooding as an enhanced oil recovery technology (1988)
    Springer
    Transport in porous media 3 (1988), S. 591-618 
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    ISSN: 1573-1634
    Keywords: Polymer flooding ; viscous fingering ; multiphase flow ; dispersion
    Source: Springer Online Journal Archives 1860-2000
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    Notes: Abstract The concept of improving oil recovery through polymer flooding is analysed. It is shown that while the injection of a polymer solution improves reservoir conformance, this beneficial effect ceases as soon as one attempts to push the polymer solution with water. Once water injection begins, the water quickly passes through the polymer creating a path along which all future injected water flows. Thus, the volume of the polymer slug is important to the process and an efficient recovery would require that the vast majority of the reservoir be flooded by polymer. It is also shown that the concept of grading a polymer slug to match the mobilities of the fluids at the leading and trailing edges of a polymer slug does not work in a petroleum reservoir. While this process can supply some additional stability to the slug, it is shown that for the purposes of enhanced oil recovery this additional stability is not great enough to be of any practical use. It is found that in this case the instability has simply been hidden in the interior of the slug and causes the same sort of instability to occur as was the case for the uniform slug.
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    Tracer Dispersion in Rough Open Cracks (1998)
    Springer
    Transport in porous media 32 (1998), S. 97-116 
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    ISSN: 1573-1634
    Keywords: dispersion ; anomalous diffusion ; Taylor dispersion ; roughness ; self-affine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Tracer dispersion is studied in an open crack where the two rough crack faces have been translated with respect to each other. The different dispersion regimes encountered in rough-wall Hele-Shaw cell are first introduced, and the geometric dispersion regime in the case of self-affine crack surfaces is treated in detail through perturbation analysis. It is shown that a line of tracer is progressively wrinkled into a self-affine curve with an exponent equal to that of the crack surface. This leads to a global dispersion coefficient which depends on the distance from the tracer inlet, but which is still proportional to the mean advection velocity. Besides, the tracer front is subjected to a local dispersion (as could be revealed by point measurements or echo experiments) very different from the global one. The expression of this anomalous local dispersion coefficient is also obtained.
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    Automaton Simulations of Dispersion in Porous Media (1998)
    Springer
    Transport in porous media 32 (1998), S. 187-198 
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    ISSN: 1573-1634
    Keywords: diffusion ; dispersion ; miscible ; automaton
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract A thermodynamic lattice gas (automaton) model is used to simulate dispersion in porous media. Simulations are constructed at two distinctly different scales, the pore scale at which capillary models are constructed and large scale or Darcy scale at which probabilistic collision rules are introduced. Both models allow for macroscopic (pore scale) phase separation. The pore scale models clearly show the effect of pore structure on dispersion. The large scale (mega scale) simulations indicate that when the pressure difference between the displacing phase and displaced phase is properly chosen (representing the average pressure gradient between the phases). The simulation results are consistent with both theoretical predictions and experimental observations.
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    Stochastic-Perturbation Analysis of a One-Dimensional Dispersion-Reaction Equation: Effects of Spatially-Varying Reaction Rates (1998)
    Springer
    Transport in porous media 32 (1998), S. 139-161 
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    ISSN: 1573-1634
    Keywords: dispersion ; reaction ; perturbation theory ; stochastic modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract We carry out a stochastic-perturbation analysis of a one-dimensional convection–dispersion-reaction equation for reversible first-order reactions. The Damköhler number, Da, is distributed randomly from a distribution that has an exponentially decaying correlation function, controlled by a correlation length, ξ. Zeroth- and first-order approximations of the dispersion coefficient, D are computed from moments of the residence-time distribution obtained by solving a one-dimensional network model, in which each unit of the network represents a Darcy-level transport unit, and the solution of the transfer function in zeroth- and first-order approximations of the transport equation. In the zeroth-order approximation, the dispersion coefficient is calculated using the convection–dispersion-reaction equation with constant parameters, that is, perturbation corrections to the local equation are ignored. This zeroth-order dispersion coefficient is a linear function of the variance of the Damköhler number, 〈(ΔDa)2〉. A similar result was reported in a two-dimensional network simulation. The zeroth-order approximation does not give accurate predictions of mixing or spreading of a plume when Damköhler numbers, Da ≪ 1 and its variance, 〈(ΔDa)2〉 〉 0.25 〈Da2〉. On the other hand, the first-order theory leads to a dispersion coefficient that is independent of the reaction parameters and to equations that do accurately predict mixing and spreading for Damköhler numbers and variances in the range √〈(ΔDa)2〉/〈Da〉≤0.3
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    On the Modelling of Generalized Taylor–Aris Dispersion in Chromatographs via Multiple Scales Expansions (1999)
    Springer
    Transport in porous media 36 (1999), S. 307-339 
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    ISSN: 1573-1634
    Keywords: dispersion ; chromatography ; porous media ; adsorption ; homogenization ; multiple scales expansions.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract This paper is devoted to the computation of effective equations for the transport of a solute in a chromatograph. We focus our attention on models that retain dispersion effects. A chromatograph is a biporous periodic heterogeneous medium, made up of macropores, and of small porous adsorbing crystals that have a retention effect on the solute. We use the method of multiple scales expansions. Various macroscopic behaviours appear, according to the respective orders of magnitude of the dimensionless characteristic parameters: Peclet number in the macropores, ratio of the characteristic time of diffusion in the macropores to the characteristic time of diffusion in the crystals, adsorption coefficient. Dispersion occurs for a Peclet number of order ε−1. We then discuss the effective behaviour of the solute, with respect to the orders of magnitude of the other characteristic parameters. To our knowledge, most of the models are new. Our modelling is not restricted to chromatographs. It applies to various situations of physic and chemical engineering: fixed bed reactors, catalytic cracking, ground water for instance.
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    Experimental Investigation of Mixing in Aperiodic Heterogeneous Porous Media: Comparison with Stochastic Transport Theory (1999)
    Springer
    Transport in porous media 37 (1999), S. 169-182 
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    ISSN: 1573-1634
    Keywords: experiment ; aperiodic heterogeneity ; dispersion ; stochastic modeling.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract An electrochemical technique was used to measure concentration distributions in an aperiodic heterogeneous model for comparison with a stochastic transport theory. Four identical columns, each filled with a homogeneous distribution of glass beads, were threaded together to create a single model with aperiodic heterogeneity. The layers in the model were arranged in different ways providing 24 realizations of the permeability distribution. Comparisons between experimental moment data and moments of simulated mean concentration distributions showed that the model was not able to accurately predict experimentally observed mixing behavior.
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    Influence of the viscoelastic properties of the respiratory system on the energetically optimum breathing frequency (1993)
    Springer
    Annals of biomedical engineering 21 (1993), S. 489-499 
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    ISSN: 1573-9686
    Keywords: Work of breathing ; Inspiratory pressure-time integral ; Respiratory modeling ; Dogs ; Humans
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract We hypothesized that the viscoelastic properties of the respiratory system should have significant implications for the energetically optimal frequency of breathing, in view of the fact that these properties cause marked dependencies of overall system resistance and elastance on frequency. To test our hypothesis we simulated two models of canine and human respiratory system mechanics during sinusoidal breathing and calculated the inspiratory work ( $$\dot W$$ ) and pressure-time integral (PTI) per minute under both resting and exercise conditions. The two models were a two-compartment viscoelastic model and a single-compartment model. Requiring minute alveolar ventilation to be fixed, we found that both models predicted almost identical optimum breathing frequencies. The calculated PTI was very insensitive to increases in breathing frequency above the optimal frequencies, while $$\dot W$$ was found to increase slowly with frequency above its optimum. In contrast, both $$\dot W$$ and PTI increased sharply as frequency decreased below their respective optima. A sensitivity analysis showed that the model predictions were very insensitive to the elastance and resistance values chosen to characterize tissue viscoelasticity. We conclude that the $$\dot W$$ criterion for choosing the frequency of breathing is compatible with observations in nature, whereas the optimal frequency predictions of the PTI are rather too high. Both criteria allow for a fairly wide margin of choice in frequency above the optimum values without incurring excessive additional energy expenditure. Furthermore, contrary to our expectations, the viscoelastic properties of the respiratory system tissues do not pose a noticeable problem to the respiratory controller in terms of energy expenditure.
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    The multiple-scale averaging and dynamics of dispersion-managed optical solitons (1999)
    Springer
    Journal of engineering mathematics 36 (1999), S. 163-184 
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    ISSN: 1573-2703
    Keywords: fiber optics ; nonlinear Schrödinger equation ; multiple scales ; dispersion ; solitons.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Technology
    Notes: Abstract Multiple-scale averaging is applied to the nonlinear Schrödinger equation with rapidly varying coefficients, and use the results to analyze pulse propagation in an optical fiber when a periodic dispersion map is employed. The effects of fiber loss and repeated amplification are taken into account by use of a coordinate transformation to relate the pulse dynamics in lossy fibers to that in equivalent lossless fibers. Second-order averaging leads to a general evolution equation that is applicable to both return-to-zero (soliton) and non-return-to-zero encoding schemes. The resulting equation is then applied to the specific case of solitons, and an asymptotic theory for the pulse dynamics is developed. Based upon the theory, a simple and effective design of two-step dispersion maps that are advantageous for wavelength-division-multiplexed soliton transmission is proposed. Theuse of these specifically designed dispersion maps allows simultaneous minimization of dispersive radiation in several different channels.
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    Adaptive two-step methods for semidiscretized wave equations (1995)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 38 (1995), S. 3855-3887 
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    ISSN: 0029-5981
    Keywords: Adaptive two-step methods ; periodicity ; dispersion ; dissipation ; P-stability ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Adaptive two-step direct integration methods are constructed for the integration of second-order semidiscrete evolution equations possessing oscillatory solutions. The methods are based on a class of adaptive multistep methods for a semilinear test model whose frequency is known. They are constructed following the notion of diagonally implicit RK-methods by using efficient rational approximations to cos v, v ≥ 0. Our interest is centered on the dispersion (or phase errors) of the dominant components in the numerical oscillations when these methods are applied to a linear homogeneous test model. Two-step methods which have high order of dispersion (up to 12), whereas the algebraic order is relatively low (2 or 4), are derived. Applications of these methods to linear as well as non-linear test models and to semidiscretized hyperbolic equations reveal a good behaviour with regard to error propagation when they are compared with other conventional methods.
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    Long-term ingrowth and apposition of porous hydroxylapatite implants (1997)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 36 (1997), S. 560-563 
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    ISSN: 0021-9304
    Keywords: bone ; implant ; hydroxylapatite ; biocompatibility ; histomorphometric implant saturation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Bone implant materials are often used to fill in bone gaps that frequently result from orthognathic and craniofacial reconstruction. The substrate hydroxylapatite (HA) is commonly implanted into the bone voids, resulting from these conditions due to its established biocompatibility and osteoconductive properties. The porous structure of HA provides a three-dimensional guideline for fibrovascular ingrowth, facilitating the process that ultimately results in the deposition of new bone. Porous HA (Interpore, 200) implants were implanted in the mandible or maxilla of nine humans and removed after 14-30 months (19.1-month mean). There was no evidence of an inflammatory response. The sample composition and apposition against the implant were determined using point counting and a digitizing tablet and software. Percent ingrowth in available space (%IAS) was defined as %Bone/(%Bone + %Void). A new measure of implant saturation (%IAS - %Apposition of bone) was established to help determine the fundamental manner in which long-term HA implants incorporate bone. In the mean, the samples were composed of 27% bone, 21% void, and 53% implant. The apposition percentages averaged 60% bone, 16% void, and 24% soft tissue. The %IAS averaged 58%, and implant saturation averaged -3%, indicating that a near-balance between the implant and surrounding bone has been established. © 1997 John Wiley & Sons, Inc. J Biomed Mater Res, 36, 560-563, 1997.
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    Osteogenic cell cytotoxicity and biomechanical strength of the new ceramic Diopside (1997)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 37 (1997), S. 100-107 
    Details
    ISSN: 0021-9304
    Keywords: Diopside ; biocompatibility ; osteogenic cell (MC3T3-E1) ; biomechanical strength ; apatite wollastonite-containing glass-ceramic (AWGC) ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Diopside was prepared by sintering a powder compact composed of CaMgSi2O6 at 1573K for 2 h. In order to clarify the biocompatibility of Diopside, the cytotoxicity of Diopside against the osteogenic cell line MC3T3-E1 and the bone-Diopside interface strength were examined. On both the 14th and 21st days of incubation of MC3T3-E1 cells with Diopside, ALP activities were not significantly lower than those of the CTRL. TEM photographs of MC3T3-E1 on Diopside after 14 days of incubation showed active secretion of crystals from osteoblast-like cells. Scanning electron microscopic analysis showed that the cells on Diopside formed multiple cell layers similar to those on the CTRL both 14 and 21 days after incubation. These results showed that Diopside had no cytotoxic effect on MC3T3-E1. The pulling test showed that failure loads of Diopside were significantly lower than those of AWGC. Histologically, there was no fibrous tissue or foreign body reaction at the bone interface. SEM-EPMA showed that Diopside had attached to the bone via a calcium-phosphorus layer. SEM back-scattered electron imaging showed that the Diopside plate had degraded to a porous state 12 weeks after implantation. These findings indicate that Diopside is a biodegradable ceramic. © 1997 John Wiley & Sons, Inc. J Biomed Mater Res, 37, 100-107, 1997.
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    Assessment of wrought ASTM F1058 cobalt alloy properties for permanent surgical implants (1997)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 38 (1997), S. 229-234 
    Details
    ISSN: 0021-9304
    Keywords: cobalt alloy ; implant ; biocompatibility ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The behavior of the ASTM F1058 wrought cobalt-chromium-nickel-molybdenum-iron alloy (commonly referred to as Elgiloy® or Phynox) is evaluated in terms of mechanical properties, magnetic resonance imaging, corrosion resistance, and biocompatibility. The data found in the literature, the experimental corrosion and biocompatibility results presented in this article, and its long track record as an implant material demonstrate that the cobalt superalloy is an appropriate material for permanent surgical implants that require high yield strength and fatigue resistance combined with high elastic modulus, and that it can be safely imaged with magnetic resonance. © 1997 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater) 38: 229-234, 1997
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    Fibroblast growth factor-2 alters the effect of eroding polylactide-polyglycolide on osteogenesis in the bone chamber (1998)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 40 (1998), S. 567-576 
    Details
    ISSN: 0021-9304
    Keywords: biocompatibility ; erodible polymer ; fibroblast growth factor-2 ; osteogenesis ; polylactide-polyglycolide ; porous ingrowth ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The effects of recombinant human fibroblast growth factor-2 (rhFGF-2) in the presence of eroding 50:50 poly(DL-lactide-co-glycolide) (PDLLG) on acute bone healing were studied in the optical bone chamber (BCI). BCIs were loaded with disks of PDLLG surrounded by one of four rhFGF-2 doses. Fifty-two female rabbit right tibias were implanted. Commencing the third week post implantation (W3) healing in the BCI compartment was observed weekly, using intravital microscopy, until W8. The doses were: unloaded, loaded with polymer only, and polymer plus 0.5, 1.0, and 10 μg rhFGF-2. Videotaped and photographed bone images were measured and analyzed using a frame-grabber digitizing system. Comparison with controls revealed that ossification rates were significantly above normal in rabbits loaded with polymer plus any of the rhFGF-2 doses. Comparison with polymer-only BCIs showed that PDLLG plus any of the three rhFGF-2 doses was linked with ossification rates significantly higher than baseline. The results indicated that FGF-2 in the dose range studied effectively can overcome the retarding effects of eroding polymer on ossification that has been reported by this laboratory. Interpretation of the retarding effects of the polymer disks, although consistent with previously studied washer-shaped devices of the same material, was complicated by a difference in erosion rate. This result supports the notion that erodible device geometry is a major factor in determining biocompatibility and must be considered in the design of carriers. Accordingly, programming of dose specificity for delivering a given polypeptide cytokine to a given host site must allow for the inhibitory effects of an eroding carrier and the influence of device geometry on these effects and erosion. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 567-576, 1998.
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    Grafting of PEO to polymer surfaces using electron beam irradiation (1998)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 40 (1998), S. 153-163 
    Details
    ISSN: 0021-9304
    Keywords: PEO ; electron beam irradiation ; polymer surface modification ; biocompatibility ; XPS ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: A new method was developed for binding poly(ethylene oxide) (PEO) to polymer surfaces that involves the use of electron beam irradiation in two steps. In the first, methacrylic acid was grafted and polymerized to a polymer surface, changing it from hydrophobic to hydrophilic. Exposure of this surface to aqueous PEO solutions resulted in strong hydrogen bonding of the PEO, which was covalently grafted in a second radiation step. The PEO grafts were stable; they could not be removed with extensive washing with water, soaking in basic solution, or gentle mechanical scraping. Both monolayers and multilayers of PEO were formed. The density of the monolayers were found to have little dependence on the molecular weight or concentration of the PEO solution; multilayers could be controlled by varying the viscosity of the PEO solution and the method of application. The PEO-grafted monolayers were tested for their ability to prevent protein adsorption of cytochrome-c, albumin, and fibronectin. Monolayers of star PEO were the most effective, at best showing a 60% decrease in adsorption from untreated controls. One million molecular weight linear PEO monolayers were almost as effective as star monolayers, and 35,000 g/mol linear PEO was bound too closely to the surface, owing to its small size, to have much impact in preventing protein adsorption. The reason for the continued protein adsorption was believed to be due to a close grafting of the PEO to the surface, as well as the grafted methacrylic acid chains being long enough to extend through the PEO monolayer, thus being accessible on the surface. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 153-163, 1998.
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    Biocompatibility analysis of different biomaterials in human bone marrow cell cultures (1998)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 40 (1998), S. 301-306 
    Details
    ISSN: 0021-9304
    Keywords: biocompatibility ; biomaterials ; human bone marrow cell culture ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: A cell culture system for biocompatibility testing of hip implant materials is described. Human bone marrow cells have been chosen because these cells are in direct contact with the biomaterial after implantation in situ. The sensitivity of this method is evaluated for materials which are already being used as implants in humans and animal, e.g., hydroxyapatite (HA) ceramic, pure titanium, and ultra-high-molecular-weight polyethylene (UHMWPE). As indicative parameters of biocompatibility primary cell adherence, cell number, cell proliferation, production of extracellular matrix, cell vitality, and cell differentiation are described. After 2 weeks in culture, obvious differences between the biomaterials with respect to the indicative parameters could be observed. Cell numbers were greatest on the HA specimens. In the case of titanium alloys, we observed a decreased number of cells. The production of extracellular matrix was high for the HA ceramics but reduced for titanium specimens. The polymers allowed only a few adherent cells and showed no signs of extracellular matrix production. The results can be correlated astonishingly well to animal experiments and clinical experiences. Therefore, we suggest that this cell culture system seems to be a useful tool for biocompatibility testing of bone implantation materials. It also helps reduce animal experiments. With the help of flow cytophotometry, we analyzed the influence of biomaterials on large numbers of cells with respect to differentiation. There were similar populations of T cells and monocytes on all specimens tested. Extended B-cell and granulocyte populations, however, were observed with titanium and UHMWPE. Most osteocalcin-containing cells adhered to the HA ceramics. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 301-306, 1998.
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    In vitro biocompatibility assessment of a nickel-titanium alloy using electron microscopy in situ end-labeling (EM-ISEL) (1998)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 41 (1998), S. 154-161 
    Details
    ISSN: 0021-9304
    Keywords: nickel-titanium ; biocompatibility ; genotoxicity ; immunogold labeling ; electron microscopy ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Shape memory nickel-titanium (NiTi) alloys are potential candidates for biomedical applications. However, their equiatomic composition (50 wt% Ni) is controversial, and concerns have been raised about their biocompatibility level because of the carcinogenicity potential. The relative in vitro genotoxicity of NiTi therefore was evaluated and compared to commercially pure titanium (cpTi), 316L stainless steel (SS 316L), and positive and negative controls. To do so, human peripheral blood lymphocytes were cultured in semiphysiological medium that previously had been exposed to the biomaterials. The electron microscopy in situ end-labeling (EM-ISEL) assay then was performed in order to provide quantification of in vitro chromatin DNA single-stranded breaks (SSBs). Chromosomes and nuclei were harvested and exposed to exonuclease III, which amplifies DNA lesions at 3′ ends of breaks. After random priming, incorporation of biotin-dUTP was labeled by immunogold binding, which then was detected using electron microscopy. Cellular chromatin exposed to the positive control demonstrated a significantly stronger immunogold labeling than when it was exposed to NiTi, cpTi, SS 316L extracts, or the untreated control. Moreover, gold particle counts, whether in the presence of NiTi, cpTi, or the negative control medium, were not statistically different. NiTi genocompatibility therefore presents promising prescreening results towards its biocompatibility approval. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 41, 154-161, 1998.
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    Biocompatibility of poly(etherurethane urea) containing dehydroepiandrosterone (1998)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 41 (1998), S. 192-201 
    Details
    ISSN: 0021-9304
    Keywords: polyurethane ; dehydroepiandrosterone ; biocompatibility ; biostability ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Poly(etherurethane urea) (PEUU) elastomers, with their broad range of mechanical properties and high biocompatibility, are used clinically for medical applications. However, the possibility exists for the ether soft segment of PEUU to degrade in long-term uses. To retard degradation, antioxidants that scavenge reactive oxygen intermediates are added. In this study, we incorporated dehydroepiandrosterone (DHEA), which functions by the alternate mechanism of modulating or down-regulating adherent macrophage activity, to retard the biodegradation of PEUUs. Biocompatibility of PEUU samples containing 1% DHEA, 5% DHEA, and 5% vitamin E (α-tocopherol) by weight were studied in vivo and in vitro. The biocompatibility was initially evaluated by examination of the inflammatory cellular exudate. Compared to PEUU without additives and PEUU with 5% vitamin E, the addition of 5% DHEA to PEUU caused a decrease in the total leukocyte exudate concentration at 4 days. The addition of 5% DHEA also caused lower macrophage adhesion and FBGC formation compared to the other materials at 7 days. Despite these short-term effects, the biocompatibility at later time points (14, 21, and 70 days) was similar for all materials. Transmission infrared analysis of the materials revealed that more than 70% of the DHEA had leached out of the samples by 3 days implantation. Furthermore, through attenuated total reflectance Fourier transform analysis and scanning electron microscopy, it was determined that unlike vitamin E, DHEA did not enhance long-term PEUU biostability. The effect of DHEA on inflammatory cell activity appeared to be dose dependent, with improved biocompatibility in vivo for higher loading levels of DHEA, but the overall effect was limited owing to the rapid diffusion of the water-soluble DHEA from the PEUU. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 41, 192-201, 1998.
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    Microgrooved subcutaneous implants in the goat (1998)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 42 (1998), S. 634-641 
    Details
    ISSN: 0021-9304
    Keywords: biocompatibility ; subcutaneous implant ; implant surface ; microgrooves ; in vivo ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: We investigated the behavior of microgrooved implants in soft tissue using polystyrene implantable disks, either smooth or microgrooved (1-10 μm) on both sides. The implants were placed subcutaneously in a goat for 1, 4, or 12 weeks. Light and transmission electron microscopy showed that fibrous capsule formation around the implants was fairly uniform. After 1 week the implants were covered with a fibrous capsule about 80 μm thick. The collagen matrix was loose, and many inflammatory cells were present. After 4 weeks the matrix was more dense and contained many newly formed blood vessels. At the implant surface a layer of inflammatory cells about 10 μm thick had accumulated. Finally, after 12 weeks the matrix had densified. One cellular layer of inflammatory cells was present at the implant surface. We carried out histomorphometric measurements of capsule thickness, inflammatory layer thickness, and the number of blood vessels. Capsule thickness appeared not to decrease with time. Further, these measurements showed that there were no differences in tissue reaction between smooth and microgrooved implants. On the basis of our observations, we suggest that 1 μm deep and 1-10 μm wide microgrooves do not influence tissue response around polystyrene implants in soft tissue. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 42, 634-641, 1998.
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    Biocompatibility response to modified Baerveldt glaucoma drains (1998)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 43 (1998), S. 99-107 
    Details
    ISSN: 0021-9304
    Keywords: biocompatibility ; biomaterials ; collagen ; glaucoma drains ; wound healing ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Glaucoma implants are designed to increase fluid outflow from the eye in order to decrease intraocular pressure and prevent damage to the optic nerve. The implant consists of a silicone tube that is inserted into the anterior chamber at one end and is attached at the other end to a silicone plate that is sutured to the outside of the globe beneath the conjunctiva. The glaucoma “implant” becomes a “drain” over the first 3 to 6 postoperative weeks as the silicone plate is enclosed by a fibrous capsule that allows a space to form into which fluid can drain and from which fluid can be absorbed by the surrounding tissues. Ideally, the size and thickness of the capsule (the filtering bleb) that surrounds the plate is such that the amount of fluid that passes through the capsule is identical to the amount of fluid produced by the eye at an intraocular pressure of 8 to 14 mmHg. The most common long-term complication of these implants is failure of the filtering bleb 2 to 4 years after surgery due to the formation of a thick fibrous capsule around the device. Micromovement of the smooth drainage plate against the scleral surface may be integral to the mechanism of glaucoma implant failure by stimulating low-level activation of the wound healing response, increased collagen scar formation, and increased fibrous capsule thickness. To test this hypothesis, we modified seven Baerveldt implants by adding porous cellular ingrowth material to the posterior surface of the drainage plate. Seven modified and five unmodified implants were placed in adult rabbit eyes. After 6 months, we found that the fibrous capsule around the modified implants was significantly thinner than the capsule surrounding the unmodified implants (p 〈 0.05), particularly on the surface between the porous ingrowth material and the sclera (p 〈 0.05). Although type I collagen predominated in the fibrous capsules around both types of implants, the amount of type III collagen in the capsules around the modified implants was significantly less than the amount around the unmodified implants (p 〈 0.05). We believe that these data suggest a reduction in the wound healing response to the modified implants, with greater stability of capsule thickness. Long-term studies are needed to verify that the stability of the capsules around the modified implants persists over a period of years, in which case this type of modification may prove useful in prolonging the functional life of these devices in the surgical treatment of glaucoma. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater) 43: 99-107, 1998
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    Culture materials affect ex vivo expansion of hematopoietic progenitor cells (1997)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 36 (1997), S. 347-359 
    Details
    ISSN: 0021-9304
    Keywords: hematopoietic cultures ; biocompatibility ; culture materials ; serum-free medium ; CD34+ cells ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Ex vivo expansion of hematopoietic cells is important for applications such as cancer treatment, gene therapy, and transfusion medicine. While cell culture systems are widely used to evaluate the biocompatibility of materials for implantation, the ability of materials to support proliferation of primary human cells in cultures for reinfusion into patients has not been addressed. We screened a variety of commercially available polymer (15 types), metal (four types), and glass substrates for their ability to support expansion of hematopoietic cells when cultured under conditions that would be encountered in a clinical setting. Cultures of peripheral blood (PB) CD34+ cells and mononuclear cells (MNC) were evaluated for expansion of total cells and colony-forming unit-granulocyte monocyte (CFU-GM; progenitors committed to the granulocyte and/or monocyte lineage). Human hematopoietic cultures in serum-free medium were found to be extremely sensitive to the substrate material. The only materials tested that supported expansion at or near the levels of polystyrene were tissue culture polystyrene, Teflon perfluoroalkoxy, Teflon fluorinated ethylene propylene, cellulose acetate, titanium, new polycarbonate, and new polymethylpentene. MNC were less sensitive to the substrate materials than the primitive CD34+ progenitors, although similar trends were seen for expansion of the two cell populations on the substrates tested. CFU-GM expansion was more sensitive to substrate materials than was total cell expansion. The detrimental effects of a number of the materials on hematopoietic cultures appear to be caused by protein adsorption and/or leaching of toxins. Factors such as cleaning, sterilization, and reuse significantly affected the performance of some materials as culture substrates. We also used PB CD34+ cell cultures to examine the biocompatibility of gas-permeable cell culture and blood storage bags and several types of tubing commonly used with biomedical equipment. While many of the culture bag materials gave satisfactory results, all of the tubing materials severely inhibited total cell and CFU-GM expansion. Taken together, our results show that many materials approved for blood contact or considered biocompatible are not suitable for use with hematopoietic cells cultured in serum-free medium. As hematopoietic cultures are scaled up for a variety of clinical applications, it will be essential to carefully examine the biocompatibility of all materials involved. © 1997 John Wiley & Sons, Inc. J Biomed Mater Res, 36, 347-359, 1997.
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    Crosslinking density and resorption of dimethyl suberimidate-treated collagen (1997)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 36 (1997), S. 478-486 
    Details
    ISSN: 0021-9304
    Keywords: collagen ; crosslinking density ; glutaraldehyde ; dimethyl suberimidate ; biocompatibility ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Collagen was purified from bovine Achilles tendon and crosslinked with dimethyl suberimidate (DMS) and glutaraldehyde (GTA). Under optimal conditions, the shrinkage temperature (TS) was raised to 74°C for collagen crosslinked with DMS and to 80°C for those crosslinked with GTA. Crosslinking density measurements were done on the hydrothermally denatured collagen by the method based on the Flory-Rehner equation. GTA treatment was found to introduce more number of crosslinks than DMS. The maximum tension attained during heating (after shrinkage has occurred) was greater for GTA-treated collagen than for DMS and control. The control collagen membranes broke during heating (at 73°C), while for the crosslinked membranes the tension kept on increasing up to 100°C. The crosslinking density correlated well with the data determined from the in vitro and in vivo degradation studies. Uncrosslinked and DMS crosslinked collagen membranes were more susceptible to degradation by enzymes in vitro, while GTA-treated collagen was highly resistant to degradation. The biocompatibility of the collagen membranes was studied by subcutaneous implantation in rats. Uncrosslinked collagen membranes degraded within 14 days with the formation of granulation tissue. DMS crosslinked membranes degraded within 21 days and the area was replaced by numerous fibroblasts and newly formed collagen. No calcification was observed. For GTA-treated membranes, necrosis was observed after 7 days implantation and by 14 days the membrane had started to calcify. © 1997 John Wiley & Sons, Inc. J Biomed Mater Res, 36, 478-486, 1997.
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    Tissue response to fast-setting calcium phosphate cement in bone (1997)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 37 (1997), S. 457-464 
    Details
    ISSN: 0021-9304
    Keywords: biocompatibility ; bone ; calcium phosphate cement ; fast-setting ; hydroxyapatite ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Fast-setting calcium phosphate cement (FSCPC) is a promising new bioactive cement with a significantly short setting time (approximately 5-6 min) compared to conventional calcium phosphate cement (c-CPC) (30-60 min) at physiologic temperatures. As a result of its ability to set quickly, it is applicable in surgical procedures where fast setting is required. In this study, FSCPC was implanted in rat tibiae to evaluate tissue response and biocompatibility. FSCPC was converted to hydroxyapatite (HAP) in bone faster than c-CPC in the first 6 h. By 24 h, significant amounts of both FSCPC and c-CPC had been converted to HAP. The conversion of FSCPC into HAP further proceeded gradually, reaching 100% within 8 weeks. Infrared spectroscopic analysis disclosed the deposition of B-type carbonate apatite, which is a biological apatite contained in human dentin or bone, on the surface of the FSCPC. Histologically, FSCPC showed a tissue response similar to that of c-CPC. A slight inflammatory reaction was observed in the soft tissue apposed to both cements in the early period, and new bone was formed along the surface of the FSCPC at the adjacent bone. However, no resorption of either cement by osteoclasts or macrophages was observed within 8 weeks. We conclude that FSCPC is superior to c-CPC in clinical applications in oral and maxillofacial, orthopedic, plastic, and reconstructive surgery, since it shows a faster setting time and higher mechanical strength in the early period that are required in these surgical procedures, as well as osteoconductivity and excellent biocompatibility similar to that of c-CPC. © 1997 John Wiley & Sons, Inc. J Biomed Mater Res, 37, 457-464, 1997.
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    Histochemical and morphometric observations on the new tissue formed around mammary expanders coated with pyrolytic carbon (1998)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 40 (1998), S. 307-313 
    Details
    ISSN: 0021-9304
    Keywords: pyrolytic carbon ; mammary tissue expanders ; biocompatibility ; image analysis ; cellular proliferation ; MIB-1 ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The authors investigated tissue reaction around implanted silicone expanders, focusing on clinical morphological and morphometrical aspects. For use in breast reconstruction in post mastectomy patients, the surface of a medical-grade silicone elastomer was modified, without changing its bulk properties, by the addition of a pyrolytic carbon film. The presence of lipophagy, the number of foreign-body giant cells of histiocytic origin, and the number of MIB-1 positive nuclei (an index of proliferation for the reactive stromal population) were all seen to be influenced by the pyrolytic carbon coating. Indeed, all these parameters were lower in the membrane formed around Carbofilm™-coated expanders, thus demonstrating the effective protective properties of pyrolytic carbon coating. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 307-313, 1998.
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    In vitro sister chromatid exchange induced by glass ionomer cements (1998)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 40 (1998), S. 545-550 
    Details
    ISSN: 0021-9304
    Keywords: glass ionomer cement ; sister chromatid exchange ; genotoxicity ; biomaterial ; biocompatibility ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The genotoxicity of three glass ionomer cements used in dentistry, manufactured by American (Vitrebond™), Japanese (Fuji I™), and European (Ketac Cem™) companies were examined. The cement components were mixed according to the manufacturers' instructions and allowed to set for two defined times: 1 h or 1 week, before extracting them, as established by ISO standard 10993 part 12. To highlight sister chromatid exchange during mitosis, the extracts then were tested with human peripheral lymphocytes in the presence or absence of metabolic activation with S9 mix. The test performed was a genotoxicity test as provided for in standard EN 30993 part 3. Vitrebond™ resulted in direct genotoxicity and was strongly cytotoxic both in the extracts performed at 1 h and those at 1 week if they were allowed to set without photoactivation. Fuji I™ was noncytotoxic and showed only uncertain indirect genotoxicity in the extracts at 1 h; genotoxicity was not present in the extracts at 1 week. Ketac Cem™ cement was not genotoxic nor was it cytotoxic either at 1 h or 1 week. The authors concluded that of the three cements tested the European cement Ketac Cem™ passed one of the tests suggested by the EEC standard for assessing genotoxicy. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 545-550, 1998.
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    Perfluorodecalin modifies the pattern of cell arrangement and induces loss of neurites in rat retinal cultures (1998)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 41 (1998), S. 608-613 
    Details
    ISSN: 0021-9304
    Keywords: perfluorodecalin ; retina ; cell cultures ; biocompatibility ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Perfluorodecalin (PFD), a high specific weight, water-immiscible perfluorocarbon, previously studied as a potential blood substitute, now is used widely in the field of ophthalmic surgery as a tool for maneuvering intraocular tissues and as a short- or medium-term vitreous substitute. In in vivo experiments, several types of lesions in retinal tissue have been described in conjunction with long-term PFD treatment. To better evaluate the biological effects of PFD on retinal cells, we tested it on primary cultures of rat retina seeded on special cyclopore wells that allow the culture to be fed from the bottom side while the top side is in contact with the water-immiscible compound. We found that PFD changed the pattern of cell arrangement and induced loss of neurites. The modification of cell arrangement was less evident at the periphery of the wells where the amount of PFD, and consequently the pressure exerted, was lower. This observation suggests that the changes may be due more to a physical than to a toxic effect of PFD. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 41, 608-613, 1998.
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    Flow cytometry for assessing biocompatibility (1998)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 41 (1998), S. 649-656 
    Details
    ISSN: 0021-9304
    Keywords: flow cytometry ; cell culture ; biocompatibility ; biomaterials ; implants ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Flow cytometry (FCM) was examined as a possible procedure for measuring in vitro the biocompatibility of implant materials for orthopedic and dental surgery. The human osteoblast-like cell line MG63 was grown on hydroxyapatite (HA) and P2O5 glass-reinforced HA composite discs and compared with the same cells grown on polystyrene culture dishes. While morphological observation at the light and electron microscopic levels showed no major deleterious effects, FCM indicated that cell size was somewhat reduced, particularly by growth on the HA composite. Moreover, this material also appeared to delay the progression of the cells from the G0/G1 into the S phase of the cell cycle. In addition to this low level of inhibition of cell growth relative to control cultures, FCM analysis also demonstrated that the glass-reinforced HA caused some down-regulation of the expression of osteocalcin and fibronectin, two antigens which play a vital part in the integrity and function of bone and soft connective tissue, respectively. These results thus show, first, that although HA and the HA composite used in these experiments were generally biocompatible, they nevertheless had certain suboptimal effects on the cells; and second, that FCM could be a highly useful procedure for effectively screening and evaluating important biological responses to implant materials. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 41, 649-656, 1998.
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    Poly(α-hydroxyacids) for application in the spinal cord: Resorbability and biocompatibility with adult rat Schwann cells and spinal cord (1998)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 42 (1998), S. 642-654 
    Details
    ISSN: 0021-9304
    Keywords: biodegradable implants ; lactic and glycolic acid polymers ; biocompatibility ; Schwann cells ; axonal regeneration ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Future surgical strategies to restore neurological function in the damaged human spinal cord may involve replacement of nerve tissue with cultured Schwann cells using biodegradable guiding implants. We have studied the in vitro and in vivo degradability of various aliphatic polyesters as well as their effects on rat Schwann cells in vitro and on spinal cord tissue in vivo. In vitro, cylinders made of poly(D,L-lactic-co-glycolic acid) 50:50 (PLA25GA50) started to degrade at 7 days, compared with 28 days for cylinders made of poly(D,L-lactic acid) (PLA50). This faster degradation of PLA25GA50 was reflected by a much higher absorption of water. In vivo, after implantation of PLA25GA50 or PLA50 cylinders between the stumps of a completely transected adult rat spinal cord, the decrease in molecular weight of both polymers was similar to that found in vitro. In vitro degradation of poly(L-lactic acid) (PLA100) mixed with increasing amounts of PLA100 oligomers also was determined. The degradation rate of PLA100 mixed with 30% oligomers was found to be similar to that of PLA50. In vitro, PLA25GA50 and the breakdown products had no adverse effect on the morphology, survival, and proliferation of cultured rat Schwann cells. In vivo, PLA25GA50 cylinders were integrated into the spinal tissue 2 weeks after implantation, unlike PLA50 cylinders. At all time points after surgery, the glial and inflammatory response near the lesion site was largely similar in both experimental and control animals. At time points later than 1 week, neurofilament-positive fibers were found within PLA25GA50 cylinders or the remains thereof. Growth-associated protein 43, which is indicative of regenerating axons, was observed in fibers in the vicinity of the injury site and in the remains of PLA25GA50 cylinders. The results suggest that poly(α-hydroxyacids) are likely candidates for application in spinal cord regeneration paradigms involving Schwann cells. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 42, 642-654, 1998.
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    Biocompatibility of nickel-titanium shape memory metal and its corrosion behavior in human cell cultures (1997)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 35 (1997), S. 451-457 
    Details
    ISSN: 0021-9304
    Keywords: biocompatibility ; nitinol ; shape memory alloy ; corrosion ; human cell cultures ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Nickel-titanium alloy (Nitinol) is a metallic biomaterial that has a unique thermal shape memory, superelasticity, and high damping properties. Nitinol is potentially very useful in orthopedic surgery, for example. At present, there are not enough confirmative biocompatibility data available on Nitinol. The aim of our study was to clarify the primary cytotoxicity and corrosion rate of Nitinol in human cell cultures. Comparisons were made with stainless steel (Stst), titanium (Ti), composite material (C), and control cultures with no test discs. Human osteoblasts (OB) and fibroblasts (FB) were incubated for 10 days with test discs of equal size, 6 × 7 mm. The cultures were photographed and the cells counted. Samples from culture media were collected on days 2, 4, 6, and 8, and the analysis of metals in the media was done using flameless atomic absorption spectrophotometry. The proliferation of FB was 108% (Nitinol), 134% (Ti) (p 〈 0.02), 107% (Stst), and 48% (C)(p 〈 0.0001) compared to the control cultures. The proliferation of OB was 101% (Nitinol), 100% (Ti), 105% (Stst), and 54% (C) (p 〈 0.025) compared to the controls. Initially, Nitinol released more nickel (129-87 μg/L) into the cell culture media than Stst (7 μg/L), but after 2 days the concentrations were about equal (23-5 μg/L versus 11-1 μg/L). The titanium concentrations from both Nitinol and Ti samples were all 〈20 μg/L. We conclude that Nitinol has good in vitro biocompatibility with human osteoblasts and fibroblasts. Despite the higher initial nickel dissolution, Nitinol induced no toxic effects, decrease in cell proliferation, or inhibition on the growth of cells in contact with the metal surface. © 1997 John Wiley & Sons, Inc. J Biomed Mater Res, 35, 451-457, 1997.
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    Glass peek composite promotes proliferation and osteocalcin production of human osteoblastic cells (1997)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 36 (1997), S. 137-144 
    Details
    ISSN: 0021-9304
    Keywords: PEEK ; composite ; biocompatibility ; cell culture ; osteoblasts ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: An isoelastic intramedullary implant has been developed using a composite of polyetheretherketone and 10% random, chopped E-glass fibers (GPEEK). The effect of this novel material on human bone cells has not been defined. The objective of this study was to test whether GPEEK supported the proliferation of the human bone cell line MG63, which exhibits osteoblastlike characteristics. Cells (1 × 105/mL) were propagated on GPEEK discs with three different surface roughnesses (3, 6, and 9 μm) and on polystyrene plates, for comparison. The reaction of MG63 osteoblastlike cells to the GPEEK polymer composite was analyzed by determination of cell yield, osteocalcin production, and levels of alkaline phosphatase. The viable cells that were retrieved from the GPEEK discs of all three surface roughness had an approximate sixfold increase in number. Osteoblastic function of the cells, indicated by osteocalcin production, was unimpaired after a 5-day culture on the three surfaces of GPEEK. The highest level of osteocalcin was produced by osteoblastic cells propagated on GPEEK with a 9-μm surface roughness. The levels of alkaline phosphatase of these cells were similarly greater for the different degrees of surface roughness. Overall, this study demonstrates that GPEEK supported proliferation of osteoblastlike cells and provided a favorable environment for the continued production of osteocalcin in vitro. © 1997 John Wiley & Sons, Inc. J Biomed Mater Res, 36, 137-144, 1997.
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    Biocompatibility of alumina ceramic and polyethylene as materials for pivot bearings of a centrifugal blood pump (1997)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 36 (1997), S. 381-386 
    Details
    ISSN: 0021-9304
    Keywords: alumina ceramic ; polyethylene ; biocompatibility ; centrifugal blood pump ; pivot bearing ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The double pivot bearings in the Gyro C1E3 centrifugal blood pump incorporate a high-purity alumina (Al2O3) ceramic and an ultra-high-molecular-weight polyethylene (UHMWPE). This centrifugal pump has been developed as a completely sealless pump for long-term usage. The combination of Al2O3 and UHMWPE are the materials of choice for the acetabular bearing in artificial joints, which have proven to be clinically reliable for over 10 years. Previous studies have examined the biocompatibility of Al2O3 and UHMWPE as bulky implant materials. The present study investigated this material as a blood-contacting material using a standard assessment in vitro and in vivo analysis. The examined items were systemic toxicity, sensitization (guinea pig maximization test), cytotoxicity (elution test), mutagenicity (Ames test), direct contact hemolysis, and thrombogenicity. The studies were performed according to the United States Pharmacopoeia and published previous studies. The samples of both Al2O3 and UHMWPE demonstrated no differences from the negative controls in all tests. These findings indicate that both Al2O3 and UHMWPE are biocompatible materials for double-pivot bearings in the centrifugal blood pump. © 1997 John Wiley & Sons, Inc. J Biomed Mater Res, 36, 381-386, 1997.
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    Subconjunctival biocompatibility of a viscous bioerodable poly(ortho ester) (1998)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 39 (1998), S. 277-285 
    Details
    ISSN: 0021-9304
    Keywords: poly(ortho ester) ; biocompatibility ; degradation ; sterilization ; opthalmology ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The biocompatibility of a viscous poly(ortho ester) (POE) intended for prolonged intraocular drug delivery was studied. This hydrophobic and bioerodable carrier was subconjunctivally injected in rabbits and evaluated both clinically and histologically. To assess the cause of the triggered transient acute inflammatory reaction, the two monomers, the intermediate and final degradation products, and the local toxicity of different solvents used during the polymer preparation were tested. Since the two initial monomers and the intermediate degradation products induced only moderate inflammation, the main acute inflammatory reaction is attributed to the formation of an acidic by-product, which has been monitored in vitro by measuring the progressive decrease of the environmental pH. The influence of the sterilization procedure on tissue biocompatibility was established by comparing two polymers of similar molecular weight: one after γ-sterilization, and an aseptically synthesized one. The biocompatibility was significantly improved by avoiding irradiation of the polymer. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 277-285, 1998.
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    Modulation of the tissue reaction to biomaterials. II. The function of T cells in the inflammatory reaction to crosslinked collagen implanted in T-cell-deficient rats (1998)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 39 (1998), S. 398-406 
    Details
    ISSN: 0021-9304
    Keywords: T cells ; phagocytosis ; collagens ; biocompatibility ; biomaterials ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Unwanted tissue reactions are often observed resulting in events such as early resorption of the biomaterial, loosening of the implant, or a chronic (immunologic) response. From immunologic studies it is known that inflammatory reactions can be modulated by use of (anti)-growth factors or anti-inflammatory drugs. Before this can be employed with respect to biomaterials, the role of individual factors (humoral and cellular) has to be studied. In this part of the investigation, the role of T cells was studied by use of T-cell-deficient (nude) rats and control (AO) rats. Hexamethylenediisocyanate-crosslinked dermal sheep collagen (HDSC) was selected as the test material. The results showed that T cells or T cell-related factors played a prominent role in the attraction of macrophages and the formation of giant cells, their antigen presentation, and their phagocytotic capacity. As a consequence, degradation of HDSC was strongly delayed. This study also showed that infiltration of fibroblasts and creation of stromal areas in HDSC was restricted to areas subjected to degradation. However, in time, absence of T cells resulted in increased formation and maturation of autologous rat collagen. Results obtained suggest that the inflammatory reaction to biomaterials might be modulated by controlling T-cell activation. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 398-406, 1998.
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    Quantification of the inflammatory response in exudates to three polymers implanted in vivo (1998)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 39 (1998), S. 637-641 
    Details
    ISSN: 0021-9304
    Keywords: quantification of inflammatory reaction in vivo ; flow cytometry ; biocompatibility ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Flow cytometry was used to quantify an inflammatory reaction in vivo as a new approach to evaluating the biocompatibility of biomaterials. The exudate formed inside cylindrical tubes composed of polyvinyl chloride (PVC), silicone elastomer (SIL), or polyurethane (PU) implanted subcutaneously in the dorsal region of rats was collected over a 3-week period. The volume, number of cells, and concentration of fibrinogen were determined in the exudate for the three biomaterials. The exudate was analyzed using a flow cytometry technique after labeling of the leukocytes with a monoclonal anti-CD45 antibody. Fibrinogen rose progressively over the 3-week period for the three polymers. After the different leukocyte lines were identified in rat blood samples, their determination in the exudate revealed differences among the three biomaterials. At day 2, PVC induced a predominantly neutrophilic inflammatory reaction whereas PU and SIL gave a mixture of monocytes and neutrophils. At day 9, the aspect of the cytograms was different, but the identification of the subpopulations was still possible. At day 23, the number of cell events became too low to distinguish the subpopulations. An even more detailed approach might be possible using specific labeling for each leukocyte line to establish a comparison among the three biomaterials. Flow cytometry associated with histomorphometric assessment might provide a precise quantitative in vivo test for determining the biocompatibility of materials. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 637-641, 1998.
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    In vivo biocompatibility evaluation of nickel-titanium shape memory metal alloy: Muscle and perineural tissue responses and encapsule membrane thickness (1998)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 41 (1998), S. 481-488 
    Details
    ISSN: 0021-9304
    Keywords: biocompatibility ; Nitinol ; shape memory alloy ; tissue response ; perineural response ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Nickel-titanium shape memory alloy (Nitinol) has properties that could be very useful in surgical applications. Thermal shape memory, superelasticity, and high damping properties make such alloys behave differently compared to other implant metals. There has previously been a lack of sufficient evidence on the biocompatibility of Nitinol. The purpose of this study was to evaluate general soft tissue response and biocompatibility to Nitinol in vivo, and to clarify neural and perineural responses, previously unreported. Seventy-five rats were randomized into three groups. Test specimens were implanted into paravertebral muscle and near the sciatic nerve. A comparison was made between Nitinol, stainless steel, and Ti-6Al-4V. The animals were euthanized at 2, 4, 8, 12, and 26 weeks after implantation. General morphologic and histologic observations were made under light microscopy. Semiautomatic computerized image analysis was used to measure the encapsule membrane thickness around the implants. The muscular tissue response to Nitinol was clearly nontoxic, regardless of the time period. The overall inflammatory response to Nitinol was very similar to that of stainless steel and Ti-6Al-4V alloy. There were no necroses, granulomas, or signs of dystrophic soft tissue calcification. The immune cell response to Nitinol remained low. Only a few foreign-body giant cells were present. The detected neural and perineural responses were also clearly nontoxic and nonirritating with Nitinol. No qualitative differences in histology between the different test materials could be seen. At 8 weeks, the encapsule membrane of Nitinol was thicker than that of stainless steel (mean 62 ± 25 μm vs. 41 ± 8 μm). At the end of the study, the encapsule thickness was equal to all the materials tested. We concluded that Nitinol had good in vivo biocompatibility after intramuscular and perineural implantation in rats in the 26-week follow-up. Based on the results of the present study, Nitinol appears to have good potential for clinical use. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 41, 481-488, 1998.
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    Assessment of an experimental bone wax polymer plus TGF-β1 implanted into calvarial defects (1998)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 41 (1998), S. 584-592 
    Details
    ISSN: 0021-9304
    Keywords: transforming growth factor-beta1 (TGF-β1) ; wax-like polymer ; biodegradation ; biocompatibility ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The study reported describes an experimental biodegradable polymer ceramic composite with wax-like handling properties that was combined with 2.0 μg of recombinant human transforming growth factor beta (rhTGF-β1). The polymer/rhTGF-β1 combination was introduced into standard-sized calvarial defects in rabbits to evaluate biodegradability, biocompatibility, hemostasis control, and bone promotion. The experimental wound model was a standard-sized circular calvarial defect 8 mm in diameter. The experimental design included 24 skeletally mature New Zealand white rabbits divided evenly between two time periods (6 and 12 weeks) and among three experimental treatments (untreated defects and defects treated with polymer with or without rhTGF-β1). Evaluations consisted of clinical examinations, standardized radiography, radiomorphometry, as well as histology and histomorphometry. Data were analyzed by an Analysis of Variance (ANOVA) and Fisher's Protected Least Significant Difference test at each time period (level of significance p≤ 0.05). Radiomorphometry data indicated that standard-sized defects treated with the wax-like polymer alone and the polymer plus 2.0 μg of TGF-β1 were significantly more radiopaque than control sites at both 6 and 12 weeks. Histomorphometric data revealed the amount of new bone was significantly greater at 6 weeks in the polymer plus 2.0 μg of TGF-β1 and in the control group than in the polymer alone. Moreover, at 12 weeks, there was significantly more new bone in the control than in either the polymer alone or the polymer plus 2.0 μg of TGF-β1. We speculate the incomplete biodegradation of the polymer ceramic composite contributed to the radiopacity and may have retarded osseous regeneration. It is important that the bone wax-like polymer material was biocompatible and acted as a hemostatic agent. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 41, 584-592, 1998.
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    Comparative histological evaluation of new tyrosine-derived polymers and poly (L-lactic acid) as a function of polymer degradation (1998)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 41 (1998), S. 443-454 
    Details
    ISSN: 0021-9304
    Keywords: poly(lactic acid) ; subcutaneous implantation ; tyrosine-derived polymers ; poly(DTE carbonate) ; poly(DTE adipate) ; biocompatibility ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Previous studies demonstrated that poly(DTE carbonate) and poly (DTE adipate), two tyrosine-derived polymers, have suitable properties for use in biomedical applications. This study reports the evaluation of the in vivo tissue response to these polymers in comparison to poly(L-lactic acid) (PLLA). Typically, the biocompatibility of a material is determined through histological evaluations as a function of implantation time in a suitable animal model. However, due to changes that can occur in the tissue response at different stages of the degradation process, a fixed set of time points is not ideal for comparative evaluations of materials having different rates of degradation. Therefore the tissue response elicited by poly(DTE carbonate), poly(DTE adipate), and PLLA was evaluated as a function of molecular weight. This allowed the tissue response to be compared at corresponding stages of degradation. Poly(DTE adipate) consistently elicited the mildest tissue response, as judged by the width and lack of cellularity of the fibrous capsule formed around the implant. The tissue response to poly(DTE carbonate) was mild throughout the 570 day study. However, the response to PLLA fluctuated as a function of the degree of degradation, exhibiting an increase in the intensity of inflammation as the implant began to lose mass. At the completion of the study, tissue ingrowth into the degrading and disintegrating poly(DTE adipate) implant was evident while no comparative ingrowth of tissue was seen for PLLA. The similarity of the in vivo and in vitro degradation rates of each polymer confirmed the absence of enzymatic involvement in the degradation process. A comparison of molecular weight retention, water uptake, and mass loss in vivo with two commonly used in vitro systems [phosphate-buffered saline (PBS) and simulated body fluid (SBF)] demonstrated that for the two tyrosine-derived polymers the in vivo results were equally well simulated in vitro with PBS and SBF. However, for PLLA the in vivo results were better simulated in vitro using PBS. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 41, 443-454, 1998.
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    Biocompatibility study of a biological tissue fixed with a naturally occurring crosslinking reagent (1998)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 42 (1998), S. 568-576 
    Details
    ISSN: 0021-9304
    Keywords: biological tissue ; crosslinking reagent ; genipin ; subcutaneous implant ; biocompatibility ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: A recognized disadvantage of the currently available chemical reagents used to fix bioprostheses is the potential toxic effects a recipient may be exposed to from residues. It is therefore desirable to provide a crosslinking reagent that is of low cytotoxicity and can form stable and biocompatible crosslinked products. To achieve this goal, a naturally occurring crosslinking reagent - genipin - was used by our group to fix biological tissues. Genipin can be obtained from its parent compound geniposide, which can be isolated from the fruits of Gardenia jasminoides ELLIS. In our previous feasibility study, it was found that the cytotoxicity of genipin is significantly lower than both glutaraldehyde and an epoxy compound. Additionally, it was shown that genipin can form stable crosslinked products. The present study further investigates the biocompatibility of a genipin-fixed porcine pericardium implanted subcutaneously in a growing rat model. The fresh, glutaraldehyde-, and epoxy-fixed counterparts were used as controls. It was noted that the inflammatory reaction of the genipin-fixed tissue was significantly less than its glutaraldehyde- and epoxy-fixed counterparts. Also, the genipin-fixed tissue has tensile strength and resistance against in vivo degradation comparable to the glutaraldehyde-fixed tissue. Additionally, the calcium content of the genipin-fixed tissue measured throughout the entire course of the study was minimal. Nevertheless, further study in calcification for the genipin-fixed tissue should be conducted in a blood-contact environment. The results obtained in this subcutaneous study indicate that genipin is a promising crosslinking reagent for biological tissue fixation. However, further durability testing in vitro and in vivo are needed to determine the relative functional merits of this new crosslinker. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 42, 568-576, 1998.
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    Behavior of bone marrow cells cultured on three different coatings of gel-derived bioactive glass-ceramics at early stages of cell differentiation (1998)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 42 (1998), S. 433-442 
    Details
    ISSN: 0021-9304
    Keywords: biocompatibility ; glass-ceramic ; bone marrow cells ; osteoblast ; osteoclast ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Previous studies have shown different macrophage responses to three compact pellets (with slightly different chemical composition) of gel-derived bioactive glass-ceramics of the CaO-P2O5-SiO2 system. In the present study primary bone marrow cells directed in vitro to form osteoblastic or osteoclastic cells were cultivated on glass slides coated by these three glass-ceramics. Glass slides were used as controls. In osteoblastic cultures alkaline phosphatase activity varied, depending on the type of coatings. Northern analysis showed high mRNA expressions of bone-related proteins on both the glass-ceramics and control glass. Mineralized nodules were not formed on the control glass, but coating glass slides with the glass-ceramics promoted mineralization without any substantial differences between the types of coatings. In osteoclastic cultures, the normal morphology of tartrate resistant acid phosphatase-positive multinucleated cells on standard culture plates was altered on the control glass and the glass-ceramics. The number of these cells differed, depending on the type of coatings, with no particular differences in the arrangement of F-actin by these cells. These analyses demonstrate complete biocompatibility of the glass-ceramic coatings but not the control glass, on which the cells failed to form mineralized nodules. The phenotype expression of the cells appeared to be influenced by microstructure, surface roughness, and the general character of the coatings rather than their surface reactivity. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 42, 433-442, 1998.
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    The effects of calcium phosphate particles on the growth of osteoblasts (1997)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 37 (1997), S. 324-334 
    Details
    ISSN: 0021-9304
    Keywords: biocompatibility ; calcium phosphate ; particle ; osteoblast ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: With advances in ceramics technology, calcium phosphate bioceramics have been applied as bone substitutes for several decades. The focus of this work is to elucidate the biocompatibility of the particulates of various calcium phosphate cytotoxicities. Four different kinds of calcium phosphate powders, including β-tricalcium phosphate (β-TCP), hydroxyapatite (HA), β-dicalcium pyrophosphate (β-DCP), and sintered β-dicalcium pyrophosphate (SDCP), were tested by osteoblast cell culture. The results were analyzed by cell count, concentration of transforming growth factor-β1 (TGF-β1), alkaline phosphatase (ALP), and prostaglandin E2 (PGE2) in culture media. The changes were most significant when osteoblasts were cultured with β-TCP and HA bioceramics. The changes in cell population of the β-TCP and HA were quite low in the first 3 days, then increased gradually toward the seventh day. The changes in TGF-β1 concentration in culture medium inversely related to the changes in cell population. The ALP titer in the culture media of the β-TCP and HA were quite high in the first 3 days, then decreased rapidly between the third and seventh days. The concentrations of PGE2 in the culture media tested were quite high on the first day, decreased rapidly to the third day, and then gradually until the seventh day. The changes in the β-DCP and SDCP were quite similar to those of HA and β-TCP but much less significant. We conclude that HA and β-TCP have an inhibitory effect on the growth of osteoblasts. The inhibitins effects of the HA and β-TCP powders on the osteoblast cell cultures possibly are mediated by the increased synthesis of PGE2. © 1997 John Wiley & Sons, Inc. J Biomed Mater Res, 37, 324-334, 1997.
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    New anionic polyelectrolyte hydrogel for corneal surgery (1997)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 37 (1997), S. 548-553 
    Details
    ISSN: 0021-9304
    Keywords: hydrogel ; biocompatibility ; permeability ; complement activation ; AN-69 dialysis membrane ; synthetic biopolymers ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: A new high-water-content (78%) anionic polyelectrolyte hydrogel was obtained by phase inversion (demixion) of a polymer solution containing 9.0% poly(acrylonitrile sodium methallylsulphonate), 85.0% dimethylformamide, and 6.0% saline solution (0.9% NaCl). The hydrogel is permeable to water, saline, urea, creatinine, glucose, human albumin, and saline-dissolved oxygen. Investigation of the interactions between human serum and surfaces prepared with the new yielded hydrogel, compared to serum interaction with silica-free silicone (RTV), regenerated cellulose (Cuprophan), MMA/PVP copolymer (Lidofilcon), PMMA (Perspex), PTFE (Gore-Tex), and poly(acrylonitrile sodium methallylsulphonate) hemodialysis membrane (AN-69), showed the hydrogel and hemodialysis membrane (both prepared with AN-69 copolymer) to be the only materials devoid of complement (C′)-activating ability. © 1997 John Wiley & Sons, Inc. J. Biomed Mater Res, 37, 548-553, 1997.
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  • 72
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    Human osteoblast-like cells (MG63) proliferate on a bioactive glass surface (1997)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 37 (1997), S. 394-400 
    Details
    ISSN: 0021-9304
    Keywords: Bioglass® ; tissue culture ; biocompatibility ; bone ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Bioglass®, a resorbable glass, previously has been evaluated as a bone graft substitute using cells of animal origin. Limited information is available on its effect on human cells. The objective of this study was to test the hypothesis that Bioglass® supports viability and proliferation of human bone cells. As a prototype of human bone cells, the osteoblast cell line MG63 was used and propagated on Bioglass® disks. MG63 cells also were seeded onto disks made of titanium (Ti-6Al-4V) and of cobalt chrome (Co-Cr-Mo) alloys. The number of viable cells recovered was similar for Bioglass®, titanium, and polystyrene control surfaces. Significantly fewer cells were recovered from CoCr (P 〈 0.05) compared to Bioglass®, Ti-6 Al-4v, and polystyrene surfaces. The proportion of cells undergoing DNA synthesis, estimated by thymidine uptake, was significantly greater on Bioglass® and titanium surfaces (P 〈 0.05) than on the CoCr surface. There were detectable differences in cell morphology on these biomaterials. Functional capacity was tested by assay of osteocalcin production and no differences were detectable among the different biomaterials. This study supports the hypothesis that 45S5 Bioglass® provides a favorable environment for human osteoblast proliferation and function. Bioglass® may have clinical potential as a bone graft substitute, a bioactive grout, or an implant coating for promoting bony ingrowth in uncemented prostheses. © 1997 John Wiley & Sons, Inc. J Biomed Mater Res, 37, 394-400, 1997
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  • 73
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    The interface of bone microstructure and an innovative coating: An X-ray diffraction study (1998)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 40 (1998), S. 86-91 
    Details
    ISSN: 0021-9304
    Keywords: X-ray diffraction ; ceramic ; external fixation ; coating ; biocompatibility ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The in vivo compatibility and degradation aspects of an innovative coating to be sprayed onto titanium implants were investigated. The surface of fluorinated apatite (fHA), consisting of fluorhydroxyapatite plasma sprayed in a vacuum atmosphere, was treated with carbonate to improve its biological compatibility. fHA coating was compared with titanium implants coated (a) with hydroxyapatite (HA) by the traditional plasma spraying, and (b) with titanium oxide (TiOx). Screw-shaped implants were inserted in the cortical bone of sheep tibiae. X-ray diffraction (XRD) analysis of bone tissue and coatings was carried out at 2, 4, 12 and 36 weeks after surgery. The crystallographic habit of the implant-facing bone, as well as the structural stability of the coating, were evaluated. For each time period and type of ceramic bone apatite lattice at the interface, no significantly different reference apatite lattice and no foreign peak were recorded. Two weeks after implantation, the bone at the interface was strongly unmineralized in all samples; after 4 weeks, poorly mineralized bone microareas decreased. At 12 weeks, the newly formed bone tissue at the interface with both the new coating and HA coating was shown to be fully mineralized; this crystallographic habit was retained at 36 weeks, when particle release from the tested material was lower compared to the controls. The XRD pattern of bone apatite surrounding the coating particles was unmodified. The innovative coating did not alter the mineralization process at the interface. It improved implant osteointegration, mainly due to a limited release of particles. Consequently, clinical performance of external fixation treatment could be improved by modifying the chemical composition of the implant surface. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 86-91, 1998.
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  • 74
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    Effects of new machinable ceramic on behavior of rat bone cells cultured in vitro (1998)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 43 (1998), S. 215-225 
    Details
    ISSN: 0021-9304
    Keywords: enstatite ; biocompatibility ; in vitro ; osteoblasts ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The behavior of cultured rat bone cells growing on modified polyethylene terephthalate (mPET), glass, and machinable ceramic substrates containing enstatite (MgO, SiO2) and glass (CaO-P2O5-Al2O3) was studied. Cell attachment was measured directly on the substrates using an image analysis system. Electron microscopy observations and the MTT test revealed that cells are able to spread and proliferate on the material surface, keeping a healthy ultrastructure on all materials tested in the present study. After having colonized the surface of the materials, as shown by immunocytochemistry, the cells synthesize an osteoid-like matrix composed of osteocalcin, type I collagen, and fibronectin fibrils. The titration of alkaline phosphatase activity showed that the cells grown on the ceramic exhibit a greater osteogenic activity than those grown on controls (glass and mPET). This osteogenic activity results in a mineralization of the extracellular matrix in cultures on ceramic or plastic whereas only few calcium phosphate crystallite traces were revealed by Von Kossa staining on glass. Enstatite constitutes, therefore, an environment compatible with in vitro bone cell life. © 1998 John Wiley & Sons, Inc. J. Biomed Mater Res (Appl Biomater) 43: 215-225, 1998
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