ALBERT

Notizen: Hollow fibers have been produced and evaluated for use as membrane oxygenators in an artificial heart device. Gas permeable capillaries now commercially available are unsuitable for this use because of: (1) low percent open cross-sectional area, (2) large internal diameter, and (3) high cost. A number of polymers were initially selected for evaluation because of their reported high gas permeabilities. Those selected include a number of rubbers of various compositions, certain poly-α-olefins and an experimental thermoplastic silicone rubber copolymer. These materials were first evaluated as flat membranes (films) for their gas permeabilities and also for ease of preparation in hollow fiber form. Hollow fibers were prepared from the most promising of those studied, poly-4-methylpentene-1 and the thermoplastic polydimethylsiloxane copolymer. Fibers, ranging in the size from 30 to 300 μ ID, were spun with open cross-sectional areas of 40-65%. Oxygen and carbon dioxide permeabilities measured on these fibers were compared to that of SilasticDow Corning medical grade poly (dimethylsiloxane). rubber membranes. These permeabilities range from 1/20 that of Silastic rubber for unmodified poly-4-methylpentene-1 to 2/3 for the thermoplastic silicone copolymer. Modification of poly-4-methylpentene-1 has made it possible to increase it's permeability by tenfold, while still maintaining physical properties necessary to spin and fabricate this material.

Notizen: Advanced forms of elemental carbon were identified as potential implantable prosthetic materials and a study was conducted to determine specific applications. A survey of the carbon industry established material sources and specifications on available types of material. Specimen materials were supplied to several research organizations for in-vivo evaluation and produced acceptable results. Specific designs have been generated for a broad range of implantable prosthetics and prototypes have been provided for preliminary evaluation. The feasibilty of an organic mechanical attachment between cortical bone tissues and elemental carbon has been successfully demonstrated.

Notizen: The success of material implants in the vascular system has been limited by the fact that the intial events of blood coagulation on foreign material surfaces are not understood. Many materials have been evaluated in the search for a suitable implant material in this system. Recent success of porous ceramic materials in bone-ceramic compatibility studies stimulated the feeling that these materials should be tested in other body tissues such as the blood.Ceramic disks of Al2O3 and TiO2 were evaluated using a contact angle measurement technique to determine the characteristics of these material surfaces before and after exposure to a blood environment. This technique involved measuring the contact angle of sessile drops of various liquids on these surfaces with a microscope fitted with a goniometer eyepiece. By plotting these contact angles according to the procedure of Zisman, the characteristics of the surfaces could be evaluated.The clean ceramic disks were found to be extremely wettable even after exposure to a physiological saline environment. On exposure of these disks to a blood environment, it was observed that some type of film was adsorbed from the blood onto the ceramic surface during the initial minutes of exposure. This film had wetting characteristics consistent with layers of fibrinogen.

Notizen: The skeletal attachment of a limb prosthesis approaches two specific and separate problems in tissue reaction to prosthetic materials: Skeletal fixation and trancutaneous interface.The skeletal fixation problem must be looked upon as a method to distribute the stress concentration of prosthetic material in such a manner so that living tissue is not embarrassed by prolonged excessive pressures. One must consider the functional mechanical stresses separate from the toxicological reaction of living tissues to prosthetic materials. Our current experience identifies the fact that vitreous carbon is extremely benign from the standpoint of living tissue reaction. Moreover, when placed in the configuration of irregular surfaces, it apparently encourages bone growth contiguous with the material. To this point, however, the reaction of living material to broad surfaces contiguous with vitreous carbon has not placed under concentration of functional stresses. Porous ceramic to this date has not supplied an appropriate answer to this problem.Transcutaneous perforation is available in the clinical sense only when a method can be presented which requires no specific hygiene and dressing. No drainage at all must be the rule at a transcutaneous perforation. Vitreous carbon in our experience so far has made contiguous epithealization feasible down the neck of a skin perforation. Four millimeters, from our experience, seems to be an appropriate location of epithelial downgrowth before transition into non epithealized connective tissue is available. The use of fixation skirts is felt to be necessary to provide stable, transcutaneous perforation.This paper presents evidence of the favorable tissue reaction both from a skeletal and cutaneous standpoint to vitreous carbon materials. A specific design for the successful skeletal fixation limb prosthesis is as yet not currently available and must await further clinical experience with human skin reaction to transcutaneous devices.

Notizen: A study has been made of the ceramic-epoxy composite “Cerosium.” Experiments were conducted to evaluate the tissue reaction to such material and the extent of bonding established between ceramic and the tissues in which it was implanted. It was found that this material was well tolerated by the body and obtained definite fixation within the tissues when implanted into both bone and tendon. This occurred, however, not by the active infiltration of tissue but by fibrous encapsulation and it is recommended that for more meaningful stabilization, material of larger pore size is required.When Cerosium was implanted into the knee joints of rabbits, it was found to be unsuitable for intra-articular use because of the abrasive effect on the opposing cartilage and bone surfaces and the susceptibility of the material itself to abrasive wear. Furthermore, a full mechanical evaluation of standard specimens of Cerosium showed it to be degraded within the body due to a breakdown of the impregnating polymer.Ceramic-epoxy composites require a strong matrix and a totally stable impregnating material. While mechanically suited to replacing weight bearing surfaces, a smooth surface glaze is essential to avoid abrasive effects upon the opposing bone surface. Further investigation is required before these materials can be fully accepted into the armamentarium of the implant surgeon.

Notizen: The compatibility of implanted ceramic materials with autogenous bone, and the subsequently noted influence of the ceramic on the rate of new bone formation, were investigated to evaluate such materials for use in orthopedic implants. Three ceramic materials, aluminium oxide (Al2O3), zirconium oxide (ZrO2), and calcium aluminate (yCaO · xAl2O3) were tested. These were placed in the femurs of rhesus monkeys for periods of 50, 100, and 350 days. Definite compatability between the autogenous bone and the materials was exhibited for the implant time periods evaluated. No toxicogenic activity was noted in any of the biochemical, biomedical, and ceramographic evolutions. An added benefit resulted from the calcium aluminate composition, which was fabricated as a two-phase oxide material to make it slightly soluble in the body fluids. In the 50- and 100- day implants, the bone penetrated the ceramic for distances up to 100 μ while the ceramic dissolved and the pores enlarged. In addition, the mineralization in the area of the calcium aluminate was greater than that found around the other ceramics. Radiographs over the entire 350-day implant period confirmed the increased callus formation around all of the materials with no signs of rejection evident in the surrounding osseous or soft tissues. After 350 days the entire pore area of the calcium aluminate ceramic was infiltrated with a columnar substance which on the basis of scanning electron microscope procedures was considered to be mineralized osteoid.

Notizen: A series of DL-methionine/L-leucine copolymers was prepared from the coresponding N-carboxy-anhydrides. The copolymers formed clear flexible films having low water vapor transmission rates. Peroxide oxidation of the pendant methyl-theioethyl groups to methyl-sulfinoethyl groups enhanced the hydrophilic properties of the membranes, and the water vapor transmission rates rapidly increased with an increase in the number of pendant methyl-sulfinoethyl groups. Increasing the leucine content of the membranes produced a 13-fold increase in the carbon dioxide permeability and a 6-fold increase in oxygen permeability, whereas, an increase in the methionine content doubled the carbon dioxide-oxygen separation factor.Synthetic poly (α-amino acids) are very similar to naturally occurring proteins with respect to composition and conformation. Because of these similarities, they are being considered in aerosol spray bandages, synthetic skin applications and as coatings for plastic prostheses. The unusual permeability characteristics of the DL-methionine/L-leucine copolymers make them interesting membranes for possible use in artificial kidney machines and blood oxygenators.

Notizen: The flexural tests on 37 whole equine metacarpus bones are described and the results are given in terms of fundamental material properties as a function of age. The moduli of elasticity, rupture, and failure increase then decrease with increasing age. The rupture and failure deformations decrease with age. The stiffness and fragility indices increase with age. Averaging the data for all ages, the modulus of rupture was 35 ksi, the deflection at rupture was 0.22 inches, and the modulus of elasticity was 1.7 × 10 psi. The flexural rupture strength is about twice the uniaxial compression strength and about five times greater than the torsional strength for whole bone tests. The moduli of elasticity are about the same for flexure and uniaxial compression, and about five times greater than the torsional modulus of rigidity for whole equine bone.

Notizen: A porous ceramic, in the form of small discs, has been implanted into the upper tibiae of adult mongrel dogs in survival experiments. A similar sized disc of a metal (vitallium, titanium, or stainless steel) was also implanted, for comparison, into each tibia. The tissue specimens were studied by microangiography and correlated histology. At the 4-month, and longer, intervals, the specimens were sectioned with the ceramic disc in situ. Injected capillaries were then observed to have penetrated the ceramic.The metals became surrounded by a shell of new-bone, lined by a fibrous membrane of varying thickness. The ceramic implants, on the other hand, appeared to have remained inert within the cancellous area of the tibiae, not surrounded by either a membrane or an osseous shell.Implications of these findings were discussed and further experiments, some of which are in progress, were proposed.

Notizen: Excellent in vivo thromboresistance has been obtained for FEP Teflon and for a polyether urethane prepared with electronegative surfaces using the electret effect. In vitro tissue culture studies have shown a marked improvement in tissue compatibility for negatively electrified Teflon. Studies on other materials, including Hypalon rubber, sulfonate cross-linked Hypalon and Kel F have shown a moderate improvement in blood compatibility. These in vitro and in vivo experiments will be described. Surface physical properties of these electrified materials, including water contact angle and charge, have been measured. Correlations between surface physical measurements and blood compatibility data will be presented.

Notizen: Flexible and rigid epoxy and urethane polymers containing heparin chemically and uniformly incorporated throughout and/or ionically complexed to quaternized amine grops were prepared and shown to have excellent thromboresistance in vitro and in vivo. These heparin-modified polymers were implanted into the vena cava of dogs and successfully passed multiple acute (2 hr) and chronic (2 week) exposure periods. It was also demonstrated that the chemically coupled heparinized epoxies had no measurable adverse effects on blood cells, platelets, or plasma proteins, and that the heparin was not extractable. Significantly, epoxies containing polyoxypropylene/polyoxyethylene glycol (an additive which had no thrombus-inhibiting properties of its own) also exhibited excellent thromboresistance when characterized in vivo in dogs. The applicability of these various materials for the fabrication of circulatory assist device components was demonstrated. The effect of polymer polarity, surface charge, and conductivity were investigated with indeterminate results and unmodified commercial polymers uniformly exhibited poor clotting characteristics. In vitro clot-inhibiting characteristics were shown to be a sufficient, but not necessary, condition for indicating in vivo thromboresistant activity in polymer systems.

Notizen: These studies have furthered the development of a flexible impermeable encapsulant for implantable electronic devices. Medical grade silicone rubber, a widely used implantable material, is well known to be permeable to water vapor. We have demonstrated that silicone rubber is apparently permeated by electrolytes. This permeability to electrolytes can be blocked by impregnation of the silicone rubber with certain naturally occurring waxes during vulcanization. Implantation into living tissue has shown this material to be well tolerated. Of the natural waxes studied thus far, spermaceti has revealed the best overall properties as an impregnant for silicone rubber.

Notizen: Expanding artificial implants are made of crosslinked hydorphilic polymers which imbibe body fluids and swell to a predetermined volume. The material is implanted in a dehydrated state; it then swells to fill a body cavity (i.e., vitreous cavity in the eye), or to give a form to the surrounding tissues (i.e., in plastic surgery). Such implants can be introduced in organs or tissues through a smaller incision than regular plastic and rubber implants, and have the advantage over injectable polymers in that they do not separate into globules and do not migrate from the area of implantation. The swelling equilibrium of slightly crosslinked poly (glyceryl methacrylate) [PGMA] hydrogels in salt solutions, urea, serum, and in the homogenized vitreous of the eye is given. Also, the swelling rate of PGMA in physiologic saline solution and in serum, as well as the swelling pressure-volume relationship of PGMA gels in water, is reported. The application of PGMA as an expanding implant inside the eye, and against its outer wall in retina surgery, is discussed.

Notizen: The true diffusive permeabilities of commercial, modified commercial, and laboratory cast regenerated cellulose membranes were measured with a batch dialyzer using 15 solutes (sodium chloride, nine radioactively labelled organic solutes, and five low molecular weight proteins) ranging in molecular weight from 58 to 68,000. Additional measurements included membrane thickness, water content, and strength properties, as well as equilibrium solute partition coefficients and solute diffusion coefficients in free solution. All commercial cellophanes were similar in sodium chloride permeability on a unit thickness basis and were significantly less permeable than hydrophilic wet gel membranes. This difference was attributed to the irreversible collapse of membrane structure upon drying. As the solute characteristic size increased, permeability decreased more sharply with commercial cellophane than with wet gel cellulose, the ratio between the two becoming an order of magnitude for large solutes. The ratio between the solute diffusion coefficient in the membrane and in free solution decreased exponentially with increasing solute size. The results suggest further work for higher permeability cellulosic hemodialysis membranes.

Notizen: Spherical-particle Ag-Sn alloy powders containing 4.3, 8.3, 12.0, 15.4, 18.5, 21.4, and 24.1 atomic per cent Sn were obtained. Amalgams from these alloys were examined by x-ray diffraction and metallography for the presence of the γ2 phase and the γ1 → β1 phase transformation. A single amalgam of the approximate composition of dental amalgam was prepared from a melt at high temperature and pressure and likewise examined.Results showed that the solubility of Sn in Ag-Hg is about 7 atoms of Sn per unit cell of the γ phase. As clinically prepared, the γ1 phase of dental amalgam contains, however, only about 5 atoms of Sn per unit cell. These 5 atoms, nevertheless, result in a very considerable stabilization of this phase due to the increase in its electron concentration.

Notizen: Radiopaque glass-resin composites were made for evaluation as denture base materials. The addition of silane-treated, radiopaque, powdered glass to clear poly(methyl methacrylate) resulted in composites that had greater optical translucency than commercially available pink denture base resins. These formulations could be pigmented and opacified to produce materials that simulated oral soft tissues in color and translucency.Other composites were made using various monomer, polymer and glass combinations. Those made from mixes of BIS-GMA, methyl methacrylate, poly(methyl methacrylate), and radiopaque glass had excellent translucency but handling characteristics were less than ideal.Removal of very small glass particles (less than a few μm) appeared to improve optical translucency.A radiographic survey of 12 specimens that contained from 29 to 57% of the radiopaque glass, indicated that all had sufficient radiopacity to aid in localization of swallowed or aspirated dentures made from such materials.Finishing procedures on composite specimens were more difficult and timeconsuming and did not produce surfaces as smooth as those obtained on poly(methyl methacrylate). The finished surfaces felt smooth to the tongue but might stain more easily in the mouth.

Notizen: One-thousand gamma particles in spherical amalgam and 1000 spherical gamma particles embedded in resin were sectioned, and the diameters for the sections were measured. Microhardness determinations were done on 50 particle sections in amaglam containing 46% mercury, 50 sections in amalgam of 52% mercury, and 50 sections of nonamalgameted particles embedded in resin.The gamma particles in amalgam seemed to have expanded as a result of their uptake of mercury. The gamma particles in amalgam had a lower hardness than the nonamalgamated particles embeded in resin. The hardness values ofthe particles were not statistically different in amalgam comtaining 46 and 52% mercury.

Notizen: A technique is described for studying shear-induced degradation of blood with near-uniform shear exposure to walls of a single material. The device used is a specially designed coni-cylindrical viscometer with essentially all blood-contacting surfaces constructed of a single test material. The technique developed permits exposure of blood only to this material under such conditions that significant shear occurs only in the viscometric region of the device. Contact with air is prevented. Preliminary data are reported for blood taken from fasting dogs and tested in a prototype device constructed of polycarbonate (Lexan). Venous blood was found to hemolyze much more than arterial blood and the extent of hemotysis increased with time. Changes were also observed in the electrophoretic pattern of the plasma proteins.

Notizen: Technic dentures were made using composite base materials containing 30,40, and 50 weight % of a silance-treated, readiopaque, powdered glass as the reinforcing filler and poly (methyl methacrylate) as the matrix. Dentures containing no glass were included for comparison. Molar-to-molar dimensional changes, effects of silance treatment fo the procelain teeth and handling and finishing characteristics were determined.Dentures containing glass had less dimensional change during curing and subsequent water storage than those without glass. Thick upper dentrues exhibited the least change and thin lowers, the most. The Differences in the magnitudes of the changes would not be clinically noticeable.Silance treatment fo the procelain teeth in thick upper dentures resulted in breakage of theposterior teeth in almost all instances. posterior teeth also freactured in thick upper dentures containing 40 and 50% of the silance-treated glass even though the teeth were not treatedwith silance.Mixing and molding properties of the composite materials, while acceptabgle, were slightly inferior to thematerial containing ono glass. Finiching characteristics were definitelyinferior in that it was more difficult and time-consuming to attain the fial surfaces and these surfaces were not as smooth as smooth as those in dentures without glass.

Notizen: New synthetic polymer membranes prepared from copolymers of dimethylaminoethyl methacrylate are reported. Membrane transport characteristics are compared with those of standard cellulose films currently used in hemodialysis. The membranes are obtained as films by casting solutions of vinyl copolymers prepared by emulsion polymerization techniques. The new membranes show selectivity towards certain blood components under the test conditions used. The clinical procedure for ethylene oxide sterilization has been adapted to give chemical modification of dimethylaminoethyl methacrylate tertiary amine groups. With acrylonitrile as comonomer, polymer membranes which are both watersensitive and insoluble are obtained. The permeability of such films is controlled by varying processing time. Infrared spectra of processed and unprocessed films are discussed and reasons put forward for the change in membrane properties brought about by processing. Membrane behavior when acrylonitrile is replaced by methacrylonitrile or methyl methacrylate indicates the probable necessity of having a strongly electron-attracting comonomer for successful modification.

Notizen: The pressure dependence of the elastic constants of dental amalgam has been examined in the 0-50 kilobar range using a solid media, pressure apparatus coupled with an ultrasonic interferometer. Computer analysis of the measured longitudinal and shear ultrasonic wave velocities yields the pressure dependence of the bulk, shear and Young's moduli and Poisson's ratio. Samples were prepared with varying compositions from micro-cut and spherical dental alloys. The elastic behavior of these samples can be directly related to the sample structure and composition as well as to the manipulation during preparation. In addition, an estimate can be made of the volume concentration of porosity.

Notizen: A model describing the elastic behavior of dental amalgam as a composite material has been developed using elastic theory for quasi-homogeneous, quasi-isotropic systems. The elastic constants of the composite amalgam can be computed using Voigt-Reuss and Hashin-Shtrikman methods if the relative volume fractions and the elastic constants of the constituent phases are known. This model also relates the elastic behavior of the amalgam to manipulation during preparation. The elastic constants of several spherical and cut amalgams, as well as the constituent γ, γ1, and γ2 alloys, have been measured in the 0-50 kilobar range using a solid media pressure apparatus and an ultrasonic interferometer. High pressure studies are necessary so that the effects of porosity can be assessed. Calculations based on this model include the effects of porosity as well as the Hg content.

Notizen: This basic introductory discussion has sought to outline the embryology and development of bone and has stressed both its function and structure. I have, also, outlined the sequence of fracture healing and discussed some of the problems of implant acceptance in the musculoskeletal system. With this information, I hope you as basic scientists will be able to better understand some of the problems our patients pose with respect to implant design and function. It should be reiterated that many men have contributed to this very vital and important field of Orthopedic Surgery. Moreover, I would like to stress that not withstanding the complications previously discussed, the availability of biologic and metallic implants has contributed immensely to the high level of patient care we know today; and they have a very important role in the future improvement of our ability to care for our patients.

Notizen: The development of a bone-bonding calcia-phosposilicate glass-ceramic is discussed. A theoretical model to explain the interfacial bonding is based upon in-vitro studies of glass-ceramic solubility in interfacial hydroxyapatite crystallization mechanisms, compared with in-vivo rat femur implant histology and ultrastructure results.

Notizen: The trachea is a rather simple structure, and partly because of this simplicity, many attempts have been made to effect replacement with various types of prosthetic tubes. Unfortunately, the basic design of the trachea is not easily duplicated, and thus far there is no completely satisfactory prosthetic replacement. A series of porous and non-porous ceramics implanted in muscle tissue of rabbits indicated that rigid, porous materials can be compatible with soft, viable tissue. A prosthesis of porous ceramic rings and alternate bands of Dacron mesh was constructed and employed to bridge 6-cm defects created in the tracheas of mongrel dogs. After 6 months an asymptomatic animal was sacrificed. Firm fixation was accomplished and the lumen was completely patent, but histological sections demonstrated that ingrowth and scarring did not satisfactorily contain bacterial infection. Encouragement of epithelial regeneration or some artificial barrier is necessary for successful implants. Work in progress includes devices using both methods to provide this barrier.

Notizen: The transport of aqueous urea, glucose, and sucrose through the cellulose membrane, Curophane, is described in terms of permeation and frictional coefficients. As for other cellulose materials, hydraulic flow for Cuprophane is predominantly of a capillary nature. While Cuprophane is relatively selective, reflecting more of these solutes than most other cellulose membranes, the observed flow rates through this very thin membrane are quite high. These permeation properties for Cuprophane are accommodated by the frictional description of membrane transport. The data are discussed and compared with other available data on related cellulose systems.

Notizen: The factor which plays the most important part in surgery of the liver is the liver suture. The considerable tenderness of the hepatic parenchyma causes the sutures to cut through easily, which leads to further complications. Therefore, in their experimental work carried out in rabbits, the authors used Hydron (USA trade-mark) foils reinforced with polyester netting to serve as bolsters for anchoring the sutures, and to prevent them from cutting through the parenchyma of the operated gland. In addition, the spongy Hydron was tried out to aid the peritonealization process of the resection-wound surface of the liver.

Notizen: A new elastomeric heparin complex containing from 7 to 16% of heparin was synthesized from commercially available polyether diisocyanates. Chemical analysis and solubility measurements of intermediates as well of the final product showed beyond doubt that an ionic bond was formed between heparin and the quaternized polyether polyurethane. The solubility of the heparin complex in specific solvents systems permitted to cast films or form coatings on commercial plastics. The films and the coatings were found to be non-thrombogenic and whole human blood could be stored in 1/8 or 3/16″ID coated tubing for at least 24 hr without occurence of clotting. The values of tensile strength, elongation at break and of the shear modulus as a function of temperature showed that the heparinized complexes were endowed with desirable mechanical properties under ambient conditions.

Notizen: A number of cements based upon polymeric systems are being utilized in both medical and dental fields. The polymethyl methacrylate rapid polymerizing monomerpolymer materials have undergone extensive development as dental materials and are used widely also for rentention of orthopedic prostheses. The cyanocrylates and the newly developed zinc polycarboxylate cements are being used for a variety of dental applications. These latter materials display adhesion to soft tissue and calcified tissue, respectively, and the investigation of adhesion to these substrates compared with the mechanical retention of the methacrylate materials is of considerable interest.The polycarboxylate cements have unusual properties including minimal tissue irritation and relatively high strength. The ability to vary their formulation and manipulative properties has permitted their trial in a variety of clinical applications including cementation of stainless steel orthodontic brackets to teeth.

Notizen: Materials conventionally used for orthopedic surgical implants are primarily metallic alloys such as stainless steel 316L, Cr-Co-Mo alloys and recently titanium and Ti-6A1-4V alloy. Modulus of elasticity of these (E = 15 to 30 × 106 psi) is an order of magnitude higher than that of bone (approximately 3 × 106 psi). Quartz filament reinforced composites were formulated with E = 6 × 106 psi and flexural stress at rupture (modulus of rupture) of approximately 200,000 psi. Similarly graphite filament reinforced epoxy composites were formulated with E = 16 × 106 psi and flexural stress at rupture (modulus of rupture) of approximately 200,000 psi. Specimens of these materials were implanted in white rats subcutaneously. At sacrifice 90 days after implantation there was no evidence of any inflammatory process, although the implants were completely encapsulated. (Similar in vivo compatibility tests in rabbit muscle tissue are currently in progress.) No significant changes in mechanical properties could be measured in the implants after the 90-day period of implantation. By adjusting the volume fraction of fibers in a given composite, the modulus of elasticity can be adjusted (with concomittant variations in strength) to meet the biomechanical and dynamic requirements of the appliance. A continuing program to investigate other biocompatible resins and other reinforcement is planned.

Notizen: Copolymers of methyl methacrylate and 2,2-di(4-methacryloxyphenyl) propane, which are suitable for crown and bridge works and artificial bones, were studied. The physical properties of the copolymer, hardness, abrasion resistance, compressive strength, and resistance against water sorption, etc. were improved by copolymerization of methyl methacrylate (MMA) with the titled co-monomer.

Notizen: Twenty-one commercial plastics were exposed to 10% red blood cell suspension in buffered saline and their hemolytic effect was determined. The depression in surface tension of physiological saline solution exposed to the plastic surfaces was recorded and brought into relationship with their hemolytic behavior. It has been shown that both effects occur simultaneously. It is proposed to use the depression in surface tension of saline exposed to prospective plastic applicants as a bloodcindependent screening test for evaluation of plastics which are intended to be exposed to a cardiovascular environment.

Notizen: The fatigue-crack propagation behavior of Type 316 stainless steel was studied under simulated body conditions. The fatigue specimens were immersed in circulating Ringers Solution at a temperature of 98°F. Cyclic loading was accomplished at a frequency and load waveform that corresponded to normal level walking. The concepts of linear elastic fracture mechanics were used to evaluate the fatigue behavior, and it was found that the crack-growth rate was higher under simulated body conditions than for a corresponding test conducted under ambient air conditions.

Notizen: The propagation velocity and absorption coefficient of a pulse of megahertz sound was measured in 25 specimens of embalmed human skull bone. The mass densities of the specimens were also measured and their specific acoustic imped- ances calculated. The data is discussed and presented in tabular as well as graphic form.

Notizen: Three different cyanoacrylate monomers were studied as adhesives for hard tooth structures. Flat plane non-retentive surfaces of extracted human teeth and cold-curing acrylic onlays were used as the adherends. Both tensile and shear adhesive strengths were investigated under wet and dry conditions at room temperature. The commonly used zinc phosphate dental cement was the control material.Under all test conditions the cyanoacrylates were shown to have greater adhesive strength than the dental cement. The MBR-4197 (β,β,β trifluoroisopropyl 2-cyanoacrylate) polymer showed the greatest bonding strength to hard tooth structures. The adhesive strengths of all cyanoacrylate polymers decreased considerably after water immersion but the control dental cement material showed no adhesive strength under the same condition.However, the results of the experimental monomers when compared to the control cement, should encourage further investigations of these monomers for use as dental adhesives.

Notizen: Experiments were investigated on animals' biological tolerance of the copolymers of N-substituted methacrylamides with the monomers which can be considered for uses in the modification of the monomeric backbone. The group of N-substituted methacrylamides is the second one in the series of hydrophilic polymers arranged according to their increasing resistance to hydrolysis, and it follows immediately after the esters of methacrylic acid. Histological analysis has shown that the copolymer of N-ethyl methacrylamide with methyl methacrylate is the best tolerated polymer of this group. In the case of copolymers with butyl acrylate and butyl methacrylate, in the first days after implantation a stronger and more cellular capsula was formed, and an inflammation was observed in the surroundings of the encapsulated implant. Starting from day 30, however, no differences are found in the encapsulation, and the result of healingin of all the polymers is always favorable. No cancerogenic effects were observed; calcification was found only sporadically in the case of the copolymer with butyl methacrylate.

Notizen: The synthesis of poly(lactic acids) from the cyclic lactides and properties of the polymers prepared have been described. Degradation rates in vitro under homogeous and heterogeneous conditions have been measured. The kinetics of deesterification under homogeneous conditions is second order and an activation energy of 11 Kcal/mol has been calculated. This is comparable to the value found for the hydrolysis of alkyl acetates. A biological in vitro method for determining the degradation of poly(lactic acids) has been described. The method indicates, in accordance with expectations, that poly(dl-lactic acid) degrades at a faster rate than L(+) lactic acid. Initial results of medical evaluation of the polymers in suture, rod, and film form are presented.

Notizen: Investigation has been made of the short-term tolerance of hydrophilic polymers on the basis of poly(hydroxy ethyl methacrylates) containing various amounts of acidic and basic groups. The worst tolerance was found with gels containing basic groups alone.

Notizen: The need for esthetic and functionally acceptable radiopaque denture base materials is reflected by numerous reports of patients who ingested or aspirated portions of dentures and reports of difficulties encountered in the removal of these dentures because they could not be located radiographically.The type of denture most commonly ingested or aspirated is a maxillary partial consisting of a palatal piece to which is attached one or more anterior teeth. It may or may not have clasps. Ingestion or aspiration of the foreign body commonly occurs when either broken or ill-fitting dentures are being worn. Few cases have been reported where patients swallowed portions of complete dentures.Previous attempts at providing radiopacity have included addition of heavy metal salts or radiopaque inserts to denture base resins. None of these attempts has been entirely successful.Elimination of dentures as foreign bodies requires a greater effort toward preventive measures by the dentist and the patient. When dentures are swallowed or inhaled, the dentist should immediately seek medical assistance for the patient. The common symptomless period following ingestion or aspiration should not lead the dentist to believe that there will not be serious subsequent complications.

Notizen: The transport of glucose and urea under electro-osmosis across two polyelectrolyte complex membrances and two othermembranns, for comparison, was analyzed in detail, both experimentallyand theoretically.The membranes were characterized by measurements of water content, concentration of coion and countrion in the membrane, and distribution coefficient of glucose and urea in the absence of electric current, as a function of external solution composition. In addition, fluxes of those solutes and solvent were measured as a function fo external solution composition and of electric currentThe observed phenomena were modelled by use of Fick's law of of diffusion, with electro-osmosis treated simply as bulk flow. the effect of stirring was accounted for in terms of a boundars layer mass transfer coefficient.The results indicate a good fit of the model to the data for glucose. For urea, the results indicate substantial binding of urea to the membrane matrix and anomalous behavior in he boundary layer adjacent to the membrane.

Notizen: Physical properties were determied for radiopaque composite denture base materials consisting of poly (methyl methacrylate) as thematrix and 30, 40, and 50% by weight fo a singlane-treated barum fluoride-containing glass powder as the reinforcing filler. Specimens without glass were include for comparision.All of the materials met the requirements of Amerrican ental Association Specification No. 12 for Denture Base Polymer except that t6he material containing 50% glass had less deflection than the minimum required at the 5000-gm load in transverse testing.There was little or no difference among thematerials with respect to hardness, in denation resistance, water sorption, color stability, and resistance to drop impact.Addition of glass of the 30% level decreased the transevers strenght while 50% means with no glass. In general, the addition of glass increased the time to reach only slight effect on densities, and Young's, bulk, shear, and flexural moduli, had only slight effect on solubility and decreased the cold-cure repairability and the coefficient of linear thermal expanision.The solubility of the glass power was aboutfour times that of powdered porcelain teeth after 24 hr, and totaled 0.55% afeter 5 days.

Notizen: This paper deals with the performance of current designs of bone fixation plates, mountedon the anterior surface of fractued equine third metacarpale and tested in uniaxial compression. A full factorial experimental design on three variables, plate length, plate width, and fasterner size provided 27 different variations of the basic design. No replicate ests were conducted. All loads were normalized on mid-shaft done gemetry and compared to he ultimate compressive strength that could be expected of a similar bone of the same age. No capacities above 33% of the strength of an unfractured bone were observed.

Notizen: Interfacing biologic material with foreign substances is a problem common to all implantable devices. This paper discusses these problems with respect to degradation of the material used in fabrication and the body's reaction to the foreign substance. The requirements dictate the type of tissue reaction sought and this in turn determines the base material. A nonreactive material may be ideal for one set of needs but tissue reactivity would be required for another. The specialized tissue “blood” is given special emphasis.

Notizen: Porous pure titanium and titanium-6% aluminum-4% vanadium alloy materials, made by several powder metallurgy techniques, have been studied for potential use as surgical implant materials. Tissue ingrowth into open porosity and favorable physical properties have been found. Tensile strength and ductility data are presented as a function of density. Microscopic observations include scanning electron microscope pictures of the surface of specimens prior to implantation in animals, photomicrographs of the internal pore structure, macrophotographs of surfaces before and after polishing, and histological photomicrographs illustrating the nature of the tissue ingrowth found.

Notizen: The purpose of the investigation was to show the ability of two calcium aluminate ceramic compositions to act as suitable implants for partial replacements of long bones. It was anticipated from previous studies that the ceramic would be well tolerated by the autogenous bone and surrounding soft tissue while the ceramic was slowly dissolving in the body fluids, allowing new osseous tissue to penetrate the resulting pore structure. It was expected that after a period of time the ceramic would no longer exist as a separate entity but would be completely infiltrated with mineralized osseous tissue and ultimately be completely replaced by bone. Two ceramic implants were prepared by slightly different techniques and CaO to Al2O3 ratios. The result was a polyphase ceramic and a nearly single phase ceramic. The polyphase material, after implantation in the test subject for 32 weeks, was completely impregnated with connective tissue while undergoing considerable alteration in microstructure. The single-phase material was not altered significantly in any way. This implant could not be fully evaluated for its ability to allow for osseous tissue formation on its surface, or within its open pore structure, due to slight variations in the original fixation of the implant and resulting attempts to correct the problems.

Notizen: The maintenance of percutaneous cables for physiological monitoring or for the introduction of power to artificial organs is an attractive concept, but two problems interfere with their long-term survival. The exit sites regularly become infected, and the preparation is subject to disruption by the animal.These two problems can be solved by the design of a suitable skin outlet fixture of Teflon and velour fabric. The skin margins proliferate and adhere to the velour, producing a dry bacteria-proof seal which prevents the development of infection. The skin outlet fixture is shaped so that it is immobilized in relation to the surrounding skin, preventing excessive strain from being applied to the fabric-skin interface.Skin outlet fixtures of porous ceramic offer theoretical advantages, but there has been little success in attempts to induce the skin margins to proliferate into the porosities of the ceramic.

Notizen: Several new surgical techniques in which artificial adhesives are used have been developed. Perforated eyeballs were glued, plastic windows were glued to hazy and opaque corneas, and techniques of retinal surgery wth a minimum use of sutures have been developed.The expanding artificial implant is also described. This is a plastic that imbibes body fluids, swelling to a predetermined volume. Upon swelling, it can fill a cavity or it can produce a deformation in the surrounding tissues. Such a plastic is being investigated as a vitreous substitute. It is also being used to buckle the wall of the eye which carries the blood supply to the retina to reapproximate these layers in order to restore the retina's sensitivity to light. The main feature of this development is that a relatively large implant can be introduced into an organ or tissue through a small incision.

Notizen: The plasminogen levels and the reactivities of plasmas in two commonly used blood coagulation tests have been compared for man and seven mammals. The plasmas of three nonhuman primates in general reacted as did human plasma in tests for plasminogen activation and in reactivity in the partial thromboplastin time test. The dog had the highest level of plasminogen, and the goat the lowest, of the eight species tested. Overall, the pig appeared to have the most reactive blood coagulation mechanism, clotting the fastest and lysing the slowest, while man's was among the least reactive in clotting and intermediate in lytic activity of those tested. Aside from the nonhuman primates, the calf's clotting and lytic mechanisms resembled those of man more nearly than did those of the other mammals tested. The influence of these species differences on selection of animals for in vivo evaluation of blood vascular prosthetic materials and devices is discussed.

Notizen: The reasons for the limitations of current techniques for the evaluation of the biohazards and biocompatibility of new candidate materials may be summarized as follows: (1) There is no agreement on how these materials are to be standardized interms of chemical, physical, mechanical, or biological criteria; (2) basic bioengineering data, needed to serve as specifications for reconstruction materials, are lacking for mosttissues in the body; (3) there is a lack of agreement as to what constitutes a valid biological test and its interpretation(s) (4) many in vitro and in vivo tests in animals have limited predictability for humans; (5) there has been an overemphasis on studies of the effect of materials on the biological environment at the expense of bioengineering and biodegration studies; (6) except in cases of obvious problems, there has been relatively little follow-up of the large numbers of patients receiving implanted materials. Little effort has been exerted to exploit this important opportunity to obtain human data: (i) By registering each implant material; (ii) by collecting data on performance; (iii) by collecting data on local or systemic side effects; (iv) by collecting data on biodegradation; (v) by obtaining biopsy or autopsy material whenever possible; and (vi) by examining implants following removal. The limitations of current techniques for the evaluation of new materials are due not so much to the lack of availability of potential test approaches as to a lack of willingness to select, adopt, and actually conduct comparative, objective tests of high predictive value for human patient response. In fact, the confusing array of test approaches and the lack of coordination and completeness of testing efforts has become one of the key factors limiting further progress in materials research, making it difficult for materials scientists and engineers to determine whether their product is likely to be of use in human patients, whether its performance is better or worse than similar products already developed, and hence its potential value as a marketable product. It is proposed that a systematic approach to the development of safe and suitable implant materials focus on three areas of investigation, namely: (1) Matching of the engineering properties of the materials and finished devices with those of the corresponding human tissues; (2) Properties of the implant materials which might exert an effect on the biological system; and (3) properties of the biological environment which might have an effect on the material. To date research on the biocompatibility and biohazards of materials has focused almost entirely on the second area of investigation to the exclusion of the other two. It can be expected that greater attention to the bioengineering specifications of living tissues, and the effects of the biological environment on materials will result in safer materials, exhibiting a closer correspondence to the tissues they are intended to replace. Also greater future emphasis on follow-up human patient material can be expected to substantially advance the knowledge necessary for the development of new implant materials.

Notizen: Although satisfactory nonabsorbable sutures made from a variety of synthetic and natural materials have been available for a number of years, since ancient times only collagenous absorbable sutures have found general acceptance. While adequate, catgut and the more recently developed regenerated collagens have inherent disadvantages common to many complex natural substances, particularly variability in composition and properties.A new synthetic absorbable suture has been developed from polyglycolic acid .This material was chosen after testing a wide variety of polymers for the appropriate absorbability behavior in animals and for the required physical and mechanical properties. Polyglycolic acid suitable for this use was most conveniently prepared by the ring opening melt polymerization of glycolide. Development of a reliable process for this commercially unavailable monomer led to the discovery of the existence of two glycolide polymorphs one of which exhibits erratic polymerization behavior after exposure to trace amounts of moisture.Polyglycolic acid was converted into fiber by melt extrusion, stretching, and heat setting. Braided sutures prepared from these fibers exhibit high strength, excellent handling properties, minimal tissue reactivity, and a similar but more reproducible absorption rate than catgut. Clinical studies with these sutures are in progress.

Notizen: This report concerns the modification of a velour fabric for use in the vascular system. A specially prepared polyurethane was sprayed on the outer surface of this fabric resulting in a negative surface charge. The advantages of this composite were the incorporation of a thin layer of neointima onto the velour surface. Because of its thinness, viability was maintained resulting in a living nonthrombogenic layer at the vascular interface. To prove the efficacy of this material the authors have implanted it into the right atrium, replaced segments of the inferior vena cava, replaced the 4-mm carotid artery, and have used it in the construction of an artificial ventricle device. All performed in a superior fashion with long-term promotion of a viable neointima. It is hoped that the concept of negatively charged velours may be applicable to other phases of biomaterial development.

Notizen: Two methods have been developed to heparinize polyester fibers. One approach involves a thermofixation process. In this process, a water-insoluble complex of heparin is “fixed” into the bulk of the polyester fiber by the application of heat. The second method uses an amino silane coupling agent. The heparin molecule is ionically bonded to the protonated primary amine. Both processes yield a heparinized fiber which maintains a high level of heparin in contact with NaCl solutions. The thermofixation method has been used to treat several Dacron vascular prostheses (10 mm OD) which have been implanted into the inferior venae cavae of dogs. These preliminary in vivo studies indicate that heparinized polyester fibers result in a vascular prosthesis with increased resistance to blood clotting. One 10 mm OD prosthesis has open for more than 9 months.

Notizen: Current trends in blood oxygenator development favor devices which separate the blood phase from the gas phase by a thin film of plastic material. The additional barrier to diffusion presented by the plastic film is a low price to pay for the advantages of the “membrane oxygenator” over its cruder competitors of the “bubbler” or “filmer” type, namely, the absence of direct exposure of blood to gas (with the ensuing damage to the most fragile blood constituents) and the physical constraint of the extracorporeal blood volume to a fixed-size compartment (obviating the need for complex volume control systems). The first generation of membrane lungs relied on the plastic materials (“Teflon” and silicone rubber) and shapes (flat sheets and tubes) available for industrial uses. A new line of devices will be made possible by the development of new biomaterials and the development of production technologies for the specific purposes of artificial organ research.

Notizen: The ability to produce a viable bond at the interface of living tissue and inert polymeric materials has been tested in three different contaminated environments. The prosthetic implants, consisting of nylon 66 velour and polyurethane, were tested in the intestinal wall of rabbits, the urinary bladder of dogs, and the skin of rats. The small (1.5 × 2.0 cm) velour implants had a tendency to slough in the intestinal wall while a tubular prosthesis (6 × 3 cm) and a large patch (4.5 × 3.0 cm) were of varying success. Utilization of the prosthesis to replace 25% of the urinary bladder wall was successful for as long as 7 months, at which time postmortem examination of the animals revealed no anastomotic leaks or calculi formation. Replacement of 20 or 40% of the rats burned and infected skin resulted in less than a 10% mortality. Furthermore, histologic studies of all successful prostheses revealed a prompt enmeshing of the velour filaments with fibrin followed at 3-4 days with an ingrowth of fibroblasts, capillaries, and a few foreign body giant cells. Maturation of the wound resulted in a dense, mature collagen matrix. Removal of the prosthesis at this time occurred only by the disruption of the sub-prosthetic tissue.

Notizen: The objective of this study was to assess the finished surfaces of various dental composite resin restorative materials using common rotating abrasive devices and diamond and iron-carbide dental burs. The “finished” surfaces were compared with surfaces created by a polyester matrix band. The “finished” composite resin materials were also compared with filled resins as well as the unfilled polymethyl methacrylate resin. Evaluation of the various finishing procedures was made from scanning electron micrographs. Results indicated that “finished” resins, both filled and composite, departed greatly from an acceptable polished surface and that the use of any resin filled with glass rods would be contraindicated.

Notizen: The past, present, and future of biocompatible materials are reviewed as they relate to cardiovascular prostheses. Many of these materials are no longer simple systems and do not lend themselves to conventional steam or heat sterilization procedures by virtue of their lability. The object of this paper is to briefly discuss sterilization problems encountered with these labile materials using ionization radiation and gases, in terms of their physico-chemical structures.

Notizen: Segmented polyurethane does not indiuce acute toxcity when subjected to intracutaneous and intravascular tests with mices and rabbits. Specimens, which have been implanted in dogs for 18 months, exhibit stability heretofore unattributed tothe general class of polyurethanes. Data on tensile properties, abraxion resistance when wet, tolerance to autoclaving, results of acute toxicity test, and stablity of long-term implants are described along with appropriate means of processing the polymer into useful biomedial devices.

Notizen: An antibiotic eluting catheter has been designed to suppress bacteriuria associated with indwelling catheter drainage of the bladder. A coating of hydrophilicgel plastic, Hydron, is used as the vehicle from which the antimicrobial agent is locally released. In 15 dogs, indwelling Hydron-cephalothin catheters provided a high degree of protection against bacteriuria up to 96 hr. After 48 hr, all 12 control animals became infected.In preliminary clinical trials involving 60 definitive cases Hydron-cephalothin (Group II) and plain Hydron (Group III)-coated indwelling catheters prevented the development of bacteriuria to a significant degree compared with uncoated latex controls (Group I). At the end of 5 days, the cumulative per cent infected for Groups I, II, and III was 75, 33, and 4.7%, respectively. Increased lubricity and reduced urethral mocosal reaction at the catheter interface promote drainage and prevent accumulation of detritus at the meatus. An indwelling antibiotic eluting catheter appears to interdict bacterial invasion of the bladder by, through, and around the catheter.

Notizen: The properties of the three main classes of orthopedic alloys (316L steel, Co-Cr alloys and titanium) are discussed, while all show good general corrosion resistance, the 316L steel have a tendency toward crevice corrosion. Fatigue fracture due to poor design and fabrication defects is discussed. A summary of some problems associated with the evaluation of tissue response is presented. Finally, a review of several new trends toward achieving tissue adhesion is presented.

Notizen: Test implantations were carried out on rats in order to investigate the effects of porosity of heterogeneous poly(glycol monomethacrylate) gels on their healingin. The porosity was varied by changing the water content in initial monomeric mixture. The histological analysis has shown that spongy polymers containing 50 and 60% of water in the initial mixture are healed-in similarly to the homogeneous gel by encapsulation with collagen fibrous tissue. In polymers having higher content of water in the initial mixture, i.e. higher porosity, the vessels from the new formed fibrous capsula penetrate into the implant. The higher the porosity, the narrower the capsula and the broader the zone of cellulization and new-formed capillaries, penetrating into the implant. In the case of polymers of higher porosity, giant multinuclear cells are observed in the margin of the implant. The positive Kóssa's calcium reaction was found only sporadically on the margin of the implant.

Notizen: The pressure variations of the elastic constants of the constituent phases of dental amalgam (γ-Ag3Sn, γ1-Ag2Hg3, and γ2-HgSn7-8) were investigated in the 0-50 kilobar range. The velocities of propagation of longitudinal and transverse ultrasonic waves were measured using an ultrasonic interferometer and a solid media pressure apparatus. Computer analysis yields the pressure dependence of the bulk modulus, shear modulus, Young's modulus, and Poisson's ratio; atmospheric pressure values are obtained by back extrapolation from the high pressure measurements. The values of these elastic constants are related to the crystallographic structures of the individual alloys. The possibility of high pressure first order polymorphic transitions in γ and γ2 is also discussed.

Notizen: The dialysis and flow properties of a selected copolymer system, consisting of polyethylene terephthalate and polyoxyethylene glycol, have been studied in some detail. Such transport information should serve as a guideline to future development of improved, synthetic, hemodialysis membrane materials. By varying the size of the polyoxyethylene glycol segment, the transport properties of this copolymer have been examined as a function of the chemical and physical properties of the system. Membrane transport has been described by three flow parameters: the filtration, reflection, and solute permeability coefficients. Data for three copolyether-ester compositions and several aqueous solutes are discussed and compared with data on cuprophane, the cellulose material currently used in the Kiil hemodialyser.

Notizen: Ideally, materials from which splints, braces, casts, and other orthopedic appliances are to be made should be capable of being shaped directly against the patient. They should be simple and quick to use, and require the minimum of special equipment. Appliances made from them should be dimensionally stable in service and acceptable to the patient in terms of comfort, weight, durability, and appearance.Synthetic trans-1,4 polyisoprene, prepared with a Ziegler catalyst system, is such a material. It crystallizes at temperatures below 130°F; it is a hard semi-rigid rubber at room temperature; and its compounds can be molded directly against the skin without discomfort. Laboratory tests show that molded shape and strength can be maintained even under stress at temperatures up to about 120°F, and service performance fully supports the results of laboratory testing.This paper describes the properties of trans-1,4 polyisoprene that make the polymer suitable for many orthopedic appliances, and includes examples of its uses in hospitals and rehabilitation institutions. Special attention is given to describing a recently developed technique for the making of artificial limb sockets using trans-1,4 Polyisoprene.