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  • Polymer and Materials Science  (4)
  • solvent effects on polymer gel rheology  (3)
  • Atmospheric circulation
  • Australia
  • Biochemistry and Biotechnology
  • Water budget
  • 1990-1994  (7)
  • 1
    Electronic Resource
    Electronic Resource
    Viscometric Study of Polyacrylic Acid Systems as Mucoadhesive Sustained-Release Gels (1991)
    Springer
    Pharmaceutical research 8 (1991), S. 1408-1412 
    Details
    ISSN: 1573-904X
    Keywords: pharmaceutical gel formulation ; Carbopol gel ; viscosity ; propranolol ; solvent effects on polymer gel rheology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract This report describes a novel nonaqueous polymeric formulation that exhibits low-viscosity fluid behavior for ease of spraying with conventional nebulizer, which when sprayed into the nasal cavity, transforms to a high-viscosity gel for efficient retention and drug absorption. The transformation occurs because of the rheological changes induced by a change in the solvent composition of the polymeric formulation in the moist nasal cavity. Such a rheological change would then facilitate enhanced residence time of the drug at the site of administration in order to avoid drainage losses. This study reports the results of the effects of a variety of factors such as solvent composition and polymer concentration on the rheological properties of a polyacrylic acid polymer. An attempt to correlate viscosity enhancement effects with enhanced and sustained-release behavior of propranolol, a drug that undergoes extensive first-pass effects, from such formulations via nasal administration in beagle dogs is also described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1015805307999
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  • 2
    Electronic Resource
    Electronic Resource
    Mixture Experimental Design in the Development of a Mucoadhesive Gel Formulation (1991)
    Springer
    Pharmaceutical research 8 (1991), S. 1401-1407 
    Details
    ISSN: 1573-904X
    Keywords: mixture model ; pharmaceutical gel formulation ; Carbopol gel ; viscosity ; solvent effects on polymer gel rheology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The objective of the present study is to apply response surface methodology to the design and analysis of composite experiments containing independent covariate(s). The approach is illustrated here by the study of viscosity characteristics of a polymeric mucoadhesive formulation in multicomponent solvent vehicles. The nonaqueous formulation will produce a gel network with significant rheological change when in contact with body fluids. The process of water inclusion will induce not only solvent compositional change of the mixture but also concomitant dilution of the polymer concentration. To study the viscosity change over the solvent compositions and polymeric concentrations of interest, an experimental design is utilized consisting of a 10-point simplex-centroid lattice augmented with three interior points at each polymeric concentration. The contour patterns are compared with the experimental, data using the variance and lack of fit, starting with the Scheffe linear model and building up to the full cubic model including the covariate terms. The fitted model provides information needed to predict optimum formulations, i.e., initial viscosity of less than 100 cP, but yielding rheological profiles commensurate with high degrees of substantivity when diluted with water. For illustrative purposes, the Carbopol resins neutralized with a 1:1 molar equivalent ratio of triethanolamine in three primary solvents, propylene glycol, glycerol formal, and water, were chosen for this study.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1015853223929
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  • 3
    Electronic Resource
    Electronic Resource
    Viscoelastic Properties of Polyacrylic Acid Gels in Mixed Solvents (1992)
    Springer
    Pharmaceutical research 9 (1992), S. 1659-1663 
    Details
    ISSN: 1573-904X
    Keywords: pharmaceutical gel formulation ; Carbopol gel ; viscoelasticity ; solubility ; solvent effects on polymer gel rheology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The objective of this study is to investigate the viscoelastic properties of Carbopol 934P polymeric systems in a variety of mixtures of pharmaceutical solvents. Carbopol 934P neutralized with a 1:1 equivalent ratio of triethanolamine was dissolved in various binary or ternary solvent mixtures consisting of propylene glycol, glycerol formal, and water. Dynamic moduli G′ and G″, complex viscosities, η′ and η″, and loss tangent, tanδ, were examined over a frequency range of 10-3 to 10 Hz using an oscillatory viscoelastic rheometer at 30°C. The results indicated that for 0.5-1.5 wt% neutralized Carbopol in ternary mixtures, G′ and G″ increased by 3-4 orders of magnitude and the phase angle decreased from 80 to 25° when the water content in the solvent mixture increased from 10 to 80 wt%. These studies also indicated that the addition of water to nonaqueous Carbopol 934P polymer systems transforms them from low-viscosity solutions to gels with significant elastic behavior involving physical interaction and entanglement of polymer segments with solvents.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1015841214591
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  • 4
    Electronic Resource
    Electronic Resource
    Measurement of the interfacial tension between polyethersulfone and a thermotropic liquid-crystalline copolyester (1993)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 31 (1993), S. 221-227 
    Details
    ISSN: 0887-6266
    Keywords: interfacial tension ; thermotropic ; copolyester ; polyether sulphone ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Due to the increasing interest in forming blends of liquid-crystalline polymers with conventional thermoplastics, it becomes important to determine the interfacial tension between two such polymers. A method for evaluating the interfacial tension between a thermotropic copolyester based on hydroxybenzoic and hydroxynaphthoic acid residues, and polyethersulfone is presented, based on the Fort and Patterson method. It is found that the value of the interfacial tension in the melt is much higher than is the case between conventional polymer pairs. It is suggested that this high value reflects an entropic effect due to the strong exclusion of the flexible coil polymer from the nematic melt. © 1993 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1993.090310211
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  • 5
    Electronic Resource
    Electronic Resource
    Extensive porosity at the cement-femoral prosthesis interface: A preliminary study (1993)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 27 (1993), S. 71-78 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: This study is the first description of the extensive porosity which is preferentially located at the cement-prosthesis interface of cemented femoral components of total hip replacements. The observation is important because the interfacial porosity may decrease the strength of the cement-femoral prosthesis interface and jeopardize the mechanical integrity of the cement mantle. We examined the cement-metal interfaces from a multiplicity of in vivo and in vitro specimens using both optical and scanning electron microscopy. These samples included several stem designs, implants made from either Co-Cr or Ti alloy, implants made with a variety of surface finishes and both centrifuged and uncentrifuged cement. All in vivo and in vitro samples had marked porosity in the cement focally concentrated at the cement-metal interface. The amount of porosity at the interface greatly exceeded the amount of general porosity found throughout the bulk cement. Centrifuging did not affect the interfacial porosity, and neither did alloy nor surface finish. The presence of these pores may be expoained by the rheological characteristics of the cement. © 1993 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jbm.820270110
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  • 6
    Electronic Resource
    Electronic Resource
    Comparison of 316LVM and MP35N alloys as charge injection electrodes (1994)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 28 (1994), S. 233-240 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: An In vitro comparison of the corrosion response of 316LVM stainless steel and MP35N (a CoNiCrMo alloy) electrodes under conditions appropriate to applications in functional electrical stimulation (FES) was made. Electrodes of both alloys were subjected to a cathodic 40 μC/cm2 charge injection protocol and the potential transient response was recorded over a 96 h period. The transient responses were compared with potentiodynamic polarization data used to establish the quasiequilibrium response of the alloys in the carbonate and phosphate-buffered saline electrolyte used in the study. The MP35N electrodes exhibited extensive pitting corrosion during charge injection, whereas little corrosion was observed on 316LVM electrodes. An explanation for the susceptibility of MP35N to corrosion during charge injection is found in the potentiodynamic polarization data, which reveal a breakdown potential (critical pitting potential) of 0.45 V (SCE) for MP35N compared with 1.05 V (SCE) for 316LVM. Factors that may influence corrosion response during charge injection from alloys exhibiting active-passive behavior are discussed. © 1994 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jbm.820280214
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  • 7
    Electronic Resource
    Electronic Resource
    Effect of vacuum mixing on the mechanical properties of antibiotic-impregnated polymethylmethacrylate bone cement2 (1990)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 24 (1990), S. 573-580 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Polymethylmethacrylate bone cement, containing either no added antibiotic, 0.5 g of Vancomycin, 1.0 g of Vancomycin, or 1.0 g of Tobramycin, was mixed either in air or a vacuum chamber. Following storage in a water bath at 37°C for 48 h, the specimens were tested in four-point bending. The porosity of the specimens was assessed radiographically, and their antibacterial activity was monitored for 21 days. The bending strength of the vacuum mixed specimens containing no antibiotic was 40% greater than that of similar air-mixed specimens. However, there were no significant differences in the bending strength of either the air-or vacuum-mixed specimens when any of the antibiotic dosages were added. The bending modulus of the vacuum-mixed specimens, containing no antibiotic, was significantly greater than the moduli of all the other specimen groups which did not differ from each other. Vacuum mixing reduced the apparent porosity of the specimens fivefold, and while the addition of antibiotic did not effect porosity of the air-mixed specimens, that of the vacuum-mixed specimens was doubled. Although initial rapid decreases were seen, leaching of antibiotic from the cement and antibacterial activity continued through the 21-day monitoring period.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jbm.820240504
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