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PubMed1988

Permeability of a heparin-polyvinyl alcohol hydrogel to thrombin and antithrombin III.

The diffusivities of thrombin and antithrombin III in a heparin-polyvinyl alcohol hydrogel were estimated and used to demonstrate that diffusion limits the effectiveness of the immobilized heparin in the interior of such hydrogels. Diffusivities were calculated from permeabilities and partition coefficients measured with films in a diffusion chamber apparatus. The diffusion coefficients were estimated to be 6 +/- 4 X 10(-8) cm2/s for thrombin and 4 +/- 2 X 10(-8) cm2/s for antithrombin III in 10% gel membranes with or without immobilized heparin. Using the diffusivity of thrombin and a Thiele-type modulus, the effectiveness factor of a spherical heparin-PVA bead used to accelerate the inactivation of thrombin by antithrombin III was found to be 4-9% (diameter range 250-150 micron). While indicating that diffusion of thrombin limited the full utilization of the immobilized heparin, these values for the effectiveness factor could not completely account for the low apparent heparin activity (0.2%) in a thrombin time test of heparin-PVA "beads" (J. Biomed. Mater. Res., 17, 359 (1983]. Other factors such as the immobilization chemistry or the diffusion of thrombin-antithrombin III complex must be considered for a full explanation of the thrombin time results.

Animals↗
PubMed1991

Platelet consumption by polyvinyl alcohol coated tubing in canines.

Polyvinyl alcohol (PVA)-coated polyethylene tubing, with or without immobilized heparin, caused severe thrombocytopenia and enhanced the production of new platelets when inserted in a chronic arteriovenous shunt in canines. A similar length of uncoated polyethylene tubing neither lead to thrombocytopenia nor significantly enhanced platelet regeneration, relative to the shunt only without a test section. Platelet regeneration was monitored by the malondialdehyde assay, which was assumed to make a distinction between "new" and "old" platelets. This distinction was combined with the platelet count values to enable calculation of the cumulative consumption curve and the initial fractional consumption rate in the presence of a non constant platelet count. The resulting initial fractional consumption rates were: 34%/day for PVA, 20.5%/day for polyethylene, and 18%/day for the shunt only blank.

Animals↗
PubMed1992

Preparation and thrombogenicity of alkylated polyvinyl alcohol coated tubing.

A polyvinyl alcohol hydrogel (PVA) was reacted with a C18 isocyanate at 80 degrees C in dimethyl formamide (DMF) in order to improve the platelet reactivity of the hydrogel through an influence on albumin adsorption or retention. A C4 isocyanate was used as a control. Surface coverage by XPS appeared to be approximately 100% for both C4 and C18 modified surfaces, although the limited solubility of C18 isocyanate in DMF may have resulted in a nonuniform surface. Relative to PVA or the solvent treated control, octadecylation resulted in increased albumin adsorption (from a single protein solution) and increased retention when the adsorbed albumin was exposed to a fibrinogen solution. However, octadecylation did not obviate the platelet reactivity problem in preliminary studies: systemic platelet counts were reduced by about half over 4 days in a canine AV shunt experiment and the initial rate of platelet destruction for C18-PVA was greater (36%/day) even than for the solvent-treated PVA. Surprisingly in preliminary studies butylation of PVA resulted in little or no thrombocytopenia and did not appear to increase significantly the fractional rate of platelet destruction relative to the shunt only blank. It is presumed that the nonspecific effect of alkylation (independent of chain length) was the dominant contribution to the reduced platelet reactivity. A similar effect of C18-PVA presumably would have been observed had the limited solubility of C18 isocyanate not precluded a uniform surface coverage.

Adsorption↗
PubMed1993

Polyvinyl alcohol plasma deposited nylon 4 membrane for hemodialysis.

Polyvinyl alcohol (PVA) is a hydrophilic and blood compatible material, but it is easily hydrolyzed in aqueous solution. Various methods, including chemical crosslinking and gamma-ray irradiation, have been investigated by many researchers for overcoming the instability of PVA in aqueous solution. This study suggests a new hemodialysis membrane, which is prepared by plasma depositing vinylacetate (VAc) onto annealled nylon 4 membrane, followed by hydrolysis treatment. This improves the blood compatibility of nylon 4 and overcomes the hydrolysis problem of PVA. In addition to conventional plasma deposition, the plasma initiated interpenetrating network (IPN) method is also investigated. The new hemodialysis membranes prepared by both conventional plasma deposited VAc onto nylon 4 (PPVA/N4) and IPN polymer of plasma initiated VAc onto nylon 4 (PIPVA/N4 IPN) show significant improvement in blood compatibility. However, the solute permeabilities of PIPVA/N4 IPN membranes are higher than those of PPVA/N4 membranes. The permeabilities of NaCl, vitamin B12, and albumin for membranes prepared by IPN at 80 W, 30 sec plasma deposited conditions, i.e., the optimized conditions, are 3.614, 0.070, and 0.000 x 10(-5) cm2/min, respectively. The mole ratio of adsorbed fibrinogen to adsorbed albumin (the mole ratio F/A) for this membrane is 0.20, and it also shows excellent blood compatibility in this study.

Biocompatible Materials↗
PubMed2006

The polyvinyl alcohol-bacterial cellulose system as a new nanocomposite for biomedical applications.

Finding materials suitable for soft tissue replacement is an important aspect for medical devices design and fabrication. There is a need to develop a material that will not only display similar mechanical properties as the tissue it is replacing, but also shows improved life span, biocompatibility, nonthrombogenic, and low degree of calcification. Polyvinyl alcohol (PVA) is a hydrophilic biocompatible polymer with various characteristics desired for biomedical applications. PVA can be transformed into a solid hydrogel with good mechanical properties by physical crosslinking, using freeze-thaw cycles. Hydrophilic bacterial cellulose (BC) fibers of an average diameter of 50 nm are produced by the bacterium Acetobacter xylinum, using a fermentation process. They are used in combination with PVA to form biocompatible nanocomposites. The resulting nanocomposites possess a broad range of mechanical properties and can be made with mechanical properties similar to that of cardiovascular tissues, such as aorta and heart valve leaflets. The stress-strain properties for porcine aorta are matched by at least one type of PVA-BC nanocomposite in both the circumferential and the axial tissue directions. A PVA-BC nanocomposite with similar properties as heart valve tissue is also developed. Relaxation properties of all samples, which are important for cardiovascular applications, were also studied and found to relax at a faster rate and to a lower residual stress than the tissues they might replace. The new PVA-BC composite is a promising material for cardiovascular soft tissue replacement applications.

Animals↗
PubMed2006

Anisotropic polyvinyl alcohol hydrogel for cardiovascular applications.

Polyvinyl alcohol (PVA) is a hydrophilic polymer with various characteristics desired for biomedical applications and can be transformed into a solid hydrogel by physical crosslinking, using a low-temperature thermal cycling process. As with most polymeric materials, the mechanical properties of the resultant PVA are isotropic, as oppose to most soft tissues, which are anisotropic. The objective of this research is to develop a PVA-based hydrogel that not only mimics the nonlinear mechanical properties displayed by cardiovascular tissues, but also their anisotropic behavior. By applying a controlled strain to the PVA samples, while undergoing low-temperature thermal cycling, we were able to create oriented mechanical properties in PVA hydrogels. The oriented stress-strain properties of porcine aorta were matched simultaneously by a PVA hydrogel prepared (10% PVA, cycle 3, 75% initial strain). This novel technique allows the controlled introduction of anisotropy to PVA hydrogel, and gives a broad range of control of its mechanical properties, for specific medical device applications.

Animals↗
PubMed1987

Effects of heat treatment on the permeability of polyvinyl alcohol films to a hydrophilic solute.

Polyvinyl alcohol (PVA) films may be useful as release-controlling membrane systems. Untreated, they are readily permeable to water and hydrophilic drugs. Because heating has been used to increase crystallinity and thus reduce the solubility and swelling in water of PVA films, we have studied the effects of heat on the permeability of PVA films to a water-soluble drug marker. Heat treatment was varied in the temperature range 100-200 degrees C for 1 h. The effect of time of heating was studied at 100 degrees C for 0.5-160 h. After pre-equilibration with water (heat-treated membranes remained intact, untreated ones dissolved), membrane permeabilities to methylene blue in aqueous solution (37 degrees C) were determined in a rotating diffusion cell. Permeabilities decreased with increased heating times (0.98-0.039 cm X min-1 for 0.5-160 h at 100 degrees C, respectively). Heating in air or N2 produced similar results. Further dramatic decreases in permeability occurred with increasing pretreatment temperatures; membrane permeability fell by a factor of approximately 500 with increasing temperature in the range 100-200 degrees C. There was no evidence of decomposition at temperatures less than or equal to 190 degrees C for 1 h. Results were consistent with literature reports of heat-induced increases in crystallinity. Membranes were simple to prepare and permeability could be controlled without recourse to chemical manipulation.

Diffusion↗
PubMed1993

Evaluation of various solvent systems for modeling solute sorption with plasticized polyvinyl chloride materials.

The partitioning behavior of 16 chemically diverse model solutes was determined for four model solvents (octanol, hexane, heptane, and chloroform) and two components of plasticized polyvinyl chloride [PVC; PVC resin and dioctyl phthalate (DOP) plasticizer]. Interactions between these model solutes and four plasticized PVC polymers, differing in their PVC-to-DOP weight ratio, were studied. The data were used to evaluate the utility of the solvents and components to act as PVC interaction models (correlating the interaction constant of the plastic with the solvent-water partition coefficients of the solute). The ability of any single solvent to model the material-solute interaction was limited because of the multiple mechanisms by which the PVC and the solute can interact. Several bimodal solvent systems, including octanol and hexane, DOP and PVC resin, and octanol and heptane, mimic the behavior of polymers studied with a higher degree of accuracy. The success of these pairings is directly related to their ability to target different potential material-solute interaction mechanisms. The interaction properties of the test plastics are strongly impacted by the amount of plasticizer in the material. The interaction properties of the materials studied could be effectively represented as a mass-related average of the interaction properties of the major components of the material.

Absorption↗
PubMed1993

Modeling of solute sorption by polyvinyl chloride plastic infusion bags.

Methods for estimating the equilibrium and time-dependent sorption of solutes by polymeric containers have been developed. The methods are specifically applied to the sorption of solutes by polyvinyl chloride (PVC) infusion bags. The methods correlate the partition coefficients and dissociation constant (when appropriate) of the solute, the physical dimensions of the container, and solution pH with single parameters that dictate the shape of the sorption profile. To determine the equilibrium sorption level for PVC containers, the fractional binding of a solute is correlated with its hexane-water and octanol-water partition coefficients. Calculations based on single partition coefficients are less effective in terms of mimicking the behavior of the PVC. To determine the sorption profile (fractional binding versus time), the partition coefficients are related to the fraction binding at a particular time through a single parameter referred to as the sorption number. Equilibrium fractional binding and sorption profiles for various drugs stored in PVC containers are generated with the models and agree well with reported behavior. The effect of pH on the sorption process is also examined.

Adsorption↗
PubMed1997

Polyvinyl alcohol cryogel: an ideal phantom material for MR studies of arterial flow and elasticity.

The authors present a unique application of polyvinyl alcohol (PVA) cryogel as an anthropomorphic, elastic, vascular phantom material that can be used in MR imaging. The composition consists of two nontoxic ingredients: water and PVA. The biomechanical and MR properties can be adjusted to be similar to those of excised porcine aortas by varying the number of freeze-thaw cycles to which the PVA solution is exposed. The authors present the T1, T2, shrinkage, and tensile properties of PVA cryogel tubes as a function of freeze-thaw cycles. MR images of a dual elastic aortic phantom undergoing pulsatile motion are shown.

Animals↗
PubMed2005

Perineal noise recording as a non-invasive diagnostic method of urinary bladder outlet obstruction: a study in polyvinyl alcohol and silicone model urethras.

AIMS: At present, an invasive pressure flow study is recommended to diagnose urinary bladder outlet obstruction. This method induces the risk of urinary tract infection and urethral trauma. We studied perineal noise recording as an alternative, non-invasive diagnostic method in three flexible/extensible model urethras and two silicone tubes. METHODS: The flexible/extensible model urethras were made of a 10% aqueous solution of polyvinyl alcohol (PVA) and differed in wall- stiffness, the silicone tubes differed in diameter and wall-thickness. Three degrees of obstruction were applied by inflating a cuff placed around the PVA-urethras and by compressing the silicone tubes with an adjustable clamp. Noise, produced during flow, was recorded at three positions distal to the obstruction using a piëzoceramic contact microphone. RESULTS: The average amplitude of the noise and the essential frequency of the power spectrum of each noise recording depended significantly on the degree of obstruction, the position of the microphone and the wall-stiffness in PVA-urethras and the diameter in silicone tubes. CONCLUSIONS: Based on the results of this study perineal noise recording shows good potential as an alternative method for diagnosing bladder outlet obstruction.

Data Interpretation, Statistical↗
PubMed2006

A biophysical model of the male urethra: comparing viscoelastic properties of polyvinyl alcohol urethras to male pig urethras.

AIMS: We aim at developing a non-invasive method for grading and diagnosing urinary bladder outlet obstruction, based on noise recording with a perineal contact microphone during voiding. We found that the noise production during voiding depends amongst others on the viscoelastic properties of the urethral wall. To further test our method, we need a realistic biophysical model of the male urethra. METHODS: We made various model urethras with different viscoelastic properties from a 10% aqueous solution of polyvinyl alcohol cryogel. We measured the viscoelastic properties of each model and compared them to those of the male pig urethra. The male pig urethra was used, as it is physiologically comparable to the human male urethra. The viscoelastic properties of both model and pig urethras were measured by applying strain to the urethral wall in a stepwise manner and recording the pressure response. We fitted the step-response of a mechanical model to this pressure response and derived the viscoelastic properties from the coefficients of this response. RESULTS: A uniform model urethra that was freeze-thawed three times, with a Y-shaped flow channel was found to best represent the male pig urethra. CONCLUSIONS: We consider the three times freeze-thawed model urethra with a Y-shaped flow channel the best model of the human male urethra. And we therefore use this model urethra for studying the relation between noise recording during urine flow and the degree of bladder outlet obstruction.

Animals↗
PubMed1993

Surface-enhanced Raman spectroscopic detection of CO2-(3), SO2-(3), and nucleic acid bases using polyvinyl alcohol film doped with Ag fine particles.

Surface-enhanced Raman scattering (SERS)-active polyvinyl alcohol films doped with Ag particles have been prepared by a counterdiffusion method. SERS spectra of CO2-(3), SO2-(3), and DNA bases have been observed by using the films. The films containing aggregated Ag particles are useful to observe SERS spectra of adsorbates. DNA bases (cytosine, uracil, thymine, guanine, and adenine) can be detected at a level of 10(-8)-10(-9) M by this method.

Adenine↗
PubMed1993

RNA-RNA in situ hybridization using digoxigenin-labeled probes: the use of high-molecular-weight polyvinyl alcohol in the alkaline phosphatase indoxyl-nitroblue tetrazolium reaction.

A nonradioactive RNA-RNA in situ hybridization method using digoxigenin-labeled probes is described. The visualization of hybrids is done using the indoxyl-nitro blue tetrazolium alkaline phosphatase reaction. The addition of polyvinyl alcohols of high molecular weight (40-100 kDa) to the reaction medium enhances the alkaline phosphatase reaction and prevents diffusion of reaction intermediates, resulting in a 20-fold increase in sensitivity without increasing the background. Due to the more localized precipitation of the formazan, the site of hybridization can be determined more precisely.

Acetylation↗
PubMed1995

Separation of mono- and divinyl chlorophyll species by high-performance liquid chromatography using an octadecyl polyvinyl alcohol polymer column.

Most of the chlorophylls and their related compounds from nonesterified chlorophyllide to esterified pheophytin were separated by high- performance liquid chromatography using a wide pore, C(18) polyvinyl alcohol polymer column with an elution using a binary gradient starting from a buffered mobile phase. The high selectivity of this system enabled not only the separation of common chlorophyll species but also the resolution of structurally similar compounds such as mono- and divinyl chlorophyllide and pheophorbide species which usually coelute on monomeric bonded phases. The method is successfully applied to analyses of the pigments extracted from green and etiolated tissues of higher plants and photosynthetic bacterial cells.

Chlorophyll↗
PubMed1986

New disposable ERG electrode made of anomalous polyvinyl alcohol gel.

We developed a disposable electrode for the electroretinogram made of anomalous polyvinyl alcohol gel. This new hydrogel is a rubber-like elastic with water content 80-90 wt%, but insoluble in water. The elastic electrode plate is approximately 0.3-1.0 mm thick, sterile, flexible, and easily cut to the desired shape. Its low cost permits it to be discarded after use.

Disposable Equipment↗
PubMed1994

Quantitative comparison between the gel-film and polyvinyl alcohol methods for dehydrogenase histochemistry reveals different intercellular distribution patterns of glucose-6-phosphate and lactate dehydrogenases in mouse liver.

The precise histochemical localization and quantification of the activity of soluble dehydrogenases in unfixed cryostat sections requires the use of tissue protectants. In this study, two protectants, polyvinyl alcohol (PVA) and agarose gel, were compared for assaying the activity of lactate dehydrogenase (LDH) and glucose-6-phosphate dehydrogenase (G6PDH) in normal female mouse liver. Quantification of enzyme activity was determined cytophotometrically in periportal (PP), pericentral (PC) and midzonal (MZ) areas. No coloured reaction product was present in PVA media after the incubation period. In contrast, the agarose gels appeared to be highly coloured after incubation. As a consequence, sections incubated with gel media were less intensely stained than those incubated in PVA-containing media. The specific G6PDH reaction (test minus control) yielded approximately 75% less formazan in sections incubated by the agarose gel method than with the PVA method. Further, the amount of formazan deposits attributable to G6PDH activity was highest in the midzonal and pericentral zones of the liver lobule with PVA media, and Kupffer cells could be discriminated easily because of their high G6PDH activity. Significant zonal differences or Kupffer cells could not be observed when agarose gel films were used for the detection of G6PDH activity. The LDH localization patterns appeared to be more uniform after incubation with both methods: no significant differences in specific test minus control reactions were seen between PP, PC and MZ. However, less formazan production (33%) was detected in sections incubated with agarose gels when compared with those incubated with PVA media.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Enzyme cytochemistry of unfixed leukocytes and bone marrow cells using polyvinyl alcohol for the diagnosis of leukemia.

Cytochemical methods for the demonstration of enzyme activities in blood and bone marrow cells were systematically improved by the addition of an inert polymer, polyvinyl alcohol (PVA), to the incubation medium and by using optimized reaction media. The methods investigated were tetrazolium salt methods for lactate, glucose-6-phosphate, succinate and glutamate dehydrogenase, the indoxyl-tetrazolium salt method for alkaline phosphatase, the diaminobenzidine method for peroxidase, and diazonium salt methods for chloroacetate esterase, beta-glucosaminidase, beta-glucuronidase, acid phosphatase, and dipeptidylpeptidase II and IV. PVA in the media preserved the morphology of cells very well and prevented leakage of large molecules such as enzymes from the cells. Therefore, fixation or long periods of air-drying prior to incubation leading to substantial loss of enzyme activity could be avoided. A brief period of drying (2 min at 37 degrees C) of the cell preparations just before the incubation was sufficient for making the cells permeable. Localization of enzyme activities was very precise and precipitation of the final reaction product was confined to sites which are known to contain the enzyme under study (granules, mitochondria, lysosomes). These advantages advocate the use of PVA in haematological enzyme cytochemistry and especially for diagnosis of leukemia.

Bone Marrow↗