Increasing Polyvinyl Alcohol Concentration Research Articles

Enhanced electrochemical performance of WO3 thin films prepared from polyvinyl alcohol-modified nanoparticle ink

Tungsten oxide (WO3) is a potential material in catalysis, sensors, electrochromic devices, etc. In this research work, porous WO3 thin films are prepared on FTO-glass employing spin coating of WO3 nanoparticle's ink modified with polyvinyl alcohol (PVA) in the concentration range of 0 to 25.0 wt%. This study explored the change in structure and morphology of WO3 thin films with varying PVA concentration in ink composition and their effect on the ability to intercalate and de-intercalate Li+ ions as a function of applied bias. The wettability of ink on FTO-glass improved by raising its PVA content. All WO3 thin films exhibited a monoclinic structure. Scanning electron microscopy images indicated that the porosity of WO3 thin films gradually increased with increasing PVA concentration up to 25 wt% but the thin film became highly nonuniform at a very high concentration of additive. WO3 thin film prepared with ink having 10 wt% of PVA had optimum porosity and uniformity, therefore, yielded better electrochemical performance compared with all other samples. The addition of an optimum amount of PVA to ink is found to be an effective approach to modulating ink's characteristics and inducing porosity in thin films which eventually improves their redox reaction characteristics.

Mechanical and Physical Properties of Biodegradable Foams Made from Sorghum Fiber and Rice Straw for Food Packaging Applications

This study investigates the potential of agricultural by-products, rich in lignocellulosic materials, as sustainable food packaging materials to mitigate the environmental issues associated with nonbiodegradable plastics and styrofoam. Starch-based biodegradable food trays were developed using agricultural by-products, including sorghum stalk, rice straw, and kraft pulp through thermopressing method. By combining varying proportions of polyvinyl alcohol (PVA) and a sorghum-rice straw fiber mixture, biodegradable foam products with notable strength, water resistance, and cost-effectiveness for large-scale production were produced, exhibiting densities between 0.7 and 0.8 gr/m³. Notably, a 5% PVA composition in the sorghum fiber biodegradable foam displayed favourable mechanical properties and water resistance, with a tensile strength of 5 MPa and a contact angle of 73.79°, coupled with an appealing physical appearance. However, increasing PVA concentration beyond this level had negligible effects, indicates the optimal limit of PVA. Additionally, the distinct roles of rice straw powder as a matrix and sorghum fiber as reinforcement within the biodegradable foam were identified. Biodegradation tests revealed natural decomposition starting from the seventh day, with over 95% growth of Aspergillus Niger fungus, suggesting that these biodegradable foam products hold promise for mass production in the packaging industry, presenting a sustainable alternative to conventional plastic packaging.

Effect of polyvinyl alcohol concentration on biomedical application of chitosan/bioactive glass composite coated on AZ91D magnesium alloy

The aim of this work is to improve the biomedical properties of AZ91D magnesium by coating it with polyvinyl alcohol (PVA), bioactive glass (BG), and natural chitosan (CH), using the electrophoretic deposition (EPD) method with different PVA concentrations (15%, 20%, and 25%). The composites were characterized by X-ray diffraction (XRD), furrier infrared spectroscopy (FTIR), and scanning electron microscopy (SEM), which showed uniformity on the surface. Bio-corrosion activities were investigated by polarization tests in phosphate buffer saline (PBS) solution, which indicated that a composite with 15% PVA has lower corrosion resistance than base metal due to the weakness of the composite coating and applied current in the EPD process. The higher corrosion resistance was observed in the 25% PVA concentration due to the presence of a higher amount of PVA in the applied composite (which induces a denser and thicker composite coating). An in vitro bioactivity test was performed in PBS solution, which showed that more hydroxyapatite was formed on the surface by increasing PVA concentration. Furthermore, adhesive analysis of composite coatings indicates that by increasing the PVA concentration in composites, more adhesivity is obtained (5%, 12%, and 30%, respectively).

Dynamic and structural studies on synergetic energy dissipation mechanisms of single-, double-, and triple-network hydrogels sequentially crosslinked by multiple non-covalent interactions

A combination of multiple non-covalent interactions has been used to fabricate strong and tough hydrogels. However, mechanisms behind toughening remain unclear. In this study, a series of single-network (SN), double-network (DN), and triple-network (TN) hydrogels sequentially crosslinked by chemical bonds, freeze-thawed polyvinyl alcohol (PVA) crystallites, and ion coordination of alginate chains are systematically prepared. The contributions of hydrogen bonding, entanglements, crystallite crosslinking, and ion coordination to the dynamics of the hydrogels are comparatively studied. Dynamic mechanical analysis (DMA) reveals the apparent activation energy of hydrogen bonding from 41.1 kJ/mol to 50.6, 56.8, and 65.5 kJ/mol for SN gels with increasing PVA concentration (from 0 to 2, 6, 10 wt/vol%, respectively), whereas the corresponding apparent activation energy of chain entanglements increases from 148.3 to 160.2, 163.5, and 167.0 kJ/mol. PVA crystallites formed upon freeze-thawing act as physical crosslinks to further improve the strength and toughness of gels, as well as the activation energy (251.7 kJ/mol). Subsequent ion coordination with alginate further enhances the activation energy to 304.7 kJ/mol (Cu2+), 309.3 kJ/mol (Fe3+). Structural evolution studies on pre-cracked hydrogels reveal that PVA crystallites render crack blunting upon stretching. Polarized optical microscopy and scanning electron microscopy reveal the rearrangement and reconstruction of internal structures during crack propagation, including orientation and alignment of PVA crystallites. This study provides first insights to synergetic energy dissipation by non-covalent interactions of multi-network hydrogels.

An Artificial PVA-BC Composite That Mimics the Biomechanical Properties and Structure of a Natural Intervertebral Disc.

Disc herniation is one of the most ubiquitous healthcare problems in modern cities—severe patients eventually require surgical intervention. However, the existing operations—spinal fusion and artificial disc replacement—alter the biomechanics of the spine, leaving much room for improvement. The appropriateness of polyvinyl alcohol (PVA) for biomedical applications has been recognised due to its high water content, excellent biocompatibility, and versatile mechanical properties. In this study, a newly-designed PVA–bacterial cellulose (PVA-BC) composite was assembled to mimic both the biomechanics and annular structure of natural intervertebral discs (IVDs). PVA-BC composites of various concentrations were fabricated and tested under unconfined compression and compressive creep in order to acquire the values of the normalised compressive stiffness and whole normalised deformation. The normalised compressive stiffness increased considerably with an increasing PVA concentration, spanning from 1.82 (±0.18) to 3.50 (±0.14) MPa, and the whole normalised deformation decreased from 0.25 to 0.13. Formulations of 40% PVA provided the most accurate mimicry of natural human IVDs in normalised whole deformation, and demonstrated higher dimensional stability. The biocompatible results further confirmed that the materials had excellent biocompatibility. The novel bionic structure and formulations of the PVA-BC materials mimicked the biomechanics and structure of natural IVDs, and ensured dimensional stability under prolonged compression, reducing the risk of impingement on the surrounding tissue. The PVA-BC composite is a promising material for third-generation artificial IVDs with integrated construction.

Emulsion-ultrasonic spray method to prepare polylactic acid microspheres

Polylactic acid (PLA) microspheres are widely used in drug delivery and bone repair, among other applications. Herein, an ultrasonic spray-assisted emulsion method was developed to prepare PLA microspheres. The key factor affecting microsphere formation—duration of ultrasonic spray circulation—was discussed, and the effect of polyvinyl alcohol (PVA) concentration on microsphere morphology was evaluated. Compared with the emulsion solvent evaporation method by mechanical stirring, microsphere preparation time was shortened from 5 h to approximately 1.5 h based on ultrasonic cavitation effect, which converted the emulsion into micro-atomized droplets and accelerated solvent volatilization. Using this approach, microspheres formed when the PVA concentration was increased to 3 mg/mL, and the particle size decreased with increasing PVA concentration. Moreover, PLA microspheres could construct spaces in favor of cell growth. Altogether, this new method provides technical assistance for the preparation of polymer microspheres for tissue engineering.

Development and evaluation of polyvinyl alcohol stabilized polylactide-co-caprolactone-based nanoparticles for brain delivery

The biodegradable polymer poly-ε-(D, l-lactide-co-caprolactone) (PLCL) can be used to produce nanoparticles with tailored release pattern. In this study; the anti-epileptic drug, lamotrigine, was loaded in PLCL nanoparticles stabilized using various molecular weights and concentrations of polyvinyl alcohol (PVA). The nanoparticles were prepared by emulsification solvent evaporation technique. Nanoparticles were characterized for their morphology, particle size (PS), Zeta potential (ZP), entrapment efficiency (EE), drug loading capacity (DLC), yield percentage (YP)-values and drug release pattern. Drug concentration in Albino rats’ blood and brain after intravenous injection of selected nanoparticles was also analyzed. Results indicated that PS, EE, DLC, YP and ZP-values for the PLCL nanoparticles decreased with increasing PVA concentration. Formulated nanoparticles using LPVA were stable under various storage conditions. Lamotrigine release from nanoparticles was sustained for nearly a week. The selected formulation showed significantly high drug concentration in the brain compared to that for oral conventional tablet. In conclusion; varying PVA concentration and molecular weight used to stabilized PLCL nanoparticles helped in providing versatile properties for designing nanoparticles with wide range of properties.

Phenol and ammonia removal in petroleum refinery wastewater using a poly(vinyl) alcohol coated polysulfone nanohybrid membrane

Petroleum refinery wastewater (PRW) contains high concentrations of phenolic compounds and ammonia that are noxious and harmful to the environment, especially to human health. The improper treatment of PRW could cause serious problems. In this study, a membrane with a polyvinyl alcohol (PVA) coating was fabricated to improve PRW treatment for phenolic compounds and ammonia removal. The fabricated membranes were investigated using scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), water contact angle, mechanical strength, permeability, pollutant rejection, and foulant resistance. The coated membranes exhibited improved surface properties and mechanical strength compared to that of uncoated pristine polysulfone (PSf) membranes. The membranes also showed excellent phenol and ammonia removal up to 82.68 % and 92.42 %, respectively. Although the permeate flux decreased with increasing PVA concentration, the antifouling behavior of the membrane was significantly improved. Therefore, the fabricated membranes showed great potential for petroleum wastewater treatment.

Cu(0)-mediated reversible-deactivation radical polymerization of n-butyl acrylate in suspension

Cu(0)-mediated reversible-deactivation radical polymerization of n-butyl acrylate was performed in suspension without the use of an organic solvent. In all cases, a 5 v% organic phase (monomer, initiator, and ligand) was used with respect to 95 v% aqueous phase. Polyvinyl alcohol (PVA) as a suspension stabilizer has been shown to be able to control the polymerization for the degree of polymerizations of 222 and higher. The polymerization reaction showed linear first-order kinetics for a PVA concentration range of 1–10 wt%, leading to polymers with dispersities from 1.22 to 1.43. Conversions as high as 96% were obtained in 55 min. Scanning electron microscopy analysis of the suspensions confirmed the formation of micron-sized polymer particles dispersed in aqueous media, and that the size of the particles decreased with increasing PVA concentration. Rheometry measurements of the aqueous phase containing PVA before and after polymerization demonstrated the increase in the viscosity of the reaction mixture after polymerization. The difference between the viscosity of the PVA solution in water and the same solution after polymerization decreased as the PVA decreased, which indicates smaller particle sizes formed with increasing PVA content. All suspensions were stable over a period of three months storage at room temperature without any precipitation or sedimentation. The maximum copper species concentration in the reaction medium and water can be as low as 7 ppm. This Cu(0)-mediated reversible-deactivation radical polymerization in suspension has the potential for industrial use, especially for paint and adhesives.

Cellulose-glycerol-polyvinyl alcohol composite films for food packaging: Evaluation of water adsorption, mechanical properties, light-barrier properties and transparency

Nowadays consumers are aware of environmental problems. As an alternative to petrochemical polymers for food packaging, researchers have been focused on biopolymeric materials as raw material. The aim of this study was to evaluate mechanical properties (toughness, burst strength and distance to burst), water adsorption, light-barrier properties and transparency of composite films based on cellulose, glycerol and polyvinyl alcohol. Scanning electron microscopy, spectral analysis (FT-IR and UV–VIS-NIR) and differential scanning calorimetry were performed to explain the morphology, structural and thermal properties of the films. Results showed that polyvinyl alcohol enhances the toughness of films up to 44.30 MJ/m3. However, toughness decreases when glycerol concentration is increased (from 23.41 to 10.55 MJ/m3). Water adsorption increased with increasing polyvinyl alcohol concentration up to 222%. Polyvinyl alcohol increased the film thickness. The films showed higher burst strength (up to 12014 g) than other biodegradable films. The films obtained have optimal values of transparency like those values of synthetic polymers. Glycerol produced a UV protective effect in the films, an important effect for food packaging to prevent lipid oxidative deterioration. Results showed that it is feasible to obtain cellulose-glycerol-polyvinyl alcohol composite films with improved properties.

CdSe quantum dots using selenourea as selenium source in polymer matrix

In this paper we have synthesized cadmium selenide quantum dots in aqueous medium at low temperature of 80 °C through chemical route. Three different concentrations of polyvinyl alcohol (PVA) 6, 8 and 10 wt% was used as a capping agent to prevent coagulation in quantum dots. An alternative precursor selenourea was used in place of selenium powder as a selenium source. Thin film of CdSe/PVA nanocomposite was made by spin coating and characterized by UV–Vis spectroscopy; Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and Fourier transform infra red spectroscopy. For electrical measurements temperature dependent DC conductivity has been performed. From UV–Visible absorption measurement it has been observed that on increasing PVA concentration the absorption edge shifts and bandgap calculated comes out to be more than the bulk CdSe material due to quantum confinement effect. This indicates blue shift and reduction in crystallite size with increase in PVA concentration. This tunability of bandgap with size is very effective in solar cell application. SEM/TEM micrograph confirms the zero dimensional shape of the prepared quantum dot with average size in the range of 6 nm. The DC conductivity measurement shows increase in conductivity with increase in temperature which confirms semiconducting behaviour of CdSe quantum dot.

Deacidification of crude palm oil using PVA-crosslinked PVDF membrane

Over recent years, there has been an explosive growth of interest in the development of alternative approaches for crude palm oil (CPO) refining. During a typical refinery process, free fatty acid (FFA) is one of the key objectionable impurities that need to be reduced if not completely removed from CPO in order to minimize their detrimental effects on the oil quality. Polyvinylidene fluoride (PVDF) membrane shows great potential in removing FFA from CPO owing to its hydrophobic properties, high mechanical strength and good thermal stability. However, low concentration of FFA in CPO, which is normally ranging from 3% to 5%, has hindered the capability of the membranes to separate the trace amount of FFA from the bulk. Thus, modification of PVDF membrane is essential to enhance the interaction between the membrane surface and FFA molecules, facilitating efficient FFA removal. In order to achieve this purpose in the present study, the outer surface of PVDF hollow fiber membranes was crosslinked with polyvinyl alcohol (PVA). Glutaraldehyde (GA) was used as a crosslinking agent to avoid the PVA dissolution. Despite the negligible morphological change observed in the resultant membranes upon PVA crosslinking, the contact angle has been significantly reduced in proportional to the concentration of PVA used for the crosslinking, suggesting the decrease in membrane hydrophobicity. Additionally, the average roughness of the crosslinked PVDF membranes increased with the increasing PVA concentration. The results obtained suggested that the PVDF hollow fiber crosslinked with 100ppm PVA exhibited the highest FFA rejection of 5.93% after 3h of operation. In addition, the membrane also showed good result in reducing the content of phosphorus in the permeate and partial reduction of its color intensity. This study served as the first attempt of CPO deacidification through UF membrane system without the addition of any chemical during the filtration process.

Observation of negative persistent photoconductivity in ZnS/PVA nanocomposite materials

From point of view of device fabrication, nanostructured ZnS functional materials have gained immense importance due to its primary band gap of 3.68eV (345nm) and high sensitivity for ultraviolet and violet radiations. Structural parameter and grain sizes for ZnS nanoparticles in polyvinyl alcohol (PVA) matrix are studied using synchrotron radiation. X-ray diffraction studies exhibit cubic structure of the ZnS samples having crystallite sizes in 3–6nm and their preferred orientation along the [111] plane while TEM reveals particle sizes in 2–5nm. Raman spectrum reveals that the observed bands are due to the combined features of surface optical phonon (SO) and longitudinal optical (LO) phonon mode. Blue shift in the optical band gap of ZnS nanoparticles with increasing PVA concentration confirms the effect of quantum confinement of electrons. Photoluminescence spectra exhibit five emission bands having peak positions at ∼385, 416, 443, 464 and ∼485nm. Dark and photocurrent decreases with increasing PVA concentration, shows nonlinear behavior for I–V plots. Time resolved persistent photocurrent measurement demonstrates initial very fast decay with time constant 5s followed by faster and slower decay of current with time constants ∼90s and ∼863s, respectively.

SYNERGISTIC INFLUENCE OF POLYVINYL ALCOHOL AND SURFACTANTS ON THE CORROSION INHIBITION OF MILD STEEL IN 0.1 M H2SO4

The corrosion inhibition behavior of mild steel in 0.1 M H2SO4 in the presence of polyvinyl alcohol (PVA) was investigated using weight loss and potentiodynamic polarization measurements in the temperature range of 30°–60°C. The inhibition efficiency (IE) increased with increasing PVA concentration, showing a maximum IE of 81.41% at 30°C at 100 mg/L and decreased with increasing temperature. The inhibiting action of PVA is synergistically enhanced on addition of very small amounts of surfactants sodium dodecyl sulfate (SDS) and cetyl pyridinium chloride (CPC). The adsorption of PVA alone or in combination with surfactants on the metal surface is found to obey the Langmuir adsorption isotherm from the fit of the experimental data of all concentrations and temperatures studied. The synergism parameter evaluated is found to be greater than unity, indicating that the enhanced IE of PVA caused by addition of surfactants is due only to synergism. The phenomenon of physical adsorption is proposed from the trend of the IE with temperature as well as the values of Ea, ΔHads, and ΔGads obtained. Thermodynamic parameters reveal that the adsorption process is spontaneous. The results obtained by weight loss measurements are consistent with the results of the potentiodynamic polarization measurements. The surface morphology of the corroded steel samples in the presence and absence of inhibitors was also evaluated using scanning electron microscopy (SEM).

Feasibility study of aerosolized prostaglandin E1 microspheres as a noninvasive therapy for pulmonary arterial hypertension

This study was designed to test the feasibility of polymeric microspheres as an inhalable carrier for prostaglandin E1 (PGE1) for treatment of pulmonary arterial hypertension. Poly(lactic‐co‐glycolic acid) (PLGA) microspheres were prepared by a double emulsion–solvent evaporation method. Six different microspheric formulations were prepared using two different blends of PLGA (50:50 and 85:15) and varying concentrations of polyvinyl alcohol (PVA) in the external aqueous phase (EAP). The particles were characterized for morphology, size, aerodynamic diameter, entrapment efficiency, release patterns, and metabolic stability. Pulmonary absorption was studied in a rat model, and safety of the formulations was evaluated by measuring cytotoxicity in Calu‐3 cells and assessing injury markers in bronchoalveolar lavage (BAL) fluid. Both actual particle size and aerodynamic diameter of the formulations decreased with increasing PVA concentration. The mass median aerodynamic diameter of the particles was within the respirable range. Entrapment efficiency increased with increasing PVA concentration; PLGA 85:15 showed better entrapment due to hydrophobic interactions with the drug. Compared to intravenously administered PGE1, microspheres prepared with PLGA 85:15 produced a 160‐fold increase in the half‐life of PGE1 following pulmonary administration. Although plain PGE1 showed rapid degradation in rat lung homogenate, PGE1 entrapped in the particles remained intact for about 8 h. Optimized formulations were demonstrated to be safe, based on analysis of cytotoxicity and lung‐injury markers in BAL fluid. Overall, the data suggest that microspheric PGE1 formulations have the potential to be used as a noninvasive and controlled‐release alternative to the current medications used for treatment of pulmonary arterial hypertension that are administered by continuous infusion or require multiple inhalations. © 2009 Wiley‐Liss, Inc. and the American Pharmacists Association J Pharm Sci 99: 1774–1789, 2010

PVA‐Assisted Hydrothermal Synthesis of SrTiO3 Nanoparticles with Enhanced Photocatalytic Activity for Degradation of RhB

Strontium titanate (SrTiO3) nanoparticles with different particle sizes have been synthesized successfully via a hydrothermal route with the help of polyvinyl alcohol (PVA). The as‐synthesized SrTiO3 nanoparticles were characterized by X‐ray diffraction, energy‐dispersive X‐ray spectroscopy, and scanning electron microscopy. It was found that the particle size and the Sr/Ti molar ratio of the as‐synthesized samples decreased with increasing PVA concentration, accompanied by an increase in the specific surface area. When the PVA concentration was no <1.6 g/L, the Sr/Ti molar ratios of the as‐synthesized samples were <1, indicating that a strontium vacancy (VSr) formed. Their photocatalytic activities were investigated through the degradation of rhodamine B (RhB) under exposure to ultraviolet (UV) radiation (λ=200–400 nm). The results indicated that the photocatalytic activities of the PVA‐assisted hydrothermally synthesized nanocrystalline SrTiO3 powders were higher than that of the sample prepared without PVA. The highest photocatalytic activity was obtained for the sample prepared with an intermediate PVA concentration, arising from the combined effect of the particle size, specific surface area, VSr formation, and the adsorption capacity.

Influences of surfactant (PVA) concentration and pH on the preparation of copper nanoparticles by electron beam irradiation

Electron beam irradiation method was successfully applied to the preparation of Cu nanoparticles in aqueous solution under room temperature and ambient pressure using polyvinyl alcohol (PVA) as the surfactant. The influences of the pH on the products were studied by X-ray diffraction (XRD), and those of the surfactant PVA concentration on the particle size and agglomeration by ultraviolet–visible spectrophotometry (UV–vis) and laser scattering particle size distribution analysis (LSPSDA). The products were characterized by XRD and transmission electron microscopy (TEM). The results showed that the grain size of Cu nanoparticles, within a certain range, can decrease with increasing PVA concentration. Pure Cu nanoparticles with the grain size distribution of 5–50 nm were prepared when the pH was adjusted between 5.0 and 9.0, and the PVA concentration was 2.20 g/100 mL.

83 DEVELOPMENT OF BOVINE IN VITRO-PRODUCED BLASTOCYSTS AFTER CRYOPRESERVATION IN CHEMICALLY DEFINED SOLUTIONS AND ONE-STEP DILUTION

Efficient embryo cryopreservartion using a protein-free defined solution would be beneficial for hygienic commercial embryo transport. In addition, one-step rehydration of frozen–thawed embryos could allow direct transfer of cryopreserved embryos after thawing. The objective of this study was to assess the viability in vitro of bovine in vitro-produced (IVP) embryos after freezing and thawing in a base cryoprotective solution [modified synthetic oviduct fluid (mSOF) medium containing 1.8 m ethylene glycol and 0.05 m trehalose] supplemented with various concentrations of polyvinyl alcohol (PVA). The methods used for in vitro embryo production and embryo cryopreservation were modified from those described previously (Murakami et al. 1998 Cryobiology 36, 206–212). Briefly, oocytes collected from cow ovaries were matured, fertilized in vitro for 5 h, and cultured in mSOF containing 0.4% bovine serum albumin (BSA) at 38.5�C in a humidified atmosphere of 5% CO2, 5% O2, and 90% N2 (reduced-O2 atmosphere; Day 0). On Day 3, only cleaved embryos were co-cultured with bovine cumulus cells in mSOF containing 5% fetal bovine serum (FBS) in a humidified atmosphere of 5% CO2 in air. On Day 7, embryos that reached the blastocyst stage were selected and immersed directly into the base cryoprotective solution supplemented with 0.4% BSA (0.4BSA group, the protein-containing control group) or 1.5, 3.0, or 6.0% PVA (1.5PVA, 3PVA, and 6PVA groups, respectively) at room temperature. After exposure to solution, embryo–cryoprotectant solutions were loaded into 0.25-mL plastic straws and cryopreserved by the standard slow freezing method (about 60 to 100 embryos in each group). The frozen straws were placed in air for 10 s, and plunged into a 38.5�C water bath for 10 s; the contents were expelled into a plastic dish. The embryos were then transferred directly to pre-incubated minimum essential medium alpha medium containing 5% FBS and MEM nonessential amino acids solution (mαMEM) for one-step rehydration. These frozen.thawed embryos were washed well and cultured in fresh mαMEM in a reduced-O2 atmosphere for 3 days to examine the developmental potential in vitro. Data were analyzed by ANOVA. The percentage of re-expanded embryos after freezing and thawing was significantly higher (P < 0.05) in 0.4BSA and 1.5PVA groups than in the 3PVA and 6PVA groups (95.4% in 0.4BSA and 90.9% in 1.5PVA v. 73.4% in 3PVA and 57.7% in 6PVA). In addition, there was no significant difference between 0.4BSA and 1.5PVA groups in the percentage of embryos developed into hatched blastocysts (82.0 v. 80.2%), but the percentage decreased with increasing PVA concentration (51.1% in 3PVA and 29.3% in 6PVA, respectively). These results suggest that the biological product BSA added in our standard cryoprotective solution can be replaced with 1.5% PVA to support similar viability of frozen.thawed bovine IVP embryos after one-step dilution. Further studies, including direct transfer of these frozen embryos after thawing, are needed to substantiate these results.

Effect of polyvinyl alcohol on kinetic and thermal properties of β-galactosidase

The effect of PVA (polyvinyl alcohol) with various degrees of polymerization and saponification on the kinetic and thermal characteristics of β-galactosidase was investigated. With ONPG (2-nitrophenyl-β- d -galactoside) as a substrate, the enzyme activity increased with increasing PVA concentration. While the influences of the properties of PVA on Michaelis constants were insignificant, the maximum reaction rate of the enzyme increased with increasing degrees of polymerization and saponification. The addition of PVA enhanced the thermal stability of the enzyme, and it increased with increasing PVA concentration. Dependency of the thermal stability on the characteristic properties of PVA was not remarkable.