Preparation of crosslinked macroporous PVA foam carrier for immobilization of microorganisms

In this work, a new and economical way to prepare macroporous poly(vinyl alcohol) (PVA) foam was explored by adding calcium carbonate as a pore-forming agent and using epichlorhydrin as a chemical crosslinking agent to improve foam stability. The mixture for foam formation has been optimized to obtain macroporous PVA foam carriers with uniform apertures, narrow distribution of pore sizes, and good elasticity. The crosslinked PVA foam (CPVAF) carrier demonstrated better chemical and thermal stability, as well as larger specific surface area and diffusion coefficients than the traditional PVA (TPVA) carrier. Nitrifying bacteria were used to test the suitability of CPVAF and TPVA carriers for immobilized microorganisms. CPVAF carriers supported higher biomass density and microbial activity than TPVA carriers. At the same biomass density, the higher nitrification rate of CPVAF carriers was attributed to excellent mass transfer of the substrate (and oxygen) between the bulk solution and the immobilized microorganisms.     

A visco-hyperelastic constitutive approach for modeling polyvinyl alcohol sponge

This study proposes the quasi-linear viscoelastic (QLV) model to characterize the time dependent mechanical behavior of poly(vinyl alcohol) (PVA) sponges. The PVA sponges have implications in many viscoelastic soft tissues, including cartilage, liver, and kidney as an implant. However, a critical barrier to the use of the PVA sponge as tissue replacement material is a lack of sufficient study on its viscoelastic mechanical properties. In this study, the nonlinear mechanical behavior of a fabricated PVA sponge is investigated experimentally and computationally using relaxation and stress failure tests as well as finite element (FE) modeling. Hyperelastic strain energy density functions, such as Yeoh and Neo-Hookean, are used to capture the mechanical behavior of PVA sponge at ramp part, and viscoelastic model is used to describe the viscose behavior at hold part. Hyperelastic material constants are obtained and their general prediction ability is verified using FE simulations of PVA tensile experiments. The results of relaxation and stress failure tests revealed that Yeoh material model can define the mechanical behavior of PVA sponge properly compared with Neo-Hookean one. FE modeling results are also affirmed the appropriateness of Yeoh model to characterize the mechanical behavior of PVA sponge. Thus, the Yeoh model can be used in future biomechanical simulations of the spongy biomaterials. These results can be utilized to understand the viscoelastic behavior of PVA sponges and has implications for tissue engineering as scaffold.     

Equilibrium and kinetics studies of adsorption of copper (II) on chitosan and chitosan/PVA beads

The adsorption of Cu(II) ions from aqueous solution by chitosan and chitosan/PVA beads was studied in a batch adsorption system. Chitosan solution was blended with poly(vinyl alcohol) (PVA) in order to obtain sorbents that are insoluble in aqueous acidic and basic solution. The adsorption capacities and rates of Cu(II) ions onto chitosan and chitosan/PVA beads were evaluated. The Langmuir, Freundlich and BET adsorption models were applied to describe the isotherms and isotherm constants. Adsorption isothermal data could be well interpreted by the Langmuir model. The kinetic experimental data properly correlated with the second-order kinetic model, which indicates that the chemical sorption is the rate-limiting step. The Cu(II) ions can be removed from the chitosan and chitosan/PVA beads rapidly by treatment with an aqueous EDTA solution. Results also showed that chitosan and chitosan/PVA beads are favourable adsorbers.     

Enhanced degradation of polyvinyl alcohol by Pycnoporus cinnabarinus after pretreatment with Fenton's reagent

Degradation of polyvinyl alcohol (PVA) was investigated by using a combination of chemical treatment with Fenton's reagent and biological degradation with the white rot fungus Pycnoporus cinnabarinus. Inclusion of the chemical pretreatment resulted in greater degradation of PVA than the degradation observed when biological degradation alone was used.     

Biosorption of gold by immobilized fungal biomass

The characteristics of polyvinyl alcohol (PVA) and calcium alginate as immobilization matrices were examined and compared for the uptake of gold by a fungal biomass. PVA-immobilized biomass showed superior mechanical strength and chemical stability. In addition, PVA beads were also stable under a wider range of pH (1-13). The lower mass transfer resistance in PVA beads was evident from kinetic studies which showed a significantly shorter period of time for the immobilized PVA beads to achieve 80% gold removal as compared with immobilized alginate beads. Calculated rate constants and maximum rates for the uptake of gold by both immobilized PVA and immobilized alginate biosorbent revealed a much more rapid uptake phenomenon by the former. BET analyses also indicated a larger surface area and larger pore size distribution in PVA beads, further indicating a lower resistance to mass transfer. Gold biosorption in the immobilized PVA bead could be modeled by both the Langmuir and Freundlich adsorption isotherms.     

Poly(vinyl alcohol) nanofibers by electrospinning as a protein delivery system and the retardation of enzyme release by additional polymer coatings

Protein-loaded (bovine serum albumin (BSA) or luciferase) poly(vinyl alcohol) (PVA) nanofibers were obtained by electrospinning. Poly(p-xylylene) (PPX, also coined as parylene) coated PVA/BSA nanofibers were prepared by chemical vapor deposition (CVD). The release of BSA from PVA nanofibers under physiological conditions was monitored by absorption spectroscopy. Burst release of BSA was noted with uncoated PVA nanofibers. In contrast, PPX-coated nanofibers exhibited a significantly retarded release of BSA depending on the coating thickness of PPX (ranging from 40 to 300 nm). Luciferase was used here as model enzyme, which after electrospinning retained its enzyme activity. This preservation of enzyme activity and the continuous release of the intact enzyme from the immersed fibers meets a fundamental prerequisite for the application of enzymes or other sensitive agents released from electrospun nanofibers under physiological conditions.     

Use of polyvinyl alcohol as a stabilizer of peroxidase-antibody conjugate for enzyme immunoassay

Summary The activity of a peroxidase-antibody conjugate was greatly stabilized while in solution through the addition of polyvinyl alcohol (PVA). This stabilizing effect was dependent upon the molecular weight and degree of hydrolysis of the PVA used. The concentrations of PVA necessary for maximum stabilization had no adverse effects upon enzyme immunoassay. Thus, the conjugate stabilized by PVA can be used without dilution for enzyme immunoassay, and without need of refrigeration during transport and storage.     

聚乙烯醇生物降解研究进展

聚乙烯醇(PVA)是一种在纺织和化工行业中广泛使用的难降解的高分子聚合物。随着人们对纺织工业清洁生产的关注,如何在退浆工艺中就实现对PVA的生物降解、减少PVA废水的排放,并避免化学退浆过程中高温和氧化造成的棉纤维损伤,是近年来纺织生物技术领域的研究热点。由于PVA降解菌种类不多、培养周期长,PVA降解酶酶活不高、提取不容易等原因,使PVA的生化降解研究还局限在PVA降解菌的筛选、PVA降解酶的酶学性质研究等方面,PVA降解酶还未在纺织工业上得到应用。本文综述了近年来国内外在PVA降解菌筛选、PVA降解酶提取及酶学性质、PVA生化降解机理等方面的研究进展,并讨论了PVA生化降解研究中存在的问题及发展方向。     

Effect of glycerol and PVA on the conformation of photosystem I

Single-molecule spectroscopy at cryogenic temperatures was used to examine the impact of buffer solution, glycerol/buffer mixtures (25% and 66%), and poly(vinyl alcohol) (PVA) films on the conformation of photosystem I (PSI) from Thermosynechoccocus elongatus. PSI holds a number of chromophores embedded at different places within the protein complex that show distinguishable fluorescence at low temperatures. The fluorescence emission from individual complexes shows inter- and intracomplex heterogeneity depending on the solution wherein PSI was dissolved. Statistical evaluation of spectra of a large number of complexes shows that the fluorescence emission of some of these chromophores can be used as sensors for their local nanoenvironment and some as probe for the conformation of the whole protein complex. Preparation in glycerol/buffer mixtures yields a high homogeneity for all chromophores, indicating a more compact protein conformation with less structural variability. In buffer solution a distinct heterogeneity of the chromophores is observed. PSI complexes in PVA show highly heterogeneous spectra as well as a remarkable blue shift of the fluorescence emission, indicating a destabilization of the protein complex. Photosystem I prepared in PVA cannot be considered fully functional, and conclusions drawn from experiments with PSI in PVA films are of questionable value.     

Enhanced Degradation of Polyvinyl Alcohol by Pycnoporus cinnabarinus after Pretreatment with Fenton’s Reagent

Degradation of polyvinyl alcohol (PVA) was investigated by using a combination of chemical treatment with Fenton’s reagent and biological degradation with the white rot fungus Pycnoporus cinnabarinus. Inclusion of the chemical pretreatment resulted in greater degradation of PVA than the degradation observed when biological degradation alone was used.     

Biomimetic Hydrophobic Surfaces with Low or High Adhesion Based on Poly(vinyl alcohol) and SiO2 Nanoparticles

Superhydrophobic surfaces are often found in nature,such as plant leaves and insect wings.Inspired by superhydrophobic phenomenon of the rose petals and the lotus leaves,biomimetic hydrophobic surfaces with high or low adhesion were prepared with a facile drop-coating approach in this paper.Poly(vinyl alcohol) (PVA) was used as adhesive and SiO2 nanoparticles were used to fabricate surface micro-structure.Stearic acid or dodecafluoroheptyl-propyl-trimethoxysilane (DFTMS) were used as low surface energy materials to modify the prepared PVA/SiO2 coating surfaces.The effects of size of SiO2 nanoparticles,concentration of SiO2 nanoparticle suspensions and the modifications on the wettability of the surface were investigated.The morphology of the PVA/SiO2 coating surfaces was observed by using scanning electron microscope.Water contact angle of the obtained superhydrophilic surface could reach to 3°.Stearic acid modified PVA/SiO2 coating surfaces showed hydrophobicity with high adhesion.By mixing the SiO2 nanoparticles with sizes of 40 nm and 200 nm and modifying with DFTMS,water contact angle of the obtained coating surface could be up to 155° and slide angle was only 5°.This work provides a facile and useful method to control surface wettability through changing the roughness and chemical composition of a surface.     

Biochemistry of microbial polyvinyl alcohol degradation

Effect of minor chemical structures such as 1,2-diol content, ethylene content, tacticity, a degree of polymerization, and a degree of saponification of the main chain on biodegradability of polyvinyl alcohol (PVA) is summarized. Most PVA-degraders are Gram-negative bacteria belonging to the Pseudomonads and Sphingomonads, but Gram-positive bacteria also have PVA-degrading abilities. Several examples show symbiotic degradation of PVA by different mechanisms. Penicillium sp. is the only reported eukaryotic degrader. A vinyl alcohol oligomer-utilizing fungus, Geotrichum fermentans WF9101, has also been reported. Lignolytic fungi have displayed non-specific degradation of PVA. Extensive published studies have established a two-step process for the biodegradation of PVA. Some bacteria excrete extracellular PVA oxidase to yield oxidized PVA, which is partly under spontaneous depolymerization and is further metabolized by the second step enzyme (hydrolase). On the other hand, PVA (whole and depolymerized to some extent) must be taken up into the periplasmic space of some Gram-negative bacteria, where PVA is oxidized by PVA dehydrogenase, coupled to a respiratory chain. The complete pva operon was identified in Sphingopyxis sp. 113P3. Anaerobic biodegradability of PVA has also been suggested.     

Biodegradation of polyvinyl alcohol by a brown-rot fungus, Fomitopsis pinicola

A brown-rot fungus, Fomitopsis pinicola, degraded polyvinyl alcohol (PVA) in quartz sand but not in liquid culture. From gel permeation chromatography analysis, the high-molecular-weight fraction of PVA was decreased by the action of F. pinicola but the coloration of the culture filtrate with I₂ solution increased. The reason for the increase in coloration was assumed to be the increase in the low-molecular-weight fraction in degraded PVA. Diffuse reflectance infrared Fourier transform spectral analysis showed that spectral changes of the fungally degraded PVA were similar to those of PVA treated with Fenton’s reagent suggesting that PVA degradation by F. pinicola was via the Fenton reaction. F. pinicola can thus be used to degrade PVA in woody wastes.     

Evaluation of polyvinyl alcohol for fatty acid supplementation in adipose tissue explant culture

Cultures of adipose tissue explants are a valuable tool for studying the intracellular mechanisms involving hormones and nutrients. However, testing how fatty acids affect cells requires a carrier molecule; bovine serum albumin (BSA) has been used for this purpose. However, contaminants can alter the cellular response. Our objectives were to: 1) test BSA as a fatty acid carrier and 2) evaluate polyvinyl alcohol (PVA) as a replacement for BSA. Adipose tissue explants from nine pigs were cultured in medium 199 for 4, 12, 24, and 48 h, with the following treatments: control, PVA (100 mM PVA added) and PVA + pGH (100 mM PVA plus 0.1 mg/mL porcine growth hormone). After each culture period, explants were collected and assayed for lipogenesis. After 48 h in culture, explants were assayed for lipolysis. A preliminary study with different commercial sources and high concentrations showed that BSA affected lipogenic rates. On the other hand, there were no effects of PVA on lipid synthesis, while pGH (positive control) reduced glucose incorporation into lipids (P < 0.01) when compared to both control and PVA (P < 0.05). There was no difference between control and PVA for lipolysis rates. However, pGH increased lipolysis when compared to control (P < 0.01) and PVA (P < 0.05). We demonstrated that BSA can alter lipogenesis, which precludes its use as a carrier molecule. On the other hand, addition of PVA had no effect on lipolysis or lipogenesis. We suggest the use of PVA instead of BSA for adding bioactive fatty acids to cultures of adipose tissue.     

Production and Characterization of Monoclonal Antibodies to Potato Virus A

Abstract Purified potato virus A (PVA) was used for immunization to produce monoclonal antibodies (MAb). The type of ELISA with purified PVA or non–purified PVA, played an essential role in selecting MAb with different specificity.
Two MAb's (MAb–1 and MAb–2) were selected, using indirect ELISA (I–ELISA) with purified PVA. Competition experiments suggested that MAb–1 and MAb–2 reacted with the same epitope on purified PVA (epitope 1). ELISA, IEM and SDS–PAGE–immunoblotting experiments showed that epitope–1 was only present on purified PVA but not on non–purified PVA, suggesting that this epitope was introduced during the purification. Assays at different steps during purification indicated that epitope–1 was only exposed after plant components and reducing agents were removed from the PVA extract.
Three MAb's (MAb–3, MAb–4 and MAb–5) were selected by indirect double antibody sandwich ELISA (IDAS–ELISA) with non–purified PVA. These MAb's reacted in I–ELISA or IDASELISA with purified PVA as well as with non–purified PVA and might be useful for routine diagnosis. MAb–3, 4 and 5 cross–reacted with some other potyviruses in I–ELISA and in IDAS–ELISA. MAb–1 cross–reacted with 5 out of 7 other potyviruses in I–ELISA, but not in IDAS–ELISA.     

Electrospun core-shell nanofibers from homogeneous solution of poly(vinyl alcohol)/bovine serum albumin

We report on the preparation and characterization of core-shell structure of bovine serum albumin (BSA) blended poly(vinyl alcohol) (PVA) composite nanofibers by using electrospinning process. The core-shell structure nanofibers have been electrospun from the homogeneous solution of BSA (as shell) and PVA (as core). The morphology, chemical compositions, structure and thermal properties of the resultant products were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDX), high-resolution transmission electron microscopy (HR-TEM), Fourier transform infrared (FT-IR) spectroscopy, differential scanning calorimetry, thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS) techniques. The blending ratio of PVA and BSA, molecular weight of BSA and the applied voltage of electrospinning process were observed to be the key influence factors on the formation of core-shell nanofibers structure. Based on the experimental findings, we proposed a possible physical mechanism for the formation of core-shell nanofibers structure of PVA blended BSA composite.     

The protective action of polyvinyl alcohol during rapid-freezing of mouse embryos

Biological products like serum and BSA are routinely used in embryo freezing solutions. These products are undefined and can potentially expose the embryos to infectious agents. Therefore, this experiment was designed to evaluate in vitro and in vivo survival of mouse embryos frozen in solutions supplemented with a chemically defined macromolecule, polyvinyl alcohol (PVA). Morula-stage embryos from superovulated mice were collected, frozen by a rapid freezing procedure, and cryoprotectant diluted out (after thawing) in media supplemented with either 10% fetal calf serum (FCS), 0.1 mg/mL PVA, or a combination of 10% FCS and 0.1 mg/mL PVA. Frozen-thawed (good to excellent quality) and nonfrozen (control, collected in FCS supplemented medium) embryos were cultured in medium M16 (32) supplemented with either 4 mg/mL BSA or 0.1 mg/mL PVA for 72 h. Embryos frozen in solutions supplemented with FCS or PVA and nonfrozen embryos were transferred to pseudopregnant recipients. Recipients were humanly killed on Day 15 after transfer, and the rate of implantation and percentage of live fetuses were recorded. The supplementation of collection, freezing and cryoprotectant dilution solutions with FCS, PVA or FCS plus PVA did not influence (P > 0.05) the rate of survival and in vitro development of embryos to hatched/hatching blastocyst-stage. However, a higher (P < 0.01) in vitro development rate to hatching/hatched-stage was recorded when frozen-thawed embryos were cultured in medium supplemented with BSA than with PVA. There was no difference (P > 0.05) in the rate of implantation (68 vs 72%) or percentage of live fetuses (62 vs 60%) between pregnant recipients with embryos frozen in medium with FCS or PVA. The rate of implantation and development of embryos frozen in medium supplemented with PVA or FCS was comparable (P > 0.05) to that of nonfrozen embryos. It may be concluded that PVA can be substituted for FCS in medium for freezing mouse embryos; however, it can not be completely substituted for BSA in the in vitro culture of embryos to the hatched blastocyst stage.     

Immobilization of porcine pancreatic lipase on glycidyl methacrylate grafted poly vinyl alcohol

Graft copolymerization of glycidyl methacrylate (GMA) on to polyvinyl alcohol (PVA) using benzophenone (BP) as initiator was carried out. Grafted PVA was used as carrier for pancreatic lipase immobilization. The effects of GMA and BP concentrations as well as grafting reaction times on grafting yields and activities of the immobilized lipase were determined. The influence of enzyme concentrations was also studied. The optimal conditions for the grafting reaction were: 1 h at 15 mM BP and 2.3 M GMA, the optimum enzyme concentration for immobilization was 1 mg/ml. After optimization of the immobilization process a physical and chemical characterization of the immobilized enzyme was performed. Furthermore, the thermal, pH, storage and operational stability of the immobilized enzyme in comparison to the free form was tested.     

Isolation and Culture Characterization of a New Polyvinyl Alcohol-Degrading Strain: Penicillium sp. WSH02-21

A fungal strain able to grow on polyvinyl alcohol (PVA) as sole carbon source was isolated from activated sludge of a textile factory. Morphological characteristics showed that this strain belonged to Penicillium sp., and, to our knowledge, this is the first report of PVA degradation by a strain of Penicillum sp. When 0.5% PVA was used as the carbon source in culture medium, it could be completely degraded after 12 days. This strain was found to produce and secrete an inducible PVA-degrading enzyme. High PVA concentration and oxygen transfer were favourable for PVA-degrading enzyme synthesis by Penicillium sp. cultured in shake-flasks. Moreover, Penicillum sp. cultured in PVA medium may spontaneously produce more catalase to decompose H₂O₂, a product of PVA oxidation by PVA oxidase, for protection of the cells from H₂O₂ damage. This revised version was published online in July 2006 with corrections to the Cover Date.     

种群生存力分析:准确性和保护应用

目前已提出了五类估计濒危物种绝灭风险的种群生存力分析模型 ,即 :分析模型、单种群确定性模型、单种群随机模型、异质种群模型和显空间模型。模型的选择取决于物种的生活史特征和可用的数据。与用于保护实践的其他方法相比 ,种群生存力分析 (PVA)是相对准确的量化工具。然而 ,一些濒危物种种群统计学数据质量差和种群动态的有关假说模糊不清可能影响到模型预测的准确性 ,因此 ,要谨慎地使用PVA。在西方国家 ,PVA在濒危物种保护计划和管理中应用越来越广泛。它主要用于 :( 1)预测濒危物种未来的种群大小 ;( 2 )估计一定时间内物种的绝灭风险 ;( 3 )评估一套保护措施 ,确定哪个能使种群的存活时间最长 ;( 4)探索不同假说对小种群动态的影响 ;( 5 )指导濒危动物野外数据的搜集工作。我国的濒危物种很多 ,然而开展PVA研究的濒危物种却很少。应大力发展适合于模拟我国特有濒危物种及其保护问题的PVA模型