Islets of Langerhans surrounded by a semipermeable membrane to prevent the host immunosystem is a potential way to treat type I diabetes mellitus. In this study, a series of poly (vinyl alcohol) membranes were formed by adding polyethylene glycols to create pores in the skin layer. The permeability study showed the skin layer structure had an influence on the diffusion of low molecular weight glucose, vitamin B12 and insulin. The mass transfer coefficient was improved from 1.04 × 10−4 to 2.16 × 10−4cm/ sec for glucose, from 2.84 × 10−5 to 8.36 × 10−5 cm/sec for vitamin B12 and from 1.45 × 10−6 to 4.15 × 10−6 cm/sec for insulin, whereas the passage of immunoglobulin G was completely prevented, indicating that these membranes could be effective in protecting islets from immunorejection. Thus such a membrane is an alternative potential material for artificial islets. In addition, we examined the insulin secretory response of islets separated by a poly(vinyl alcohol) membrane. We found that the insulinsecretion rate is relatively rapid compared to the permeation rate of insulin; thus, the process of the artificial islets is insulin-diffusion-controlled.
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"Amongst them, PVA is the most commonly used polymer for biomedical applications as it is biocompatible, economical and water soluble . PVA finds its biomedical applications in hemodialysis , artificial vitreous , contact lenses , artificial pancreas [30,31] and implant materials to repair bone  and cartilage replacement template to grow from its precursor solutions. In this process, the ionizable OH groups of PVA play an important role as they show affinity towards positively charged calcium ions helping nucleation of HA. "
[Show abstract][Hide abstract]ABSTRACT: Hydroxyapatite (HA) shows diverse biomedical applications as bone filler and coating material for metal implants to enhance osteoconduction. Four different PVAHA composites were synthesized in situ by an economical co-precipitation wet methodology. The FTIR spectra of PVAHA composites showed characteristic signals of HA and PVA. The BET surface area of PVAHA composites were in range of 41.3–63.7 m2/g. The composites showed type IV nitrogen adsorption/desorption isotherm, a characteristic for mesoporous material. The pore diameter range (6.3–8.1 nm) of PVAHA composites also confirmed their mesoporous nature. The Barrett–Joyner–Halenda (BJH) pore size distribution curves indicated a narrow pore size distribution. To obtain a homogeneous crack free coating with EPD on stainless steel (SS) plates, different parameters such as PVA percentages in PVAHA composites, solvent, deposition time and voltage were optimized. The PVAHA composites were stable after EPD as confirmed by FTIR spectra recorded before and after EPD. The SEM images of the coating showed a homogeneous morphology. The thickness of the coating was controlled by varying voltage and time. The best results were obtained with c-PVAHA composite at 30 volts for 5–10 min and current density was around 4.5 to 5 mA. The adhesion strength of c-PVAHA coating was measured by using ASTM standard F1044-99. The average value was approximately 9.328 ± 1.58 MPa.
Full-text · Article · Dec 2015 · Applied Surface Science
"There are some studies in the literature dealing with membranes prepared from poly(vinyl alcohol) by the phase-inversion method. Young et al.  made a solution of PVA in water and used Na 2 SO 4 /KOH aqueous solution as the coagulation bath. They obtained asymmetric membranes with dense top layers and porous sub layers. "
[Show abstract][Hide abstract]ABSTRACT: Poly(vinyl alcohol)–polyethylene glycol, PVA–PEG, blended membrane were prepared using supercritical fluid assisted phase-inversion method, in which scCO 2 was used as the anti-solvent. Poly(vinyl alcohol) was utilized as the main polymer, polyethylene glycol as the additive, and dimethyl sulfoxide (DMSO) as the solvent of these polymers. Taguchi method was used to investigate the effect of some operating parameters on the morphology of the membranes. The L16 orthogonal array was selected under the following conditions: pressure (100, 135, 165 and 200 bar), temperature (40, 45, 50 and 55 • C) and PEG weight percent (0, 0.33, 0.66, and 1%). Total polymer concentration of solutions in all experiment was constant at 10% (w/w). The morphology of the obtained porous membranes was characterized by scanning electron microscopy. Through changing the conditions in each experiment, the average pore diameter changed between 3.75 and 12.2 m. Results from analysis of variance (ANOVA) indicate that PEG concentration was the most significant factor on the average pore size of prepared membranes by 78.7%. This is the first work announcing preparation of PVA–PEG membrane using supercritical CO 2 .
Full-text · Article · Nov 2014 · Journal of Supercritical Fluids The
"The use of synthetic membranes is therefore restricted to cases where the cells are encapsulated after membrane formation (Youngsukkasem et al. 2012). Synthetic membranes can also be constructed into larger devices, with a planar or cylindrical arrangement (Young et al. 1996; Cheryan and Mehaia 1983). In this approach, a large amount of cells is enveloped in large flat-sheet, hollow-fiber, or encased membranes. "
[Show abstract][Hide abstract]ABSTRACT: This paper reviews the latest developments in microbial products by encapsulated microorganisms in a liquid core surrounded by natural or synthetic membranes. Cells can be encapsulated in one or several steps using liquid droplet formation, pregel dissolving, coacervation, and interfacial polymerization. The use of encapsulated yeast and bacteria for fermentative production of ethanol, lactic acid, biogas, L-phenylacetylcarbinol, 1,3-propanediol, and riboflavin has been investigated. Encapsulated cells have furthermore been used for the biocatalytic conversion of chemicals. Fermentation, using encapsulated cells, offers various advantages compared to traditional cultivations, e.g., higher cell density, faster fermentation, improved tolerance of the cells to toxic media and high temperatures, and selective exclusion of toxic hydrophobic substances. However, mass transfer through the capsule membrane as well as the robustness of the capsules still challenge the utilization of encapsulated cells. The history and the current state of applying microbial encapsulation for production processes, along with the benefits and drawbacks concerning productivity and general physiology of the encapsulated cells, are discussed.
No preview · Article · Oct 2012 · Applied Microbiology and Biotechnology