Molecular Weight Of PVA Research Articles

Protein permeation through poly(vinyl alcohol) hydrogel membranes

Hydrogel membranes were prepared by radiation and chemical cross-linking of poly(vinyl alcohol) (PVA) in aqueous solutions. Effects of PVA concentration, PVA molecular weight and radiation dose, as well as concentration of cross-linking agent, in the case of the chemical cross-linking procedure, on the permeation of insulin, albumin and immunoglobulin (IgG) through the membranes were investigated. Glucose permeation was also studied. The cross-linking density affected the size of the macromolecular mesh of the hydrogel network and thus the water content of the membrane responsible for the diffusion of the solutes. The diffusion coefficient linearly increased for all the solutes with increasing water content in the PVA hydrogels, indicating that diffusion occurs primarily through the water hydrating the polymer network. The permeability study showed that the water content as well as the mesh size had an influence on the diffusion of low molecular weight glucose and insulin. Although the diffusion of higher molecular weight solutes, such as albumin and IgG, was not so much affected by the mesh size of elaborated PVA hydrogel membranes, the diffusion of these proteins was very low.

Microencapsulation with carrageenan-locust bean gum mixture in a multiphase emulsification technique for sustained drug release.

A multiphase emulsification technique was modified in this process of micro-encapsulating gentamicin sulphate, thus avoiding the necessity for a surfactant in preparing the secondary emulsion for a W/O/W emulsion. Various proportions of iota-carrageenan (i-C) and locus bean gum (LBG) were investigated for the W/O/W emulsion after forming the primary W/O emulsion with sorbitan trioleate, Span 85. Upon removal of the oil phase (chloroform) from the W/O/W emulsion by heating (60-65 degrees C), microcapsules or 'W/W' particles containing drug dissolved in sodium hyaluronate were spontaneously formed. These were dispersed in a solution of a mixture of 5-10 per cent w/v polyvinyl alcohol, PVA (average MW 50,000-106,000; 98 per cent hydrolysed) and 3 per cent v/v polyethylene glycol 200 (PEG 200), and dried to form the hydrogel film casts. Our in vitro experiments in isotonic phosphate buffer solution (pH 7.4) at 37 degrees C, showed that the release of gentamicin sulphate was dependent on concentration of LBG, and concentration or molecular weight of PVA. With the exception of PVA hydrogel matrix preparations containing 20 per cent w/v LBG, all other formulations showed a significant initial 'burst' release of drug within 6 h. The drug-containing microcapsules in the PVA hydrogel film with 20 per cent w/v LBG, exhibited an almost zero-order release of drug up to 140 h. It is postulated that an effective barrier or high-density membrane enveloping the microcapsules was formed between i-C and LBG because of their unique molecular configurations. This phenomenon, together with the possible adsorption of i-C molecules at the transient oil and outer aqueous phase interface, presumably eliminated the need for a permanent oil phase and/or an O/W surfactant normally required for preparing W/O/W emulsions.

Protein Permeation through Polymer Membranes for Hybrid-type Artificial Pancreas.

Hydrogel membranes were prepared by radiation crosslinking of poly (vinyl alcohol) (PVA) in aqueous solutions. Effects of PVA concentration, PVA molecular weight, and radiation dose on the permeation of insulin and immunoglobulin through the membranes were investigated. Glucose permeation was also studied. The crosslinking density affected the size of macromolecular mesh of hydrogel network as well as the water content of membrane responsible for the diffusion of the solutes. The diffusion coefficient linearly increased for all the solutes with the increasing water content in PVA hydrogels, indicating that diffusion occurs primarily through the water hydrating the polymer network. The increase in crosslinking density of hydrogels by changing PVA molecular weight brought about the decrease in mesh size of the hydrogels, which, in turn, had an influence on the diffusion of immunoglobulin, but not of insulin and glucose.

Study of cryostructurization of polymer systems VII. Structure formation under freezing of poly(vinyl alcohol) aqueous solutions

Rheological properties of the cryogels produced by freezing of concentrated aqueous solutions of poly(vinyl alcohol) have been studied. These properties were shown to depend on the polymer concentration in the initial solution, on PVA molecular weight, cryostructurization duration and temperature. Electron microscopy demonstrates the heterogeneous porous structure of these cryogels and the dependence of the observed pattern on the conditions of formation of the studied objects.

Relative hydrophobicity of synthetic macromolecules : II. Poly(vinyl alcohol) with various degrees of acetylation

Partitioning of poly(vinyl alcohol) (PVA) of various molecular weights and degrees of acetylation (from 1% up to 18%) in the aqueous Ficol-400—dextran-70 two-phase system was studied at pH 7.4 at varied ionic compositions of the system. The relative hydrophobicity of the polymers was estimated. It was established that the relative hydrophobicity of PVA depends on the degree of acetylation of the polymer but not on the molecular weight of PVA in the range from 2 · 10 4 to 1 · 10 5. The results obtained are considered in comparison with those reported previously for polyethylene glycols, polyacrylamides and polyvinylpyrrolidones. The effect of the macromolecular nature of a compound on its hydrophobic character is discussed.

The influence of temperature on the adsorption and adsorbed layer thickness of various molecular weight fractions of poly(vinyl alcohol) on polystyrene latex particles

A comparison of the adsorption, at 5, 25, 37, and 50°C, of poly(vinyl alcohol) (PVA) on polystyrene latex particles from water has been made, in terms of the adsorbed amount (Γ) and the adsorbed layer thickness (δ), for various PVA molecular weight fractions (13,600 to 65,100). Solution properties of these PVA fractions (i.e., the radius of gyration and the χ-parameter), at various temperatures, have also been determined from viscometry studies. Γ would appear to increase slightly with temperature (at least for the higher molecular weights), while δ decreases. However, there is evidence for multilayer adsorption of PVA, and, therefore, it is considered that the average volume fraction (φ) of segments in the adsorbed layer (obtained from a combination of Γ and δ) is a better indication of the role of temperature on adsorption. φ is found to increase significantly with increasing temperature, for all the molecular weight fractions studied. This reflects the decreasing solvency of water for PVA with increasing temperature; this effect is also apparent in the trend in the values of the radius of gyration and the χ-parameter.

Stress-induced crystallization of poly(vinyl alcohol) from its aqueous solution under steady-state flow

In order to clarify the mechanism of crystallization under molecular orientation, crystallization of poly(vinyl alcohol) from solution was studied under the steady-state flow brought about under such conditions that the distance between the surface of the rod for stirring and the inner surface of glass vessel was 4 mm and the speed of rotation was 2070 rpm. The process of crystallization was classified in three types. (1): When air bubbles were scarcely formed by stirring, many bulk crystals were produced successively falling downward from the surface of solution irregularity arranged. (2): When a large quantity of air bubble was formed, finally film-like precipitates wound around the stirrer were obtained. (3): Two kinds of processes described above occurred simultaneously. In this condition, the nucleation and crystallization of PVA from solution by shearing force are considered to be caused by the turbulent flow at the surface of solution and that owing to air bubbles. The first type was observed when the molecular weight of PVA and the polymer concentration are low and the temperature of solution is high. The type was transferred to (3) or (2) with increasing molecular weight and polymer concentration and decreasing temperature.