Concentration Of Ionizable Groups Research Articles

Investigation of loading and release in PVA‐based hydrogels

AbstractWe used Methylene Blue (MB) and Methyl Orange (MO) as model drugs to investigate the controlled release behavior of hydrogels from poly(vinyl alcohol) crosslinked with ethylenediaminetetraacetic dianhydride. The cationic or anionic character of these compounds and the molecular weight between crosslinks of the hydrogel and the concentration of ionizable groups in the hydrogel greatly affected the loading and release of the drugs. MB loading was favored, therefore, by a higher content of negative charges in the hydrogel, although this implied a greater degree of crosslinking and, therefore, a lower mesh size. On the other hand, the overall loading of negative MO, favored by a higher mesh size, was very low because of unfavorable interactions with the electrolyte charges. Release studies showed that one of the parameters that most affected the drug release behavior of these hydrogels was the pH of the solution. MB and MO were not completely released, even at pH 1. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1644– 1651, 2002.

An analysis of partially film-controlled membrane potentials of weak cation exchange membranes using the space–charge model

Membrane potentials of weak acid ion exchange membranes separating almost neutral (pH = 5.7) solutions of NaCl, KCl and LiCl are studied both experimentally and theoretically. The space–charge model is applied in the theoretical description taking into account the proton flux, the variation of the effective fixed charge concentration in the transport direction and concentration polarization at the membrane/solution interfaces. For the case of perfectly stirred solutions, the validity of a general equation for the membrane potential similar to a well known relationship of non-equilibrium thermodynamics is discussed. Using the above model, the experimental results of membrane potentials of weak acid membranes are analyzed. These membranes were prepared by treating a cellulose acetate filter with a solution of a polyacid. Unstirred boundary layer effects are traced by comparing two types of potential measurements. Assuming free solution values of the diffusion coefficients and using a known value of the acid dissociation constant, respectively, the pore radius, the concentration of ionizable groups and a parameter related to the thickness of the unstirred layers are obtained. For the case of KCl solutions also, specific adsorption of K + to the fixed negative charges (counterion binding) is considered. Finally, the influence of the electrolyte concentration on the conformational state of the adsorbed polyacid is also discussed from the results of hydrodynamical permeability measurements.

Radiation synthesis of poly(N-vinyl 2-pyrrolidone/itaconic acid) hydrogels and their controlled release behaviours

N-vinyl 2-pyrrolidone/itaconic acid copolymeric hydrogels were prepared by irradiating the ternary mixtures of N -vinyl 2-pyrrolidone/itaconic acid/water by γ-rays at ambient temperature. For the characterization of network structure of these hydrogels, swelling properties in phosphate buffer solutions and molecular weight between crosslinks were investigated. Methylene Blue was used as a model drug for the investigation of controlled release behaviour of hydrogels. Specific Methylene Blue adsorption capacity of hydrogels are found to increase from 0.36 to 47.7 (mg MB/g gel) with increasing amount of itaconic acid in the gel system. The influence of molecular weight between cross-links, the concentration of ionizable groups, ionization and concentration of MB in the hydrogel were examined. The release studies show that one of the basic parameters affecting the drug release behaviour of hydrogels is the pH of the solution.