RESUMO
Studies of dynamic and equilibrium swelling of ionic gels are important in understanding the diffusion of physiologically important fluids in materials for site-specific controlled drug delivery applications. The dynamic and equilibrium swelling properties of dry glassy poly(2-hydroxyethyl methacrylate-co-methacrylic acid) and poly(2-hydroxyethyl methacrylate-co-acrylic acid) polymeric networks were studied as a function of pH, ionic strength, nature of the counterion and buffer composition. The mechanism of water diffusion in these gels became more anomalous as the pH of the swelling medium increased and as the ionic strength decreased at a constant pH > or = pKa,gel. The mechanism of water diffusion was Fickian in all unbuffered swelling media at pH 4.0, which is lower than the pKa,gel. The pKa,gel of these gels was between 5.5 and 6. At pH 4.0, the diffusion mechanism was independent of ionic strength. This swelling behaviour is explained in terms of the concept of ion osmotic swelling pressure and ion exchange kinetics.
Assuntos
Materiais Biocompatíveis/química , Resinas Compostas/química , Metilmetacrilatos/química , Poli-Hidroxietil Metacrilato/análogos & derivados , Poli-Hidroxietil Metacrilato/química , Materiais Biocompatíveis/metabolismo , Soluções Tampão , Resinas Compostas/metabolismo , Sistemas de Liberação de Medicamentos , Eletrólitos , Géis , Concentração de Íons de Hidrogênio , Cinética , Metilmetacrilatos/metabolismo , Concentração Osmolar , Poli-Hidroxietil Metacrilato/metabolismo , Próteses e ImplantesRESUMO
Controlled release systems of theophylline, proxyphylline and oxprenolol.HCl exhibiting modulated drug delivery were prepared by using pH-sensitive anionic copolymers of 2-hydroxyethyl methacrylate with acrylic acid or methacrylic acid. Drug release studies were carried out in simulated biological fluids. The initial drug release rates and the drug release mechanisms were dependent upon the pH and ionic strength of the buffer solution as well as its salt composition. Initial drug diffusion coefficients in these swelling-controlled release systems were calculated from the release curves; they were of the order of 10(-7) cm2/s and were dependent upon the degree of swelling. The drug release mechanism was non-Fickian in all the dissolution media studied. Lowest release rates were observed for drug release from nonionized polymer networks in agreement with the relationship between ionization, swelling and drug release.
