GLASS-IONOMER CEMENTS BASED ON POLY(ACRYLIC ACID-CO-VINYL ALCOHOL) INDRUG-RELEASE MODEL FORMULATIONS

The release of methylene blue from glass-ionomer cements based on a co mmercial glass powder and partly hydrolysed poly(acrylic acid-co-vinyl alcohol) has been studied. A series of random copolymers were synthes ized from acrylic acid and vinyl acetate monomers, using feed ratios o f 10-90 mol% acrylic acid. The acetate group was hydrolysed using sodi um hydroxide. According to proton nuclear magnetic resonance analysis, the degree of hydrolysis was about 40%. The residual Na+ content in t he samples after hydrolysis was in the vicinity of 3 mmol g(-1) polyme ric sample. The viscosity average molecular weight of the copolymers w as the region of 60 000 g mol(-1) for samples with low acrylic acid co ntent and in the region of 300 000 g mol(-1) for samples with a larger fraction of acrylic acid. Cement sample discs were prepared and the p orosity of the cement was determined using N-2 adsorption-desorption i sotherms. The specific surface area was 10 m(2) g(-1), and the volume of the pores (<20 nm) 0.035 cm(3) g(-1). The swelling indices and the release rates in two different buffers, pH 2.0 and pH 7.4, were determ ined for fresh and dried samples. An acidic environment did not bring about significant swelling in the samples and release of the model age nt at pH 2.0 was limited. At a physiological pH value the cements swel led in a hydrogel manner and the fractional release of model agent inc reased.