Incorporation of salicylic acid derivatives to hydrophilic copolymer systems with biomedical applications

Hydrogels based on polymeric derivatives of salicylic acid have been prepar ed for biomedical applications by free radical copolymerization of 2-hydrox y-4-methacrylamidobenzoic acid, 4HMA, and 2-hydroxy-5-methacrylamidobenzoic acid, 5HMA, with 2- hydroxyethylmethacrylate, HEMA, in a wide range of com positions. The reactivity ratios of 4HMA and 5HMA with HEMA in radical copo lymerization processes have been determined from their H-1 NMR spectra by a pplying linearization methods and non-linear least square treatments. Tgs o f the corresponding copolymers were analyzed by DSC. The swelling behavior in water of the prepared copolymers was studied in comparison to poly-(HEMA ), poly-(4HMA) and poly-(5HMA) hydration degrees, being in all cases superi or to 35%. The hydrolytical behavior of the synthesized copolymers was stud ied at three different pHs (2, 7.4 and 10) determining the release percenta ge of the salicylic acid derivatives, 4-amino salicylic acid, 4ASA, and 5-a mino salicylic acid, 5ASA, analyzed by high performance liquid chromatograp hy (HPLC). The release analysis was followed during 230 days and a pH depen dence was observed obtaining the highest release percentages at pH=10, wher eas at physiological pH (7.4) the release percentages were in range from 2 to 5% at that time for all copolymer systems. The hydrolytical stability is enough for long-term applications like bone cements, ionomers, etc. (C) 20 01 Kluwer Academic Publishers.