Swelling and ketoprofen release characteristics of thermo- and pH-responsive copolymer gels

Swelling-controlled drug delivery copolymer gels were newly synthesized by introducing thermo- and pH-responsive methacryloyl-glycine (MA-Gly) or pH-r esponsive methacrylic acid (MA-Ac) for comparison with thermoresponsive acr yloyl-L-proline ethyl ester (A-ProOEt). A homopolymer gel of A-ProOEt was k ept at degrees of swelling that were less than 0.5 at a pH from 2.5 to 7.5 at 37 degrees C. The thresholds of swelling for copolymer gels consisting o f A-ProOEt/MA-Gly and A-ProOEt/MA-Ac with a composition of 40/60 mol% were found to be pH 3.0 and pH 5.5, respectively, in buffer solutions at 37 degr ees C. The diffusion characteristics of 2-(3-benzoly-phenyl)propionic acid (ketoprofen) from such copolymer gels was evaluated in buffer solutions at pH's more than 5.5, and it was found that A-ProOEt/MA-Gly gel possesses a c ase II transport mechanism that is completely linear time dependent in both the amount diffused and the penetrating swelling front position. On the ot her hand, A-ProOEt/MA-Ac gel exhibited a non-Fickian (or anomalous) diffusi on behavior under the same conditions.