THERMOSENSITIVE INTERPENETRATING POLYMER NETWORKS - SYNTHESIS, CHARACTERIZATION, AND MACROMOLECULAR RELEASE

Thermosensitive semiinterpenetrating polymer networks (semi-IPNs) comp osed of cross-linked poly(N-isopropylacrylamide) (NiPAAm) and linear p oly(ether(urethane-urea) (Biomer) were obtained via UV-initiated solut ion polymerization. The semi-IPNs exhibited negative thermosensitivity , i.e., lower swelling levels with increasing temperature. The incorpo ration of a relatively small content of Biomer (up to 10 wt %) strongl y influenced the mechanical properties, equilibrium swelling, and desw elling kinetics of synthesized networks. The semi-IPNs exhibited great er mechanical strength compared to the cross-linked poly(NiPAAm). Equi librium swelling levels of the semi-IPNs at low temperatures were mark edly decreased due to hydrophobic contribution of Biomer and higher ap parent effective cross-linking densities of these networks. The gel co llapse point, related to the lower critical solution temperature of po ly(NiPAAm), was not affected. The semi-IPNs showed much faster deswell ing rates compared to the cross-linked poly(NiPAAm). It was hypothesiz ed that the presence of Biomer prevented the formation of a skin-type layer which normally retards the deswelling process of cross-linked po ly(NiPAAm). Loading and release of heparin, a model macromolecule, was studied as a function of temperature and Biomer content in semi-IPNs. The partition coefficients of heparin within the networks decreased w ith increasing temperature and Biomer content. Similarly, a linear rel ationship between partition coefficients and equilibrium swelling in l oading solutions was found for all synthesized networks. Heparin relea se profiles correlated with deswelling kinetics of cross-linked poly(N iPAAm) and NiPAAm/Biomer semi-IPNs. Release profiles were in agreement with the proposed mechanism of solute release from swollen thermosens itive gels.