| Silk is a natural protein that is mainly made of sericin and fibroin proteins. Silk siricin is a valuable protein resource discarded during producing fabrics. Studies have proved that sericin can be made into gels, membrane, foam, fiber and other materials. In order to make use of the unique properties of sericin, materials made mainly from sericin were synthesized by interpenetrating polymer networks to form environmental sensitive hydrogels. And the hydrogles were used as protein drug carrier to control the release of drug.Interpenetrating polymer networks (IPNs) composed of silk sericin (SS) and poly(N-isopropylacrylamide) (PNIPAAm) were prepared by the simultaneous-IPN method. The properties of the resultant IPN hydrogels were characterized by differential scanning calorimeter (DSC), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The single glass transition temperature (T_g) presented in the IPNs thermograms indicated that SS and PNIPAAm form a miscible pair which may be deduced from the interaction between SS and PNIPAAm. The intermolecular interaction between PNIPAAm and SS revealed by FTIR spectroscopy was believed to be the main driving force for the miscibility of the two components. The morphology of the IPNs was examined with TEM and there showed a micro-phase separation between SS and PNIPAAm phase, a relative homogeneous distribution of the two polymers was exhibited when the content of SS was 50 wt%. The swollen morphology of the IPNs obtained by SEM demonstrated that water channels (porous presented in the SEM photographs) were distributed homogeneously through out the network membranes. The sizes of the pores intend to decrease with the increase of SS content. Lower critical solution temperature (LCST) of IPNs was determined by DSC, LCST was increased slightly with the increase of SS content. The thermal stability of IPNs was improved by PNIPAAm interpenetrated into the networks.The swelling kinetics of the IPN hydrogels demonstrated that, at the temperaturebelow LCST (25 °C), the rate of water diffusion is relatively lower than that of the macromolecular relaxation;at the temperature near and above the LCST, the collapse rate of the PNIPAAm moiety is relatively higher than that of water diffusion. The transport of the water molecules into the hydrogel matrix is significantly blocked. The swelling ratio of the IPNs depended significantly on temperature, it decreased dramatically as the temperature increased toward their LCST. The IPN hydrogels showed swelling-deswelling recycle behavior with the changing of the temperature. The swelling behavior of the IPN hydrogels also showed pH dependence. Regardless the composition of the hydrogels, all the samples swelled lower at pH 4.4 (near the PI of SS) and pH 7.5(salting-out effect), but had a higher swelling ratio at acidic or basic conditions. It also indicated that the equilibrium swelling ratio was significantly affected by the composition of the IPNs, and therefore, the swelling profile of the IPN could be readily modulated by changing the feed ratio when preparing the IPNs.Bovine serum albumin (BSA) was chosen as a model drug to study the behavior of drug release from SS/PNIPAAm IPNs. The practical amount of BSA loaded in the hydrogels was lower than the amount of theory. The amount of BSA in hydrogels was in accordance with the swelling ratio and the size of the mesh of the IPNs. The release profiles at 17°C are the same as those at 37°C. The release of BSA showed a burst release within first 12 hours. Beyond the burst period, the release rate showed down. The release rate was faster at 17°C, and the amount was higher than those at 37°C.In order to improve the pH sensitivity of SS hydrogels, poly(methacrylic acid) (PMAA) was interpenetrated into IPNs with SS. According to FTIR analysis, the hydrogen bonding interaction was formed between SS and PMAA. The interior morphology of the swollen samples exhibited a porous structure. The hydrogels swelled rapidly in deionized water, controlled by water diffusion. SS/PMAA hydrogels had a strong pH sensitive property, maximal swelling ratio appeared under basic buffer solution. The IPN hydrogels showed swelling-deswelling recycle behavior with the changing of pH. The deswelling of IPNs was faster than that of neat PMAA. The practical amount of BSA absorbed in SS/PMAA hydrogels was higher than the amount of theory, in accordance with the swelling ratio of the IPNs. Therelease of BSA showed a burst release within first hours at pH 2.6 with little increase afterwards. While at pH 7.4, the release amount was increased gradually with time. The release amount was higher than those at pH 2.6.It looks forward to use these IPN hydrogels based on SS as drug carrier in drug controlled release.
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