Preparation and properties of a temperature- and pH- responsive polypeptide hydrogel

Stimuli-responsive polypeptide hydrogel has attracted a great deal of interests because of the biodegradability, biocompatibility and the response-ability to external stimuli. Here we synthesized triblock copolymers methoxy-poly (ethylene glycols)-b-poly (L-lysine)-b-poly (L-valine) (mPEG-PLys_x-PV_y) by sequential ring opening polymerization. Through adjusting the length of hydrophilic and hydrophobic segments, we constructed a temperature- and pH- responsive hydrogel system using polymer mPEG-PLys₂-PV₇. The phase diagram from test tube inversion method showed that the gel transition temperature could cover the body temperature (37 °C) and decreased with the elevated pH value. TEM and FTIR measurements proved that the secondary structure of the polymer solution was mainly β–sheet structure, and the sol-gel transition process was caused by both the dehydration of mPEG and the change of the secondary structure. After loading DOX in hydrogels, we investigated the drug release behavior in vitro at different pH values. The results showed that the drug release at pH5.5 was faster than that at pH 7.4. About 36% and 100% of loaded drug was respectively released from hydrogels at 37 °C within 48 h at pH 7.4 and pH 5.7. This polypeptide hydrogel material might be used as drug targeting release system and does not affect normal tissues due to its significant pH sensitivity. (paper)