pH- and Temperature-responsive Hydrogels Based on Tertiary Amine-modified Polypeptides for Stimuli-responsive Drug Delivery

Graphical pH- and temperature-responsive monomethoxy poly(ethylene glycol) (mPEG)-polypeptide hydrogels were synthesized using ring-opening polymerization and post-polymerization modification. Aqueous solutions of the mPEG-polypeptides exhibited α-helix-to-β-sheet transitions when the pH was increased from 6.5 to 7.0, leading to a marked reduction in gelation concentration and prolonged drug release profiles at neutral pH. pH- and temperature-responsive hydrogels have attracted considerable attention due to their responsiveness to dual physiologically-relevant stimuli. In this study, we developed stimuli-responsive hydrogels based on monomethoxy poly(ethylene glycol) (mPEG)-polypeptide block copolymers containing various tertiary amine pendants (EEP-TAs). The EEP-TAs were synthesized via ring-opening copolymerization of α-amino acid N -carboxyanhydrides, and further modified post-polymerization with click chemistry. The EEP-TAs exhibited an α-helix-to-β-sheet transition when the pH was increased from 4.0 to 7.4. At elevated polymer concentrations, aqueous solutions of the EEP-TAs underwent thermo-induced sol–gel phase transitions, which were dependent on the pH. The hydrogels almost fully degraded within 3 weeks in the subcutaneous layer of mice and exhibited good histocompatibility in vivo. Additionally, doxorubicin (DOX)-loaded hydrogels exhibited pH-responsive drug release profiles in vitro, which were composed of rapid release at acidic pH and more sustained release at neutral pH. Thus, these polypeptide hydrogels hold potential as depots for environment-responsive delivery of therapeutic agents.