Photosensitive poly(o-nitrobenzyloxycarbonyl-l-lysine)-b-PEO polypeptide copolymers: synthesis, multiple self-assembly behaviors, and the photo/pH-thermo-sensitive hydrogels

Abstract

A photoresponsive poly(o-nitrobenzyloxycarbonyl-L-lysine)-b-PEO (PNBL-b-PEO) polypeptide copolymer was synthesized and its photosensitive cleavage and self-assembly were monitored by means of UV-vis spectroscopy, ¹H NMR, DLS, and TEM. Three kinds of dual-sensitive (i.e., photo/pH-thermo) polypeptide normal and reverse micellar hydrogels were then fabricated by the physical cross-linking of the self-assembled micelles. Utilizing the inclusion complexation between α-cyclodextrin (α-CD) and PEO of the normal micelles of PNBL-b-PEO or polylysine-b-PEO, photo/pH-thermo-sensitive normal micellar hydrogels were fabricated; in contrast, the reverse micelles of polylysine-b-PEO@α-CD self-assembled at pH = 3 and then were transformed into a pH-thermo-sensitive reverse micellar hydrogel at pH = 10. The multiple self-assembly and hydrogel properties were thoroughly characterized by means of UV-vis spectroscopy, circular dichroism (CD), wide angle X-ray diffraction (WAXD), DLS, zeta potential, rheology, TEM, and SEM. Notably, these dual-sensitive polypeptide hydrogels with a higher mechanical modulus (10–105 kPa) were facilely constructed and the mechanical modulus can be further tuned by varying the UV-irradiation time, the amount of α-CD added, and the copolymer concentration. Consequently, this work provides a versatile platform for constructing polypeptide copolymer hydrogels with tunable mechanical and stimuli-sensitive properties.