Injectable hydrogels self-assembled from oligopeptide-poly(2-methacryloyloxyethyl phosphorylcholine) hybrid graft copolymers for cell scaffolds and controlled release applications

In this paper, we report the synthesis and characterization of novel peptide based hybrid graft copolymers that can form injectable hydrogels. These hybrid graft copolymers are composed of a biocompatible poly(2-methacryloyloxyethyl phosphorylcholine) main chain and self-assembling oligoalanine-block-poly(ethylene glycol) grafts (grafting ratio (m) = 6, 10, 20, 28, 32, and 40%), which are readily synthesized using a macromonomer by combining the solid phase peptide synthesis and conventional radical polymerization methods. Conformational analyses under a wide range of dilute aqueous solutions (pH 3-10 and 4-70 degrees C) revealed stable beta-sheet formation. With an increase in solution concentration, the graft copolymers, except those with a low grafting ratio of m = 6, formed hydrogels displaying shear-thinning and self-healing behaviors because of the reversible self-assembly property of peptide grafts. Interestingly, the mechanical properties of hybrid graft copolymers were strongly dependent on the grafting density of the hybrid copolymers. Thus, it was observed that an increase in grafting ratio strengthened the inter-polymer network. These features enabled the graft-type hybrids to be used as injectable hydrogels for 3D cell scaffolds and controlled-release applications.