Polypeptide‐Poly(Ethylene Glycol)‐Polypeptide Amphiphilic Triblock Copolymer Hydrogels With Tunable Stiffness via Varying Polypeptide Side‐Chain Moiety

This study investigates the hydrogelation behavior of amphiphilic triblock copolymers composed of a long poly(ethylene glycol) (PEG) chain as the hydrophilic central block and various aromatic polypeptides—poly(S‐benzyl‐ L ‐cysteine) (PBLC), poly(O‐benzyl‐ L ‐tyrosine) (PBLY), poly( L ‐phenylalanine) (PLF), poly(γ‐benzyl‐ L ‐glutamate) (PBLG), and poly(Z‐ L ‐lysine) (PZLL)—as hydrophobic terminal blocks. The results reveal that the long PEG chain, polypeptide chain length, and side‐chain functional group critically influence amphiphilic balance and non‐covalent interactions, which govern hydrogel formation and mechanical properties. Structural analysis identified intermolecular hydrogen bonding, π–π interactions on aromatic side chains, and PEG backbone entanglement as key factors stabilizing the hydrogel network. The PBLC‐PEG‐PBLC and PBLY‐PEG‐PBLY samples with a short polypeptide segment exhibited enhanced gel network stability and stiffness, evidenced by the crossover points of the moduli at the strain values higher than 300.0%. Among all the studied samples, PBLC 4.8 ‐PEG20000‐PBLC 4.8 and PLF 6 ‐PEG20000‐PLF 6 exhibited superior hydrogelation performance due to optimal hydrophilic/hydrophobic balance. Rheological studies demonstrated shear‐thinning behavior and recovery post‐deformation, highlighting suitability for injectable applications. However, higher stiffness was found to hinder smooth extrusion through needles. Additionally, the in vitro cytotoxicity proved their biocompatibility for normal cells. These findings underscore the potential of PEG‐based triblock copolymers with aromatic polypeptides for designing tunable hydrogels with tailored mechanical properties for biomedical applications.