Block length and topology affect self-assembly and gelation of poly(L-lysine)-block-poly(S-benzyl-L-cysteine) block copolypeptides

We report the self-assembly and hydrogelation of linear and star-shaped poly(L-lysine)-block-poly(S-benzyl-L-cysteine) (PLL-b-PBLC) block copolypeptides with degrees of polymerization (DPs) between 15 and 70, driven by the amphiphilic balance between PLL and PBLC segments as well as both aromatic and hydrogen bonding interactions between PBCL segments. The hydrogelation ability, molecular assembly, and mechanical strength of PLL-b-PBLC could be tuned by manipulating the non-covalent interactions via varying polypeptide chain length and arm number. The confinement of PLL chains due to the packing of hydrophobic, sheet-like PBLC segment led to the percentage of β-sheet/turn conformation much higher than the mole fraction of PBLC segment, faciliating polypeptide self-assembly and hydrogelation. Due to the differences in the degree of freedom for linear and star-shaped polypeptides to self-assembly, the linear PLL-b-PBLC would undergo morphological transformation of the nano-assemblies from 2D bilayers to 3D spherical aggregates upon hydrogelation, but not for the star-shaped counterparts. This study clearly illustrated that the sheet-like PBCL segment is an excellent hydrogelator to trigger hydrogelation of these block copolypeptides.