Hydrogels from amphiphilic star block copolypeptides†
A range of 8-arm star-shaped diblock copolypeptides were developed to investigate their potential as self-assembling amphiphiles in aqueous media. These star-shaped block copolypeptides were sythesised by sequential N-carboxyanhydride (NCA) polymerisation from a polypropylene imine (PPI) dendrimer core to comprise a poly(L-lysine) core and poly(L-tyrosine), poly(L-phenylalanine), poly(L-valine) and poly(L-alanine) outer blocks. All star block copolypeptides except the poly(alanine) copolymer spontaneously self-assemble into hydrogels at a low polymer concentration of ≤2 wt%. Investigation of the secondary structure by FTIR and Circular Dichroism (CD) spectroscopy confirm a largely random coil conformation. The hydrogels were further investigated for their viscoelastic properties revealing a strong structure dependence of the hydrogel strength. The highest gel strength was achieved with the star block copolypeptide containing the poly(L-phenylalanine) outer blocks. The versatility of the hydrophilic/hydrophobic system allows for straightforward modification of the hydrophobic sequence, which can be utilised to modulate the mechanical strength for various applications.