Peptides have been used as building blocks for responsive materials due to their tunable hierarchical structure driven by self-assembly behavior. However, few studies have focused on the relationship between secondary structure (α-helix and β-sheet), morphology, and shape memory effect (SME) in peptidic hybrids. To expand this understanding, we probed the impact of secondary structure and hierarchical organization on thermo-responsive shape memory properties by utilizing bioinspired peptide-polyurea hybrids. Peptide motifs were incorporated to the soft segment of non-chain extended polyureas as poly(β-benzyl-L-aspartate)n-b-poly(dimethylsiloxane)-b-poly(β-benzyl-L-aspartate)n (PBLAn-b-PDMS-b-PBLAn) to control the soft segment ordering and degree of phase segregation driven by secondary structure. The α-helical arrangement stabilized by intra-molecular hydrogen bonding led to a microphase-separated and hierarchically-ordered morphology, resulting in an increase of the shape fixing ratio. In contrast, β-sheet ordering yielded a lower shape fixity, which was attributed to a phase-mixed structure via extensive inter-intermolecular hydrogen bonding between the hard block and peptide segments. These findings suggest that, while a microphase-segregated morphology is critical for shape memory performance, the inclusion of peptide building blocks provide an additional handle of SME due to variations in secondary structure. We also explored the effect of thermal annealing on the shape memory behavior of these peptide-polyurea hybrids to demonstrate the tunability of this platform. Overall, this research highlights the role of hydrogen bonding arrangement (inter- vs. intra- molecular) and hierarchical structure on shape memory response.

Interplay of peptide secondary structure, microphase-separated morphology, and shape memory response in bioinspired peptide-polyurea hybrids

ACS Spring 2022

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