Inspired by spider silks, of which properties are driven by structural organization, we employed peptide motifs as an approach to tailor not only hierarchical structure but also thermo-responsive shape memory properties of conventional polymeric materials. Specifically, peptide-containing polyureas were synthesized by incorporating poly(-benzyl-L-aspartate)n-b-poly(dimethylsiloxane)-b-poly(-benzyl-L-aspartate)n (PBLAn-b-PDMS-b-PBLAn) as the soft segment, where secondary structure can be controlled via modulation of peptide repeat length and loading. We chose 5 and 20 peptide repeats, yielding dominantly β-sheet conformation and a mixture of α-helix and β-sheet conformations, respectively. Based on this platform, we explore the effect of secondary structure on shape memory behavior (shape fixity and recovery) of peptidic polyureas. The shorter peptide length or β-sheet ordering leads to decreased shape fixity and increased shape recovery compared to a control polyurea. As the ratio of β-sheet to α-helix decreases, an increase in the shape fixing ratio is observed, suggesting that the β-sheets reinforce elasticity of the soft phase and disrupt the hard segmental packing. The shorter peptide length, containing dominantly β-sheets, exhibits a higher glass transition temperature of the PBLA blocks compared to the longer peptide length, which is attributed to a higher fraction of inter-chain hydrogen bonding and phase-mixed structure. In this research, the hydrogen bonding arrangement of the soft phase and the degree of phase separation play important roles in determining shape memory properties. We also demonstrate that the shape memory response can be tuned by shifting secondary structure with thermal annealing.

Tuning shape memory response in polymer-peptide hybrids

ACS Spring Meeting 2021

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