Peptidic Materials: Nature Inspired Mechanical Enhancement

Résumé du livre

Bio-inspired materials design is an important strategy used in the fabrication of tunable and mechanically-enhanced polymeric systems. In this research, we have experimentally and computationally explored two central concepts from nature, hierarchical organization, polypeptide secondary structure and hydrogen bonding arrangement, in order to determine their effects on the morphological, thermal and mechanical development of fully synthetic peptidic polyurethane\ureas. Through the inclusion of multiple levels of organization, namely the addition of ß-sheet peptidic ordering within the soft domain of a family of polyurethane/ureas, tensile modulus was shown to increase by more than a factor of 3, but elongation-at-break was limited. Nonetheless, X-ray analysis confirmed the presence of a hierarchical microstructure with ß-sheet ordering thus inspiring further investigations into designing a flexible peptide/hard segment interface and the effects of secondary structure. In order to tailor the peptide/hard segment interface a peptidic soft segment which placed flexible poly(dimethylsiloxane) at the outer blocks was proposed. Unfortunately, poor end group fidelity in poly(¿-benzyl-L-glutamate) (PBLG), extensive cross linking in poly(ß-benzyl-L-aspartate) (PBLA) and lack of solubility in poly(e-carbobenzyloxy-L-lysine) (PZLY) hindered a successful synthetic methodology. To determine the consequences of secondary structure and hydrogen bond arrangement on mechanical response, a-helix and ß-sheet forming PBLA and PZLY were incorporated into a series of non-chain extended polyureas. It was found that ß-sheet structures produced materials with increased tensile modulus, however, due to extensive H-bonding, PZLY systems were flaw tolerant and capable of reaching greater elongations. To gain a greater understanding of the fundamental principles governing morphological development and mechanical response, computational efforts were conducted. Coarse-grained molecular dynamics (MD) simulations revealed that the bulky benzylic side chains of PBLG disrupted curved interface formation, thus limiting spherical and cylindrical morphology growth. Utilizing atomistic MD tensile deformation simulations, secondary structure and side chain mechanical effects were conducted on solid state, amorphous ensembles. These simulations revealed the influences of H-bonding arrangement and how side chain flexibility may lead to reduced modulus. This compiled work, sets the stage for future investigations into tailorable or tunable peptidic-hybrid materials.