The Effect of PZLY on Hierarchy and Mechanics in Peptide-Polymer Hybirds

By combining the hierarchy of biological species with synthetic concepts, peptide-polymer hybrids can control the molecular design and material properties. By further incorporating covalent cross links, the molecular complexity is enhanced so that both a physical and covalent network is allowed. Through the process, both the structure and function of polyethylene glycol (PEG)-network hybrids are regulated by changing peptide block length and overall peptide content.

Researchers discussed about the effect of poly(ε-carbobenzyloxy-l-lysine) (PZLY) units on block interactions and mechanics by exploring secondary structure, PEG crystallinity and hierarchical organization. By incorporating PZLY, a mixture of α-helices and β-sheets at smaller repeat lengths ( n = 5) as well as selective α-helix formation at a higher peptide molecular weight ( n = 20) was revealed. The change of the secondary structure determined the hierarchy of the solid film, while the sizes of the nanoscale fibers and microscale spherulites are dependent on the amount of α-helices and β-sheets.

The long-range ordering affected mechanical properties so that the elongation-at-break (from 400 to 20%) was decreased with increasing spherulite diameter. In addition, the soft segment crystallinity was reduced, resulting in a decrease in moduli. In conclusion, a balance of physical associations and self-assembly is achieved by controlling PZLY content so that the PEG crystallinity, spherulite formation, and mechanics can be regulated

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