Tunable, temperature-responsive polynorbornenes with side chains based on an elastin peptide sequence.

Natural mammalian elastin fibers are crosslinked networks of the protein tropoelastin, which functions as the primary component of human blood vessels. Extensive physical and theoretical studies on this protein have shed light on the mechanism behind its unique elasticity.[1] Tropoelastin is comprised of hydrophobic domains of the repeating amino acid sequence -(VPGVG)nand domains rich in alanine and lysine residues for intermolecular crosslinking. The hydrophobic domains are conformationally dynamic and transition between random coils and tightly wound β-sheets, resulting in large changes in the hydration sphere of the protein. This process has been determined to be fundamental to the elasticity of the crosslinked networks.[2] In the absence of chain crosslinking, the conformation change is manifested by a temperature-dependent phase transition known as a lower critical solution temperature (LCST) below which the protein is soluble and above which it is insoluble. In order to take advantage of the physical properties of tropoelastin, elastin-like polypeptides (ELPs) have been synthesized by microbial expression systems[3] and have been studied for use as biomaterials.[4] The promise presented by ELPs has inspired us to search for readily accessible synthetic derivatives of these proteins for the development of new materials that promote endothelial cell growth. We hoped to incorporate the elastin amino acid sequence, -(VPGVG)-, as the side chain on biomimetic polynorbornenes to obtain a synthetic polymer that exhibits the phase transition behaviour of its polypeptide model.