Design of Bioelastic Materials

Elastic protein-based polymers fold and assembly by relatively unrestricting contacts involving bulky hydrophobic side chains. This leaves most of their backbone peptide moieties without structurally constraining inter- and intramolecular hydrogen bonding, and so these moieties are free to undergo large amplitude high-entropy rocking motions that become damped on extension. These protein-based elastomers are nearly ideal elastomers, with limited straining and breaking of bonds on extension resulting in the potential for extraordinary functional lifetimes. This decrease in entropy, caused by the damping of internal chain dynamics on extension (i.e. a decrease in the amplitude of the peptide-moiety rocking motions) has been called the peptide-librational-entropy mechanism of elasticity. The literature data and analyses affirm that components of elastin, and purified elastin fibre itself contain dynamic, non-random, regularly repeating structures that exhibit dominantly entropic elasticity by means of a damping of internal chain dynamics on extension. The resulting structure is termed a ?-spiral, as the ?-turn is the dominant repeating secondary structural feature. The term spiral is used instead of helix to emphasize in the structure that there is not obligatory hydrogen bonding between repeating units as in the classical helical structures of polypeptides. The interturn interactions are hydrophobic; there is water within the ?-spiral; and the ?-turns function as spacer between the turns of the ?-spiral. Experimental studies on the inverse temperature transitions exhibited by elastic protein-based polymers, as they relate to the performance of various forms of work or energy conversions of relevance to biology, have resulted in some axioms: "Variables including temperature, pressure, chemical concentration, and light-elicited changes in chemical structure can be used to alter the value of temperature transition to perform mechanical work by producing folding and assembly" and "The above energy conversion can be demonstrated to be more efficient when carried out using more-hydrophobic protein-based polymers". On these bases, we have observed the conformational behaviour of different sequences containing hydrophobic amino acids in order to design news bioelastic polymers. References Urry D.W., Phil. Trans. R. Soc. Lond. B (2002) 357, 169-184 Fenude Schoch E., Römer U.D., Lorenzi G.P., Int. J. Peptide Protein Res.(1994) 44, 10-18 Römer U.D., Fenude Schoch E., Lorenzi G.P., Helv. Chim. Acta (1993) 76, 451-458 Navarro E., Fenude E., Celda B., Biopolymers (2001) 59, 110-117 Navarro E., Fenude E., Celda B., Biopolymers (2002) 64, 198-209