(227b) Gelation and Phase Equilibria of Responsive Elastin-Mimetic Triblock Hydrogels

Elastin-mimetic triblock polypeptides can thermally gel in aqueous solution to form a stable 3-dimensional polymer network. The sequence of this polypeptide is based on the VPGVG (valine-proline-glycince-valine-glycine) pentamer repeat of elastin within BAB block copolymers. End B-blocks are modified to be relatively hydrophobic, while the center A-block is modified to be more hydrophilic. The network forms through the aggregation of the end blocks, and swells to a stable equilibrium in excess water. Above the gelation temperature, the gels are thermally responsive, shrinking with an increase in temperature. Dependence of equilibrium swelling of the gel on polymer concentration at synthesis suggests stabilizing interactions persist after network formation and do not reorganize above the gelation temperature. Laser Raman spectroscopy and ATR-FTIR (attenuated total reflectance-Fourier transform infrared) spectroscopy were used to investigate the changes in secondary structure associated with the sol-gel transition in H2O and D2O. The Amide I regions of these deconvoluted spectra suggest that the stabilizing interactions include intermolecular β-sheets of the B-blocks with significant fractions also containing β-turns and unordered structures. Swelling and shrinking cycles of the gel can be repeated as long as they are not cooled below the gel-sol transition. A phase diagram describing the thermally responsive behavior of equilibrium swelling has been developed. Overall, these physically-gelling elastin-mimetic triblock hydrogels have properties similar to chemically cross-linked, thermally responsive gels such as poly(N-isopropylacrylamide) with regard to equilibrium swelling, swelling kinetics and solute diffusion.