4th Annual Mountain West
Biomedical Engineering Conference

A novel hybrid hydrogel based on a copolymer of poly[N-(2-hydroxypropyl)methacrylamide] [poly(HPMA)] grafted with a β-sheet peptide, Beta11 (Ac-TTRFTWTFTTT-Am) was designed. The copolymer, poly(HPMA)-g-CGGBeta11, was synthesized via the formation of thioether bonds between the cysteine-terminated modified Beta11 peptide (CGGTTRFTWTFTTT-Am) and maleimido-terminated side chains of poly(HPMA). By taking advantage of the poly(HPMA) random coil conformation, the Beta11 grafts were expected to self-assemble in aqueous solutions, therefore imposing the strong tendency of the peptide to associate into fibrils and to form gels onto the copolymer. Circular dichroism spectroscopy indicated that the ability of the peptide to form a β-sheet structure was indeed retained upon conjugation to poly(HPMA). Interestingly, the polymer backbone had a shielding effect, decreasing the sensitivity of Beta11 toward temperature and pH variations. The polymer also prevented the twisting of the β-sheet fibrils formed in the copolymer, as demonstrated by Fourier transform infrared spectroscopy. Transmission electron microscopy imaging and thioflavin T binding experiments further showed that fibrils with minimal lateral aggregation were present in poly(HPMA)-g-CGGBeta11. The tendency of the peptide to form hydrogels was preserved in the hybrid copolymer, depending on the density of grafts, concentration, and incubation time. Scanning electron microscopy imaging performed on hydrogel samples revealed a particular morphology of the copolymer network characterized by long-range order and uniformly aligned lamellae. The gelation process mediated by association of β-sheet domains was then monitored by microrheology as a function of concentration. Gels, depicted by plateau formation in mean square displacement and higher G’ values when compared to G”, were formed at peptide concentrations as low as 0.8 wt%, whereas higher concentrations, 3 wt%, were needed for the poly(HPMA)-g-CGGBeta11.