Rohan A. Hule, University of Delaware, Newark, DE, Radhika P. Nagarkar, University of Delaware, Newark, DE, Boualem Hammouda, National Institute of Standards and Technology, Gaithersburg, MD, Joel P. Schneider, University of Delaware, Newark, DE, and Darrin Pochan, University of Delaware, Newark, DE.
Hydrogels have been established as promising biomaterials for applications such as tissue engineering, controlled release of drugs and cell encapsulation. De novo designed beta hairpin peptides, capable of undergoing intramolecular folding and consequent intermolecular self assembly and hydrogel formation, were investigated containing asymmetric beta strand arms surrounding a turn sequence. The stimuli responsive self assembly of the hydrogels occurs via a strand interdigitation mechanism, resulting in a fibrillar nanostructure. Fibril dimensions as measured by TEM and AFM corroborate the interdigitated assembly. Bulk material properties studied using oscillatory rheology vary significantly for the different morphologies. Hydrogels consisting of laminated fibrils exhibited enhanced moduli over non-twisting or twisting fibrils and yielded at lower strain values. A lag in the G' increase during the initial period in time sweeps hints at slower assembly kinetics that can be related to higher number of monomers involved in the interdigitated assembly. SANS provides direct evidence of different fibril morphologies in terms of higher scattering intensities and lower correlation lengths for laminating fibrils vs. twisting or non-twisting structures. Inter and intramolecular associations during the self assembly process can also be related to Porod exponents indicative of mass fractals at high Q values. The formation of fibrils as a result of the self-assembly can be precisely tracked by changes in the Porod exponents and correlation lengths. Differences in the peptide registry that drive hydrogel nanostructure and properties can be potentially utilized in specific biomaterial applications.