Development of Stimuli-responsive Polypeptide-based Gelators for Bioapplications and Photo-patterning Technologies

The past decade has witnessed significantly increased interest in the development of smart polypeptide based organo- and hydrogel systems with stimuli responsiveness, especially those that exhibit sol–gel phase-transition properties, with an anticipation of their utility in the construction of adaptive materials, sensor designs, and controlled release systems, among other applications. This dissertation highlights the rational design and development of polypeptide-based gelators for simple and easily-controlled preparations toward bioapplications and photo-patterning technologies, including full characterization studies of the compositions, structures and properties. The continuous N2 flow technology for controlled ring-opening polymerization of N-carboxyanhydride (NCA) was recently developed in our lab for construction of well-defined polypeptides, facilitating the investigations of structure-property relationships within polypeptide materials. Based upon this technology, a multi-responsive triblock hydrogelator was synthesized, which exhibited heat-induced sol-to-gel transitions and either sonication- or enzyme-induced gel-to-sol transitions. The formation of β sheets further displayed tertiary ordering into fibrillar structures that, in turn generated a porous and interconnected hydrogel matrix. The reversible macroscopic sol-to-gel transitions triggered by heat and gel-to-sol transitions triggered by sonication were correlated with the transformation of nanostructural morphologies, with fibrillar structures observed in gel and spherical aggregates in sol, respectively. The enzymatic breakdown of the hydrogels was also investigated. This allyl-functionalized hydrogelator can serve as a platform for the design of smart hydrogels, appropriate for expansion into biological systems as bio-functional and bio-responsive materials. This hydrogelator also displayed capability to dispersing and gelating single-walled carbon nanotubes (SWCNTs) noncovalently in organic solvents, resulting in significant enhancement of the mechanical properties of polypeptide based organogels and unique supramolecular structures, with results presenting in the second study. Based on the above two studies, a strategy for reversible patterning of soft conductive materials is developed. This strategy was enabled by a responsive composite that comprises peptide-based block copolymer hydrogelators and photo-thermally-active carbon nanotubes. This composite photo-responsive gelation at application relevant timescales ( 100 S m-1), which, additionally, hold the capability to revert to sol upon sonication for reprocessing