Biomaterials requirements nowadays are becoming more and more specialized to meet increasingly demanding needs for biomedical applications such as matrices for tissue scaffolds. Among various useful classes of biomaterials, protein-based materials have been extensively pursued as they can offer a wide range of material properties to accommodate a broader spectrum of functional and performance requirements. The advent of genetic engineering and recombinant DNA technology has enabled the production of new protein-based biopolymers with precisely controlled amino acid sequence. As an example, silk-elastinlike protein (SELP) polymers consisting of polypeptide sequences from native silk of remarkable mechanical strength and polypeptide sequences from native elastin that is extremely durable and resilient have been produced. In this dissertation, a particular silk-elastinlike protein copolymer, SELP-47K, was cast into film form, and fully characterized for its material properties, including the mechanical property, secondary structure transition, optical transparency, surface, and other physical, chemical properties. The relationship between mechanical property and protein secondary structure was investigated as well. In addition, the material property tunability which can be induced by physical, mechanical, and chemical treatments has been explored. It is worth noting that the physically crosslinked SELP-47K films displayed mechanical properties comparable to those of native elastin obtained from bovine ligament. Secondary structure study through Raman and FTIR spectra showed that methanol treatment is capable of inducing theβ-sheet crystallization of silklike blocks, which act as physical crosslinks in the protein polymer chain network, thus stabilizing the protein structure and conferring the improved material integrity. The SELP-47K protein polymer thin films displayed excellent optical transparency. In particular, its excellent optical transmittance (over 90%) in visible light range may indicate SELPs can be a family of promising biomaterial candidate for ocular applications. Besides material property characterization, SELP-47K protein polymer has been fabricated into a variety of drug delivery devices to sustainably release a common ocular antibiotic, ciprofloxacin over a period of up to 220 h, with near-first order kinetics.

Biomimetic materials that recapitulate the complex mechanical and biochemical cues in load-bearing tissues are of significant interest in regenerative medicine and tissue engineering applications. Several investigators have endeavored to not only emulate the mechanical properties of the vasculature, but to also mimic the biologic responsiveness of the blood vessel in creating vascular substitutes. Previous studies in our lab generated the elastin-like protein polymer LysB10, which was designed with the capability of physical and chemical crosslinks, and was shown to display a range of elastomeric properties that more closely matched those of the native artery. While extensive validation of the mechanical properties of elastin-mimetic polymers has demonstrated their functionality in a number of tissue engineering applications, limited cell growth on the surfaces of the polymers has motivated further optimization for biological interaction. Recent biologically-inspired surface strategies have focused on functionalizing material surfaces with extracellular matrix molecules and bioactive motifs in order to encourage integrin-mediated cellular responses that trigger precise intracellular signaling processes, while limiting nonspecific biomaterial interactions. Consequently, this dissertation addresses three approaches to modulating cellular behavior on elastin-mimetic analogs with the goal of promoting vascular wall healing and tissue regeneration: genetic engineering of elastin-like protein polymers (ELPs) with cell-binding domains, biofunctionalization of elastin-like protein polymers via chemoselective ligation of bioactive ligands, and incorporation of matrix protein fibronectin for engineering of cell-seeded multilamellar collagen-reinforced elastin-like constructs. The synthesis of recombinant elastin-like protein polymers that integrate biologic functions of the extracellular matrix provides a novel design strategy for generating clinically durable vascular substitutes. Ultimately, the synthesis of model protein networks provides new insights into the relationship between molecular architecture, biomimetic ligand presentation, and associated cellular responses at the cell-material interface. Understanding how each of these design parameters affects cell response will contribute significantly to the rational engineering of bioactive materials. Potential applications for polymer blends with enhanced mechanical and biological properties include surface coatings on vascular grafts and stents, as well as composite materials for tissue engineered scaffolds and vascular substitutes.