Order and Disorder in Protein Biomaterial Design

Crystalline and amorphous materials have been extensively studied for their interesting properties, but they comprise a very small portion of the total materials space. The properties of most materials are a consequence of the interactions between their ordered and disordered components. This phenomenon is especially important in biology with materials such as silk and elastin owing their extraordinary attributes to the interactions of ordered and disordered domains at the inter- and intra- molecular levels. Recent insights in the emerging field of intrinsically disordered proteins have further highlighted the importance of order-disorder interactions as determinants of structural and chemical functions in multivalent proteins. While the significance of order-disorder interactions is well known and much work has been devoted to understanding their biological implications, little effort has been made to functionalize them for the development of new materials.

Recombinant protein polymers offer an interesting platform for determining how combinations of order and disorder lead to unique material properties as their molecular level control enables these components to be precisely mixed within a single polypeptide chain. This dissertation reports the successful design and application of a new class of recombinant materials inspired by the protein elastin, termed partially ordered polymers (POPs), to uncover the impact of single chain interactions between ordered domains and disordered regions on macroscopic material properties. These ‘smart’ protein materials: (1) are the first biopolymer system with temperature dependent phase behavior in which the aggregation and dissolution temperatures can be independently controlled, (2) are injectable as a solution that assembles under the stimulus of body heat into fractal-like, porous networks suitable for cell infiltration and remodeling, and (3) can be used to create microstructures with complex architectures and spatially segregated regions for applications in drug delivery and tissue engineering. This work expands the biomedical potential for protein-based materials as well as the available microarchitectures for biocompatible polymers, demonstrating that sequence level modulation of order and disorder is an untapped principle for the design of functional biomaterials.