Engineered Proteins as Building Blocks for Responsive Biomaterials

Abstract

Biomaterials have long been important players in the advancement of medical treatments. However, new therapeutic approaches, driven by the field of regenerative medicine, have spurred the creation of new classes of biomaterials. One such type of material is hydrogels, which have broad usability as therapeutic delivery vehicles and tissue engineering scaffolds. Hydrogels uniquely replicate the cellular microenvironment, the extracellular matrix (ECM), offering opportunities for advancement in our understanding of cellular behavior in 3D environments that better mimic native tissues. Historically, hydrogels have been made from a variety of material precursors, most commonly synthetic polymers and naturally occurring biomolecules. While synthetic polymers (PEG, PLGA, etc.) offer advantages in their cost and ease of modification, enabling the relatively straightforward creation of hydrogels with tunable and stimuli-responsive characteristics, they lack an intrinsic ability to interface with cells. In contrast, naturally occurring biomolecules (collagen, alginate, silk, etc.) provide a baseline level of bioinstructivity but are challenging to control, suffering from high batch-to-batch variation and lacking tunability. Advances in our ability to make and modify proteins have enabled the use of recombinantly expressed, engineered proteins as alternative building blocks for the creation of hydrogels that blend the advantages of their synthetic and natural predecessors. This thesis focuses on using both rational and de novo protein design to create entirely protein-based hydrogels with stimuli-responsive behaviors. We first introduce a rationally designed hydrogel that is single component, injectable, and degradable via cytocompatible light. This material, named “PhoCoil”, can serve as a vehicle for the delivery of therapeutic cells via non-invasive injection and also allows for user-specified post-delivery degradation to release cells with light. We next share a suite of de novo designed proteins that can be used to create hydrogels with varied network valencies. This work showcases the potential of de novo design as transformative tool that could rapidly expand the diversity of proteins used to create biomaterials. Notably, these two-component hydrogels form in response to the addition of a small molecule, rapamycin, and can form condensate-like structures at low concentrations. De novo design approaches like this one may enable the creation of materials that mimic both the ECM and intracellular structures like condensates. Both of these material platforms offer exciting opportunities to advance our understanding of cell biology and fuel new approaches in regenerative medicine.