Exploiting Engineered Polyproteins in the Modular Design of Robust, Tuneable and Biofunctional Hydrogels

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Proteins are bionanomachines. These workhorses of the cell are responsible for a vast array of biological functions. Acting in isolation or as part of larger, often complex machinery, they perform their function through structural and mechanical changes. Studies on the mechanical properties of proteins found in nature have provided much inspiration for the design of new materials that have a balance of advanced mechanical properties. This includes the remarkable combination of high mechanical strength, fracture toughness and elasticity in the giant muscle protein titin and the intriguing mechanical properties of natural silk fibres. Despite the apparent biological complexity of nature, studies have shown that proteins can be designed to successfully mimic the strength and passive elasticity of muscle. This has been achieved through the design of polyproteins, which contain a specific number and arrangement of protein domains. Polyproteins are important because they provide a clear mechanical fingerprint in experiments for monitoring the response of proteins to an applied mechanical force. Polyproteins can be described using polymer physics and can be manipulated using tools such as single molecule force spectroscopy (SMFS), which provides information on their mechanical stability and softness. The hierarchical structures and intermolecular interactions present in polyproteins and the networks they form present new opportunities. In particular, a recent exciting development is the use of polyproteins as building blocks in hydrogels. Hydrogels are three-dimensional, hydrated, highly porous, percolating polymer networks spanning macroscopic dimensions. The hydrogel field is now extensive, with considerable strengths in the UK. However, it is only very recently that polyprotein-based hydrogels can be explored, due to advances in a biological technique called recombinant DNA technology.Hydrogels composed of engineered polyproteins offer three key advantages (i) the modular design of the polyprotein chain can be used to mimic the attractive mechanical and structural hierarchy found in nature, (ii) folded globular proteins offer building blocks with sequence dependent and tuneable thermodynamic and mechanical properties, (iii) functionality is intrinsic to protein fold, allowing for the incorporation of specific biological recognition capabilities that respond to biomolecular cues. Polyprotein-based hydrogels are therefore an exciting, emerging area in soft matter and biophysics. The integral functionality of the folded protein offers huge opportunities for applications, such as tissue engineering and stem cell differentiation, as well as offering a route towards smart, responsive materials for micro-optics, biosensors, and controlled release for drugs. While tools exist for measuring the structure, dynamics and mechanics of both proteins and of hydrogels, little is known about how this information translates between the nano- and mesoscopic length scales. A systematic and rational approach to hydrogel design requires the mechanical and structural properties of the system to be understood at all levels of hierarchical organisation. This fellowship will deliver a platform for the production of polyprotein hydrogels that possess specific biological function capabilities, enabling dynamic changes in mechanical and structural properties in response to biomolecular cues. The experimental and theoretical methods employed will provide a rich area for exploration in soft matter physics and biophysics, define exciting new directions in the hydrogel field, and lead to the discovery of novel biomaterials for exploitation.