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

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.

Economical impact: In the UK, the biomaterials industry is rapidly expanding. The proposed research will help to contribute to the economic success of the biomaterial sector. The overall output will be a platform for the production of a novel class of biomaterial, as well as scientists trained in their design, construction, characterisation and exploitation. As the platform will provide an understanding of the underlying process of the hydrogel assembly, it will define exciting new directions in the hydrogel field, leading to the discovery of novel biomaterials for exploitation. At the heart of the fellowship is the ability to understand the 'design rules' for the structure and mechanics of the hydrogel building blocks and the networks they form. Without this ability, the capabilities would be extremely limited. We will disseminate the work from the project and maximise the potential impact of the hydrogels as an underpinning technology for robust biomaterial applications. To enable wider access to engineered polyproteins and to increase uptake of their use in hydrogels by industry, we will explore opportunities for facilitating proof of concept plans through to market placement (see Pathways to Impact). We will make use of the UoL sector-facing interdisciplinary networks, which include Healthcare, and specifically 'Structure & Function in BioMedicine'. We will engage with the Medical Technologies Innovation Catalyst project, funded by the Higher Education Funding Council for England (HEFCE), which aims to translate the Yorkshire region's best healthcare and medical technology research into practical outputs. To efficiently engage with the widest possible cross-section of UK biomaterials industries we will also participate in events organised through the Medical Technologies IKC.

Ethical and Societal Impact: I aim to follow a responsible innovation approach in this project, maximising opportunities for innovation which are socially responsible, desirable and in the interests of the public. As life expectancy increases, the biomaterials field needs to be at the forefront of developing pioneering methods to replace and restore tissues and organs to the body, to create artificial hips and knees and to use tissue engineering to make complex organs. These advances are all critical for the development of medical treatments. Therefore it is crucial that the general public are engaged with the aims of the scientific research, and that the outputs meet their expectations. This engagement will enhance education and awareness, as well as promoting informed debate in the wider public area. Given the huge potential of polyprotein hydrogels to be used in a wide range of applications, it is important that public engagement begins from the outset of the project. This will allow for the identification of misunderstanding, on both the scientists and the public, and allow difficult questions to be raised early on in the process. To facilitate this process we have requested funds to engage with the public and to communicate the goals and concepts of the research. This will be achieved through public and schools events, detailed in the Pathways to Impact. It will also involve engagement through an organisation called Leeds involving people (LIP), which aims to represent the independent voice of people through the promotion of effective involvement. This provides an opportunity to advise statutory and other agencies on the development of policy and good practise, to improve people's quality of life. We will also engage with the Leeds Musculoskeletal Biomedical Research Unit, which is a National Institute for Health Research funded centre of excellence for translational research in a partnership between the UoL and the Leeds Teaching Hospitals Trust. This organisation has a focus on Public and Patient Involvement (PPI), allowing for an open dialogue between the goals of the project and public perception and expectation.