Synthetic Systems (Nash)

From the beating of our hearts, to the wave-like (peristaltic) motion of our intestines, the human body is a hive of activity. Dynamic processes are not only essential to our health but also to the differentiation, growth and regeneration of motile tissues, in particular, the intestines. Despite strong interest in the regeneration of intestinal tissue and gaining a clearer insight into the role of peristalsis in intestinal function, matrices used for the culture of intestinal organoids (IOs) and tissues are static. This limits their quality and viability and poses an obstacle to the accuracy of IO models and regenerative medicine. However, hydrogel matrices that exhibit the peristaltic motion required by intestinal tissues, specifically motion that is responsive to environmental cues, do not currently exist. Hydrogels cross-linked by responsive protein receptor-ligand (RL) complexes have the potential to harness the unique properties of their protein cross-links on the macroscale, including their response to mechanical and chemical stimulation. The main objective of the proposed research is to incorporate mechanoresponsive protein complexes into a hydrogel matrix, quantify their ability to alter the viscoelastic properties of the hydrogel as a function of environmental stimuli and assess the impact of this dynamic behaviour on cultured IOs. Combining microscale (AFM imaging and microrheology) and macroscale (rheology and mechanical testing) analytical techniques with biochemical characterisation (fluorescence microscopy and flow cytometry) and prior knowledge of biopolymer chemistry, I will rationally design biopolymer scaffolds, in which mechanically active proteins are embedded, and examine their responsive behaviour alongside their ability to support IO growth. By examining both the influence of the IOs on the hydrogel and that of the hydrogels on the IOs, knowledge of dynamic behaviour will be obtained in a cyclic manner that will permit tuning of the mechanical and chemical responsivity of the matrices to optimise dynamic behaviour and the impact on the cultured IOs. A rationally designed dynamic hydrogel that can adjust its viscoelastic behaviour in a periodic manner in response to local chemical and mechanical cues and support the growth of accurate and viable IOs will be the successful conclusion of this project. Insights gained in this study will lay the foundations for further exploration of responsive protein complexes in the design of dynamic cell culture matrices and their applicability to other organoid and tissue types, ultimately leading to significant leaps in organoid technology and regenerative medicine.

Catch bonds are one of Nature’s truly remarkable designs, which exhibit increased adhesive force as tensile force is applied, in contrast to traditional slip bonds whose adhesive force decreases under similar conditions. On reaching a maximum applied force, the catch bond then reverts to traditional slip bond behaviour resulting in a catch-and-roll type action that bacteria and cells use to move in a targeted fashion along a particular surface. The current research project aims to transplant this behaviour from bacterial systems into bio-based synthetic polymer networks, allowing the development of truly biomimetic mechanically adaptable materials. The aims of the project will be achieved by exploring a number of recently identified bacterial catch bonds, isolating the specific amino acid sequence responsible for this behaviour and using them to functionalise bio-based polymer chains. Using the receptor-ligand complexes specific to each bacterial adhesive, dynamic polymer networks will be constructed that display an adaptable response to force as observed in bacterial catch bonds. This represents an important area of research, for whilst the observation of ‘catch’ bond behaviour is relatively recent, their ability to revolutionise biomimetic materials is enormous. Their behaviour under stress is reminiscent of that of smooth muscle during peristaltic motion and materials mimicking this behaviour have the potential to drive new developments in synthetic organ and disease model research. Thoughout this project, fundamental insights will be gained into the intrinsic workings of bacterial catch bonds, specifically environmental factors affecting their behaviour, as well as how their behaviour is modified or scaled by inclusion in a macroscale material. The interdisciplinary project aims to push the boundaries of biology and materials science, from the molecular to the macroscale.