Material Interfaces Inspired by Catch Bond Adhesins

Dansuk, Kerim Can

doi:https://doi.org/10.21985/n2-cmn8-zm07

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Material Interfaces Inspired by Catch Bond Adhesins

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Over the last few years, there has been a transition away from traditional engineering materials to new advanced materials that exhibit complex architectures with improved mechanical properties. Most of the inspiration for these new materials comes from nature, where organisms have evolved an immense variety of macro and nanoscale shapes and structures with clever mechanisms. Adhesion proteins are particularly inspiring for novel materials because they exhibit conformational dynamics that enables them to form special non-covalent interactions called ‘catch bonds’ with their ligand, where dissociation lifetime of ligand-protein complexes is enhanced by mechanical force. Intuition suggests that application of a tensile force on a chemical bond should tend to shorten the bond’s lifetime, making it more likely to break, but catch bonds defy this notion. If implemented in material systems, catch bonds are predicted to address trade-offs between strength and reconfiguration, two diametric material properties that are primarily governed by the strength of intermolecular interactions. One specific approach to developing this bioinspired material is biomimicry, replicating what nature does well in terms of structure, however; to date, the physical principles underlying catch bond phenomena have remained disputed among scientists, hampering efforts to make synthetic catch bonds. This work is a multifaceted approach combining molecular simulations and adhesion theory to establish strategies for designing material interfaces that incorporates catch bond features. A better understanding of catch bond physics would enable synthetic materials systems with catch bond linkages; hence, we begin with investigating chaperone-usher (CU) pilus—a bacterial adhesive protein with catch bond properties. By outlining adhesin properties determined by previous experimental investigations, we modeled the protein and systematically vary its catch bond parameters to determine key adhesion properties. Based on these properties, we proposed design guidelines for reproducing the catch bond phenomenon in synthetic systems and created a tweezer-shaped mechanical design that mimicked protein ligand interaction and exhibited catch bond behavior reliably and predictably under thermal excitations. After demonstrating the success of our guidelines, we adopted two strategies to implement catch bonds in nanocomposite systems. First, by introducing allosteric pathways, we designed X-shaped nanoparticle that can change shape and transition to a stronger bond state in presence of tensile force. Second, by grafting tethers with tunable lengths to the surface of nanoparticles, we created an interface with two failure modes: one where the load is shared among the tethers and the other where it is not. Both strategies present man-made alternatives to biological catch bond mechanisms and provides insight into how interfaces can be engineered to create nanoparticle networks with force-enhanced linkers. All-together these studies demonstrate that catch bond functionality can be achieved using simple molecular mechanisms and provides design rules for making catch bond nanoparticles and linkages, which paves the way for engendering emergent force-tunable interfacial kinetics in synthetic materials.

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