Supramolecular Approaches to Viscoelastic Biomaterials and Their Applications

Viscoelasticity encompasses the characteristics of both the shape-conserving elasticity and the shock-absorbing viscosity. The extracellular matrices (ECM), or the protein-polymer scaffolds surrounding the cells in our body, possess unique tissue-dependent viscoelasticity to protect and provide mechanical queues to the nearby cells. Viscoelasticity in polymeric hydrogels can be achieved in several ways, one of which is by incorporating the host-guest supramolecular components. The following works explore the application of cucurbit[8]uril (CB[8])-based host-guest chemistry to achieve tuneable viscoelasticity in hydrogels. First, an ECM-mimetic CB[8]-based biomaterial tuned to the viscoelasticity of the lung is developed for stem cell engraftment into the solid organs. The crosslinker designed with a MMP-cleavable sequence enabled the enzymatic and cell-mediated changes in the gel mechanical properties, supported the organoid culture, and facilitated the functional engraftment and differentiation of the lung stem cells in the mouse lungs, highlighting the importance of tuning the viscoelasticity and cell-responsiveness of stem cell-carrying biomaterials for engraftment into solid organs. The second work reports of biofabricating the flexible electronics through a parylene surfacemodification chemistry and a novel hybrid network consisting of CB[8] and 1-benzyl-3vinylimidazolium (BVI) host-guest crosslinkers and gelatin-methacrylate (GelMA). The gel was designed to match the stress relaxation profile of the brain, facilitating a more brain ECM-mimetic biomaterial that is resistant to the high strain of the flexible neural devices. Combined with the ability to photo-pattern and combine with the different types of cells, this work presented the potential ways of multiplexing different types of biomaterials and cells to augment the bioelectronics functionalities, opening a new era of regenerative bioelectronics. The final work describes a new coumarin-based monomer that can be incorporated into the various free-radical-polymerised and-crosslinked materials to achieve reversibly phototuneable viscoelasticity. Harnessing coumarin’s UV wavelength-dependent cyclo-additionvi and-reversion, an extraordinary range ( 0.01 seconds to 1 million seconds) of stress relaxation half time (τ1/2) and storage modulus (100-10,000 Pa) were achieved with UV irradiation alone without changing the molecular composition. Unlike the previous approaches of directly functionalising the coumarin onto the polymer backbones, generating a CB[8]-coumarin monomer provided a powerful platform to augment the existing materials to possess reversibly tuneable viscoelasticity.