Functional materials: Exploiting dynamic self-assembly at interfaces

Professor Oren Scherman, University of Cambridge. Part of the Physical Seminar Series.

Abstract: We are interested in the development of controlled polymer architectures, hybrid nanoparticle-soft matter assemblies and the integration of dynamic supramolecular systems at interfaces. Current research projects in the group include the application of macrocyclic host-guest chemistry using cucurbit[n]urils in the development of novel microcapsules, supramolecular hydrogels, drug-delivery systems based on dynamic hydrogels, adhesion between a variety of surfaces, the conservation and restoration of important historical artefacts through the exploitation of supramolecular polymer chemistry and sensing and catalysis using self-assembled nanophotonic systems. Modification of solution viscosity using multivalent polymers has been accomplished through dynamic cross-linking in water using CB[8].

These hydrogels, with extremely high water content (up to 99.75% water by weight), have also been prepared by utilising renewable cellulose derivatives and other polysaccharides. Their rapid formation and shear-induced flow properties make these materials perfectly suited for use as injectable hydrogels for delivery of therapeutics. Polymer-inorganic composite materials can be readily prepared based on the CB[8] coupling of multivalent gold nanoparticles (AuNPs) to functional copolymers. When these systems are attached onto gold surfaces intricate control is achieved over the site-selective immobilisation of colloids and peptides. This has great scope for the development of optical materials, biological separations, and chemical sensors at the single molecule level. Additionally, we have developed an innovative new technique for manufacturing 'smart' microcapsules in large quantities using continuous flow in a single step from tiny droplets of water.

The major advantage of this manufacturing platform over current methods is that a variety of cargos can be efficiently loaded during the microcapsule formation at room temperature, and the dynamic supramolecular interactions provide control over the porosity of the capsules and the timed release of their contents using stimuli. Our CB[n] based host-guest systems exhibit dynamic self assembly and are capable of responding to stimuli (photochemical, chemical, and thermal) allowing for external control and function to be built into the materials. We recently reported the formation of a supramolecular polymeric colloidal hydrogel mediated by CB[8] interactions. The hybrid material comprises 98 wt% water and can be drawn into uniform ‘supramolecular fibers’ of arbitrary length (up to ca. 6 m) at room temperature. These ductile fibers exhibit a unique combination of stiffness and high damping capacity (60-70%), the latter of which exceeds that of biological silks.

These hybrid supramolecular composites open a window into fiber technology through low-energy manufacturing. In another example we reported a CB[8] mediated hydrogel that mimicked the structure/function relationship of skeletal muscle Titin. The new class of dual network gels formed through in situ polymerization incorporated both dynamic and covalent crosslinks exhibited remarkable toughness, energy dissipation and self-recovery, behaving like an “artificial muscle”. The hydrogel network exhibits extreme stretchability (>100x), remarkable toughness (> 2000 J/m2) and strength (fracture stress ~1.8 MPa), fast room temperature self-healing, with promising applications such as wearable electronics, super-tough interfacial adhesion, as well structural biomaterials.

References 1. (a) Walsh, Z.; Janecek, E.R.; Hodgkinson, J.T.; Sedlmair, J.; Koutsioubas, A.; Spring, D.R.; Welch, M.; Hirschmugl, C.J.; Toprakcioglu, C.; Nitschke, J.R.; Jones, M.; Scherman, O.A. Proc. Nat. Acad. Sci. USA, 2014, 111, 17743–17748. (b) Appel, E.A.; Forster, R.A.; Koutsioubas, A.; Toprakcioglu, C.; Scherman, O.A. Angew. Chem. Int. Ed., 2014, 53, 10038–10043. (c) Rowland, M.J.; Parkins, C.C.; McAbee, J.H.; Kolb, A.K.; Hein, R.; Loh, X.J.; Watts, C.; Scherman, O.A. Biomaterials 2018, 179, 199-208. 2. (a) Herrmann, L.O.; Valev, V.K.; Tserkezis, C.; Barnard, J.S.; Kasera, S.; Scherman, O.A.; Aizpurua, J.; Baumberg, J.J. Nat. Commun., 2014, 5, 4568. (b) Kasera, S.; Herrmann, L.O.; del Barrio, J.; Baumberg, J.J.; Scherman, O.A. Sci. Rep., 2014, 4, 6785. (c) Chikkaraddy, R.; Nijs, B.d.; Benz, F.; Barrow, S.J.; Scherman, O.A.; Rosta, E.; Demetriadou, A.; Fox, P.; Hess, O.; Baumberg, J.J. Nature, 2016, 535, 127–130. 3. (a) Zheng, Y.; Yu, Z.; Parker, R.M.; Wu, Y.; Abell, C.; Scherman, O.A. Nat. Commun. 2014, 5, 5772. (b) Zhang, J.; Coulston, R.J.; Jones, S.T.; Geng, J.; Scherman, O.A.*; Abell, C.* Science, 2012, 335, 690–694. 4. (a) Wu, Y.; Shah, D.U.; Liu, C.; Yu, Z.; Scherman, O.A. et al., Proc. Natl. Acad. Sci. USA, 2017, 114, 8163-8168. (b) Wu, Y.; Shah, D.U.; Want, B.; Liu, J.; Ren, X.; Ramage, M.H.; Scherman, O.A. Adv. Mater., 2018, 30, 1707169. 5. (a) Liu, J.; Tan, C.S.Y.; Yu, Z.; Lan, Y.; Abell, C.; Scherman, O.A., Adv. Mater., 2017, 29, 1604951. (b) Liu, J.; Tan, C.S.Y.; Yu, Z.; Li, N.; Abell, C.; Scherman, O.A., Adv. Mater., 2017, 29, 1605325.

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