Soft Nanotechnology. My research involves i) understanding the self-assembly of stimuli-responsive polymers into dynamic nanostructures. Materials like this can form assemblies that respond to environmental stimuli – like changes in temperature, pH, or chemical potential. We’re going to use these materials to ii) control the chemical and electronic properties at liquid-solid interfaces and iii) use biocatalysis – enzymes or membrane proteins – to change the properties and morphologies of these self-assembly nanomaterials.
Designing and Controlling the Self-Assembly of Stimuli-Responsive Polymers. Amphiphilic molecules, like surfactants and lipids, spontaneously organize into aggregated nanostructures, like micelles and vesicles. Polymer amphiphiles offer a rich library of self-assembling molecules that may be finely tuned for specific applications. Incorporating functional groups that are responsive to pH, temperature, or chemical potential makes it possible to change the properties and shape of these assemblies. Students interested in this area will develop skills designing, synthesizing, and interrogating stimuli-responsive nano-structures, which will be useful for a range of applications from sensors to drug delivery.
Schematic representation of a cyborg material consisting of a localized biotic catalyst – an enzyme or a membrane transport protein (purple) – bound to a bilayer membrane prepared from abiotic stimuli-responsive polymers. The action of the catalyst produces localized changes (e.g. pH, heat, or electrochemical) that will alter the morphology (i.e. the shape parameter) of the individual polymers (left) and, by extension, the synthetic membranes they comprise (right).
Tuning the Chemical and Electronic Properties of Interfaces. Some polymer amphiphiles readily adsorb and fuse to hydrophilic surfaces to form layered structures with tunable thicknesses on the nanometer scale. These adsorbed layers may be used as models of cell surfaces and also allow tuning the chemical properties of interfaces. Understanding how these adsorbed layers change the electronic properties of interfaces can be especially important for developing new kinds of sensors. Students interested in this area will develop expertise in forming supported polymeric and hybrid (lipid/polymer) bilayers and measuring their electronic properties using electrochemical methods, like cyclic voltammetry.
Integrating Biological Function in Stimuli-Responsive Vesicles and Bilayers. We are also interested in creating materials that change their shape to favor the dynamic transformation between micelles, bilayers, and other structures depending on their local environment. Stimuli-responsive polymers coupled to hetero-geneous catalysts, including enzymes, make it possible to translate chemical signals into physical changes to self-assembled nano-structures. Clever designs of such systems would enable the development of biohybrid “cyborg materials” that respond via catalysis to stimuli that are (otherwise) unrelated to the normal stimuli these materials are sensitive to. Such materials would find tremendous value as self-actuating nanomaterials.
- Paxton et al. “Self-Assembly/Disassembly of Giant Double-Hydrophilic Polymersomes at Biologically-Relevant pHs,” Chem. Commun. 2018, accepted.
- Paxton et al. “Adsorption and Fusion of Hybrid Lipid/Polymer Vesicles onto 2D and 3D Surfaces,” Soft Matter, 2018, under review.
- Paxton et al. “Capable Crosslinks: Polymersomes Reinforced with Catalytically Active Metal-Ligand Bonds,” Chem. Mater. 2015, 27, 4808–4813.
Shin, S. H. R.; McAninch, P. T.; Henderson, I. M.; Gomez, A.; Greene, A. C.; Paxton, W. F. “Self-Assembly/Disassembly of Giant Double-Hydrophilic Polymersomes at Biologically-Relevant pHs,” Chem. Commun. 2018, 9043-9046.
Paxton, W. F.; McAninch, P. T.; Shin, S. H. R.; Brumbach, M. T. “Adsorption and Fusion of Hybrid Lipid/Polymer Vesicles onto 2D and 3D Surfaces,” Soft Matter, 2018, accepted.