Reversibly responsive and selective microcapsules
Properties of polymeric materials can be controlled by the monomeric chemical functionality, the polymer architecture, and the meso- and macroscale morphology. We develop novel microcapsules with thin polymeric shells that exhibit tailored functionality for on-demand release, purification, and separation applications. Properties of the polymeric shells include selectivity towards certain permeates by charge, polarity, and size on the nanometer scale, as well as responsiveness of said permeability towards external triggers, such as changes in pH, temperature, or light.
Responsive nanoporous microcapsule shells
Parts of this work are in collaboration with the Wiesner lab at Cornell University.
We develop polymeric microcapsules with homogeneous nanoporosity for size-selective uptake and release of actives in the range of 10s of nanometers such as proteins, macromolecules, and nanoparticles. For this goal, we study the co-assembly of block copolymers with small molecule porogens to obtain polymeric membranes with ordered nanostructures and continuous nanopores with narrow pore size distribution tunable in the 10s of nanometers. We confine the block copolymer self-assembly in the shell of water-in-oil-in-water double emulsion drops made in glass capillary microfluidic devices, which allows us to tune and screen the influence of macroscopic structural parameters such as film curvature and thickness on the obtained morphology. We screen properties such as osmolarity, pH, surfactants, etc. that show large impacts over multiple length scales on the self-assembling system and the polymer-water interface, to control the meso- and macroscale features of the microcapsules. Ultimately, these capsules will be tested towards recyclable size-selective encapsulation for separation applications.
Figure 1. Microcapsules from microfluidic double emulsion drop templating (top row) with self-assembled block copolymer shells comprising a three-dimensional gyroidal porous nanostructure. Scanning electron microscopy image (bottom) of the cross-section of the homogeneous, mesoporous shell of a block copolymer microcapsule.
Water-filled hydrogel capsules
Hydrogels are of immense importance in a wide variety of applications ranging from sorbents to drug delivery. Hydrogels are hydrophilic polymer networks with high water-swelling capacity and properties that are highly tunable through, for example, the choice of monomers and the mesh size. Charged hydrogels in particular represent a group of materials that exhibit charge-dependent diffusion and pH-responsive properties such as swelling behavior and permeability. These properties make hydrogels a desired polymeric material for controlled release and membrane applications. Water-filled capsules with hydrogel shells are challenging to fabricate, however, using emulsion based polymerization techniques, due to the miscibility of water and many hydrogel monomers and precursors. We explore synthetic pathways with chemical hydrophilicity conversion to obtain highly-charged hydrogel microcapsules with aqueous cores and control over microstructure (mesh-size) and macroscopic architecture. These microcapsules will find use in single-cell biological research, small-molecule separation, as well as on-demand and self-adjustable release applications.
Figure 2. Optical microscopy images of the glass-microfluidic fabrication of monodisperse water-filled microcapsules with dynamically responsive permeability (top). Water-filled poly(acid) thiol-ene hydrogel microcapsules (bottom left) in acidic and alkaline conditions demonstrating pH-dependant permeability. Release profile of dynamically pH-responsive microcapsuels (bottom right) with repeated on- and off-switching of release.
- J. G. Werner, B. T. Deveney, S. Nawar, D. A. Weitz, “Dynamic Microcapsules with Rapid and Reversible Permeability Switching” Adv. Funct. Mater. 1803385 (2018).
- J. G. Werner*, S. Nawar*, A. A. Solovev, D. A. Weitz, “Hydrogel Microcapsules with Dynamic pH-Responsive Properties from Methacrylic Anhydride” Macromolecules 51, 5798–5805 (2018).