Designer Soft Microparticles for a Changing Environment

Harvard University, Cambridge MA

Investigators

Abstract

Non-technical Abstract Polymeric particles and capsules with diameters of tens to hundreds of micrometers, similar to the size of a human hair, are extensively used for the encapsulation and protection of chemically or environmentally sensitive active molecules or nanoparticles, with uses, for example, for food and detergent additives, for cosmetics, as well as for drug delivery. During storage and delivery, the encapsulant protects the cargo, and releases it at the desired location, often through some external stimulus that breaks or degrades the encapsulant. Microcapsules, particles with thin shells and large hollow cores, are particularly valuable because only small amounts of encapsulant is needed to protect large amounts of the desired payload. In this project, novel microcapsules are developed with shells that release the capsule content reversibly in response to different external stimuli without shell destruction, leaving the capsule intact for reuse or repeated on-off switching of the release. These capsules are ideal for applications such as waste removal in water, where they can be opened to collect the waste, closed to remove it, and reopened to release the waste in appropriate storage containment. These capsules are obtained from complex emulsions, such as water-cored oil drops, that are fabricated using microfluidic devices with channel architectures of comparable size to the drops. This technology enables precise manufacturing of capsules with control over size, shell thickness, and composition with very low dispersity. The students involved in this project, both undergraduates and graduates, are trained in functional polymer synthesis, microfluidic technology, and materials characterization, giving them a broad set of tools that is indispensable for modern multidisciplinary research in materials science. Technical Abstract Encapsulation of chemically or environmentally sensitive active molecules or nanoparticles is crucial in numerous applications, from food additives, to detergents and drug delivery; traditionally sacrificial encapsulants are used in a one-time, one-way encapsulate-and-release design. A primary aim of this project is to develop and fabricate a new class of dynamic encapsulant systems based on functional polymer microcapsules that exhibit active and reversible interactions with their environment. Microfluidic devices are used to create well-defined multiple emulsion drops of immiscible fluids that form templates for soft encapsulation materials. The physics of the assembly of functional materials in complex emulsions, and the dynamic functionalities of the materials themselves, are investigated, as is the influence of liquid confinement on these processes and properties. An additional aim of the project is to investigate the interactions of these functional polymeric microcapsules with solutes, the environment, and external stimuli for responsive and selective permeability in and out of the capsule. Encapsulation systems with such responsive permeability enable the reversible, on-demand release of actives, and allow the replenishment of actives inside the capsules through triggered uptake and trapping of cargo. This research extends the application of such encapsulants from one-way delivery systems to utilization in purification and separation. An additional objective of this project is the development of designer porous media with controlled mechanical properties to study fundamental mechanisms of the behavior of porous media and multiphase flow within it. These model systems provide insight into processes that are widely practiced but not well understood, including the fracturing of porous media due to pressure shocks, and the effects of polymer solutions on multiphase fluid flow in porous media.