(656a) Encapsulation of Thermotropic Liquid Crystals in Hollow Polymer Microcapsules: Design of Colloidal Liquid Crystal-Based Chemical Sensors That Function in Cellular Environments

This presentation will focus on the design of ultrathin, covalently crosslinked, and amine-reactive polymer microcapsules, and on fundamental investigations of these microscale objects as containers for the confinement and control of droplets of thermotropic liquid crystals (LCs) in aqueous environments. The goals of this work are motivated broadly by potential applications of microscale LC droplets as environmental sensors in biological contexts, and oriented specifically toward the design of hollow microscale containers that are (i) stable in physiologically relevant environments (e.g., in culture media or inside cells), and (ii) chemically reactive in ways that allow the inner and outer walls of the polymer capsules to be functionalized independently (e.g., to create microenvironments inside the capsules that interface with and direct the orientational order of the LC, and outer surfaces that confer water solubility or the ability to enter into cells or attach to their surfaces). 

Our approach builds on the results of past studies demonstrating methods for the encapsulation of thermotropic LCs within “polyelectrolyte multilayer” microcapsules, but exploits new methods for the “reactive/covalent” assembly of azlactone-containing polymer multilayers developed recently by our group. We used this reactive “layer-by-layer” approach to design monodisperse, amine-reactive microcapsules (~5 micrometers in size) using a sacrificial colloidal template. Subsequent treatment of these reactive capsules with the small-molecule dimethylaminopropylamine lead to water-soluble, amine-functionalized capsules that could be filled with LC by direct immersion in mixtures of LC and ethanol. This general approach could also be used to design bi-functional capsules having hydrophobic (amine-functionalized) and hydrophilic (alkyl-functionalized) inner- and outer-walls to explore the impacts of these parameters on both capsule solubility and the defect structure of the LC contained within it.

Partial or complete filling of these permeable capsules with thermotropic LCs yielded encapsulated LC droplets with defect structures (e.g., either radial or bipolar defects) that can respond to the presence or absence of analytes (e.g., surfactants and other amphiphiles) present in surrounding aqueous phases. Our results demonstrate that the walls of the surrounding capsules are semi-permeable, and that they can be used to discriminate between model analytes (and thus tune or predict the responses of the LC droplets) based on parameters such as size and charge. These observations suggest opportunities to use these LC-filled containers as selective reporters of molecular events in complex media (e.g., by protecting the aqueous/LC interface from contact with proteins, but permitting the transport of small-molecule substrates or products to the interface).

Our results demonstrate that these LC-filled capsules can be incubated in the presence of mammalian cells without inducing cytotoxic effects observed when cells are exposed to bare (uncoated) LC droplets. Capsules functionalized with cationic outer surfaces adhere to the outer surfaces of mammalian fibroblast cells, and these cell surface-bound LC-filled capsules retain their ability to respond rapidly to the addition of cytotoxic amphiphiles to culture media. Experiments aimed at understanding (i) the influence of the surrounding capsule on the orientation of the LC (e.g., defect structures), (ii) the sensitivity of orientation of the LC to the presence of surfactant (e.g., induced changes in defect structures), and (iii) the ability of these LC-filled microcapsules to function as sensors of toxic agents in biological/cellular environments will be discussed.