Covalent Immobilization of Caged Liquid Crystal Microdroplets on Surfaces

Microscale droplets of thermotropic liquid crystals (LCs) suspended in aqueous media (e.g., LC-in-water emulsions) respond sensitively to the presence of contaminating amphiphiles and, thus, provide promising platforms for the development of new classes of droplet-based environmental sensors. Here, we report polymer-based approaches to the immobilization of LC droplets on surfaces; these approaches introduce several new properties and droplet behaviors and thus also expand the potential utility of LC droplet-based sensors. Our approach exploits the properties of microscale droplets of LCs contained within polymer-based microcapsule cages (so-called “caged” LCs). We demonstrate that caged LCs functionalized with primary amine groups can be immobilized on model surfaces through both weak/reversible ionic interactions and stronger reactive/covalent interactions. We demonstrate using polarized light microscopy that caged LCs that are covalently immobilized on surfaces can undergo rapid and diagnostic changes in shape, rotational mobility, and optical appearance upon the addition of amphiphiles to surrounding aqueous media, including many useful changes in these features that cannot be attained using freely suspended or surface-adsorbed LC droplets. Our results reveal these amphiphile-triggered orientational transitions to be reversible and that arrays of immobilized caged LCs can be used (and reused) to detect both increases and decreases in the concentrations of model contaminants. Finally, we report changes in the shapes and optical appearances of LC droplets that occur when immobilized caged LCs are removed from aqueous environments and dried, and we demonstrate that dried arrays can be stored for months without losing the ability to respond to the presence of analytes upon rehydration. Our results address practical issues associated with the preparation, characterization, storage, and point-of-use application of conventional LC-in-water emulsions and provide a basis for approaches that could enable the development of new “off-the-shelf” LC droplet-based sensing platforms

Stimuli-Responsive Polymer Coatings for the Rapid and Tunable Contact Transfer of Plasmid DNA to Soft Surfaces

We report the design and characterization of thin polymer-based coatings that promote the contact transfer of DNA to soft surfaces under mild and physiologically relevant conditions. Past studies reveal polymer multilayers fabricated using linear poly(ethylene imine) (LPEI), poly(acrylic acid) (PAA), and plasmid DNA promote contact transfer of DNA to vascular tissue. Here, we demonstrate that changes in the structure of the polyamine building blocks of these materials can have substantial impacts on rates and extents of contact transfer. We used two hydrogel-based substrate models that permit identification and manipulation of parameters that influence contact transfer. We used a planar gel model to characterize films having the structure (cationic polymer/PAA/cationic polymer/plasmid DNA)x fabricated using either LPEI or one of three poly(β-amino ester)s as polyamine building blocks. The structure of the polyamine influenced subsequent contact transfer of DNA significantly; in general, films fabricated using more hydrophilic polymers promoted transfer more effectively. This planar model also permitted characterization of the stabilities of films transferred onto secondary surfaces, revealing rates of DNA release to be slower than rates of release prior to transfer. We also used a three-dimensional hole-based hydrogel model to evaluate contact transfer of DNA from the surfaces of inflatable catheter balloons used in vascular interventions and selected a rapid-transfer coating for proof-of-concept studies to characterize balloon-mediated contact transfer of DNA to peripheral arterial tissue in swine. Our results reveal robust and largely circumferential transfer of DNA to the luminal walls of peripheral arteries using inflation times as short as 15 to 30 s. The materials and approaches reported here provide new and useful tools for promoting rapid, substrate-mediated contact transfer of plasmid DNA to soft surfaces in vitro and in vivo that could prove useful in a range of fundamental and applied contexts