We describe the creation of polymeric microcapsules that can exhibit autonomous motion along defined trajectories. The capsules are made by cross-linking aqueous microdroplets of the biopolymer chitosan using glutaraldehyde. A coflow microfluidic tubing device is used to generate chitosan droplets containing nanoparticles (NPs) with an iron (Fe) core and a platinum (Pt) shell. The droplets are then incubated in a Petri dish with the cross-linking solution, and an external magnet is placed below the Petri dish to pull the NPs together as a collective "patch" on one end of each droplet. This results in cross-linked capsules (∼150 μm in diameter) with an anisotropic (patchy) structure. When these capsules are placed in a solution of H2O2, the Pt shell of the NPs catalyzes the decomposition of H2O2 into O2 gas, which is ejected from the patchy end in the form of bubbles. As a result, the capsules (which are termed micromotors) move in a direction opposite to the bubbles. Furthermore, the micromotors can be steered along specific paths by an external magnet (the magnetic response arises due to the Fe in the core of the NPs). A given micromotor can thus be directed to meet with and adhere to an inert capsule, i.e., a model cargo. Adhesion occurs due to the soft nature of the two structures. Once the cargo is picked up, the micromotor-cargo pair can be moved along a specific path to a destination, whereupon the cargo can be released from the micromotor. We believe these soft micromotors offer significant benefits over their existing hard counterparts because of their biocompatibility, biodegradability, and ability to encapsulate a variety of payloads.

Disaccharides are known to protect sensitive biomolecules against stresses caused by dehydration, both in vivo and in vitro. Here we demonstrate how interfacial accumulation of trehalose can be used to (1) produce rugged supported lipid bilayers capable of near total dehydration; (2) enable spatial patterning of membrane micro-arrays; and (3) form stable bilayers on otherwise lipophobic substrates (e.g., metal transducers) thus affording protecting, patterning, and scaffolding of lipid bilayers.

Using lithographically defined surfaces consisting of hydrophilic patterns of nanoporous and nonporous (bulk) amorphous silica, we show that fusion of small, unilamellar lipid vesicles produces a single, contiguous, fluid bilayer phase experiencing a predetermined pattern of interfacial interactions. Although long-range lateral fluidity of the bilayer, characterized by fluorescence recovery after photobleaching, indicates a nominally single average diffusion constant, fluorescence microscopy-based measurements of temperature-dependent onset of fluidity reveals a locally enhanced fluidity for bilayer regions supported on nanoporous silica in the vicinity of the fluid-gel transition temperature. Furthermore, thermally quenching lipid bilayers composed of a binary lipid mixture below its apparent miscibility transition temperature induces qualitatively different lateral phase separation in each region of the supported bilayer: The nanoporous substrate produces large, microscopic domains (and domain-aggregates), whereas surface texture characterized by much smaller domains and devoid of any domain-aggregates appears on bulk glass-supported regions of the single-lipid bilayer. Interestingly, lateral distribution of the constituent molecules also reveals an enrichment of gel-phase lipids over nanoporous regions, presumably as a consequence of differential mobilities of constituent lipids across the topographic bulk/nanoporous boundary. Together, these results reveal that subtle local variations in constraints imposed at the bilayer interface, such as by spatial variations in roughness and substrate adhesion, can give rise to significant differences in macroscale biophysical properties of phospholipid bilayers even within a single, contiguous phase.

The integration of ion-channel transport functions with responses derived from nanostructured and nanoporous silica mesophase materials is demonstrated. Patterned thin-film mesophases consisting of alternating hydrophilic nanoporous regions and hydrophobic nanostructured regions allow for spatially localized proton transport via selective dimerization of gramicidin in lipid bilayers formed on the hydrophilic regions. The adjoining hydrophobic mesostructure doped with a pH sensitive dye reports the transport. The ease of integrating functional membranes and reporters through the use of patterned mesophases should enable high throughput studies of membrane transport.