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This work reports the fabrication of AuNR@MSNs [i.e., gold nanorods (AuNRs) coated with mesoporous silica nanoshells (MSNs)] with independent sensitivities to pH and near-infrared (NIR) light for reversible on–off switching of drug release without premature drug leakage. The fabrication involves the incorporation of lauric acid (LA) as a thermosensitive gatekeeper, followed by the coating of tannic acid (TA) layers as a pH-sensitive gatekeeper. The protonation–deprotonation of the TA layers according to change in pH can result in their swelling–deswelling to induce pH-sensitive drug release, while the solid–liquid phase transition of LA by NIR light-induced heat generation in AuNRs enables the NIR light-controlled release of preloaded drug molecules. The interplay between these dual gatekeepers allows the release of pre-loaded drug from the AuNR@MSN-LA@TAs (i.e., AuNR@MSNs incorporating LA and TA) only at acidic conditions under NIR light irradiation, without premature drug leakage under inactive conditions (neutral pH or no NIR light). Moreover, the reversibility of the gatekeepers can make an on–off mannered drug release. Benefiting from the capability of the gatekeepers to induce pH-/temperature-sensitive release, along with the photothermal ability of AuNRs, the AuNR@MSN-LA@TAs can exhibit a satisfactory anticancer performance without undesired drug leakage.

Particles combining multiple anisotropy dimensions offer possibilities for self-assembly that have not been extensively explored to date. The scope for assembly of microparticles in which the anisotropy dimensions of internal bond angle and chemical ordering have been varied is investigated. Colloidal assemblies with interesting open (i.e., non-close-packed) structures can be assembled from these building blocks. The structure of the assemblies formed is linked to thebuilding blockanisotropybecausethesteric constraintsintroducedinduce deviations from close packing. Key challenges addressed in pursuit of these structures are parallelization of microfluidic synthesis methods, simulation to efficiently search the available anisotropy space, and methods that characterize the properties of the resulting assemblies. This combined program of synthesis, simulation, assembly, and characterization may be applied to develop design rules that guide efforts to fabricate microparticle building blocks and their assemblies.

We study fluidic assembly and packing of spherical particles in rectilinear microchannels that are terminated by a flow constriction. First, we introduce a method for active assembly of particles in the confined microchannels by triggering a local constriction in the fluid channel using a partially closed membrane valve. This microfluidic valve allows active, on-demand particle assembly as opposed to previous passive assembly methods based on terminal channels and weirs. Second, we study the three-dimensional assembly and packing of particles against a weir in confined rectilinear microchannels. The packings result in achiral particle chains with alternating (zigzag) structure. This structure is characterized by a single, repeated bond angle whose components projected into the frame of the channel are quantified by confocal microscopy and image processing. Brownian dynamics simulation of the packing comprehensively delineates the range of bond angles possible in narrow, rectilinear microchannels as well as the complex dependence of these angles on the relative dimensions of the channel and particles. The simulations of the three-dimensional packings are accurately modeled by a compact theory based on trigonometric relationships. The experimentally measured bond angles show excellent agreement with the simulations, thereby validating the functional dependence of the achiral packing bond angles on channel dimensions. This functional relationship is immediately useful for the design of anisotropic particles by microfluidic synthesis.

A microfabrication technique that uses a photolithographically patterned film as a microstencil has been developed. This microstencil has a bilayer structure comprised of parylene and SU-8 films with thicknesses from 4 to 100 microm. The parylene layer enables the microstencil to be mechanically peeled from hydrophilic substrates. Since no chemicals are required to release the microstencil, this technique can be used to pattern chemically and biologically sensitive materials. The amount of material deposited can be automatically controlled by the height of the SU-8 structures or externally controlled by spin coating or other thin film deposition techniques. This patterning method is very versatile and has been used to pattern features as small as 25 by 25 microm on silicon, glass, and polymer substrates. As an initial demonstration, we have patterned wax, cells, proteins, sol, and CYTOP.

We have found that the surface and bulk solution properties in a microfabricated device affect the degree and probability of electrostretching of DNA molecules. Using lambda phage DNA, we found that significantly hydrophilic surfaces between the electrodes decrease the efficiency of stretching. Surfaces treated with higher silane (trimethylchlorosilane) concentrations performed better presumably due to the decreased nonspecific adsorption of DNA on these surfaces compared to their more hydrophilic counterparts. The shape and dimensions of the electrodes also affected the efficiency of stretching. Both liftoff and metal etching methods produced electrodes with random microscopic peaks along the electrode's edge and were poorly suited for stretching. Annealing the electrodes (450 degrees C for 10 min) removed most of these peaks and allowed for more controlled stretching to be obtained. We also found that thin electrodes (65 nm) gave close to a 90% success rate of DNA stretching but stretching with thick electrodes (350 nm) produced only a 20% success rate.

Particles combining multiple anisotropy dimensions offer possibilities for self-assembly that have not been extensively explored to date. The scope for assembly of microparticles in which the anisotropy dimensions of internal bond angle and chemical ordering have been varied is investigated. Colloidal assemblies with interesting open (i.e., non-close-packed) structures can be assembled from these building blocks. The structure of the assemblies formed is linked to the building block anisotropy because the steric constraints introduced induce deviations from close packing. Key challenges addressed in pursuit of these structures are parallelization of microfluidic synthesis methods, simulation to efficiently search the available anisotropy space, and methods that characterize the properties of the resulting assemblies. This combined program of synthesis, simulation, assembly, and characterization may be applied to develop design rules that guide efforts to fabricate microparticle building blocks and their assemblies.

We report a technique for continuous production of microparticles of variable size with new forms of anisotropy including alternating bond angles, configurable patchiness, and uniform roughness. The sequence and shape of the anisotropic particles are configured by exploiting a combination of confinement effects and microfluidics to pack precursor colloids with different properties into a narrow, terminal channel. The width and length of the channel relative to the particle size fully specify the configuration of the anisotropic particle that will be produced. The precursor spheres packed in the production zone are then permanently bonded into particles by thermal fusing. The flow in the production zone is reversed to release the particles for collection and use. Particles produced have linear chain structure with precisely configured, repeatable bond angles. With software programmable microfluidics, sequence and shape anisotropy are combined to yield synthesized homogeneous (type "A"), surfactantlike (type "A-B") or triblock (type "A-B-A") internal sequences in a single device. By controlling the dimensions of the microfluidic production zone, triangular prisms and particles with controlled roughness and patchiness are produced. The fabrication method is performed with precursors spheres with diameter as small as 3.0 microm.