Three-dimensional heterogeneous assembly of coded microgels using an untethered mobile microgripper.

Three-dimensional (3D) heterogeneous assembly of coded microgels in enclosed aquatic environments is demonstrated using a remotely actuated and controlled magnetic microgripper by a customized electromagnetic coil system. The microgripper uses different 'stick-slip' and 'rolling' locomotion in 2D and also levitation in 3D by magnetic gradient-based pulling force. This enables the microrobot to precisely manipulate each microgel by controlling its position and orientation in all x-y-z directions. Our microrobotic assembly method broke the barrier of limitation on the number of assembled microgel layers, because it enabled precise 3D levitation of the microgripper. We used the gripper to assemble microgels that had been coded with different colours and shapes onto prefabricated polymeric microposts. This eliminates the need for extra secondary cross-linking to fix the final construct. We demonstrated assembly of microgels on a single micropost up to ten layers. By increasing the number and changing the distribution of the posts, complex heterogeneous microsystems were possible to construct in 3D.

Programming magnetic anisotropy in polymeric microactuators.

Polymeric microcomponents are widely used in microelectromechanical systems (MEMS) and lab-on-a-chip devices, but they suffer from the lack of complex motion, effective addressability and precise shape control. To address these needs, we fabricated polymeric nanocomposite microactuators driven by programmable heterogeneous magnetic anisotropy. Spatially modulated photopatterning was applied in a shape-independent manner to microactuator components by successive confinement of self-assembled magnetic nanoparticles in a fixed polymer matrix. By freely programming the rotational axis of each component, we demonstrate that the polymeric microactuators can undergo predesigned, complex two- and three-dimensional motion.

Three-dimensional fluidic self-assembly by axis translation of two-dimensionally fabricated microcomponents in railed microfluidics.

A method for high-throughput 3D self-assembly of 2D photopatterned microstructures using railed microfluidics is presented. Vertical device patterning of heterogeneous materials requires high-level integration using conventional microelectromechanical system (MEMS) technology; however, 3D railed assembly enables easy and fast self-assembly via a fluidic axis-translation process and simple material exchange in microfluidic channels. Individually photopatterned 2D microstructures are axis-translated from in-plane to out-of-plane and fluidically self-assembled, guided by side-rails in microfluidic channels to form a 3D morphology. Since the structures are fabricated in fluidic environments, there are no fixed initial points on the channel substrate allowing fluidic horizontal stacking of erected 2D structures. The guiding mechanism of railed microfluidics enables efficient fluidic handling and deterministic 3D self-assembly of heterogeneous components such as electronic components or polymeric microstructures using only fluidic force.

Optofluidic encapsulation and manipulation of silicon microchips using image processing based optofluidic maskless lithography and railed microfluidics.

We demonstrate optofluidic encapsulation of silicon microchips using image processing based optofluidic maskless lithography and manipulation using railed microfluidics. Optofluidic maskless lithography is a dynamic photopolymerization technique of free-floating microstructures within a fluidic channel using spatial light modulator. Using optofluidic maskless lithography via computer-vision aided image processing, polymer encapsulants are fabricated for chip protection and guiding-fins for efficient chip conveying within a fluidic channel. Encapsulated silicon chips with guiding-fins are assembled using railed microfluidics, which is an efficient guiding and heterogeneous self-assembly system of microcomponents. With our technology, externally fabricated silicon microchips are encapsulated, fluidically guided and self-assembled potentially enabling low cost fluidic manipulation and assembly of integrated circuits.

Three-dimensional fabrication of heterogeneous microstructures using soft membrane deformation and optofluidic maskless lithography.

We propose a method for high-throughput generation of 3D microstructures using a membrane-mounted microfluidic channel. Utilizing an optofluidic maskless lithography system, photopolymerized 3D microstructures are fabricated in a layer-by-layer fashion with the thickness of each layer controlled by the deformation of the membrane. The combination of low numerical aperture optical systems for photopolymerization and a soft membrane for height control allows large area projection lithography with high vertical resolution, overcoming the trade-off between vertical resolution and the field-of-view. The material composition of each layer is varied using microfluidic control of photocurable resin and composite microstructures with heterogeneity in both lateral and vertical directions are generated. Using this technique, we demonstrate three-dimensional patterning of different types of cells in a hydrogel for a microfluidic platform to study co-culture and cell-to-cell interactions. The proposed technique is fast and simple, allowing parallel synthesis of complex heterogeneous 3D microstructures and in situ biomaterial patterning for microfluidic bioassays.

Guided and fluidic self-assembly of microstructures using railed microfluidic channels.

Fluidic self-assembly is a promising pathway for parallel fabrication of devices made up of many small components. Here, we introduce 'railed microfluidics' as an agile method to guide and assemble microstructures inside fluidic channels. The guided movement of microstructures in microfluidic channels was achieved by fabricating grooves ('rails') on the top surface of the channels and also creating complementary polymeric microstructures that fit with the grooves. Using the rails as a guiding mechanism, we built complex one- and two-dimensional microsystems in which all the microstructures initially involved in the fabrication method were incorporated as components in the final product. Complex structures composed of more than 50 microstructures (each sized smaller than 50 microm) were fluidically self-assembled with zero error. Furthermore, we were able to use the rails to guide microstructures through different fluid solutions, successfully overcoming strong interfacial tension between solutions. On the basis of rail-guided self-assembly and cross-solution movement, we demonstrated heterogeneous fluidic self-assembly of polymeric microstructures and living cells. In addition to such assembly of in situ polymerized structures, we also guided and assembled externally fabricated silicon chips-demonstrating the feasible application of railed microfluidics to other materials systems.