LAUSR

DOI: 10.1002/adom.201900669 sequestration.[5–7] There are three categories of techniques that have been used to manufacture TMPs; the first (canonical) category relies on photoor electron-beam (e-beam) lithography and etching. These methods permit unparalleled flexibility in user determination of feature size and spatial positioning, but they are expensive, require a cleanroom (and are not accessible to all users), and have some limitations on throughput (particularly for e-beam lithography). In recognition of these limitations, a second category of “dry” cleanroom-free methods has been developed, including 3D printing,[8–10] laser machining,[11] and “pick-and-place” technologies.[12,13] These techniques are useful, but they also rely on expensive and specialized tools and well-trained personnel, and can have limited throughput. A third category of “wet” cleanroom-free techniques has recently been proposed for forming topographical micropatterns, relying on dielectrophoresis tweezers (DEPT),[14–16] acoustic tweezers (AT),[17–19] magnetic tweezers (MT),[20,21] and optical tweezers (OT).[22–25] These techniques, in which patterns of 3D particles are assembled in a fluidic environment and are later dried for use in TMP applications, are creative and interesting, and preserve many of the advantages of the canonical methods while allowing for accessible, cleanroom-free operation. But each of the individual techniques has disadvantages; for example, DEPT and AT require the manufacture of micropatterned electrodes (typically using canonical cleanroom methods) and lack the flexibility to pattern large numbers of features. Likewise, MT-based methods can only assemble micro-objects that respond to magnetic fields, and OT-based techniques have sub-nanoNewton (90% for a wide range of different structures. The optofluidic assembly method described here is facile and accessible, suggesting utility for a wide range of microfabrication and microassembly applications in the future.