Light-directed forces have been widely used to pattern micro/nanoscale objects with precise control, forming functional assemblies. However, a substantial laser intensity is required to generate sufficient optical gradient forces to move a small object in a certain direction, causing limited throughput for applications. A high-throughput light-directed assembly is demonstrated as a printing technology by introducing gold nanorods to induce thermal convection flows that move microparticles (diameter = 40 µm to several hundreds of micrometers) to specific light-guided locations, forming desired patterns. With the advantage of effective light-directed assembly, the microfluidic-fabricated monodispersed biocompatible microparticles are used as building blocks to construct a structured assembly (≈10 cm scale) in ≈2 min. The control with microscale precision is approached by changing the size of the laser light spot. After crosslinking assembly of building blocks, a novel soft material with wanted pattern is approached. To demonstrate its application, the mesenchymal stem-cell-seeded hydrogel microparticles are prepared as functional building blocks to construct scaffold-free tissues with desired structures. This light-directed fabrication method can be applied to integrate different building units, enabling the bottom-up formation of materials with precise control over their internal structure for bioprinting, tissue engineering, and advanced manufacturing.

In article number https://doi.org/10.1002/smll.201700684, Chia‐Hung Chen, and co‐workers, introduce a novel light assembly method on the microscale by suspending gold nanorods (GNRs), as photothermal transducers, in a fluidic medium to induce thermoplasmonic convections for the assembly. The assembly of hydrogel microparticles, cell‐laden microgels and microtissues to form desirable patterns is demonstrated. This method can revolutionize current biofabrication processes that otherwise would have been difficult to achieve using 3D printing and other assembly technologies.