Printing on Particles: Combining Two-Photon Nanolithography and Capillary Assembly to Fabricate Multi-Material Microstructures.

Additive manufacturing at the micro- and nanoscale has seen a recent upsurge to suit an increasing demand for more elaborate structures. However, the integration and precise placement of multiple distinct materials at small scales remain a challenge. To this end, we combine here capillarity-assisted particle assembly (CAPA) and two-photon polymerization direct laser writing (2PP-DLW) to realize a new class of multi-material microstructures. We use 2PP-DLW both to fabricate 3D templates to guide the CAPA of soft- and hard colloids, and to link well-defined arrangements of functional micro-particle arrays produced by CAPA, a process we term "printing on particles". The printing process is based on automated particle recognition algorithms and enables the user to connect colloids into one-, two-, and three-dimensional tailored structures, via rigid, soft or responsive polymer links. Once printed and developed, the structures can be easily harvested and re-dispersed in water. We report particle clusters and lattices of varying symmetry and composition, and fabricate thermo-responsive micro-actuators and magnetically-driven "micro-machines", which can efficiently move, capture and release DNA-coated particles in solution. The flexibility of our method allows the combination of a wide range of functional materials into complex structures, which we envisage will boost the realization of new systems and devices for a broad range of fields, including microrobotics, micromanipulation and metamaterials. This article is protected by copyright. All rights reserved.