Automated actuation of multiple bubble microrobots using computer-generated holograms

Microrobots, sub-millimeter untethered microactuators, have applications including cellular manipulation, microsurgery, microassembly, tissue culture, and drug delivery. Laser-induced opto-thermocapillary flow-addressed bubble (OFB) microrobots are promising for these applications. In the OFB microrobot system, laser patterns generate thermal gradients within a liquid media, creating thermocapillary forces that actuate the air bubbles that serve as microrobots. A unique feature of the OFB microrobot system is that the optical control enables the parallel yet independent actuation of microrobots. This paper reports on the development of an automated control system for the independent addressing of many OFB microrobots in parallel. In this system, a spatial light modulator (SLM) displayed computer-generated holograms to create an optical pattern consisting of up to 50 individual spots. Each spot can control a single microrobot, so the control of array of microrobots was accomplished with sequence of holograms. Using the control system described in this paper, single, multiple, and groups of microrobots were created, repositioned, and maneuvered independently within a set workspace. Up to 12 microrobots were controlled independently and in parallel. To the best knowledge of the authors, this is the largest number of parallel, independent microrobot actuation reported to date.