Ultraclean Self-Assembly on Micro-Bubble Lattice.

Water-based processing represents a technological solution to the safe, sustainable, and efficient fabrication and is key to advanced industries such as biomaterials, wearable electronics, and medical studies. In many of these, massive micro-patterning adds extra functionality but demands stringent factors which are incompatible with delicate micro-constituents. Here we show an ultraclean self-assembly of micro-objects on an underwater microbubble lattice generated on a surface of contrasting wettability. The water-air interface of these gaseous receptors provides capillarity adhesion to bind micro-objects that come into contact, leaving no tenacious residues upon subsequent transfer, which preserves objects' original states to the fullest. Leveraging such a removable and residue-free feature, heterogeneous micro-objects can be coassembled through selective bubble regeneration and its biocompatibility is verified by patterning cell-laden microgels. The air-bridge-mediated adhesion on a curved surface is numerically studied and two key impacting factors, wettability and particle-to-bubble size ratio, are extracted. Our approach enables massive patterning in an ultraclean and physico-chemically-benign manner and forms a part of water-based manufacturing that bridges the initial component microfabrication and final device application.