A Digital Microfluidic Droplet Robotic System Enabled by Programmed Electrostatic Tweezer Arrays and Femtosecond Laser-Engineered Insulating Superhydrophobic Platforms

This paper reports a novel contactless droplet robotic system combining an array of electrostatic tweezers (ESTs) with an insulating superhydrophobic platform, enabling programmable droplet manipulation. First, we show that the EST can precisely trap and transport droplets on diverse insulating superhydrophobic surfaces─previously deemed unsuitable for such manipulation─by optimizing the applied electrostatic potential and EST height. The combination of the EST and insulating superhydrophobic substrates enables the trapping and manipulation of droplets across a wide volume range (covering at least 3 orders of magnitude) and a variety of liquid types (such as HCl, NaOH, and NaCl droplets). As a proof of concept, we finally prepare a simple droplet robotic system based on an EST array and achieve the digital control of droplet motion via selective electrode activation. The results successfully demonstrate the system's potential as a versatile, high-performance platform for digital microfluidics (DMF) applications.