High Precision Dynamic Manipulations of Large-Volume-Range Water-Based Droplets by a Soft Gripper with Robust Water-Repellent Superhydrophobic Surface

Droplet manipulation has emerged as a key enabling technology in various scientific and engineering fields with great potentials in advanced applications such as bioanalysis and reagent microreactors. The current strategies generally involve external stimuli or chemical/structural surface gradients to provide the driving force for in plane droplet manipulations, which suffer from low efficiency, poor controllability, and small volume ranges (generally V max / V min < 10) due to their inherent limitations. Herein, a dynamic gripping based droplet manipulation method is proposed by employing a flexible gripper with a notch covered by superhydrophobic silicon rubber membrane (SRM) between the gripper fingers to dynamically pick up, constrain and release droplets, capable of consecutively manipulating large-volume-range ( V max / V min >130) droplets with minimal liquid loss. The robust Cassie-to-Wenzel transition (CWT) resistance and mechanical stability of the produced superhydrophobic surface well support the dynamic operations of various droplets, where the superhydrophobic surface presents great water-repellent performance during stretching and impinging experiments as well as remains superhydrophobicity even after mechanical abrasion against 600 grit SiC sandpaper for 15 m at an applied pressure of 3.2 kPa. Lossless manipulations of 3–180 µL droplets have been experimentally validated, where an application of the proposed method in droplet-based microreactors for chemical analysis and bioassay is demonstrated.