Additive Manufacturing of Stretchable Zipping Electrostatic Actuators through Spray Encapsulation of a Frozen Liquid

The fabrication of soft fluid-filled systems with mm or sub-mm scale features such as tuneable lenses, microfluidic tactile sensors, and electrohydraulic zipping actuators often relies on manual filling. This final step of injecting fluid limits throughput and repeatability. This study presents an additive manufacturing process to create complex stretchable systems in which the liquid is directly printed as part of the fabrication process. The devices actuate straight out of the printing setup, with no further filling or sealing steps. In our fully printed approach for multi-layered structures, the key steps are the deposition of precisely shaped liquid droplets with sub-µL resolution, followed by their encapsulation using a freezing process to allow printing or spraying over the temporarily solid fluid drops. Printing both the fluid and the structure has advantages of: a) no filing channel, enabling very high fill-factors; b) design freedom as each device in array can be filled with a different volume; c) accuracy in filling. We demonstrate this process by printing arrays of 5 mm diameter stretchable hydraulically amplified taxels (HAXELs), consisting of nine flexible layers, with the working fluid included as part of the printing process.