2. Multi-Chamber SPA Fabrication

These classical type of SPAs comprise multiple air chambers connected by narrow passages. The SPAs are fabricated using a conventional soft lithography process. The fabrication steps are listed below:

STEP 1. A 3D-printed mold defining the locations of the SPA chambers and their inter-connecting air channels is created.

STEP 2. Next, an elastomer in liquid form (EcoflexTM 00-30 from Smooth-on Inc.) is mixed using a centrifugal mixer then de-gassed in a vacuum chamber at 1.10−4 kPa.

STEP 3. This liquid is poured into the molds, de-gassed again, then cured for 45 min at 70 ◦C.

STEP 4. (1) For linear actuators two of the cured elastomer blocks are joined using a thin layer of uncured, de-gassed silicone applied by a procedure similar to sandwich micro-contact printing. (2) Using the same procedure, bending actuators are assembled by bonding the cured silicone block to a thin inextensible layer, fabricated by embedding a layer of silk fabric in a 0.75 mm-thick layer of de-gassed silicone cured at room temperature (image sequence for bending actuators at end of page).

STEP 5. The assembly is then cured at room temperature for two hours to guarantee proper bonding.

STEP 6. Finally, the assembly process is completed by inserting the air tubing (for all the SPAs in this work the tube length is 300 mm) and applying a flexible epoxy around it to ensure a proper seal.

The following images show step-by-step fabrication sequence for bending SPAs by including the additional un-stretchable layer.