#  2. Multi-Chamber SPA Fabrication 

 



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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.

 ![molds](/sites/g/files/omnuum4601/files/2024-11/molds.jpg)

 

***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.

 ![liquid_elastomer](/sites/g/files/omnuum4601/files/2024-11/liquid_elastomer.jpg)

 

***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).

 ![cured_elastomer](/sites/g/files/omnuum4601/files/2024-11/cured_elastomer.jpg)

 

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

 ![glued_halves](/sites/g/files/omnuum4601/files/2024-11/glued_halves.jpg)

 

***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.

 ![bending_actuators_fab](/sites/g/files/omnuum4601/files/2024-11/bending_actuators_fab.jpg)