This is a variation on Viscous Fingering: How to Make Fluid Channels in Silicone Membranes. It is a more complicated setup but can be repeated more easily due to a smaller bed and therefore less expensive material costs.
In this Instructable I build on the technique of injecting air into silicone to cast its shape as a hollow cavity. The steps are condensed. For a closer look at the process of making these channels please take a look at the link above.
Step 1: Build the Hele-Shaw Cell
This step I have compacted into one, as it is explained in greater depth in Viscous Fingering: How to Make Fluid Channels in Silicone Membranes.
-Gang up a sheet of plywood and HDPE
-Add a boundary of double sided outdoor adhesive tape and miter cut corners
-Measure length of barbed fitting and add washers to offset depth so that barb remains shy of HDPE surface
-Add some hosing and measure outer diameter. Find a spade bit that is just smaller than that.
-Drill with spade from HDPE surface straight through. The plywood hole could be made bigger to allow for easier penetration of the hose. Clamp a scrap piece of wood to the exit of the hole to ensure a cleaner cut.
-Hammer in barb connector and cut excess tubing from HDPE side.
-Use double sided tape to adhere shrink film to surface. Heat shrink film, test for leaks.
-Attach hosing and valves, and add a base.
Step 2: Build Dynamic Frame
The Dynamic Frame is what creates space in the cell for air to enter. I have used a waterjet and laser cutter to create a guided stencil that raises and lowers to accommodate injection.