The bimaterial structures were created with 3D-printed built plaster and silicone resin (PDMS), Sylgard 184 (Dow Corning, Midland, MI). The plaster was built by a commercial powder-based 3D printer, ProJet 160 (3D Systems, Rock Hill, SC). The powder was VisiJet PXL, which contained 80–90% of calcium sulfate hemihydrate (also known as plaster). The bimaterial structure was designed based on an open-cellular unit cubic cell to hold silicone resin, as shown in Fig. 1(a), controlled by two parameters: cell size and solid-to-cell ratio. Cell size defines the length of the cubic cell; the solid-to-cell ratio determines the content of plaster in the part. For example, Figs. 1(b) and 1(c) show the 50% cell with 6.5 and 3.25 mm cell size, which denoted L and S, respectively. The procedures to manufacture the open cell structure are: (1) first print the cell structure with the ProJet 160, (2) dry the parts in the oven to evaporate binder residue, and (3) finally mold the parts with silicone resin along with several degassing cycles. Complete samples are shown in Fig. 2.