Polymer investment molding: Method for fabricating hollow, microscale parts

Polymer investment molding combines traditional injection molding with investment casting to create hollow parts on the microscale. Silicon mold inserts are manufactured using reactive ion etching or anisotropic wet etching. Then, a sacrificial element is placed in the mold. Plastic is injected into the mold and around the sacrificial element using an injection molding press. After removing the plastic part from the mold, liquid etchant dissolves the sacrificial element leaving a hollow plastic part. To demonstrate the process microneedles were formed by injection molding Cyclic Olefin Copolymer (Ticona Topas®) around 32 μm diameter aluminum bond wire. Hollow, in-plane, microneedles were then achieved by dissolving the bond wire away in liquid aluminum etchant. Rectangular cross-section needles were created with dimensions of 130 μm × 100 μm, overall lengths of 280 μm, and approximate inner diameter of 35 μm. Tapered needles were also created having an approximately triangular cross-section with two 105 μm sides and one 150 μm side. These needles had a base-to-tip length of 300 μm and approximate inner diameter of 35 μm.