Investment molding is used to create hollow, in-plane, polymer microneedles. Sacrificial investment pieces (. 32 µ m-diameter aluminum bond wires) are bonded into silicon micromachined molds. Needles are formed by filling these molds with Cyclic Olefin Copolymer (Ticona Topas ®) using an injection molding machine. These needles are immersed in etchant, dissolving the investment and leaving a hollow part. Two micromachining techniques are used to make molds, RIE and KOH. The RIE molds deliver microneedles 280 µ m in length with rectangular (130 µ m x 100 µ m) cross-sections and inner diameter of ~ 35 µ m. The KOH molds are used to create 300 µ m long microneedles with 150 µ m wide triangular shafts with tapered tips.
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