Microfabrication of conical microfunnels for drug delivery applications

A cost‐effective fabrication methodology for the mass production of conical microfunnels for drug delivery applications is presented. The fabrication methodology originates from a technique previously used for fabricating suspended or hollow microstructures. The process comprises six stages: in stage 1, a UV‐opaque resin substrate is formed by mixing photocurable SU‐8 with a UV‐opaque impurity; in stage 2, an embossing stamp with an array of microrods is fabricated; in stage 3, the upper surface of the UV‐opaque resin substrate (from the first stage) is mechanically deformed by stamping with the embossing stamp from stage 2; in stage 4, the regions in which microfunnels are photolithographically defined are selectively exposed to UV light; in stage 5, the wafer from stage 4 is subjected to heat and then developed in 1‐methoxy‐2‐propanol acetate; finally, a hole on the tip of each microfunnel is formed by dry etching with oxygen plasma. The sharpness of the funnel tips can be flexibly adjusted by changing the stroke speed of the stamping in stage 3. The overall process can be carried out photolithographically with conventional photolithographic equipment. Using the proposed fabrication methodology, a matrix of polymeric microfunnels tapering from the base measuring 300 μm to the tip measuring 50 μm over a funnel height of 100 μm has been fabricated. Each fabricated microfunnel features a wide base and a sharp tip so that it has sufficient mechanical strength and sharpness to pierce the human skin. The conical geometry used in this study had a volume in excess of 24.4 nl.