Design and fabrication of hollow out-of-plane silicon microneedles

The design and fabrication of hollow out-of-plane silicon microneedles that mimic the function and dimensions of a mosquito´s mouthparts are proposed. Two-step etching and deep reactive ion etching from both sides of the wafer were used to etch the boreholes completely and to ensure the holes have lateral smoothness. Microneedles composed of {411} exterior crystal planes were formed by anisotropic etching in 40% KOH solution at a water-bath temperature of 87°C. Finally, hollow silicon microneedles with a shank height of 100-120 μm and needle borehole diameter of 10-25 μm were fabricated. Flow rate tests using hollow microneedles were performed and demonstrated that the correlation between the flow rate and the inner diameter follows the Hagen-Poiseuille law. Sample tests were performed using pig skin and have shown that the microneedles have sufficient strength to withstand breakup. The microneedles, that the authors fabricated by using the microelectromechanical system, have potential applications in painless transdermal drug delivery systems.