Novel, side opened out-of-plane microneedles for microfluidic transdermal interfacing

We present the first hollow out of wafer plane silicon microneedles that have openings in the shaft rather than having an orifice at the tip. These structures are suited for transdermal microfluidic applications, e.g. drug- or vaccine delivery. The developed deep reactive ion etching (DRIE) process allows fabrication of two dimensional, mechanically highly resistant needle arrays offering low resistance to liquid flows and offering a large exposure area between the fluid and the tissue. The presented process does not require much wafer handling and only two photolithography steps are needed. Using this chip in a typical application, e.g. vaccine delivery, a 100 mul volume of aqueous fluid injected through a chip of 30 mm(2) in 2s would cause a pressure drop of less than 2kPa. The presented needles are approximately 2 10 pm long.