Hollow silicon microneedles, fabricated using combined wet and dry etching techniques, for transdermal delivery and diagnostics

Microneedle-based technologies are the subject of intense research and commercial interest for applications in transdermal delivery and diagnostics, primarily because of their minimally invasive and painless nature, which in turn could lead to increased patient compliance and self-administration. In this paper, a process for the fabrication of arrays of hollow silicon microneedles is described. This method uses just two bulk silicon etches - a front-side wet etch to define the 500 mu m tall octagonal needle structure itself, and a rear-side dry etch to create a 50 mu m diameter bore through the needle. This reduces the number of etches and process complexity over the approaches described elsewhere. Ex-vivo human skin and a customised applicator were used to demonstrate biomechanical reliability and the feasibility of using these microneedles for both transdermal delivery and di-agnostics. Microneedle arrays show no damage even when applied to skin up to 40 times, are capable of delivering several mL of fluid at flowrates of 30 mu L/min, and of withdrawing 1 mu L of interstitial fluid using capillary action.