A movable polymeric microneedle array actuated by thermopneumatic force

Abstract

A movable microneedle array, which can be switched on–off electrically, is reported. Unlike conventional microneedle arrays, which are usually fixed on substrates, the active microneedle array can move in and out by thermopneumatic force, so that drugs can be delivered or body liquid can be extracted through the skin surface (epidermis) only when needed. The active microneedle array consists of four layers: an air microchamber, a microfluidic channel, a microneedle array, and a protection layer. These four layers are made of PDMS and SU-8, and are assembled together on a glass substrate. As the microheater (Ti/Pt), integrated with a temperature sensor, heats up the air inside the microchamber, the microchamber volume expands, moving the microneedle array in the outward direction. The microfluidic channel layer acts as not only a fluidic path but also a mechanical support for the microneedle array. The microneedle array moves out to 413μm, which distance is sufficient to deliver drugs or extract body liquid through the skin surface. The measured actuation force was 40mN when the initial gap between the microneedle tip and the force gauge was 50μm. Operation conditions for successful skin penetration using the fabricated movable microneedle array were confirmed in the experimental study using chicken flesh.