Hollow Microneedle Fabrication and Characterization for Interstitial Fluid Extraction in Minimally Invasive Sensors

Interstitial fluid (ISF) is a rich source of relevant biomarkers, which surrounds the cells and tissues of the body and its composition is very similar to blood. Whereas in contrast to blood it does not clot and thus is an ideal matrix for the continuous monitoring of biomarkers. However, due to a number of technological challenges in its application it is still a largely unexplored niche in the context of wearable sensors. The main challenge is hereby the ISF collection, its transport to the sensor and its sensing in real time. Due to the direct accessibility of the ISF through the human skin by passing the stratum corneum and reaching the viable epidermis, hollow microneedles (MN) with lengths of about 1 mm are a highly promising approach for ISF sampling. In this contribution, we propose the fabrication of hollow MNs by using hot embossing of polymer foils into Laser generated master patterns on Borofloat® glass wafers. With this cost effective approach MNs can be fabricated on a flexible substrate, which make them ideal for the integration into flexible patch like sensor devices. The MNs are characterized by means of penetration and liquid extraction and transportation on a laboratory scale towards its application in a sensor patch in a real world scenario.