Fabrication of Hollow Silicon Microneedle Arrays for Transdermal Biological Fluid Extraction

Abstract

This thesis presents the research in the field of microelectromechanical systems with the specific aim of investigating a microneedle based transdermal skin fluid extraction concept. This work presents an innovative double-side Deep Reactive Ion Etching (DRIE) approach for producing hollow silicon microneedle arrays for transdermal biological fluid extraction. The microneedles are fabricated from a double side polished wafer to a shank height of 200-300 μm with 300 μm center-to-center spacing. Moreover, the in vivo testing results are provided as well. In this thesis, several microfabrication techniques are investigated, developed and applied in the fabrication process. The first chapter brings an overview of nano-/microfabrication and MEMS for biomedical applications (drug delivery and biofluid extraction). Furthermore, the fundamental background of skin structure and interstitial fluid (ISF) is introduced as well. The second chapter clearly illustrates three key techniques specifically employed in the microneedle fabrication process which are photolithography, wet etching and dry etching. The third chapter presents a detailed literature review of microneedles in terms of its general concepts, structures, materials and integrated fluidic system. Eventually, Chapter 4 introduces the details of our method to fabricate hollow silicon microneedle arrays step by step. SEM images and in vivo testing results confirm that hollow silicon microneedle arrays are not only sharp enough to penetrate the stratum corneum but also robust enough to extract ISF out of skin. Ongoing work will focus on the optimization of the assemble extraction apparatus and the capillary filling of the holes.