Fabrication of Silicon In-plane and Out-ofplane Microneedle Arrays for Transdermal Biological Fluid Extraction
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Date
2019-04-23
Authors
Tazrin, Fahima
Journal Title
Journal ISSN
Volume Title
Publisher
University of Waterloo
Abstract
This thesis presents research in the field of microelectromechanical systems and
specifically in the area of microneedle-based transdermal skin fluid extraction and
drug delivery. The objective of this thesis is to highlight the potential role of
microneedles in achieving painless transdermal skin biofluid extraction and drug
delivery of macromolecular drugs across the skin barrier. The work represents the
design and fabrication of silicon out-of-plane and in-plane microneedles and an
innovative double-side Deep Reactive Ion Etching (DRIE) approach was presented for
producing hollow silicon microneedle arrays for transdermal biological fluid
extraction. The solid silicon out-of-plane microneedles are fabricated from a single
side polished wafer whereas the hollow out-of-plane microneedles are fabricated from
a double side polished wafer to a shank height of 200-300 μm with 300 μm center-tocenter spacing. The single-step Bosch DRIE is performed for “in-plane” silicon
microneedles to simultaneously etch the needle shaft (parallel to silicon substrate, etch
through the wafer) and the narrow trenches as open capillary fluidic channels (partly
etched into the wafer), taking advantage of the aspect-ratio dependent DRIE etching.
Furthermore, the double-sided two stage DRIE is performed to etch the open trenches
on the backside of wafer and then the needle shaft on the front side. The in-plane
needles have the advantages of making long needles up to 2 mm. Moreover, the in
vivo testing results are provided as well.
In this thesis, different microfabrication techniques are investigated, developed,
optimized, and applied in the fabrication process. The first chapter conveys an
overview of nanotechnology, nano-/microfabrication and their role in medicine. The
second chapter illustrates an introduction to transdermal drug delivery and
extraction. Furthermore, the fundamental background of skin structure and interstitial
fluid (ISF) is introduced as well. Device fabrication tools and techniques are shown in
chapter three. The fourth chapter presents a detailed literature review of microneedles
in terms of its general concepts, structures, materials and integrated fluidic system.
Eventually, Chapter 5 introduces the details of our method to fabricate solid and
hollow silicon microneedle arrays step by step. SEM images and in vivo testing results
confirm that silicon microneedle both out-of-plane and in-plane arrays are not only
sharp enough to penetrate the stratum corneum but also robust enough to extract ISF
out of skin or to deliver drug.
Description
Keywords
Deep reactive ion etching, Microneedles, Lithography, Wet etching, Dry etching, Out-of-plane microneedle, In-plane microneedle