Design and Fabrication of Out-of-Plane Silicon Microneedles with Integrated Hydrophobic Microchannels Design and Fabrication of Out-of-Plane Silicon Microneedles with Integrated Hydrophobic Microchannels
This research presents fabrication procedures developed to produce pyramidal-shaped microneedles with microchannels that will allow for fluid delivery. The microchannels are etched into the substrate surface of a  silicon wafer using inductively coupled plasma etching. After the channel etch a layer of silicon nitride is deposited onto the inner walls of the microchannels and on the surface of the substrate. The nitride on the substrate surface provides the hard mask necessary to etch the microneedles, which are wet etched in a bath of potassium hydroxide (KOH). The selectivity of the KOH on  silicon is such that octagonal shaped pyramids are etched into the surface of the wafer. The pyramids are aligned with the previously etched microchannels to allow for needles with channels running through them. This research presents the first needles demonstrated with drug delivery channels running through the robust pyramidal needle shape.
In addition to the microchannel/microneedle fabrication procedure, microchannels were developed with inner structures as a method of creating hydrophobic surfaces on the inner walls of the channels. It was found that the channels developed had far too much variability in the diameter to accurately create a measurable reduction in flow; however, a loss coefficient was calculated showing increased flow rates in hydrophobically coated microchannels when hydrophobic structures are incorporated into the channel design.
It was also discovered that a hydrophobic coating, typically used to increase flow rates through a channel, can impede flow rate. There was no evidence found to suggest that hydrophobically coated microchannels of this size, with or without structures, will yield higher flow rates than non-coated microchannels.
School:Brigham Young University
School Location:USA - Utah
Source Type:Master's Thesis
Keywords:microneedle microchannel koh icp transdermal drug delivery
Date of Publication:06/29/2007