A method for the rapid fabrication of solid metal microneedles

Abstract

Microneedles are an emerging technology that offer an alternative to traditional hypodermic needles for drug and vaccine delivery. Less than 1 mm in length, microneedles can penetrate the skin with little to no pain making them a suitable option for the 1-in-10 people that may avoid seeking medical care due to needlephobia. However, there are significant challenges with adapting existing microneedle fabrication methods for large scale manufacturing while matching the repeatability, reliability, and cost of current hypodermic needle mass production processes. In this work we present a novel method of fabricating microneedles using a modified automated wire bonding process that is highly suited for mass production due to existing widespread use of this process and equipment in the semiconductor industry. Microneedle arrays of different densities were fabricated on FR-4 based printed circuit board substrates using this automated process and tested by inserting into porcine skin tissue to determine insertion forces. The required insertion force generally increased with increasing array density due to the "bed of nails" effect and decreased with increasing insertion speed due to the viscoelastic properties of porcine skin tissue. Characterizing the correlations between insertion force, insertion speed, and array density are important for designing microneedle-based devices and applicators that can reliably penetrate skin. Microneedle arrays were also successfully created by automated wire bonding on polyimide-based printed circuit boards to demonstrate that this process can be done on flexible substrates. Further investigation with larger samples sizes is required to expand on the preliminary findings of this work.

Adaptable gold solid microneedle arrays for drug delivery

“…Additionally, the manipulation of the MNA density limits the insertion due to the "bed of nails" effect, which is avoided by reducing the density of MNAs or by increasing the width of the MNs [14]. In other findings, different MN widths and densities were manipulated, and it was found that higher widths the reliability of insertion increases, due to the physical properties against needle fracture [15]. Ahn designed a customizable single MN that dramatically affects the insertion force; with those single MN tests, they showed that width minimally affects the required insertion force, whilst the tip radius, or the overall microneedle length increases the resistance significantly after 40 µm [16].…”

“…Hence, curving the substrate as shown in Figure 1d pushes the air sideways during insertion. To achieve this, MNs were fabricated onto a flexible substrate using a similar bonding technique as for the solid substrates that were published previously [15]. Only the single microchannel configuration is assessed for the flexible substrate.…”