Hollow silicon microneedle fabrication using advanced plasma etch technologies for applications in transdermal drug delivery.

Chris J W Bolton,Olivia Howells,Benedetta Gualeni,Kerry Roberts,Owen J Guy,James C Birchall,Huma Ashraf,Pey F Eng,Gareth J Blayney

doi:10.1039/d0lc00567c

Abstract

A novel production process flow is presented here for the manufacture of hollow silicon microneedles using deep reactive-ion etching (DRIE) technology. The patent-pending three-step process flow has been developed to produce multiple arrays of sharp-tipped, hollow microneedles, which facilitate easy insertion and controlled fluid injection into excised skin samples. A bevelled tip and vertical sidewalls for the microneedle have been achieved with good uniformity, despite >45% open etch area. Processing steps and etch challenges are discussed, and preliminary skin testing results are presented, showing effective needle insertion and delivery of fluorescent dye into ex vivo skin from human breast tissue.

Highlights

Microneedles do not have the same potential for physical or infectious harm presented by conventional hypodermic needles, and use of hollow microneedles in place of hypodermics would significantly decrease the risk of sharps injuries to medical professionals.[4,7,8,9,10]
Hypodermic needle is similar to the hollow silicon microneedles presented here, but the risk associated with the much increased length of the hypodermic requires continuous training programmes in order to be handled safely,[18,19] and their use results in more pain compared to microneedles.[3]
To control the uniformity of these applications, mask sets were designed whereby excess silicon was available around the edge of the wafer

Summary

Introduction

Microneedles are typically constructed from plastic,[11,12] metal[13] or silicon.[14] Examples of hollow plastic needles are available,[11] the majority of commercially available polymer microneedles remain solid due to the difficulty involved with integrating the bore.[12,15,16] The plastic moulding process restricts flexibility in the design whereas dry silicon etching allows for tailoring of processes to individual applications, for example needle length to target different skin depths. Metal MNs are expensive to produce[17] and it has proven difficult to machine hollow metal MNs in a cost effective production process. In terms of width dimensions, the 32G hypodermic needle is similar to the hollow silicon microneedles presented here, but the risk associated with the much increased length of the hypodermic requires continuous training programmes in order to be handled safely,[18,19] and their use results in more pain compared to microneedles.[3]

Methods

Results

Conclusion