Dense vertical SU-8 microneedles drawn from a heated mold with precisely controlled volume

Abstract

Drawing lithography technology has recently become a popular technique to fabricate (3D) microneedles. The conventional drawing process shows some limitations in fabricating dense, scale-up and small microneedles. In this study, we demonstrate a new drawing lithography process from a self-loading mold which is able to overcome these challenges. Different from the conventional molds which have difficult alignment and loading issues, a released SU-8 membrane is attached onto a SU-8 coated wafer to generate an innovative self-loading mold. The physically distinct SU-8 colloid in this mold successfully avoids the merging of the microneedle tips in the drawing process. Meanwhile, the same SU-8 colloid in mold can provide microneedles with uniform lengths on a large surface area. Furthermore, a low temperature drawing process with this improved technique prevents sharp tips from bending during the solidification stage. Remarkably, this new drawing lithography technology can fabricate microneedles with various lengths and they are strong enough to penetrate the outermost skin layer, namely the stratum corneum. The spacing between two adjacent microneedles is optimized to maximize the penetration rate through the skin. Histology images and drug diffusion testing demonstrate that microchannels are successfully created and the drugs can permeate the tissue under the skin. The fabricated microneedles are demonstrated to deliver insulin in vivo and lower blood glucose levels, suggesting future possible applications for minimally invasive transdermal delivery of macromolecules.

A flexible three-dimensional electrode mesh: An enabling technology for wireless brain–computer interface prostheses

“…Next, a 300-μm SU-8 2100 layer was deposited by two continuous spin-coating processes, which were patterned into the SU-8 pillar array (Figure 2e). The SU-8 sharp tips were formed using the drawing lithography technology we reported previously [31][32][33] ( Figure 2f). Drawing lithography technology is a maskless fabrication approach to build 3D structures based on the polymers' different viscosities under different temperatures.…”

Engineering Microneedles for Therapy and Diagnosis: A Survey

“…However, drawing lithography also has demerits. Xiang et al pointed out that drawing lithography was limited by alignment and material loading [50]. It was hard to produce dense, scale-up, and small MNs.…”

Microdroplet-based On-Demand Drawing of High Aspect-Ratio Elastomeric Micropillar and Its Contact Sensing Application

“…High aspect-ratio (HAR) micropillars have been attracting an increasing level of research interest thanks to their unique mechanical and optical properties. They are already playing crucial roles in biomimetic dry adhesives 1 , 2 , super-hydrophobic surfaces 3 – 5 , microneedles for drug delivery 6 , tunable optical windows 7 , 8 , actuators 9 , air flow sensors 10 , and nanonewton-scale force sensors 11 , 12 . A number of materials have been utilized for the realization of HAR micropillars 13 .…”