Parametric optimization of two-photon direct laser writing process for manufacturing polymeric microneedles

Laser-based additive manufacturing methods have been rapidly developed in recent years and it is anticipated that this new generation of microfabrication tools will dominate the market in the near future. Three-dimensional (3D) microprinting based on two-photon polymerization allows manufacturing of complex microstructures with a resolution down to hundreds of nanometers. In recent years, the technology has been used for the manufacturing of a variety of nano- and micro-sized features such as microfluidic devices, photonics, micro-optics, and microneedle arrays. Microneedles have been mainly studied for transdermal drug delivery of therapeutic agents across the skin and withdrawing bio samples for point-of-care (POC) diagnostics. With significant development being made, it is now possible to 3D print complex microneedle structures directly from computer-aided design (CAD) models by the two-photon direct laser writing technique. However, selecting the optimal parameters and investigating the possible arrangement for the print process often involves intensive optimization process and testing. Herein we report on fabrication of highly detailed microneedles using the two-photon direct laser writing process with a discussion of optimization and parameter selection for microprinting tall microneedles with side-channels and other complex designs. Due to the long printing time, this manufacturing process is currently best suited to print master microneedles. Therefore, we further demonstrate the replication capabilities of the master microneedles by the soft embossing process. Additionally, the mechanical characteristics and insertion force of the microneedle replicas are investigated.