Fabrication of microneedles using wire electric discharge machining and improving surface quality by electrochemical polishing

Abstract

Microneedle (MN) arrays have many applications in biomedical engineering to deliver drugs transdermally or extract biomarkers from the interstitial fluid from the human skin. Several methods have been developed to fabricate different sizes and shapes of MN using polymers, ceramics and metals. However, most of these methods require expensive sophisticated machines and clean room facilities. So, it is difficult to fabricate microneedle arrays in large quantities at a reasonable cost. This study reports the fabrication of a high-quality stainless steel master pattern for an MN array using a wire-cut electric discharge machining (WEDM) process followed by electrochemical polishing (ECP). Different densities of a 5×5 array of microneedles with pyramidal shapes were fabricated by machining channels onto the workpiece surface in a crisscross pattern. A systematic experimental study was carried out with reference to the offset between the two consecutive channel faces and the depth of channels. The output parameters are MN height (MNH), MN base (MNBW) and tip width (MNTW). The average needle tip width, base width, and height of microneedles were found to be 55.3 µm, 680 µm, and 914.7 µm. Finally, the sharpness of the MN tips and the overall surface finish of the MN array were improved with ECP. The reductions in MNH, MNBW, and MNTW were reported to be -18.3 %, -9.7 %, and -95.4 %, respectively, with a final tip width of 2.55 ± 1.62 µm. The MNs' tip angle was reported to be 32.52° ± 1.56.