Rapid fabrication of microneedles using magnetorheological drawing lithography.

Microneedles are micron-sized needles that are widely applied in biomedical fields owing to their painless, minimally invasive, and convenient operation. However, most microneedle fabrication approaches are costly, time consuming, involve multiple steps, and require expensive equipment. In this study, we present a novel magnetorheological drawing lithography (MRDL) method to efficiently fabricate microneedle, bio-inspired microneedle, and molding-free microneedle array. With the assistance of an external magnetic field, the 3D structure of a microneedle can be directly drawn from a droplet of curable magnetorheological fluid. The formation process of a microneedle consists of two key stages, elasto-capillary self-thinning and magneto-capillary self-shrinking, which greatly affect the microneedle height and tip radius. Penetration and fracture tests demonstrated that the microneedle had sufficient strength and toughness for skin penetration. Microneedle arrays and a bio-inspired microneedle were also fabricated, which further demonstrated the versatility and flexibility of the MRDL method. STATEMENT OF SIGNIFICANCE: Microneedles have been widely applied in biomedical fields owing to their painless, minimally invasive, and convenient operation. However, most microneedle fabrication approaches are costly, time consuming, involve multiple steps, and require expensive equipment. Furthermore, most researchers have focused on the biomedical applications of microneedles but have given little attention to the optimization of the fabrication process. This research presents a novel magnetorheological drawing lithography (MRDL) method to fabricate microneedle, bio-inspired microneedle, and molding-free microneedle array. In this proposed technique, a droplet of curable magnetorheological fluid (CMRF) is drawn directly from almost any substrate to produce a 3D microneedle under an external magnetic field. This method not only inherits the advantages of thermal drawing approach without the need for a mask and light irradiation but also eliminates the requirement for drawing temperature adjustment. The MRDL method is extremely simple and can even produce the complex and multiscale structure of bio-inspired microneedle.