Safety Evaluation of Solid Polymer Microneedles in Human Volunteers at Different Application Sites

The focus of solid microneedles technology to date has largely been on cosmetology, vaccination, and insulin delivery, etc. However, limited information is available about the safety of solid polymer microneedles applied in different parts of the human body. In consideration of the different application sites of cosmetology, vaccination, and insulin delivery involved with microneedles technique, factors influencing user acceptance to microneedles including the length and density as well as the size of microneedle patches were systematically investigated by applying different microneedle patches on the forehead, forearm, and abdomen skins of 18 healthy human participants. Multiple insertion tests demonstrated that solid microneedles with a length of 400 μm, a density of 100 MN/cm², and an array size of 10 × 10 were optimal for forehead pretreatment. Microneedles with lengths of 400 and 600 μm, densities of 49 and 100 MN/cm², and an array size of 10 × 10 caused less pain and slight skin irritation in the forearm, whereas 400 μm height, 49 and 100 MNs/cm² densities, and 5 × 5, 10 × 10, and 10 × 20 arrays of the solid microneedles were not considered painful and were well-tolerated in abdomen insertion. In conclusion, the optimization of the dimensions of microneedles according to application sites could improve medication compliance and the safety of clinical use of solid microneedles.