Design and characterization of 3D-printed hollow microneedle arrays for transdermal insulin delivery

The delivery of insulin to diabetic patients remains a challenge due to the limitations of current insulin delivery paradigms including painful cannula insertion, potential infections, interference with activity, embarrassment, and sometimes cost. To address this problem, we designed and fabricated nine prototypes of stereolithographic (SLA) 3D-printed microneedle arrays (MNAs) appropriate for the minimally invasive delivery of insulin. We characterized their transdermal penetration performance by delivering fluid at a constant rate to porcine skin through these MNAs. Moreover, we characterized the force required for these MNAs to puncture porcine skin using a mechanical testing apparatus. We developed an improved method of mechanical testing for the MNAs against porcine skin by incorporating an imitation soft tissue layer under the skin and compared the MNA results with those using a single microneedle and a hypodermic needle. In addition, we investigated the mechanical flexural strength of the MNAs by performing a flexural failure load test on them. We confirmed that the prototype MNAs are mechanically robust and do not fracture during skin penetration, setting the stage for future trials in vitro and in vivo. The final, optimized designs are freely available in STL format.