What Is the Optimal Geometry of Dissolving Microneedle Arrays? A Literature Review

The application of dissolving microneedle arrays (DMNAs) is an emerging trend in drug and vaccine delivery as an alternative for hypodermic needles or other less convenient drug administration methods. The major benefits include, amongst others, that no trained healthcare personnel is required and that the recipient experiences hardly any pain during administration. However, for a successful drug or vaccine delivery from the DMNA, the microneedles should be inserted intact into the skin. A successful penetration into the upper skin layers may be challenging because of the elastic nature of the skin; therefore, a minimum insertion force is required to overcome the total resistance force of the skin. In addition, the microneedles need to stay intact, which requires a certain mechanical strength, and be able to resist the required insertion force. In addition to the type of material with which the DMNAs are produced, the geometry of the DMNAs will also have a profound effect, not only on the mechanical strength but also on the number of insertions and penetration depth into the skin. In this review, the effects of shape, aspect ratio, length, width of the base, tip diameter and angle, and spacing of DMNAs on the aforementioned effect parameters were evaluated to answer the following question: 'What is the optimal geometry of dissolving microneedle arrays?'.