Reflections on the Insertion and Fracture Forces of Microneedles

Background: The use of microneedles for transdermal drug delivery is a feasible alternative to injections and tablets. As different types of microneedles are being developed from a variety of materials, it is important to understand their insertion and fracture forces. In this review, it has been emphasized that for microneedles to be clinically useful, they must penetrate the skin without breaking. It means that the insertion force must be smaller than fracture force. Methods: Transdermal experiments involving these forces have been described and theoretical models highlighted. The knowledge of these forces is important for microneedle design and experimental/ clinical use. Results: From an experimental standpoint, different techniques are used to measure insertion and fracture forces. To measure insertion and failure forces, a texture analyzer can be used. In this review, the measurement of insertion and fracture forces has been discussed and their utility in transdermal experiments presented. Conclusion: This review has focused on insertion and failure forces in transdermal drug delivery experiments. Although the question is complex since there is a wide variety of skin models and forces involved, studies carried out in the last few years have thrown more light to aid better understanding of these forces in transdermal drug delivery research. Keywords: Bending forces, buckling forces, drug delivery, fracture force, insertion force, microneedles, transdermal.