Advances in adhesion of microneedles for bioengineering

Microneedles have provided promising platforms in various fields thanks to their safety, painlessness, minimal invasiveness and ease of operation. The excellent adhesion of microneedles is the key characteristic to achieve long-term and comfortable treatment. However, a complex environment, such as the roughness of skin, various bodily fluids in vivo, and the movement of the body, presents great challenges to the adhesion characteristics of microneedles. This review mainly reports the remarkable adhesion properties of microneedles based on interlocking by shape effects, chemical bonds, and suction forces. Firstly, the main mechanisms of adhesion and various types of microneedles are introduced, with an emphasis on the progress in adhesive microneedles. Combined with the preparation and application of microneedles, the challenges and future trends of adhesive microneedles are discussed.