Recent approaches for enhancing the performance of dissolving microneedles in drug delivery applications

Dissolving microneedles (dMNs) are promising versatile drug delivery systems for the transdermal delivery of numerous drugs, enabling their use in a wide range of biomedical and pharmaceutical applications. Being made of water-soluble polymers, dMNs own several advantages, including fast dissolution and short application time which enhance patients' compliance and minimize the damage to skin tissue. Moreover, they possess no biohazard risk as they leave no sharp waste behind. For these reasons, the research on dMNs has increased dramatically in recent years. The formulation of successful dMNs requires a well-defined pre-set design, considering the goal and the payloads that will be used. Every aspect of formulation as patch design, needles geometry, polymer composition, method of formation and payloads, has a direct effect on the mechanical properties of the MNs, affecting their administration and efficacy. Thus, there is the need to understand how each factor affects the final formulation and how to optimize each MN. Taking this into consideration, this review serves as a guide for dMN formulation, discussing the different setbacks of each step and possible strategies to overcome them, improving their administration, and enhancing the loading of various molecules and their controlled release.