Hydrogel-forming microneedles for the treatment of skin diseases

The painless, non-invasive and highly efficient microneedle drug delivery method has received extensive attention from the medical community in recent years. Among all the microneedle technologies, the hydrogel-forming microneedle (HFM) technology demonstrates extremely promising application prospects. HFMs are composed of hydrogel-based micron-sized needle arrays that can penetrate the stratum corneum barrier of skin in a minimally invasive method and efficiently deliver drugs to the dermis layer. Compared to traditional microneedling technology with rapid drug release capability, HFMs can not only retain the drug in a biodegradable hydrogel matrix (Gelatin Methacryloyl (GelMA), chitosan(CS), hyaluronic acid(HA), polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP),etc.) for slower release, thus achieving the goal of long-term treatment of disease, while reducing the frequency of dosing and improve patient compliance. The main factors affecting the performance of HFMs include size/surface morphology, bioadhesive/mechanical strength, in vitro drug release kinetics and transdermal permeation behavior, biosafety, and short-and/or long-term stability. These HFMs can be designed to have additional functions, including both photothermal therapy and drug sustained-release functions. This review systematically summarizes recent achievements on HFMs for the treatment of skin diseases and discusses the challenges posed on the development of novel and highly efficient HFMs, aiming to clarifying the key issues that hinders their practical applications.