Much attention has been paid to the transdermal delivery of medicinal agents owing to its advantages in the administration. The first pass effect in the liver can be avoided and the bioavailability is enhanced by the drug delivery through the skin. The patients’ compliance is good because almost no pains are involved in applying transdermal dosage forms (e.g., ointments and patches). The long-lasting efficacy of medicines is obtainable as long as the dosage forms adhere to the skin. The administration is easily stopped by removing the dosage forms when necessary.

However, the transdermal delivery has been suffering from the poor skin permeation of medicinal agents due to the barrier function of the stratum corneum. Various strategies have been proposed to avoid the skin barrier and enhance the skin permeation. The usage of the skin permeation enhancers is one of the most frequently adopted methods. Most of the enhancers are surface-active and were reported to disorder well-packed lipidic layers in the intercellular space. Nanoparticles with the diameter below 50 nm were reported to permeate the skin with maintaining their integrity and they have been exploited to promote the skin permeation.

On the other hand, microneedle matrices have been attracting the interest of scientists in the field of transdermal delivery because the needles can bypass the barrier of the stratum corneum. Owing to their tiny size, microneedles can perforate the stratum corneum without any pain. Although various drugs were dermally and trans-dermally delivered using microneedle matrices for clinical trials in humans, the microneedles of matrices need to be optimized in several aspects for their practical application. The mechanical strength of microneedles is a critical factor governing their skin penetration efficiency. Previous studies have demonstrated that enhancing microneedle mechanical properties can be achieved through various strategies, such as physical or chemical crosslinking of polymer matrices, as well as the incorporation of reinforcing materials among others.

In a recent study reported from Zhao et al. published by Frontiers of Materials Science, cinnamoyl-functionalized poly(hydroxyethyl acrylate-co-butyl methacrylate) (Cin-poly(HEA-co-BMA)) was incorporated into dissolving microneedles as a photo-crosslinkable and thermo-responsive polymer component, aiming to enhance the compressive strength of needles and to modulate the transdermal permeation behavior. Upon ultraviolet (UV) irradiation, the photo-dimerization of cinnamoyl groups introduces additional crosslinking points among copolymer chains, leading to the improved mechanical robustness of microneedles. Moreover, at the body temperature (i.e., 37 °C), the skin permeation of cargo loaded in microneedles is significantly higher than that observed at 25 °C. These features enable the stimulus-dependent regulation of both mechanical reinforcement and transdermal delivery behavior within a single dissolving microneedle system. Microneedle matrices developed in this work would be applicable to the development of a dermal/transdermal drug delivery patch.
DOI:10.1007/s11706-026-0756-1