The hygroscopicity of polymer microneedles on the performance of dissolving behavior for transdermal delivery

This study reported a method for quickly detecting the moisture sorption of microneedle materials to predict the dissolving properties of the materials, and the flexibility of the microneedle materials can be preliminarily evaluated by bending strength test. Fifteen common microneedle matrix materials were selected, the dynamic vapor sorption analyzer (DVS) was used to obtain the moisture sorption data of different microneedle materials. Among the four types of microneedle materials, the dissolution rate within 5 min of hydroxypropyl methylcellulose (HPMC)was the slowest, while chondroitin sulfate (CS) was the fastest. By adding solubilizing agents to polyvinyl alcohol (PVA) microneedle, it was found that both the moisture sorption and the dissolving property of PVA are improved. The results proved that there was a correlation between the moisture sorption of microneedle materials and their dissolving properties in skin. The bending strength and hardness test results of model materials showed that the bending strength of flexible microneedle materials was generally higher than that of brittle microneedle materials, and the hardness of flexible materials could also be no less than that of brittle materials. Further investigation on the crystallization kinetics of microneedle materials under different relative humidity and the dissolving properties and mechanical properties of common microneedle matrix materials are needed.