Fabrication and characterization evaluation of sustained-release dissolving microneedles with skin soothing function

In recent years, microneedles (MNs) have drawn significant attention as a new strategy for drug delivery. Especially, dissolving microneedles (DMNs) are the most suitable system for their degradability and low biological hazard. However, MNs will inevitably cause skin irritation, which needs to be improved. The goal of this study is to develop soothing and sustained-release DMNs to reduce skin irritation during drug delivery. The MNs were successfully fabricated using biocompatible sodium hyaluronate, resilient hydroxyethyl cellulose, and γ-polyglutamic acid, which possess skin repair functions. An orthogonal experiment was designed and the performance of different DMNs was characterized to explore the optimal formation, including morphology and mechanical performance. We found that the optimal formulation was 13% HA-Na, 7% HEC and 5% γ-PGA at 30℃ for 3 h. The morphology of the DMNs had structural integrity with sharp tips and a uniform array. They could withstand a force of up to 20 N without fracture, demonstrating sufficient mechanical strength for skin penetration. Subsequently, further characterization of the optimal formulation of DMNs was performed, including skin penetration ability, compression resistance, and in vitro/in vivo dissolution behavior. The DMNs successfully penetrated porcine skin and simulated skin models under a force of 2 N. In vivo dissolution in mouse skin was completed within 1 h, supporting their soothing and sustained-release potential. The skin repair function was validated through a skin irritation experiment; the mice treated by DMNs with 5% γ-PGA had no erythema and edema during the whole process and the pinholes were observed to fully disappear in 5 min, indicating rapid skin repair function. Through these tests, our fabricated DMNs possessed soothing and sustained-release properties and skin repair function. To further realize the drug delivery application of the DMNs, some experiments should be conducted in the future, including drug loading and transdermal release performance.