Fabrication of hollow microneedles with double-layer shell structure for rapid and prolonged local anesthesia

Pain is a subjective sensation associated with actual or potential tissue damage, presenting a global clinical challenge that not only significantly impacts individuals' quality of life, but also incurs substantial economic burdens. In this study, polymer microneedles (MNs) with hollow double-layer shell structure had been designed for local long-lasting analgesia. The hollow and inner-shell layer were formed by a microtemplate method under vacuum and UV cross-linking. The formed cavities in MNs could be utilized for loading lidocaine hydrochloride (LidH) powder to increase the drug loading capacity. The outer-shell layer formed a frozen dip-coating process was composed of poly(vinylpyrrolidone) (PVP), citric acid (CA), sodium bicarbonate (NaHCO3), and small amount of LidH. After insertion into skin, the outermost shell of MNs could been rapidly dissolved, leading to a rapid release of LidH to achieve a rapid analgesia. Subsequently, the LidH loaded within the cavity could be continuously released due to swelling of the inner shell, thereby to obtain long-term analgesic effect. In vivo local analgesic tests reveled that local analgesic time could be extended up to 48 h, showing a potential possibility to reduce administration frequency and improve patient comfort.