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 (NaHCO 3 ), 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.