Targeted local anesthesia: a novel slow-release FeO-lidocaine-PLGA microsphere endowed with a magnetic targeting function.

Purpose: Lidocaine microspheres can prolong the analgesic time to 24-48 h, which still cannot meet the need of postoperative analgesia lasting more than 3 days. Therefore, we added FeO to the lidocaine microspheres and used an applied magnetic field to attract FeO to fix the microspheres around the target nerves, reducing the diffusion of magnetic lidocaine microspheres to the surrounding tissues and prolonging the analgesic time.

Methods: FeO-lidocaine-PLGA microspheres were prepared by the complex-emulsion volatilization method to characterize and study the release properties in vitro. The neural anchoring properties and in vivo morphology of the drug were obtained by magnetic resonance imaging. The nerve blocking effect and analgesic effect of magnetic lidocaine microspheres were evaluated by animal experiments.

Results: The mean diameter of magnetically responsive lidocaine microspheres: 9.04 ± 3.23 μm. The encapsulation and drug loading of the microspheres were 46.18 ± 3.26% and 6.02 ± 1.87%, respectively. Magnetic resonance imaging showed good imaging of FeO-Lidocain-PLGA microspheres, a drug-carrying model that slowed down the diffusion of the microspheres in the presence of an applied magnetic field. Animal experiments demonstrated that this preparation had a significantly prolonged nerve block, analgesic effect, and a nerve anchoring function.

Conclusion: Magnetically responsive lidocaine microspheres can prolong analgesia by slowly releasing lidocaine, which can be immobilized around the nerve by a magnetic field on the body surface, avoiding premature diffusion of the microspheres to surrounding tissues and improving drug targeting.