Targeted local anesthesia: a novel slow-release Fe3O4–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 Fe 3 O 4 to the lidocaine microspheres and used an applied magnetic field to attract Fe 3 O 4 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 Fe 3 O 4 –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 Fe 3 O 4 –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.