Objective: In order to improve the clinical efficacy and reduce the side effects, PLGA nanoparticles loaded with psoralen for external use were prepared, and the permeation, distribution and influencing factors of PLGA nanoparticles delivered via microneedles in human skin were investigated. Methods: The psoralen nanoparticles were prepared by solvent replacement and interfacial polymer deposition. The percutaneous process of PLGA nanoparticles loaded with psoralen was observed with Franz diffusion cell and laser confocal microscope. The distribution of the nanoparticles in each cortex was qua...