Achieving rapid and precisely controllable drug loading via spontaneous imbibition in porous microneedles: mechanistic and optimization strategies.

Porous microneedles (PMNs) feature a unique pore structure that may facilitate the distribution of medications and biological fluids by spontaneous imbibition (SI). Their versatility in drug delivery and skin interstitial fluid extraction has been well proved. However, uncontrolled capillary forces lead to inconsistent drug loading capacity, fundamentally undermining precise dosing control in PMNs manufacturing. In this study, we employ an integrated approach combining finite element model with experimental methods to investigate the spontaneous imbibition mechanism during drug loading, aiming to elucidate the relationship between pore characteristics, the fluid dynamics of drug solutions and loading efficiency and contamination risk. This mechanistic insight enables the facile fabrication of PMNs with precisely adjustable and high drug loading capacities. Applying this strategy, we developed diclofenac sodium-loaded PMNs capable of delivering local analgesia via SI, with drug loading completed within 10 s (up to 3 μg per needle). This study offers valuable insights into the mechanisms governing the drug loading process and optimization strategies that could facilitate the industrial development and market application of porous microneedles.