Chitosan-based dual-release core-shell microneedle patches for sequential transdermal delivery of hydrophilic and hydrophobic drugs: An in vitro approach.

Drug release using polymeric microneedles (MNs) plays a significant role in medical applications and the treatment of various diseases. However, conventional MNs are often limited by complex fabrication procedures and inadequate mechanical strength. This study introduces a dual-function core/shell MN patch fabricated through a novel method that integrates 3D printing and casting techniques. The patch features two distinct layers: a rapid-release shell and a sustained-release core, enabling controlled delivery of therapeutics over different timeframes within a single application. The shell layer is composed of polyvinyl alcohol and polyvinylpyrrolidone, while the core is made of chitosan. Morphological characterization using confocal and scanning electron microscopy confirmed the successful formation of well-defined core and shell layers. Mechanical testing, insertion studies, and histological analysis on rat skin demonstrated that the MNs possess sufficient strength for effective skin penetration. Furthermore, ex vivo release studies using Franz diffusion cells demonstrated that approximately 99 % of Rhodamine B, a hydrophilic model drug loaded in the shell layer, was released within 180 min, while around 92 % of methylene blue, a hydrophobic model drug incorporated into the core layer, was released over 24 h. These results validate the effectiveness of the core-shell MN platform in achieving sequential and dual-phase drug release.