A dissolving microneedle patch enables minimally invasive riboflavin delivery and enhances corneal crosslinking in keratoconus therapy

Corneal collagen cross-linking (CXL) is an effective surgical approach to halt the progression of keratoconus. A key challenge lies in maintaining epithelial integrity while achieving sufficient stromal riboflavin (RF) concentration to ensure CXL efficacy. Additionally, the efficacy of CXL under RF-mediated cross-linking still has room for improvement. In this study, we developed a silk fibroin methacryloyl (SFMA)-based dissolvable microneedle (MN) system (termed RF/SFMA MNs). <i>In vitro</i> and <i>ex vivo</i> experiments showed that RF/SFMA MNs exhibited excellent mechanical strength, dissolution profile, drug release profile and biocompatibility. <i>In vivo</i>, RF/SFMA MNs were characterized by suitable corneal penetration capability through a minimally invasive approach. MNs with different RF concentrations (0-2%) and tip lengths (330-800 µm) were tested. RF/SFMA MNs with a 1% RF concentration and a tip length of 550 µm achieved sufficient RF permeation and delivery depth within the corneal stroma. Furthermore, integrating SFMA into the CXL procedure allowed RF to mediate multiple crosslinking events between SFMA and collagen, resulting in an enhanced increase in corneal biomechanical strength compared to conventional Epi-on and Epi-off CXL strategies. Over a two-week observation period, MN-based CXL enhanced corneal biomechanics more effectively than Epi-off and Epi-on CXL, while maintaining collagen arrangement without adverse effects on the epithelium or endothelium. Therefore, RF/SFMA MNs, designed for minimally invasive RF delivery and enhanced CXL efficacy, present a promising and innovative approach to optimize CXL in the treatment of keratoconus.