Large-Scale Synthesis of 3D Nanonetworked Silica Film for Polymer-Free Drug-Eluting Stents

Self-expandable metallic stents (SEMSs) are interventional implants for treating esophageal strictures, and require additional drug therapeutics to suppress stent-induced tissue hyperplasia and restenosis. However, methods of loading drugs on SEMSs are challenging in terms of fabrication, mechanical stability, and therapeutic. There are several strategies to produce polymer-free drug-eluting stent (DES): top-down approaches such as patterning micro-pores via femtosecond laser beam etching, and bottom-up approaches such as decorating surfaces with nanomaterials (e.g., nanoparticles and nanowires). However, poor mechanical stability or peeling off of the coating materials, makes it difficult to observe therapeutic effects. we developed a large-scale, 3-dimensional, and flexible nanonetworked silica film (NSF) as a promising alternative drug carrier for polymer-free DESs. Here, using facile bottom-up synthesis, a 3-dimensional NSF is constructed to function as a drug carrier on the entire surface of the SEMS. Enlarged micelles as nanonetwork structure templates, are adhered to the surface via van der Waals interactions, and hydrolyzed silicates are assembled and deposited with the templates via electrostatic interactions. NSF is synthesized without defects, even on a large area and curved surface, with only 0.4% increase in thickness compared to the SEMS wire. Owing to the full range coating of nanonetwork structures, the NSF is fixed well on the surface and is flexible enough to withstand mechanical stress during dynamic expansion. NSF was grafted with octyltrimethoxysilane (OTMS) and hexadecyltrimethoxysilane (HDTMS) to induce surface hydrophobicity. 3-fold more sirolimus (approximately 30 μg/cm²). Sirolimus can be loaded on NSF than on a polymer coating of the same thickness. The NSF stents show extremely slow elution compared to samples without NSF. The hydrophobic interaction and structural confinement of nanonetworks enable slow drug release even without polymers. Thus, NSF opens new avenues for manufacturing high-performance polymer-free drug-eluting stents and is a promising platform for drug delivery, protein adsorption, virus capture and generating flexible biosensors.