Fabrication Technology of Self-Dissolving Sodium Hyaluronate Gels Ultrafine Microneedles for Medical Applications with UV-Curing Gas-Permeable Mold.

Microneedles are of great interest in diverse fields, including cosmetics, drug delivery systems, chromatography, and biological sensing for disease diagnosis. Self-dissolving ultrafine microneedles of pure sodium hyaluronate hydrogels were fabricated using a UV-curing TiO2-SiO2 gas-permeable mold polymerized by sol-gel hydrolysis reactions in nanoimprint lithography processes under refrigeration at 5 °C, where thermal decomposition of microneedle components can be avoided. The moldability, strength, and dissolution behavior of sodium hyaluronate hydrogels with different molecular weights were compared to evaluate the suitability of ultrafine microneedles with a bottom diameter of 40 µm and a height of 80 µm. The appropriate molecular weight range and formulation of pure sodium hyaluronate hydrogels were found to control the dissolution behavior of self-dissolving ultrafine microneedles while maintaining the moldability and strength of the microneedles. This fabrication technology of ultrafine microneedles expands their possibilities as a next-generation technique for bioactive gels for controlling the blood levels of drugs and avoiding pain during administration.

Cationic Gas-Permeable Mold Fabrication Using Sol-Gel Polymerization for Nano-Injection Molding.

Cationic gas-permeable molds fabricated via sol-gel polymerization undergo cationic polymerization using epoxide, resulting in gas permeability owing to their cross-linked structures. By applying this cationic gas-permeable mold to nano-injection molding, which is used for the mass production of resins, nano-protrusion structures with a height of approximately 300 nm and a pitch of approximately 400 nm were produced. The molding defects caused by gas entrapment in the air and cavities when using conventional gas-impermeable metal molds were improved, and the cationic gas-permeable mold could be continuously fabricated for 3000 shots under non-vacuum conditions. The results of the mechanical evaluations showed improved thermal stability and Martens hardness, which is expected to lead to the advanced production of resin nano-structures. Furthermore, the surface roughness of the nano-protrusion structures fabricated using injection molding improved the water contact angle by approximately 46°, contributing to the development of various hydrophobic materials in the future.