Aspirin microcrystals deposited on high-density microneedle tips for the preparation of soluble polymer microneedles

To reduce mucosal damage in the gastrointestinal tract caused by aspirin, aspirin microcrystals were loaded in soluble polymeric microneedle (MN) tips. Aspirin was prepared into aspirin microcrystals by jet milling. Aspirin microcrystals with particle sizes of 0.5-5 μm were loaded on MN tips with a height of 250 µm or 300 µm. The aspirin microcrystals suspended in a polymer solution were concentrated in the MN tips under negative pressure. The aspirin microcrystals had high stability in the MNs since they were not dissolved in solution during the fabrication process. The MN patch packaged in an aluminum-plastic bag containing silica gel desiccant can be stored at 4 °C. The MN tips implanted in the skin of Institute of Cancer Research (ICR) mice dissolved within 30 min. Isolated porcine ear skin was punctured by MNs with heights of 300 μm and 250 μm to depths of 130 μm and 90 μm, respectively. The fluorescent red (FR) release from MNs reached 98.59% within 24 h. The MNs delivered aspirin microcrystals to the epidermis and dermis, providing a smooth plasma concentration in rats. The MNs loaded with aspirin microcrystals did not evoke primary irritation on the dorsal skin of Japanese white rabbits. In summary, MNs loaded with aspirin microcrystals provide a new approach to improve the stability of aspirin in MN patches.