In this study, dissolving polymeric microneedle (MN) patches composed of gelatin and\nsodium carboxymethyl cellulose (CMC) were used to localize insulin. Their in vitro skin insertion\ncapabilities were determined using tissue-marking dye to stain the skin after patches removal.\nScanning electron microscopy (SEM) was used to determine changes in the MNs over time, and optical\ncoherence tomography (OCT) was used to monitor their real-time penetration depth. Confocal\nmicroscopy images revealed that rhodamine 6G gradually diffuses from the puncture sites to deeper\ndermal tissue. Using an in vivo imaging system (IVIS), skin areas that received FITC-insulin-loaded\nMNs were found to present strong fluorescent signals that greatly decreased 1 h after application.\nResults show that dissolving MNs rapidly release FITC-insulin, and it then gradually diffuses into\nthe skin. This study verifies that using a gelatin/CMC MN patch for insulin delivery achieves\nsatisfactory relative bioavailability compared to a traditional hypodermic injection and can be a\npromising delivery device for poorly permeable protein drugs such as those used to treat diabetes.\nInsertion tests on human cadaveric skin demonstrate that dissolving MNs could serve as efficient\ndevices for transdermal drug delivery in clinical practice and that the volar aspect of forearm skin is\nthe ideal location for their applications.
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