Purpose: To gather sub-surface in situ images of microneedle-treated human skin, in vivo, using optical coherence tomography (OCT). This is the first study to utilise OCT to investigate the architectural changes that are induced in skin following microneedle application.
Methods: Steel, silicon and polymer microneedle devices, with different microneedle arrangements and morphologies, were applied to two anatomical sites in human volunteers following appropriate ethical approval. A state-of-the-art ultrahigh resolution OCT imaging system operating at 800 nm wavelength and <3 µm effective axial resolution was used to visualise the microneedle-treated area during insertion and/or following removal of the device, without any tissue processing.
Results: Transverse images of a microneedle device, in situ, were captured by the OCT system and suggest that the stratified skin tissue is compressed during microneedle application. Following removal of the device, the created microchannels collapse within the in vivo environment and, therefore, for all studied devices, microconduit dimensions are markedly smaller than the microneedle dimensions.
Conclusions: Microchannels created in the upper skin layers by microneedles are less invasive than previous histology predicts. OCT has the potential to play a highly influential role in the future development of microneedle devices and other transdermal delivery systems.