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Mechanics of Microneedle-Based Fluid Injection into Skin Tissue

Hollow microneedles are a promising alternative to conventional drug delivery techniques such as oral drug administration and hypodermic injections, and are used for delivering drugs and therapeutics into the skin. Hollow microneedles can improve patient compliance and potentially reduce the required drug dose due to the dose-sparing effect of the skin. However, the mechanics of fluid flow into the skin have not been visualized mainly because the skin is a highly scattering biological material. Here, we report the results from ex-vivo injection experiments into excised porcine skin tissue using hollow microneedles and introduce the use of optical coherence tomography (OCT) for real-time imaging of skin tissue at the micro-scale during intradermal injections. The OCT images are analyzed to measure the distribution of strain in cross-sections of the tissue and to compute correlation maps showing that the skin tissue behaves like a deformable porous medium and absorbs fluid by locally expanding. Our experimental results, relating tissue deformation to fluid flow, can guide theoretical models of fluid flow into biological porous medium and help optimize microneedle-based intradermal drug delivery systems.