UBC Theses and Dissertations
Intradermal injections through hollow microneedles Shrestha, Pranav
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. Although the benefits of intradermal drug delivery have been known for decades, our understanding of fluid absorption by skin tissue has been limited due to the difficulties in imaging a highly scattering biological material such as skin. In this thesis, we report the results from ex-vivo injection experiments into excised porcine skin tissue using hollow microneedles. We introduce the use of optical coherence tomography (OCT) for real-time imaging of skin tissue at the micro-scale during intradermal injections through hollow microneedles. We identify two modes of flow into the skin – microinjection, a region of high transient flow-rate, and microinfusion, a region of lower steady-state flow-rate. We relate the two modes of flow to tissue deformation. Using images from the OCT, we find that the skin tissue behaves like a deformable porous medium and absorbs fluid by locally expanding rather than rupturing to form a fluid filled cavity. We measure the strain distribution in a cross section of the tissue to quantify local tissue deformation using digital image correlation (DIC), and find that the amount of volumetric expansion of the tissue corresponds closely to the volume of fluid injected. Mechanically restricting the tissue expansion limits fluid absorption into the tissue, and allowing the tissue to expand leads to increased fluid absorption. Our experimental findings can provide physical insights for optimizing the delivery of drugs into the skin for different therapeutic applications, and for better modelling fluid flow into biological tissue.
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