Optical coherence tomography is used to image microneedle injections into tissue

Hollow microneedles, typically less than a millimeter in height with an inner diameter of around 100 μm, have revolutionized medical injections such as insulin and vaccines. These tiny needles can inject drugs directly into the skin, which eliminates risks associated with hypodermic injections and have benefits such as the dose sparing effect.

Pranav Shrestha and Boris Stoeber are working to optimize the use of hollow microneedles and understand the spatial and temporal evolution of the skin tissue due to the injected fluid. They used a non-invasive imaging technique known as optical coherence tomography (OCT) to produce two-dimensional cross-sectional images and three-dimensional images of internal tissue microstructure in real time.

“Even with OCT, the imaging depth is limited to around 1 – 2.5 mm in biological tissues. We had to use a thin skin sample, supported by a transparent backing. This was crucial for visualizing the skin mechanics. The dermis layer of the skin, which we were interested in to study intradermal injections, falls right in the range viewable using OCT,” said Shrestha.

They developed a semi-empirical model based on the results of 7 different experiments of injecting water into pig skin tissue. The model assumed a spherically symmetric deformation in the tissue and the fluid flow and was able to predict the flow rate using optimized model parameters and the experimental data over time.

“In this work, we simply measured the skin expansion during the injection process, the next step will be to be predictive and to develop a model for skin tissue expansion as a function of fluid injection pressure,” said Stoeber.

Source: “Imaging fluid injections into soft biological tissue to extract permeability model parameters,” by Pranav Shrestha and Boris Stoeber, Physics of Fluids (2020). The article can be accessed at https://doi.org/10.1063/1.5131488 .