Needle-free interstitial fluid acquisition using a Lorentz-force actuated jet injector

Abstract

Interstitial fluid (ISF) provides information on a patient's health as it contains regulatory molecules that are correlated with disease-related processes. However, current ISF acquisition techniques can be slow, resulting in patient discomfort and erroneous measurements. This thesis presents a fast (< 4 s), minimally-invasive, needle-free technique of extracting ISF samples using a Lorentz-force actuated jet injector. The jet injector is used to first inject a small volume of physiological saline to breach the skin, and the actuator is subsequently back-driven to create a vacuum in the ampoule and collect a sample that contains a mixture of ISF and injectate. The scope of this thesis is twofold: the first part aims to investigate the effect of jet injection on tissue, while the second part focuses on the development of the novel ISF acquisition method. A micro-CT imaging study identifies the magnitudes of injected jet speed that will influence injectate delivery to specific skin layers. A histology study highlights the differences in tissue damage between needle injections and jet injections. A new tool for quantifying the jet dynamics in tissue-a high-speed X-ray imaging system-is built and characterized. The system, which has a capture rate of up to 2,000 fps, is used to visualize jet injections into tissue in real-time, and for the first time measurements are made of the fluid speed in tissue. To develop the jet injector for ISF acquisition, a finite element model that describes the effect of different injection and extraction parameters on the ISF acquisition process is developed. The model is used to explain the trends seen in experimental work on post-mortem tissue, and the lessons learned from both the model and experimentation are used to identify the parameters for a live animal study. The feasibility of the acquisition process is successfully demonstrated on live rats; the process is revealed to extract samples that have been diluted by a factor of 111-125.