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Objective: Needle-free jet injection is a drug delivery technique that uses the momentum of the fluid drug to break through the skin. This technique has recently also been applied to blood release, aiming to collect samples from capillaries in the skin without needing a lancet prick. This work provides new information about the wound geometry and tissue disruption caused by shallow jet injection with circular-shaped and slot-shaped jets. Methods: We use histological analysis to compare the disruption of tissue, including blood vessels, caused by lancet-pricking and jet injection with a circular-shaped jet and a lancet-inspired slot-shaped jet. Results: Intradermal injection into porcine skin using a slot-shaped jet disrupted more vascular endothelium in the tissue than a circular-shaped jet and did so at a smaller penetration depth with smaller wound volume. Our results suggest that shallow jet injections may have the potential to release more capillary blood than a lancet prick. Conclusion: These findings demonstrate that a reversible jet injector might be used in diabetes management as a device to release and collect blood samples, in addition to being used to deliver insulin. Significance: Tissue disruption is crucial to consider when using jet injection to deliver drugs and release capillary blood. [ABSTRACT FROM AUTHOR]

Objective: Jet injectors use a high-pressure liquid jet to pierce the skin and deliver drug into underlying tissues. This jet is formed through a short, narrow orifice; the geometry of the orifice and the properties of the fluid affect the nature of the flow. We aimed to discover information about the turbulent and viscous processes that contribute to pressure loss and flow patterns during jet injection. Methods: We used computational fluid dynamics methods and experimental observation to investigate the effects of nozzle geometry, fluid viscosity, and viscous heating on jet production. We experimentally verified the temperature change of the jet during ejection, using an infrared camera. Results: Our models accurately predict the average jet speed produced for two example nozzle geometries over two orders of magnitude of viscosity. The models reveal the previously unreported importance of viscous heating in the formation of the jet. Temperatures >65 °C were predicted at the edge of the flow as a result of viscous heating. These caused a significant local reduction in viscosity and effectively allowed the fluid to lubricate itself. Our experiments confirmed changes in mean jet temperature of up to 2.5 °C, which are similar to those predicted by our model (∼2.8 °C). Conclusion: These results reveal the importance of the viscous heating properties of a fluid in the formation of high-speed jets for drug delivery. Significance: This property is crucial to consider when formulating new drugs for needle-free jet injection. [ABSTRACT FROM AUTHOR]