Capillary blood sampling using a jet injector

Abstract

This thesis presents a new lancet-free method of capillary blood collection for blood glucose concentration measurement, using a needle-free jet injector. Needle-free jet injection is a drug delivery technique that uses a high-speed stream of fluid drug to penetrate the skin and deliver the fluid into underlying tissues. In this thesis, jet streams of different shapes were used to penetrate skin and disrupt blood vessels, releasing blood for capillary blood sampling. Six custom-made nozzles were studied, including ‘slot nozzles’ with rectangular outlets to mimic the narrow wound resulting from a lancet prick. The shape and speed of fluid jets were predicted using computational fluid dynamics. The fluid dispersion patterns in tissue resulting from various jet shapes were investigated. Two slot nozzles showed their potential for performing shallow injections, within the standard penetration depth of a lancet prick, using low-volume and slightly divergent jets. Jet injection with a slot nozzle was tested on living porcine ear, and directly compared to the current common practice, lancet pricks. The slot nozzle demonstrated its ability to penetrate the skin and release blood, which might be mixed with the injectate upon collection, although the average volume of blood samples retrieved was less than one-third of that from lancet pricks. Jet injection with the slot nozzle was revealed, by microCT imaging, to create a wound shape i.e., a narrow, non-cylindrical channel across the dermis, similar to that of a lancet prick. Tissue disruption and estimated blood volume resulting from skin penetration by a circular jet, a slot-shaped jet and a lancet prick were investigated by staining vascular endothelium in post-mortem tissue. This slot nozzle was designed to have a larger outlet aspect ratio and area, aiming to release more blood. The slot-shaped jet disrupted more vascular endothelium in the tissue but was predicted to result in less blood release than jet injection with the circular jet, mainly due to its small wound volume. The efficacy of jet injection with three various-shaped nozzles for capillary blood collection was then evaluated on the fingertips of 20 living participants in a human study. The results showed that a jet injector was able to effectively release blood from human fingertips, with no significantly different skin reactions compared to a lancet prick. The use of a jet that mimics the wound shape resulting from a lancet prick increased the blood volume released, with no difference in pain compared to a circular jet. Additionally, increasing the outlet length of the nozzle also increased the volume of blood collected. 92 % of the fluid samples collected following jet injection contained at least 50 % blood. This work has revealed new knowledge that will assist in the development of a lancet-free blood sampling device that can be used in a clinical setting. It is hoped that the development of a single lancet-free device for capillary blood sampling and insulin delivery based on the glucose measurement will be achieved through the above novel contributions. Ultimately, this will lead to an improvement in human healthcare, especially in the management of diabetes.