Pressure ischemia is a medical condition characterised by the necrosis of the skin and underlying tissues in body areas exposed to prolonged pressure. This condition leads to the development of bedsores and affects 9% of hospitalised patients, costing the NHS between £1.4 and £2.1 billion per year. The severity of pressure ischemia has been linked to the concentration of sweat lactate, a product of sweat gland metabolism under anaerobic conditions, such as hypoxia. Normal levels of lactate in human sweat are 20±7 mM, but under ischemic conditions these can rise up to approximately 70 mM. This project presents the development of a novel flexible electrochemical enzyme-based biosensor for the continuous and non-invasive monitoring of sweat lactate with the potential for becoming a body-worn device for the early detection of pressure ischemia onset. The core of the recognition system is a flexible laminate, comprising two highly porous polycarbonate membranes, which provide support for the lactate oxidase enzyme, immobilised via covalent cross-linking. Oxidation of lactate produces H2O2, which is subsequently determined electrochemically. The transducer comprises a two-electrode system on a single flexible polycarbonate membrane, sputter-coated with gold (CE/RE) and platinum (WE) to render it conductive. The developed design has been improved through investigation into different factors regarding the immobilisation method of the enzyme in the laminate and the lowering of interferences from oxidising compounds present in sweat. The sensing system exhibits lactate selectivity at physiologically relevant concentrations in sweat for pressure ischemia (0–70 mM), with good reproducibility (7.2–12.2% RSD) for a hand-manufactured device. The reliability of the sensor’s performance and the capability to detect lactate fluctuations on human sweat samples has been demonstrated. The sensing system showed excellent operational and mechanical stability. The application of Nafion® on the WE lowered interferences from ascorbic acid and uric acid by 96.7 and 81.7% respectively. These results show promise towards the further development of a body-­‐worn monitoring device for determining lactate levels in undiluted human sweat samples in a reproducible, fast and accurate manner.

Pressure ischemia is a medical condition characterised by the necrosis of the skin and underlying tissues in body areas exposed to prolonged pressure. This condition leads to the development of bedsores and affects 9% of hospitalised patients, costing the NHS between £1.4 and £2.1 billion per year. The severity of pressure ischemia has been linked to the concentration of sweat lactate, a product of sweat gland metabolism under anaerobic conditions, such as hypoxia. Normal levels of lactate in human sweat are 20±7 mM, but under ischemic conditions these can rise up to approximately 70 mM. This project presents the development of a novel flexible electrochemical enzyme-based biosensor for the continuous and non-invasive monitoring of sweat lactate with the potential for becoming a body-worn device for the early detection of pressure ischemia onset. The core of the recognition system is a flexible laminate, comprising two highly porous polycarbonate membranes, which provide support for the lactate oxidase enzyme, immobilised via covalent cross-linking. Oxidation of lactate produces H2O2, which is subsequently determined electrochemically. The transducer comprises a two-electrode system on a single flexible polycarbonate membrane, sputter-coated with gold (CE/RE) and platinum (WE) to render it conductive. The developed design has been improved through investigation into different factors regarding the immobilisation method of the enzyme in the laminate and the lowering of interferences from oxidising compounds present in sweat. The sensing system exhibits lactate selectivity at physiologically relevant concentrations in sweat for pressure ischemia (0–70 mM), with good reproducibility (7.2–12.2% RSD) for a hand-manufactured device. The reliability of the sensor’s performance and the capability to detect lactate fluctuations on human sweat samples has been demonstrated. The sensing system showed excellent operational and mechanical stability. The application of Nafion® on the WE lowered interferences from ascorbic acid and uric acid by 96.7 and 81.7% respectively. These results show promise towards the further development of a body-­‐worn monitoring device for determining lactate levels in undiluted human sweat samples in a reproducible, fast and accurate manner.

The development of an organ preservation system (primarily kidneys and livers, but could be adapted to fit hearts, lungs, and even limbs in the future) that can provide surgeons and doctors with real-time quantitative feedback on the health of the organ would be a significant improvement on current transplant practices. This organ transport system will provide surgeons and doctors the opportunity to make more educated decisions towards whether or not to proceed with organ transplantation. Here, we discuss the use Smart Perfusion's organ preservation system as a platform for determining the optimal perfusion temperature of an organ. Porcine kidneys were procured and perfused with a modified PBS solution on the Vasowave™. While on this organ preservation system, a heart emulating pressure waveform (90/50 mmHg) was generated and sent to the specimen. The pressure response, flow rate, temperature, pH, dissolved oxygen content, and conductivity of the fluid stream were all monitored throughout the duration of experimentation. In addition to inline sensors, IR imaging captured the surface temperature of the organ while on the system. Lastly, the use of a combined heat flux-temperature (CHFT) sensor, previously developed at Virginia Tech, was applied for the first time to monitor and measure local tissue perfusion of an explanted organ. A total of 12 experiments were performed (6 at a set fluid temperature of 15°C, and 6 at 20°C). All system data was collected, statistically evaluated and finally compared against blind histological readings (taken at the termination of each experiment at the hilum and pole) to investigate the effects of temperature on organ vasculature. The results of this experiment indicated that the effects of temperature on explanted kidneys can be affectively measured using a non-invasive bioheat perfusion sensor. Specifically, the lower temperature group of kidneys was measured to have lower perfusion. Furthermore, an enhancement to the CHFT sensor technology (CHFT+) was developed and tested for compliance. A controllable thin filmed heat resistor was added to the CHFT assembly to replace the current convective thermal event. This enhancement improved the measured heat flux and temperature signals and enables autonomy. Also, the thin and semi-flexible nature of the new CHFT+ sensor allows for perfusion measurements to be taken from the underside of the organ, permitting a quantitative measure of pressure ischemia. Results from a live tissue test illustrated, for the first time, the effects of pressure ischemia on an explanted porcine kidney. / Master of Science