Abstract There has been considerable interest in developing microsensors integrated within lab-on-a-chip structures for the analysis of single cells; however, substantially less work has focused on developing "active" assays, where the cell‘s metabolic and physiological function is itself controlled on-chip. The heart attack is considered the largest cause of mortality and morbidity in the western world. Dynamic information during metabolism from a single heart cell is difficult to obtain. There is a demand for the development of a robust and sensitive analytical system that will enable us to study dynamic metabolism at single-cell level to provide intracellular information on a single-cell scale in different metabolic conditions (such as healthy or simulated unhealthy conditions). The system would also provide medics and clinicians with a better understanding of heart disease, and even help to find new therapeutic compounds. Towards this objective, we have developed a novel platform based on five individually addressable microelectrodes, fully integrated within a microfluidic system, where the cell is electrically stimulated at pre-determined rates and real-time ionic and metabolic fluxes from active, beating single heart cells are measured. The device is comprised of one pair of pacing microelectrodes, used for field-stimulation of the cell, and three other microelectrodes, configured as an enzyme-modified lactate microbiosensor, used to measure the amounts of lactate produced by the heart cell. The device also enables simultaneous in-situ microscopy, allowing optical measurements of single-cell contractility and fluorescence measurements of extracellular pH and cellular Ca2+ from the single beating heart cell at the same time, providing details of its electrical and metabolic state. Further, we have developed a robust microfluidic array, wherein a sensor array is integrated within an array of polydimethylsiloxane (PDMS) chambers, enabling the efficient manipulation of single heart cells and real-time analysis without the need to regenerate either working electrodes or reference electrodes fouled by any extracellular constituents. This sensor array also enables simultaneous electrochemical and optical measurements of single heart cells by integrating an enzyme-immobilized microsensor. Using this device, the fluorescence measurements of intracellular pH were obtained from a single beating heart cell whose electrical and metabolic states were controlled. The mechanism of released intracellular [H+] was investigated to examine extracellular pH change during contraction. In an attempt to measure lactate released from the electrically stimulated contracting cell, the cause of intracellular pH change is discussed. The preliminary investigation was made on the underlying relationship between intracellular pH and lactate from single heart cells in controlled metabolic states.

The Large Eddy Simulation (LES) technique is used to simulate the different types of Newtonian and non-Newtonian pulsatile blood flow in a constricted as well as in a dilated channel to gain insight of the transition-to-turbulent blood flow due to the arterial stenosis and aneurysm. In the stenosed model, a cosine shape stenosis is placed at the upper wall of a 3D channel which reduces the cross-sectional area, whereas the aneurysm which is also placed at the upper wall dilates the channel cross-sectional area. In LES, a top-hat spatial grid-filter is applied to the Navier-Stokes equations of motion to separate the large scale flows, which carry the majority of the energy, from the small scale known as sub-grid scale (SGS).The large scale flows are resolved fully while the unresolved SGS motions are modelled using two different dynamic models to determine the Smagorinsky constant at each time step. Initially, an additive sinusoidal pulsatile velocity profile is used at the inlet of the model stenosis to generate the unsteady oscillating flow and a comparison is made between the results obtained by the additive and non-additive pulsation. Secondly, the physiological pulsatile flow in the same model stenosis is investigated, where the physiological pulsation is generated at the inlet using the first four harmonics of the Fourier series of pressure pulse. A comparison between the LES and the coarse Direct Numerical Simulation (DNS) results is drawn and the effects of the various harmonics of pressure pulse, length and percentage of the stenosis on the flow field are examined. Transition-to-turbulent physiological flow through the model of a double stenosis and an aneurysm is also investigated. Finally, the physiological pulsatile flow in a model of single stenosis is investigated using the various non-Newtonian blood viscosity models and the results are compared with the Newtonian model. For the additive sinusoidal pulsation case the maximum ratio of the SGS to molecular viscosity is 0.709 and for the non-additive case is 0.78 while Re =2000. The shape of the post-stenotic re-circulation region is totally different between the additive and non-additive case. In the additive case the upper wall pressure drop is larger than the non-additive case. Due to the large amplitude of the oscillation, transition happens earlier and the peak turbulent kinetic energy occurs at the post-lip of the stenosis. The intensity of the turbulent kinetic energy is higher in the additive sinusoidal pulsation case than the physiological pulsation. The maximum contribution of the SGS motion to the large -scale motion is 37.4 percent for the first harmonic physiological pulsation while 97 percent contribution from the first four harmonics case for Re =2000. The centreline turbulent kinetic energy is slightly higher in the first harmonic case than the first four harmonics. For the higher area reduction of the stenosis, the stress drop at the upper wall, the maximum shear stress at the lower wall and the turbulent kinetic energy increased. The intensity of the shear stress and the turbulent kinetic energy decreased when the length of the stenosis is increased. The break frequency of the energy spectra found from -5/3 to -10/3 for the velocity fluctuations and from -5/3 to -7/3 for the pressure fluctuations. Due to the presence of the second stenosis, the stress drop, the adverse pressure gradient and the turbulent intensity of the flow enhance significantly. Inside the aneurysm a large re-circulation region exists and the flow is turbulent for a asymmetric aneurysm and maximum turbulent intensity occurs between the centre and the ending segment of the aneurysm. Owing to the effects of the non-Newtonian viscosity, the length of the post-stenotic re-circulation region increased as well as the streamwise velocity and the turbulent kinetic energy decreased.