Dielectrophoretic force stimulation for bone fracture healing

On the average, a person has two bone fractures during a lifetime. The healing time depends on the age, the health of the patient, the type and the severity of the fracture and can be quite long, especially if there is an infection. This is very frustrating for patients during this time, since they require help and are unable to work. Although a number of invasive and non-invasive techniques have been studied for shortening fracture healing times, including the application of direct current, electromagnetic fields, pulsed electromagnetic fields, ultrasound and low-intensity x-ray. However none of these techniques are entirely satisfactory. In the present thesis we propose a novel technique based on the use of dielectrophoretic forces (DEPFs). By applying a non-uniform electromagnetic field around a fracture site, red blood cells within the blood will be polarized, creating electrical dipoles. Due to the interaction of these dipoles and the electromagnetic field, the red blood cells will be subjected to dielectrophoretic forces that will accelerate them and thus the blood flow will be increased. This will, in turn, increase vascularization, transmembrane signalling, the supply of nutrients, necessary hormones and growth factors at the fracture site and thus help bone healing. For the generation of non-uniform fields we considered three different coil designs (linear, parabolic and square root). Using Mathcad we numerically studied extensively, the dielectrophoretic forces for a long bone fracture where the main arteries are vertically-oriented and the blood flow is downward. The gravitational force and the drag force on the red blood cells determine the steady state blood flow. The dielectrophoretic force added to the force balance is functional in increasing the blood flow. The ratio of the velocity in the presence of dielectrophoresis to the velocity without dielectrophoresis (called here as the Dielectrophoretic Force Factor) is a good measure of the performance of the dielectrophoresis, since it indicates the increase in blood flow. It was found that the dielectorophoretic force reaches the peak levels at a frequency range between 5-15 Hz. At 5 Hz, the average value of dielectrophoretic force factor is 1.90, 2.51 and 1.61 for the linear, parabolic and the square root coils, respectively. Thus, the parabolic coil seems to be the best choice for bone healing.