An Implantable Low Pressure Biosensor Transponder

The human body’s intracranial pressure (ICP) is a critical element in sustaining healthy blood flow to the brain while allowing adequate volume for brain tissue within the relatively rigid structure of the cranium. Disruptions in the body’s maintenance of intracranial pressure are often caused by hemorrhage, tumors, edema, or excess cerebral spinal fluid resulting in treatments that are estimated to globally cost up to approximately five billion dollars annually. A critical element in the contemporary management of acute head injury, intracranial hemorrhage, stroke, or other conditions resulting in intracranial hypertension, is the real-time monitoring of ICP. Currently such monitoring can only take place short-term within an acute care hospital, is prone to measurement drift, and is comprised of externally tethered pressure sensors that are temporarily implanted into the brain, thus carrying a significant risk of infection. To date, reliable, low drift, completely internalized, long-term ICP monitoring devices remain elusive. In addition to being safer and more reliable in the short-term, such a device would expand the use of ICP monitoring for the management of chronic diseases involving ICP hypertension and further expand research into these disorders. This research studies the current challenges of existing ICP monitoring systems and investigates opportunities for potentially allowing long-term implantable bio-pressure sensing, facilitating possible improvements in treatment strategies. Based upon the research, this thesis evaluates piezo-resistive strain sensing for low power, sub-millimeter of mercury resolution, in application to implantable intracranial pressure sensing.