Abstract:
Fully implantable pressure sensors have the potential to provide accurate monitoring of disease progression of chronic conditions, including hydrocephalus. However, the implantation lifetime of the current state of the art is limited to less than a month and represents the most significant limitation for clinical uptake. The purpose of this thesis is to present work performed to address the challenges in extending the lifetime of implantable pressure sensors. The current convention of catheter-tip sensor encapsulated with medical grade silicone is adequate for acute implantation. Despite excellent biocompatibility, silicone is not an effective moisture barrier, which leads to rapid device failure. A novel thin film encapsulation topology consisting of 20 nm of Al2O3 and 25 nm TiO2 provided excellent protection of pressure sensors over one month when immersed in saline and heated to 37 °C. However, 60 % of tested sensors failed when immersed in saline. SEM imaging revealed poor coating quality in the failed sensors and is likely to have caused failure. Furthermore, EDS showed that residual carbon and nitrogen species remained within the film, which could be a contributing factor to poor coating quality. A ‘can’ style enclosure was constructed as an alternative encapsulation methodology and consists of a sensor immersed in silicone oil and separated from biological material with a 25μm thick grade-2 titanium diaphragm. The device displayed excellent long-term stability (within ± 2 mmHg) over one month in a controlled 34 °C environment. This research has produced two alternative encapsulation topologies for long-term protection of fully implantable pressure sensors.