Michela Peisino
Medical devices have gone a long way since their beginning. In the last decades, the trend has been towards Implanted Medical Devices (IMDs). The technology evolution has provided the necessary tools for longer-term, less invasive devices. Several devices for sensing and actuation are commercially available and ease therapy management, while preserving the patient’s life quality. An ideal implant would integrate both sensing and actuating possibilities in a feedback loop, thus achieving optimum therapy. To reach this goal, several challenges remain, in particular concerning power supply and miniaturization. Solving these issues would open new possibilities and allow applications which are not possible yet: better diagnosis could be achieved wherever a continuous, long-term monitoring of physiological parameters in real life conditions is required. For instance, smaller and deeper implanted devices would allow deploying several IMDs in the body, achieving a Body Sensor Network (BSN). Beside therapy, implants could be used for diagnosis in populations at risk. Furthermore, minimal invasive implants would greatly improve medical research, by allowing closer observation, thus helping to understand physiological mechanisms. This thesis describes the author’s contribution to the development of a novel IMD concept, proposed within the European FP7 project ULTRAsponder. The author focused on the integration aspects in the design and manufacturing process of the novel implantable device platform: definition of the technical specifications, assessment of appropriate commercial components, geometrical placement of the Printed Circuit Boards (PCBs) inside the casing, choice of a suitable housing material, and assessment of its effect on the energy transmission. The target is a generic BSN node, which can be implanted wherever needed on a long-term basis and which can operate autonomously. Key features of the proposed system include remote powering of the implanted device and communication with an external Control Unit (CU) by backscattering modulation. For both energy and data transfer, an ultrasonic carrier is used instead of Electromagnetic (EM) waves because it is compatible with Magnetic Resonance Imaging (MRI) and does not interfere with EM emitters like mobile phones and electronic equipment. It also proved to be more efficient than the use of Radio Frequency (RF) waves or magnetic induction to reach deep implants and when using small transducers. The user requirements and the technical constraints towards an optimal implant were evaluated and the characteristics of the proposed system were defined. Appropriate commercial components and emerging technologies were identified, which allowed the development of the device. The originality of this work lies in the integration of different technologies, components and scientific approaches into a novel, promising IMD. In particular, the challenge of achieving an ultrasonic link through a standard medical grade titanium casing is addressed. Titanium casings are the golden standard for biocompatible device housing, but they have a strong influence on ultrasonic energy transfer. Successful integration of ultrasonic transmission and titanium casing ensures the ability of the proposed device to be industrially exploited and commercialized. A demonstrator implant and an external CU have been manufactured, focusing on energy transfer, signal treatment, and backscattering. A commercial, rather large housing was used, in order to demonstrate the industrial viability of the device. In vitro tests validated the energy transfer and the communication between the CU and the Transponder (TR), as well as the user interface. Assessment in real conditions is achieved by in vivo tests on pigs. Functionality was proved, however at a much smaller distance than intended. Future work includes optimization of the ultrasonic transfer, integration of the sensing circuitry, and miniaturization of the resulting device.
EPFL2013
