06/4 WIPSS - polymer - ETHZ

		A potential application of the WIPSS system: The wireless passive sensor is implemented into the fixation plate on a fractured bone. The sensor signal is monitored via an ultrasound transceiver and displayed via a signal imaging process.

This subproject addresses the development of an implantable wireless in-situ passive strain-sensor (WIPSS) including the option for complete biodegradability of the whole sensor unit.

In phase 1 of Co-Me, our medical partners Proff. Zeilhofer and Sader (Kantonsspital Basel) and Prof. Nolte (MEM Research Center Bern) made a thorough analysis and evaluation of the state-of-the art of load sensing systems and expertises on the medical need for load monitoring. As a consequence of this work, the following sensor principle has been identified, allowing for the abdication of any active circuits and thus, for the implementation of materials which exhibit only poor or negligible electrical or magnetic properties like biocompatible and biodegradable polymers:

A small orthopedic strain is transmitted via a fixed interface from the bone or implant into a volume deformation of a liquid containing elastic reservoir attached to a long air filled micro-channel. Due to the high ratio (ca. 100:1) between the diameter of the reservoir and the diameter of the micro-channel, small volume changes of the reservoir are amplified into large local displacements of the fluid/air interface in the micro-channel.

This sensor principle is designed to allow for a relative strain resolution as small as 10-4 - 10-5. In vivo remote determination of the interface's local position, even through inhomogeneous human tissue, will be achieved by advanced ultrasound imaging technologies developed by our partners Dr. Sennhauser and co-workers at the EMPA in Dübendorf.