Novel ultrasound read-out for a wireless implantable passive strain sensor (WIPSS)

In vivo monitoring the deformation of orthopedic implants during rehabilitation helps preventing their possible failure and enables the observation of healing processes. For these reasons we propose a completely new load-monitoring concept, which consist of a passive load sensor and its associated external ultrasound-based read-out unit. The new concept allows the sensor to be built from inexpensive biocompatible or even bioresorbable polymers and the read-out will be carried out with a standard medical ultrasound scanner. The measurement principle is based on the transformation of an external force into a varying amount of fluid in a microchannel integrated into the sensor. A novel ultrasound read-out method based on an integral evaluation of C-scans of the microchannel is proposed to determine the amount of fluid in the microchannel. Furthermore, suitable reference reflectors inside the sensor will be used to calibrate the ultrasound echoes. In this paper we will present first ultrasound in vitro experiments, which shows promising results for in vivo load monitoring.