Electronics for Implants

Fraunhofer Institute for Photonic Microsystems

Implants have been in use for many years in orthopaedics and trauma surgery.

The great advances which microelectronics and microsystem technology have made over the last few years have opened up possibilities to expand the functionality of implants considerably. The microelectronic and micromechanical components take over the task of recording important measurements, and then usually process the measurements right within the implant itself. The provision of required energy is of considerable importance to the integration of electronics in implants. Transponder technology is a good solution because, in addition to bi-directional data transfer, wireless energy transfer is also made possible. For example, measurements of temperature, pressure, acceleration / movement and pH level can be taken within the instrument. One emphasis of our work is the signal processing of the measurements directly at the sensor. The slightly increased energy consumption is more than compensated for by the high degree of data compression and, therefore, the realized reduction of the data to be transferred.

One example of our new generation of implants is a hip prosthesis with an integrated microsystem. Here, it is possible for the physician to check whether or not the prosthesis is still well anchored in the bone or how osseointegration is progressing – all within a routine examination. The microsystem consists of an accelerator sensor and an IPMS developed transponder circuit ST1. When the leg is stimulated mechanically at the knee, the resonance frequency of the system can be determined in the prosthesis. Changes in this frequency are indicators that make it possible to effectively evaluate the osseointegration process. If the frequency rises, then the connection will be stronger. If the frequency falls, then the prosthesis is loosening itself. Energy is coupled in wirelessly through the transponder system with a carrier frequency of 125 kHz. The system has just recently been successfully tested. Now the surgeon or orthopaedist will have a new system at his or her disposal, which makes it possible to evaluate the success of a hip replacement prosthesis with very little effort.

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