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Home | DTI | 2008–09 funded proposals | Rajesh Rajamani, Joan E. Bechtold, William D. Lew

Initiatives in Digital Technology: 2008–09 Funded Proposals

Rajesh Rajamani, Joan E. Bechtold, William D. Lew

Battery-Less Wireless Interface Pressure Sensors for Total Knee Replacement Implant Applications

In a total knee replacement (TKR) operation, the knee joint is resurfaced and replaced with a metal and plastic implant. More than 300,000 TKR surgeries are conducted in the US each year. A TKR can help put an end to severe arthritic pain and can enable you to resume a functional and fully active lifestyle.

Problems associated with total knee replacement (TKR) include the challenges associated with obtaining proper bone alignment and tissue balance during the surgery and problems later with misalignment, wear and loosening during the life of the implant.

This project proposes to develop an embedded wireless sensor system that would provide measurement of the magnitude and location of the resultant interface forces in the implant. The sensor system would aid the balancing of the joint via release of soft tissues to achieve alignment during surgery. After the completion of surgery, the sensors would provide in-vivo diagnostic capabilities that include monitoring implant duty cycles, detection of component wear, measurement of changes in alignment and detection of loosening of the implant. By enabling early detection of implant wear and incipient failure, the sensors would significantly extend the lifespan of implants and improve their function.

Due to the long life and tight space constraints required in a knee implant, the developed system will be a battery-less wireless system that obtains the power required for its operation entirely from piezoelectric power generation during walking.

A new control algorithm for harvesting energy from vibrations specifically suited to this application is proposed. The proposed algorithm is suitable for extracting energy from the low duty cycle loads that occur in the knee implant. Preliminary analysis and computer simulations have been completed and show that the proposed algorithm can extract roughly four times the energy as that from the best synchronous damping algorithms that have been suggested in literature. The primary tasks that will be undertaken in this project include design of the knee implant tibial component, analysis and computer simulations of control algorithms for energy harvesting, experimental implementation of control algorithms and associated electronics and experimental testing of the developed integrated knee implant device on MTS material test machines.

The project includes a matching in-cash contribution of $20,000 and significant additional in-kind support from the Minnesota Orthopedic Research Foundation.