Powering smart orthopedic implants using acoustic waves: An ex vivo study

Area of Science:

• Biomedical Engineering
• Acoustics
• Orthopedics

Background:

• Smart orthopedic implants require reliable power sources.
• Existing power transfer methods like electromagnetic induction face limitations.
• Acoustic power transfer offers a potential alternative for powering implants wirelessly.

Purpose of the Study:

• To investigate the feasibility of acoustic power transfer for battery-free full-metal smart orthopedic implants.
• To evaluate different receiver placements and their impact on power transfer efficiency.
• To compare acoustic power transfer with electromagnetic techniques regarding power density and safety.

Main Methods:

• Experimental investigation of acoustic power transfer in a human cadaver model.
• Design and simulation of acoustic receivers using finite element analysis and analytical modeling.
• Evaluation of two receiver placements: stem (including cancellous bone) and tray (avoiding bone).
• Measurement of transmitted power, acoustic intensity, mechanical index, and volumetric power density.

Main Results:

• Acoustic power transfer achieved milliwatt-level power (up to 29 mW and 20 mW for stem and tray placements, respectively).
• Higher frequencies significantly reduced transmitted power due to cancellous bone attenuation.
• Volumetric power densities reached 91 mW/cm³ (stem) and 1400 mW/cm³ (tray), comparable or exceeding electromagnetic methods.
• Acoustic intensity and mechanical index remained within safe exposure limits.

Conclusions:

• Acoustic power transfer is a feasible method for powering smart orthopedic implants.
• Receiver placement significantly impacts power transfer efficiency, with bone-avoiding placements showing higher volumetric power density.
• Challenges include transmitter alignment and the narrow operating bandwidth of acoustic systems.