Design considerations for piezocomposite materials for electrical stimulation in medical implants

Abstract

Incidence of nonunion following long bone fracture fixation and spinal fusion procedures is increasing, and very costly for patients and the medical system. Direct current electrical stimulation has shown success as an adjunct therapy to stimulate bone healing and increase surgery success rates, though drawbacks of current devices and implantable battery packs have limited widespread use. Energy harvesting utilizing piezoelectric materials has been widely studied for powering devices without a battery, and a preclinical animal study has shown efficacy of a piezocomposite spinal fusion implant resulting in faster, more robust fusion. Most piezoelectric energy harvesters operate most effectively at high frequencies, limiting power generation from loads experienced by orthopedic implants during human motion. This work characterizes the efficient power generation capability of a novel composite piezoelectric material under simulated walking loads. Building on compliant layer adaptive composite stacks (CLACS), the power generation of mixed-mode CLACS (MMCLACS) is defined. Utilizing poling direction to capitalize on in-plane strain generation due to compliant layer expansion, MMCLACS significantly increased power output compared to a standard piezo stack. The combination of radial and through-thickness poled piezoelectric elements within a stack to create MMCLACS significantly increases power generation under low frequency dynamic loads. This technology can be adapted to a variety of architectures and assembled as a load-bearing energy harvester within current implants. MMCLACS integrated with implants would provide enough power to deliver bone healing electrical stimulation directly to the fusion site, decreasing nonunion rates, and also could provide quantitative assessment of healing progression through load sensing.

Four-Point Bending Piezoelectric Energy Harvester with Uniform Surface Strain Toward Better Energy Conversion Performance and Material Usage

“…This study originates this boundary condition fundamentally, and since this paper's focus is introducing this new boundary design, it studies a standard rectangular piezoelectric case study for sensitivity analysis. Nonetheless, the present fundamental idea can be applied to advanced piezoelectric materials (such as functionally graded piezoelectric [17] and piezocomposite materials [18]) and configurations (such as non-uniform [19], variable thickness [20], and hybrid piezo-magnetic harvesters) for complex and high-performance energy conversion systems. Analytical modeling of the PEHs under the FPB condition is presented for a piezoelectric composite material.…”