Abstract
Electrical stimulation devices can be used as adjunct therapy to lumbar spinal fusion to promote bone healing, but their adoption has been hindered by the large battery packs necessary to provide power. Piezoelectric composite materials within a spinal interbody cage to produce power in response to physiological lumbar loads have recently been investigated. A piezoelectric macro-fiber composite spinal interbody generated sufficient power to stimulate bone growth in a pilot ovine study, despite fabrication challenges. The objective of the present study was to electromechanically evaluate three new piezoelectric disc composites, 15-disc insert, seven-disc insert, and seven-disc Compliant Layer Adaptive Composite Stack (CLACS) insert, within a spinal interbody, and validate their use for electrical stimulation and promoting bone growth. All implants were electromechanically assessed under cyclic loads of 1000 N at 2 Hz, representing physiological lumbar loading. All three configurations produced at least as much power as the piezoelectric macro-fiber composites, validating the use of piezoelectric discs for this application. Future work is needed to characterize the electromechanical performance of commercially manufactured piezoelectric stacks under physiological lumbar loads, and mechanically assess the composite implants according to FDA guidelines for lumbar interbody fusion devices.
Highlights
Upwards of 30% of the general population will experience low back pain due to degenerative disc disease, with even higher incidence rates for those over the age of 45 [1]
The implant size and shape chosen for this study was modeled after a transforaminal lumbar interbody fusion (TLIF) implant previously cleared by the U.S Food and Drug Administration (FDA), Bioengineering 2018, 5, 90 with dimensions of 23 × 10 × 17 mm and a graft window size of 5 × 5.5 × 17 mm (Figure 1)
In contrast to previous studies, investigating piezoelectric composite spinal fusion implants that used a nine-layer stack of 48 PZT macro fibers, the current study investigated the impact on power output when switching to a stack of PZT discs [25]
Summary
Upwards of 30% of the general population will experience low back pain due to degenerative disc disease, with even higher incidence rates for those over the age of 45 [1]. For those whose pain cannot be controlled using conservative treatment options, lumbar spinal fusion is the most common surgical treatment used to alleviate pain associated with severe disc degeneration [2]. To address the lower success rates in the difficult-to-fuse patient population, adjunct therapies have been used to supplement bone growth and increase bone healing. The use of adipose-derived stem cells have been investigated to promote bone regeneration; there are still many obstacles to overcome before it can be used clinically [13]
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