A team at the Thayer School of Engineering at Dartmouth College worked with UT Health San Antonio (part of the University of Texas) to developed a new way to build a piezoelectric harvesting transducer for these medical implants.
Providing implanted power is a formidable challenge, says Dartmouth engineering professor John X.J. Zhang, “How do you create an effective energy source so the device will do its job during the entire life span of the patient, without the need for surgery to replace the battery?” Research associate Lin Dong added, “Of equal importance is that the device not interfere with the body’s function. We knew it had to be biocompatible, lightweight, flexible, and low profile, which also makes it not only fit into the current pacemaker structure, but also scalable for future multifunctionality.”
To build the harvester transducer, the researchers used a combination of thin-film energy-conversion materials with a minimally invasive mechanical approach in a modified pacemaker design. They harnessed the kinetic energy of the lead wire that’s attached to a beating heart, and then converted it into electricity to continually charge the batteries – see figure 1. The power-generating material, a specialized polymer piezoelectric film called polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE), is designed with porous structures and then built into either an array of small beams or a flexible cantilever.
The team created a dual-cantilever peizoelectric structure that wraps around the pacemaker’s lead, with the structure’s two free ends available for connection and subsequent energy collection – see figure 2.
The maximum output was 0.5V at 43nA at 1Hz, a little over 20nW. By adding a small proof mass of 31.6 mg on the tip of the dual-cantilever tip, the power output increased by a little over 80% since the added mass enabled a larger bending curvature, resulting in higher electrical output from the harvester.
For comparison, today’s ultra-low-power implantable biomedical devices require 0.3μW for cardiac-activity sensing, 10 to 100 μW for pacemakers, 100 to 2000 μW for cochlear implants, and 1 to 10 mW for neural recording. An advantage of this design is that it’s scalable: two (or more) units can be connected in parallel for a corresponding increase in power output. Initial testing is done using a mechanical shaker, of course, to simulate the motion of the myocardium and the corresponding deformation of a pacemaker lead – see figure 3.
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