Implantable medical devices have made a major impact in improving healthcare. Increasingly in recent years, devices have become active rather than passive - for example cardiac pacemakers. A key challenge for these active systems, as well as for others on the horizon is their need for an internal electrical power source.
A downside of present systems is the limitation of internal batteries, which must be changed frequently, requiring follow-up surgical procedures, with associated complication risks and additional healthcare costs. One compelling solution would be to employ energy harvesting as a means of recharging or completely replacing batteries. Energy harvesting, through chemical reactions, heat extraction, blood flow, and natural mechanical movements of organs, could help address energy depletion in implants. However, most harvesting units being considered today are like conventional batteries, in that they also rely on rigid electronics and subcomponents, and therefore, are incapable of providing intimate mechanical contact with soft tissue.
In this study, materials and devices that enable high efficiency mechanical to electrical energy conversion from the natural contractile and relaxation motion of the heart, lung and diaphragm, demonstrated in several different animal models, each of which has organs with sizes that approach human scales are reported. A combination of such energy harvesting elements with rectifiers and microbatteries provides an entire flexible system, capable of viable integration with the beating heart via medical sutures and operation with efficiency of ~2%. Additionally, in vitro experiments, computational models and results in multilayer configurations capture the key behaviors, illuminate crucial design features and provide sufficient power outputs for operation of pacemakers, with or without battery assist. The key findings consist of in vivo demonstrations of ultra-thin lead zirconate titanate (PbZr0.42Ti0.58O3, PZT) based energy harvesting devices on flexible polyimide substrate:
With output open-circuit voltages and short-circuit currents that are greater by three and five orders of magnitude, respectively, than previous in vivo results;
Monolithically integrated with rectifiers and millimeter-scale batteries for simultaneous power generation and storage, including high power, multilayer designs;
In biocompatible forms, evaluated through cell cultures and large-scale, live animal models, on various locations/orientations on different internal organs;
For harvesting inside the body, via open and closed left thoracotomy experiments with a bovine model.