Despite the continual evolution of medical implant technologies, such as making smaller and smaller pacemakers, we still power these devices with traditional batteries. Such batteries contain toxic chemicals that aren't ideal to have inside the human body and also need to be periodically replaced, resulting in painful, and risky surgical procedures. A new energy storage system dubbed a "biological supercapacitor" could enable battery-free implantable devices that never need to be replaced.
Over the years we have seen a variety of innovative alternatives for powering medical implants. A German research team developed a type of biological fuel cell that draws its power from a patient's blood sugar; a Korean team looked into harnessing electricity from the body's own muscles; and an electrical engineer from Stanford developed a technique that allowed devices to be wirelessly recharged by radio waves.
Now a team of researchers from the University of California, Los Angeles (UCLA) and the University of Connecticut have designed a biofriendly supercapacitor system that charges up using electrolytes from biological fluids, such as blood serum and urine. It works in tandem with an energy harvester that can convert heat and motion into electricity that is stored in the supercapacitor.
"Unlike batteries that use chemical reactions that involve toxic chemicals and electrolytes to store energy, this new class of biosupercapacitors stores energy by utilizing readily available ions, or charged molecules, from the blood serum," explains Islam Mosa, graduate student and first author of the study.
The new biosupercapacitor consists of an electrode that is made of graphene layered with modified human proteins, while biological fluids act as electrolytes. Unlike unmodified graphene oxide, which was found to cause toxic cell damage at low doses, the protein-modified graphene oxide nanocomposite material developed by the team showed no toxicity in mouse embryo fibroblasts and cell cultures at high concentrations.
The team says the bioelectrical capacitor device measures just one micrometer thick, is flexible, allowing it to stand up the mechanical stresses of being twisted and turned inside the body, and boasts an energy density comparable to lithium thin film batteries that are currently used in pacemakers. Although supercapacitors haven't yet been widely incorporated in medical implant devices, the researchers claim the technology holds potential for such uses.
"Combining energy harvesters with supercapacitors can provide endless power for lifelong implantable devices that may never need to be replaced," said Maher El-Kady, a UCLA postdoctoral researcher. "Our research focused on custom-designing our supercapacitor to capture energy effectively, and finding a way to make it compatible with the human body."
The team has published the research in the journal Advanced Energy Materials.
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