Researchers Develop Biocompatible Supercapacitor
19-01-2021 | By Sam Brown
Recently, researchers developed a new thin, flexible supercapacitor that is not only biocompatible but can degrade inside living tissue safely. What challenges do implanted devices face, what materials make this supercapacitor, and what applications can be used in?
What challenges do implanted medical devices face?
When designing electronics for the medical field, some stringent measures and regulations must be followed. The human body, being organic in nature, doesn’t like to have things inside it that are explicitly supposed to be there.
When the human body, or most animals for that matter, detect a foreign object, it immediately surrounds the foreign body with white blood cells (in the form of puss). If left untreated, this can lead to serious complications, including dead tissue, sepsis, and blood poisoning.
Such a reaction does not only occur with organic foreign bodies; even pieces of sterile metal can trigger the same response. Only specific metals can survive inside the human body (such as titanium), without triggering such a response, and as such are the go-to materials for implanted medical objects.
Of course, there are other complications that designers have to face. Objects implanted inside the human body need to be constructed so that if they fail and break, the contents of the object do not cause damage such as through poisoning. Implanted objects must also be readily accessible for removal if powered, and powered objects need to use a battery that is safe for implantation into the human body.
Researchers Develop Biocompatible Supercapacitor
Researchers have recently developed a biocompatible, biodegradable, flexible, and deformable supercapacitor, making it ideal for temporary medical implantation. The 2D device utilises amorphous molybdenum oxide bound to a Molybdenum oxide foil to create the conductive plates, and a solution of Sodium Alginate forms an electrolyte.
The resulting supercapacitor has a capacitance of 112.5mF/cm2, and energy density of 15.64uWh/cm2, and a power density of 2.53mW/cm2. Not only does the supercapacitor express high energy density capabilities, but its lifespan, when implanted into living tissue, can also be controlled from a few days to a few weeks.
Metabolic processes in living tissue break the supercapacitor down, and the resulting by-products are biologically inert, thus are safely absorbed into the body without any long-term effects. Testing on the supercapacitor demonstrates that it can be flexed, rolled, and bent without damage to the device. Placement of the supercapacitor in Phosphate-buffered saline shows the device breaking up after three months.
What applications can such supercapacitors take on?
Using biocompatible and biodegradable devices in implanted devices provides several advantages: the first and most obvious, being a lack of rejection from the human body.
Providing power to an implanted medical device is difficult as access to the said device is next to impossible without a surgical procedure. Implanted devices such as pacemakers often rely on long-life biocompatible power sources, but the first pacemakers actually took advantage of plutonium power sources (these are no longer available).
However, instead of the pack all the power a device will ever need, it can be easier to instead harvest the needed power from the naturally occurring energy from the surrounding environment. Such energy harvesting often requires an energy storage device because naturally occurring energy is so small, and devices often require far more than what instantaneous background energy can provide. The use of such a supercapacitor provides an ideal energy storage unit as it provides high energy densities and biocompatibility.
Another major advantage to using a device that can degrade safely inside living tissue is using one-off implanted devices for basic monitoring of a temporary condition. Surgery always runs the risk of infection and complication, therefore reducing the overall number of procedures can greatly reduce risk. A device that can be implanted once and then forgotten about reduces the number of surgeries to one, thereby providing a safer option to patients.
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