Biodegradable Batteries to Power Smart Medical Devices
Prototype batteries that dissolve safely in the body could power ingested devices.
Edible electronics could track the progression of disease, monitor wound healing, and release drugs—if a power source can be found.
Batteries made from pigments found in cuttlefish ink may lead to edible, dissolvable power sources for new kinds of medical devices. Researchers led by Carnegie Mellon University materials scientist Christopher Bettinger demonstrated the new battery. “Instead of lithium and toxic electrolytes that work really well but aren’t biocompatible, we chose simple materials of biological origin,” Bettinger says.
Conventional battery materials are not safe inside the body unless they’re encased in bulky protective cases that must eventually be surgically removed. Electronics that can either be swallowed or implanted in the body without causing harm could monitor wound healing and disease progression, release drugs, and enable more sensitive neural and cardiovascular sensors and stimulators.
The prototype sodium-ion battery from the CMU researchers uses melanin from cuttlefish ink for the anode and manganese oxide as the cathode. All the materials in the battery break down into nontoxic components in the body.
The CMU group is working on edible electronics that can be swallowed like pills. These electronic medicines could let doctors deliver sensitive protein drugs—which are ordinarily destroyed in the stomach—orally rather than by injection. This could make therapies such as arthritis drugs that currently have to be given intravenously at the hospital much easier to take. Smart pills, says Bettinger, could carry sensors and circuits and release drugs only after they’ve passed the harsh environment of the stomach and reached the intestine, where the drugs would be absorbed into the body. Edible electronics could also be used by athletes to monitor their core body temperature and other body metrics.
The melanin batteries don’t match the performance of lithium-ion batteries, but they don’t have to in order to be useful, says Bettinger, who was named one of MIT Technology Review’s 35 innovators under 35 in 2011. The prototypes, described in the journal Proceedings of the National Academy of Sciences, currently provide enough power to run simple sensors. Bettinger says they’re working to improve their power output and storage capacity by experimenting with different forms of melanin.
Bettinger’s group is not the first to propose electronic pills. A few companies, including Olympus, already make capsules that contain cameras; but these kinds of systems, which use traditional electronic and optical components to image the digestive system, can’t be swallowed regularly, says Bettinger.
Another company, Proteus Digital Health of Palo Alto, California, makes a personal-health monitoring system that includes pills affixed with digital identification tags. A small chip that stores an identifying number is sandwiched between two metal foils that act as a partial battery that the company’s chief technology officer, Mark Zdeblick, calls a “biogalvanic cell.” When the pill is swallowed, the metals come into contact with ions in the stomach, activating the device by enabling current to flow between the metal foils. The chip modulates the current flowing between the metal foils to produce a weak electrical field that is sensed by a patch worn by the patient. This allows people and medical professionals to monitor when they take their drugs.
John Rogers, a materials scientist who makes biodegradable electronics at the University of Illinois at Urbana-Champaign, says more power will be required for more sophisticated edible and implantable electronics, and one way to provide that is with full batteries like Bettinger’s.
Rogers is also working on biodegradable batteries for medical use. In a paper that will be published in the journal Advanced Materials, his team describes batteries made out of the dissolvable metals and trace minerals magnesium and molybdenum. Biodegradable batteries, Rogers says, will enable “devices that go into the body monitor wound healing, deliver therapy as necessary, and then naturally disappear after the wound is completely healed, thereby eliminating unnecessary strain on the body.”