Ingestible Paper Battery Powers Biodegradable Medical Devices

Typically, if you swallow a battery, it’s a mistake that calls for a trip to the hospital. But that’s not the case with a new ingestible paper battery developed by scientists at MIT. The battery could be used to power medical devices inside the body before safely breaking down.

In tests in live pigs, the paper battery “generated sufficient power to perform meaningful functions inside the gastrointestinal tract, including meter-scale wireless communication and continuous electrical stimulation over several days,” says Giovanni Traverso, a professor of mechanical engineering at MIT. Smart Pills and Ingestible Electronics There is a broader trend in healthcare to develop smart pills. These ingestible electronics can analyze and treat the body from within in real time.

Ingestible electronics need a safe and reliable source of power. Conventional alkaline or lithium-ion batteries can prove deadly if their protective casings leak inside a person. Previous research has sought to develop energy-harvesting techniques for ingestible electronics, but these usually generate low and inconsistent levels of power.

Scientists have also designed biodegradable batteries, but these often can only store limited amounts of energy. Traverso and his colleagues developed a paper-based battery with electrodes made from magnesium and molybdenum trioxide, as detailed in a paper published 21 September in Nature Chemical Engineering.

Prior work had explored both materials for use as biodegradable batteries, but had used bulky adhesives to bind large particles of these materials into batteries, resulting in thick electrodes that took longer to break down. The new batteries instead use cellulose nanofibrils (essentially paper, in other words) to bind the electrode materials to the battery.

These fibrils are sturdy, can load electrode particles into their porous structures, and can be thin and biodegradable, Traverso says. Battery electrolytes—which help electric charges shuttle between a battery’s electrodes to discharge electricity—are often toxic.

The new paper battery uses a biodegradable ionic liquid gel based on choline chloride and lactic acid as its electrolyte, which yielded more stable performance than several other biodegradable electrolyte approaches, Traverso says. “Encapsulation was also critical,” Traverso says.

“If gastric fluid reached the battery too quickly, its capacity declined prematurely. If the encapsulation persisted for too long, the device would not degrade as intended.

Natural wax coatings provided a way to delay fluid penetration and tune the operating lifetime.” Researchers developed bioresorbable electrodes for an ingestible paper battery. After 90 days under accelerated conditions, the electrode material has almost completely dissolved.

Source images: Mehmet Girayhan Say, Ada Erus, et al. Paper Battery for Gastrointestinal Devices In tests in live pigs, the batteries generated a peak voltage of 1.84 volts and remained operational in the stomachs of the swine for up to three days.

They could power a RFID tag in a pill that, after it was swallowed, maintained stable wireless communication with a receiver 1.5 meters away. Similar smart pills could theoretically help doctors track whether a patient has indeed taken prescribed medication.

The batteries could also power a capsule that electrically stimulated the stomach for 20 minutes, an electroceutical technique used to treat gastrointestinal conditions involving impaired digestive function, nausea, or loss of appetite. There was no notable tissue damage from this stimulation.

The RFID tag and the circuit board used for electrical stimulation was not biodegradable, but was naturally excreted. “The battery could potentially power ingestible sensors that measure temperature, pH, pressure, motility, or biochemical signals; systems that transmit physiological information; controlled drug-delivery devices; temporary electrophysiological recording systems; and gastric or intestinal electroceutical devices,” Traverso says.

“It may be particularly valuable for devices designed to remain in the stomach for several days, because a bioresorbable power source could reduce or eliminate the need for retrieval.” The scientists are now prototyping devices that combine these new batteries with biodegradable antennas and RFID system. The goal is a human clinical trial of a device that can monitor how well patients are taking medicine, “which we aim to start in about two years,” Traverso says.