Biodegradable batteries power technology you can swallow

Swallowing a battery typically requires a trip to the emergency room, but now researchers have developed a battery designed to be safely ingested—and dissolved in the body.

Ingestible medical devices have been monitoring internal health since 1957, but powering them remains a challenge. Standard battery technology risks leaking toxic materials inside the body, while previous attempts to design biodegradable alternatives have produced weak or unreliable power.

Mehmet Say and colleagues at MIT and Harvard Medical School have now designed and tested a battery capable of producing 1.84 V using nontoxic components that can be reabsorbed in the gut. ¹ After successfully testing the battery in pigs, the researchers are working to advance the technology to in-human clinical trials.

Figure 1.

Instead of typical battery materials like lithium and silver oxide, the team designed batteries that use magnesium and molybdenum trioxide, small amounts of which are safe for human consumption. As seen in figure 1 , the biodegradable batteries are composed of an Mg alloy anode, an electrolyte solution made from a biodegradable ionic liquid, and a cathode and current collector made of MoO₃. The researchers selected the materials based on how they perform individually—Mg, for example, corrodes at a predictable rate and has previously been used in implanted medical devices. They also considered the voltage the materials produce together compared with other combinations of biocompatible materials.

Working with a simulated gastric environment, the researchers found that the batteries survived intact in the acidic solution for up to two weeks before fully dissolving over several months. The team then used the battery design to power two devices: a radio-frequency identification (RFID) tag that signals an external receiver when a medication is taken, and an electrode array that delivers electrical impulses to the stomach to treat gastrointestinal conditions such as impaired digestion.

Figure 2.

The researchers packaged the battery-powered devices into digestible gelatin capsules, as seen in figure 2 , and implanted them via endoscopy into the stomachs of live pigs. The battery capsules produced voltages of 1.77 V for the RFID tag and 1.84 V for the electrical-impulse device. (For comparison, lithium batteries have nominal voltages of 1.5–3.7 V; silver oxide batteries, 1.55 V.) The voltages from the battery capsules enabled the RFID chip to transmit a stable signal up to 1.5 m from the capsule and the electrode capsule to stimulate the stomach for 20 minutes.

The capsules survived in the pigs’ stomachs for three days before they started to dissolve and the battery components began to degrade. By that point, the RFID tag’s voltage had dropped to about 1.35 V and the impulse device’s voltage dropped to 1.45 V. A few days later, the RFID tag and the circuit board that controlled the stimulation device—the only nonbiodegradable components—were safely excreted.

With the success of large-animal trials, the team is now working toward clinical trials to evaluate the feasibility of the RFID-powered capsules to monitor medication adherence in humans. Those trials are projected to take place in the next two years.

The team also wants to extend the operational lifetime of the batteries in vivo for longer-term clinical applications. To reach that goal, they plan to explore thicker electrodes, increased cathode capacity, and more-robust encapsulation methods.