Scientists invent biobatteries that can be powered inside the human body

“There are some regions in the small intestine that are not reachable, and that is why ingestible cameras have been developed to solve this issue,” Choi said. “They can do many things, such as imaging and physical sensing, even drug delivery. The problem is power. So far, the electronics are using primary batteries that have a finite energy budget and cannot function for the long term.”

A new solution based on past research

The new solution is based on findings that Choi has made over the past decade about utilizing bacteria to create low levels of electricity that can power sensors and Wi-Fi connections.

However, options inside the small intestine are less viable: traditional batteries can be harmful to human health, wireless power transfer from outside the body is ineffective, the body does not provide enough changes for thermal energy and intestinal movement is too slow for mechanical energy. So, Choi’s biobatteries utilize a completely new approach consisting of microbial fuel cells with spore-forming Bacillus subtilis bacteria that remain inert until they reach the small intestine.

“How do you make your micro-fuel cell selectively work in the small intestine? We use a pH-sensitive membrane that requires certain conditions to activate,” Choi said. “When you look at our gastrointestinal tract, the esophagus has a neutral pH, the same as the small intestine, but the transit time is only 10 seconds. It will not activate in this area, and it will never work in the stomach because the stomach has a very low pH. It only works in the small intestine.”

Ingesting bacteria

To those that might balk at ingesting bacteria, Choi says that our bodies are filled with nontoxic microbes that help with digestion and other functions.

“We use these spores as a dormant, storable biocatalyst,” he said. “The spores can be germinated when the nutrients are available, and they can resume vegetative life and generate the power.”

The research is very fresh (it has just been published) but Choi and his students are already looking ahead to improving the biobatteries. They want to increase the speed at which the fuel cell germinates completely. It currently takes about an hour. 

In addition, the cell generates around 100 microwatts per square centimeter of power density — enough for wireless transmission, but 10 times more would offer many more options for use. “I believe that our micro-fuel cell has a huge potential, but we have a long way to go,” he said.

The batteries now have to undergo animal and human testing as well as biocompatibility studies.

 Abstract:

Functioning ingestible capsules offer tremendous promise for a plethora of diagnostic and therapeutic applications. However, the absence of realistic and practical power solutions has greatly hindered the development of ingestible electronics. Microbial fuel cells (MFCs) hold great potential as power sources for such devices as the small intestinal environment maintains a steady internal temperature and a neutral pH. Those conditions and the constant supply of nutrient-rich organics are a perfect environment to generate long-lasting power. Although previous small-scale MFCs have demonstrated many promising applications, little is known about the potential for generating power in the human gut environment. Here, this work reports the design and operation of a microbial biobattery capsule for ingestible applications. Dormant Bacillus subtilis endospores are a storable anodic biocatalyst that will provide on-demand power when revived by nutrient-rich intestinal fluids. A conductive, porous, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate hydrogel anode enables superior electrical performance in what is the world's smallest MFC. Moreover, an oxygen-rich cathode maintains its effective cathodic capability even in the oxygen-deficit intestinal environment. As a proof-of-concept demonstration in stimulated intestinal fluid, the biobattery capsule produces a current density of 470 µA cm−2 and a power density of 98 µW cm−2, ensuring its practical efficacy as a novel and sole power source for ingestible applications in the small intestine.