Today we have two main types of batteries. The first are from either lithium metal anode with cathode systems including iodine, manganese oxide, carbon monofluoride, silver vanadium oxide and hybrid cathodes.

The second type of batteries are lithium ion types, whereby such batteries are rechargeable. However, the chief requirement remains, that any batteries in use in the body must exhibit high safety standards, be reliable, have a high volumetric energy density, and a long service life.

The batteries of today are far from perfect

Batteries of today are in use in a myriad of applications in our bodies, such as a neurostimulator in the brain; cochlear implants in the ears; pacemakers, implantable cardiac defibrillator, and cardiac resynchronisation device in our hearts; a drug delivery system in our digestive system, and even a bone growth generator in the calve bones.

We do have other battery technologies; a nuclear based battery (betavoltaic cell) for its long-lasting properties -up to 20 years of use. However, such a cell raised a huge concern of proper nuclear waste disposal systems. Nuclear waste is required to be stored in a way that would not endanger society.

An additional concern was the effects on patients, and their family, with long term exposure to radiation. Also, such cells were unsuitable for to be passed through the digestive system; the failure of excrement would present a massive health hazard.

Next, we poured into the viability of an inductively rechargeable (wireless) battery, which eliminated the need for frequent replacements. Such technologies are present in the latest high-tech phones today. However, this raised another set of concerns; if such technology was employed for use in a life sustaining application (pacemakers), then hackers might be able to wirelessly disable such systems, placing the patient in unnecessary danger. The patient might also not remember to charge such devices religiously, placing his own life in danger. Additionally, such long-term batteries are not suitable for use in the digestive tract.

There was no other solution for a battery that would be safe to be administered regularly in one’s gut; only a biodegradable battery, able to be absorbed by the body naturally, would be viable for use in the patient’s gut on a routine basis for medication or vaccination delivery systems.

Frequent usage risky

Devices that are designed to be passed through our digestive system could not be frequently administered as such high frequency would dramatically increase the probability of the failure to pass stools, causing severe toxicity issues. The safety aspect for such an application would not be justified.

The limited frequency of usageincreased efforts for research into biodegradable batteries that can be swallowed, and after a said amount of time would be naturally absorbed, and disposed of, by the body in a harmless manner.

Breakthrough in research

The findings would be presented at the 252nd National Meeting & Exposition of the American Chemical Society (ACS) by a group of researchers’ spearheaded byChristopher Bettinger.

The findings are for a non-toxic, ingestible battery that could one day power devices for diagnosing, and administering medications for treating illnesses. Such a battery is made from melanin pigments, which is naturally found in the skin, hair and eyes.

"For decades, people have been envisioning that one day, we would have edible electronic devices to diagnose or treat disease. But if you want to take a device every day, you have to think about toxicity issues. That's when we have to think about biologically derived materials that could replace some of these things you might find in a RadioShack,” said Bettinger.

Today’s devices with a battery component contain a safety requirement that makes it compulsory for the toxic batteries to be shielded away from the body. That did not mean that the shielding was 100% failure free, hence, there was a pressing need for biodegradable batteries. Such ingestible, non-toxic batteries would be ideal for low-power, repeated applications such as drug-delivery devices, while at the same time exhibiting the highest safety standards.

"The beauty is that by definition an ingestible, degradable device is in the body for no longer than 20 hours or so. Even if you have marginal performance, which we do, that's all you need," Bettinger says.

Melanin based batteries

The choice to turn to a melanin based batteries is a natural one. Melanins absorb ultraviolet light to quench free radicals and protect us from damage in our skin, hair and eyes. They also happen to bind and unbind metallic ions. All these properties essentially made melanin a natural battery.

Building on this idea, the researchers experimented with various battery designs that utilised melanin pigments at either the positive or negative terminals. The various electrode materials utilised compounds such as manganese oxide and sodium titanium phosphate, and cations used either copper and iron. Such compounds are chosen as the body uses them for normal functioning.

While the exact power would depend on the configuration, but as an example, research has shown that it can power a 5 kilowatt device for up to 18 hours using 600 milligrams of active melanin material as a cathode.

Next step: ingestible packaging materials

Although the capacity of a melanin battery is low compared to lithium-ions, it would be sufficient to power an ingestible drug-delivery or sensing device. Bettinger envisions using his battery for sensing gut microbiome changes and responding with a release of medicine, or for delivering regular doses of a vaccine over several hours before degradation.

In tandem with the melanin batteries, the team is also exploring with other biomaterials such as pectin, which are natural compound from plants used as a gelling agent in jams and jellies.

Next, they would research on the packaging materials that will safely deliver the battery to the stomach.

While the timeframe for the development to enter human clinical trials, and ultimately widespread adoption, is uncertain, the group has already found another application for them; they have used the batteries to probe the structure and chemistry of the melanin pigments themselves to gain better understand how they work. MIMS


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