A small battery made of silk hydrogel can power a pacemaker in mice

The smallest soft lithium-ion battery ever made consists of just three tiny droplets formed from a silk-based hydrogel. Droplet batteries can provide pacemaker-style control and deliver defibrillator electric shocks to beating mouse hearts, but could eventually be used in biomedical implants or wearable electronic devices for humans. may provide power.

“Potentially, our tiny battery could be used as an implantable microrobotic battery, moved to a target location by a magnetic field and releasing its energy for medical purposes,” said Yujia Zhang from the University of Oxford. states.

Zhang and colleagues designed the small battery as three connected droplets that can self-assemble in solution after injecting various components into the liquid with a microsyringe. One droplet contains lithium manganese oxide particles and serves as the battery’s negative electrode. The second droplet contains lithium titanate particles and acts as the positive electrode. A central droplet filled with lithium chloride separates these electrodes. UV light energizes the battery by breaking down the layers that separate each droplet, allowing lithium ions to flow freely between the droplets.

Droplet batteries are one-tenth the length of traditional soft lithium-ion batteries. At just 600 micrometers, it is about six times as wide as a human hair. The battery is also 1000 times smaller in volume than similar flexible lithium-ion batteries. The central droplet can also incorporate magnetic nickel particles, allowing the battery to be controlled remotely via an external magnetic field.

According to Wei Gao of the California Institute of Technology, such small batteries can also provide unprecedented amounts of energy considering their small size. “This energy density is significantly higher than what has been achieved with other similarly sized batteries,” he says.

The droplet battery was tested on a mouse heart removed from the animal’s body. These successfully functioned as defibrillators to restore normal heartbeats and as pacemakers to regulate heartbeats. Additional testing showed that the battery retained 77% of its original capacity after 10 charge/discharge cycles.

The simplicity and scalability of such droplet batteries could be a potential advantage over traditional battery manufacturing in the future, Gao said. He suggested that such batteries could power minimally invasive biomedical implants and biodegradable medical devices.

“What impressed me most is how this soft battery mirrors the aqueous environment of human tissue by being hydrogel-based,” Gao says. “However, we still need to consider the safety and biocompatibility of the materials used in this battery, especially as we move towards commercialization and further research applications.”