The development of tiny smart devices, measuring just a few cubic millimeters, requires equally miniature power sources. For minimally invasive biomedical devices that interact with biological tissues, these power sources must be made from soft materials. Ideally, they should also exhibit characteristics such as high capacity, biocompatibility, biodegradability, triggerable activation, and the capability for remote control. So far, no battery has managed to meet all of these criteria all at once. Now, a team of researchers has made significant progress toward developing miniature, soft batteries suitable for various biomedical applications, including the defibrillation and pacing of heart tissues.

Researchers at the University of Oxford (Oxford, UK) have designed a small, soft lithium-ion battery made from biocompatible hydrogel droplets. The assembly of three microscale droplets, each with a volume of 10 nanoliters, is achieved using surfactant-supported assembly (a method facilitated by soap-like molecules), a technique the same group reported last year in the journal Nature. Different lithium-ion particles contained in each end of the battery generate the output energy. The droplet battery is activated by light, can be recharged, and is biodegradable after use. To date, it is the smallest hydrogel lithium-ion battery and also boasts a superior energy density.

In proof-of-concept heart treatments conducted in the laboratory, the researchers utilized the droplet battery to power the movement of charged molecules between synthetic cells and to control the beating and defibrillation of mouse hearts. The findings, published in the journal Nature Chemical Engineering, show that by incorporating magnetic particles to regulate movement, the battery can also serve as a mobile energy carrier. This proof-of-concept application in animal models marks an exciting new direction for wireless and biodegradable devices in managing arrhythmias. The researchers anticipate that this tiny, versatile battery, especially relevant for small-scale robots in bioapplications, will create new possibilities in various fields, including clinical medicine. 

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