University of Oxford researchers have made a significant step towards realizing miniature, soft batteries for use in a variety of biomedical applications, including the defibrillation and pacing of heart tissues. The work has been published today in the journal Nature Chemical Engineering.

The development of tiny smart devices, smaller than a few cubic millimeters, demands equally small power sources, reports ScienceDaily.

For minimally invasive biomedical devices that interact with biological tissues, these power sources must be fabricated from soft materials.

Ideally, these should also have features such as high capacity, biocompatibility and biodegradability, triggerable activation, and the ability to be controlled remotely.

To date, there has been no battery that can fulfil these requirements all at once.

To address these requirements, researchers from the University of Oxford's Department of Chemistry and Department of Pharmacology have developed a miniature, soft lithium-ion battery constructed from biocompatible hydrogel droplets.

Surfactant-supported assembly (assembly aided by soap-like molecules), a technique reported by the same group last year in the journal Nature, is used to connect three microscale droplets of 10 nanoliters volume.

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Different lithium-ion particles contained in each of the two ends then generate the output energy.

'Our droplet battery is light-activated, rechargeable, and biodegradable after use.

To date, it is the smallest hydrogel lithium-ion battery and has a superior energy density' said Dr Yujia Zhang (Department of Chemistry, University of Oxford), the lead researcher for the study and a starting Assistant Professor at the École Polytechnique Fédérale de Lausanne.

'We used the droplet battery to power the movement of charged molecules between synthetic cells and to control the beating and defibrillation of mouse hearts.

By including magnetic particles to control movement, the battery can also function as a mobile energy carrier.'

Proof-of-concept heart treatments were carried out in the laboratory of Professor Ming Lei (Department of Pharmacology), a senior electrophysiologist in cardiac arrhythmias.

He said: 'Cardiac arrhythmia is a leading cause of death worldwide.

Our proof-of-concept application in animal models demonstrates an exciting new avenue of wireless and biodegradable devices for the management of arrhythmias.'

Professor Hagan Bayley (Department of Chemistry), the research group leader for the study, said: 'The tiny soft lithium-ion battery is the most sophisticated in a series of microscale power packs developed by Dr Zhang and points to a fantastic future for biocompatible electronic devices that can operate under physiological conditions.'

The researchers have filed a patent application through Oxford University Innovation. They envisage that the tiny versatile battery, particularly relevant to small-scale robots for bio applications, will open up new possibilities in various areas including clinical medicine.