Battery free medical implants could be a step closer thanks to a spontaneously beating miniature pump developed by Japanese scientists.

The news is reported in the latest edition of the Royal Society of Chemistry journal Lab on a Chip.

Implants usually rely on batteries - which are inconvenient for patients.

But Dr Takehiro Kitmori and his team at the University of Tokyo have created their pump using heart cells to provide the power, rather than an external energy source.

The tiny device - just five millimetres in diameter - was made by wrapping a sheet of the beating muscle cells around a hollow silicone polymer sphere. 

When the sphere was filled with liquid and fitted with inlet and outlet ports, the liquid was pumped back and forth. Remarkably, the pump worked continuously over five days, so long as the cells were kept supplied with nutrients.

Dr Kitamori said: "The next step is to add chambers and valves to the device, so it can pump the liquid in one direction only."

Dr Piotr Garstecki, a microfluidics specialist from the Polish Academy of Sciences, Warsaw, said: "The solution is simple and elegant and as such it sets a benchmark in the field."

Dr Paul Kenis, an expert in microchemical systems based at the University of Illinois, USA, said: "The device could be useful for many medical situations where pump and power source cannot easily be combined."

with thanks to David Barden for the original article.