Bioengineers go retro to build a calculator from living cells.

Scientists in the US have developed a calculator from living cells, using old-fashioned analog programming. Their hope is that the technology could be used in the future to program cells to kill cancer.

Researchers have previously built electronic circuits using living cells. They achieved this by forcing living cells to behave in binary (digital) systems. But this is not energy efficient.

And many cells are required to implement simple functions that transistors, the basic units of electronic circuits which are ten times smaller than a cell and more reliable, can perform.

Instead analog technology, which uses not just two states like digital but many, could be used to make cells do more complex tasks. Rahul Sarpeshkar, of the Massachusetts Institute of Technology, realised that chemical reactions inside a living cell are also analog in nature.