A network of artificial cells that work together to act as an AC/DC converter has been built. Demonstrating that synthetic cells can team up to achieve such feats is a step towards building synthetic tissues to interface biology with electronics, says the team of chemists behind the work.
Synthetic biologists have show they can reprogram living cells to make them produce drug compounds, and are even working towards building cells from scratch to create artificial life.
But that work focuses on only individual cells, says Hagan Bayley at the University of Oxford. He's more interested in making artificial tissue in which individual synthetic cells work together.
Bayley's group, working with colleagues at the University of Massachusetts in Amherst, has made a step towards that goal by connecting together multiple artificial "protocells" so that they share electrical signals.
Like real cells, the protocells are droplets of watery fluid enclosed in an oily membrane, although they lack any proteins or any of the other internal features that make true life.
When two protocells are brought together, the membranes around them fuse on contact to form a double-thickness boundary membrane. They can be stuck together like "liquid Lego", says Bayley.
To transform such groups into electronic devices, the researchers added pores to the double membranes between protocells, using a bacterial toxin that punches holes in the membranes of mammalian cells during an infection.
The pores allow charged ions to flow from one protocell to another if electrodes are connected to the protocells to supply a current. Because those pores only remain open if current flows in one direction, it is possible to use the cells to form electronic circuits. "If you connect the battery one way around the current will flow, but if you switch it around then no current flows – it behaves like a diode."
By connecting four droplets together into a two-by-two square, the team created a more complicated device – a rectifier that converts alternating current into direct current. A single protocell could never perform as a rectifier, says Bayely. "The droplets work together to do something that's greater than the sum of their parts." It's analogous to the way that the individual cells can work together to create biological tissue with unique properties, he says.
Bayley thinks in future the droplet networks could be used as an interface between electronic implants and living tissue, which does not interact well with materials like metal electrodes. "The droplets are made of the same materials as biological life, but they can be connected to electrodes," says Bayley. "They already act as an interface between biology and electronics."
Donald Leo works on protocell networks at Virginia Tech in Blacksburg points out that flowing ions make for much slower connections than electrons moving through conventional wires. But he adds that networking protocells in this way does have potential, particularly at larger scales such as 10,000 or 100,000 droplets: "If we can approach this level of complexity one can take advantage of the functional diversity of proteins to create new 'biological composites' that may exceed the properties of traditional synthetic or natural materials."
Such materials might be used as tissue scaffolds to guide the regrowth of complex organs, or to provide low-power energy sources if they contained the right chemicals in situations in which conventional wiring is not appropriate.