A biomaterial with neuron and muscle properties

Printing of extended droplet network: Time-lapse movie of an extended droplet network being printed in bulk lipid-in-oil solution. The interval between frames is 20 s. Each frame of the video was cropped around the constructed-network for ease of viewing, as the original recording focused on the stationary capillary-tip, whilst the oil-well was moved in relation to the tip during printing. [Video courtesy of Alexander Graham]

In a paper just out in Science, researchers at the University of Oxford in the U.K. describe making materials in three dimensions that can transmit electrical signals and move in ways similar to how neurons and muscles do. The goal is to make biomaterials  compatible with humans for controlled drug release and repair of damaged organs.

Hagan Bayley says the work began as a basic science project. The investigators were using lipid-coated aqueous droplets in a miniaturized platform  to carry out single-channel recordings of membrane channels and pores. “We quickly realized that we could make interesting devices from collections of droplets,” says Bayley. “Our initial efforts were with just a few droplets, less than 10, and in two dimensions.”

To set up droplets in a network in three dimensions, Gabriel Villar, one of the investigators, made a special 3D printer from scratch. Then taking advantage of the well-established fact that oil and water don’t mix, Villar, Bayley and Alex Graham injected aqueous picoliter droplets into an oil bath. The investigators were able to set up tens of thousands of these droplets and remove most of the oil to form a 3D network of droplets connected by single lipid bilayers.

Each droplet can carry its own specific set of chemicals or biochemicals. When the investigators added a membrane protein called staphylococcal alpha-hemolysin, a pore that incorporates into lipid bilayers, a droplet could use the membrane protein to communicate with its neighbors. It did so by allowing an electric current to flow through the membrane proteins. In this manner, the investigators were able to send a rapid electrical signal along a specific path through the droplet network, much like a neuron.

A rectangular printed droplet network spontaneously folding into a circle.
[Image courtesy of Gabriel Villar, Alexander D. Graham and Hagan Bayley (University of Oxford)]

Bayley says that the investigators would like to move onto making larger networks. (The ones described in the paper were on the order of a few hundred micrometers.) They aim to make more intricate patterns of droplets and fill the droplets with more complex solutions.”The basic principles of how this might be achieved are now clear and further progress will just require time and patience,” says Bayley. “Our ultimate goal is to make materials that can replace or enhance living tissues, but which lack the problems associated with the use of living, replicating cells.”