Scientists have programmed a 3-D printer to build synthetic networks of water droplets, connected in a way that mimics the cell membranes of living human tissues. 3-D printing has been used to create artificial cells before, but this new biotechnology breakthrough gets even more basic, and more potentially useful.

The new substance is formed by a network of thousands of water droplets enmeshed in a double layer of fat-like lipid molecules, much like the membranes that surround all the cells in the human body, which can last on its own for weeks.

"Conventional 3-D printers aren't up to the job of creating these droplet networks, so we custom built one in our Oxford lab to do it," said study leader Professor Hagan Bayley, of Oxford University's Department of Chemistry, in a statement.

Each water droplet is about 50 microns (one twentieth of a millimeter), about five times larger than the average living cell. The researchers have formed networks of up to 35,000 droplets, and with more resources, they say even more complex networks are possible.

The 3-D printed materials can fold themselves into different shapes, using basic chemical properties of water and lipid molecules. [Credit: Oxford University/G Villar]

The custom 3-D printer was built by Gabriel Villar, a graduate student in Professor Bayley's lab and the lead author of the paper, published in the journal Science this week.

The 3-D printer can program the water droplet networks to fold themselves into all sorts of different shapes after printing, using basic chemical properties of water and lipid molecules. For example, the researchers said in a statement, a muscle-like contraction can fold a flat flower-shaped droplet network into a hollow sphere that would otherwise be difficult to print.

The droplet networks aren't meant to work exactly like human cell tissues, but to carry out some of their functions. The researchers say that the networks can be printed with pores that let molecules pass through, just like real cell membranes, and can even transmit electrical signals like nerve cells.

Since the tissue-like materials contain no genetic material and do not replicate, there's little chance of them being rejected by living tissue, as stem cell transplants sometimes are.

"The printed structures could in principle employ much of the biological machinery that enables the sophisticated behavior of living cells and tissues," said Villar in the team's statement.

The Oxford team expects the 3-D printed droplet networks to lead to groundbreaking biotechnologies, like microscopic drug capsules that dissolve organically, or artificial cell membrane replacements for damaged tissues.