The initial hype surrounding 3-D printing may have started to fade, but researchers using the technique to create living tissue are showing encouraging results.

3-D printing parts of our anatomy is not a new idea. The basic premise: insert the correct cells into a polymer or gel, print them out into a 3-D structure, and then allow the cells to grow into a living entity. If such a feat can be achieved, it could provide a supply of organs for transplant patients and remove the need for donors.

This week, Spanish scientists from Madrid have published research describing new hardware that’s capable of printing functional human skin. The device creates the individual layers of skin, such as the dermis and epidermis, one atop the other. It does that by depositing plasma containing skin cells into precise geometries that allow the cells to flourish.

The researchers claim that the end results will be suitable for both transplantation and lab testing of new products. Initial transplants into mice also suggest that it’s safe, though the synthetic skin has yet to be approved for use in humans. Other organizations, such as L’Oreal, are also attempting to create skin using similar approaches.

But while this success lines up alongside other notable achievements, such as creating blood vessels and even synthetic ovaries for mice, 3-D-printing techniques have yet to yield entire organs for use in humans. That’s largely because printing cells in complex geometries without killing them remains difficult. Because it is flat and neatly layered, skin lends itself to printing—but rendering a heart is rather more difficult.

So just how far away from 3-D-printed human organs are we, exactly? The Economist has just taken a look at the entire bio-printing landscape to establish that. It suggests that recent advances in producing some of the more simple organs mean that the first 3-D-printed livers and kidneys for human transplant could flop out of a device within the next six years.

(Read more: Biofabrication, The Economist, "Microscale 3-D Printing," "3-D-Printed Kidney Parts Just Got Closer to Reality," "Artificial Organs May Finally Get a Blood Supply")