EUROMOLD, a big manufacturing trade fair held in Frankfurt from November 29th to December 2nd, was—as might be expected—full of machines and robots demonstrating their ability to cut, bend, weld and bash all sorts of objects into shape. But in one of the halls the scene was very different. It was here that 300 or so exhibitors working in three-dimensional printing (or “additive manufacturing” as they prefer to call it) were gathered. Some of their 3D printers were the size of cars; others were desktop models. All worked, though, by building products up layer by layer from powered metal, droplets of plastic or whatever was the appropriate material.

The range of those products was as unusual as the way they were made: an exhaust manifold; an artificial leg; an aircraft door-hinge; dozens of shoes; even entire dresses can be fashioned this way. Many of these printed items look strikingly different from their conventional counterparts. They are more elegant, less clunky and have flowing lines. The result, shown off on plinths and in display cases, was more like an art gallery than an industrial exhibition.

Additive manufacturing, then, is changing not only how things are made, but what is made. In particular, many of the objects on display had an organic look to them. That is no accident. In some cases, designers have deliberately copied nature. In others, they have started from first principles, drawn conclusions (usually aided by clever software), and found that nature got there first. And in some, the decisions have been aesthetic—presumably reflecting an evolved preference in the human psyche for objects that look natural.

Growing goods

An excellent example of deliberately copying nature is an artificial hip made by Materialise, a Belgian firm. Not only do real bones have curves that mass production would find it impossible to reproduce, they are also slightly different from one individual to another. Additive manufacturing has no difficulty with such bespoke products. Each hip can be crafted precisely for the intended patient. All that is required is a slight tweak of the software that controls the printer. Even better, the technique can do something that not even a human craftsman could manage: it can copy in the titanium of which the implant is made, the fine, lattice-like internal structure of natural bone. This makes the implant lighter, without loss of strength. It also lets it integrate easily with the patient's actual bone.

Similarly, researchers at the Massachusetts Institute of Technology, led by Neri Oxman, have found that you cannot beat the basic design of a plant stem—a bundle of vertical filaments of different densities—when it comes to making a structure that is both light and able to support a heavy load. They have used that insight to print a load-bearing column constructed from filaments of concrete.

That an artificial hip looks like a natural one, and that a concrete “tree” behaves like a real one, is, of course the whole point of the exercise. Other additive manufacturers, though, have found that they are copying nature by accident—natural selection having arrived at a similar way of solving the problem first.

A British firm called Within Technologies, for example, makes heat exchangers. These need to pack a large surface area into a small space—an ideal task for additive manufacturing. Freed from the need to worry about how to make what they design, the company's engineers have found that the optimum shape resembles a fish gill. Exchanging heat is a similar process to exchanging oxygen and carbon dioxide.

The nervous systems of animals, too, turn out to be similar to things made possible by additive manufacturing. Lionel Dean, the head of a firm called FutureFactories, has designed a car mirror that includes channels which carry the electrical signals that operate its adjustment and folding mechanisms. The result resembles the nerves in an arm, which are also carried in channels (the joints in the mirror behave like the arm itself). At the moment, Mr Dean cannot find suitable conductive materials with which to print his new mirror. The rate of progress in the field suggests, though, that he will not have to wait long.

The flow of hydraulic fluid in a gearbox also turns out to be surprisingly biological. Ian Halliday, the boss of 3T RPD, a British engineering firm, says that by making a gearbox's hydraulics using additive manufacturing, its weight can be reduced by 30%. These days, that is par for the additive-manufacturing course. What is novel is that the box will also change gear faster, because the pathways through which the fluid flows can be made smoother. Like blood, hydraulic fluid flows better through smooth arteries than ones filled with obstructions and sharp corners.

Some designs even resemble sub-cellular structures. At Southampton University in Britain, researchers have printed an unmanned aircraft from laser-sintered nylon (sintering is a way of making objects by heating powders). This drone, which has a wingspan of 1.2 metres, incorporates a geodetic structure—a lattice-like frame developed in the 1930s by Barnes Wallis, a British aeronautical engineer. Though Wallis could not have known this at the time, his geodetic approach is similar in concept to the “cytoskeleton” of fibrous proteins that holds a cell in shape. While notably strong and light, geodetic structures are slow and costly to make by traditional methods—but not by 3D printing.

The hole is greater than the parts

That ability to create light, strong structures which have complex internal shapes may well turn out to be additive manufacturing's killer app. The layering of powders or droplets that are then sintered into solidity, or cured with heat or ultraviolet light, allows spaces to be left inside the product. And if such a space would otherwise collapse, it can be filled with a powder that remains intact during curing and is then washed out or blown away. Even moving parts, like clock mechanisms, have thus been made in one go in a 3D printer.

3D printing can even mix materials that could not be compounded with traditional methods. According to David Leigh, the president of Harvest Technologies, a Texan firm that uses additive manufacturing, it is now possible to produce things that are rubberlike at one end and stiff at the other. A camera body, for instance, could be made in one piece but be soft where it is gripped and hard where the lens and the operating mechanism are installed.

All of which is very useful and practical. But additive manufacturing can also be fun. Ping Fu, the boss of Geomagic, an American firm that specialises in 3D design software, prints her own shoes. Their elegant, twisting shapes make them look intriguingly plantlike. A BlackBerry case which Mr Dean has made looks as if it has been constructed from linguini. His lamps, chairs and jewellery borrow heavily from natural history. And Iris van Herpen, a Dutch fashion designer, has (see picture) taken 3D printing to the catwalks, with striking clothing collections that reflect natural shapes and yet seem to come from a future age.