Research into plastic bottles may lead to molecular robots that repair damage to the body, writes Anjana Ahuja IN Tony Ryan's otherwise neat office at Sheffield University, the table is scattered with rubbish. On it lie a crumpled crisp packet and an empty plastic Dr. Pepper bottle. These are not the trappings of a professor too disorganized to find the bin, but essential props for our conversation.

For Ryan, a physical chemist who heads the university chemistry department, wants to know the secrets of how molecules arrange themselves in the shape that they do.

Of course, crisp packets and soft drink bottles don't build themselves, but scientists haven't worked out exactly what goes on when molten plastic is blown into the shape of a tube, and is then encouraged to harden into the shape of a bottle. At some point the molecules behave like a collection of boisterous children who have been told to form orderly queues for their dinner - they mysteriously disentangle and fall into alignment.

This chemical discipline is widespread, but what orchestrates it is not. Stitch two or three different chemicals together and they will relax into distinctive architectures. Some paired substances build themselves into cubes, with the molecules of one enfolding the molecules of the other, some stack themselves into alternating layers. If molecules can organize themselves in this way, what is to stop scientists designing molecular machines that can build themselves ? This possibility is the subject of Ryan's lecture at the Royal Institution on May 30. It is the third event in the Scientists for the New Century series, sponsored by The Times and Novartis.

A wax candle, says Ryan, provides a perfect example of molecular chaos becoming order, known as crystallization. "Imagine pouring molten wax on to a plate," he says. "As it hardens, the molecules go from being tangled to being partly parallel. We want to understand how that crystallization process starts."

Researchers can study what's going on at the level of individual atoms using X-rays - the X-rays diffract, or are deflected by, the atoms, exposing their location. When we meet, Ryan is about to depart for a high -energy X-ray facility in Grenoble, where he will work through the night making X-ray diffraction movies studying crystallization of the kind of plastics used to make bin bags (demand) for the machine means that it is in use 24 hours a day, with other teams working day shifts). He says: "From waking up to going to bed, I'll be in the lab. It's terrible, but you have to do it. And it can be very exciting.

As in the case of the melting wax and natural crystal formations such as quartz, crystallization can happen of its own accord, but industry usually wants to tweak things to achieve, for example, more alignment in one direction than another.

This is the case with a plastic bottle - it doesn't need to be particularly strong in the lengthwise direction (from cap to bottom) but it needs to be sturdy across its cross section, to withstand the cola pressing outwards on its sides. This tweaking is achieved by stretching the molecules in one direction - it creates a template on which the crystals are built. By knowing exactly what happens in the tweaking process, industry can work out whether the same bottle can be manufactured more cheaply. Ryan says : "The aimis to go faster and lighter. If you can use less plastic for the same effect, it saves money."

Industrial collaborates include Dow Chemicals, ICI and Durex - yes, he has studied the condom-making process.

However, there are more profound reasons why self-organizing molecules are intriguing. The first is that proteins, which help the human body to function, are long chains of up to 20 different types of molecule sewn together. Each protein has its constituent molecules linked in a different order, and that sequence determines how the protein folds itself and, therefore, its chemical effect.

"In our bodies, the way these 20 different molecules, or colors, are organized will determine the protein's organization and job," Ryan explains. "We've studied what happens when you put two or three colors together." His molecules, or colors, are simpler than those in the body, but the results are striking. By varying the relative lengths of each color chain, different structures can be formed. A long red chain tied to a short green chain results in the green molecules forming spheres, with each sphere trapped in a red cage. The neighboring cages make a lattice, or "matrix". As the green chain gets longer, the spheres lengthen and become rods inside the matrix. When the length of both chains are equal, the result is alternating layers of red and green.

Ryan explains: "By changing then lengths of the chains, we can dial up all these different structures in the lab. We can write the information into the molecule. We want to build technologies using this control. Take, for example, the green rods inside the red matrix - if the rods could be made conductive and the matrix could be made insulating, we could make a nano wire."

That would be an example of nanotechnology - engineering on the nanoscale, the scale of individual atoms (a nanometer is a billionth of a meter).

The ultimate goal, says Ryan, would be to produce molecules that could not only build themselves, but would be able to respond in a certain environment. This is exactly what happens in your body - a healthy body regulates its own biology. When you fall ill your immune system responds by producing chemicals to combat infection - you don't have to flick a switch to turn your immunity on (when this self regulation falters, diseases such as cancer can result).

Imagine if a molecular machine could show the same autonomy - a nano robot, sometimes called a nanobot, could be engineered to detect when your arteries are becoming furred and leap into action to clear them.

"You could make nanobots that go into the body and repair damage." Says Ryan. "In ten years' time we'll know the nasty protein that sits on the outside of a cancer cell. Then we have to design something that recognizes the cancer site, carries a poisonous drug in a protective coating to the site, and releases it there. It's fascinating stuff - this is about making science fiction come to life."