Substances: Material Rush Hits Medicine (Part 2)

by Wiebke Heiss / MEDICA.de15/12/2008

„Imagine a pot full of spaghetti“, Ulrich Suter says. The topic is polymers – very large molecules that are made up of the same units, so called monomers. „When one spaghetto stands for a monomer, the whole pot is the polymer“, the professor for macromolecular chemistry explains. Polymers were responsible for changing medicine - it put an end to the century-long sole use of wood and metal instruments, they became one of the most important materials of the 20th century par excellence. This is due to a big advantage they exhibit: These materials can be designed in any possible way - it all just depends on the contents of the pot: Polymers have different properties depending on the kind of monomers used and the length of the chain – that way it is possible to create linear, branched or cross-linked polymers.

Long, longer, the longest:
Polymer chains; © Y. Roiter
and S. Minko

These materials occur everywhere in our life with the most famous example being the plastic bag that is actually made up of the gas ethene bound to each other so many times until it is called polyethylene - the main ingredient of the modern shopping bag. Styrofoam, teflon or nylon are synthetically produced polymers, cellulose, paper, starch or hair are naturally occurring ones.

„There are hardly more versatile substances around than polymers“, Suter, who has been studying the large moelcules his whole life and works at ETH Zurich, raves. They are virtually a neurotic's dream because they can be totally controlled - it is feasible to influence them in order to create any desired property. „They are adjustable – a little harder, a little softer, a bit of another colour, that all is no problem at all“, Suter says. The reason why polymers are so important in medicine and are in use in diagnostics as well as for surgery and in the laboratory.

Implants that disappear into nowhere

Other polymers have the property that they are degradable by the human body over time without leaving toxic substances behind. For example, suture material and bone nails disappear after having fulfilled function. „In future such resorbable materials will be used predominantly during controlled drug release“, Suter explains. In addition also in tissue engineering where they could serve as scaffolds for muscle, fat and connective tissue cells. Rigid scaffolds made of ceramics render good services in order to culture and grow bone graft substitutes, however soft tissue needs soft scaffolds - polymers could solve this problem.

As has been done with cardiac valves. „At the moment heart valves are made of pig tissue or hard artificial material that causes a loud click with every heartbeat“, Suter says. Since the patient almost always feels uncomfortable walking around with a foreign object inside physicians try to use polymers to change this. “We need a degradable substance that is present as long as it takes to build the house“, Suter talks about a polymer similar to a sponge. Heart cells can settle well on such a structure and grow there. The more abundant the tissue becomes the more of the spongy polymer dissolves - until the heart valve out of own body cells is ready.

On top of these properties polymers have the ability the exhibit intelligent behaviour - when the scientist manipulates them accordingly. That results in plastics with shape memory that are able to change when heated up or being illuminated. The idea behind it is to create polymers in such a form that they can turn themselves into any imaginable shape and at the same time memorising their original state. That would enable scientists to program sutures that contracts with feeling and not with forcing maximum pressure upon the tissue as well as suture material that makes a knot under the influence of warm temperatures similar to those created by the body.

- Part 1: Material Rush Hits Medicine
- Part 2. Biosilicates from the Abyss
- Part 3: Transistor at Nanolevel

Part 2: Biosilicates from the Abyss


It is because of a very special polymer why Werner Müller disappears a few hundred meter underneath the chinese sea. The molecular biologist of the University of Mainz in Germany is searching for new materials for medicine – and throws a glance into the sea looking for sponges, soft tissued animals that live on reefs and stones all over the world and filter water to feed.

A sponge: A glassfabric
located in the sea
© Werner Müller

He is interested in their skeletons made of silicium dioxide, the main component of glass. „The animals produce glass being surrounded by cool sea water, spicular structures with thorns, knobs or small globes“, Müller explains. Humans nees very high temperatures and toxic chemicals in order to achieve this - the sponge seems to just use its genes.

And as a matter of fact Müller and his colleagues discovered a sponge protein and on top of that a totally new process in nature: an anorganic polymer - glass - is being created with the help of an organic enzyme. „Nobody ever observed something like this“, Müller says. Now, the enzyme has been patented and the scientists hope to use it for biotechnological applications, for example in order to manufacture biomaterials for the cultivation of bone tissue or for implants made of titanium that will not be recognised by the body as foreign material anymore. The idea is to cover the implant with the sponge enzyme resulting in a sheath of biosilicates that is not going to be recognised and in turn be repelled by the human body's immune system.

Sponges communicate like telephone companies

However, sponges seem to be capable of more: The glas filaments belonging to the skeleton have the same high quality as glass fibres used for telecommunication.

The sientists have observed that the sponges use a certain quality of light, they use their glass fibres as some kind of nano fibre in order to transport just one wavelength and they therefore "hypothesize that sponges communicate with light". If you pinch the animal it flinches – even though it does not have a nervous system. "The stimuli arrive", Müller says. The sponge's glass fibre in terms of an extraordinary nerve tract may provide totally new approaches for research.

Travel to the Moon and back with Nanotubes

The scientific world hoped for totally new approaches also with carbon nanotubes (CNTs). „In theory, a single nanotube possesses so much inert strength that it would be imaginable to stretch a rope from Earth to the Moon in order to get an elevator getting up and down“, Uwe Vohrer says, doctor of the Fraunhofer Institute for Interfacial Engineering and Biotechnology. Visionary ideas boomed when these tiny tubes were discovered about ten years ago.

CNTs exhibit very special properties: They are light, have a special electrical conductivity, are mechanically stable. „We thought that CNTs being incorporated into other materials could render materials with new properties too“, says Vohrer. However, the properties of a sibgle fibre just represents half of reality. That is why the initial euphoria went soon and material scientists now are studying CNTs thoroughly.

This is especially important for medicine since a few years ago everybody thought that these tubes could not be harmful for the body since they are just made up of carbon - just in nanosize. But they may be toxic after all because of their tiny size since they may be capable of penetrating deeply into the body or may be due to contaminants during manufacturing of nanotubes. „Comparing them to toxic asbestos is valid only to a limited extent“, Vohrer explains. „Only CNTs of a very defined length cause irritations in the abdominal cavity of mice.“ None the less, the new materials need to checked carefully before being applied in humans.

Use of CNTs outside the human body is part of Vohrer's and his team's research: They are trying to culture bone marrow cells on bucky paper, ultrathin paper made up of nanotubes, in order to then implant the cells in the body. „We are also working on using CNTs as an artificial muscle in order to move a prostheses outside the body“, Vohrer explains. The theory behind the idea is based upon the tiny tubes behaving similar to human muscle when they move. Therefore, they could theoretically take the muscle part of a hand prosthesis. The problem ist that this only works on a scale of micrometers yet - the fibres are needed on a centimeter scale though.

There are obviously still many technical difficulties. „However, CNTs have a future“, Vohrer is convinced. „They are called one of the important materials of the 21st centuries since there are so many application areas for them.“ If it was not possible to find any within medicine, the CNTs were at least suitabel for other areas - already they are being worked into barrels to prevent them to get an electrical charge so that explosives can be transported safely.

- Part 1: Material Rush Hits Medicine
- Part 2. Biosilicates from the Abyss
- Part 3: Transistor at Nanolevel

Part 3: Transistor at Nanolevel


Also in terms of biosensors research is taking a close look at the nano world. „We need to do that since our current sensors are not sensitive enough“, Janos Vörös explains, professor at the Institute for Biomedical Technology at in Zurich. He hopes that one day it will be possible to diagnose cancer with just a single drop of blood earlier than is being done with CT and MRI at the moment.

That is a nice concept with just one problem: „Cancer markers are not very abundant. They are present in such low concentrations that we need a new technology in order to measure them“, Vörös says. This is when nanowires get into action – tiny wires that are being home in experimental laboratories only. They do not occur in nature, they need to be produced artificially from metall and are a few thousand times thinner than a single hair. They have a very special property though: they work like a transistor that amplifies electrical signals.

Since nanowires are so ectremely thin anything passing by touches upon their surface“, Vörös explains. The energy that arises when an antibody or some other receptor molecule bind to viruses, bacteria or cancer markers is being transformed into digital or electrical signals. This can all take place on a small chip. „In the end, we are trying to develop a portable and handy device that measures these electrical signals“, the researcher says. That would be more convenient and cheaper than having to handle large devices able to read out fluorescent signals on the search for cancer markers.

However, the researchers at ETH thin further: They have ideas such as using the nanowires as implantable sensors for sensing and transmitting telemedical data about the patient's health status one day. Also stents that support coronary blood vessels from the inside could be monitored by nanowires just by integrating the wire that measures the electrical properties that occur when the vessel expands. And since energy as we all know hides in all areas of our bodies nanowires may possibly have a lot of measuring to do in the future.

Wiebke Heiss
MEDICA.de

- Part 1: Material Rush Hits Medicine
- Part 2. Biosilicates from the Abyss
- Part 3: Transistor at Nanolevel