US researchers have used the material Kevlar to make synthetic cartilage that is as strong as real cartilage. It could help people with joint problems or who have just undergone joint surgery get back on their feet faster.
No material as strong as the cartilage in our bodies had been found until now. Researchers at the University of Michigan, who collaborated with Jiangan University, now think they have developed a material that can meet this requirement. To do so, they used the polymer Kevlar, which belongs to the aramids. Kevlar is used in bullet-proof vests, among other things, and is therefore a very strong material. It forms the basis for the hydrogel, Kevlartilate, developed by researchers at the University of Michigan. It seems that this material can withstand as much pressure as real cartilage.
Water
In natural cartilage, the network of proteins and other biomolecules gets its strength by resisting the flow of water in its chambers. The pressure of the water reconfigures the network, allowing it to deform without breaking. Water is released in the process and the network recovers by absorbing water later. This mechanism enables joints that receive a lot of pressure, such as knees, to resist.
'We know that we are composed mainly of water - this is true of all life - and yet our bodies have a lot of structural stability,' says Nicholas Kotov, the person who led the study. 'Understanding cartilage well means understanding how life forms can combine features that sometimes don't seem to go together.'
Right combination
Existing variations of synthetic cartilage - already undergoing clinical trials - consist, on the one hand, of materials that cannot find the unlikely combination between strength and water content and, on the other hand, synthetic materials that do not contain enough water to transport the nutrients needed by cells, Kortov argues. Therefore, they cannot be implanted in the body.
Hydrogels - which can absorb water in a network of long, flexible molecules - can be designed with enough water to support the growth of chondrocyte cells that strengthen natural cartilage. However, those hydrogels are not strong enough and cannot handle nearly as much pressure as real cartilage.
The Kevlartilage (from Kevlar and cartilage) that the scientists developed consists of a mix of Kevlar nanofibres and polyvinyl alcohol (PVA). It uses the same mechanism as natural cartilage; releasing water under pressure and later recovering by absorbing water like a sponge. The aramid nanofibres build the framework of the material, while the PVA stores water in the network when the material is subjected to stretching or compression. Even versions of the material consisting of 92 per cent water were comparable to the strength of natural cartilage, while the 70 per cent water-containing version was found to have the same resilience as rubber.
Patent
The Kevlar fibres and PVA are not harmful to surrounding cells. Therefore, researchers think this cartilage is a suitable implant in the deeper areas of the knee. Lead researcher Nicholas Kotov even hopes for a hybrid form of the cartilage, when the natural cartilage cells will settle into the artificial network.
The scientists plan to patent their technological and seemingly groundbreaking idea. They are also looking for partners to market the artificial cartilage.
By: Kelly Bakker
Source: University of Michigan/Look
Photo: Joseph Xu, Michigan Engineering
