Replicating nature’s lubricant
The fluid in our joints is a vital lubricant to keep our bodies moving, just the same as saliva is needed to moisturise and lubricate the mouth. While the mechanism of these fluids has long baffled scientists, Malmö University researchers are making breakthroughs.
Javier Sotres is trying to find the answers and, by extension, a way to make such lubricants by artificial means.
The body's fluid has the same function as, for example, engine oil in a car — allowing the various parts to move without creating too much friction.
"The body's lubricant is much better than anything we can manufacture," he says, referring to how these fluids counteract the friction between two surfaces.
The body's fluid has the same function as, for example, engine oil in a car — allowing the various parts to move without creating too much friction. In a knee joint, it is the joint fluid — known as synovial fluid — that will reduce friction and, consequently, wear on the cartilage. In the mouth it is the saliva that does that job.
“Basically, the fluid consists of water with different biological components. What we want to know is which molecules can help bind water to the surfaces,” says Sotres.
It is known what types of components reduce friction but, according to Sotres, not what happens at the actual lubrication moment — how the fluids work when a joint is subjected to stress, such as horizontal or vertical pressure.
“Does the structure and the order between the molecules change at that point? Understanding that is the key to being able to make artificial lubricants,” the researcher says.
How easily a liquid flows depends on its viscosity. This, in turn, is determined by its composition of molecules. In many cases, however, it is not the viscosity but the structure of the surfaces themselves that is most important for achieving low friction.
Sotres is researching which molecules can work with water and reduce friction. Joint fluid and saliva have different components that help to reduce friction, but also common features. With saliva as a reference, he is investigating which and how many components need to be added in order to make a saliva substitute.
Sotres has developed a prototype for a measuring instrument that, with the help of neutron reflectance, can measure the structure of surface molecules at a given load and frictional force.
Text:Magnus Jando