How does the lubricating fluid in human joints work? And what material could serve as a substitute for human cartilage in the future? These are some of the topics that biotribologist David Nečas of the Department of Design of the BUT Faculty of Mechanical Engineering deals with. Last year, he managed to receive a prestigious grant from the Japan Society for the Promotion of Science. He spent seven months studying joint cartilage friction in the laboratories of Kyushu University in Japan.

What does biotribology actually do?

It is the science exploring friction, wear and lubrication in biological systems. Thanks to it, we can find out why and under what conditions wear of artificial joint replacements occur. However, it is also used in many other areas. Scientists are dealing with, for example, rubbing action of the eyelid against a contact lens, contact of a toothbrush with gums or challenges related to food processing. Almost all major business that deal with food development are trying to make the consumption of their products pleasant for humans. Therefore, for example, they test on what oil to fry potato chips and for how long so that people do not feel unpleasant scratching in the mouth.

But you specialize in joint tribology...

Yes, at the Department of Tribology at FME we mainly deal with lubrication and wear of artificial hip and knee joints. The number of artificial joints is constantly increasing, because people live longer and are more active. Although the development is constantly moving forward, the problem which remains is that most replacements fail after some time. More than half of the cases are due to the surfaces rubbing against each other. There is a loss of material, the released particles react with the surrounding tissues and inflammatory reactions occur. Eventually, the implant is released from the bone and it is necessary to undergo a new surgical intervention. In elderly people, a replacement hip joint can last up to fifteen years. Those younger and more active may use the replacement only for three years. It is very individual. Therefore, we are trying to find out how to extend the useful life of artificial joint replacements. Scientists have been trying to resolve this for decades. For the most part, they focused only on wear and tear and not on the entire tribological process, which includes friction and lubrication.

What role does lubrication play in the whole process of wear of the artificial joint?

Its role is great. If there is impaired lubrication in the joint, the friction between the joint head and its socket increases during movement. The material is rubbed more and after some time the replacement fails and the patient has to undergo surgery again. At BUT, we were one of the first in the world to look at the lubrication film inside an artificial hip joint. Of course, this must be done on the simulator – to perform such measurements in the human body is not possible. Joint replacements are made of combination of metal or ceramics and plastic. Neither of these materials is transparent, so we have built a simulator that has a joint socket made of transparent plastic. We can see inside and get an insight in how a lubricating layer forms in the joint. We see how strong it is and what substances it consists of. We combine methods of optical interferometry and fluorescence microscopy. The first method was developed at our institute more than twenty years ago. In my dissertation, I dealt with the development of the second method. We found, for example, that hyaluronic acid with phospholipids plays a crucial role in the lubrication process.

Last year you got a grant and went to Japan. What was your research at Kyushu University about?

The project was focused on the study of super-low friction of human cartilage. The aim of Japanese scientists is to develop a material that could replace articular cartilage if necessary. We would like to avoid the need to introduce complete joint replacements. The replacement is inserted into a person when the cartilage is so damaged that there is direct bone contact, and this is extremely painful. However, a complete joint replacement represents, of course, a significant intervention in the patient's life. In order not to have to replace the entire joint, my Japanese colleagues are trying to develop a material that would behave similarly to cartilage. It can provide such low natural friction in the joint that its level corresponds to skating on ice. Therefore, for a healthy person, movement is natural and painless. The biological system of the joint is practically perfect and we are trying to get as close to it as possible.

And did you manage to develop such material?

In Japan, they have been investigating this topic for more than twenty years and have developed several generations of this material. This is the so-called hydrogel, which is based on polyvinyl alcohol. It largely resembles human cartilage. It is soft, has good lubricating characteristics and shows very low friction. But the problem is that it does not withstand the load in the joint and after some time it breaks down during tests on the simulator. We want to continue to work with Kyushu University to develop this material further. Japanese colleagues will send us samples that we will test using our methods. The aim is to find out how the lubricating film between the hydrogel and the articular head is formed. We would like to contribute to reducing the number of complete joint replacements and their reoperations.

How did you enjoy your research work at a Japanese university?

In the beginning, I did not even hope that it would work out. In cooperation with Professor Sawa, we applied for a prestigious grant from the Japan Society for the Promotion of Science and the chances of obtaining it were very slim. Over the past ten years, only about ten scientists from the Czech Republic have been successful, and projects in the field of mechanical engineering are not very supported. In the end, we were successful and I could spend seven months at Kyushu University. It was interesting seeing that the Japanese doctoral students do not teach during their studies devoting themselves to work in the laboratory only. And they are also very responsible, because in case their results were poor, they would take it very personally. This is related to the fact that they pay high amounts for their doctoral studies. Therefore, they try to work in such a way that they will be successful in the future. The people there are very skillful. We have been working with Kyushu University in the field of tribology for six years and I believe we will continue to do so also in the future.