Tough as cartilage
Scientists have developed a material that has the properties of cartilage
Maria Krivochenko, Naked Science
Cartilage is a connective tissue strong enough to withstand the weight of a person and the friction from each step, but at the same time soft, elastic and facilitates damage from blows. Unfortunately, the cartilage can wear out over time or tear from injuries and recover very poorly. Until now, the material similar to it was difficult to reproduce in the laboratory: any alternatives could not cope with the load.
Hydrogel has been used to replace cartilage since the 1970s - it is quite slippery, takes root well and does not harm neighboring cells. But for bearing joints, like the knee, it is too weak, so if a person starts having problems with the knee, it has to be changed entirely. Scientists from Duke University believe that they have finally developed a hydrogel that can match the properties of cartilage tissue. The study is published in the journal Advanced Functional Materials (Yang et al., A Synthetic Hydrogel Composite with the Mechanical Behavior and Durability of Cartilage).
The gel consists of three polymer networks: one is woven from elastic threads; the second is made of tougher ones with negative charges along the entire length, the third is made of cellulose fibers. "Only this combination of all three components is simultaneously flexible, rigid and, therefore, strong," says Feihen Yang, co-author of the study. When the material is stretched, the cellulose fibers resist and save it from tearing. When compressed, the negative charges along the rigid polymer chains repel each other and stick to the water, helping it to return to its original shape.
"We decided to make the first hydrogel that has the mechanical properties of cartilage," said Ben Wiley, professor of chemistry. The team showed the possibilities of the new material. Only one disc the size of an American quarter (24.3 mm) held a 45-kilogram kettlebell without losing its shape, but with sprains (stretched it about 100,000 times) it copes as well as porous titanium, which is used for the manufacture of bone implants. Finally, to test its wear resistance, it was rubbed about a million times: it turned out that the material withstands friction like natural cartilage – and is four times better than modern synthetic ones.
The development can help people who have problems with the knee joint and who do not want to agree to its replacement for some reason (this is a complex operation that requires a long recovery, and the queue for it can be waited for years). The leaders of the study, Ben Wiley and Ken Gall, believe that one day they will offer an alternative to the 600 thousand operations performed in the United States every year. Clinical use of the new hydrogel will begin in the best case in a few years, before that it will have to pass tests for its safety. Meanwhile, chemists are planning to create an implant that can be tested on sheep.
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