The knee joint is one of the most used and stressed joints and its destruction is irreversible. Duke University researchers have developed a super-strong synthetic hydrogel Composite that could help replace defective cartilage in high-stress joints such as those in the knees.
As any athlete knows, the knee is one of the most stressed joints in the body. Keep in mind that every impact on the ground during a race puts stress on the knee equal to three to eight times the body weight. But after repeated trauma, overweight, or age, the knee cartilage wears down and no longer acts as a shock absorber. In the US more than 790,000 knee prosthetics are implanted every year. However, these metal prostheses have a limited life span (maximum 20 years) and often lead to reduced mobility. For several years, researchers have therefore been trying to develop hydrogels that can replace the joint. This is a difficult objective, as the gel must be strong enough to support the body weight and flexible and lubricated enough to act as a shock absorber. The researchers at Duke University in North Carolina were able to combine precisely these a priori opposite qualities.
Stretched 100,000 times without bending or tearing
“A disc the size of a coin, although it consists of 60% water, can carry a weight of 100 pounds,” say Feichen Yang and colleagues in his article on Advanced Functional Materials. In tests, the disc could be stretched 100,000 times without deforming or tearing, a mechanical resistance comparable to the titanium prostheses currently in use. In addition, it is extremely wear-resistant and non-toxic to surrounding cells, the university reports.
A network of interlaced polymers
The secret of this new hydrogel, which resembles a kind of gelatinous disc, lies in its structure. It consists of two networks of interlaced polymer wires, one of which is highly extensible in the form of “spaghetti”, while the other is more rigid in the form of “basket” and has negative charges that go through it. The former gives the material its strength, while the latter serves to resist compression as the negative charges repel each other. This is reinforced by a third web of cellulose fibers that reinforce the structure and prevent it from tearing when stretched. “It is this combination of three components that makes the structure flexible and rigid,” says Feichen Yang, the lead author of the study.
However, it will take at least three years before these prostheses are available for the new generation, the authors warn. The authors will perform tests on sheep to verify the feasibility of their concept.