Research inspired by nature – human cartilage; development of a support material. Engineers have developed a new material that mimics human cartilage, the body's shock-absorbing and lubricating system, and could herald the development of a new generation of lightweight bearings. Cartilage is the soft, fibrous tissue found around joints that provides protection from the compressive stress that occurs when walking, running or lifting. It also provides a protective, lubricating layer that allows bones to slide over each other without friction.

Scientists have been trying to create a synthetic material with the properties of cartilage for years, but have had mixed results to date. The research team believes that a cartilage-like material could have widespread use in engineering. Cartilage is a two-phase porous material, meaning it exists in a solid and a liquid phase. It switches to the liquid phase by absorbing a viscous substance produced in joints called synovial fluid. This fluid not only lubricates the joints, but is also retained within the cartilage's porous matrix, providing a hydroelastic cushion against compressive forces. Because cartilage is porous, the synovial fluid eventually drains away, helping to dissipate the energy forces that travel through the body, protecting the joints from wear and tear and damage. At that point, the cartilage returns to its original phase and is ready to repeat the cycle. Dr. Siavash Soltanahmadi, a research fellow at Leeds' School of Mechanical Engineering who led the research, said: "Scientists and engineers have been trying for years to develop a material that has the incredible properties of cartilage.

We have now developed an engineering material that mimics some of the most important properties found in cartilage, and this was only possible because we found a way to translate a solution from nature into technology. Many synthetic materials are used in technology that are soft but cannot withstand high loads with minimal wear, for example in bearings. There is potential in technology for a material that behaves like cartilage.

Previous attempts to develop a synthetic cartilage system have focused on using hydrogels, materials that absorb water. Hydrogels are good at reducing friction, but they don't perform well under compressive forces. One problem is that after compression, the hydrogel takes time to return to its normal shape.

They overcame the problem by creating a synthetic porous material made of a hydrogel embedded in a matrix of polydimethylsiloxane, or PDMS, a silicone-based polymer. The matrix maintains the shape of the hydrogel. In the paper, the scientists report that the load-bearing behavior of the hydrogel in the PDMS matrix was 14 to 19 times greater than that of the hydrogel alone. The equilibrium elastic modulus of the composite was 452 kPa over a strain range of 10 % -30 %, close to the value reported for the tested modulus of cartilage. The hydrogel also had a lubricating layer. The scientists believe that future applications of the new material based on cartilage function would challenge many traditional oil-lubricated engineering systems. Dr. Michael Bryant, an associate professor in the School of Mechanical Engineering who supervised the research, said; “The ability to use water as an effective lubricant has many applications, from energy generation to medical devices. However, this often requires a different approach compared to traditional engineering systems, which often use oil-based lubricants and hard surface coatings. “This project has helped us better understand these requirements and develop new tools to address this need.”

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Summarized by ScienceDaily.com