Have you ever heard your grandparents complain about their joint pain or perhaps started feeling this chronic pain yourself? The most common cause of joint pain, particularly among the elderly, is the wearing down of the cartilage that cushions the joints. Overuse or repetitive strain on your joints over time can also cause chronic pain.
Joints are where two or more bones meet: for example, your elbows, hips, knees, and fingers. Articular cartilage is a type of tissue that enables smooth movements at these junctions by giving bones a smooth surface to move against. The strength and elasticity of articular cartilage surpass many man-made materials. Just think about your knees—they can support the weight of your body and weather the impacts of your daily movements for decades.
Articular cartilage is extremely important to our movements but vulnerable to damage and disease due to daily wear and tear. According to the Centers for Disease Control and Prevention (CDC), osteoarthritis, a condition characterized by the degeneration of articular cartilage, affects over 32.5 million Americans and occurs most often in the knee joint. Unfortunately, cartilage cannot regenerate or heal by itself. But scientists are developing solutions, such as hydrogels, to replace damaged cartilage in the body.
Above: An example of a hydrogel, which has many uses across fields such as tissue engineering and biomedicine. Image courtesy of Scapa Healthcare.
Hydrogel is a three-dimensional structure made of polymers or long chains of molecules. Hydrogels can absorb and retain water or biofluids—like a sponge—while maintaining their structure. This property is extremely similar to articular cartilage, which is submerged in synovial fluid found in joints. While hydrogels are a promising cartilage substitute, a major challenge is that they are usually fragile. To replace damaged articular cartilage in human knees, hydrogels need to be able to hold the patient’s weight and allow them to move and stretch freely.
Led by Dr. Benjamin Wiley, Scientists at Duke University recently created the first hydrogel with the strength and elasticity of human cartilage. First, the team conducted an in-depth examination of cartilage structure. Articular cartilage is made of a network of collagen fibers, giving it high tensile strength and allowing it to stretch very far without breaking. To mimic this collagen network, researchers implemented a bacterial cellulose network into their new hydrogel, giving it higher tensile strength. Before this research, no other reported hydrogel worked as well as regular cartilage.
Above: The BC-PVA-PAMPS hydrogen easily holds the weight of a 100 lb. kettlebell (C) compared to other hydrogels before and after compression (D). Image courtesy of Yang et al., 2020.
After developing this new variety of hydrogel, scientists performed thirty different mechanical tests, focusing on its compressive and tensile strength. To test compressive strength, the scientists repeatedly squished the hydrogels with varying amounts of weight to mimic environments in the human body. To test tensile strength, the scientists put the hydrogels in a machine to stretch them until the hydrogels broke. After repeating these tests for 100,000 cycles, the researchers concluded that their hydrogel was the first to show the compressive and tensile strength equivalent to articular cartilage. They also found that the hydrogel’s slippery surface was similar to articular cartilage.
While more testing is still needed before this innovative hydrogel can be used for medical treatments, this new creation is a promising solution to replacing damaged cartilage and providing relief to millions who suffer from chronic pain.
Written by Arianna Lee, this article was selected as a winner of our 2024 High School Science Communication Challenge. From Greenville, N.C., Lee is a junior at the North Carolina School of Science and Mathematics. She is passionate about biomedical engineering, robotics, and STEM equity issues in rural areas of the state. She hopes to bridge the gap between biomedical research and product development to turn innovation into life-saving realities. Outside of school, you can find her at robotics and swim practice or enjoying baking and reading.