Over 500 million individuals globally suffer from osteoarthritis, with the knee being the joint most often affected. The condition often arises from years of activities like running and jumping that cause the protective cartilage in joints to wear out, leading to the painful rubbing of bone against bone. Surgical interventions to fix or remove damaged knee cartilage are frequent but not always effective, and adults seldom regrow cartilage naturally. Although biomedical engineers have created scaffolds that support cartilage regrowth when implanted, these still necessitate surgery. Now, the cartilage cushioning the joints that have been gradually eroded by a lifetime of activity could be repaired by simply injecting a novel gel.

Researchers at University of Connecticut (Storrs, CT, USA) have developed this injectable gel as a less invasive alternative to surgical implants. The research team’s area of expertise lies in piezoelectric materials, which are substances that generate a low-level electric field when flexed or bent. This mimics the body's own electric fields that help in recruiting stem cells to repair damaged cartilage. The team decided to try this piezoelectric stimulation approach in a gel form that would offer a simpler, injectable solution.

The researchers created the gel using poly-L-lactic acid, a piezoelectric material, which they spun into minute fibers and mixed into a gel. This gel was then injected into the knees of rabbits that had suffered cartilage damage. Ultrasound was applied five times a week, starting two weeks after the injection, to activate the piezoelectric fibers in the gel. Remarkably, the cartilage in the rabbits' knees began to regrow. Approximately two months later, functional cartilage was observed in the animals' knees. This method appears to be as effective as using solid piezoelectric scaffolds but eliminates the need for surgical implantation. The team is now planning to test this technique on larger animals that are more similar to humans.

“A solid scaffold [that encourages regrowth] is really nice. But making it injectable would much reduce patients’ pain and suffering,” said UConn biomedical engineer Thanh Nguyen. 

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