For millions of people with crippling osteoarthritis – caused by the breakdown of cartilage and the subsequent painful rubbing together of bone – a new breakthrough could well be the key to relief.
US bioengineers have invented an ingenious device that appears to regrow cartilage in a damaged knee with every step taken.
The two things that make this invention so promising is its simplicity, and that it draws on how the body naturally heals itself.
A little charge
The device is based on a novel discovery made by the University of Connecticut bioengineers: Mild electrical signals are the key to promoting cartilage growth in the body.
That suggests batteries are required. But no.
The process is self-contained and self-powered via a phenomenon known as ‘Piezoelectric effect’ – where certain materials, usually crystals, give off a small electrical charge when squeezed or otherwise mechanically influenced.
Dr Yang Liu, one of the inventors, and lead author of a paper published in Science, said: “Piezoelectricity is a phenomenon that also exists in the human body. Bone, cartilage, collagen, DNA and various proteins have a piezoelectric response.”
To see a fascinating video explainer of the ‘Piezoelectric effect’ go here.
How the engineers exploited Piezoelectricity
The engineers created a tissue scaffolding – think of it as a platform or bed on which the cartilage would grow – made from nanofibres of poly-l lactic acid (PLLA), a biodegradable polymer often used to stitch up surgical wounds.
It’s these nanofibres in the scaffold that, under pressure, generate piezo-electricity: When they are squeezed they produce a little burst of electrical current.
The scaffold was placed into the knee of a rabbit.
The rabbit was placed on a treadmill and when it began its walking-hopping movement, a weak but steady electrical field was generated.
This encouraged cells to colonise the scaffold and – just as the engineers predicted – the cartilage grew back normally.
The researchers now plan to try the process on a larger animal, one weighing as much as a human.
Why such a big deal
As the engineers explain it: The best treatments available try to replace damaged cartilage with a healthy piece taken from elsewhere in the body or a donor.
“But healthy cartilage is in limited supply. If it’s your own, transplanting it could injure the place it was taken from; if it’s from someone else, your immune system is likely to reject it,” the authors say.
The dream has been to regrow healthy cartilage in the damaged joint itself.
Some researchers have tried “amplifying chemical growth factors to induce the body to grow cartilage on its own; other attempts rely on a bioengineered scaffold to give the body a template for the fresh tissue”.
But neither of these approaches has worked, even in combination.
“The regrown cartilage doesn’t behave like native cartilage. It breaks, under the normal stresses of the joint,” said project leader Dr Thanh Nguyen, an assistant professor in the Departments of Mechanical and Biomedical Engineering.
He said that no outside growth factors or stem cells (which are potentially toxic or risk undesired adverse events) are necessary in the regrowth process, and crucially, “the cartilage that grows is mechanically robust”.
So when can arthritic people sign up for treatment?
Dr Nguyen is taking a cautious approach.
“This is a fascinating result, but we need to test this in a larger animal,” one with a size and weight closer to a human,” he said.
He plans to to observe the animals treated “for at least a year, probably two, to make sure the cartilage is durable”.
He said it would be ideal to test the scaffold in older animals, too.
“Arthritis is normally a disease of old age in humans. Young animals heal more easily than old,” he said.
But if the piezoelectric scaffolding helps older animals heal as well, it truly could be a bioengineering breakthrough.