Material stimulates cartilage growth

Northwestern University researchers have designed a unique bioactive nanomaterial that promotes the growth of new cartilage in vivo and without the use of expensive growth factors.

Minimally invasive, the therapy is said to activate bone marrow stem cells and produce natural cartilage in a way that conventional therapy can not.

‘Unlike bone, cartilage does not grow back, and therefore clinical strategies to regenerate this tissue are of great interest,’ said Northwestern’s Samuel I. Stupp, Board of Trustees professor of chemistry, materials science and engineering, and medicine, and director of the Institute for BioNanotechnology in Medicine.

Damaged cartilage can lead to joint pain and loss of physical function and eventually to osteoarthritis, a disorder with an estimated economic impact approaching $65bn (£41bn) in North America alone.

Type II collagen is the major protein in articular cartilage, the smooth, white connective tissue that covers the ends of bones where they come together to form joints.

‘Our material of nanoscopic fibres stimulates stem cells present in bone marrow to produce cartilage containing type II collagen and repair the damaged joint,’ said Ramille N. Shah, assistant professor of materials science and engineering at the McCormick School of Engineering and Applied Science and assistant professor of orthopaedic surgery at the Feinberg School of Medicine.

‘A procedure called microfracture is the most common technique currently used by doctors, but it tends to produce cartilage having predominantly type I collagen, which is more like scar tissue.’

The Northwestern gel is injected as a liquid to the area of the damaged joint, where it then self-assembles and forms a solid. This extracellular matrix binds by molecular design one of the most important growth factors for the repair and regeneration of cartilage. By keeping the growth factor concentrated and localised, the cartilage cells have the opportunity to regenerate.

The researchers implanted their nanofibre gel in an animal model with cartilage defects.

The animals were treated with microfracture, where tiny holes are made in the bone beneath the damaged cartilage to create a new blood supply to stimulate the growth of new cartilage. The researchers tested various combinations: microfracture alone; microfracture and the nanofibre gel with growth factor added; and microfracture and the nanofibre gel without growth factor added.

They found their technique produced better results than the microfracture procedure alone and also found that addition of the expensive growth factor was not required to get the best results.

The matrix only needed to be present for a month to produce cartilage growth. The matrix, based on self-assembling molecules called peptide amphiphiles, biodegrades into nutrients and is replaced by natural cartilage.

The results will be published online this week by the Proceedings of the National Academy of Sciences (PNAS).