For some time, scientists have been aware that synovial fluid in joints contains a natural substance that helps keep them well lubricated. Now, by mimicking its properties, engineers at Johns Hopkins University in Baltimore, MD, hope to develop a new material that delivers long-lasting lubrication in artificial joints, and other specific spots in the body where surfaces move against each other.
The team writes about the new material, and the potential it offers, in the journal Nature Materials. As well as helping to ease joint pain, other areas of possible use include making contact lenses more comfortable.
The molecule they are investigating is called hyaluronic acid (HA), which exists in several forms in the body where lubrication is needed.
One form of HA reduces inflammation and protects cells from metabolic damage. In the body, HA is bound to the surfaces it protects by a protein. Research shows that in damaged, diseased and aging knees, hips, shoulders and elbows, this protein is no longer able to hold onto HA.
Viscosupplementation is a popular treatment for painful joints and consists of injecting HA into the painful joint. However, if the cause of the pain is the lack of the protein that helps bind HA to the affected surface, then it does not offer long-lasting benefit. The injected HA is soon washed away by the body’s natural cleaning processes.
‘Chemical handle’ holds HA in place
Thus, led by Jennifer H. Elisseeff, a professor at the Wilmer Eye Institute at Johns Hopkins, the team sought to find a way to keep HA in place. They found their answer in molecules known as HA-binding peptides (HABpeps).
The scientists used HABpep as a “chemical handle” to attach HA onto natural and artificial surfaces with the help of another synthetic molecule, polyethylene glycol.
In the lab, they tested the new material in cultured tissue and joint and eye surface tissue in live animals. They found the bound HA did not wash away easily, and it reduced friction as well as when the tissues were immersed in a bath of HA:
“Tissue surfaces treated with the HA-binding system exhibited higher lubricity values, and in vivo were able to retain HA in the articular joint and to bind ocular tissue surfaces,” they note.
HABpep holds HA in place 12 times longer
In another set of experiments, they also tested an HABpep designed to attach to cartilage. They injected rats’ knees first with some HABpep, then with some HA, and found the HA stayed in place 12 times longer than it did in rats that had received only HA injections without HABpep.
The team suggests this shows HABpeps may be a useful addition to viscosupplementation by helping the HA to stay in place longer. They also conclude:
“Biomaterials-mediated strategies that locally bind and concentrate HA could provide physical and biological benefits when used to treat tissue-lubricating dysfunction and to coat medical devices.”
Although it will be some time before such a material is ready for use in humans, the team highlights that theirs is yet another example of where nature has inspired the solution to a medical problem.
Prof. Elisseeff, who is also of the Johns Hopkins University departments of Biomedical Engineering and of Materials Science and Engineering, says:
“What I like about this concept is that we’re mimicking natural functions that are lost using synthetic materials.”
Meanwhile in November 2013, Medical News Today learned how another team of researchers – also inspired by nature – is refining sea coral for use in bone grafts.
Written by Catharine Paddock PhD