Chemical snapshots could lead to better engineered cartilage

Normal healthy articular cartilage

Taking "chemical photographs" of the cartilage between joints and comparing it to engineered versions could lead to better implants, say researchers.

Articular cartilage is the smooth, white tissue that covers the ends of bones where they come together to form joints, allowing the bones to glide over each other with little friction. In the UK, 8.75 million people suffer osteoarthritis, which is associated with damage to their articular cartilage leading to a range of treatments including joint replacements.

In regenerative medicine, scientists are exploring ways of growing cartilage-like material in the lab, which could replace damaged real cartilage. However, researchers have so far not been able to successfully mimic the complex structure of natural articular cartilage in the lab. Researchers in Professor Molly Stevens’ group at Imperial College London have been growing cartilage-like material using cells seeded onto scaffolds made from a biologically compatible material.

Now, this team is using Raman spectroscopy, a form of biochemical analysis using the properties of light, to compare how close their engineered cartilage is to the real thing. This could ultimately help scientists to design improvements to enable it to act more like real cartilage, and make implants more functional for patients in the future.

Raman spectroscopy involves using lasers to image the structural and chemical composition of samples at the molecular level. The team compared ten natural articular cartilage samples with eighteen engineered cartilage samples. They were able to accurately map human cartilage, and they compared it to the engineered cartilage at various stages while it is being grown in the lab.

Raman spectroscopy also has other advantages over standard techniques such as histology - the study of tissue at the microscopic level. Histology requires more time to carry out an analysis, and is less accurate, compared to Raman spectroscopy.

Dr Jean-Philippe St-Pierre, co-author of the study from the Department of Materials at Imperial College London, said: “Using Raman spectroscopy is like taking a complex chemical photo of a sample. It means we can analyse a sample and get a deep understanding of its makeup. This approach has great potential in regenerative medicine because it means we can learn more about real tissue like cartilage and compare it to our engineered samples. Ultimately, we want to create the perfect conditions in the lab to enable us to engineer more life-like implants.”

In the study, the team’s use of Raman spectroscopy gave in-depth insights into human articular cartilage. Articular cartilage has previously been classified as having three distinct zones, but the team were able to image at least six different layers using Raman spectroscopy. They mapped the distribution throughout the layers of the three main components in human cartilage: water, a group of sugars called glycosaminoglycan, and collagen. They were also able to image how the collagen fibres were orientated, which is important for understanding cartilage’s mechanical properties.

In the engineered cartilage, they used Raman spectroscopy to determine at very high resolutions the chemical composition of each engineered sample. They looked at important indicators during the growth of the engineered cartilage samples such as the amount of collagen and water compared to the real samples, which indicate how closely it mimics real cartilage.

The next step will see the team using Raman spectroscopy to systematically evaluate the conditions in the lab that can influence the growth of articular cartilage. This will lead them to identifying the settings that improve conditions for engineering tissue so that it more accurately mimics the structure of real cartilage.

The research is published today in the journal ACS Central Science and funded from the UK Regenerative Medicine Platform, and the Wellcome Trust.