The 2022 Kappa Delta Anne Doner Vaughn Award was presented to Lawrence J. Bonassar, PhD, for his research on the microscale mechanics and composition of articular cartilage and their relevance to musculoskeletal disease. The Kappa Delta Awards recognize research in musculoskeletal disease or injury with great potential to advance patient care. These discoveries by Dr. Bonassar and his colleagues will not only aid in disease prevention and identifying therapeutic windows for treatment, but will play a crucial role in determining the key components and structures in diseased tissues to be targeted for tissue preservation, repair, or regeneration.
For many types of arthritis, such as osteoarthritis (OA), damage begins at the articular cartilage, a very thin surface which covers the ends of bones. This process occurs when inflammatory mediators induce the release of enzymes, resulting in degradation of the extracellular collagen and aggrecan networks,i two of the most important constituents responsible for the mechanical properties of cartilage. Aggrecan is the major proteoglycan in articular cartilage, providing the hydrated gel structure that allows the cartilage to bear loads and dissipate energy.
“A striking feature of connective tissues, such as articular cartilage, is their heterogeneity of composition and structure at multiple length scales, which is a concept used in physics to define length or distance determined with the precision of one order of magnitude,” said Dr. Bonassar, the Daljit S. and Elaine Sarkaria professor at the Meinig School of Biomedical Engineering and Sibley School of Mechanical and Aerospace Engineering at Cornell University in New York. “Given the importance of this region, remarkably little is known about the unique mechanical function and biological role in cartilage health and disease. Our research started with a very basic understanding of how cartilage behaves.”
The Critical Role of the Articular Surface
More than 15 years ago, Dr. Bonassar, partnered with Itai Cohen, PhD, professor at Cornell University’s Department of Physics, who studies the behaviors of soft materials, including cartilage. He had already developed microrheology techniques to examine the micromechanics of soft tissues. Microrheology is the study of mechanics (e.g., microviscosity) of complex materials at small length scales.
Drs. Bonassar and Cohen created a testing device that was small enough to fit on a microscope and could capture images at 10-100 milliseconds to observe how the tissue deforms on the length scale/diameter of a human hair. They discovered that the top 100μ (100 microns; a metric unit of measurement where one micron is equivalent to one one-thousandth of a millimeter) of articular cartilage has extremely different mechanical behavior than the rest of the tissue. In fact, it was 10-100 times more compliant (e.g., less stiff or more likely to be deformed).