The functional properties of cartilage (e.g., load bearing and lubrication) depend on the concentration, distribution, structure, and interaction of cartilage constituents. The load bearing behavior is sensitive to both biochemical and microstructural changes occurring in development, diseases, degeneration, and aging. Degradation of the collagen network as well as decrease of the proteoglycan content result in the deterioration of cartilage’s biomechanical properties. To study cartilage behavior, an array of complementary techniques is required. To quantify the effect of hydration on the load bearing properties we developed a micro-osmometer to perform experiments in a practical and rapid manner. This instrument is capable to measure very small changes in the amount of water absorbed by small tissue samples (less than 1 microgram tissue) as a function of the equilibrium activity (vapor pressure) of the surrounding tissue water. We used osmotic pressure measurements to determine the contributions of individual components of ECM (e.g., aggrecan, hyaluronic acid, collagen) to the total tissue swelling pressure. We have developed a method for mapping the local elastic and osmotic properties of cartilage using the Atomic Force Microscope (AFM) together with the tissue micro-osmometer. Many of the impediments that previously hindered the use of AFM to probe inhomogeneous samples, particularly biological tissues, were addressed by our new approach. In conjunction with results obtained from high-resolution scattering measurements, tissue micro-osmometry, and biochemical analysis, this technique allows us to map the spatial variations in the osmotic modulus (Mos) within tissue specimens. Knowledge of the local osmotic properties of cartilage is particularly important, given that Mos determines the compressive resistance of the tissue to external load. The significance of Mos in the biomechanical properties of cartilage will be discussed.

Osmotic and load-bearing properties of cartilage on microscopic and macroscopic levels

2019 Spring National Meeting

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