Atomic Force Microscopy Investigation on Young’s Modulus of Cartilage for Osteoarthritis Study

Wear occurs between two contacting cartilage surfaces of knee joints, resulting in osteoarthritis (OA), a wear and tear related disease worldwide. Young’s modulus describes the elastic properties of a material. With OA progression, Young’s modulus reveals information about the changes in the elastic behaviour of cartilage which is important to its function. This research used atomic force microscopy to investigate the elastic behaviour of sheep knee cartilage on nanometre scale for OA study. All indentation tests were conducted in a hydrated mode. The results have shown that the Young’s modulus of a healthy joint cartilage ranges from 0.39 to 1.10 MPa and 0.14 to 2.00 MPa for the most severe OA grade. The corresponding indentation depth was 800–1,560 nm for a healthy joint and 420–1,106 nm for a severe OA grade. This study has also revealed that no significant change of the elastic property occurs to early OA. A sharp rise of the Young’s modulus of OA grade 2 indicates that the cartilage is rapidly stiffening in advanced OA. This research has demonstrated that the Young’s modulus measured on a nanometre scale has the potential to be used for monitoring and discriminating early and advanced OA

Nanoscale study of cartilage surfaces using atomic force microscopy

Articulating cartilage wear plays an important role in cartilage degeneration and osteoarthritis (OA) progression. This study investigated the changes of mechanical properties and surface roughness of sheep cartilages with wear progression at a nanometre scale. Young sheep's rear legs were subjected to a series of wear tests to generate worn cartilage samples to simulate the OA progression. Atomic force microscopy (AFM) was used to determine the effective indentation modulus and to measure the surface morphology of moist cartilage surfaces. The study has found that the mean effective indentation modulus values of worn cartilages were lower than that of healthy cartilage as the control sample. A medium-to-strong correlation between the effective indentation modulus values and the OA grades has been found. The relation between surface topography and effective indentation modulus values of the cartilage surfaces with OA progression was weakly correlated. The method established in this study can be implemented to investigate the effective indentation modulus values of clinical osteoarthritic cartilages and to assist in the understanding and assessment of OA