Three dimensional surface characterization of human cartilages at a micron and nanometre scale

As reported, the pathological changes of osteoarthritis (OA), caused by wear in knee joints, initiate at a nanometre scale. However, very limited study has been done using quantitative techniques to study comprehensive surface morphology information of worn cartilages in three dimensions (3D) and at a nanometre scale. The aim of the study was to develop a technique for numerically characterizing the surface topographies of human cartilages and their changes in the wear process. Clinically collected healthy and osteoarthritic cartilage samples were prepared and then imaged using atomic force microscopy. Both conventional numerical parameters and a group of recently advanced feature parameters were used to characterize and compare dominant topographical features of the healthy and worn cartilage surfaces. 3D measurements of the samples were also conducted at a micrometre scale to compare differences in the surface features revealed at the nano- and micro-metre scale. This study has revealed that early surface alterations can be detected at the nanometre scale, while the micrometre scale surface characterizations provide more comprehensive surface evolution information from the healthy to severe OA condition. The work has also demonstrated a new approach to reveal the surface functional information which cannot be characterized using the conventional surface parameters. The quantitative surface characterization results may be utilised to develop an objective OA assessment method for clinical application and assist in tissue generation process.