Individual collagen fibrils of osteoarthritic cartilage are mechanically inferior outside in

Abstract

OBJECTIVE: It was reported in Nature Nanotechnology in 2009 that the disruption of collagen fibrils meshwork of articular cartilage could be detected by atomic force microscopy ahead of proteoglycan loss and cartilage erosion in osteoarthritis. Yet few studies have been done on individual collagen fiber although a very recent study suggested that individual collagen fibril disruption triggered the breakdown of the meshwork in osteoarthritis initiation. METHODS: The fresh specimens of articular cartilage were collected with informed consent from postmenopausal women, who underwent arthroplasty due to the end-stage of osteoarthritis (OA) or hip fracture. The articular cartilage from the patients of hip fracture served as age-match control. The fresh specimens were cryo-sectioned by the layers with 500 μm outside in and put for indentation-type atomic force microscope (AFM). AFM was used to image and locate the collagen fibrils for nanoindentation. The tip of the nanoindentator was 10 nm in diameter and the indentation depth was 20 nm. Twenty indentations were performed for each layer of the specimens under ambient condition. RESULTS: In the control group, the Young's modulus of individual collagen fibril in deep layer was significantly higher (2.6± 0.6 GPa) than that in superficial layer (2.2±0.4 GPa, p<0.05). It was echoed by the larger collagen fibril diameter in deep layer. Yet in OA group, the Young's modulus of individual collagen fibril in deep layer was significantly lower (2.4±0.4 GPa) than that in superficial layer (3.1±0.9 GPa, p<0.01). There was no significant difference between the superficial and deep layer of the remaining OA cartilage in the diameter of individual collagen fibril, which spread in a wide range from 80 nm to 240 nm. CONCLUSIONS: The Young's modulus of individual collagen fibrils of cartilage is compatible with the data previously reported. Our findings firstly addressed that individual collagen fibrils of osteoarthritic cartilage are mechanically inferior outside in. The weakened deep layer of OA cartilage might contribute to the progression of articular cartilage erosion.