The Mechanical Properties Of Living Osteoarthritis Chondrocytes By Using Magnetic AC Mode Atomic Force Microscopy

The Mechanical Properties of Living Osteoarthritis Chondrocytes by Using Magnetic AC mode Atomic Force MicroscopyBackground Osteoarthritis (OA) is one of the most common articular diseases, with major clinical symptoms of articular cartilage degeneration and abrasion, and brings on joint pain and dysfunction. Mechanical factor has a close relationship with OA and plays a crucial role in the development of joint degeneration. Mechanical properties of chondrocytes is the foundation and key influence in chondrocyte engineering and cartilage tissue-engineering. The three dimensional culture of seed cells is tightly related to the mechanical behavior of chondrocytes. Our understanding of how chondrocytes responds to force loading and adjusts correspondingly can further reveal the best mechanical circumstance for articular cartilage cell implantation. Traditional cytomechanics research focus upon average mechanical properties of a single cell, and the methods used such as micropipette aspiration are unable to undergo mechanical detection in terms of in vitro live adhered culture cells and can not provide mechanical properties in various parts of living cells. In order to make an in-depth investigation regarding the mechanical properties at various parts of cells and the difference between reaction of local force stimulation, it's required to develop a new instrument of stress loading and biological measurement without damaging the cell. All these basic information obtained will greatly benefit the extensive spread of cultured chondrocytes in vitro and the development and clinical application of tissue-engineered cartilage repair and cells transplantation. Objective Studies on the topography and mechanical properties in different region of living normal and osteoarthritis chondrocytes in vitro by using the novel tapping mode atomic force microscopy (AFM) named magnetic AC mode AFM (MAC mode AFM).Methods The MAC mode AFM was carried out to observe the topographic details and dynamic state of the cultured normal and osteoarthritis human knee joint chondrocytes under the physiological state in vitro. Meantime, the force curve of MAC mode AFM was performed at certain regions to compare the mechanical properties of the nuclear area with its cytoplasm. Analyze the difference of mechanical properties and response of local force loading in different areas of normal and osteoarthritis chondrocytes.Results The high resolution imaging and time-lapse development of the living chondrocytes was successfully acquired by this experimental system. The force curve showed the much higher elasticity of nuclear region comparing with the body region in normal chondrocytes (P＜0.001) and there was no obvious difference of surface viscosity between them (P＞0.05). Either of nuclear and body region of osteoarthritis chondrocytes has a much lower elasticity (P＜0.001) and a lower surface viscosity (P＜0.001) than that of normal chondrocytes.Conclusions By using MAC Mode AFM, we can obtain high-resolution imaging, carry out real-time observation of living cells, and study such mechanical properties at various parts of the cell as elasticity and glutinosity through loading force on partial single cell and portraying change of force curve. Cytoplasmic and nuclear area of living chondrocytes represents different mechanical properties. The mechanical properties of osteoarthritis chondrocytes is obviously distinct with that of normal chondrocytes.