Cartilage loading

Papachristou DJ, Pirttiniemi P, Kantomaa T, Papavassiliou AG and Basdra EK (2005) JNK/ERK-AP-l/Runx2 induction "paves the way" to cartilage load-ignited chondroblastic differentiation. Histochem. Cell Biol. 124 215-223. 

Papachristou, D. 1., P. Pirttiniemi, T. Kantomaa, A. G. Papavassiliou, and E. K. Basdra. 2005. JNJC/ERK-AP-1 / Runx2 induction paves the way to cartilage load-ignited chondroblastic differentiation. Histochem Cell Biol 124(3-4) 215-23. 

Osteoarthritis is a disease of the load-bearing joints, characterised by gradual erosion of cartilage and deformation of bone. Pain is the main symptom, initially eased by rest, but later analgesics such as aspirin-like drugs are indicated. 

Hydropolymer gel has been considered as a possible candidate for an artificial articular cartilage in artificial joints because it exhibits very low friction when it is in contact with a solid. The origin of such low friction is considered to be associated with the water absorbed in the gel [83-86], some of which is squeezed out from the gel under the load and serves as a lubricant layer between the gel and solid surface, resulting in hydrodynamic lubrication [87, 88]. Although the structural information about the interfacial water is important to understand the role of water for the low frictional properties of hydrogel in contact with a solid and the molecular structure of lubricants other than water at solid/solid interfaces have been investigated theoretically [89-91] and experimentally [92-98], no experimental investigations on water structure at gel/solid interfaces have been carried out due to the lack of an effective experimental technique. 

The latter issue was addressed more recently by Hamilton et al. who developed a trilayer composite consisting of CPP, articular cartilage (CEP), and NP tissue [125]. By sequential seeding of chondrocytes onto the CPP surface followed 2 weeks later by seeding NP cells onto the matrix produced by the chondrocytes, the authors were able to form a tissue composite construct. Although it appeared that the NP cells were able to maintain a rounded morphology, the interfacial shear load required to... 

Here, is the electrical potential and a is the mechanical load. The value for the electrokinetic coefficient ke for bovine cartilage was found to be in the range from -2 to -12 mV MPa-1 [2],... 

In our confined swelling and compression experiment, we also applied a mechanical load to the sample (t = 12.5 h). We measured a streaming potential A = 0.85 0.65 mV. The change in the mechanical load A a equals -0.117 MPa. Thus, the value for the electrokinetic coefficient is —7.3 5.6 mV MPa-1. This was in the same range as measured for bovine cartilage. 

We were able to measure the electrical potential difference over a sample, that was caused by a change in the mechanical load or by a change in the chemical load. When altering only the mechanical load, the measured electrical potential difference was in the same range as reported for bovine cartilage. 

Bassett, C.A.L. and Pawluk, R.J. (1972) Electrical behavior of cartilage during loading. Science 178, 982-983... 

Articular cartilage has to sustain changes of chemical composition of the electrolyte and mechanical loads. Its overall bearing capacity is believed to... 

ECMs contain a variety of cell types (see Table 1.2) such as fibroblasts in the skin, chondrocytes in cartilage, and osteoblasts in bone. The role of these cells is to synthesize and deposit the ECM surrounding the cell and to change the amount and location of the ECM in response to trauma and changes in external loading. For instance, collagen synthesis in these cells is typically up-regulated by the application tensile forces and is down-... 

The most well characterized of the p38 kinases, the final MAPK phosphorelay pathway, is p38a, which is expressed by most cells and regulates the expression of many cytokines. Interleukin 1, IL-1, a product of inflammatory cells, has been implicated in modulating the response to mechanical loading in a number of tissues. IL-1 is a product of inflammatory cells thought to be involved in cartilage destruction in osteoarthritis and in bone resorption associated with total joint implant failure. 

Figure 9.6. Diagram illustrating the pretension present in the superficial zone of articular cartilage. Normal articular cartilage shown at the top is loaded in tension across the surface like a drumhead that is pulled taut over a drum. When a piece of cartilage is cut from the surface, it curls as a result of release of this tension, as shown in the lower diagram. The presence of tension in the superficial zone makes articular cartilage behave like a drumhead, allowing compressive forces applied to the surface at specific points to be distributed across the surface to lower local stresses. The presence of tension on the chondrocytes in the superficial layer may be important to limit inflammation and support reparative processes by stimulating mechanochemical transduction.

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