Abstract 13

Transport of large molecules through articular cartilage subjectED to dynamic load

Bruce Gardiner, David Smith, Peter Pivonka and Alan Grodzinsky

University of Melbourne

Osteoarthritis is a common and often debilitating disorder resulting from disease and injury of articular cartilage. Cartilage has limited ability to repair itself due to a lack of blood vessels to enable nutrient transport. Insulin-like Growth Factor-I (IGF-I) is a large molecule with an important role in cartilage growth and metabolism. Experiments have shown that the anabolic effects of IGF-I may be enhanced by dynamically loading the cartilage. We have developed a mathematical model for the transport of IGF-I through cartilage undergoing dynamic loading. The model is based on mixture theory and as such treats the cartilage as a three phase porous continuum: a solid phase (representing the various collagen and proteoglycans), a fluid phase and a solute phase. It is found that enhanced transport of IGF-I through cartilage can be obtain if the capture, and later release, of IGF-I by IGF-I binding proteins embedded in the cartilage matrix is included in the model, otherwise the rate of diffusion and the steady state concentration of IGF-I in the cartilage is the same as for static cartilage. Interestingly, this result refutes the conclusions draw by previous models (Mauck et al., 2003) that dynamic loading alone (i.e. neglecting IGF-I sources/sink effects) can enhance IGF-I transport.

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