Solute transport in cartilage undergoing cyclic deformation

There are no blood vessels in cartilage to transport nutrients and growth factors to chondrocytes dispersed throughout the cartilage matrix. Insulin-like growth factor-I (IGF-I) is a large molecule with an important role in cartilage growth and metabolism, however, it first must reach the chondrocytes to exert its effect. While diffusion of IGF-I through cartilage is possible, it has been speculated that cyclic loading can enhance the rate of solute transport within cartilage. To better understand this process, here a one-dimensional axisymmetric mathematical model is developed to examine the transport of solutes through a cylindrical plug of cartilage undergoing cyclic axial deformation in the range of 10− 3–1 Hz. This study has revealed the role of timescales in interpreting transport results in cartilage. It is shown that dynamic strains can either enhance or inhibit IGF-I transport at small timescales ( < 20 min after onset of loading), depending on loading frequency. However, on longer timescales it is found that dynamic loading has negligible effect on IGF-I transport. Most importantly, in all cases examined the steady state IGF-I concentration did not exceed the fixed boundary value, in contrast to the predictions of Mauk et al. (2003 Mauck, R.L., Hung, C.T. and Ateshian, G.A. 2003. Modeling of neutral solute transport in a dynamically loaded porous permeable gel: implications for articular cartilage biosynthesis and tissue engineering. J. Biomech. Eng., 125: 602–614. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar]).