Solute Transport in Porous Medium Under External Loads Available to Purchase

Dynamic compression of soft tissues affects tissue mechanical properties and metabolic activities. The effect is attributed, in part, to the movement of water and solutes in extracellular matrix, which alters the mechanical (e.g. fluid shear stress) and chemical (e.g. growth factors, cytokines and hormones) microenvironments for cells in the tissue. To quantify contributions of external dynamic loads on solute transport in extracellular matrix, we have applied a poroelastic theory to calculate the deformation of the matrix and the movement of the fluid. In the simplified two-dimensional model, the solid phase represented the matrix of collagens and proteoglycans and the liquid phase represented the interstitial fluid. Deformable matrix embedded with cells was immersed in a solution inside a well with rigid, impermeable walls. On top of the matrix, solution with known solute concentration existed. Solute moved into the matrix and was consumed by cells. Mechanical cyclic loads were applied over a central area on the top surface of the matrix, causing its deformation and extracellular fluid movement. Resulting cell density in the matrix changed with the time during the loading cycle and it varied with the location in the matrix as well. Movement of the extracellular fluid coupled with solute diffusion contributed to the overall solute transport in the matrix. Effects of different loading frequencies and amplitudes were investigated. Different sized molecules were also considered in the study. Results from the model confirmed experimental findings that cyclic loads facilitated solute transport in soft tissues. The effect was more significant for large sized molecules. Special attention was given to regions of the matrix where cells would initially remain metabolically inactive due to lower than the critical value of the solute concentration. Quantitative analysis of solute concentration distribution in the matrix made it possible to predict regions where cells became activated by the improved solute supply. The fact that more cells in tissues became metabolically active under dynamic loads exemplified most directly the effect of external dynamic loads on solute transport in soft tissues.