SWELLING AND CURLING BEHAVIORS OF ARTICULAR-CARTILAGE

A new experimental method was developed to quantify parameters of swel ling-induced shape change in articular cartilage. Full-thickness strip s of cartilage were studied in free-swelling tests and the swelling-in duced stretch, curvature, and areal change were measured. In general, swelling-induced stretch and curvature were found to increase in carti lage with decreasing ion concentration, reflecting an increasing tende ncy to swell and ''curl'' at higher swelling pressures. An exception w as observed at the articular surface, which was inextensible for all i onic conditions. The swelling induced residual strain at physiological ionic conditions was estimated from the swelling-induced stretch and found to be tensile and from 3-15 percent. Parameters of swelling were found To vary with sample orientation, reflecting a role for matrix a nisotropy in controlling the swelling-induced residual strains. In add ition, the surface zone was found to be a structurally important eleme nt, which greatly limits swelling of the entire cartilage layer. The f indings of this study provide the first quantitative measures of swell ing-induced residual strain in cartilage ex situ, and may be readily a dapted to studies of cartilage swelling in situ.