DIFFERENTIAL-EFFECTS OF SERUM, INSULIN-LIKE GROWTH-FACTOR-I, AND FIBROBLAST GROWTH FACTOR-II ON THE MAINTENANCE OF CARTILAGE PHYSICAL-PROPERTIES DURING LONG-TERM CULTURE

The effects of fetal bovine serum, insulin-like growth factor-I, and f ibroblast growth factor-2 on the regulation of the functional physical properties of adult bovine cartilage explants during an incubation pe riod of 18-20 days was determined, and the relationship between the me asured functional properties of the cartilage and the tissue compositi on was assessed. Cartilage disks were tested in the uniaxial radially confined configuration by the application of low amplitude oscillatory displacement and measurement of the resultant load and streaming pote ntial. For the control cartilage terminated just after explant, the mo dulus was 0.39 +/- 0.28 MPa, the open circuit hydraulic permeability w as 2.0 +/- 1.0 x 10(-15) m(2)/(Pa . sec), and the electrokinetic (stre aming potential) coefficient was -2.3 +/- 0.6 mV/MPa. Incubation of ca rtilage in medium supplemented with serum or insulin-like growth facto r-I resulted in maintenance of the modulus and electrokinetic coeffici ent, whereas incubation in basal medium or medium supplemented with fi broblast growth factor-2 led to a marked decrease from control values in the modulus and the amplitude of the electrokinetic coefficient. Al l of the culture conditions examined resulted in an increase in permea bility that was not statistically significant. The variation in the el ectromechanical properties of all the cartilage samples tested was rel ated to the density of tissue proteoglycan and collagen (hydroxyprolin e). The modulus was correlated with both the density of tissue proteog lycan (+0.014 MPa/[mg/ml]) and the density of tissue hydroxyproline (0.008 MPa/[mg/ml]). The electrokinetic coefficient was also correlated with the density of proteoglycan (-0.080 [mV/MPa]/[mg/ml]) and the de nsity of hydroxyproline (+0.064 [mV/MPa]/[mg/ml]). These data indicate that the regulation of chondrocyte matrix metabolism by growth factor s can significantly affect the physical properties and function of car tilage.