MECHANICAL REGULATION OF CARTILAGE BIOSYNTHETIC BEHAVIOR - PHYSICAL STIMULI

The biosynthetic response of calf cartilage disk explants to small-amp litude dynamic compression was studied in radially unconfined compress ion over a wide range of frequencies. The relative importance of oscil latory fluid flow, hydrostatic pressure, streaming potential, and cell deformation in modulating chondrocyte metabolism was explored by quan tifying the frequency dependence and the spatial (radial) distribution of the biosynthetic response within the 3-mm-diameter explant disks. At frequencies greater than 0.001 Hz (cycle/s), dynamic compression in creased biosynthesis of proteoglycans and proteins. While compression at frequencies between 0.002 and 0.01 Hz caused a stimulation of biosy nthesis that was distributed throughout the disk, compression at 0.1 H z caused a stimulation that was confined mainly to the outer radial pe riphery. These distributions were compared to previous estimates of th e radial distribution of physical forces and flows within the matrix. The results suggest that the stimulation of chondrocyte biosynthesis b y dynamic mechanical compression at amplitudes up to 10% (stresses up to 0.5 MPa) is related to changes in fluid flow and/or cell shape rath er than changes in hydrostatic pressure. Since static compression to t he original cut thickness caused a slight decrease in biosynthesis in the center of the disks, we also studied the possible role of limited diffusive transport in the marked inhibition of synthesis seen during large displacement static compression. Experiments in which the surfac e area-to-volume ratio of disks or the concentration of labeling subst rate or serum were varied provided no evidence that limited diffusive transport was responsible for the inhibition of biosynthesis by large displacement static compression. Recovery of biosynthesis from static compression and histological analyses of compressed tissue suggested t hat there was no significant cell damage even during 12 h of 50% stati c compression. (C) 1994 Academic Press, Inc.