Biosynthetic response of cartilage explants to dynamic compression

The biosynthetic response of calf articular cartilage explants to dynamic compression was examined over a wide range of amplitudes, waveforms, and frequencies. Glycosaminoglycan synthesis was assessed by 35S‐sulfate incorporation, and amino acid uptake and protein synthesis were assessed by 3H‐proline incorporation. Two culture chambers were designed to allow uniaxial radially unconfined compression and mechanical testing of cartilage disks: one chamber was used inside a standard incubator; the other was used with a mechanical spectrometer and allowed load and displacement to be monitored during compression. Dynamic stiffness measurements of 3‐mm diameter disks identified a characteristic frequency [0.001 Hz (cycles/sec)] that separated low‐ and high‐frequency regimes in which different flow and deformation phenomena predominated; e.g., at 0.0001–0.001 Hz, significant fluid was exuded from cartilage disks, whereas at 0.01–1 Hz, hydrostratic pressure increased within disks. At the higher frequencies, oscillatory strains of only ∼1–5% stimulated 3H‐proline and 35S‐sulfate incorporation by ∼20–40%. In contrast, at the lower frequencies (a) compressions of