A mechanical apparatus with microprocessor controlled stress profile for cyclic compression of cultured articular cartilage explants

An apparatus was designed for mechanical compression of cultured articular cartilage explants with a cylindrical plain-ended loading head (diameter 2–5 mm) driven by a stepping motor. A load cell under the culture dish was applied for feedback regulation utilizing a microprocessor-based control unit. The operating programs allowed either continuous or cyclic loading, the latter with adjustable loading/resting ratio. The improvements in the present design compared with previously described apparatuses for similar purposes include: (1) the accurately controlled compression by a load cell and a rapid feedback circuit; (2) the wide range of selectable stresses (25 kPa–12.5 MPa) with both continuous and cyclic loading modes; (3) the ability to handle cycles as short as 1 s with 15 ms peak loading phase. Using a 4s cycle and 0.5 MPa load for 1.5 h resulted in a significantly enhanced incorporation of radiosulphate in cultured bovine articular cartilage explants, suggesting a stimulation of proteoglycan synthesis. Light and scanning electron microscopic examinations revealed a slight depression and superficial alterations in cartilage structure at the impact site following high pressures. We expect that this apparatus will help in revealing how articular cartilage tissue and chondrocytes respond to external mechanical stimuli.