Preparation of a Pressurization System to Study the Effect of Hydrostatic Pressure on Chondrocyte Cultures

Articular cartilage is a tissue specialized in supporting intermittent compressive loads and in reducing attrition between the articular bony heads. The cartilage cells are constantly exposed to loads that depend on body weight and on muscular tension, and which vary with the posture and physical activity. At rest, the hydrostatic pressure on the articular cartilage is about 2 atm but during normal physical activity it can increase up to 100-200 atm in the space of a msec (9,2). In this condition, the physiological environment of the chondrocytes is altered in a complex fashion. This loading modulates the metabolism of the cartilage, which is an avascular tissue where nutrient transport takes place principally through the synovial liquid and diffusion from the matrix. The increase in hydrostatic pressure in fact brings about a deformation at the tissular and cellular levels, which causes a reduction of cellular volume, an increase in proteoglycan (PG) concentration, and also an increase in cation concentration and in osmolarity. In vitro studies on chondrocyte cultures constitute simplified biological models for the evaluation of cartilagineous metabolism. Such models contain within themselves a series of limits that allow them to reproduce only a small proportion of the physiopathological conditions of the chondrocytes and cartilage. One of the most serious limits is represented by lack of the effects related to movement and articular loading, which have a considerable influence on the inflow and outflow of anabolic and catabolic materials in the matrix structure (9,10). Various pressurization systems have been constructed in the past with the objective of submitting chondrocyte cultures or explants of articular cartilage to cycles of controlled pressure. These devices have permitted the evaluation of the effects of hydrostatic pressure on the metabolism of human articular chondrocytes cultivated in a monolayer and on cartilagineous explants. In this work, we describe a system for the study in vitro of the effects of hydrostatic pressure on chondrocyte cultures with the objective of reproducing in the laboratory, the pressures corresponding to the articulations at rest and during standing, walking, and running. Our pressurization system has special characteristics as compared with those constructed up until now.