Combination of reduced oxygen tension and intermittent hydrostatic pressure: a useful tool in articular cartilage tissue engineering

Cartilage cells are normally studied under atmospheric pressure conditions and without loading. However, since cartilage exists in a condition of redu ced oxygen and intermittent hydrostatic pressure we hypothesized lower part ial oxygen pressures (PO2) and different intermittent hydrostatic pressures (IHP) would increase articular chondrocyte proliferation and matrix produc tion and to stabilize chondrocyte phenotype in vitro. Monolayers of adult b ovine articular chondrocytes were cultured under 5% or 21% PO2 in combinati on with IHP (0.2 MPa amplitude, frequencies 5/5 s = 0.1 Hz, 30/2 or 2/30 mi n on/off loading). We measured proliferation (3H-thymidine incorporation) a nd collagen secretion (protein-binding assay, collagen type II-ELISA and im munocytochemical staining of pericellular collagen types I, II and IX). Red uced PO2 stimulated proliferation and collagen type II and IX secretion of chondrocytes in comparison to 21% PO2. Additionally, collagen type I expres sion was delayed by low PO2 indicating a stabilization of the cell phenotyp e. IHP 5/5 s and 30/2 min inhibited proliferation but increased collagen se cretion (pericellular collagen type IX was decreased). IHP 30/2 min delayed first expression of collagen type I. In contrast, IHP 2/30 min increased p roliferation, but lowered collagen expression. All stimulating or inhibitin g effects of PO2 and IHP were additive and vice versa. Reduced PO2 and diff erent settings of IHP increased proliferation, collagen secretion, and phen otype stability of chondrocytes. The oxygen- and IHP-induced effects were a dditive, suggesting that a combination of these parameters might be a usefu l tool in cartilage tissue engineering. (C) 2001 Elsevier Science Ltd. All rights reserved.