Characterization of the mineral in calcified articular cartilagenous tissue formed in vitro.

Cartilagenous tissue with mineralized and nonmineralized layers was generated in vitro using bovine chondrocytes isolated from the deep zone of articular cartilage. Mineralization was induced by addition of either beta-glycerophosphate (beta-GP), phosphoethanolamine (PEA), or adenosine triphosphate (ATP). As this tissue might be suitable for use in joint resurfacing, the mineral of the calcified layer was characterized and compared to that present in the in vivo mineralized zone of bovine articular cartilage. Von Kossa staining demonstrated the presence of mineralization in the lower half of the tissue. The calcium content in the tissue varied from 4.9% to 7.8% of dry weight. Electron diffraction demonstrated a pattern consistent with hydroxyapatite. Brightfield transmission electron microscopy showed that the crystals were acicular and when measured under electron diffraction dark field imaging were 16.6 +/- 3.8 (beta-GP), 16.4 +/- 3.8 nm (ATP), and 17.0 +/- 6.3 nm (PEA) in length. The crystals were similar in size (16.0 +/- 5.5 nm) and appearance to the crystals in the in vivo calcified cartilage. This data suggests that the mineralization that occurs in vitro is similar to the in vivo cartilage.