Comparison of the early production of extracellular matrix on dense hydroxyapatite and hydroxyapatitecoated titanium in cell and organ culture

In order to investigate the earliest changes at the bone-hydroxyapatite (HA) interface, two materials, dense HA and HA-coated titanium alloy, were investigated for their ability to stimulate production of extracellular matrix both in cell and organ culture. Osteoblast-like cells were obtained from rabbit calvariae after preliminary culture for 3 d and seeded out onto the two materials. When these cells were grown in culture on the dense HA no matrix production was seen with the scanning electron microscope after 4 d, but there did appear to be matrix produced on the rougher surface of the HA coating. In contrast, extracellular matrix production was greatly increased in organ culture where the material was placed on a section of bone, particularly on the HA coating, where it formed an organized layer of collagen within 4 d. These results showed that extracellular matrix production by both osteoblastic cells and in calvarial culture was greater on the HA coatings than dense HA. In addition, organ culture allows the investigation of the earliest changes in the bone-HA interface without having to undertake in vivo implantation studies of such short duration.