Cells and Materials


Rat bone marrow cells, capable of forming bonelike tissue, were cultured on three types of plasma sprayed hydroxyapatite that differed in degree of crystallinity from 15%, 43% to 69%. The interface between the mineralized extracellular matrix and the hydroxyapatite was studied with scanning and transmission electron microscopy. At the onset of bone formation, calcium and phosphorous-rich afibrillar globules, with a diameter varying from 0.2 to 0.8 μm, were produced and deposited onto the different substrata. These globules subsequently fused to form a homogeneous layer to which collagen fibres became anchored. Individual globules could be distinguished on the non-degrading 69 % crystalline hydroxyapatite, but were partially fused with the degrading surfaces of 15 % and 43 % crystalline materials. Transmission electron microscopy revealed distinctly different interfacial structures with the various types of hydroxyapatite. A 20 to 60 nm thick, glycosaminoglycan containing electron dense layer was clearly visible on 69 % crystalline hydroxyapatite, but was less well defined on the more amorphous materials. On the latter, a 0.4 to 1 μm wide amorphous zone was regularly seen to which both parallel and oblique aligned collagen fibres were attached . The results of this study show that the crystallinity of plasma sprayed hydroxyapatite is an important parameter which influeces the establishment of the bony interface and may, as a result, have an effect on the bone formation rate and bonding strength between hydroxyapatite and bone tissue.