ULTRASTRUCTURAL-STUDY OF CALVARIA-RELEASED OSTEOBLASTS CULTURED IN CONTACT WITH TITANIUM-BASED SUBSTRATES

Rat calvaria cells obtained by enzymatic digestion were used to invest igate the interaction between osteoblasts and several substrates [poly styrene culture dishes, commercially pure titanium (CP-Ti), and a tita nium alloy (Ti6Al4V)]. To allow investigation of the interfacial area between the cells and the metallic substrates, these materials were re moved by an electrodissolution process. With such samples, a remaining titanium oxide layer was observed in close apposition with the bottom of the cell sheet. This layer was discontinuous, variable in thicknes s, and contained large amounts of carbon but no calcium. Contamination of the cell layer by titanium, due to the electrochemical process, wa s detected by electron energy loss spectrometry. The presence of miner alized matrix was demonstrated in the nodules formed by the cells on e very type of specimen, but was never found in direct contact with the substrates. The thin layer of extracellular material ensuring the link age with the substrates was not mineralized. Matrix-mediated contacts were composed of patches of collagenous material or fibrillar non-orga nized material. Fibronectin was detected on the substrates by fluoresc ence microscopy after mechanical detachment of the cell layer. The abs ence of a mineralized interface appears to be related to the surface p roperties of the substrates, but also to the cell origin. This might r eflect the in vivo case of osteointegration failure, when the tissue i s composed of a layer of non-mineralized connective tissue in contact with smooth materials.