INFLUENCE OF CRYSTAL-STRUCTURE ON THE ESTABLISHMENT OF THE BONE-CALCIUM PHOSPHATE INTERFACE IN-VITRO

An in vitro rat bone marrow cell system was used to examine the interf acial ultrastructure established between various calcium phosphates an d mineralized tissue. The investigated calcium phosphates comprised hy droxyapatite (HA), fluorapatite (FA), tricalcium phosphate (TCP), tetr acalcium phosphate (TECP) and magnesium whitlockite (MWL). Both scanni ng and transmission electron microscopy were used to examine the elabo rated interface. The time in which a mineralized extracellular matrix was formed on the various materials differed from 2 weeks on HA, TCP a nd TECP, to 8 weeks on FA. It was only occasionally observed in some a reas on MWL, which might have been due to aluminum impurities in the c oating. With transmission electron microscopy, three distinct interfac ial structures were observed. They differed in the presence or absence of a collagen free, 0.7 to 0.8 mu m wide, amorphous zone and a 20 to 60 nm thick electron dense layer, interposed between the material surf ace and the mineralized extracellular matrix. The electron dense layer was considered to be at least partially caused by protein adsorption, which would precede or concur with biological mineralization events, while the amorphous zone was regarded to represent partial degradation of the calcium phosphate surfaces. The results of this study show tha t plasma sprayed calcium phosphates will display different bone-bondin g and biodegradation properties, depending on their chemical compositi on and crystal structures.