Journal of Thermal Analysis and Calorimetry, Vol. 71 (2003) 927–937 THERMODYNAMICS OF NON-BRIDGING OXYGEN IN SILICA BIO-COMPATIBLE GLASS-CERAMICS Mimetic material for the bone tissue substitution N. Koga 1 , Z. Strnad 2 , J. Šesták 3* and J. Strnad 2 1 Chemistry Laboratory, Department of Science Education, Graduate School of Education, Hiroshima University, 1-1-1 Kagamiyama, Higashi-Hiroshima 739-8524, Japan 2 Laboratory for Glass and Ceramics (LASAK), Papírenská 25, CZ-16000 Praha 6, Czech Republic 3 Institute of Physics of the Academy of Sciences, Cukrovarnicka 10, CZ-16253 Praha and Institute of Interdisciplinary Studies, The West Bohemian University, Husova 17, CZ-30114 Pilsen, Czech Republic Abstract Correlations between the structural properties of Na 2 O–CaO–SiO 2 glasses characterized by the ac- tivity of oxygen ions and the bioactivity were examined by comparing the compositional de- pendence of the structural parameters calculated on the basis of a thermodynamic consideration with that of the bioactivity. A simple model of characterizing the glass structure by considering the bridg- ing and non-bridging oxygen ions was employed as the first step for this purpose. Further detailed thermodynamic analysis on the anionic constitution in the glass was performed and the composi- tional dependences of the relative proportions of bridging, non-bridging and free oxygen ions were calculated. The bioactive region corresponded to the compositional region characterized by the higher relative proportion of non-bridging oxygen ions with co-existing an appreciable concentra- tion of bridging oxygen ions, suggesting a possible important role of the non-bridging oxygen ions on the surface chemical process of bone-like apatite layer formation. Kevwords: bio-compatible, bone-like apatite, glass-ceramics, mimetic material, thermodynamics Introduction Degeneration of a human skeletal system in time results in dysfunction of bones, teeth and joints. Extensive bone defects, left after the removal of tumors, infections or as a result of injuries, are ideally replaced by autogenous bone tissue. As the amount of this material for the patient is limited and the use of allogenic bone is accompanied by biological, mechanical and also sociological difficulties, there is a great need for alternate non-human synthetic sources. Merely four decades ago it was considered inconceivable that a man-made material could bond to living tissues in view of the deep-rooted experience that it would result in a 1388–6150/2003/ $ 20.00 © 2003 A kadémiai Kiadó, Budapest A kadémiai Kiadó, Budapest Kluwer Academic Publishers, Dordrecht * Author for correspondence: E-mail: sestak@fzu.cz