HA forming ability of some glass-ceramics of the CaMgSi₂O₆–Ca₅(PO₄)₃F–CaAl₂SiO₆ system

Abstract

A new bioglass-ceramics based on various content of the diopside [CaMgSi₂O₆]–fluorapatite [Ca₅(PO₄)₃F]–Ca-Tschermak's [CaAl₂SiO₆] system with minor additives of (Na₂O, B₂O₃ and TiO₂) were formulated.

The surface reactivity of the glass-ceramic specimens was studied in vitro in Kokubo's simulated body fluid (SBF). EDAX–SEM, and inductively coupled plasma (ICP) emission spectroscopy were used to characterize the glass-ceramic surfaces and the SBF compositional changes. Different bioactivity behaviour could be detected. Some samples showed a high reactivity with the (SBF) solution forming apatite rich layer on their surfaces as indicated from the EDAX–SEM and (ICP) data. However, other samples, which contain high percentage of Ca-Tschermak's component, i.e. rich in Al₂O₃, showed minimum presence or absence of apatite layer, which indicated that moderate or inert bioactive materials were also formed.

The prepared glass-ceramics had hardness, 6925–8055 MPa; thermal expansion coefficients in the 25–700 °C temperature range, 72 × 10⁻⁷ to 105 × 10⁻⁷ °C⁻¹ and density values in the range, 2.78–2.94 g/cm³.

Introduction

Ceramics and glasses are frequently used as biomaterials for the repair of bone tissue. They are popular because of their generally biocompatibility and the ability of certain compositions to encourage the direct deposition of new bone tissue on their surface after implantation into established bone. This latter property is described as bioactivity or osteoconductivity [1]. Interestingly, the bioactivity of this ceramics can be studied in vitro, and the biological apatite layer can be formed when it is soaked in simulated body fluids [2].

A glass-ceramic processing route is an attractive method. It enables the component to form at high temperature in the glassy state, for example by lost wax die-casting, and then converted to the glass-ceramic by a controlled heat treatment [3]. For the in vitro study of the glass-ceramic A/W, Kokubo et al. [4] proposed in 1990 the Tris-buffered simulated body fluid (SBF) with an ion concentration nearly equal to that of human blood plasma. Since, unlike Tris-buffer alone, SBF contains calcium and phosphorous ions, it can be used to study the in vitro bioactivity of a wide variety of materials.

Natural bone and teeth are multiphase materials; their combination of properties probably can be simulated only by multiphase materials. Crystallization of glasses seems to be a very effective way to simulate hard tissues for those applications where elastic modulus mismatch and toughness are not important [5].

It should be mentioned that minerals capable of wide isomorphous substitution in their crystal structure and having the necessary physical and chemical characteristics, such as pyroxenes may form the basis for production of many melt casts and ceramic-like materials [6].

The system Ca₅(PO₄)₃F–CaMgSi₂O₆ provide fundamental knowledge for the development of new kinds of ceramics, glasses and bioglass-ceramics. It is claimed that the Ca₅(PO₄)₃F–CaMgSi₂O₆ glass-ceramic show a combination of high mechanical strength, a good chemical resistance and a good biocompatibility. Such materials are used as artificial implants in orthopedic surgery [7]. Ca-Tschermak's like diopside is a member of pyroxene group has good chemical and mechanical properties [6].

The aim of the present work was to determine the bioactivity behaviour by using (SBF) solution, hardness, thermal expansion and density properties of glass-ceramics based on various content of the stoichiometric compositions of diopside [CaMgSi₂O₆]–fluorapatite [Ca₅(PO₄)₃F]–Ca-Tschermak's [CaAl₂SiO₆] system with minor additions of Na₂O, B₂O₃ and TiO₂ to produce bioglass-ceramic suitable for medical applications.