Ca, P‐rich layer formed on high‐strength bioactive glass‐ceramic A‐W

TLDR

Glass‑ceramic A‑W, composed of crystalline apatite and wollastonite in a MgO‑CaO‑SiO₂ glassy matrix, exhibits high bioactivity and mechanical strength, unlike other ceramics with similar crystalline phases in different glassy matrices. The authors aimed to investigate the bone‑bonding mechanism of this glass‑ceramic by analyzing surface structural changes after exposure to simulated body fluid. They used a simulated body fluid with ion concentrations close to human plasma and examined surface changes with thin‑film X‑ray diffraction and other conventional techniques. The study showed that only bioactive glass‑ceramics form a Ca‑P‑rich carbonate‑containing hydroxyapatite layer on their surface in simulated body fluid, a feature absent in non‑bioactive ceramics, and that this surface apatite layer—common to Bioglass‑type glasses—is the essential condition for bone bonding, allowing in‑vitro bioactivity assessment by observing its formation.

Abstract

Abstract Glass‐ceramic A‐W, containing crystalline apatite and wollastonite in a MgOCaOSiO 2 glassy matrix shows high bioactivity as well as high mechanical strength, but other ceramics containing the same kinds of crystalline phases in different glassy matrices do not show the same bioactivity. In order to investigate the bone‐bonding mechanism of this type of glass‐ceramic, surface structural changes of the glass‐ceramics after exposure to simulated body fluid were analyzed with various techniques. A solution with ion concentrations which are almost equal to those of the human blood plasma was used as the simulated body fluid, instead of Tris‐buffer solution hitherto used. For analyzing the surface structural changes, thin‐film x‐ray diffraction was used in addition to conventional techniques. It was found that a bioactive glass‐ceramic forms a Ca, P‐rich layer on its surface in the fluid but nonbioactive ones do not, and that the Ca, P‐rich layer consists of carbonate‐containing hydroxyapatite of small crystallites and/or defective structure. These findings were common to those of Bioglass‐type glasses. So, we conclude that the essential condition for glass and glass‐ceramic to bond to bone is the formation of the surface apatite layer in the body environment but it is not essential to contain apatite within the material. Bioactivity of glass and glass‐ceramic can be evaluated in vitro by examining the formation of the surface apatite layer in the simulated body fluid described above.