Knowledge of the local concentration and species of ions released at the bioactive glass particles/biological fluids interface is primordial to the understand of the complex interfacial reactions and physico-chemical properties of bioactive glasses. This work characterises the interface that bioactive glass particles develop after immersion into biological fluids for different delays (1, 2, 4, 28 days). The distribution of silicon, phosphorus, calcium and aluminium varied across bioactive

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... les periphery. After 1 day of immersion into biological fluids, a Si-Al rich layer appeared at the bioactive glass surface. After 2 days, significantly higher concentrations of Ca and P are observed on top of this newly formed Si-Al layer compared to the center of the glass particles. Then, an apatite (Ca-P) layer starts to built up and grows with time after immersion into biological fluids. The Ca/P atomic ratio increases with time from 1 to 1.6. A thick Ca-P rich layer was formed after 28 days. The Ca-P layer appeared to be generated by calcium and phosphate ions diffusing through the Si-Al layer, which contain at least traces of these ions.