Platinum crucibles are widely used in glass melting. However, these crucibles are costly, and involves potential health risks with immersion in hydrofluoric acid (HF) by the cleaning procedure. Furthermore, phosphate contents may cause damage to the platinum crucibles [1]. Alumina crucibles are less costly than platinum crucibles, although they promote inclusions into the glass melt by diffusion [1]. Alumina crucibles are not commonly used for the melting of bioactive glasses due to the suppression effect of Al₂O₃ on Hydroxyapatite (HA) formation [2]. Nonetheless, it has been shown that Al₂O₃ does not impede HA formation and osteosarcoma cell growth was observed on the bioactive glass surface up to 1.5 mol% [2]. Moreover, Al₂O₃ retards the high crystallization ability of silicate-based bioactive glasses [3].

Magnesium is the fourth most prevalent element in the human body and is well-known for stimulating osteoblast growth [4]. Furthermore, since Mg²⁺ ions have a higher field strength than Ca²⁺ ions, MgO reduces the crystallization tendency of bioactive glasses, and SEM images indicate that a half-substitution of MgO/CaO for Bioglass® 45S5 resulted in highly sintered particles [5].

In this work, the effect of alumina diffusion was investigated in terms of the structure-bioactivity relationship of the obtained bioactive glass. Raman, MAS-NMR, and DSC techniques were employed for this objective. Bioactivity tests were evaluated in simulated body fluid (SBF) at 37 °C for predefined periods. HA formation was investigated with XRD, SEM and FTIR. The dissolution of glasses is also examined with ion release by ion-coupled plasma (ICP).

Acknowledgment
This study was carried out in the framework of the project FunGlass that has received funding from the European Union´s Horizon 2020 research and innovation programme under grant agreement No 739566. This study is supported by the Slovak Grant Agency for Science under the grants and VEGA 2/0091/20 and by the Research and Development Support Agency APVV-21-0016.

References
[1] N. Sawangboon et al.; International Journal of Applied Glass Science, 2020, 11(1), 46-57.
[2] H. Tripathi, C. Rath, A. S. Kumar, P. P. Manna, S. P. Singh; Materials Science and Engineering C, 2019, 94, 279-290.
[3] K. Dimitriadis, D. U. Tulyaganov, S. Agathopoulos; Journal of the European Ceramic Society, 2021, 41(1), 929-940.
[4] I. Cacciotti, A. Bianco, M. Lombardi, L. Montanaro: Journal of the European Ceramic Society, 2009, 29(14), 2969-2978.
[5] R. Wetzel, M. Blochberger, F.Scheffler, L. Hupa, D.S. Brauer; Scientific Reports, 2020, 10(1), 1-10.