Controlled Release of Oxygen from Calcium Peroxide in a Weak Acidic Condition by Stabilized Amorphous Calcium...

Calcium peroxide (CaO₂) has recently attracted much attention as an oxygen-releasing biomaterial for tissue engineering. CaO₂ has also been used in cancer therapies, such as photodynamic therapy. However, the uncontrollability of oxygen release after immersion in water is a challenge. Furthermore, the nanoscale surface chemistry of CaO₂ on the oxygen release properties under cell culture conditions has not been taken into account in these applications. Herein, we report the stabilized amorphous calcium carbonate (ACC) nanocoating on CaO₂ in a cell culture medium, which suppressed the reaction between CaO₂ and water. Stabilized ACC was produced by the reaction between calcium hydroxide (Ca(OH)₂) derived from CaO₂ and sodium hydrogen carbonate (NaHCO₃) including sodium dihydrogen phosphate (NaH₂PO₄) in a cell culture medium. In contrast, surface modification of CaO₂ by calcium carbonate crystals was difficult due to the crystallization process via dissolution-reprecipitation. Strikingly, ACC-CaO₂ showed pH-dependent oxygen release in a cell culture medium probably because of the dissolution of ACC under weak acidic condition. Since the environments in ischemic tissue and cancer are weakly acidic, our findings should be important for understanding and designing properties related to biomaterials and drugs using CaO₂.