Hydroxyapatite Nanocoating on Calcium Peroxide Microparticles for Sustained Oxygen Release

In the tissue engineering field, cell death due to oxygen shortage is still a major challenge for the construction and transplantation of three-dimensional (3D) tissues. To address this problem, oxygen-releasing materials have attracted much attention in recent years. Although calcium peroxide (CaO2) is one of the most common oxygen sources for these types of materials, limitations have also been reported concerning the burst release of oxygen after immersion in water. Herein, we introduce a new strategy to delay the oxygen release from CaO2 microparticles through coating with a hydroxyapatite (HAp) layer (HAp-CaO2) that serves as a diffusion barrier. Strikingly, this coating can be applied by simple immersion of CaO2 microparticles in phosphate buffer (PB) solution. We demonstrate that gelatin hydrogels with embedded HAp-CaO2 microparticles release oxygen for 10 days as compared to only 3 days for identical hydrogels including uncoated CaO2 microparticles. In addition, we demonstrate that the sustained oxygen supply from these hydrogels shows a drastic improvement in cell proliferation under hypoxic conditions. Taken together, this study introduces an easy strategy for sustained oxygen release based on inorganic microparticle formation that can be applied to a broad range of biomaterials for the development of oxygen-releasing materials.