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 (CaO 2 ) 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 CaO 2 microparticles through coating with a hydroxyapatite (HAp) layer (HAp-CaO 2 ) that serves as a diffusion barrier. Strikingly, this coating can be applied by simple immersion of CaO 2 microparticles in phosphate buffer (PB) solution. We demonstrate that gelatin hydrogels with embedded HAp-CaO 2 microparticles release oxygen for 10 days as compared to only 3 days for identical hydrogels including uncoated CaO 2 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.