Bubble Formation Control: Fabrication of Centimeter-Sized Tissue-Like Constructs by Catalase-Coated Oxygen-Releasing...

Developing thick three-dimensional (3D) scaffolds remains challenging due to oxygen depletion and limited cell viability. Calcium peroxide (CaO₂)-catalase-based oxygen-releasing biomaterials are a common solution, but the uncontrolled release of oxygen bubbles often leading to structural damages is rarely discussed. Herein, we present a strategy to control the site of bubble formation in an oxygen-releasing hydrogel, by applying a catalase nanocoating to its surface. CaO₂ undergoes hydrolytic decomposition with water, generating hydrogen peroxide (H₂O₂), subsequently converts into O₂ and H₂O. Because H₂O₂ can induce cytotoxicity, direct catalase incorporation into hydrogel systems may accelerate O₂ bubble formation, leading in hydrogel collapse within 1 h of aqueous immersion. In comparison, catalase-coated hydrogels exhibited improved structural stability, showing a 5.9-fold smaller bubble size than hydrogels with mixed catalase after 24 h in ambient air. Under hypoxic conditions (O₂< 0.1%), centimeter-scale constructs containing catalase-coated hydrogels preserved up to 86% viable human fibroblast cells after 5 days of culture, compared with only 47% in non-catalase coated hydrogels. Furthermore, the incorporation of catalase-coated hydrogels promoted cell survival and neurite outgrowth of human neural stem cells cultured in neuronal differentiation conditions under severe hypoxia. These findings suggest the potential of the proposed strategy for oxygen-supportive tissue engineering applications.