Fabrication of oxygen and calcium releasing microcarriers with different internal structures for bone tissue engineering: Solid filled versus hollow microparticles

The survival of cells in a three-dimensional scaffold until the ingrowth of blood vessels is an important challenge in bone tissue engineering. Oxygen generating biomaterials can provide the required oxygen and prevent hypoxia in a tissue-engineered scaffold. In this study, poly (L-lactic acid) (PLLA) microspheres loaded with synthesized calcium peroxide (CPO) nanoparticles were fabricated using two different methods, which resulted in hollow and solid filled internal structures. Catalase enzyme was grafted onto the microsphere surfaces to accelerate the conversion of hydrogen peroxide (H₂O₂) to oxygen and prevent the accumulation of H₂O₂ and cell damages. CPO loaded PLLA microspheres-graft-catalase could provide dissolved oxygen and calcium ions in release media up to 15 days. The oxygen release profile of solid filled microspheres was more sustained than the hollow structure, and the amount of calcium ions was higher for hollow microspheres due to the high loading content of CPO. MTT assay showed that CPO loaded PLLA microspheres without catalase exhibited a decrease in the cell viability below 75 %, and catalase grafting could prevent cytotoxicity. Human adipose-derived mesenchymal stem cells (hASCs) could adhere to the microsphere surfaces, maintain their morphology, and spread well. Based on these results, CPO loaded PLLA microspheres-graft-catalase, with the ability of cell carrying and controlled release of oxygen and calcium ions, can be a promising injectable cell microcarrier system for regeneration of bone tissue defects.