Fabrication of Uniform Casein/CaCO₃ Vaterite Microspheres and Investigation of Its Formation Mechanism

Uniform Casein/CaCO₃ microspheres were fabricated with well tuned properties and the formation mechanism based on the templating effect of casein micelles was proposed. In bone tissue engineering, vaterite microspheres were promising because of the biocompatibility and easy fabrication. Here Casein/CaCO₃ microspheres were precipitated by mixing CaCl₂ and Na₂CO₃ solutions under stirring in the presence of casein. All samples were mainly in vaterite, composed of aggregates of nanosized crystals. With the increase of casein concentration, the amount of calcite and microsphere size decreased while the loading content of casein increased, suggesting that casein induced the formation of vaterite and also stabilized the crystal phase. The formation mechanism was further investigated. With the increase of CaCl₂ amount, the size of the forming microspheres increased while the zeta potential was stabilized, the polycrystalline nature was shown, and the presence of Ca inside microspheres was confirmed. Hence, the formation mechanism based on casein micelles which demonstrated the template effect was proposed. Casein/CaCO₃ microspheres enhanced the deposition of hydroxyapatite crystals and sample II-8 was tested as the most cytocompatible on mesenchymal stem cells. The properties of Casein/CaCO₃ microspheres could be well controlled; for better performance in bone tissue engineering, formation of composite scaffolds may be preferred.