Alginate combined calcium phosphate cements: mechanical properties and in vitro rat bone marrow stromal cell responses

Here, we prepared self-setting calcium phosphate cements (CPCs) based on alpha-tricalcium phosphate with the incorporation of sodium alginate, and their mechanical properties and in vitro cellular responses were investigated. The addition of alginate enhanced the hardening reaction of CPCs showing shorter setting times within a range of powder-to-liquid ratios. When immersed in a body simulating fluid the alginate-CPCs fully induced a formation of an apatite crystalline phase similar to that of bare CPCs. The compressive and tensile strengths of the CPCs were found to greatly improve during immersion in the fluid, and this improvement was more pronounced in the alginate-CPCs. As a result, the alginate-CPCs retained significantly higher strength values than the bare CPCs after 3-7 days of immersion. The rat bone marrow derived stromal cells (rBMSCs) cultured on the alginate-CPCs initially adhered to and then spread well on the cements surface, showed an on-going increase in the population with culture time, and differentiated into osteoblasts expressing bone-associated genes (collagen type I, osteopontin and bone sialoprotein) and synthesizing alkaline phosphatase. However, the stimulated level of osteogenic differentiation was not confirmative with the incorporation of alginate into the CPC composition based on the results. One merit of the use of alginate was its usefulness in forming CPCs into a variety of scaffold shapes including microspheres and fibers, which is associated with the cross-link of alginate under the calcium-containing solution.