In vivo evaluation of an injectable Macroporous Calcium Phosphate Cement

Although Calcium Phosphate Cements (CPC) are highly biocompatible and osteconductive materials, its resorption rate still remains too slow for some applications. In this work the introduction of Macroporosity in an injectable CPC is evaluated as a way to accelerate resorption and to increase bone ingrowth. A Macroporous and a standard CPC were injected just after preparation in a defect drilled in rabbit femur for their in vivo evaluation. The foaming agent used was Albumen, which gave up to a 75% porosity. Sodium Alginate was added to promote the cohesion of the foamed paste after implantation. In the case of the Macroporous Cement, bone growth and neovascularisation was observed inside the pores of the material, not only at the margins of the cement but also in some central pores. After 12 weeks of implantation, the residual material volume of the Macroporous Cement was approximately 35% of the initial value, whereas only the outer layers of non-Macroporous CPC were resorbed, being the residual material volume close to 100%. The higher resorption rate was due to the higher surface contact with body fluids which increased the dissolution rate, and to the enhancement of the cellular activity.