Promotion of bone formation using highly pure porous beta-TCP combined with bone marrow-derived osteoprogenitor cells

Beta-tricalcium phosphate (TCP) exhibits rapid degradation and weak mechanical properties, which has limited its application as bone graft substitutes, though it has good biocompatibility and osteoconductivity. We hypothesized that a composite of highly pure porous beta-TCP and bone marrow-derived osteoprogenitor cells (BMO) could improve bone formation, and slow down the degradation of beta-TCP. A highly pure porous beta-TCP with 75% porosity was fabricated. The pores averaged 200-400 microm in diameter, with interconnecting paths 100-200 microm. Blocks of beta-TCP 5 mm3 were combined with BMO, and incubated 2 weeks with (+) or without (-) osteogenic medium. They were then implanted into subcutaneous sites of syngeneic rats for 24 weeks. These composites were harvested at different time points. The alkaline phosphatase activity and bone osteocalcin content of the composites (+) were much higher than corresponding values in the composites (-) of the control group (p<0.01). Light microscopy revealed mature bone and lots of blood vessels only in the TCP/BMO composite (+). The amount of newly formed bone increased until week 24. Slow resorptive activity could be found. The mechanical parameters of the composites were much improved over those of dry beta-TCP blocks. These results showed that tissue engineering treatment on incubating the composites of beta-TCP and BMO cells in osteogenic medium results in a good osteogenic activity.