Three-dimensional matrices of calcium polyphosphates support bone growth in vitro and in vivo

Novel macroporous calcium polyphosphate (CPP) scaffolds, with three-dimensional interconnected structure, were fabricated using a polyurethane sponge method. They were then employed in both in vitro and in vivo assays to examine their suitability as bone tissue engineering scaffolds. In the former, subcultured rat marrow cells were seeded on the scaffolds at 7.0 x 10(5) cells/sample and cultured for 2 wk. Cell-free controls were employed to monitor changes in the scaffold itself. In the in vivo assay, CPP rods were implanted in rat distal femur and recovered after 2 wk. Samples were examined by scanning electron microscopy following freeze-fracturing. Both in vitro and in vivo assays demonstrated the growth of bone within the scaffolds. In vitro, the bone/CPP interface was occupied by a morphologically distinguishable cement line, while in vivo non-mineralized fibrous tissue was seen at the interface together with bone ingrowth into the scaffold microporosity. The morphology of the individual surface grains of the CPP scaffolds employed in vivo changed to a more rounded form, while no change in geometry was observed in the in vitro cell-free group. These preliminary studies indicate that three-dimensional CPPs can be successfully used as scaffolds for bone tissue engineering.