Injectable and biodegradable composite bone filler composed of poly(propylene fumarate) and calcium phosphate ceramic for vertebral augmentation procedure: An in vivo porcine study

Despite its common usage in vertebral augmentation procedures (VAPs), shortcomings of commercial polymethylmethacrylate (PMMA) still remain. Accordingly, injectable and biodegradable composite cements, which are composed of poly(propylene fumarate)/α-tricalcium/hydroxyapatite (PPF/α-TCP/HAP) and PPF/tetracalcium phosphate/dicalcium phosphate (PPF/TtCP/DCP), were developed. A porcine model was used and cylindrical holes in critical size were created at the center of the lateral cortex of vertebral bodies of the lumbar spine. A fixed volume of testing materials and PMMA were randomly injected into the defects. Results showed that both composite groups had a comparable radiolucency as PMMA but a significantly lower setting temperature. Histological inspections revealed new bone formation and remodeling along the border of the two composite cements. New bone substitution and irregular sclerotic bone mantles were found along the composite cements but not in the PMMA group. Radiological and histological changes were observed in the two composite groups and these modifications were diminished along the block boundaries. These findings imply gradual substitution of decomposed composite by new bone formation, which could not be found around the PMMA block. Comparing PPF/α-TCP/HAP with the PPF/TtCP/DCP cement block, smaller particles that were spreading out were observed in the TtCP/DCP group, which represents rapid degradability. In conclusion, the composite cements have advantages such as a low setting temperature, radio-opacity, biodegradability, and osteoconductivity. The injectable PPF/calcium phosphate ceramic composite has the potential to be used in VAPs.