New Injectable Nanostructured Calcium Phosphate Pastes for Bone Tissue Regeneration

Objectives: Calcium phosphate bioceramics are employed widely as bone graft substitutes. While partially successful, particulates may be difficult to place while cements do not always elicit a reproducible bone tissue response. New nanoscale calcium phosphates may be combined with water to generate a paste for direct delivery via a syringe. While promising, relatively little work has been directed at the bone tissue response to these new materials. The aim of this study was therefore to investigate the in vivo response of bone tissue to a nanostructured ceramic paste. Methods: Sterile nanostructured calcium phosphates were provided in ready-to-use syringes (20 ml) by Ceramisys Ltd. (Sheffield, UK). Commercial Ostim® paste was used as a reference material. Materials were injected into 1 mm healing defects in the midshaft of rat femora, and tissue response investigated using micro-computerised tomography (µCT) and scanning electron microscopy (SEM) following 2, 4 and 12 weeks implantation. Results: Bone tissue healing progressed normally in the presence of experimental and reference materials without evidence of impairment or infection at all time periods. Bone tissue grew in close apposition to the surface of nanostructured hydroxyapatite, with further evidence of significant bone growth detected using µCT, suggesting that the material was osteoconductive. By 12 weeks, µCT showed evidence of some resorption of the paste with no impairment of healing or bone regeneration. Conclusions: Injectable, nanostructured calcium phosphates appear to be suitable for use as osteoconductive bone substitutes in dental and craniofacial surgery. Acknowledgements: The authors are grateful to the Technology Strategy Board and EPSRC for funding the NANO4MED collaborative project (Reference TP/8/BIO/6/I/Q0034H).