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Brushite and Self-Healing Flexible Polymer-Modified Brushite Bone Adhesives for Fibular Osteotomy Repair


  • ** The authors thank EPSRC for funding EP/F01970X/1 and loaning the Skyscan micro-computerized tomography. NMR of the monomer was conducted at the MRC Biomedical NMR Centre, NIMR, London with help from Dr. Geoff Kelly.


The study aim was to compare in vitro properties of two experimental bone adhesives (brushite cement and polymer-modified brushite composite) and then assess their in vivo suitability for fixation of a fibular osteotomy using a lapine model. The composite was produced by replacement of the aqueous phase of the brushite cement (800 × 10−3M citric acid) by polypropylene glycol-co-lactide dimethacrylate. FTIR showed this modification enabled pre-mixing and better control of set through light activated polymer crosslinking instead of the acid–base brushite reaction. Raman confirmed the brushite component [equimolar monocalcium phosphate (MCPM) and β-tricalcium phosphate (β-TCP)] of the composite could react upon water-sorption to enable long-term “bulk composite self-healing.” SEM demonstrated precipitation of brushite crystals in cell culture medium on the composite surface (“surface self-healing”) and improved cell attachment. The composite was considerably more flexible than the cement (33% strain before yield compared to 4.6% before sharp brittle fracture). This flexibility was used to explain the more complete union of the fibula osteotomy and high callus index observed with composite use. The presence of cartilage at the osteotomy site in one fibula treated with brushite cement, however, indicated the absence of complete bone healing in this case. Raman mapping also confirmed the composite enabled more rapid mineralization of the fracture site compared with the cement. Both materials provided immediate fixation in vivo. More surprisingly both brushite and adhesive composite showed complete degradation by 5 weeks in vivo enabling complete union particularly with the adhesive composite within this time.