Bone 'spackling' paste: Mechanical properties and in vitro response of a porous ceramic composite bone tissue...

Bone defects are treated with bone grafts, replacing damaged or diseased bone tissue with either natural bone or bone substitutes. This study investigates the structure, mechanical properties, and in vitro response of an all-ceramic composite designed for use as a bone 'spackling' paste: a formable synthetic bone graft paste used to repair bone defects in place, reacting with CO₂ gas in ambient conditions to become a void-filling, rigid scaffold. The composite is comprised of bioactive glass frit and a soluble liquid silicate precursor combined to form an air-setting, open porous scaffold with compressive strength within the low range for trabecular bone (1.3-4.4 MPa). Characterization of scaffolds, with varying amounts of binder, was executed in accordance with established design criteria of porosity, load-bearing capacity, and bioactivity. Bioactivity was assessed via morphological, structural, and chemical changes in surface mineralization that occurred during in vitro immersion in simulated body fluid. All phases of composite specimens were observed to form calcium phosphate minerals, indicating that a chemical change occurred between the bioactive glass and sodium silicate binder phase. Ion exchange between the two phases was likely, as sodium silicate (control) was not found to produce calcium phosphate in the absence of bioactive glass. Of the selected compositions, composites with 7.4 vol% sodium silicate binder were observed to possess the highest open porosity (44 vol%), highest rate of calcium phosphate mineralization, most uniform surface mineral distribution, and largest amount of hydroxycarbonate apatite formation. The structure, mechanical properties, and in vitro response of the composite scaffolds analyzed in this research signify their potential success as bone tissue scaffolds.