Comparing the Rate of Dissolution of Two Commercially Available Synthetic Bone Graft Substitutes

This study characterized the dissolution properties of two commercially available bone substitutes: (1) A calcium sulfate (CaS)/brushite/β-tricalcium phosphate (TCP) graft containing 75% CaS and 25% calcium phosphate; and (2) a CaS/hydroxyapatite (HA) bone graft substitute composed of 60% CaS and 40% HA. Graft material was cast into pellets (4.8 mm outer diameter × 3.2 mm). Each pellet was placed into a fritted thimble and weighed before being placed into 200 mL of deionized water. The pellets were removed from the water on days 1, 2, 3, 4, 6, 8, 14, 18, or until no longer visible. The mass and volume of each pellet were calculated at each timepoint to determine the rate of dissolution. Analysis of variance was performed on all data. Statistical significance was defined as p < 0.05. The CaS/HA pellets were completely dissolved after day 8, while the CaS/brushite/β-TCP pellets remained until day 18. The CaS/brushite/β-TCP pellets had significantly more mass and volume at days 1, 2, 3, 4, 6, and 8 timepoints. The CaS/brushite/β-TCP pellets lost 46% less mass and 53% less volume over the first 4 days as compared to CaS/HA pellets. The CaS/brushite/β-TCP pellets had a rough, porous texture, while the CaS/HA pellets had a smooth outer surface. Overall the CaS/brushite/β-TCP pellets dissolved approximately twice as slowly as the CaS/HA pellets in vitro. As these in vitro findings might have in vivo implications, further clinical data are required to further confirm and establish the optimal synthetic bone substitute strategy or antibiotic delivery carrier.