Injectable calcium phosphate cement: Effects of powder‐to‐liquid ratio and needle size

Abstract

Calcium phosphate cement (CPC) sets in situ and forms apatite with excellent osteoconductivity and bone‐replacement capability. The objectives of this study were to formulate an injectable tetracalcium phosphate‐dicalcium phosphate cement (CPC_D), and investigate the powder/liquid ratio and needle‐size effects. The injection force (mean ± SD; n = 4) to extrude the paste increased from (8 ± 2) N using a 10‐gauge needle to (144 ± 17) N using a 21‐gauge needle (p < 0.05). With the 10‐gauge needle, the mass percentage of extruded paste was (95 ± 4)% at a powder/liquid ratio of 3; it decreased to (70 ± 12)% at powder/liquid = 3.5 (p < 0.05). A relationship was established between injection force, F, and needle lumen cross‐sectional area, A: F = 5.0 + 38.7/A^0.8. Flexural strength, S, (mean ± SD; n = 5) increased from (5.3 ± 0.8) MPa at powder/liquid= 2 to (11.0 ± 0.8) MPa at powder/liquid = 3.5 (p < 0.05). Pore volume fraction, P, ranged from 62.4% to 47.9%. A relationship was established: S = 47.7 × (1 – P)^2.3. The strength of the injectable CPC_D matched/exceeded the reported strengths of sintered porous hydroxyapatite implants that required machining. The novel injectable CPC_D with a relatively high strength may be useful in filling defects with limited accessibility such as periodontal repair and tooth root‐canal fillings, and in minimally‐invasive techniques such as percutaneous vertebroplasty to fill the lesions and to strengthen the osteoporotic bone. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2008