Degradation Characteristics of a Novel DCPD Cement Made From MCPM/HA

Objective: To evaluate the degradation characteristics of a novel DCPD cement made using monocalcium phosphate monohydrate (MCPM) and hydroxyapatite (HA).

Methods: Cylindrical specimens of DCPD cements were made by mixing MCPM and HA in molar ratios of 2:0.5, 2:1, 2:3 and 2:5, adding 100mM sodium citrate in a powder to liquid mass ratio of 1.0, and then casting into Teflon molds (1/8in diameter, 1/4in height). For each molar ratio, the initial phase composition was determined by x-ray diffraction analysis, and the initial compressive strength was evaluated using a materials tests system. The degradation characteristics were then evaluated by statically soaking specimens in PBS (pH 7.4) for 14 days. Changes in pH, mass, and compressive strength were evaluated at 2, 4, 6, 8, 10, 12 and 14 days, and all measurements were made in triplicate. Final phase compositions were determined by x-ray diffraction analysis.

Results: Specimens made with a 2:0.5 molar ratio initially consisted of pure DCPD, and had an initial compressive strength of 1.76±0.09MPa. All other treatments contained mixtures of DCPD and un-reacted HA, and compressive strength decreased with increasing HA content. After 14 days in PBS, HA content increased for all treatments, indicating the hydrolysis of DCPD to HA. The pH of the PBS dropped to 5.50±0.11, 5.10±0.08, 5.90±0.02, and 6.35±0.06 for the four molar ratios respectively. This data mirrored the mass loss data, which showed decreases of 17.09±0.24, 23.30±2.18, 10.93±1.58, and 5.89±0.85 percent for the four molar ratios respectively. Degradation was detrimental to compressive strength for all of the molar ratios except 2:0.5, which maintained a compressive strength of about 1MPa.

Conclusion: DCPD cements made with a 2:0.5 molar ratio may offer a desirable balance between strength and degradation. Future studies will investigate the effects of different processing variables, as well as the biological response to this material.