Comparing the physicochemical properties of dicalcium phosphate dihydrate (DCPD) and polymeric DCPD (P-DCPD) cement...

We developed a new and injectable poly-dicalcium phosphate dihydrate (P-DCPD) forming cement. The key structural difference between P-DCPD and classical DCPD is that P-DCPD is composed of interconnected P-DCPD crystals by interlocking to the polyphosphate chains. In contrast, DCPD is composed of a package of DCPD crystals with weak mutual ionic bonding. The purpose of this continuing study was to compare the physicochemical properties between P-DCPD and DCPD cement particles. Data collected from SEM, X-ray diffraction, and Raman Spectroscopy approaches demonstrated that P-DCPD has a more stable chemical structure than DCPD as evidenced by much less transformation to hydroxyapatite (HA) during setting. Nanoindentation showed a similar hardness while the elastic modulus of P-DCPD is much lower than DCPD that might be due to the much less HA transformation of P-DCPD. P-DCPD has much lower zeta potential and less hydrophilicity than DCPD because of its entangled and interconnected polyphosphate chains. It is expected that superhydrophilic DCPD undergoes faster dissolution than P-DCPD in an aqueous environment. Another interesting finding is that the pH of eluent from P-DCPD is more neutral (6.6-7.1) than DCPD (5.5-6.5). More extensive experiments are currently underway to further evaluate the potential impacts of the different physiochemical performance observed of P-DCPD and DCPD cement particles on the biocompatibility, degradation behavior and bone defect healing efficacy both in vivo and in vitro.