Investigation of Brushite Cement Based on α-Tricalcium Phosphate and Its Composite with Polylactic Framework

Abstract

Brushite cement based on alpha-tricalcium phosphate (α-TCP) and its composite with polylactide (PL) frame with a Kelvin structure were developed. The composite was obtained by filling the PL frame with liquid cement paste by extrusion. A 30% aqueous solution of magnesium dihydrogen phosphate was used as a cement liquid. The cement phase composition was studied before soaking in a physiological solution: the main phases are dicalcium phosphate dihydrate (DCPD), tricalcium phosphate, and amorphous calcium phosphate. It was found that magnesium does not form a separate phase but, probably, is a part of a DCPD crystal lattice. During soaking of cement in a physiological solution, two processes occur simultaneously, namely, the release of calcium ions into the solution, mostly through the dissolution DCPD, and the precipitation of calcium ions from the solution on the cement surface in the form of apatite, which is confirmed by the data of X-ray phase analysis and microstructure studies. After the exposure in a physiological solution, the apatite phase becomes the main phase and the DCPD content decreases, which is related to the transformation of DCPD into the apatite phase. The solubility was studied in a physiological solution containing a Tris buffer. In the absence of a buffer, the solution pH increased and, as a result, the solubility of the composite increased too. In the presence of a buffer, the solubilities of cement and composite varied insignificantly.