Polymeric calcium phosphate cements incorporated with poly-g-glutamic acid: Comparative study of poly-g-glutamic acid and citric acid

Polymeric calcium phosphate cements (PCPC) derived from biodegradable poly-glutamic acid (-PGA) were prepared in an attempt to improve the mechanical strength of calcium phosphate cement (CPC). The characteristics of the PCPCs were compared with those of cement incorporated with citric acid. The diametral tensile and compressive strengths of the CPC incorporated with -PGA were significantly higher than that of cement incorporated with citric acid at equivalent concentrations (P < 0.05). The maximal diametral tensile and compressive strengths of the CPC incubated for 1 week in physiological saline solution were approximately 18.0 and 50.0 MPa, respectively. However, the initial setting time of the PCPC was slower than that of CPC incorporated with citric acid. The formation of ionic complexes between calcium ions and -PGA was observed using FTIR spectroscopy. Hydroxyapatite (HA) formation was retarded by -PGA incorporation according to scanning electronic microscopy (SEM) and powder X-ray diffraction (XRD) observations.