title: Phase transformations during processing and in vitro degradation of porous calcium polyphosphates.
abstract: A 2-Step sinter/anneal treatment has been reported previously for forming porous CPP as biodegradable bone substitutes [9]. During the 2-Step annealing treatment, the heat treatment used strongly affected the rate of CPP degradation in vitro. In the present study, x-ray diffraction and (31)P solid state nuclear magnetic resonance were used to determine the phases that formed using different heat treating processes. The effect of in vitro degradation (in PBS at 37 °C, pH 7.1 or 4.5) was also studied. During CPP preparation, β-CPP and γ-CPP were identified in powders formed from a calcium monobasic monohydrate precursor after an initial calcining treatment (10 h at 500 °C). Melting of this CPP powder (at 1100 °C), quenching and grinding formed amorphous CPP powders. Annealing powders at 585 °C (Step-1) resulted in rapid sintering to form amorphous porous CPP. Continued annealing to 650 °C resulted in crystallization to form a multi-phase structure of β-CPP primarily plus lesser amounts of α-CPP, calcium ultra-phosphates and retained amorphous CPP. Annealing above 720 °C and up to 950 °C transformed this to β-CPP phase. In vitro degradation of the 585 °C (Step-1 only) and 650 °C Step-2 annealed multi-phase samples occurred significantly faster than the β-CPP samples formed by Step-2 annealing at or above 720 °C. This faster degradation was attributable to preferential degradation of thermodynamically less stable phases that formed in samples annealed at 650 °C (i.e. α-phase, ultra-phosphate and amorphous CPP). Degradation in lower pH solutions significantly increased degradation rates of the 585 and 650 °C annealed samples but had no significant effect on the β-CPP samples.
authors.affiliation: Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, ON, Canada.
authors.forename: Youxin
authors.initials: Y
authors.lastname: Hu
authors.affiliation: Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, ON, Canada. bob.pilliar@utoronto.ca.|Faculty of Dentistry, University of Toronto, Toronto, ON, Canada. bob.pilliar@utoronto.ca.
authors.forename: Robert
authors.initials: R
authors.lastname: Pilliar
authors.affiliation: Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, ON, Canada.|Mount Sinai Hospital, Toronto, ON, Canada.
authors.forename: Marc
authors.initials: M
authors.lastname: Grynpas
authors.affiliation: Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, ON, Canada.|Mount Sinai Hospital, Toronto, ON, Canada.
authors.forename: Rita
authors.initials: R
authors.lastname: Kandel
authors.affiliation: Department of Chemistry, Dalhousie University, Halifax, NS, Canada.
authors.forename: Ulrike
authors.initials: U
authors.lastname: Werner-Zwanziger
authors.affiliation: Faculty of Dentistry, Dalhousie University, Halifax, NS, Canada.
authors.forename: Mark
authors.initials: M
authors.lastname: Filiaggi
mesh_terms: D001672:Biocompatible Materials / Q000737:chemistry; D001843:Bone Cements / Q000737:chemistry; D018786:Bone Substitutes / Q000737:chemistry*; D001842:Bone and Bones / Q000502:physiology; D002130:Calcium Phosphates / Q000737:chemistry*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D008855:Microscopy, Electron, Scanning; D010759:Phosphorus Isotopes / Q000737:chemistry; D011122:Polyphosphates / Q000737:chemistry; D016062:Porosity; D011208:Powders; D013696:Temperature; D013816:Thermodynamics; D014961:X-Ray Diffraction
chemical_list: D001672:Biocompatible Materials; D001843:Bone Cements; D018786:Bone Substitutes; D002130:Calcium Phosphates; D010759:Phosphorus Isotopes; D011122:Polyphosphates; D011208:Powders; C020243:calcium phosphate