title: Effect of sodium polyacrylate on the hydrolysis of octacalcium phosphate.
abstract: Octacalcium phosphate (OCP) hydrolysis into hydroxyapatite (HA) has been investigated in aqueous solutions at different concentrations of sodium polyacrylate (NaPA). In the absence of the polyelectrolyte, OCP undergoes a complete transformation into HA in 48 h. The hydrolysis is inhibited by the polymer, which is significantly adsorbed on the crystals, up to about 22 wt.%. A polymer concentration of 10(-2) mM is sufficient to cause a partial inhibition of OCP to HA transformation, which is completely hindered at higher concentrations. The small platelet-like crystals in the TEM images of partially converted OCP can display electron diffraction patterns characteristic either of OCP single crystals or of polycrystalline HA, whereas the much bigger plate-like crystals exhibit diffraction patterns characteristic of OCP single crystals. The polyelectrolyte adsorption on OCP crystals is accompanied by an increase of their mean length and by a significant reduction of the coherence length of the perfect crystalline domains along the c-axis direction. It is suggested that the carboxylate-rich polyelectrolyte is adsorbed on the hydrated layer of the OCP (100) face, thus inhibiting its in situ hydrolysis into HA.
authors.affiliation: Department of Chemistry G. Ciamician, University of Bologna, Italy. bigi@ciam.unibo.it
authors.forename: A
authors.initials: A
authors.lastname: Bigi
authors.forename: E
authors.initials: E
authors.lastname: Boanini
authors.forename: G
authors.initials: G
authors.lastname: Falini
authors.forename: S
authors.initials: S
authors.lastname: Panzavolta
authors.forename: N
authors.initials: N
authors.lastname: Roveri
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry*; D002130:Calcium Phosphates / Q000737:chemistry*; D017886:Durapatite / Q000737:chemistry; D006868:Hydrolysis; D008855:Microscopy, Electron, Scanning; D014961:X-Ray Diffraction
chemical_list: D000180:Acrylic Resins; D002130:Calcium Phosphates; C022045:octacalcium phosphate; C006903:carbopol 940; D017886:Durapatite