Solid-State ³¹P and ¹H NMR Investigations of Amorphous and Crystalline Calcium Phosphates Grown Biomimetically From a Mesoporous Bioactive Glass

Abstract

By exploiting 1H and 31P magic-angle spinning nuclear magnetic resonance (NMR) spectroscopy, we explore the proton and orthophosphate environments in biomimetic amorphous calcium phosphate (ACP) and hydroxy-apatite (HA), as grown in vitro at the surface of a 10CaO–85SiO2–5P2O5 mesoporous bioactive glass (MBG) in either a simulated body fluid or buffered water. Transmission electron microscopy confirmed the presence of a calcium phosphate layer comprising nanocrystalline HA. Two-dimensional 1H–31P heteronuclear correlation NMR established predominantly 1H2O↔31PO43– and O1H↔31PO43– contacts in the amorphous and crystalline component, respectively, of the MBG surface-layer; these two pairs exhibit distinctly different 1H→31P cross-polarization dynamics, revealing a twice as large squared effective 1H–31P dipolar coupling constant in ACP compared with HA. These respective observations are mirrored in synthetic (well-crystalline) HA, and the amorphous calcium orthophosphate (CaP) clusters that are present in the pristine MBG pore walls: besides highlighting very similar local 1H and 31P environments in synthetic and biomimetic HA, our findings evidence closely related NMR characteristics, and thereby similar local structures, of the CaP clusters in the pristine MBG relative to biomimetic ACP.

How High Concentrations of Proteins Stabilize the Amorphous State of Calcium Orthophosphate: A Solid-State Nuclear Magnetic Resonance (NMR) Study of the Casein Case

“…Moreover, the chemical shift of this bound H2O is very close (∆ 1 δ = 0.05 ppm) to that for free H2O (displayed in SI) indicating that H2O molecules bound to 31 PACP , (as well as H2O bound to 31 PpSer,) are in fast exchange with the free molecules in the medium. These results indicate that the H2O molecules corresponding to this signal are the ones localized in the interstitial space between the surface of the cluster and the protein, and not those that are potentially more deeply buried inside the cluster core 18,19 (where the direct exchange with free H2O would probably be strongly hindered). …”

“…However, those strong bonded protons do not display a chemical shift higher than ~8-9 ppm. 18,19 Thus, it is possible that the proton signal between 6 and 9 ppm comes from firmly bonded H2O protons but any signal at higher ppm values (between 10 to 16 ppm) definitively could not be assigned to H2O. On the other hand, proteins side chains with terminal groups such as R-COOH, R-NH3 + or R-NH2 can strongly interact with inorganic phosphorous present as colloidal phosphates.…”

Development of Mg-containing porous β-tricalcium phosphate scaffolds for bone repair

“…Calcium phosphates (CaP) constitute inorganic mineral phase in mammalian bones and teeth [1][2][3]. Therefore it is well recognized by body and biocompatible according to all current standards.…”

“…Therefore it is well recognized by body and biocompatible according to all current standards. CaP ceramics and related compounds represent the most important class of biomaterials for bone regeneration [1][2][3][4][5][6]. β-Tricalcium phosphate (β-TCP, Ca 3 (PO 4 ) 2 ) is one of calcium phosphate-based bioceramic used as bone replacement material due its close chemical similarity to biological apatite.…”

“…β-TCP bioceramics as bioresorbable materials have been considered as ideal temporary scaffolds in bone tissue engineering, which would facilitate the initial formation of new bone tissue and finally be replaced by the new bone [2]. Nowadays interest is turning towards modified synthetic CaP involving substitution of ions found in natural bones [3,4]. Incorporation of such ions into the CaP structure is important for a number of reasons; including better understanding of biomineralization processes, increase in bioactivity of the materials, and ion delivery able to act on bone diseases [4].…”