Mg, Zn Substituted Calcium Phosphates-Thermodynamic Modeling, Biomimetic Synthesis in the Presence of Low-Weight Amino Acids and High Temperature Properties.

The preparation of specially doped calcium phosphates (CaPs) is receiving a great deal of attention from researchers due to CaPs' enhanced capabilities for application in medicine. Complexation and precipitation in a complicated electrolyte system including simulated body fluids that are enriched with Mg2+ and Zn2+ ions and modified with glycine, alanine and valine were first evaluated using a thermodynamic equilibrium model. The influence of the type and concentration of amino acid on the incorporation degree of Mg and Zn into the solid phases was predicted. Experimental studies, designed on the basis of thermodynamic calculations, confirmed the predictions. Amorphous calcium phosphates double-doped with Mg and Zn were biomimetically precipitated and transformed into Mg, Zn-ß-tricalcium phosphates (TCP) upon calcination. The Rietveld refinement confirmed that Mg2+ and Zn2+ substituted Ca2+ only at the octahedral sites of ß-TCP, and in some cases, fully displacing the Ca2+ from them. The resulting Mg, Zn-ß-TCP can serve as a reservoir for Mg and Zn ions when included in the formulation of a biomaterial for bone remodeling. The research conducted reveals the effect of combining mathematical models with experimental studies to pre-evaluate the influence of various additives in the design of materials with predetermined properties.

Polycarboxy/Sulfo Betaine-Calcium Phosphate Hybrid Materials with a Remineralization Potential.

Biomacromolecules control mineral formation during the biomineralization process, but the effects of the organic components' functionality on the type of mineral phase is still unclear. The biomimetic precipitation of calcium phosphates in a physiological medium containing either polycarboxybetaine (PCB) or polysulfobetaine (PSB) was investigated in this study. Amorphous calcium phosphate (ACP) or a mixture of octacalcium phosphate (OCP) and dicalcium phosphate dihydrate (DCPD) in different ratios were identified depending on the sequence of initial solution mixing and on the type of the negative functional group of the polymer used. The more acidic character of the sulfo group in PSB than the carboxy one in PCB determines the dominance of the acidic solid phases, namely, an acidic amorphous phase or DCPD. In the presence of PCB, the formation of ACP with acicular particles arranged in bundles with the same orientation was observed. A preliminary study on the remineralization potential of the hybrid material with the participation of PSB and a mixture of OCP and DCPD did not show an increase in enamel density, contrary to the materials based on PCB and ACP. Moreover, the latter showed the creation of a newly formed crystal layer similar to that of the underlying enamel. This defines PCB/ACP as a promising material for enamel remineralization.

Bioinspired Remineralization of Artificial Caries Lesions Using PDMAEMA/Carbomer/Calcium Phosphates Hybrid Microgels.

Dental caries remains one of the most prevalent bacterium-caused chronic diseases affecting both adults and children worldwide. The development of new materials for enhancing its remineralization is one of the most promising approaches in the field of advanced dental materials as well as one of the main challenges in non-invasive dentistry. The aim of the present study is to develop novel hybrid materials based on (PDMAEMA)/Carbomer 940 microgels with in situ deposited calcium phosphates (CaP) and to reveal their potential as a remineralization system for artificial caries lesions. To this purpose, novel PDMAEMA/Carbomer 940 microgels were obtained and their core-shell structure was revealed by transmission electron microscopy (TEM). They were successfully used as a matrix for in situ calcium phosphate deposition, thus giving rise to novel hybrid microgels. The calcium phosphate phases formed during the deposition process were studied by X-ray diffraction and infrared spectroscopy, however, due to their highly amorphous nature, the nuclear magnetic resonance (NMR) was the method that was able to provide reliable information about the formed inorganic phases. The novel hybrid microgels were used for remineralization of artificial caries lesions in order to prove their ability to initiate their remineralization. The remineralization process was followed by scanning electron microscopy (SEM), X-ray diffraction, infrared and Raman spectroscopies and all these methods confirmed the successful enamel rod remineralization upon the novel hybrid microgel application. Thus, the study confirmed that novel hybrid microgels, which could ensure a constant supply of calcium and phosphate ions, are a viable solution for early caries treatment.

Indium silicate with an imandrite-type structure.

This work reports the synthesis and characterization of novel zeolite-like indium silicate MS-2 (Minho-Sofia, solid number 2). The structure of this material is analogous to that of the mineral imandrite (Na6Ca1.5FeSi6O18), with In instead of Fe in the octahedral position. MS-2 is the first structurally confirmed indium silicate prepared under mild hydrothermal conditions and the only synthetic indium silicate related to the lovozerite mineral group. MS-2 (Na6.23Ca1.62In0.68Si6O18) exhibits significant indium deficiency in the octahedral position thus having the highest Si/In (8.8) ratio among the known indium silicates. The framework consists of occupationally disordered InO6 octahedra interconnected by 6-membered rings of [Si6O18] tetrahedra. The three-dimensional (3D) tunnel system is occupied by Na+ and Ca2+ charge-balancing ions. The low framework density (16.2 FC/1000 Å3) and high thermal stability (up to 900 °C) are comparable to other molecular sieves.

Effect of Multiply Twinned Ag(0) Nanoparticles on Photocatalytic Properties of TiO2 Nanosheets and TiO2 Nanostructured Thin Films.

Ag-decorated TiO2 nanostructured materials are promising photocatalysts. We used non-standard cryo-lyophilization and ArF laser ablation methods to produce TiO2 nanosheets and TiO2 nanostructured thin films decorated with Ag nanoparticles. Both methods have a common advantage in that they provide a single multiply twinned Ag(0) characterized by {111} twin boundaries. Advanced microscopy techniques and electron diffraction patterns revealed the formation of multiply twinned Ag(0) structures at elevated temperatures (500 °C and 800 °C). The photocatalytic activity was demonstrated by the efficient degradation of 4-chlorophenol and Total Organic Carbon removal using Ag-TiO2 nanosheets, because the multiply twinned Ag(0) served as an immobilized photocatalytically active center. Ag-TiO2 nanostructured thin films decorated with multiply twinned Ag(0) achieved improved photoelectrochemical water splitting due to the additional induction of a plasmonic effect. The photocatalytic properties of TiO2 nanosheets and TiO2 nanostructured thin films were correlated with the presence of defect-twinned structures formed from Ag(0) nanoparticles with a narrow size distribution, tuned to between 10 and 20 nm. This work opens up new possibilities for understanding the defects generated in Ag-TiO2 nanostructured materials and paves the way for connecting their morphology with their photocatalytic activity.

Three-Dimensional (3D) Microporous Iron Silicate with an Imandrite Type of Structure.

Small-pore iron silicate MS-1 (Minho-Sofia, solid number 1) with a 3D porous system, an analogue of the rare mineral imandrite, has been synthesized and characterized. This material is the lowest framework density iron silicate, one of the most siliceous (Si/Fe = 6) iron silicates, the first iron cyclosilicate achieved at hydrothermal conditions, and the only synthetic iron-based member of the lovozerite mineral group.

Precipitation and phase transformation of dicalcium phosphate dihydrate in electrolyte solutions of simulated body fluids: Thermodynamic modeling and kinetic studies.

The metastable and stable equilibria of a precipitation in the biomimetic system Simulated Body Fluid (SBF)-CaCl2 -K2 HPO4 -KOH-H2 O were modeled in the pH region 3-7 at a Ca/P molar ratio of 1 using a thermodynamic approach. Saturation indices (SI) of the solid phases were calculated and used to prognose the salt precipitation/dissolution processes. At рН < 4, the solutions are undersaturated (SI < 0) in respect of all solid phases; co-precipitation of dicalcium phosphate dihydrate (DCPD) and hydroxyapatite (HA) occurs at рН 4 while at рН > 4 the stable phase is DCPD but the number of other co-precipitated solid phases increases. This result is associated with the increase in HPO42- , CaHPO40 , and KНРО4- species in the studied solution. The phase transformations of five model DCPD-based calcium phosphate precursors in three simulated body fluids differing in their composition, to more stable octacalcium phosphate and hydroxyapatite was thermodynamically prognosed and experimentally confirmed by kinetic studies, as well as by chemical, XRD, SEM, and IR methods.