Synthetic Calcium Phosphate Ceramics for Treatment of Bone Fractures

Bone is a complex natural material with outstanding mechanical properties and remarkable self-healing capabilities. The mechanical strength is achieved by a complex structure of a mineral part comprising apatitic calcium phosphate crystals embedded in an organic matrix. Bone also contains several types of cells constantly replacing mature bone with new bone. These cells are able to seal fractures and fill gaps with new bone in case of structural damage. However, if a defect exceeds a critical size, surgery is necessary to fill the void with a spacer in order to prevent soft tissue from growing into the defect and delaying the healing process. The spacers, also known as bone grafts, can either be made of fresh bone from the patient, of processed bone from donor organisms, or of synthetic materials chemically similar to the mineral part of bone. Synthetic bone void fillers are also known as bone graft substitutes. This review aims at explaining the biological and chemical background that lead to the development of synthetic bone graft substitutes and gives an overview of the current state of development. It also highlights the multidisciplinary nature of biomaterials research, which combines cell biology and medicine with chemistry, mineralogy, crystallography, and mechanical engineering

Facile synthesis of magnetically separable CoFe2O4/Ag2O/Ag2CO3 nanoheterostructures with high photocatalytic performance under visible light and enhanced stability against photodegradation

Riga Technical University supported the preparation of this manuscript from the Scientific Research Project Competition for Young Researchers No. ZP-2016/7. The authors wish to kindly acknowledge the financial support of HZB, Estonian Research Council (PUT1096, PUT735 and IUT2-25) and Estonian Centre of Excellence in Research Project “Advanced materials and high-technology devices for sustain-able energetics, sensorics and nanoelectronics” TK141 (2014–2020.4.01.15-0011).We have developed magnetically separable and reasonably stable visible light active photocatalysts containing CoFe2O4 and mixture of Ag2O/Ag2CO3 nanoheterostructures. Obtained ternary nanoheterostructures outperform previously reported magnetically separable visible light photocatalysts, showing one of the highest visible light photocatalytic dye degradation activities in water by a magnetically separable photocatalyst. Photocatalytically active part is Ag2O/Ag2CO3 whereas the CoFe2O4 mainly has stabilizing and magnetic separation functions. The Ag2CO3 phase junction on Ag2O nanoparticle surface were obtained by straightforward phase transformation from silver oxide to silver carbonate in air due to ambient CO2. The phase transformation was followed using X-ray diffraction (XRD), and hard X-ray photoelectron spectroscopy (HAXPES) measurements.Riga Technical University No. ZP-2016/7; Estonian Research Council (PUT1096, PUT735 and IUT2-25); Estonian Centre of Excellence in Research TK141 (2014–2020.4.01.15-0011); Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Interlaboratory study on the quantification of calcium phosphate phases by Rietveld refinement

An interlaboratory study (ILS, round robin) was conducted to assess the accuracy and precision of the phase quantification of calcium phosphate (CaP) bioceramics by X-ray diffraction (XRD) and Rietveld refinement. For that purpose, a mixture of hydroxyapatite and β-tricalcium phosphate, two CaP phases commonly used in synthetic bone graft substitutes, was prepared and sent to 12 laboratories for XRD analysis. Results from 26 different instruments were received and evaluated statistically according to ASTM E691 - 13. The statistical analysis revealed that the reproducibility standard deviation of phase quantities was approximately two times greater than the repeatability standard deviation, which is obtained by repeating the analysis on a single instrument configuration multiple times. The 95% reproducibility limit for phase quantities was R = ±1.67 wt%. The study also demonstrated that several participants overinterpreted their data in an attempt to refine crystallite sizes of the minor phas

Microporous titanosilicate AM-2: Rb-exchange and thermal behaviour

Abstract Rb-exchange and thermal stability of the microporous titanosilicate AM-2 were analysed by powder X-ray diffraction, thermogravimetric analysis, and chemical analysis of the mother liquid after exchange. The dehydration and thermal stability of the exchanged structure were monitored with in situ high temperature powder X-ray diffraction. Crystal structures were refined with Rietveld methods at 25 and 400 8C. The AM-2 structure was found to incorporate Rb + by replacing K + . After four exchange cycles and 166 h reaction time at 90 8C, the chemical composition was refined to K 0.18 Rb 1.82 TiSi 3 O 9 ÁH 2 O. Extrapolation suggests that higher exchange ratios may be obtained after further cycles. H 2 O was expelled by heating, leading to a dehydrated structure at 360 8C. Dehydration was associated with a change of space group symmetry from orthorhombic P2 1 2 1 2 1 to monoclinic P2 1 , which proved to be reversible after rehydration. This change of symmetry leaves the AM-2 characteristic structural topology uninfluenced and causes only minor distortions. The monoclinic AM-2 structure breaks down above 600 8C to become X-ray amorphous, and at 750 8C a wadeite-type phase (K x Rb 2Àx TiSi 3 O 9 ) crystallises. This transformation is irreversible and leads to immobilisation of Rb +

Stepwise dehydration of Sr-exchanged heulandite: A single-crystal X-ray study

A Sr-exchanged heulandite crystal of composition Sr4.35Ca0.13(Al8.96Si27.04O72)·26H2O was used for stepwise dehydration experiments. The crystal was heated for approximately 12 h from room temperature to 250 °C in steps of 50 °C using an airflow-heater device. For single-crystal X-ray data collection the crystal was quenched to −173 °C with liquid-N2 on the diffractometer. Due to pronounced Sr order deviating from the topological symmetry C2/m, the structure was refined in space group Cm for each dehydration state. The initial H2O content of 26 molecules per formula unit (pfu) at room temperature decreased to 17 molecules pfu after heating at 250 °C. Heating to 270 °C mechanically destroyed the crystal and a completely dehydrated state could not be studied. The loss of H2O and accompanying migration of Sr caused a change of cell parameters: a and c slightly decreased, b decreased, and β remained invariant, leading to a reduction of the cell volume. As Sr loses H2O upon dehydration, it moves toward the C rings and forms stronger bonds to the tetrahedral framework. With increasing dehydration the A and B ring become slightly compressed and elongated. Initially highly populated Sr sites split into less populated sites caused by the loss of surrounding H2O molecule

A thermodynamic approach to surface modification of calcium phosphate implants by phosphate evaporation and condensation

It has been reported in the literature that thermal treatment of calcium phosphate ceramics chemically alters the surface composition by phosphate evaporation. To predict the compositional changes, we have developed a thermodynamic model for the evaporation of phosphorous species from CPP, TCP, HA, and TetCP. In an open atmosphere, the model predicts the formation of a surface layer consisting of a sequence of increasingly phosphate-depleted phases. In a closed system, the atmosphere reaches equilibrium with a single-phase surface layer. To verify our model, we performed a series of experiments which confirmed the predicted formation of phosphate-depleted surface layers. These experiments further demonstrated that controlled supersaturation of the atmosphere led to formation of a phosphate-enriched surface layer as a result of phosphate condensation. In conclusion, our thermodynamic model is capable of predicting the surface modification by phosphate evaporation and condensation of calcium phosphate phases during high-temperature processing in different environments