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Nanocrystalline hydroxyapatite (HA) is the bone mineral phase in vertebrate animals. When bones suffer illness or injuries, natural hydroxyapatite reconstructs and remodels its structure. It has been demonstrated that synthetic hydroxyapatite materials emulate bone properties and enhance bone-bonding ability through a biomimetic apatite coating, obtained when bioactive materials are immersed in a physiological-like media. In this research, the biomimetic apatite structure deposited in three synthetic hydroxyapatites (HAs: HAMS, HAUB, and HAUT), after being immersed in a simulated body fluid (SBF), is studied. The synthetic HAs are obtained by co-precipitation, using three different stirring methods: magnetic stirring (HAMS), ultrasonic bath (HAUB), and ultrasonic tip (HAUT). The synthetic HAs are characterized by X-Ray Diffraction (X-RD), High-Resolution Scanning Electron Microscopy (HR-SEM), Energy Dispersive X-ray (EDX) microanalysis and Transmission Electron Microscopy (TEM) before and after SBF assays. The crystal sizes of synthetic HAs are 12.567 nm, 15.188 nm, and 17.903 nm for HAMS, HAUB, and HAUT, respectively. Additionally, HAs have values between 0.940 and 0.942 nm for a-cell parameter, and values between 0.688 and 0.689 nm for c-cell parameter. After 28 days of immersion in Simulated Body Fluid (SBF), the materials show poor crystalline-fine films of biomimetic apatite covering their surfaces. These biomimetic apatite films have values between 0.946 and 0.969 nm for the a-cell parameter and values between 0.698 and 0.710 nm for the c-cell parameter. Hence, crystallinity, crystal size, and morphology of synthetic HAs are dependent on the stirring method used during the synthesis process, which affects the structural characteristics of the biomimetic apatite layers deposited on the synthetic HAs surfaces.

Samples of enamel and dentin from human molar teeth were heated in air from room temperature (25°C) up to 1200°C and the phase transition from hydroxyapatite (HAP) to tricalcium phosphate (β-TCP) was recorded. The changes produced in morphology and chemical composition in the tooth during heating were analysed by light microscopy, scanning electron microscopy (SEM), characteristic x-ray energy dispersion spectroscopy (EDS), x-ray diffraction (XRD), electron diffraction, transmission electron microscopy (TEM) and high-resolution electron microscopy (HRTEM). The results indicated a high correlation relationship among Ca content, P content, O content and Na content, and the existence of the Kirkendall effect during the HAP- β-TCP phase transition. LAY DESCRIPTION: This work is related with tooth materials. Samples of enamel and dentine from human molar teeth were heated in air from 25°C up to 1200°C and the phase transition from hydroxyapatite (HAP) to tricalcium phosphate (β-TCP) was recorded. The β-TCP phase is also known as whitlockite. The changes produced in morphology and chemical composition in the tooth during heating were analysed by electron microscopy and X-ray diffraction. The results indicated a high correlation relationship among Ca, P, O and Na contents, and the existence of the Kirkendall effect, the atomic diffusion producing voids, during the HAP- β-TCP phase transition.

The crystalline indexes obtained through infrared spectroscopy (CIIR) and X-ray diffraction (CIXRD) were used to analyze the structural changes of dentin and enamel in human teeth when subjected to heat treatments between room temperature (25 °C) to 1200 °C in atmospheric air and argon. Thermogravimetric (TGA) and differential scanning calorimetry (DSC) analyses of sound powders were also used to support the analysis. As the temperature increased, the CIXRD increased exhibiting a behavior like that of the crystal grain size, and the CIIR increased until the β-TCP phase appeared. These results indicated that the CIIR was more variable to structural changes than the CIXRD.

The phase transformation of hydroxyapatite (HAP, Ca10(PO4)6(OH)2) to the beta tricalcium phosphate phase (β-TCP, β-Ca3(PO4)2) at 1100°C is well known. However, in the case of human tooth, the HAP phase transformation is still an open area. For example, the CaO phase has sometimes been reported in the set of phases that make up the teeth. In this study, physical changes of human teeth when subjected to heat treatment in inert atmosphere (argon) were studied. The results were compared with those obtained in air atmosphere, from room temperature (25°C) up to 1200°C. Morphological changes were analyzed by light and scanning electron microscopy (SEM). The HAP to β-TCP phase transformation was followed in powder samples by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Heating of teeth results in the removal of organic material and structural water before the HAP to β-TCP phase transformation, the increment in hardness and the induced crystal growth. The percentage of the phases, crystal growth and lattice parameter variations as a function of temperature was quantified by Rietveld analysis. The black color was observed in dentin heated under argon atmosphere. Differences in expansivity produce fractures in dentin at 300°C in argon and at 400°C in air. In dentin, the coexistence of the HAP and β-TCP phases was observed after 800°C in argon and after 600°C in air; in enamel it was observed at 600°C in argon compared with 400°C in air. In general, the role played by the argon atmosphere during the thermal treatment of the teeth is to retard the processes observed in air.

The improvement of the conductive and inhibitory properties of the stainless-steel electrodes used in an electrochemical environment by the application of coatings is of great interest in the field of, for example, heavy crudes, among others. And titanium-based materials, such as titanium dioxide (TiO 2 ), titanium oxide (TiO x ) and titanium nitride (TiN), are good candidates as coatings because of their anti-corrosive properties. This work reports the contact angle variation of a water drop measured on the surfaces of samples of AISI 304 and 316 stainless steel and of glass when coated with TiO 2 , TiO x and TiN films of approximately 600 nm thick. The films were produced by sputtering by varying the power and the gas flow parameters. Chemical and structural analysis by X-ray diffraction (XRD), energy division of the characteristic x-ray spectroscopy (EDS) and selected area electron diffraction (SAED) patterns in the transmission electron microscope (TEM) confirm the presence of the TiO 2 , TiO x and TiN phases in the films produced. On the glass surface, the contact angle ranged from 10° (hydrophilic behavior) on uncoated glass to 92° (hydrophobic behavior) on coated glass. Coating the surface of the AISI 316 and 304 stainless steel with these films also increased the contact angle up to 90°. The TiN films roughness, measured by atomic force microscopy (AFM), and average particle size, measured by scanning electron microscopy (SEM) and TEM, favored the increment of the contact angle.

The characteristics of the electron-mirror effect (EME) image depend on both the scanning electron microscope parameters and the sample's physical properties. The behavior of human tooth (dentin and enamel) and synthetic hydroxyapatite samples submitted to the EME procedure is presented in this work. Polyethylene terephthalate (PET) and epoxy resin, two good EME producers, were used for comparison. A distorted EME image was observed in the obtained dentin's surface, but enamel and synthetic hydroxyapatite surfaces did not produce the EME. After ex situ calcination treatments of the teeth at 700 and 1,200°C, the EME was observed in dentin, enamel, and synthetic hydroxyapatite, but highly deformed EME images were produced. We show that these last observations are the result of the well-known charge-edge effect. After EME analysis, the calculated dielectric constant was 8.7 for dentin and 3.8 for PET. RESEARCH HIGHLIGHTS: Electron-mirror effect (EME) was observed in dentin but not in enamel or synthetic hydroxyapatite. Highly deformed EME images are produced in all samples after calcination at above 700°C. For dentin the calculated dielectric constant was 8.7 and for PET is was 3.8.

Direct and converse piezoelectric effects have been observed in human tooth enamel and dentin. In this study, organic material was removed from dentin and enamel using a chlorinated solution to measure the sole contribution of the inorganic phase. In the direct mode, piezoelectricity is observed when a force applied to the sample produces a voltage. A variable load was applied to the samples with a Shimadzu universal testing machine. In the converse mode, mechanical deformation of the sample occurs under an electric field, which was detected using an atomic force microscope in the piezoelectric mode (piezoresponse force microscope, PFM). For comparison, measurements were also performed on samples where organic (collagen) and inorganic (hydroxyapatite) phases were present. Although a decrease in of the electromechanical response of the organic free sample was observed, the results indicate that the inorganic phase contributes to the piezoelectric property in dentin and in a lesser extent in enamel. This suggests that tooth dentin and enamel apatite nanocrystals present piezoelectric non-centrosymmetric (P63 and P21), as with centrosymmetric (P63/m) structure domains in different percentages.

The preparation of apatite–alendronate hybrid materials by reactive milling is proposed in this work. Calcium phosphate compounds of various compositions have been associated to bisphosphonates and found suitable for local application with release kinetics of the drug compatible with the inhibition of bone resorption. Hybrid compounds have been obtained by reactive milling. The compositions used were: AP(X-100), Alendronate(X) where X=7 and X=15. An interaction between the hydroxyl group of the apatite and the amine group of alendronate can be identified with FTIR and enables to confirm the formation of the hybrids. The incorporation of the alendronate hinders the growing of the apatite crystals resulting in smaller coherent domains of diffraction for the apatite phase.

Pechini method is a materials synthesis method based on the preparation of a polymeric matrix. The advantage of this method is the ability to obtain materials with different particle sizes depending on the synthesis condition with a homogeneous distribution. In this work, carbonated hydroxyapatite (c-OHAp) nanoparticles were obtained by a modified Pechini method. To obtain the polymeric precursor of the c-OHAp, the polymeric matrix was prepared through a polyesterification reaction between citric acid and ethylene-glycol. Adding calcium hydroxide and ortophosphoric acid in aqueous solutions, raising the temperature up to 140 C/2 h and keeping constant the pH at 8. The polymeric matrix was calcinated at different ranges of temperature from 200 to 600 C in order to obtain the c-OHAp powder. The results show the presence of c-OHAp a as unique phase. The thermal analysis indicates that the c-OHAp phase was obtained at 600 C. The particle size of the obtained material was\50 nm