X-ray Diffraction Analysis and Williamson-Hall Method in USDM Model for Estimating More Accurate Values of Stress-Strain of Unit Cell and Super Cells (2 × 2 × 2) of Hydroxyapatite, Confirmed by Ultrasonic Pulse-Echo Test.

Taking into account X-ray diffraction, one of the well-known methods for calculating the stress-strain of crystals is Williamson-Hall (W-H). The W-H method has three models, namely (1) Uniform deformation model (UDM); (2) Uniform stress deformation model (USDM); and (3) Uniform deformation energy density model (UDEDM). The USDM and UDEDM models are directly related to the modulus of elasticity (E). Young's modulus is a key parameter in engineering design and materials development. Young's modulus is considered in USDM and UDEDM models, but in all previous studies, researchers used the average values of Young's modulus or they calculated Young's modulus only for a sharp peak of an XRD pattern or they extracted Young's modulus from the literature. Therefore, these values are not representative of all peaks derived from X-ray diffraction; as a result, these values are not estimated with high accuracy. Nevertheless, in the current study, the W-H method is used considering the all diffracted planes of the unit cell and super cells (2 × 2 × 2) of Hydroxyapatite (HA), and a new method with the high accuracy of the W-H method in the USDM model is presented to calculate stress (σ) and strain (ε). The accounting for the planar density of atoms is the novelty of this work. Furthermore, the ultrasonic pulse-echo test is performed for the validation of the novelty assumptions.

Measurement Modulus of Elasticity Related to the Atomic Density of Planes in Unit Cell of Crystal Lattices.

Young's modulus (E) is one of the most important parameters in the mechanical properties of solid materials. Young's modulus is proportional to the stress and strain values. There are several experimental and theoretical methods for gaining Young's modulus values, such as stress-strain curves in compression and tensile tests, electromagnetic-acoustic resonance, ultrasonic pulse echo and density functional theory (DFT) in different basis sets. Apparently, preparing specimens for measuring Young's modulus through the experimental methods is not convenient and it is time-consuming. In addition, for calculating Young's modulus values by software, presumptions of data and structures are needed. Therefore, this new method for gaining the Young's modulus values of crystalline materials is presented. Herein, the new method for calculating Young's modulus of crystalline materials is extracted by X-ray diffraction. In this study, Young's modulus values were gained through the arbitrary planes such as random (hkl) in the research. In this study, calculation of Young's modulus through the relationship between elastic compliances, geometry of the crystal lattice and the planar density of each plane is obtained by X-ray diffraction. Sodium chloride (NaCl) with crystal lattices of FCC was selected as the example. The X-ray diffraction, elastic stiffness constant and elastic compliances values have been chosen by the X'Pert software, literature and experimental measurements, respectively. The elastic stiffness constant and Young's modulus of NaCl were measured by the ultrasonic technique and, finally, the results were in good agreement with the new method of this study. The aim of the modified Williamson-Hall (W-H) method in the uniform stress deformation model (USDM) utilized in this paper is to provide a new approach of using the W-H equation, so that a least squares technique can be applied to minimize the sources of errors.

Comparing Methods for Calculating Nano Crystal Size of Natural Hydroxyapatite Using X-Ray Diffraction.

We report on a comparison of methods based on XRD patterns for calculating crystal size. In this case, XRD peaks were extracted from hydroxyapatite obtained from cow, pig, and chicken bones. Hydroxyapatite was synthesized through the thermal treatment of natural bones at 950 °C. XRD patterns were selected by adjustment of X-Pert software for each method and for calculating the size of the crystals. Methods consisted of Scherrer (three models), Monshi-Scherrer, three models of Williamson-Hall (namely the Uniform Deformation Model (UDM), the Uniform Stress Deformation Model (USDM), and the Uniform Deformation Energy Density Model (UDEDM)), Halder-Wanger (H-W), and the Size Strain Plot Method (SSP). These methods have been used and compared together. The sizes of crystallites obtained by the XRD patterns in each method for hydroxyapatite from cow, pig, and chicken were 1371, 457, and 196 nm in the Scherrer method when considering all of the available peaks together (straight line model). A new model (straight line passing the origin) gave 60, 60, and 53 nm, which shows much improvement. The average model gave 56, 58, and 52 nm, for each of the three approaches, respectively, for cow, pig, and chicken. The Monshi-Scherrer method gave 60, 60, and 57 nm. Values of 56, 62, and 65 nm were given by the UDM method. The values calculated by the USDM method were 60, 62, and 62 nm. The values of 62, 62, and 65 nm were given by the UDEDM method for cow, pig, and chicken, respectively. Furthermore, the crystal size value was 4 nm for all samples in the H-W method. Values were also calculated as 43, 62, and 57 nm in the SSP method for cow, pig, and chicken tandemly. According to the comparison of values in each method, the Scherrer method (straight line model) for considering all peaks led to unreasonable values. Nevertheless, other values were in the acceptable range, similar to the reported values in the literature. Experimental analyses, such as specific surface area by gas adsorption (Brunauer-Emmett-Teller (BET)) and Transmission Electron Microscopy (TEM), were utilized. In the final comparison, parameters of accuracy, ease of calculations, having a check point for the researcher, and difference between the obtained values and experimental analysis by BET and TEM were considered. The Monshi-Scherrer method provided ease of calculation and a decrease in errors by applying least squares to the linear plot. There is a check point for this line that the slope must not be far from one. Then, the intercept gives the most accurate crystal size. In this study, the setup of values for BET (56, 52, and 49 nm) was also similar to the Monshi-Scherrer method and the use of it in research studies of nanotechnology is advised.

Fabrication and characterization of polycaprolactone fumarate/gelatin-based nanocomposite incorporated with silicon and magnesium co-doped fluorapatite nanoparticles using electrospinning method.

The aim of this study was to fabricate and characterize biodegradable polycaprolactone fumarate(PCLF)/gelatin-based nanocomposite incorporated with the 0, 5 and 10 wt% silicon and magnesium co-doped fluorapatite nanoparticles (Si-Mg-FA) membranes using electrospinning process for guided bone regeneration (GBR) and guided tissue regeneration (GTR) applications. Results demonstrated the formation of randomly-oriented and defect-free fibers with various fiber sizes depending on the Si-Mg-FA content. Moreover, incorporation of 5 wt% Si-Mg-FA significantly improved the mechanical strength (1.5times) compared to the mechanical strength of PCLF/gelatin membrane and nanocomposite with 10 wt% nanoparticles. There was no clear difference between degradation rate of PCLF/gelatin and PCLF/gelatin with 5 wt% nanoparticles at 7, 14 and 28 days of immersion in phosphate buffer saline while 10 wt% nanoparticles significantly increased biodegradation of PCLF/gelatin, and no cytotoxic effect of membranes was seen. Finally, scanning electron microscopy (SEM) micrographs of fibroblast cells cultured on the samples demonstrated that the cells were completely attached and spread on the surface of nanocomposites. In summary, PCLF/gelatin membranes consisting of 5 wt% Si-Mg-FA nanoparticles could provide appropriate mechanical and biological properties and fairly good degradation rate, making it appropriate for GTR/GBR applications.

Evaluation of the effects of nano-TiO2 on bioactivity and mechanical properties of nano bioglass-P3HB composite scaffold for bone tissue engineering.

To emulate bone structure, porous composite scaffold with suitable mechanical properties should be designed. In this research the effects of nano-titania (nTiO2) on the bioactivity and mechanical properties of nano-bioglass-poly-3-hydroxybutyrate (nBG/P3HB)-composite scaffold were evaluated. First, nBG powder was prepared by melting method of pure raw materials at a temperature of 1400 °C and then the porous ceramic scaffold of nBG/nTiO2 with 30 wt% of nBG containing different weight ratios of nTiO2 (3, 6, and 9 wt% of nTiO2 with grain size of 35-37 nm) was prepared by using polyurethane sponge replication method. Then the scaffolds were coated with P3HB in order to increase the scaffold's mechanical properties. Mechanical strength and modulus of scaffolds were improved by adding nTiO2 to nBG scaffold and adding P3HB to nBG/nTiO2 composite scaffold. The results of the compressive strength and porosity tests showed that the best scaffold is 30 wt% of nBG with 6 wt% of nTiO2 composite scaffold immersed for 30 s in P3HB with 79.5-80 % of porosity in 200-600 µm, with a compressive strength of 0.15 MPa and a compressive modulus of 30 MPa, which is a good candidate for bone tissue engineering. To evaluate the bioactivity of the scaffold, the simulated body fluid (SBF) solution was used. The best scaffold with 30 wt% of nBG, 6 wt% of P3HB and 6 wt% of nTiO2 was immersed in SBF for 4 weeks at an incubation temperature of 37 °C. The bioactivity of the scaffolds was characterized by AAS, SEM, EDXA and XRD. The results of bioactivity showed that bone-like apatite layer formed well at scaffold surface and adding nTiO2 to nBG/P3HB composite scaffold helped increase the bioactivity rate.

Evaluation of mechanical property and bioactivity of nano-bioglass 45S5 scaffold coated with poly-3-hydroxybutyrate.

One of the major challenges facing researchers of tissue engineering is scaffold design with desirable physical and mechanical properties for growth and proliferation of cells and tissue formation. In this research, firstly, nano-bioglass powder with grain sizes of 55-56 nm was prepared by melting method of industrial raw materials at 1,400 °C. Then the porous ceramic scaffold of bioglass with 30, 40 and 50 wt% was prepared by using the polyurethane sponge replication method. The scaffolds were coated with poly-3-hydroxybutyrate (P3HB) for 30 s and 1 min in order to increase the scaffold's mechanical properties. XRD, XRF, SEM, FE-SEM and FT-IR were used for phase and component studies, morphology, particle size and determination of functional groups, respectively. XRD and XRF results showed that the type of the produced bioglass was 45S5. The results of XRD and FT-IR showed that the best temperature to produce bioglass scaffold was 600 °C, in which Na2Ca2Si3O9 crystal is obtained. By coating the scaffolds with P3HB, a composite scaffold with optimal porosity of 80-87% in 200-600 µm and compression strength of 0.1-0.53 MPa was obtained. According to the results of compressive strength and porosity tests, the best kind of scaffold was produced with 30 wt% of bioglass immersed for 1 min in P3HB. To evaluate the bioactivity of the scaffold, the SBF solution was used. The selected scaffold (30 wt% bioglass/6 wt% P3HB) was maintained for up to 4 weeks in this solution at an incubation temperature of 37 °C. The XRD, SEM EDXA and AAS tests were indicative of hydroxyapatite formation on the surface of bioactive scaffold. This scaffold has some potential to use in bone tissue engineering.

Preparation and corrosion behavior evaluation of amalgam/titania nano composite.

BACKGROUND: Many attempts have been performed and continued for improvement of dental amalgam properties during last decades. The aim of present research was fabrication and characterization of amalgam/titania nano composite and evaluation of its corrosion behavior. MATERIALS AND METHODS: In this experimental research, nano particles of titania were added to initial amalgam alloy powder and then, dental amalgam was prepared. In order to investigate the effect of nano particle amounts on properties of dental amalgam, proper amount of 0, 0.5, 1, 2 and 3 wt% of titania nano particles were added to amalgam alloy powder and the prepared composite powder was triturated by a given percent of mercury. X-ray Diffraction, Scanning Electron Microscopy and Energy-Dispersive Spectroscopy techniques were use to characterize the prepared nano composites. Potentiodynamic polarization corrosion tests were performed in the Normal Saline (0.9 wt% NaCl) and Ringer's solutions as electrolytes at 37°C. Immersion corrosion tests were also performed immediately 2 h after preparation of cylindrical samples (4 mm in diameter and 8 mm height) via immersion into a 100 ml volumetric flask consisting of artificial saliva. RESULTS: The results indicated that the current corrosion density of amalgam/titania nano composite changes a bit with adding 1% of nano particles of titania. Also, during the 1(st) h after preparation, initial released mercury from prepared nano composite dental amalgam decreased. CONCLUSION: By adding nano particles of titania and preparing amalgam/titania nano composite as a dental amalgam, corrosion behavior and mercury release during the 2(st) h after preparation could be improved.

Cytotoxicity evaluation of 63s bioactive glass and bone-derived hydroxyapatite particles using human bone-marrow stem cells.

BACKGROUND: In recent years, bioceramics have been favored by biomaterials scientists and researchers. Due to their special and distinctive features, bioactive glass and hydroxyapatite possess a higher place among different types of bioceramics. METHOD: In this study, the effect of 63S bioactive glass and bone-derived hydroxyapatite particles on the proliferation of human bone-marrow stem cells (hMSCs) was investigated. Bioactive glass particles were made via sol-gel method and hydroxyapatite was obtained from bovine bone. The particle size and morphology were investigated by scanning electron microscope (SEM). Then the in vitro cytotoxicity of particles was evaluated using MTT assay. SEM showed that bioactive glass particles were in the nanoscale range and had tendency towards agglomeration. It was also confirmed that the hydroxyapatite particles were agglomerations of crystals cca 50-500 nm across. RESULTS: The results of MTT assay confirmed the viability and proliferation of hMSCs in contact with bioactive glass and bone-derived HA particles. The fabricated particles in combination with stem cells were shown to hold promising potential for further applications in tissue engineering and regenerative medicine.