Hydroxyapatite is the main mineral part of natural bone tissue with nanometric structure scale. In its chemical compound, there are different iones that magnesium and carbonate are most important of them. This iones cause changes in hydroxyapatite from stoichiometry state to biologic hydroxyapatite. In order to investigation of the effect of magnesium and carbonate on hydroxyapatite structure, first hydroxyapatite with magnesium and hydroxyapatite with carbonate were synthesized by wet chemical deposition. Then, structural changes were studied by SEM, FTIR and XRD. The results showed magnesium decreased the size of c-axis and increased the size of a-axis of hydroxyapatite unit cell parameters and carbonate with more effect cause to increase the c-axis and decrease the a-axis. Also, the presence of both iones causes reduction of crystallinity of hydroxyapatite. Investigation of the synthetic samples showed that the particles size got smaller around 30-100 nanometer with presence of magnesium and carbonate lattice of crystal.

Hydroxyapatite have been studied intensively for bone repairing and replacement applications due to their biocompatibility, bioactivity and the ability to bond to bone. Despite the poor mechanical properties of hydroxyapatite, its unique biological properties leads to study improving its properties rather than completely replacing it with other biomaterials. One of the ways to improve the properties of hydroxyapatite as a bioceramic, is preparing composite based hydroxyapatite.
In this study, Nitinol was used as a reinforce phase in order to improve the mechanical properties of hydroxyapatite. Pure hydroxyapatite (HA) was obtained by the calcination of calf femoral bone.Then the hydroxyapatite composite reinforced with 5, 10 and 15 Wt% Nitinol was produced by powder metallurgy successfully. In order to examine changes occurring in the composite phase after sintering and fracture surface, XRD, FTIR and SEM were used, Respectively. Also, the compressive strength were measured to compare the bone properties.
The results showed that hydroxyapatite composite with 10% Nitinol has the sutable conditions. It also optimizes the mechanical properties compared to other compounds intended.

Hydroxyapatite nanoparticles have a more surface contact and solubility than conventional hydroxyapatite. Hydroxynanoparticles enhances the biological and mechanical properties of new regenerated tissues. The hydroxyapatite nanoparticles have received attention as a new and effective osseous graft for using as scaffolds in bone regeneration. The reports on hydroxyapatite nanoparticles biocompatibility are controversial. It has been shown that hydroxyapatite nanoparticles induces inflammatory reaction and apoptosis. The aim of the present study was to evaluate the cytotoxicity of nano-hydroxyapatite on the human epithelial cells.
The study was experimental and completed in vitro. The study was carried out in department of Immonulogy, Faculty of Medicine, Shahid Beheshti University of Medical Sciences in November 2014. The human-derived oral epithelium cell line (KB) obtained from Pasteur Institute, Tehran, Iran were exposed to hydroxyapatite nanoparticles at 0.01, 0.05, 0.1, 0.5, 0.75, 1, 2.5 and 5 mg/ml concentrations in 24, 48 and 72 hours. Rod-shaped hydroxyapatite nanoparticles with 99% purity and maximum 100 nm sized particles were used. Methylthiazol tetrazolium bromide (MTT) method was employed for cell vitality evaluation. Enzyme-linked immunosorbent assay (ELISA) was used for assessing the viability of cells. Distilled water and fetal bovine serum (FBS) were positive and negative controls. ANOVA and Duncan tests were used for statistical analysis.
The cytotoxicity of different concentrations of hydroxyapatite nanoparticles on human-derived oral epithelium cell line in 24 (P Hydroxyapatite nanoparticles had a good biocompatibility. The biocompatibility of hydroxyapatite nanoparticles were dose and time dependent. The lower concentrations than 0.05 mg/ml of nano-hydroxyapatite had the best biocompatibility over time.

Due to its bioactivity and biocompatibility properties,hydroxyapatite (HA) with Ca10(PO4)6OH2 chemical formula has been broadly employed for bone and teeth treatment applications as hard tissue. In the present research, hydroxyapatite was synthesizedvia sol-gel and natural (extraction from bovine cortical bone) methods. Natural hydroxyapatite had an average particle size of about 5 μm and synthetic hydroxyapatite powders wereless than100 nm. Therefore, synthetic hydroxyapatite powders size was smaller than natural hydroxyapatite powders. Scaffolds were prepared by cold isostatic pressing method (CIP) and sintered at 1300°C. In order to evaluate the characteristics of the produced hydroxyapatite and morphological investigation, X-ray diffraction (XRD) and Fourier Transform infra-red spectroscopy (FTIR) were performed on the samples. Scanning electron microcopy (SEM) and Atomic force microscopy (AFM) were carried out to investigate the particle size, size and morphology of porosities and to study thetopography of surfaces. The results of scanning electron microscopy were in agreement with the AFM topography.After measuring the density of scaffolds, the compression tests were carried out on standard samples. Accordingly, the compression strength and density of samples from synthetic hydroxy apatite were more than those of the samples produced from natural hydroxyapatite. The compression strength of synthetic hydroxyapatite scaffold was 55.6 MPa and its density was 2.97 g/cm3. Cell culture was done on hydroxyapatite scaffolds with human osteoblast stem cells after14 days. Results showed that cell proliferation on natural hydroxyapatite scaffolds were less than synthetic hydroxyapatite scaffolds.

This study aims to know how to composite hydroxyapatite-collagen by freeze-drying method, and the characterization of hydroxyapatite-collagen composites using XRD, FTIR, and SEM. Hydroxyapatite nanocrystals are synthesized using the precipitation method by reacting CaO and (NH4)2HPO4 and the freeze-drying method in composite manufacturing by reacting hydroxyapatite nanocrystals with collagen. The results showed that hydroxyapatite nanocrystals can be composite with collagen using the freeze-drying method, and the results of characterization of XRD, FTIR, and SEM hydroxyapatite-collagen composites show the formation of chemical bonds between hydroxyapatite and collagen. The XRD spectrum of HAp-Collagen shows a peak at 2θ 10.45°, showing a physically formed composite. FTIR characterization shows the presence of absorption bands PO43- and OH- from HA, slight wavenumber shifts also occur in C-H, C-N, N-H, and C=O groups which are characteristic of collagen, this indicates that composites are formed physically. SEM characterization shows HAp is perfectly deposited into collagen molecules.

In the past two decades, there has been a growing trend towards the development and use of biomaterials such as hydroxyapatite and fluor-hydroxyapatite. Hydroxyapatite and fluor-hydroxyapatite have good bioactivity in human body and thus have good potential in biological applications. In this study, hydroxyapatite (HA; Ca10(PO4)6(OH)2) and flour-hydroxyapatite (FHA; Ca10(PO4)6(FOH)) nano powders were synthesized with two different methods of calcination and without calcination (adjust the pH value to about 11) by sol-gel processing. The Phase analysis, powder morphology, thermal behaviors, the bonds configuration, functional groups and biological assesment of the sinthesized samples were studied by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Thermo-gravimetric and Differential Thermal Analysis (TG-DTA), Fourier transform infrared spectroscopy (FTIR) and Cell culture method respectively. The results of XRD analysis and FTIR showed the presence of hydroxyapatite and flour-hydroxyapatite phases. The average crystallite size estimated from XRD patterns using the Scherrer equation increased from 16 and 25 nm at adjust pH method to 34 and 35 nm at 600 C° for hydroxyapatite and flour-hydroxyapatite respectively. The SEM results showed that the morphology of all of the nanopowders was spherical and semi-spherical shape with size particles are less than 100 nanometers and also, the nanoparticle size of the powders increased with fluoride substitution and calcination. The result of Cell culture of samples without calcination indicates that the substitution of fluorine (F) into the hydroxyapatite (HA) crystal causes a significant increase in the cell proliferation.

In this study the bioactivity of hydroxyapatite/poly(ε-caprolactone)–poly(ethylene glycol) bilayer coatings on Nitinol superelastic alloy was investigated. The surface of Nitinol alloy was activated by a thermo-chemical treatment and hydroxyapatite coating was electrodeposited on the alloy, followed by applying the polymer coating. The surface morphology of coatings was studied using FE-SEM and SEM. The data revealed that the hydroxyapatite coating is composed of one-dimensional nano sized flakes and the polymer coating is uniformly covered the sublayer. Also, High resolution TEM studies on the hydroxyapatite samples revealed that each flake contains nano-crystalline grains with a diameter of about 15 nm. The hydroxyapatite monolayer coating was rapidly covered by calcium phosphate crystals (Ca/P=1.7) after immersion in simulated body fluid confirming the bioactivity of the nanostructured flakes. However, the flakes were weak against applied external forces because of their ultra-fine thickness. Scratch test was applied on hydroxyapatite/polymer coating to evaluate delamination of the coating from substrate. It was shown that, the polymer coating has a great influence on toughening the hydroxyapatite coating. To assess the degradation effect of the polymer layer on hydroxyapatite coating, samples were immersed in phosphate-buffered saline at 37 ᵒC. SEM studies on the samples revealed that the beneath layer of hydroxyapatite appears after 72 h without any visible change in morphology. It seems that, application of a biodegradable polymer film on the nanostructured hydroxyapatite coating is a good way to support the coating during implantation processes

In the present study, in-situ synthesis of carbon nanotube/hydroxyapatite nano composite powder with stable homogeneous dispersions of carbon nanotubes (CNTs) have been prepared using surfactant as dispersing agent. By applying sol-gel method, dispersion in the hydroxyapatite matrix and its effects on the microstructure were investigated. The chemical and phase composition, structure and morphological and size analyses were performed using XRD, FT-IR, SEM, TEM/SAED/EDX, Raman, UV-Vis spectroscopy and differential scanning calorimetry (DSC). The influences of different dispersing agents (sodium dodecyl sulfate, SDS) as a benchmark for future dispersion experiments and excitation wavelength are discussed and the results are compared to the commonly used UV-Visible spectroscopic analysis. The results indicated that synthesis of hydroxyapatite particles in the presence of the carbon nanotubes had the best result in homogenization of the carbon nanotube dispersion and faster crystallization of hydroxyapatite, and usage of SDS for dispersion carbon nanotubes at hydroxyapatite matrix, the render formation hydroxyapatite coating on CNTs surface. The average crystallite size of heat-treated (at 600°C) samples, estimated by Scherrer,s equation was found to be ~50-60 nm that confirmed by TEM.

Hydroxyapatite (Ca10(PO4)6(OH)2) with the hexagonal crystal structure is the only identifiable mineral phase of bone. In this work, magnesium ferrite-hydroxyapatite nanocomposites were synthesized for the purpose of medical applications. The first step of this work is the synthesis of mesoporous hydroxyapatite nanorods via co-precipitation method in combination with micelles template. Non-ionic surfactant Pluronic P123 was used as a micelles template. At the second step, magnesium ferrite-hydroxyapatite nanocomposites were synthesized by the sonochemical method. The crystal structure of nanopowders was determined using X-ray diffraction pattern. Transmission electron microscopy was also applied for the morphology of the samples. From TEM image of the nanocomposite, it was observed that magnesium ferrite nanopaticles have spherical shape with diameter of about 8 nm on the surface of hydroxyapatite nanorods. Hysteresis loops (M-H) of magnesium ferrite nanoparticles and magnesium ferrite-hydroxyapatite nanocomposites were measured at room temperature by a vibrating sample magnetometer. The results revealed the superparamagnetic behavior of the produced nanostructures.

Combination of organic polymer with Hydroxyapatite (HAP) credible composites would be used widely in biomaterial and environmental engineering. The surface chemical characterization of chitosan/ Hydroxyapatite nanoparticles (HAPNPs) was investigated by X-ray diffraction (XRD) and Fourier transform infrared (FTIR). Morphology images of composite samples were detected by Transmission electron microscopic (TEM) and Field emission scanning microscope (FESM). These results were confirmed homogeneous structure, and interaction between the chitosan and HAP. The antibacterial responses to the hydroxyapatite/chitosan matrix coatings were studied as a function of hydroxyapatite concentration. The results of antibacterial test showed that the antimicrobial activity was proportional to the concentration of hydroxyapatite nanoparticles. The synthesis process for the proposed nano hydroxyapatite is also very simple, low cost, and friendly environmental. Moreover, All the above advantages indicated the intriguing potential of the samples can be used in biomedical and practical wastewater treatment applications.