HA Crystals Research Articles

Improved HA Coating on Titanium Substrate Using Induction Heating and Hydrothermal Treatment Methods

An adherent apatite coating was deposited on titanium substrate through the three steps. First, titanium substrate was modified in 10M NaOH solution at 60°C, and then immersed in acidic solution of calcium phosphate resulting in the deposition of monetite (CaHPO4) coating using induction heating technique. Finally the monetite crystals were transformed to HA by a hydrothermal process at 160°C for 2 hours. Composition、morphology and structure of the initial and final coatings were identified using X-ray diffraction (XRD), Scanning Electron Microscopy, and Energy Dispersive Spectroscopy (EDS). The final coating consisted of compact HA crystals and these HA apatite crystals stacked tightly and kept the initial morphology of the monetite crystals. The coating adhesion measured using scratch test was 25.25N. In conclusion, hydrothermal treatment and induction heating techniques are effective surface coating methods that improve bonding to titanium substrate.

Effect of storing on the microstructure of Ag/Cu/HA powder

The nanosized Ag/Cu/HA powder is thermodynamically unstable and easily congregates during storing, which may make it lose the nanomaterial's properties. In this work, the performances of Ag/Cu/HA during storing were studied. The Ag/Cu/HA powders were prepared using a one-step co-precipitation method. The effects of storing on powder microstructures were investigated. The microstructures of Ag/Cu/HA powders were characterized by X-ray diffraction and scanning electron microscopy. The results show that the diffraction intensities and the sizes of the calcined Ag/Cu/HA powders are reduced during storing. Storing makes the diffraction angles of 0 0 2 and 3 0 0 peaks decreased and makes that of 2 1 1 peak increased. In addition, storing increases the crystal growth along the c-axis without the effect on the crystal morphology of powders. The stored Ag/Cu/HA powders can induce the formation of new HA crystal the same as the stored Ag/Cu/HA powders with platelet morphology and low intensity and crystallinity similar to nature bone.

Preparation and characterization of hydroxyapatite/chondroitin sulfate composites by biomimetic synthesis

Abstract Based on the principles of biomineralization, flakelike hydroxyapatite/chondroitin sulfate composites were synthesized through biomimetic method using Ca(NO3)2·4H2O and (NH4)3PO4·3H2O as reagents and chondroitin sulfate as template. The crystalline phase, microstructure, chemical composition, morphology and thermal behavior of the composites obtained in the experiment were characterized by means of X-ray diffraction (XRD), Fourier transform infrared spectroscope (FTIR), transmission electron microscope (TEM), Thermogravimetry-Differential thermal analyzer (TG-DTA) and Elemental analyzer, respectively. The interaction between the functional groups of ChS and HA was investigated by electrical conductivity and UV–vis spectrum. The results demonstrate that the as-prepared powders with small amount of carbonate have the component similar to human bone. It can be concluded that the nucleation and growth of HA crystals occurred through the chemical interactions between the HA crystals and preorganized functional groups of the ChS template. Furthermore, the concentration of ChS significantly affects the morphology of the composites. Short fiberlike crystals could be obtained at a low concentration of ChS, but flakelike crystals could be synthesized using a high concentration (≥0.5 wt%) of ChS as template.

GEPIs-HA hybrid: A novel biomaterial for tooth repair

Dental caries are slowly progressive and infectious disease, which result in localized dissolution and destruction of the calcified tissues. In routine clinical treatments, microleakage following with secondary caries usually occurs due to the discrepancy in physico-chemical property between filled materials and tooth. Ideal filling materials for tooth defect should be similar to the structure and chemical composition of natural tooth. Recently, molecular biomimetics developed a novel nanotechnology through biology, which fabricate materials based on molecular recognition between genetically engineered peptides for inorganics (GEPIs) and inorganic crystal. Since GEPIs can be used in the assembly of functional nanostructures, we hypothesis that an analogue of dental hard tissue, hybrid of GEPIs and HA crystal, might be engineered using the recognition properties between GEPIs and HA crystal.

Preparation and mechanism of calcium phosphate coatings on chemical modified carbon fibers by biomineralization

In order to prepare HA coatings on the carbon fibers, chemical modification and biomineralization processes were applied. The phase components, morphologies, and possible growth mechanism of calcium phosphate were studied by infrared spectroscopy(IR), X-ray diffractometry(XRD) and scanning electron microscopy(SEM). The results show that calcium phosphate coating on carbon fibers can be obtained by biomineralization. But the phase components and morphologies of calcium phosphate coatings are different due to different modification methods. Plate-like CaHPO 4·2H 2O (DCPD) crystals grow from one site of the active centre by HNO 3 treatment. While on the para-aminobenzoic acid treated fibers, the coating is composed of nano-structural HA crystal homogeneously. This is because the —COOH functional groups of para-aminobenzoic acid graft on fibers, with negative charge and arranged structure, accelerating the HA crystal nucleation and crystallization on the carbon fibers.

Microstructural self-healing effect of hydrothermal crystallization on bonding strength and failure mechanism of hydroxyapatite coatings

Hydroxyapatite coatings (HACs) are synthesized on Ti–6Al–4V substrates using the plasma spraying process followed by autoclaving hydrothermal treatment at 125 and 150 °C. The quantitative analysis of X-ray diffraction indicates that the hydrothermal treatment is available to promote HA crystallization and further eliminate the amorphous and impurity phases of the HACs. The microstructural self-healing effect of hydrothermally treated HA coatings (HT-HACs) can be recognized as a nucleation and grain growth of nano-crystalline HA which tends to diminish the spraying defects through the hydrothermal crystallization. The significant hydroxy ion (OH −) peak in XPS spectra detected from HT-HAC specimens represents that the hydroxyl-deficient state of plasma-sprayed HACs is significantly improved with the abundant replenished OH − groups during the hydrothermal treatment. XPS analysis also demonstrates that the hydrothermal crystallization helps to promote the interfacial Ti–OH chemical reaction. The bonding strength of HA coatings is significantly improved from 32.4 MPa for the as-sprayed HACs to 38.9 MPa after 150 °C hydrothermal treatment. Through the statistical analysis of Weibull distribution function, the strengthening HT-HACs are generally reliable materials with a wear-out failure model. The failure morphologies of HT-HACs represent homogeneity with a larger area fraction of cohesive failure and a decreased adhesive failure area. The phenomena were resulted from the microstructural self-healing effect and the enhanced interfacial adhesion of HT-HACs to Ti–6Al–4V substrate.

Chitosan-mediated crystallization and assembly of hydroxyapatite nanoparticles into hybrid nanostructured films

The synthesis and subsequent assembly of nearly spherical nano-hydroxyapatite (nHA) particles in the presence of trace amounts of the polysaccharide chitosan was carried out employing a wet chemical approach. Chitosan addition during synthesis not only modulated HA crystallization but also aided in the assembly of nHA particles onto itself. Solvent extraction from these suspensions formed iridescent films, of which the bottom few layers were rich in self-assembled nHA particle arrays. The cross-section of these hybrid films revealed compositional and hence structural grading of the two phases and exhibited a unique morphology in which assembled nHA particles gradually gave way to chitosan-rich top layers. Transmission electron microscope and selected area electron diffraction studies suggested that the basal plane of HA had interacted with chitosan, and scanning electron microscope studies of the hybrid films revealed multi-length scale hierarchical architecture composed of HA and chitosan. Phase identification was carried out by X-ray diffraction (XRD) and Rietveld analysis of digitized XRD data showed that the basic apatite structure was preserved, but chitosan inclusion induced subtle changes to the HA unit cell. The refinement of crystallite shape using the Popa method clearly indicated a distinct change in the growth direction of HA crystallites from [001] to [100] with increasing chitosan concentration. The paper also discusses the likelihood of chitosan phosphorylation during synthesis, which we believe to be a pathway, by which chitosan molecules chemically interact with calcium phosphate precursor compounds and orchestrate the crystallization of nHA particles. Additionally, the paper suggests several interesting biomedical applications for graded nHA-chitosan nanostructured films.

Biomimetic synthesis of spherical nano-hydroxyapatite in the presence of polyethylene glycol

Spherical nano-hydroxyapatite (nano-HA) was synthesized successfully by a biomimetic method using Ca(NO 3) 2·4H 2O and (NH 4) 3PO 4·3H 2O as reagents in the presence of polyethylene glycol (PEG). The crystalline phase, microstructure, chemical composition, and morphology of the obtained samples were characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM). The results show that spherical nano-HA with diameter of 30–50 nm can be synthesized in the presence of a certain concentration (2–6%) of PEG. The crystallinity of HA powder synthesized in the presence of PEG was higher than that synthesized in the absence of PEG, but the crystallinity of HA reduced with increasing the concentration of PEG. The electrical conductivity (EC) of the solution revealed that PEG reduced the transfer rate of Ca 2+ in the process of HA crystallization, indicating the interaction between PEG and HA. The possible mechanism of formation spherical nano-HA was discussed.

Surface characteristics of titanium anodized in the four different types of electrolyte

This study evaluated the surface characteristics of titanium modified by anodic spark oxidation and a subsequent hydrothermal treatment. The electrolytic compositions of the experimental groups are as follows: GA: 0.015 M dl-α-glycerophosphate disodium salt hydrate ( dl-α-GP) and 0.2 M calcium acetate (CA), GB: anodized in 0.015 M β-GP (glycerophosphate disodium salt) and 0.2 M CA, GC: anodized in 0.015 M GP (glycerophosphate disodium salt) and 0.2 M CA, and GD: anodized in 0.015 M GP-Ca (glycerophosphate calcium salt) and 0.2 M CA. Anodic spark oxidation was carried out at 30 mA/cm 2 to 290 V. In addition, the anodized samples were treated hydrothermally at 300 °C for 2 h in an autoclave system. Regardless of the electrolytic composition, the anodic oxide films on the titanium surface contained pores ∼5 μm in size and the diameter was larger at the protrusion parts than that at the lower parts. The phase of the anodic oxide layer consisted mainly of anatase with a small amount of rutile. HA crystals precipitated on the porous titanium oxide layer after a hydrothermal treatment. Moreover, the morphology of the HA crystals was a dense fine needle shape, which changed according to the electrolytic composition. The mean surface roughness ( R a) was highest in group GB at 0.437 μm. The R a values of the hydrothermally treated group was approximately 0.14–0.2 μm higher than the anodized groups. Anodic spark oxidation and the hydrothermal treatment resulted in increasing corrosion potential and decreasing corrosion current density, which means an improvement in the corrosion resistance. The surface activity of the specimens in Hanks’ solution was GD > GA > GB > GC.

Preparation of Unsintering Calcium Phosphate Macroporous Materials with Hydroxyapatite Nanowhisker In Situ Growth

Unsintering macroporous calcium phosphate scaffolds with macropore sizes of 200∼400μm and hydroxyapatite nanofiber of in-situ growth were prepared by coating porous polyurethane templates with α-tricalcium phosphate bone cement (CPC) slurry, and their subsequent hydrolysis to calcium deficient hydroxyapatite (HAp) during the self-setting processes are presented. The effects of Sr2+ (SrNO3) on the nucleation, growth of the hydroxyapatite nanofiber and phase constitution were studied. The results show that the main component of the coating is HA after hydrolysis for 72h and the Sr2+ added could depress the growth of block or sheet HA crystal and promote the nanowhisker growth. This new processing technique can be used to improve the bioactivity of porous polymer template while maintaining its macroporous structure.

TEM Analysis on Bio-Functional Gradient Hydroxyapatite/ZrO<sub>2</sub> Coatings

In the present study, bioactive functional gradient coatings were prepared using net-energy controlled plasma spraying technology. The microstructure and phases of the bioactive functional gradient coating were examined by means of transmission electron microscope, scanning electron microscopy and X-ray diffraction. The results revealed that: (1) as-sprayed coatings contained a large amount of amorphous phases and some nano-sized HA crystals formed during rapid solidification, (2) surface of the coating was very rough with different-sized micropores, and the gradient layer was much denser which firmly bonded to the substrate without gaps and obvious interface between the coating and the substrate

Phase transformation of plasma-sprayed hydroxyapatite coating with preferred crystalline orientation

Highly oriented hydroxyapatite coatings (HACs) were obtained on titanium substrates through a radio-frequency thermal plasma spraying (TPS) method. XRD patterns showed that the HACs had crystallites with [0 0 l] preferred orientation vertical to the coating's surface. XRD results also indicated that tetracalcium phosphate crystallites in the as-sprayed HAC were oriented in the (1 0 0) direction. XRD peaks corresponding to tetracalcium phosphate, tricalcium phosphate and calcium oxide were absent after heat and hydrothermal treatment. The orientation degree of the HAC was influenced little by such post-heat treatments. Considering the crystallographic relationship between the tetracalcium phosphate in the as-sprayed HAC and the HA crystallites formed in the heat-treated HAC, these XRD results indicate that the tetracalcium phosphate in the as-prepared coatings transformed topotaxially into HA during the post-heat treatment. TEM and SEM analyses of the highly oriented HAC were conducted. The characteristic lamellar structure of TPS deposits was observed in cross-sections of the HAC. A prismatic texture was also observed in magnified SEM images. TEM observation showed that 200–800-nm-wide prismatic crystallites were formed in HA splats, and their longitudinal axis was oriented vertically to the coating's surface. SAD patterns showed that the longitudinal axis of the prismatic crystallites corresponded to the [0 0 1] zone axis of the HA crystal.

The effect of fluoride treatment on titanium treated with anodic spark oxidation

This study examined the effect of fluoride on the surface characteristics of an anodized titanium implant. Commercial pure titanium plate 20mm×10mm×2mm in size, and discs 1.5 mm thick and 1.5 mm in diameter, were used. The prepared samples were polished with #200 to #1, 000 SiC papers and were then washed sequentially with distilled water, alcohol and acetone. Anodic oxidation was performed using a regulated DC power supply in an electrolyte containing a mixture of 0.015 M DL-α-glycerophosphate disodium salt hydrate (DL-α-GP) and 0.2 M calcium acetate hydrate (CA) with an electric current density of 30mA/cm2 and voltage ranging from 0 to 290 V. The specimens were divided into four groups and a fluoride treatment was carried out. Group 1 was thermally treated in a 0.05 M TiF3 solution at 90°C, Group 2 was electrochemically treated at 150 V in a 0.05 M TiF3 solution, Group 3 was electrochemically treated at 150 V in a 0.05 M NaF solution, and Group 4 was electrochemically treated at 150 V in a 0.05 M HF solution. A porous oxide layer containing pores 1–4 μm in size was observed on the surface treated with anodic oxidation. The diameter of the pores was higher in the protrusion areas than in the sunken areas. A significant amount of fluoride ions was released in the initial period, with small amounts being released continuously thereafter. The viability of MC3T3 cells was high when the fluoride ion concentration was 10 ppm, but decreased with further increases in the fluoride concentration. A six-week immersion test in simulated body fluid (SBF) showed dense HA crystals in the group immersed in 0.05 M TiF3 at 90°C, which indicated good biocompatibility.

Biocompatibility of Calcium Phosphate Ceramics Synthesized from Eggshell

The aim of this paper was the HA and β-TCP powers were synthesized by a new wetchemical method using eggshell and phosphoric acid. The biocompatibility of synthesized natural HA, HA/β-TCP(50:50) and β-TCP derived from eggshell was compared with those of as commercial chemical powder with mesenchymal stem cells derived from human bone marrow. Development of crystalline phases of the mixtures was studied as functions of mixing ratio and temperature using X-ray diffractometer. The morphological characteristics of the calcined eggshell and synthesized powders were examined by scaning electron microscopy. The in-vitro cytotoxicity and cell attachment of sintered disks were examined using human bone marrowderived multipotent stem cells(hBMSCs). Cell response was characterized by MTT assay , Alkaline phosphatase stain and RT-PCR analysis. Pure HA was synthesized in the mixing ratio of 1:1.1 wt% at 900°C for 1h. the crystallization of HA was started at 800°C in the 1:1.1 mixing ratio, ant the HA phase was continued up to the high temperatures. In the ratio of 1:1.3 and 1:1.5 wt%, β-TCP was effectively synthesized at 900°C. In the 1:1.5 ratio, β-TCP phase was detected at 700°C, and complete crystallized β-TCP was observed above 900°C. At the higher temperature than 1000°C, the β-TCP was gradually decreased and α-TCP was observed. The HA and β-TCP disk does not exert cytotoxic effect on the hBMSCs undergoing osteoblastic differentiation. In addition, the hBMSCs are adhered on the surface of synthesized natural HA and β-TCP disk as successfully as on the culture plate or as commercial chemical HA and β-TCP disk. The hBMSCs adhered on either synthesized natural HA, β-TCP or as commercial chemical HA, β-TCP disk displays undistinguishable actin arrangement and cellular phenotypes, indicating that synthesized natural HA, β-TCP does not disrupt normal cellular responses. Analysis of differentiation of the hBMSCs cultured on culture plate, synthesized natural HA, β-TCP and as commercial chemichal HA, β-TCP disk shows that three matrices are able to support osteoblastic differentiation of the hBMSCs as accessed by alkaline phosphatase staining.

Effect of Dehydration Methods on Mechanical Strength of Nanohydroxyapatite/Collagen Composites

Hydroxyapatite/collagen composites were prepared in-situ synthesis. The composites were finally achieved by dehydration including air-drying and freeze-drying methods. FTIR, XPS and DSC were employed to investigate the composites dehydrated by two methods. The air-dried composites had better mechanical properties than those of the composites dried by freeze drying. Air-drying of the composite induced more bond formation and crosslink between collagen fibers and HA crystals compared with freeze-drying of the composite, as indicated by the shifting of amide A and I bands to the lower wavenumber and by the changes in the binding energy of O1s, Ca2p, and P2p, leading to the increase of the peak temperature of the composites. Collagen crosslink and bond formation in the air-dried composites were key factors to increase the bending strength of the composites. The results of this study confirm that in situ synthesis and air-dry method are effective ways to obtain nanoHA/COL composites with high mechanical properties.

Preparation and Cytocompatibility of Novel Nano-HA/PLA Composite

In order to prepare nano-hydroxyapatite/poly(lactide) (n-HA/PLA) composite with good interfacial interaction, some groups which could bind with Ca ions in HA crystals need to be introduced onto PLA surface. Poly(α-methacrylic acid) (PMAA) was grafted on the PLA surfaces via photooxidization and subsequent UV induced polymerization. Suspension of PMAA-PLA microparticles with an average size as 133.1nm was prepared with solvent evaporation technique. Then utilizing the action of template manipulating of PMAA-PLA microparticles, n-HA/PLA composite were synthesized. Zeta potentials measurement and SEM indicated that there were good interfacial interactions between two phases of n-HA/PLA composite. The results of cell viability confirmed that n-HA/PLA composite possessed good cytocompatibility, so the n-HA/PLA composite scaffold obtained by electrospun technology might be used as bone tissue engineering scaffold.

Effect of pH on the fibroin regulated mineralization of calcium phosphate

The effect of pH on the mineralization of calcium phosphate regulated by fibroin is investigated in this paper. Calcium phosphates were prepared under different pH of the solution. The products were characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results demonstrated the great influence of pH on the formation of calcium phosphate, both in the presence and in the absence of fibroin. Pure hydroxyapatite (Ca 10 (PO 4 ) 6 (OH) 2 ,HA) can be obtained at relatively high pH (pH 8.0), while brushite (CaHPO 4 · 2H 2 O, DCPD) is the usual product at low pH (pH 4.0, 5.2) in 10 h. Additionally, the presence of the fibroin can accelerate the transformation from DCPD to HA and regulate the morphology and structure of the HA crystals obtained.

Molecular modeling and mechanics studies on the initial stage of the collagen-mineralization process

Abstract A molecular modeling and mechanics method was employed to study the initial stage of the collagen-mineralization process. Collagen was modeled as a collagen-like peptide CH 3 CO-(Gly-Pro-Pro) 10 -NHCH 3 . Calcium ions were placed at a certain distance from specified C=O groups. Molecular mechanics simulations were then carried out to find the optimized structures. Calculation results showed that the calcium ions were attracted to an equilibrium position by the collagen-like peptide. The binding energies for the first, second, and third attracted calcium ion are 145.7 kCal/mol, 69.8 kCal/mol, and 47.1 kCal/mol, respectively. When more than one calcium ion was placed, the special spatial structure of the collagen-like peptide could arrange the attracted calcium ions. Simulation results for three calcium ions showed that the final structure was similar to that in HA crystal.

Effect of Crystallization on the Bonding Strength and Failures of Plasma-Sprayed Hydroxyapatite

Hydroxyapatite coatings were synthesized on Ti-6Al-4V substrates using the plasma spraying process followed by vacuum and atmospheric post-heat treatments at various elevated temperatures. This study provides an evaluation of the bonding strength and crystallization rate of HACs resulting from the variations in crystallinity and thermal induced cracking. Experimental results provide evidence that the atmospheric heat-treated HACs possessed higher crystallization rate than the vacuum-heated specimens. It implies that the presence of an atmosphere with moisture plays an important role in improving the crystallization of HACs. The bonding strength of all samples was improved with increasing HA crystallization, and the optimal heating condition was found to be about 600 � C. However, the crystallization-induced defects result in a serious microstructure and bonding strength degradation when the heating temperatures were higher than 600 � C for both post-heat methods. On the basis of the fracture morphologies observation and the bonding strength data fluctuation of both heating conditions, the Weibull distribution function provides a powerful statistical analysis for assessing the failure mechanism and the reliability of plasma-sprayed and post heat-treated HACs. [doi:10.2320/matertrans.48.211]

Hydroxyapatite Coatings Produced by Right Angle Magnetron Sputtering for Biomedical Applications

AbstractHydroxyapatite coatings have been widely recognized for their biocompatibility and utility in promoting biointegration of implants in both osseous and soft tissue. Conventional sputtering techniques have shown some advantages over the commercially available plasma spraying method; however, the as-sputtered coatings are usually non-stoichiometric and amorphous which can cause some serious problems such as poor adhesion and excessive coating dissolution rate. A versatile right-angle radio frequency magnetron sputtering (RAMS) approach has been developed to deposit HA coatings on various substrates at low power levels. Using this alternative magnetron geometry, as-sputtered HA coatings are nearly stoichiometric, highly crystalline, and strongly bound to the substrate, as evidenced by analyses using x-ray diffraction (XRD), atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). In particular, coatings deposited on oriented substrates show a polycrystalline XRD pattern but with some strongly preferred orientations, indicating that HA crystallization is sensitive to the nature of the substrate. Post deposition heat treatment under high temperature does not result in a marked improvement in the degree of crystallinity of the coatings. To study the biocompatibility of these coatings, murine osteoblast cells were seeded onto various substrates. Cell density counts using fluorescence microscopy show that the best osteoblast proliferation is achieved on an HA RAMS-coated titanium substrate. These experiments demonstrate that RAMS is a promising coating technique for biomedical applications.