Hydroxyapatite Grains Research Articles

Synthesis and characterization of hydroxyapatite/chitosan nanocomposite materials for medical engineering applications

Incorporation of hydroxyapatite (HA) with organic polymer in favor of composites would be used in biomaterial engineering. According to prior researches, because of its chemical similarity to natural bone and dental, this product could improve bioactivity and bone bonding ability. In this research, nano-hydroxyapatite/chitosan composite material was prepared via in situ Hybridization route. The surface chemical characterization on the nanocomposite was evaluated by Fourier transformed infrared (FTIR) and X-ray diffraction (XRD). Surface topography, roughness and morphology of the samples were observed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The characterization results confirmed homogeneity, interaction and integration between the HA and chitosan matrix. It was indicated that composite samples consist of homogeneous aggregations around 40–100nm, in which many HA nanocrystals align along the chitosan molecules. HA grain gradually decreased in size when amount of chitosan increased from 0 to 6g into 100cc solution. It can be seen that by increasing chitosan, the aggregation of nanoparticles enhance and subsequently, improve the expected compatibility among HA filler and chitosan matrix. Furthermore, the mechanical compressive testing indicated that the synthesized composites have acceptable mechanical behavior for tissue substitution. The mechanistic of the biodegradable nanocomposite systems, their preparation and characterization for medical usage are strongly discussed.

Influence of metal artifacts on in vivo micro-CT for orthodontic mini-implants

This study aimed to show the effects of metal artifacts on the in vivo micro-CT of mini-implants by measuring bone volume. We drilled a hole in the cortical bone of a rat tibia and embedded a titanium orthodontic mini-implant (diameter, 1.5 mm) in the hole. Twelve individually weighed hydroxyapatite grains (HA grains) were placed around the implant either by one dentist (method 1) or separately by 12 dentists (method 2). In vivo micro-CT was used to scan the model after placement of each grain to measure increases and decreases in bone volume voxel number. The subtracted bone voxel volume increased with HA weight in both methods. Simple linear regression analysis showed a significant correlation between weight and volume in both methods (method 1: regression coefficient: 516.502, P < 0.05; method 2: regression coefficient: 4837.432, P < 0.05). Metal artifacts did not appear to influence measurements of bone volume, although further studies are required to determine the effect of thicker implants.

Induction plasma sprayed Sr and Mg doped nano hydroxyapatite coatings on Ti for bone implant

In this study, we report fabrication of strontium (Sr) and magnesium (Mg) doped hydroxyapatite (HA) coating on commercially pure titanium (Cp-Ti) substrates using inductively coupled radio frequency (RF) plasma spray. HA powder was doped with 1 wt % Sr (Sr-HA) and 1 wt % Mg (Mg-HA), heat treated at 800°C for 6 h and then used for plasma spray coating. X-ray diffraction (XRD) and Fourier transformed infrared spectroscopic (FTIR) analysis indicated that the coatings were primarily composed of phase pure crystalline HA. When compared to undoped HA coating, physical properties such as microstructure, grain size, and adhesive bond strength of the doped HA coatings did not change significantly. Microstructure of the coatings showed coherency in the structure with an average grain size of 200-280 μm HA particles, where each of the HA grains consisted of 20-30 nm sized particles. An average adhesive bond strength of 17 MPa ensured sufficient mechanical strength of the coatings. A chemistry dependent improvement in bone cell-coating interaction was noticed for doped coatings although it had minimal effect on physical properties of the coatings. In vitro cell-materials interactions using human fetal osteoblasts (hFOB) showed better cell attachment and proliferation on Sr-HA coatings compared to HA or Mg-HA coatings. Presence of Sr in the coating also stimulated hFOB cell differentiation and alkaline phosphatase (ALP) expression. Improvement in bioactivity of Sr doped HA coatings on Ti without compromising its mechanical properties makes it an excellent material of choice for coated implant.

Elaboration of Sol-Gel Derived Hydroxyapatite / Yttria Stabilized Zirconia Composite Coatings Obtained for Biomedical Application

In this study, nanostructured composite coatings of hydroxyapatite (HA)/ 30wt% yttria stabilized zirconia (YSZ) coatings containing 0, 3, 5, and 8 mol% Y2O3 (namely; HA-0YSZ, HA-3YSZ, HA-5YSZ, and HA-8YSZ) were successfully synthesized using the sol-gel method. The crystallite size of the coating was about ~44-58 nm for tetragonal and cubic zirconia grain size and 75-87 nm for hydroxyapatite grain size. Crack-free and homogeneous HA-YSZ composite coatings were obtained with no observable defects. The uniform distribution of zirconia particles in a composite would be highly beneficial for obtaining homogeneous coatings of HA-YSZ film and would hinder grain growth of HA phase during calcinations. In vitro evaluation in 0.9% NaCl showed that Ca2+ dissolution rate of composite coatings was lower than pure HA coatings.

Microstructure: Surface and cross-sectional studies of hydroxyapatite formation on the surface of white Portland cement paste in vitro

The formation of hydroxyapatite was investigated at the surface and at the cross-section of white Portland cement paste samples before and after immersion in simulated body fluid. Scanning electron microscope images showed that hydroxyapatite were found at the surface of white Portland cement after immersion in simulated body fluid. Hydroxyapatite grains of mostly ≈1 μm size with some grain size of ≈2–3 μm were seen after 4 days immersion period. More estabilshed hydroxyapatite grain size of ≈3 μm grains were observed at longer period of immersion at 7 and 10 days. The cross-section of the samples was investigated using line scanning technique and was used to determine the hydroxyapatite layer. A strong spectrum of phosphorus is detected up to 6–8 μm depth for samples after 4, 7 and 10 days immersion in simulated body fluid when compared to weak spectrum detected before immersion. The increase in the phosphorus spectrum corresponds to the hydroxyapatite formation on the surface of the samples after the samples were placed in simulated body fluid.

Induction plasma sprayed nano hydroxyapatite coatings on titanium for orthopaedic and dental implants

This paper reports preparation of a highly crystalline nano hydroxyapatite (HA) coating on commercially pure titanium (Cp-Ti) using inductively coupled radio frequency (RF) plasma spray and their in vitro and in vivo biological response. HA coatings were prepared on Ti using normal and supersonic plasma nozzles at different plate powers and working distances. X-ray diffraction (XRD) and Fourier transformed infrared spectroscopic (FTIR) analysis show that the normal plasma nozzle lead to increased phase decomposition, high amorphous calcium phosphate (ACP) phase formation, and severe dehydroxylation of HA. In contrast, coatings prepared using supersonic nozzle retained the crystallinity and phase purity of HA due to relatively short exposure time of HA particles in the plasma. In addition, these coatings exhibited a microstructure that varied from porous and glassy structure at the coating-substrate interface to dense HA at the top surface. The microstructural analysis showed that the coating was made of multigrain HA particles of ~ 200 nm in size, which consisted of recrystallized HA grains in the size range of 15–20 nm. Apart from the type of nozzle, working distance was also found to have a strong influence on the HA phase decomposition, while plate power had little influence. Depending on the plasma processing conditions, a coating thickness between 300 and 400 μm was achieved where the adhesive bond strengths were found to be between 4.8 and 24 MPa. The cytotoxicity of HA coatings was examined by culturing human fetal osteoblast cells (hFOB) on coated surfaces. In vivo studies, using the cortical defect model in rat femur, evaluated the histological response of the HA coatings prepared with supersonic nozzle. After 2 weeks of implantation, osteoid formation was evident on the HA coated implant surface, which could indicate early implant-tissue integration in vivo.

Nanoelectrochemical coatings on titanium for bioimplant applications

Nanometre sized hydroxyapatite grains improve bioactivity and improve osteoblast functions, and are better than the micron sized hydroxyapatite. The surface of titanium can be modified to coat nanosized hydroxyapatite by electrochemical deposition from electrolytes containing calcium and phosphorus precursors. Recently, ultrasonic agitation has been employed to obtain thin coatings of hydroxyapatite. This coating contains nanosized apatite that shows a promising osteoblast cell activity. Moreover, titanium oxide nanotubes have attracted the attention of various researchers due to the increased exploitation of specific functional properties of TiO2 in various applications. TiO2 nanotubes have been formed by anodic oxidation in fluoride based acid electrolytes and these have thicknesses of up to a maximum of 500 nm. Use of fluoride containing glycerol electrolyte is shown to produce smooth tubes of very high aspect ratio. Ultrasonic agitation of the electrolyte has also been employed to produce good quality TiO2 nanotubes. This review describes the cathodic deposition of nanohydroxyapatite first and the formation of anodic nanotubular TiO2 later along with their properties.

Mechanical properties of suspension plasma sprayed hydroxyapatite coatings submitted to simulated body fluid

Home synthesized (HA) powder was formulated with water and alcohol to obtain a suspension used to plasma spray coatings onto titanium substrate. The deposition process was optimized and the resulting coatings were soaked in simulated body fluid (SBF) for the periods of 3, 7, 14, 28, and 60 days at controlled temperature of 37 °C. The microstructural research enabled to find in the as-sprayed deposits two characteristic zones: (i) dense zone corresponding to the lamellas, observed usually in thermally sprayed coatings; (ii) sintered zone containing fine hydroxyapatite grains corresponding to the fine solids from initial suspension. The sintered zone disappears after soaking in SBF and the pores get filled by the reprecipitated calcium phosphates. The adhesion of the soaked coatings to the substrate was characterized by the critical load in the scratch test and was about 10 to 12 N. The Young modules of the coatings were determined with help of depth-sensing indentation test by the use of the technique developed by Oliver and Pharr. The modules were not depending on the time of soaking and their mean values were 15.6 and 28.4 GPa, depending on the coating operational parameters. The scratch test enables to determine the hardness of the coatings, which remained fairly constant during the time of soaking in the range of 3 to 5 GPa. This hardness was compared to that the Martens microhardness which doubled with time of soaking to reach up to 1 GPa.

Carbon nanotube toughened hydroxyapatite by spark plasma sintering: Microstructural evolution and multiscale tribological properties

Carbon nanotube (CNT) reinforced hydroxyapatite (HA) composite synthesized using spark plasma sintering is investigated in this study. Quantitative microstructural analysis suggests that CNTs play a role in grain boundary pinning and are responsible for the improved densification and retention of nanostructure throughout the thickness of the sintered pellet. HA crystal forms coherent interface with the CNT, resulting in a strong interfacial bond. The uniform distribution of 4 wt.% CNTs in the HA matrix, good interfacial bonding and fine HA grain size help to improve the fracture toughness by 92% and elastic modulus by 25% as compared to the HA matrix without CNT. Toughening mechanisms have been explained in terms of interfacial shear strength and pull-out energy of CNT from the HA matrix. CNT plays a major role in improving the wear resistance of HA matrix at both macro- and nano-scale. It is concluded that graphene layer removal from the CNT surface occurs during macro-wear, but not for nano-wear. Thus, the coefficient of friction (CoF) in HA–CNT decreases in macro-wear due to lubrication available through delaminated graphene layers.

Advanced Microstructural Study of Suspension Plasma Sprayed Hydroxyapatite Coatings

Fine, home-synthesized, hydroxyapatite powder was formulated with water and alcohol to obtain a suspension used to plasma spray coatings onto a titanium substrate. The deposition process was optimized using statistical design of 2 n experiments with two variables: spray distance and electric power input to plasma. X-ray diffraction (XRD) was used to determine quantitatively the phase composition of obtained deposits. Raman microscopy and electron probe microanalysis (EPMA) enabled localization of the phases in different positions of the coating cross sections. Transmission electron microscopic (TEM) study associated with energy-dispersive x-ray spectroscopy (EDS) enabled visualization and analysis of a two-zone microstructure. One zone contained crystals of hydroxyapatite, tetracalcium phosphate, and a phase rich in calcium oxide. This zone included lamellas, usually observed in thermally sprayed coatings. The other zone contained fine hydroxyapatite grains that correspond to nanometric and submicrometric solids from the suspension that were agglomerated and sintered in the cold regions of plasma jet and on the substrate.

Abnormal grain growth of hydroxyapatite ceramic sintered in a high magnetic field

An investigation has been made on the abnormal grain growth of crystal oriented hydroxyapatite in sintering using a high magnetic field. According to X-ray diffraction and microstructure analysis, a high magnetic field in sintering could not affect the crystal direction of the hydroxyapatite, which was previously oriented by a high magnetic field in a slip casting, but influence the growth of hydroxyapatite grains. If the magnetic field, the direction of which was perpendicular to the a- and b-axis crystal orientation of the hydroxyapatite, was applied during the sintering process, abnormal growth grains were produced. On the other hand, if the applied magnetic was parallel to the a- and b-axis crystal orientation of the hydroxyapatite, the abnormal growth was restrained and grains with rather uniform sizes were produced.

Phase evolution of hydroxapatite coatings suspension plasma sprayed using variable parameters in simulated body fluid

Abstract Fine, hydroxyapatite (HA) powder, synthesized using calcium nitrate and diammonium nitrate was formulated with water and alcohol to obtain a suspension used to plasma spray coatings onto titanium substrates. The deposition process was optimized using statistical design of 2 n experiments with two variables: spray distance and electric power input to arc plasma. The sprayed coatings were soaked in simulated body fluid (SBF) for the periods of 3, 7, 14, 28, and 60 days at controlled temperature of 37 °C. The reference intensity ratio (RIR) method basing onto X-ray diffraction (XRD) data was used to determine quantitatively the phase composition of as-sprayed and soaked deposits. Electron probe microanalysis (EPMA) enabled to make the profiles of calcium to phosphorus atomic ratio along a line though the coatings' cross sections. Raman spectroscopy of selected samples enabled to localize the different crystal phases in sprayed coatings. The coatings included some porosity and have two characteristic zones: (i) dense zone corresponding to the lamellas, observed usually in thermally sprayed coatings; (ii) sintered zone containing fine hydroxyapatite grains which correspond to the fine solids from the suspension which were agglomerated in the cold regions of plasma jet and sintered on the substrate. The soaking in SBF homogenizes the morphology of coatings. The sintered zone disappears and the pores get filled by the reprecipitated calcium phosphates.

Dense Nanostructured Hydroxyapatite Coating on Titanium by Aerosol Deposition

In order to improve biocompatibility of Ti metal substrates, 1‐μm‐thick nanostructured hydroxyapatite (HAp) coatings were deposited on the substrates through aerosol deposition, which sprays HAp powder with an average particle size of 3.2 μm at room temperature in vacuum. The original HAp particles were fractured into nanoscale fragments to form highly dense coating during the deposition process. Density of the HAp coating was 98.5% theoretical density (TD). Transmission electron microscopy observation revealed that the as‐deposited coating consisted of HAp crystallites with average grain size of 16.2 nm and amorphous phase. Tensile adhesion strength between the coating and the substrate was 30.5±1.2 MPa. Annealing up to 500°C in air increased crystallinity and grain size in the coating without any delamination or crack according to X‐ray diffraction analysis and electron microscopy. MTS assay and alkaline phosphatase activity measurements with MC3T3‐E1 preosteoblast cell revealed that the biocompatibility was greatly improved by postdeposition heat treatment at 400°C in air due to well‐crystallized HAp with average grain size of 29.3 nm. However, further heat treatment at 500°C deteriorated biocompatibility due to rapid growth of HAp grains to average size of 99 nm. Cross section of the coating on a commercially available Ti dental implant revealed full coverage of the surface with HAp.

Reaction of sodium calcium borate glasses to form hydroxyapatite

This study investigated the transformation of two sodium calcium borate glasses to hydroxyapatite (HA). The chemical reaction was between either 1CaO . 2Na(2)O . 6B(2)O(3) or 2CaO . 2Na(2)O . 6B(2)O(3) glass and a 0.25 M phosphate (K(2)HPO(4)) solution at 37, 75 and 200 degrees C. Glass samples in the form of irregular particles (125-180 microm) and microspheres (45-90 and 125-180 microm) were used in order to understand the reaction mechanism. The effect of glass composition (calcium content) on the weight loss rate and reaction temperature on crystal size, crystallinity and grain shape of the reaction products were studied. Carbonated HA was made by dissolving an appropriate amount of carbonate (K(2)CO(3)) in the 0.25 M phosphate solution. X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy were used to characterize the reaction products. The results show that sodium calcium borate glasses can be transformed to HA by reacting with a phosphate solution. It is essentially a process of dissolution of glass and precipitation of HA. The transformation begins from an amorphous state to calcium-deficient HA without changing the size and shape of the original glass sample. Glass with a lower calcium content (1CaO . 2Na(2)O . 6B(2)O(3)), or reacted at an elevated temperature (75 degrees C), has a higher reaction rate. The HA crystal size increases and grain shape changes from spheroidal to cylindrical as temperature increases from 37 to 200 degrees C. Increase in carbonate concentration can also decrease the crystal size and yield a more needle-like grain shape.

Mapping the structure, composition and mechanical properties of human teeth

The structure-property relationship in human adult and baby teeth was characterised by grazing-incidence synchrotron radiation diffraction, optical and atomic-force microscopy, in addition to Vickers indentation. Similarities and differences between both types of teeth have been highlighted and discussed. Depth-profiling results indicated the existence of contrasting but distinct gradual changes in crystal disorder, phase abundance, crystallite size and hardness within the baby and adult enamel, thus confirming the graded nature of human teeth. When compared to the adult tooth, the baby enamel is softer, more prone to fracture, but has larger hydroxyapatite grains. Vickers hardness of the enamel was load-dependent but load-independent in the dentine. The use of a “bonded-interface” technique revealed the nature and evolution of deformation-microfracture damage around and beneath Vickers contacts.

Crystallographic texture in pulsed laser deposited hydroxyapatite bioceramic coatings

The orientation texture of pulsed laser deposited hydroxyapatite coatings was studied by X-ray diffraction techniques. Increasing the laser energy density of the KrF excimer laser used in the deposition process from 5 to 7 J/cm 2 increases the tendency for the c-axes of the hydroxyapatite grains to be aligned perpendicular to the substrate. This preferred orientation is most pronounced when the incidence direction of the plume is normal to the substrate. Orientation texture of the hydroxyapatite grains in the coatings is associated with the highly directional and energetic nature of the ablation plume. Anisotropic stresses, transport of hydroxyl groups and dehydroxylation effects during deposition all seem to play important roles in the texture development.

In situ Formation of Hydroxyapatite‐Whisker Ceramics by Hydrothermal Hot‐Pressing Method

Hydroxyapatite (HAp) ceramics have been prepared from α‐tricalcium phosphate (α‐TCP) with addition of water or ammonia water by hydrothermal hot‐pressing (HHP) method under a condition of 300°C/40 MPa/2 h. When the additive is water, it appears that the HAp grains produced show whisker‐like and plate‐like features. The bending strength of the HAp ceramic obtained is measured to be 24.5 MPa. When the additive is ammonia water, the obtained HAp ceramic consists of HAp‐whiskers only. The bending strength and fracture toughness reach 56 MPa and 1.52 MPa·m1/2, respectively. Treating α‐TCP with addition of ammonia water by the HHP method is thus a useful method for in situ fabrication of HAp‐whisker ceramics.

Synthesis of nanocrystalline hydroxyapatite by using precipitation method

In this investigation, hydroxyapatite powder has been synthesized from the calcium nitrate hydrated and di-ammonium hydrogen phosphate solution by precipitation method and heat treatment of hydroxyapatite powders. In order to study the structural evolution, the Fourier transform infrared spectroscopy (FTIR), the X-ray diffraction (XRD) and simultaneous thermal analysis (STA) were used. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to estimate the particle size of the powder and observe the morphology and agglomeration state of the powder. Results show that hydroxyapatite nanocrystalline can successfully be produced by precipitation technique from raw materials. Hydroxyapatite grain gradually increased in size when temperature increased from 100 to 1200 °C, and the hydroxyapatite hexagonal-dipyramidal phase was not transformed to the other calcium phosphates phases up to 1200 °C.

Bioactive ceramic composites sintered from hydroxyapatite and silica at 1200∘C: preparation, microstructures and in vitro bone-like layer growth

Bioceramic composites were synthesized by sintering the powders of hydroxyapatite (HAp) mixed directly with additive of 0.5, 1.0, 2.0, 5.0 and 10 wt.%SiO(2), respectively, at 1,200( composite function)C. X-ray diffraction (XRD) analysis indicated that the phase transformation from HAp to tricalcium phosphate (TCP) comprising alpha-TCP and Si-TCP occurred and became more prominent with the addition of SiO(2) and the increase in SiO(2) content. The observations of their surface microstructures showed that the addition of SiO(2) suppressed the grain growth and promoted the formation of crystalline-glassy composites denoted HAp + TCP/Bioglass. As the SiO(2) content is as high as 5 wt.%, the composite made a feature of crystalline clusters with different sizes consisting of HAp and TCP grains surrounded by the matrix of glassy phase. Furthermore, the dependence of in vitro bioactivity of these composites on the SiO(2) content was biomimetically assessed by determining the changes in surface morphology, i.e., bone-like apatite layer growth, after soaking in an acellular stimulated body fluid (SBF) for 3 days at 36.5( composite function)C. It was found that the HAp-SiO(2) composites showed a much faster bone-like layer growth than pure HAp, and the propensity of composites to exhibit a better bioactivity was getting more notable with increasing SiO(2) content, except for the case of the highest content of 10 wt.%. It was believed that the formation of the bone-like layer on the surfaces of these bio-composites is closely related to the increasingly provided silanol groups and transformed TCP phase in materials associated with the content of SiO(2) added.

Shape memory properties of poly(d,l-lactide)/hydroxyapatite composites

Poly(D,L-lactide) (PDLLA) and Hydroxyapatite (HA) are compounded, which possess biodegradation, biocompatibility and shape memory properties. In the paper, we prepared serial imposing shape memory composites with different shapes, composite ratios and sample thicknesses. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were carried out to examine surface morphology, glass transition temperature (Tg), dynamic mechanical properties, and shape memory effect of PDLLA/HA composites, respectively. Moreover, some interesting shape memory behaviors were investigated. The results show that the better disperse morphology of HA grains using the experiment methods, and PDLLA/HA composites at a definite range of compound ratio have much better shape memory effect than pure PDLLA polymer. It indicates that HA particles can improve shape memory effect and PDLLA/HA composites are potential for biomedical applications.