Pure Crystalline Hydroxyapatite Research Articles

Effects of annealing in vacuum on the microstructure of silicon-containing calcium phosphate films deposited on a ZrNb alloy by radio-frequency magnetron sputtering

Coatings were deposited on the surface of a ZrNb alloy by radio-frequency magnetron sputtering using targets consisting of either pure crystalline hydroxyapatite (HA) or silicon-containing HA (Si-HA). The coated ZrNb samples were heated in a vacuum furnace at a pressure of 5 × 10−5 Torr and temperature 700 °C for 2 h. Precursor powders of silicate-substituted HA [Ca10(PO4)6−x(SiO4)x(OH)2−x, x = 0, 0.5, or 1.72] were used to fabricate the targets for sputtering. The aim of this study was to analyze the effect of Si addition to HA on crystallization behavior and structure of the resulting films using transmission electron microscopy and electron diffraction patterns of selected sites. The average thickness of the films was in the range of 175–345 nm. The Si substitution in HA played a major role in the mechanisms of coating formation and crystallization behavior, which influenced the structure and crystallinity of the layers deposited by radio-frequency magnetron sputtering. Moreover, the results indicate that surface-induced crystallization of the deposited thin films is more pronounced than internal crystallization. A possible mechanism underlying the observed decrease in the crystallization rate with the increasing silicate content in the HA-based films is discussed.

Nano-size hydroxyapatite extracted from tilapia scale using alkaline heat treatment method

In biomedical research, hydroxyapatite (HAp) has been commonly used as the coating materials, filler and as a drug delivery system. This is mainly due to the similarity of the chemical composition of HAp to human bone and teeth that make it have excellent bioactivity and biocompatibility. Hence, the recovery of HAp from a natural resource such as from the animal scale and bone is a promising alternative to produce natural HAp, which is much similar to the human bone. Thus, in this research, the nano-size HAp was extracted from tilapia fish scale using alkaline heat treatment. The fish scale was pre-treated with 0.1% HCl to deproteinize the scale prior to the alkaline heat treatment. The alkaline heat treatment was performed in two stages to ensure complete removal of the organic compound from the tilapia scale. Upon completing the procedure, off white HAp powder was obtained. The HAp powder was characterised using X-ray diffraction analysis (XRD), field emission scanning electron microscopy analysis (FESEM), energy dispersive spectroscopy (EDS), and fourier-transform infrared spectroscopy (FTIR). The XRD pattern demonstrated that the obtained powder was a pure crystalline HAp. The FESEM micrograph revealed that the HAp powder exhibited rod shapes with a size ranged between 50 and 60 nm width and 30–200 nm length. The EDS result revealed that the extracted HAp powder had a Ca/P ratio of 1.74, which was higher compared to stoichiometric HAp. Lastly, the corresponding functional groups of PO43- and CO32– were identified using FTIR were corresponded to the HAp functional group. In summary, the natural HAp extracted from the tilapia scales using alkaline heat treatment method has the potential to be used as biomaterials for the biomedical implant.

Pure hydroxyapatite as a substitute for enamel in erosion experiments

ObjectivesThe study evaluated the suitability of pure crystalline hydroxyapatite (HA) as a substitute for human (H) and bovine (B) enamel in erosion experiments. MethodsHuman and bovine enamel and hydroxyapatite specimens (n = 18 each) were submitted to demineralisation by HCl at pH values of 3.0, 2.6 and 2.0 (1.0, 2.5, and 10 mmol/l concentration). Specimens were eroded in a superfusion chamber for 7 min (flow rate: 1 μl/s). Multiple fluid samples were taken per specimen throughout the exposure period. The dissolved calcium content was measured using a colorimetric assay with Arsenazo III reagent, to serve as surrogate for erosive substance loss. Additionally, erosive tissue loss was quantified by profilometry. Differences in erosive substance loss were assessed by the Kruskal-Wallis and Conover’s posthoc test. ResultsGood agreement in erosive substance loss between HA and human specimens was found at pH 2.6, as no statistically significant difference and considerable overlap of their respective interquartile ranges was observed. At pH 2.0 and 3.0, a statistically significant difference between HA and human and bovine enamel was determined. HA consistently tended to have lower mean dissolution rates, with a maximum deviation from human enamel of -16% at pH 3. It displayed lower specimen variability with an average coefficient of variation of 17%, compared to 25% (H) and 25% (B), respectively. ConclusionsCrystalline hydroxyapatite may not be suitable for full substitution of biologic enamel in erosion experiments focusing on absolute measurement values, but is useful for establishing consistent relative trends between erosive agents due to biosimilar erosion behavior and lower experimental variability. This is especially true for preliminary studies where approval for use of biological samples is restricted. Clinical significanceCrystalline hydroxyapatite is a useful substitute of human or bovine enamel in experiments studying chemical aspects of dental erosion.

In Vitro Assessment of the Functional Dynamics of Titanium with Surface Coating of Hydroxyapatite Nanoparticles.

Manipulation of implant surface characteristics constitutes a promising strategy for improving cell growth and tissue response on a variety of materials with different surface topographies. Mesenchymal progenitor cells with a capacity to respond to titanium surface stimuli and differentiate into osteoblasts were used to perform comparative tests between two different implant topographies, including their functional interaction with pre-osteoblasts directly seeded onto the implants. Functional analysis of nanostructured implant surfaces was performed by in vitro assay analysis. The machined surface of titanium implants (mach group) was used as a control and compared with a nanoparticle HA activated surface implant (nano group), developed by the deposition of pure crystalline hydroxyapatite. Cell culture on the nano group surface resulted in higher cell adhesion and cultured osteoblast viability compared with the mach group. Scanning electron microscope (SEM) images revealed a stable interaction, indicated by the presence of focal cell adhesion formation. These results together with positive mineralization assays showed the nano group to be an excellent scaffold for bone-implant integration.

Investigation of in vitro mineralization of silicate-based 45S5 and 13-93 bioactive glasses in artificial saliva for dental applications

Bioactive glasses are important class of materials that have a wide range of applications in tissue engineering and dentistry. In dental tissue engineering, nanofibrous structures exhibit interesting features, such as high surface area, surface functionalization and porosity. In this study, silicate-based 45S5 and 13-93 bioactive glass fibers were fabricated using electrospinning technique and their in vitro mineralization behavior was investigated in two different artificial saliva solutions for various time intervals. Results revealed that both 45S5 and 13-93 bioactive glass fibers show high mineralization behavior in artificial saliva solutions. However different hydroxyapatite (HA) formation rates were observed depending on the glass type and the artificial saliva composition. HA formation initiated earlier in 45S5 glass fibers treated in artificial saliva compared to 13-93 glass. On the other hand, after 30 days of treatment, the surface of 13-93 glass fibers converted to pure crystalline HA, whereas, 45S5 glass surface contained some additional crystalline phases such as aragonite and calcite. Treatment in SAGF medium resulted with better HA conversion ability compared to Carter-Brugirard saliva for both types of glass fibers. In conclusion, the use of electrospun nanofibrous 45S5 and 13-93 bioactive glass scaffolds could be one approach suitable to dental applications.

Synthesis and Characterization of Hydroxyapatite Using Ammonium Hydroxide and Ethylenediaminetetraacetic Acid

High purity hydroxyapatite was synthesized with ammonium hydroxide and ethylenediaminetetraacetic acid (EDTA) through a hydrothermal synthesis process, using calcium hydroxide and phosphoric acid as the precursors for calcium and phosphorus. The newly synthesized hydroxyapatite was characterized by the techniques of X‐ray diffraction (XRD), scanning electron microscopy (SEM), Fourier‐transform infra‐red spectroscopy (FTIR), thermal analysis system (TG/DTA), electron probe micro analyzer (EPMA), and energy dispersive X‐ray (EDX) spectrometer. The results achieved from the above analyses demonstrated that pure crystalline hydroxyapatite can successfully be produced by using ammonium hydroxide and EDTA through the hydrothermal method. SEM revealed that the hydroxyapatite particles consisted of crystallized dandelion‐like structures with an average size of about approximately 10 µm. The Ca/P molar ratio of synthesized hydroxyapatite was determined as 1.66, which is almost close to the stoichiometric ratio (1.67) that is expected for a pure hydroxyapatite phase. TG/DTA indicated that there was almost no weight loss by the temperature change and confirmed that it was an ultra pure substance. XRD and FTIR results indicated that hydroxyapatite could be decomposed into tricalcium phosphate as the calcinations temperature increased to 900 °C.

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.

A novel process for the fabrication of nanoporous apatites from Moroccan phosphate rock

Naturally-abundant Moroccan phosphate (Bengurir ores) was used as a source for calcium and phosphorus precursors for the synthesis of nanoporous apatites, following a dissolution–precipitation method. The influence of temperature, ripening time and solvent nature on the crystal growth of apatite was investigated. For all products, poorly crystalline apatite phases were obtained after drying, exhibiting a mesoporous structure with specific surface area up to 150 m 2 g −1. These materials could be converted into a pure crystalline hydroxyapatite phase after treatment at 800 °C. This simple, eco-friendly and cheap procedure may be useful for the future development of sorbents for water treatment.

Hydroxyapatite-Electroplated cp–Titanium Implant and Its Bone Integration Potentiality: An In Vivo Study

This study was designed to precipitate hydroxyapatite coating on the surface of commercially pure titanium (cpTi) implants using an electroplating technique. After characterization of the hydroxyapatite coating, the bone-implant interface and bone integration of both cpTi and hydroxyapatite-coated implants were assessed. Twenty implants were divided equally into 2 main groups (n = 10). Ten cpTi implants were utilized as received, while the others were hydroxyapatite coated and then sterilized. The implants of both groups were inserted in the tibiae of New Zealand rabbits. The purity and crystallinity of the hydroxyapatite coat were characterized using x-ray diffraction. A scanning electron microscope examined the grain morphology. Profilometer evaluated the surface texture before and after sterilization. Histological examination using a scanning electron microscope was performed to qualify osseointegration of the regenerated bone and measure the gap distance at the bone-implant interface. Pure crystalline hydroxyapatite precipitate of thickness (range 69-78 microm) and rough surface (2.7 +/- 0.2 microm) compared to smooth cpTi (1.3 +/- 0.5 microm). The gamma-radiation sterilization resulted in finer grains and insignificant smoother surface. Histological examination of the cpTi implant exhibited less bone regeneration with few and less dense bone trabeculae, and gap distance was significantly high (1.29 +/- 0.51 microm). Meanwhile, the hydroxyapatite-coated implant showed a recognizable amount of bone regeneration with more and denser bone trabeculae, and gap distance ranged from 0 to 1.32 microm. The employed technique provided a thin and uniform pure crystalline hydroxyapatite coating. The characterization of the precipitated film is promising for clinically successful long-term bone fixation.

Dissolution behaviour of calcium phosphate coatings obtained by laser ablation

Pulsed laser deposited calcium phosphate coating on titanium alloy have been tested under simulated physiological conditions in order to evaluate the changes in morphology, composition and structure. The coatings were deposited under different conditions to obtain different crystalline structures, ranging from amorphous and mixed crystalline phases to pure crystalline hydroxyapatite (HA). The coated samples were immersed in a Ca-free Hank’s balanced salt solution for up to 5 days. Characterization of the coatings was performed by X-ray diffraction, scanning electron microscopy and Fourier-transform Raman spectroscopy before and after immersion. Their dissolution behaviour was also monitored through their mass loss and calcium release. Coatings of pure HA preserve their morphology and structure during the exposure time in solution. In multiphasic coatings, consisting of HA with tetracalcium phosphate (TetraCP) or β-tricalcium phosphate ( β-TCP) with a-tricalcium phosphate ( α-TCP), microporosity is induced by the complete dissolution of TetraCP or α-TCP. Amorphous calcium phosphate coatings totally dissolve.

Energy-dispersive X-ray microanalysis and scanning electron microscopy of developing and mature cat enamel

Calcium and phosphorus distribution in forming, maturing and mature enamel of cat teeth and the microstructures manifest in all these were examined in fractured enamel from the dentine-enamel junction toward the enamel surface. Concentrations of both Ca and P increased gradually from the forming enamel, through the maturing enamel and into the mature enamel. The innermost layer, adjacent to the dentine-enamel junction showed the greatest and the superficial layer the lowest concentration of Ca. Still the mature enamel of the erupted tooth was not yet completely mineralized and Ca and P concentrations only slightly higher than those in maturing enamel. Molar Ca:P ratio of each enamel stage was lower than that of pure crystalline hydroxyapatite. Simultaneously-performed SEM observations revealed microstructural changes in the enamel: in the forming-front layer of the forming enamel, the enamel was a rough, immature structure but began to show more compact, tighter structures as concentrations of Ca and P altered. The results suggest that the enamel organ excercises intense cellular control over increases of Ca and P concentration during the formation and maturation stages of amelogenesis.