Crystalline Hydroxyapatite Research Articles

Properties and Mechanism of Hydroxyapatite Coating Prepared by Electrodeposition on a Braid for Biodegradable Bone Scaffolds.

Hydroxyapatite (HA) coating is successfully prepared by electrodeposition on the surface of polyvinyl alcohol (PVA)/polylactic acid (PLA) braid which serves as a potential biodegradable bone scaffold. The surface morphology, element composition, crystallinity and chemical bonds of HA coatings at various deposition times (60, 75, 90, 105 and 120 min) are characterized by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), respectively. Average Surface roughness (Ra) of HA coating is observed by confocal microscopy. The results reveal that the typical characteristic peaks of the FTIR spectrum confirm that HA coating is successfully prepared on the rugged surface of the PVA/PLA braid. The XRD results indicate that the crystallinity of HA can be improved by increasing deposition time. In the 90 min-deposition, hydroxyapatite has a dense and uniform coating morphology, Ca/P ratio of 1.7, roughness of 0.725 μm, which shows the best electrodeposition performance. The formation mechanism of granular and plate-like hydroxyapatite crystals is explained by the structural characteristics of a hydroxyapatite unit cell. This study provides a foundation for a bone scaffold braided by biodegradable fibers.

Sorption of Co2+, Pb2+, and Sr2+ Ions on Hydroxyapatite, Synthesized in the Presence of Oxyethylidenediphosphonic Acid

The physicochemical and sorption properties of hydroxyapatite synthesized in the presence of oxyethylidenediphosphonic acid, as crystallization inhibitor, were studied. The effect of acid concentration and calcium phosphate reagents was established on the sorption properties of hydroxyapatite with respect to ions Co2+, Pb2+, and Sr2+. It was shown that the sorption capacity of amorphous hydroxyapatite obtained in the presence of 1.0 mol % oxyethylidenediphosphonic acid, for Co2+ and Sr2+ ions, increases by 2–2.5 times, and for Pb2+ ions, by 4–5 times compared to crystalline hydroxyapatite obtained without acid additives. It was revealed that the observed differences in the sorption capacity of amorphous and crystalline hydroxyapatite with respect to the studied metal ions are due to different mechanisms of their adsorption.

Ascorbic Acid-Assisted Microwave Synthesis of Mesoporous Ag-Doped Hydroxyapatite Nanorods from Biowaste Seashells for Implant Applications.

Post-surgery implant infection is one of the most challenging issues in orthopedics and it is mainly caused by infective micro-organisms. A potential approach to overcome this issue is developing biomaterials with efficient antibacterial activity. The main intention of this present research is devoted to ascorbic acid-assisted microwave synthesis of mesoporous (silver) Ag-doped hydroxyapatite (HAp) nanorods using biowaste seashells with antibacterial properties. XRD, FTIR, and Raman spectroscopy results revealed that the synthesized nanoparticles are hexagonal crystalline HAp. Further, the silver-doped HAp was also successfully produced without affecting the HAp crystalline phase by forming electrostatic interaction with PO43- ions during the synthesis. The morphological features confirm that the pure HAp is elongated mesoporous nanorods with 20 nm width and 300-500 nm length. However, silver doped HAp nanoparticles such as AgHA-1, AgHA-2, and AgHA-3 are found to be similar mesoporous rods but with different aspect ratios in sizes of 15, 10-15, and 5-10 nm width and 80-100, 10-15, and 20-30 nm length. The BET specific surface areas were obtained as 29 ± 3, 84 ± 2, 87 ± 2, and 128 ± 3 m2 g-1, and pore diameters were 4.68, 4.18, 9.30, and 3.77 nm, respectively, for pure HA, AgHA-1, AgHA-2, and AgHA-3. Therefore, HAp nanoparticles with different dimensions and mesoporous structures could be rapidly prepared using a microwave-assisted method and ascorbic acid as a supporting material. In addition, the synthesized HAp nanoparticles are analyzed for its antibacterial and cytotoxicity studies. The antibacterial and cytotoxicity study clearly reveals that the Ag-doped HAp nanorods are efficiently antibacterial and nontoxic in nature. Hence, it is clear that the ascorbic acid-enabled microwave-assisted method will be one of the best methods for the rapid production of HAp nanoparticles with different dimensions and mesoporous structures for its application as an implant material.

Orientation control for a-axis or c-axis oriented crystal films of hydroxyapatite, and a possible growth mechanism derived from X-ray diffraction

Hydroxyapatite (HA), the main component of living hard tissues, owes its specificity to electrical anisotropy resulting from its hexagonal crystal structure. The strong demand for technology to control the crystal orientation prompted us to develop techniques to fabricate uniaxial a- or c-axis crystalline HA films. C-axis-oriented HA was grown epitaxially on a ZnO (001) film, on an Al2O3(001) single crystal with a hexagonal lattice by pulsed laser deposition, and on the amorphous native oxide layer of a Si wafer, confirming the importance of hexagonal lattice formation as a first layer for c-axis orientation. In contrast, a-axis-oriented HA film was grown on Au and Pt films of which low reactivity enable HA constituent elements to migrate unrestrictedly before undergoing nucleation. The ability to separately produce a- and c-axis HA contributes to device development and to fundamental biochemical research on bones and teeth in the living body.

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.

Synthesis of CPC/chitosan and its endurance test in simulated body fluid

Hydroxyapatite (HA) has been synthesized by solid state reaction method by using CaHPO4 and CaCO3 as reactants. The reaction was done at 1200°C for 7 hours in a local ceramic industry. The synthesized HA has Ca/P ratio of 1.7, crystallite size of 60 nm and morphology of rod-like shape. Then HA was used as a powder phase to produce calcium phosphate cement/chitosan (CPC/chitosan). A mixture of 2.5% Na2HPO4 and 1% chitosan solution was used as liquid phase. Structure and morphology of HA were slightly changed by the hardening of CPC/chitosan. Endurance test of CPC/chitosan in simulated body fluid (SBF) was performed for 36 days. CPC/chitosan was not washed out in the SBF. HA crystallinity as well as Ca/P ratio decreased by the testing time. The change of CPC/chitosan surface morphology into needle-like crystals indicated the surface growth of CPC/chitosan in SBF.

The Influence of Processing Conditions on the Structure of Magnetron Sputtered Hydroxyapatite Thin Films

The growing demand for functionality of implants is necessary to cater for the growing elderly population in need of repair for damaged or diseased tissues and organs. Radiofrequency magnetron sputtered crystalline hydroxyapatite thin films with preferred crystal orientation on polished titanium substrates were produced without additional substrate heating. No hydroxyl absorption bands were detected in hydroxyapatite thin films even after the addition of water vapour during the sputtering process or hydrothermal post-treatment of the films.

The Extraction of pure hydroxyapatite from porcine bone by thermal process

Natural hydroxyapatite (HA) has been extracted from porcine bone by thermal decomposition without any chemical treatment. The suitable condition to synthesize HA was chosen as a heating bone at 750 °C during 6 hours. XRD and FTIR analyses confirmed the high purity and crystallinity of synthetic HA. Furthermore, the transformation of the obtained HA to other phases did not mention up to 1200 °C. TG curve showed a slight loss of mass at 950 °C, but the DSC analysis did not present any physic-chemical phenomena during the period of measurement. FE-SEM images showed the different particles including spheres, scales, and rods in the structure of natural HA. EDX analysis indicated that the Ca/P ratio of the synthetic HA is 1.64, nearly the theoretical value of 1.67. Overall, the results obtained in this study confirmed the success of the thermal process to extract the natural HA from porcine bone.

Influence of MgO nanoparticles on the mechanical properties of coated hydroxyapatite nanocomposite scaffolds produced via space holder technique: Fabrication, characterization and simulation

In the current study, hydroxyapatite (HA)-MgO scaffolds are fabricated with the aid of the space holder technique using NaCl as the spacer type. After that, the fabricated samples are deposited in gelatin (GN) with ibuprofen (IBO) substitution to create GN-IBO thin surface coating. The samples are then synthesized chemically and the associated properties are studied using X-ray diffraction (XRD) and scan electron microscopy (SEM) equipped with the energy dispersive spectroscopy (EDS). The compressive strength, fracture toughness, hardness, porosity, bioactivity, degradation rate, wettability, and roughness of the manufactured HA-MgO bio-nanocomposite scaffolds containing different weight fractions of MgO nanoparticles are predicted. Accordingly, nonlinear mechanical behaviors including nonlinear free vibration and nonlinear vibrations associated with the prebuckling and postbuckling domains of an axially loaded plate-type bone implant made of the HA-MgO bio-nanocomposites coated with the GN-IBO thin layers are investigated analytically via a sandwich plate model. The obtained results reveal that magnesium has no considerable effect on the porosity, however it causes to enhance the compressive strength significantly. The presence of magnesium ions also leads to reduce the crystallinity of HA about 30–100 nm due to entering MgO nanoparticles into the network. The results related to the sample with 10 wt% MgO nanoparticles indicate that the microscopic structure of the fabricated bio-nanocomposite scaffold is three-dimensional with porous architecture. Also, it is shown that the solubility of the HA composed with MgO nanoparticles decreases with higher bioactivity.

Ammonium Hydroxide Mediated Hydrothermal Crystallization of Hydroxyapatite Coatings on Titanium Substrate

Controlled growth of hydroxyapatite (HAp) coatings on titanium substrate plays an important role in the fabrication of the composites for bone tissue engineering. We describe the synthesis of the crystalline hydroxyapatite coatings on the Ti/TiO2 substrate through a hydrothermal method by using ethylenediamine tetraacetic acid disodium salt (Na2EDTA) and varying concentrations of ammonium hydroxide (NH4OH) in calcium-phosphate precursor solution. Na2EDTA serves as a chelating agent, while NH4OH is used as an alkaline source and crystal growth modifier. We characterized the HAp coatings using x-ray diffraction, scanning electron microscopy, and Raman spectroscopy. We also performed the elemental chemical analysis by means of a particle induced x–ray emission method. Our results show that there is a pH limit for which the hydrothermal deposition of HAp on titanium occurs. Moreover, we observed that NH4OH had a measurable influence on the coating thickness as well as on the size and shape of the HAp crystals. We found that with the increase of NH4OH concentration, the thickness of the Hap layer increases and its morphology changes from irregular flakes to well-defined hexagonal rods.

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.

A Comparative Investigation on Bioactivity and Antibacterial Properties of Sol-Gel Derived 58S Bioactive Glass Substituted by Ag and Zn

The bioactive glass systems of xAg2O-SiO2-P2O5-CaO and xZnO-SiO2-P2O5-CaO (x = 2 and 4% mol) were successfully synthesized through sol-gel method. The effect of silver and zinc contents on the in-vitro formation of hydroxyapatite (HA), cell viability, and antibacterial properties were studied. The HA formation and its microstructure were investigated through scanning electron microscopy (SEM) and Energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction analysis (XRD). The results showed that the rate of crystalline HA formation on SiO2-P2O5-CaO-xAg2O bioactive glass, in which x = 0 and 2, (B (58S) and BA2), was higher than other specimens. The evaluation methods of 3-(4,5 dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and alkaline phosphatase (ALP) illustrated that low silver (2% Ag2O) amount had a stimulating influence on both differentiation and proliferation promotion of cells (G292 osteoblastic). Furthermore, the antibacterial investigations showed that Ag bioglass samples had better antibacterial effect in comparison to Zn bioglass samples. Accordingly, the results revealed that specimen BA2 can be a good candidate for bone tissue application due to its significant bioactivity, antibacterial potential and optimal cell viability.

Diammonium Hydrogenphosphate Treatment on Dolostone: The Role of Mg in the Crystallization Process

The diammonium hydrogenphosphate (DAP, (NH4)2HPO4) reaction with calcite has been extensively investigated. The availability of free calcium ions in the reaction environment has been acknowledged as a crucial factor in the crystallization of calcium phosphates with a high (hydroxyapatite, Ca/P 1.67) or low Ca/P molar ratio (dicalcium phosphate dihydrate, Ca/P 1.00; octacalcium phosphate, Ca/P 1.33). On the contrary, no data are available on the DAP interaction at room temperature with dolomite in terms of reaction mechanism and composition of the reaction products. Here, a multi-analytical approach based on scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectrometry (EDS) and X-ray powder diffraction before and after heating treatments is proposed to explore how the formation of calcium phosphates occur on Mg-enriched substrates and if the presence of magnesium ions during the reaction influences the crystallization process of calcium phosphates. The DAP reaction with polycrystalline dolomite gives rise to the formation of struvite and of poorly crystalline hydroxyapatite. Calcium and magnesium ions mutually interfered in the crystallization of magnesium and calcium phosphates, respectively, whose effects influenced the properties (size, micro-morphology, composition and crystallinity) of the newly-formed phases.

Biomimetic fabrication of hydroxyapatite hollow spheres with polyoxyethylene chain-containing quaternary ammonium salt cationic Gemini surfactant as template

ABSTRACTThis paper reports a biomimetic fabrication of hydroxyapatite (HAp) with a hollow spherical three-dimensional architecture, using Ca(NO3)2 and (NH4)3PO4 as the starting materials, and a polyoxyethylene chain-containing quaternary ammonium salt cationic Gemini surfactant [C12C2C12 (EO)] as the template. The effects of the surfactant concentration, aging time, and temperature on the morphology and the degree of crystallinity of HAp were investigated. We also proposed a possible mechanism for the formation of hollow spherical HAp. The results showed that the cationic Gemini surfactant was the most important parameter for the formation of spherical HAp. We obtained uniform well-defined hollow spherical HAp with semidiameter about 1.5 μm, using 0.1% mass fraction of template, at 37°C for 7 days.

Low crystalline apatite in bone char produced at low temperature ameliorates phosphorus-deficient soils

Globally, more than 30% of soils are poor in phosphorus (P) and the productivity of these soils is severely restricted without the addition of P fertiliser. With future P supplies becoming limited, it is becoming increasingly important to identify ways of optimising the use of waste materials as P fertilisers. One technology that has been promoted extensively in recent years to improve quality of degraded soils is the application of biochar. In this context, char produced from recycled animal bone is of special interest because of its high P content (∼15%). This study investigated how production temperature affects chemical P forms in bone char and the impact on soil P availability in different P-deficient soils.The major P form in dried bone meal was poorly crystalline hydroxyapatite. As the pyrolysis temperature increased to 1050 °C, the hydroxyapatite structure measured with X-ray absorption near edge structure (XANES) spectroscopy persisted. Furthermore, crystallinity increased at temperatures above 750 °C, as revealed by X-ray powder diffraction (XRD). Plant availability was highest for bone char produced between 300 °C and 500 °C in three acidic soils from three continents, and declined rapidly above 750 °C. This strongly indicated that crystallinity of hydroxyapatite limits plant availability at high pyrolysis temperatures. In a high pH soil, all materials resulted in low P availability. As pyrolysis increased the P availability in comparison with dried bone, it was concluded that bone char produced at temperatures between 300 °C and 500 °C has the potential to improve fertility of P-poor, low pH soils.

Starch:Pectin Acidic Sachets Development for Hydroxyapatite Nanoparticles Storage to Improve Phosphorus Release

The importance of fertilizers in boosting crop production has motivated the development of novel high-performance systems capable of improving the phosphorus release in the soil. For instance, methods capable of increasing the surface area of fertilizer particles and promoting the solubilization of low-solubility compounds, including phosphates, are highly pursued. This study was aimed at synthesizing hydroxyapatite nanoparticles and investigating their solubility in relation to crystallinity, size, and morphology for phosphorous fertilizer applications. To improve the phosphate ions release, the hydroxyapatite nanoparticles were storage in biodegradable sachets composed of thermoplastic starch/pectin blends with different polymer ratios. The results showed that the smallest and less crystalline hydroxyapatite nanoparticles presented the highest solubility. After storage in polymeric thermoplastic starch:pectin sachets, solubility for all samples was greatly improved, enhancing the phosphorus release due to pH decrease, independent on the nanoparticle size, shape, and crystallinity. The results highlight that the use of acidic sachets is a valuable approach for enhancing phosphorus and other macronutrients release from fertilizers with basic surface properties, aiming at increasing agricultural crop productivity.

Effect of Pre-treatment and Calcination Process on Micro-Structural and Physico-Chemical Properties of Hydroxyapatite derived from Chicken Bone Bio-waste

Abstract This study reports the feasibility of isolation of hydroxyapatite (HA) from chicken bone bio-waste and the effect of pre-treatment and calcination process of bones on micro-structural and physico-chemical properties of HA. Chicken bones are treated with acid, alkali and acid-alkali solution followed by calcination at 700, 800 and 900°C respectively. The calcined bones are characterized and compared. It is found that acid treated bones calcined at 900°C yields pure phase of crystalline HA particles of size 600 nm with good pore morphology having pore diameter 208 nm, Ca/P atomic ratio of 1.653 and high thermal stability, ideal for biomedical applications.

Microwave treatment and pH influence on hydroxyapatite morphology and structure

This paper reports the influence of microwave treatment duration and pH conditions of initial precursors on the morphological and crystalline dispersity of the hydroxyapatite (HAp) synthesized by hydrothermal method.The obtained HAp samples were studied by scanning electron microscopy, X-Ray diffraction method and low nitrogen adsorption method. We have obtained nanostructured crystalline hydroxyapatite with 95% crystallinity, porous structure and average particles size in interval 17…46 nm consolidated in aggregates with size distribution of 0.5…25 μm. The pH growth from 8 to 13 results in double increase of HAp specific area(from 69 up to 133 m2/g), meanwhile microwave irradiation brings to particles aggregation: HAp treated during 0… 10…30 min have specific surface are 112…67…41 m2/g, respectively. As a result at pH=13 and without microwave irradiation treatment we synthesized HAp with maximum surface compared to the surface of natural HAp that makes obtained HApto be promising material in biotechnological applications.

Nano-Hydroxyapatite Powder for Biomedical Implant Coating

Abstract Bioceramic crystalline hydroxyapatite (HA) is effectively used as bioimplant material due to its compositional resemblance to the bone mineral and promising biocompability. It is can be defined as a major member of bioceramic materials world. HA was successfully synthesized via a wet chemical precipitation with pH 10, stirring rate of 500 rpm and acid-addition rate of 3ml/min. HA powder has been studied at different synthesis temperature (30°C, 40°C and 60°C) and different calcination temperature (600 °C, 700 °C and 850 °C) to achieve the stoichiometric Ca/P ratio 1.667 and rod or spherical morphologies with particle size

Effect of Aging Time in the Synthesis of Biogenic Hydroxyapatite Derived from Cockle Shell

Abstract Cockle shell wastes are abundant, easily available and can be obtained at low cost. It is rich in calcium carbonate (CaCO3) that can be precursor to synthesis hydroxyapatite (HAP). The HAP has potential to be used in numerous applications such as biomedical and wastewater treatment. The overall objective of this study is to determine the effect of aging time on the production of HAP derived from cockle shells waste. There are two aging times used in this study which are 3 and 5 h. The processes involved in synthesizing HAP were pretreatment of the cockle shells, production of CaCO3 in aragonite form, calcination of the CaCO3 to form CaO, production of Ca(OH)2 and finally reaction of the Ca(OH)2 solution with the phosphate source to obtain HAP. All samples have undergone physicochemical analyses to determine their phases, crystallinity, purity, functional group, surface morphology and elemental analysis using X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscope (SEM) and Electron Dispersive X-ray Analysis (EDX). This study found that 5 h aging time produced higher crystalline HAP compared to the others. Overall, this study proved that aging time play vital role in the quality of the synthesized HAP.