Stability Of Hydroxyapatite Research Articles

Development of hydroxyapatite reinforced alginate–chitosan based printable biomaterial-ink

This study reports synthesis of sodium alginate/ chitosan/ hydroxyapatite (HAp) based biomaterial-ink. An ionic interaction between polyanionic alginate and polycationic chitosan has been observed that forms a physical gel. The dispersion of HAp has been achieved through ultra-sonication, and stability of HAp in the hydrogel system has been achieved through hydrogen bonding with chitosan. Post printing crosslinking has been carried out with a 10 w/v % aqueous calcium chloride (CaCl2) solution. The combinations of biomaterial-ink have been characterized through Attenuated Total Reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), Scanning Electron Microscope (SEM), contact angle measurements. Further, the inks were characterized to estimate the printability and rheological responses. ATR-FTIR study confirms the ionic interaction between alginate and chitosan and identifies the presence of HAp in the biomaterial-ink. SEM morphology depicted the post-printing shape retention ability of the bioprinted constructs and revealed the structure’s rough morphology. All the biomaterial-ink combinations depicted hydrophilic nature as confirmed by the contact angle measurements. Rheological studies of the printable ink with hydroxyapatite revealed shear thinning properties and acceptable viscosity, essential for extrusion during bioprinting. The biomaterial-ink comprised only sodium alginate, and chitosan also displayed shear thinning abilities and showed lower working viscosity resulting in poor printability. The addition of hydroxyapatite to the hydrogel revealed acceptable post-printing structural stability. However, beyond 0.2% by weight of HAp imparts brittleness in the final structure. The linear viscoelastic regime, elastic modulus, and viscous modulus of the inks have been determined through the oscillatory strain sweep test. Creep recovery study, essential for predicting material behaviour immediately after ejection from the nozzle, indicated the material’s viscoelastic behaviour. The power law model has been used to estimate the flow index that predicted shear thinning abilities of the biomaterial-ink, and a correlation between the experimental and theoretical model was established. Herschel–Bulkley empirical model was used to determine yield stress (minimum stress required for extrusion from the nozzle) of the biomaterial-ink. Rheological studies and printability studies indicated Ink 5% 2% 0.1% as a promising combination for tissue engineering applications.

The effect of KF on the structural evolution of natural hydroxyapatite during conventional and microwave sintering

In this work, we studied the effect of microwaves and addition KF on the structural development of natural hydroxyapatite (bovine bone) during sintering using two types of furnaces: conventional: 1100–1300 °C and microwave: 900–1200 °C. Chemical as well as mechanical evolution monitoring of the material is ensured by X-ray diffraction, infrared and micro-hardness tests.Thanks to these characterization methods, we have shown that KF plays an important role in the stability of hydroxyapatite during sintering and mechanically enhances it with the emergence of the new phase resulting from the interaction between KF and hydroxyapatite called “Fluorapatite".

Cytotoxicity of a titanium alloy coated with hydroxyapatite by plasma jet deposition

Background/Aim. The deposition of hydroxyapatite (HAP) on the surface of titanium (Ti) alloys enhances bioactivity and osseointegration of the alloys which are widely used as implant materials in dentistry and orthopaedic surgery. However, the stability of HAP and subsequent biocompatibility of such alloys depends on the coating technique. The aim of this work was to test the cytotoxicity of a Ti alloy (Ti6Al4V), coated with HAP by a new plasma deposition method. Methods. The Ti6Al4V samples prepared as discs, 10 mm in diameter and 2 mm in thickness, were coated with HAP (one or both sides of the alloy) by an innovative atmospheric plasma jet method. The cytotoxicity of uncoated and HAP coated Ti6Al4V samples was evaluated by examining the morphological changes and viability of L929 fibroblasts in direct contact with the test materials. Adequate negative (polystyrene) and positive (nickel) control discs of the same size were used. The indirect cytotoxicity was determined by cultivating L929 cells with conditioning medium (CM), prepared as extract of the test samples incubated in the complete Roswell Park Memorial Institute (RPMI) 1640 medium for cell cultures. The cytotoxic effect was evaluated based on the degree of metabolic activity, necrosis, apoptosis and proliferation of L929 cells, using the appropriate assays. Results. Uncoated and one side HAP coated Ti6Al4V alloys were classified as non-cytotoxic according to the current ISO 10993-5 criteria, whereas two sides HAP coated Ti6Al4V alloy samples were slightlymoderate cytotoxic. The cytotoxicity manifested as the inhibition of metabolic activity and proliferation of L929 cells as well as the induction of their apoptosis and necrosis was significantly reduced by conditioning of HAP/Ti6Al4V alloys for 24 hours. The cytotoxic effect of HAP/Ti6Al4V CM only partly decreased in the presence of nifelate, a calcium (Ca) channel blocker, suggesting that Ca ions were not the only responsible cytotoxic agent. Conclusion. The original HAP coating procedure by atmospheric plasma spraying with high energy input enables the production of the stable adhesive coatings on Ti6Al4V alloys. Their cytotoxicity, which depends on the quantity of HAP coating layer, could be significantly reduced up to the non-cytotoxic level by prior conditioning of the alloys in culture medium. Such a procedure, which removes leachable toxic components, could be useful before implantation of HAP coated alloys in vivo.

Synthetic hydroxyapatite and its use in bioactive coatings.

An approach to solve the limitations of autologous bone grafting procedures in bone injury treatment is to develop bioactive coatings in the implantation system. The objective of this work is to compare the temperature effect on the stability of hydroxyapatite, graphene, and collagen colloidal suspensions to be used as biocompatible and bioactive coatings on a carbon fiber composite surface. Synthesized hydroxyapatite was assessed by X-ray diffraction. Zeta potential at different temperatures was evaluated. Specimens were characterized using scanning electron microscopy and Raman analysis. The results showed that the best hydroxyapatite/graphene ratio was 85/15, while those of the hydroxyapatite/collagen mixtures were 85/15. A hydroxyapatite/graphene/collagen mixture was synthesized based on these results.

Physicochemical Stability of Hydroxyapatite–Low-Molecular Polyethylene Glycol 400 Composite Systems in Biological Media

The physicochemical stability of the composite system consisting of hydroxyapatite (HAP) including 10, 25, and 50% polyethylene glycol (PEG) with a molecular weight of 400 in different physiological solutions has been studied. In the interaction of HAP + PEG 400 composite systems with physiological solutions, the amount of Ca in the filtrate changes versus the PEG content of the composite and the salt composition of the reaction media. The rate of calcium release in Ringer and Ringer–Lokk solutions, whose chemical composition is close to that of the tissue fluid of living organisms, is almost twice as high as in a 0.9% NaCl solution. Chemical analysis has shown that the HAP +10% PEG 400 composite system interacts with physiological solutions and is likely to promote calcium interchange between the experimental material and tissue fluid. Infrared spectroscopy has demonstrated that polyethylene glycol is present in the HAP + 10% PEG system over 120 h of interaction with biological media of living organisms, which will promote the restoration of nervous impulses in the treatment of bone defects. The HAP + 10% PEG 400 composite system can be recommended for further study in the development of novel composite materials for rehabilitation orthopedics.

Sr- and/or Mg-Containing Nanocrystalline Hydroxyapatite: Study from Synthesis to Calcined Products

In this work, nanocrystalline hydroxyapatite (HAp) powders were synthesized through wet precipitation method by adjusting the reaction temperature between 0 °C and 5 °C. The influence of biologically active Mg and Sr addition on HAp crystalline structure and thermal behavior was assessed. In all synthesis, nanocrystalline and/or amorphous HAp was found to be the major phase, and was accompanied by Ca(OH)2 as the minor phase. Results suggested that Sr and Mg have an impending effect on nucleation, crystallization and thermal stability of HAp. The addition of Sr or Mg promoted deviation from stoichiometry and formation of amorphous components, which affected thermal stability and sintering behavior of the synthesis products.

Stability analysis of hydroxyapatite in the system P-Ca-H2O aided prediction of the mechanisms of dephosphorization from the high phosphorus iron ore by hydrometallurgy process

Stability of hydroxyapatite (HA) in the system P-Ca-H2 O at room temperature (298 K) and elevated temperature (363 K) were analyzed in terms of log [P]-pH diagrams to discuss the mechanisms of phosphorus removal from high phosphorus iron ore. The effects of system pH value and temperature on the concentrations of species in the P-Ca-H2 O system were elaborated according to thermodynamic calculation. Lower temperature contributes to improve the dissolution of HA and this effect is more obvious at pH values lower than 11.3. At higher pH values, it is easy to remove phosphorus from iron ores at elevated temperature, attributing to the predominance area of highly soluble PO4 3- and HPO4 2- expansion. On the basis of these thermodynamic analyses, a suitable dephosphorization method of acid leaching at room temperature was proposed for high phosphorus iron ore.

Low-temperature crystallization and high-temperature instability of hydroxyapatite thin films deposited on Ru, Ti, and Pt metal substrates

We investigated the crystallinity, orientation, and stability of hydroxyapatite (HAp) thin films on structural materials including SiO2 and metals (Ru, Ti, and Pt). The HAp films were deposited by electron cyclotron resonance (ECR) plasma sputtering with an Xe sputtering gas under simultaneous flow of H2O vapor. The HAp films as-crystallized during deposition and solid-phase crystallized by post annealing were analyzed with X-ray diffraction, Fourier-transform infrared spectroscopy, and Raman scattering. The lowest solid-phase crystallization temperatures were 350°C on Ru, 300°C on Ti, and 300°C on Pt. These crystallization temperatures are much lower than those on silicon and SiO2 substrates (550°C). For HAp films as-crystallized at temperatures above 400°C, the elements out diffused and reacted with substrates. Precipitation of CaO was observed for HAp films deposited on SiO2 and Ru substrates. Diffusion of PO43− into SiO2 and Ru-catalyzed decomposition of HAp crystals are suggested for the mechanism. When deposited on Pt substrates, CaPt2O4 alloy byproducts were created for solid-phase crystallized films and CaPt2 alloy byproducts were created for as-crystallized films, indicating reaction of Ca atoms with Pt substrates.

Formation and characterization of silica-coated HAP particles

AbstractNanophase hydroxyapatite (HAP) particles were coated with silica via the hydrolysis of tetraethyl orthosilicate after a dodecyl alcohol based esterification reaction. The nanocomposite particles were characterized by transmission electron spectroscopy, scanning electron microscopy, X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, thermogravimetry and differential scanning calorimetry, sedimentation time and zeta potential (ζ) studies. A sequential change in infrared spectral features characteristic of HAP was accompanied by an increase in features characteristic of silica as revealed by FTIR. The silica coating enhanced the colloidal stability of HAP in aqueous suspensions. This behavior can be explained based on a heterocoagulation coating mechanism in which silica clusters adsorb onto the HAP particle surface.

Electrophoretic deposition of PVA coated hydroxyapatite on 316L stainless steel

Polyvinyl alcohol (PVA) coated hydroxyapatite was deposited onto a 316L stainless steel substrate by electrophoretic deposition. Deposition was carried out in a methanol suspension at pH 5.5 using a graphite rod as an anode. Parameters such as PVA concentration, deposition voltage and time were optimized to achieve a homogeneous, crack-free adhesive coating. Techniques such as X-ray diffraction and Fourier transform infrared spectroscopy were used to study the phase composition of the coated materials and the stability of hydroxyapatite in the presence of PVA.

Biomimetic Self-Assembling Copolymer−Hydroxyapatite Nanocomposites with the Nanocrystal Size Controlled by Citrate

Citrate binds strongly to the surface of calcium phosphate (apatite) nanocrystals in bone and is thought to prevent crystal thickening. In this work, citrate added as a regulatory element enabled molecular control of the size and stability of hydroxyapatite (HAp) nanocrystals in synthetic nanocomposites, fabricated with self-assembling block copolymer templates. The decrease of the HAp crystal size within the polymer matrix with increasing citrate concentration was documented by solid-state nuclear magnetic resonance (NMR) techniques and wide-angle X-ray diffraction (XRD), while the shapes of HAp nanocrystals were determined by transmission electron microscopy (TEM). Advanced NMR techniques were used to characterize the interfacial species and reveal enhanced interactions between mineral and organic matrix, concomitant with the size effects. The surface-to-volume ratios determined by NMR spectroscopy and long-range 31P{1H} dipolar dephasing show that 2, 10, and 40 mM citrate changes the thicknesses of the HAp crystals from 4 nm without citrate to 2.9, 2.8, and 2.3 nm, respectively. With citrate concentrations comparable to those in body fluids, HAp nanocrystals of sizes and morphologies similar to those in avian and bovine bones have been produced.

Improvement of the Stability of Hydroxyapatite Through Glass Ceramic Reinforcement

Hydroxyapatite has achieved significant application in orthopedic and dental implants due to its excellent biocompatibility. Sintered hydroxyapatites showed significant dissolution, however, after their immersion in water or simulated body fluid (SBF). This grain boundary dissolution, even in pure hydroxyapatites, resulted in grain separation at the surfaces, and finally, in fracture. In this study, hydroxyapatite ceramics containing apatite-wollastonite (AW) or calcium silicate (SG) glass ceramics as additives were prepared to prevent the dissolution. AW and SG glass ceramics were added at 0-7 wt% and powder-compacted uniaxially followed by firing at moisture conditions. The glass phase was incorporated into the hydroxyapatite to act as a sintering aid, followed by crystallization, to improve the mechanical properties without reducing the biocompatibility. As seen in the results of the dissolution test, a significant amount of damage was reduced even after more than 14 days. TEM and SEM showed no decomposition of HA to the secondary phase, and the fracture toughness increased, becoming even higher than that of the commercial hydroxyapatite.

LA-ICP-MS heavy metal analyses of fish scales from sediments of the Oxbow Lake Certak of the Morava River (Czech Republic)

Heavy metal concentrations were studied in the scales of recent and subrecent (2–25 years old) fish buried in the oxbow lake sediments of the Morava River. The samples were taken from two cores up to 4-m deep and analysed using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and an electron microprobe analysis (EMPA). The results were compared with heavy metal concentrations of bulk samples of the embedding sediment. The study has revealed substantial differences in heavy metal contents existing between the recent and subrecent fish scales documenting an extreme rapidity of the diagenesis/fossilization processes. The most apparent features of the early fossilization include the quick loss of the mucous envelope, collagen and magnesium and an enormous increase in the heavy metal concentrations in particular iron, which is connected with a colour change. The variations in heavy metal contents in fish scales within a sample are attributed to variations in heavy metal content in the environment and variable amounts of organic matter in the embedding sediment. In contrast to the contamination of the embedding sediment, no general increase in heavy metal concentrations in fish scales was observed down to the cores. It is inferred that the rapid sorption stabilizes the biologic hydroxyapatite of the fish scales, which thus rapidly attain a thermodynamic equilibrium with the embedding water-saturated sediment. The results show that the processes of sorption, fossilization and stabilization of hydroxyapatite can act very quickly over a time scale of several years and represent thus a great advantage in the preservation of the original signals of the ancient environments.

Influence of Hydrothermal Processing Parameters on Phase Stability of Hydroxyapatite

Nanosized hydroxyapatite(HAp) was synthesized hydrothermally and influence of processing parameters, such as reaction temperature and time, pH, and Ca/P ratio, on the phase stability of HAp was evaluated after pressureless sintering at 1250°C in air. The highest stability was achieved from the powder obtained at a processing condition for the lowest solubility of Ca2+, which corresponds to temperature close to 200°C, time <4h, pH>9.0, and Ca/P = 1.67. The stability of nanosized HAp in HAp/3Y-TZP composites was slightly inferior to commercial one, but the involvement of hydrothermally synthesized HAp improved sintered density of the composites and stability of t-ZrO2 phase in the composites.

Effect of Ca/P Molar Ratio and Heat Treatment on Thermal Decomposition and Reconstitution of Hydroxyapatite

Stability of hydroxyapatite(HA) structure is influenced by preparation conditions and afterwards heat treatment. In this paper, the powders with different Ca/P molar ratio were calcined to investigate the influence of Ca/P and heat treatment on thermal decomposition and reconstitution of HA. The results show that the Ca/P has little change even calcined at a high temperature of 1500°C. The Ca/P molar ratio close to 1.67 is beneficial to form high purity HA. HA gradually releases its OH- ions in the temperature range of 800-1200°C. The decomposition takes place at about 1200°C and will become more and more severe with the increase of temperature. Cooling with slow rate and post-heat treatment in wet atmosphere are beneficial to both the rehydration and the recovery of HA from the decomposition products (TTCP and α-TCP).

Influence of Hydrothermal Reaction Temperature and pH on Phase Stability of Hydroxyapatite

The effect of hydrothermal reaction temperature and pH on crystallite size, phase stability, and sintered density of hydroxyapatite (HAp) has been investigated. The crystallite size increased with the increase in temperature but was not significantly affected by pH. The decomposition of HAp into tricalcium phosphate was observed at 1250°C and the extent of decomposition decreased with increase in pH. The influence of temperature and pH on the crystallite size and the decomposition was related to the decrease in solubility of Ca2+. The phase stability of HAp, prepared hydrothermally, in HAp/zirconia composites was higher than that of commercial HAp due to its high sintered density.

Plasma Sprayed Zirconia-Hydroxyapatite Composite Coatings

In order to overcome the fragility and to improve the physical stability of hydroxyapatite (HA) on the implant, 5, 10, and 15 % yttria stabilized zirconia (YTZP) was added to the starting plasma spraying HA powder Metco XPT-D-703. From the recent literature it is already known that HA coatings tend to dissolve in body fluid environment. To decrease the dissolution effect many additives like zirconia (Zr) could be added to HA powder. In this study, prepared HA composite powders were sprayed onto titanium (Ti) surfaces with a Metco plasma gun. As a control group, pure HA powder was sprayed onto other Ti samples. All samples were subjected to tensile tests according to the ASTM C-633-79. SEM images were taken using back-scattering from prepared cross-sections. X-ray diffraction images were taken from the surface. It was seen that with the increase of the Zr content, the tensile test values increased. Pure HA showed also that the addition of Zr had improved the tensile bond strenght (TBS) values.

Structure and stability of hydroxyapatite: Density functional calculation and Rietveld analysis

A study on the structure and energetics of hydroxyapatite has been carried out using generalized gradient approximation density functional theory. The previously proposed $P{6}_{3}∕m$ and $P{6}_{3}$ hexagonal structural models have been found to be energetically unfavorable as compared with the previously proposed $P{2}_{1}∕b$ symmetry and a newly proposed monoclinic $P{2}_{1}$ structural model. A detailed analysis of the symmetry restrictions and inconsistencies between the reported physical properties, such as diffraction and birefringence, with hexagonal symmetry question the validity of these models. Rietveld analysis carried out on a synthetic sample, reported to be predominantly hexagonal at room temperature, shows that the diffraction pattern of this material can be interpreted as a mixed monoclinic phase, 23% monoclinic $P{2}_{1}∕b$ and 77% monoclinic $P{2}_{1}$. This interpretation reconciles many anomalies in reported experimental observations.

Rheological behavior of aqueous suspensions of hydroxyapatite (HAP).

The aim of this study is to characterize the influence of organic dispersants on the stability of hydroxyapatite (HAP) dispersions, using viscosity measurements, electrokinetic sonic amplitude (ESA) measurements and adsorption isotherms. Colloidal stability of aqueous suspensions of HAP as a function of solids loading and of the type and concentration of deflocculant has been studied. The interaction between particles and dispersant molecules was characterized. Adsorption measurements of the amount of dispersants on the particles surface, viscosity and electrophoretic measurements as a function of the dispersant concentration are correlated. Suspension parameters have been adjusted in order to obtain a high solids loading slurry with a plastic viscosity which will allow its use in colloidal processing.

Structural study and stability of hydroxyapatite and β‐tricalcium phosphate: Two important bioceramics

The stability of hydroxyapatite (OHAP) and β-tricalcium phosphate (β-TCP) ceramics depends on the temperature of preparation and the partial pressure of water in the reaction atmosphere. In bioceramics used in the study of biomaterials, these two phosphates often coexist in distinct proportions; therefore, structural characterization of the individual phases is hindered. The structure of these two individual calcium phosphates have been studied using X-ray diffraction, and mainly by high-resolution electron microscopy. Whereas the X-ray diffraction profile of OHAP has been refined in the space group P63/m, the HREM images oriented along the [001] direction at the edges of the crystal show a threefold symmetry. The X-ray diffraction pattern of β-TCP has been refined in the space group R3c and the HREM image oriented along [0001] zone axis shows regular contrast. Both these calcium phosphate ceramics are unstable to the electron beam for a prolonged exposure time, and show areas of decomposition in HREM images of thin regions of the crystal. The regions of decomposition in the β-TCP crystal show the presence of CaO as one of the major phases. © 2000 John Wiley & Sons, Inc. J Biomed Mater Res, 51, 660–668, 2000.