Hydroxyapatite Crystals Research Articles

Periodic Graphics: What are our skeletons made of?

Chemical educator and Compound Interest blogger Andy Brunning explores the biochemistry of our bones To download a pdf of this article, visit http://cenm.ag/skeletons. References used to create this graphic: McLarnon, Andy. “ Bone Marrow .” British Society for Immunology. Accessed Oct. 17, 2022. Tomoaia, Gheorghe, and Roxana-Diana Pasca. “On the Collagen Mineralization. A Review.” Clujul Med . (2015). DOI: 10.15386/cjmed-359 . Weiner, Stephen, and Wolfie Traub. “Organization of Hydroxyapatite Crystals within Collagen Fibrils.” FEBS Lett . (1986). DOI: 10.1016/0014-5793(86)80993-0 . A collaboration between C&EN and Andy Brunning, author of the popular graphics blog Compound Interest To see more of Brunning’s work, go to compoundchem.com. To see all of C&EN’s Periodic Graphics, visit http://cenm.ag/periodicgraphics .

Gradient Magnesium Content Affects Nanomechanics via Decreasing the Size and Crystallinity of Nanoparticles of Pseudoosteodentine of the Pacific Cutlassfish, Trichiurus lepturus Teeth.

The formation of biomaterials such as enamel, dentin, and bone is important for many organisms, and the mechanical properties of biomaterials are affected by a wide range of structural and chemical factors. Special dentins exist in extant aquatic gnathostomes, and many more are present in fossils. When a layer of compact orthodentine surrounds the porous osteodentine core in the crown, the composite dentin is called pseudoosteodentine. Using various high-resolution analytical techniques, including micro-computed tomography (micro-CT), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Raman spectroscopy, and nanoindentation, we analyzed the micro- and nanostructures, chemical composition, and mechanical properties of pseudoosteodentine in the Pacific cutlassfish, Trichiurus lepturus teeth. Nanoscale oval-shaped hydroxyapatite (HA) crystals were distributed in a disordered manner in the pseudoosteodentine, and a cross-sectional analysis showed that the mineral crystallinity and crystalline particle size of the outer orthodentine were greater than those of middle and inner osteodentine. Moreover, the outer orthodentine comprised a mixture of smaller crystals and larger, more mature crystals. The nano-hardness and nano-stiffness of outer orthodentine were significantly higher than those of middle and inner osteodentine along a radical direction. The hardness and stiffness of pseudoosteodentine were inversely proportional to its magnesium (Mg) content. These data are consistent with the concept that Mg delays crystal maturation. The crystal size, crystallinity, nano-hardness, and nano-stiffness of pseudoosteodentine all decreased commensurately with the increase of its Mg concentration. The pseudoosteodentine of T. lepturus also can be regarded as a functional gradient material (FGM) because its mechanical properties are closely related to its chemical composition and nanostructure. Special pseudoosteodentine may therefore serve as a design standard for biomimetic synthetic mineral composites.

Hydroxyapatite Coating on Ti-6Al-7Nb Alloy by Plasma Electrolytic Oxidation in Salt-Based Electrolyte.

Titanium alloys have good biocompatibility and good mechanical properties, making them particularly suitable for dental and orthopedic implants. Improving their osseointegration with human bones is one of the most essential tasks. This can be achieved by developing hydroxyapatite (HA) on the treating surface using the plasma electrolytic oxidation (PEO) method in molten salt. In this study, a coating of titanium oxide-containing HA nanoparticles was formed on Ti-6Al-7Nb alloy by PEO in molten salt. Then, samples were subjected to hydrothermal treatment (HTT) to form HA crystals sized 0.5 to 1 μm. The effect of the current and voltage frequency for the creation of the coating on the morphology, chemical, and phase composition was studied. The anti-corrosion properties of the samples were studied using the potentiodynamic polarization test (PPT) and electrochemical impedance spectroscopy (EIS). An assessment of the morphology of the sample formed at a frequency of 100 Hz shows that the structure of this coating has a uniform submicron porosity, and its surface shows high hydrophilicity and anti-corrosion properties (4.90 × 106 Ohm·cm2). In this work, for the first time, the process of formation of a bioactive coating consisting of titanium oxides and HA was studied by the PEO method in molten salts.

The multi-scale meso-mechanics model of viscoelastic dentin

Human dentin is a hierarchical material with multi-level micro-/nano-structures, consisting of tubule, perti-tubular dentin (PTD) and intertubular dentin (ITD) as the major constituents at microscale; and the PTD and ITD are further composed of collagen and hydroxyapatite (HAp) crystals with different volume fractions at nanoscale. In most cases, the HAp is considered as elastic while the collagen as viscoelastic material. It is of great significance to study the hierarchical structure and viscoelasticity of human dentin to understand the mechanical properties of dentin for further development of restorative materials. Based on this, this paper focuses on multiscale modeling of the elastic properties and dynamic viscoelastic response of dentin and establishes a bottom-up micromechanics model from nano-to macro-scale. In order to study the nanostructural effect on the viscoelastic behavior of hierarchical structures, the homogenization theories of random platelets composites (HTRPC) and the locally-exact homogenization theory (LEHT) are introduced for the homogenization of heterogeneous materials of microstructures at different levels. The HTRPC, based on Eshelby Inclusion theory, is used to predict the effective modulus of PTD and ITD. The LEHT is a method for homogenizing multiphase dentin characterized by repeated unit cells (RUCs). The resulting predictions are in very good agreement with several experimental data from the literature. In addition, the results of nanostructrual effect on dentin show that the viscoelasticity of dentin is majorly contributed by collagen and the HAp greatly provide the strength and hardness of dentin. Furthermore, the ageing effect on dentin's viscoelasticity is considered from the proposed multiscale micromechanics model. It is demonstrated that the ageing effect is much more influential in affecting the loss moduli of dentin than the storage.

The fracture mechanical behavior simulation of calcium-deficient hydroxyapatite crystals by molecular dynamics and first-principles calculation

Natural hydroxyapatite provides certain strength and stiffness to biological bones, and most of the studies on the strength of bone tissues have been carried out on hydroxyapatite (HAP). However, the Ca/P ratio of hydroxyapatite in bones is actually about 1.50, and the natural hydroxyapatite belongs to calcium-deficient hydroxyapatite (CDHA) with Ca vacancy defects. Therefore, this work focused on the effect of Ca vacancy defects on CDHA crystals through investigating the generation and expansion of microcracks under uniaxial tensile loading by combining molecular dynamics and first principles method. A series of crystal models with different Ca vacancy ratios are constructed and find that Ca vacancies degrade the mechanical properties of hydroxyapatite. Meanwhile the fracture behavior of crystals is detailed and find that the cracks arise at vacancies and extend along the direction of vacancies. Also, first-principles calculation is performed to reveal the mechanism of crack formation in MD simulations. It is found that the decrease of Ca–O bonding of CDHA causes the decrease of the stability of the crystal structure by analyzing the DOS of HAP and CDHA, and the cracks originate from Ca vacancies. This work performs more realistic simulations of CDHA with calcium vacancy defects in actual bone tissue and directly reveals the development and progression of bone fragility at the nanometer scale.

Effect of natural phosphate content on the growth kinetics of hydroxyapatite crystals grown from kaolin clay

In the present study, the kinetics of hydroxyapatite formation in different kaolin-natural phosphate mixtures was investigated using X-ray diffraction (XRD) and differential thermal analysis (DTA) measurements. The XRD patterns revealed the presence of both kaolinite and hydroxyapatite phases in all of the mixtures and full disappearing of kaolinite phase in the heat-treated samples. According to the DTA curve results, both the peak temperature formation of hydroxyapatite and the relative fraction-transformed increased as the heating rate increased and the amount of phosphate in the mixture decreased. The activation energy of hydroxyapatite phenomenon was estimated using Kissinger and Ligero analytical methods. The obtained values of the activation energy were in the range of ∼196.5 and 210.6 kJ/mol. The growth morphology parameters n and m were both found to be near to half unity indicating that the surface nucleation with plate-like growth was dominant in hydroxyapatite formation controlled by diffusion.

Preparation of Bacterial Nanocellulose-Hydroxyapatite Composite

Nowadays, new materials for the preparation of synthetic bone grafts are being sought after. Bones consist mainly of collagen fibres and hydroxyapatite crystals, so using synthetic grafts with a similar structure is logical. Therefore, a composite material was prepared by adding hydroxyapatite particles in the cultivation medium of bacterial nanocellulose (in-situ method). The composites were dried via air-drying and lyophilization to obtain solid materials. The formation of the composite was confirmed by infrared spectroscopy, which showed cellulose (OH vibrations) as well as hydroxyapatite (PO43- vibrations) absorption bands. Energy dispersive X-ray spectroscopy showed presence of 14 wt% of calcium and 48 wt% of phosphorus in the composites. The structure of the hydroxyapatite crystals embedded in fibrous cellulose was observed by scanning electron microscopy. The higher porosity of the lyophilized samples was confirmed as well. Water contact angle of the air-dried composites was lower (25 ± 3.6)° compared to pure bacterial nanocellulose (30 ± 2.7)°. The mechanical strength of the air-dried composites was (20.3 ± 7.9) MPa. These results suggest the prepared material is promising for construction of synthetic bone grafts.

Dördüncü ve Beşinci Parmak Metakarpofalangeal Eklemde Kalsiyum Depolanması

Acute calcium deposition disease is characterized by calcium hydroxyapatite crystal deposition within tendons and surrounding tissue of joints. It can manifest acute or chronic. It’s most common symptom is pain in affected area. Two patients applied to our outpatient clinic with complaints of hand pain. Calcific masses were detected by radiological imaging. After radiological imaging and laboratory examinations the patients diagnosed acute calcium deposition disease. One of the patients had ongoing symptoms for 2 years, the other one had ongoing symptoms for 3 years. Both of the patients had tried conservative treatment multiple times. These patients were treated surgically because of long-standing symptoms. Although acute calcium deposition disease usually resolves spontaneously with conservative treatment, patients with recurrent or persistent lesions can be treated surgically.

Tailoring Biotribological Performance of Polytetrafluoroethylene Nanocomposites through Control of Diameters and Aspect Ratios of In Situ Filled Hydroxyapatite Nanowires

Excellent biocompatibility and biotribological performance are necessary for artificial acetabular cups in total hip replacement. Herein, polytetrafluoroethylene (PTFE) nanocomposites are fabricated via an in situ filling of hydroxyapatite nanowires. The resulting nanocomposites are characterized and evaluated by sliding friction against a high‐speed steel ring in the presence of simulated body fluid. Markedly enhanced hydrophobicity, heat resistance, and stiffness are observed for the fabricated nanocomposites in comparison with the matrix PTFE. The ethanol/water ratios for the in situ fabrication of the nanocomposites showed a predominant role in the diameters and aspect ratios of the hydroxyapatite nanowires filled in the nanocomposites. This might be related to the competition between the nucleation and growth of the hydroxyapatite crystals under applied synthetic conditions because the concentration of ethanol can influence the size and morphology of the oleic acid micelles. Furthermore, the diameters and aspect ratios of the nanofiller are found a decisive role in the tribological performance of the resulting PTFE nanocomposites, and those fabricated using a low ethanol/water ratio showed an enhanced diameter and aspect ratio and remarkable improvement in biotribological performance. The fabrication method is believed promising for the design and controllable synthesis of artificial acetabular cups or other artificial tissues.

Effect of tantalum interlayer on hydroxyapatite biointerface for orthopedic applications

Various attempts have been made during recent decades to improve the functionality, biocompatibility and osseointegration of metallic implants. With technological advancement, modifying superficial properties of orthopedic implants has undergone great evolution. Current efforts of scientists and the orthopedic industry have focused on modifying surface properties to achieve a specific biointerface that can reduce patient's healing time and prevent aseptic loosening. This study investigates the contribution of a protective tantalum interlayer deposited on titanium substrates on the growth of hydroxyapatite (HAp) crystals with hydrothermal synthesis method. We investigated the morphology and structure of the produced coatings, as well as in vitro bioactivity in simulated body fluid and biocompatibility in osteoblast-like cell culture. The hydrothermal method allows to synthesize coating with micro-sized HAp crystallites that exhibit rod-like hexagonal shape. The diameter of HAp crystallites may be controlled and driven by nature of the interlayer (tantalum, tantalum oxide or titanium oxide) previously formed on the titanium substrate. Coatings with smaller diameters of HAp crystals (between 0,3 μm and 0,6 μm) synthesized on tantalum-based films were found to be more favorable for cell viability and attachment. High bioactivity and positive effect on the osteoblast-like cells of the HAp biointerface with a tantalum intermediate layer was observed.

Effect of reaction time, heating and stirring rate on the morphology of HAp obtained by hydrothermal synthesis

Hydroxyapatite (HAp) whiskers were prepared in reaction of calcium lactate pentahydrate and orthophosphoric acid. Synthesis were carried out in different conditions with using hydrothermal reactor. The benefit of the hydrothermal technique is the simple and precise control of the HAp crystals morphology, which is achieved by employing varying initial concentrations of starting reagents as well as different conditions of synthesis. The effect of time of synthesis, stirring and heating rate of the reaction on HAp morphology and composition was investigated. During the synthesis the following experimental parameters were varied independently: time of synthesis (3, 5, 7 h), stirring rate (0, 62.5, 125, 250, 500, 750 rpm), the reaction heating rate (0.2, 0.5, 0.7, 1.0, 1.5, 2.5 °C min−1). All syntheses were carried out with the constant molar Ca/P ratio of 1.67 in starting solutions, which is equivalent to that of stoichiometric HAp. The Ca2+ ion concentrations in starting solutions for synthesis were 0.05 and 0.1 mol dm−3. Syntheses were carried out under 20 bar. The obtained products were characterized using different method like XRD, SEM, and FTIR. It was shown that the significant majority of samples prepared were identified as pure HAp.

Calcined hydroxyapatite powders with increased chemical stabilities and dispersibility

Biocompatible hydroxyapatite (HAp) powders have thermodynamically driven tendencies to lower their surface areas due to the formation of irreversible aggregates. To address this challenge, HAp hybrid powders are herein prepared by using a traditional wet-precipitation method with subsequent hydrothermal carbonization for surface modification. The crystallite size, crystallite degree and area ratio of the infrared peak assigned to bonding water against those of free water are determined to investigate the variation of HAp crystallization with processing parameters. The crystallization of HAp is facilitated by enriched water in a stealth layer with water molecules evolved by citrate, nitrogen (N)-containing methylene blue (MB), hydrogen-group-rich β-cyclodextrin (CD) and oxygen-containing organic carbon shells. The low surface areas result in fabrication of nano-sized HAp powders with a uniform size distribution, well-dispersed morphologies and smooth surfaces through calcination of HAp-CD-MB@C. The pH values of acidic buffers increase slowly during incubation of HAp-CD-MB@C powders with chemical stability and a large grain size after calcination at 550°C for 2 h. The present study will shed light on the preparation of nano-sized inorganic powders with a uniform size distribution, well-dispersed morphologies and modulated chemical stability for potential applications as carriers of small molecular substances and fillers in composite materials.

2,3-Diphospho-D-glyceric acid inhibits calciprotein particle growth and calcification in MOVAS cells but not in MC3T3-E1 cells

Anionic polyphosphate compounds are well-known to inhibit the formation of hydroxyapatite crystals. Vascular calcification (VC) is associated with an increase in crystalline calciprotein particles (CPPs) in the bloodstream. 2,3-Diphospho-D-glyceric acid (2,3-DPG) is a highly anionic Poly-P compound found in the concave center of erythrocytes where it binds to hemoglobin, thereby reducing oxygen affinity. Since 2.3-DPG exists in plasma, we hypothesized that 2,3-DPG may act as an endogenous inhibitor of VC. In comparison to widely recognized calcification inhibitors such as myo-inositol hexakisphosphate, 2,3-DPG significantly delayed the formation of crystalline CPPs. Additionally, 2,3-DPG inhibited calcification in a mouse vascular smooth muscle cell line (MOVAS) without cytotoxic effects. Taken together with the result that 2,3-DPG did not impact bone-like nodule formation in mouse osteoblast-like MC3T3-E1 cells, these results suggest that 2,3-DPG may inhibit VC selectively.

Fabrication of functional and nano-biocomposite scaffolds using strontium-doped bredigite nanoparticles/polycaprolactone/poly lactic acid via 3D printing for bone regeneration

Bone tissue engineering is a field to manufacture scaffolds for bone defects that cannot repair without medical interventions. Ceramic nanoparticles such as bredigite have importance roles in bone regeneration. We synthesized a novel strontium (Sr) doped bredigite (Bre) nanoparticles (BreSr) and then developed new nanocomposite scaffolds using polycaprolactone (PCL), poly lactic acid (PLA) by the 3D-printing technique. Novel functional nanoparticles were synthesized and characterized using field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS: map). The nanoparticles were uniformly distributed in the polymer matrix composites. The 3D- printed scaffolds were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), attenuated total reflection-fourier transform infrared (ATR-FTIR), degradation rate porosity, mechanical tests, apatite formation and cell culture. Degradation rate and mechanical strength were increased in the PLA/PCL/Bre-5%Sr nanocopmposite scaffolds. Hydroxyapatite crystals were also created on the scaffold surface in the bioactivity test. The scaffolds supported viability and proliferation of human osteoblasts. Gene expression and calcium deposition in the samples containing nanoparticles indicated statistical different than the scaffolds without nanoparticles. The nanocomposite scaffolds were implanted into the critical-sized calvarial defects in rat for 3 months. The scaffolds containing Bre-Sr ceramic nanoparticles exhibited the best potential to regenerate bone tissue.

Comparison of Dentin Caries Remineralization with Four Bioactive Cements.

The treatment of deep carious lesions involves the use of ion-releasing agents to seal the lesions. These agents release minerals, leading to the remineralization of the remaining demineralized dentin. This study aimed to compare the dentin caries remineralization with bioactive cements. 60 Dentin blocks were prepared from the dentin of human third molars. Artificial carious lesions were induced on the blocks with pH cycling. The samples were divided into five groups (n=12). Dycal, Oxford ActiveCal PC, Biodentine, and ACTIVA BioACTIVE were applied using a mold. One group did not receive any cement. The samples were stored in remineralization solution for 30 days. The cement was removed using a #15 blade, and the dentin surface was evaluated using Energydispersive X-ray Spectroscopy and X-ray Diffraction. One-way ANOVA did not show a significant difference in the weight percentages of calcium and phosphorus and the calcium-to-phosphorus ratios between the groups. The highest and the lowest weight percentages of calcium and phosphorus were observed in Biodentine and control groups, respectively. There were no significant differences in the remineralization properties of bioactive cements. Hydroxyapatite crystals were not formed in any of the adjacent dentin using these cements.

Improve Dentin Bonding Performance Using a Hydrolytically Stable, Ether-Based Primer.

The objective of this study is to replace a traditional methacrylate-based primer (glycine, N-(2-hydroxy-3-(2-methyl-1-oxo-2-propenyl)propyl)-N-(4-methylphenyl) monosodium salt, NTG-GMA) with a hydrolytically stable ether-based primer (glycine, N-2-hydroxy-3-(4-vinylbenzyloxy)-propyl-N-(4-methylphenyl), monosodium salt, NTG-VBGE). The performance and durability of bonding composites to detin of two primers combined with methacrylate-based or ether-based adhesives were evaluated using shear bond strength (SBS) and micro-tensile bond strength (μTBS) combined with thermal cycling. The hydrolysis resistance of NTG-VBGE against hydrolysis was tested by challenging primed hydroxyapatite crystals with an esterase. The hydrophilicity of the primers and the resin spreading kinetics of adhesives on primed dentin were characterized by water contact angle measurements. The new primer NTG-VBGE was found to be compatible with both methacrylate-based adhesives and ether-based adhesives. The highest μTBS values were found in the test group of NTG-VBGE and ether-based adhesive, which was consistent with the resin spreading kinetics results. The more hydrophobic and hydrolytically stable primer/adhesive achieved improved dentin infiltration and bonding strength, suggesting significant potential for further developing dental restorative materials with extended service life.

Synthesis of nano hydroxyapatite from Hypopthalmichthys molitrix (silver carp) bone waste by two different methods: a comparative biophysical and in vitro evaluation on osteoblast MG63 cell lines.

More than a thousand tonnes of fish bone wastes can be transformed into biomedical products annually. Alkaline hydrolysis and thermal calcification were used to create nanosized hydroxyapatite (HAp) crystals from Silver carp bone wastes. Biophysical tests were used to determine the nano size and chemical composition of synthesised hydroxyapatite. Alkaline hydrolysis hydroxyapatite (AH-HAp) was 58.3nm, while Thermal calcination hydroxyapatite (TC-HAp) was 64.3nm in size, confirmed by Atomic Force Microscopy. Energy Dispersive X-ray Analysis studies showed Ca/P (Calcium phosphate) ratio of AH-HAp to be 1.65, whereas TC-HAp as 1.45, confirming AH-HAp to be organically rich along with a similar Ca/P ratio as natural HAp. Fourier Transform Infrared Spectroscopy spectra indicated HAp formation from both procedures, however AH-HAp had superior crystallinity than TC-HAp confirmed from X-Ray Diffraction spectra. MG63 osteoblast cell lines showed 91% cell viability in cytotoxicity studies and 70.1% proliferation efficiency in Alkaline Phosphatase assay, which was higher than TC-HAp. The present study shows that HAp produced via alkaline hydrolysis has better biocompatibility which enhances its applicability as a biomaterial, than HAp synthesized through thermal calcination, which tends to incinerate organic moieties.

Complementary biomarker detection for bisphosphonate use in racehorses

Determining the use of off-label bisphosphonates (BPs) in young horses (< 4 years old) is of interest due to the threat to racing integrity and welfare associated with this class of drugs that have the potential to manipulate bone structure. The analysis of BPs in biological matrices is challenging by liquid chromatography coupled to mass spectrometry (LC-MS/MS) and alternative sample preparation approaches are needed to detect their misuse in racehorses. There are currently two classes of BPs: non-nitrogen and nitrogen-containing with each having a distinct mode of action. Currently two non-nitrogenous based BPs are available for use in horses, tiludronic acid (or tiludronate) and chlodronate for the treatment of navicular syndrome (Mitchell et al. BMC Veterinary Research 2019;15(1):211) in horses over the age of 4. There is, however, evidence that BPs can persist in the bone for several years after administration since they can form hydroxyapatite crystals prior to being fully absorbed by active osteoclasts where full inhibitory action is performed (Riggs et al. Equine veterinary journal 2021;53(6):1287–1295). Therefore, with this prolonged detection time for the BPs, it is necessary to investigate whether the use of metabolomic biomarkers can provide a complementary method for the detection of their misuse. The aim of this research was to develop a biomarker approach for complementary direct detection of bisphosphonate drugs in equine plasma. BPs are hydrophilic therefore the targeted detection of tiludronic acid in equine plasma required an orthogonal solid phase extraction (SPE) method using both a polymeric reversed-phase sorbent and a weak anion exchange cartridge prior to derivatisation using trimethyl orthoacetate and reverse LC-MS/MS. Endogenous lipids and corticosteroids in equine plasma were detected after protein precipitation and SPE with a polymeric reverse phase cartridge prior to liquid chromatography high-resolution mass spectrometry. Data was analysed using the Shimadzu Insight Explore software to determine up- or down-regulation of biomarkers. Results were then profiled using a Parametric Empirical Bayes algorithm to propose individual reference limits (IRLs). Tiludronic acid was detected up to the final collection point of 28 days post-administration. Following a targeted approach, up- and down-regulation of the eicosanoid and corticosteroid ratios were observed with the corticosteroid ratio exceeding both the proposed population reference limit (PRL) and IRL. Using a semi-targeted approach, several additional lipids were identified to have activity during the administration and will require further confirmatory analysis. Monitoring the impact on endogenous biomarkers following an administration of Tiludronic Acid in racehorses is limited therefore little is known if BPs have a direct or indirect effect on the inflammatory pathways. However, research in humans has linked BPs with possible effects of analgesia in addition to bone remodelling that BPs are primarily used for. Therefore, it is necessary to further extend detection capabilities to ensure endogenous eicosanoids and corticosteroids are monitored. This, however, should not negate the need for the detection of the drug itself as tiludronic acid has the potential to be detected as far as 28 days post-administration. Therefore, a complementary biomarker approach would be preferable for the detection of non-nitrogen-based BPs, which can be further applied for the nitrogen-based BPs. A complementary biomarker approach to direct detection of administered drugs can improve the understanding of effect and support non-targeted detection strategies for analogues of specific drug classes.

Modification of hydroxyapatite coating in the presence of adipic acid for Mg-based implant application

This study investigated the role of adipic acid (AA) in improving the anti-corrosion performance and in-vitro bioactivity of hydroxyapatite coating applied on AZ31 Mg alloy. Firstly, hydroxyapatite (HA) coating was applied on the AZ31 Mg alloy. In the next step, the optimized hydroxyapatite-based coating, modified with adipic acid by direct addition and post-treatment methods. Corrosion behavior of uncoated sample and different coated samples were studied by Electrochemical Impedance Spectroscopy (EIS) and Direct Current (DC) Polarization techniques. Surface characterization was examined by Field Emission Scanning Electron Microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDXS), X-ray diffraction (XRD) and contact angle measurements. According to the contact angle results, all coated samples reveal high hydrophilic behavior. Additionally, the XRD analysis confirms the formation of hydroxyapatite crystals in all coated samples and the presence of the AA in HA + AA and HA − AA coatings does not change the crystal structure of the hydroxyapatite. Electrochemical studies display that the Rp value of HA coating is increased from 3630 Ω.cm2 to 10784 Ω.cm2 by the direct addition method also by the post-treatment method the polarization resistance reached 10294 Ω.cm2. In addition, an in-vitro bioactivity assessment was performed in a simulated body fluid (SBF). Based on FE-SEM studies, a protective layer of AA is formed on HA coating by the post-treatment method which improves the anti-corrosion behavior efficiently. The results showed that the adipic acid-modified hydroxyapatite coatings by direct addition and post-treating methods display better anti-corrosion properties and bioactivity compared to the optimal hydroxyapatite coating.

Biomimetic Mineralization of Tooth Enamel Using Nanocrystalline Hydroxyapatite under Various Dental Surface Pretreatment Conditions.

In this report, we demonstrated the formation of a biomimetic mineralizing layer obtained on the surface of dental enamel (biotemplate) using bioinspired nanocrystalline carbonate-substituted calcium hydroxyapatite (ncHAp), whose physical and chemical properties are closest to the natural apatite dental matrix, together with a complex of polyfunctional organic and polar amino acids. Using a set of structural, spectroscopy, and advanced microscopy techniques, we confirmed the formation of a nanosized ncHAp-based mineralized layer, as well as studying its chemical, substructural, and morphological features by means of various methods for the pretreatment of dental enamel. The pretreatment of a biotemplate in an alkaline solution of Ca(OH)2 and an amino acid booster, together with the executed subsequent mineralization with ncHAp, led to the formation of a mineralized layer with homogeneous micromorphology and the preferential orientation of the ncHAp nanocrystals. It was shown that the homogeneous crystallization of hydroxyapatite on the biotemplate surface and binding of individual nanocrystals and agglomerates into a single complex by an amino acid booster resulted in an increase (~15%) in the nanohardness value in the enamel rods area, compared to that of healthy natural enamel. Obtaining a similar hierarchy and cleavage characteristics as natural enamel in the mineralized layer, taking into account the micromorphological features of dental tissue, is an urgent problem for future research.