Hydroxyapatite Structure Research Articles

Ionic substituted hydroxyapatite for bone regeneration applications: A review

Biological apatites are characterised by various ionic substitutions within the HAp lattice that are crucial for bone metabolism. The introduction of key role elements within synthetic calcium phosphates (CaP), mainly hydroxyapatite (HAp), can increase osteogenesis and enhance bone regeneration process. The lattice structure of HAp enables cationic and anionic substitutions leading to the enhanced biological performance of synthetic bone graft materials. This review summarises recent and relevant studies on cationic and anionic substitutions in the HAp lattice that are commonly found in the human body. Furthermore, co-substituted HAp obtained from synthetic and biological precursors, along with their influence on the bone regeneration process, has been discussed. Finally, future perspectives for the use of substituted HAp have been presented.

Green synthesis of Sodium alginate mediated Fluorapatite Nanoparticle via Sol-Gel method

Fluorapatite (FA) can be used as a bioactive substance in the body, especially the teeth implants. The FA nanoparticle was synthesized by adding the fluorine to the structure of HA using sol–gel method and the heat treatment of 700 °C. Being low costs, eco-friendly and safer features are obvious advantages of the green synthesis of FA nanoparticles by using bio stabilizer of sodium alginate. Calcium nitrate tetrahydrate, diammonium phosphate, ammonium fluoride were used as precursors of Ca, P and F respectively with the ratio of 1:67 Ca/P. The presence of crystal structure of HA and FA investigated by the results of XRD which confirmed the substitution of hydroxyl groups with the fluorine in the crystal structure of apatite. FTIR obtained that fluorine was substituted by hydroxyl groups in the structure of fluoridated hydroxyapatite by disappearing the hydroxyl groups at 3600 cm-1 in the FA. TGA investigated the thermal stability of the nanoparticles that showed the discrepancy of weight loss for HA and FA between 600?C to 800?C. By using TEM, average sizes of 35 and 49 nm were determined for HA and FA respectively. FESEM results confirmed the shapes and distribution of particles of HA and FA in that, round like for the former and rode like for the later. The overall performance of utilizing sodium alginate (SA) as a bio-stabilizer is to obtain better precipitate which leads to having better crystallinity and smaller particle size and thermal stability remarkably improved.

Investigations of gold nanoparticles-mediated carbon nanotube reinforced hydroxyapatite composite for bone regenerations

An excellent combination of biomaterials permits prompt features and high-throughput investigations in various fields, particularly in the biomedical applications. This article investigates the bone regeneration ability and compatibility of the Gold (Au) Nanoparticles (NPs) medicated carbon nanotube reinforced hydroxyapatite (HAP) composite. The morphologies of the synthesized Au NPs, HAP and HAP/CNT, and HAP/CNT-Au composites vary suggestively with modifying the components and the final composite showing as bone mimic extracellular matrix morphology. The structure, phase, and composition of the as-synthesized HAP were studied by FTIR, XRD, EDAX, and TEM techniques. The materials' biocompatibility was investigated in the Stimulated Body Fluid (SBF) solution, which resulted in the composite having good biocompatibility, bioactivity nature and hydroxyapatite layer formed on the composite surface. The composite shows good viability with Adipose Tissue-derived Stem Cells (ADSC) to cell growth and cell proliferation in the biological evaluation. It represented the composites having a good ability for cell formation development. Since the HAP/CNT-Au composite are useful in medicinal applications such as orthopedic and orthodontic repair/regenerations after the evaluations of animal and clinical investigations.

Synthesis of Gd+3 doped hydroxyapatite ceramics: optical, thermal and electrical properties

ABSTRACT In this study, hydroxyapatite powder Ca10(PO4)6(OH)2 (HAp) doped with gadolinium (Gd3+) (HAp:Gd3+) in different mole percentage of between 0.1 and 1.6 was synthesized by sol−gel method at 900°C. The reaction was carried out by hydrolysis of Ca(OH)2 and DCPD (CaHPO4.2H2O) in aqueous solution and then analyzed through XRD, SEM, FTIR, TGA and Four-Point Probe method (custom-made). The results show that Gd3+ has been successfully doped into the hydroxyapatite structure. Then, the photoluminescence, thermal and electrical properties of pure and Gd3+ doped hydroxyapatite were studied and compared with the pure hydroxyapatite. In conclusion, the emission band of Ca10-xGdx(PO4)6(OH)2 was observed at 263, 278, 294, 312 nm) under excitation with 185 nm. The Stokes shift of HAp:Gd3+ was calculated to be 16.031 cm−1. On the other hand, the electrical and thermal conductivity of HAp increased with the increase in Gd3+ concentration due to Ca2+ cation vacancies caused by Gd3+doping.

Bioactive materials for bone regeneration based on zinc-modified hydroxyapatite

Samples of zinc-modified hydroxyapatite (HA) Ca (10− x ) Zn x (PO 4 ) 6 (OH) 2 with different zinc content ( x = 0.1 and 0.5) were synthesized by the liquid-phase method. It was found that the addition of zinc affects the original hydroxyapatite structure and changes the parameters of the crystal lattice. The materials obtained show antibacterial activity.

Bioactive materials for bone regeneration based on zinc-modified hydroxyapatite

Samples of zinc-modified hydroxyapatite (HA) Ca(10−x)Znx(PO4)6(OH)2 with different zinc content (x = 0.1 and 0.5) were synthesized by the liquid-phase method. It was found that the addition of zinc affects the original hydroxyapatite structure and changes the parameters of the crystal lattice. The materials obtained show antibacterial activity.

The Synthesis of Hydroxyapatite Powder Using Shaker Mill Technique

Hydroxyapatite is a material that has the same structure and composition as the main minerals of human teeth and bones. This study's purpose was hydroxyapatite synthesis and determining the effect of variations in the ball sizes, the ratio of a mass of precursors to balls size, milling time, and ball size ratio of crystals and particles, surface area and morphology of hydroxyapatite produced by the mechanochemical method. Two different ball sizes (3mm and 6mm) and three different powder to ball ratio of 1:1.44; 1:2.88; and 1:4.32 were milled for 6 hours. Furthermore, the ball size ratio between the small ball (3 mm) and large ball (6 mm) was 1:1, 1:3, and 3:1 were milled for 2, 4, and 6 hours. The synthesized powder was analyzed by X-ray diffraction, Particle Size Analysis, Brunauer-Emmet-Teller analysis, and Scanning Electron Microscopy to confirm hydroxyapatite structure formation with nanocrystallite size and morphology in all variables. The crystallite size increased as the powder to ball ratio increased. The surface area at powder to ball ratio of 1:2.88 and ball size of 3 mm was 19.51 m2/g, while at ball size ratio of 1:1, it was 18.82 m2/g. The morphology of hydroxyapatite was uniform to granular with mol ratio Ca/P 1.81 for powder to ball ratio and ball size variation.

Characterization of magnesium doped sol-gel biomaterial for bone tissue regeneration: The effect of Mg ion in protein adsorption

Magnesium is the fourth most abundant element in the human body with a wide battery of functions in the maintenance of normal cell homeostasis. In the bone, this element incorporates in the hydroxyapatite structure and it takes part in mineral metabolism and regulates osteoclast functions. In this study, sol-gel materials with increasing concentrations of MgCl2 (0.5, 1, and 1.5%) were synthesized and applied onto Ti surfaces as coatings. The materials were first physicochemically characterized. In vitro responses were examined using the MC3T3-E1 osteoblastic cells and RAW264.7 macrophages. Human serum protein adsorption was evaluated employing nLC-MS/MS. The incorporation of Mg did not affect the crosslinking of the sol-gel network, and a controlled release of Mg was observed; it was not cytotoxic at any of the tested concentrations. The cytoskeleton arrangement of MC3T3-E1 cells cultured on the Mg-doped materials changed in comparison with controls; the cells became more elongated, with protruded lamellipodia and increased cell surface. The expression of integrins (ITGA5 and ITGB1) was boosted by Mg-coatings. The ALP activity and expression of TGF-β, OSX and RUNX2 genes were also increased. In RAW264.7 cells, TNF-α secretion was reduced, while TGF-β and IL-4 expression rose. These changes correlated with the altered protein adsorption patterns. The Mg-doped coatings showed increased adsorption of anti-inflammatory (CLUS, IC1, CFAH, and VTNC), cell adhesion (DSG1, FILA2, and DESP) and tissue regeneration (VTNC and CYTA) proteins. This integrated approach to biomaterial characterization revealed the potential of Mg in bone tissue regeneration.

Direct growth of structurally controllable hydroxyapatite coating on Ti-6Al-4V through a rapid hydrothermal synthesis

Titanium alloys have been used as an implant material for many years due to their high ductility, high strength, excellent corrosion resistance and better biocompatibility. However, this biomaterial as an implant still requires the functionally bioactive surface coating to improve the osseointegration between the implant and bone tissue. Herein, we develop a facile hydrothermal synthesis of using the mixture of calcium hydroxide and sodium tripolyphosphate to directly form a structurally tunable hydroxyapatite coating on the Ti-6Al-4V surface. The result shows that the structure of hydroxyapatite can be readily controlled by modifying the Ti-6Al-4V surface with TiO2 via a short heat treatment. The treated Ti-6Al-4V can provide the rapid growth of hydroxyapatite fibers to form a porous structure interwoven with wire-like shapes in comparison with untreated Ti-6Al-4V presenting needle-like shapes. This structural difference results from the formation of TiO2 assisting in initial nucleation of hydrothermal hydroxyapatite growth. The bioactivity result reveals a better proliferation rate on the wire-like sample is enabled to correlate with the porous structure, crystallinity, and wettability of hydroxyapatite. Our results here not only indicate the feasibility of a structurally controllable hydroxyapatite through a rapid hydrothermal synthesis but also provide insights into optimizing preferred structures on implant surfaces.

Antibacterial Composite Materials Based on the Combination of Polyhydroxyalkanoates With Selenium and Strontium Co-substituted Hydroxyapatite for Bone Regeneration.

Due to the threat posed by the rapid growth in the resistance of microbial species to antibiotics, there is an urgent need to develop novel materials for biomedical applications capable of providing antibacterial properties without the use of such drugs. Bone healing represents one of the applications with the highest risk of postoperative infections, with potential serious complications in case of bacterial contaminations. Therefore, tissue engineering approaches aiming at the regeneration of bone tissue should be based on the use of materials possessing antibacterial properties alongside with biological and functional characteristics. In this study, we investigated the combination of polyhydroxyalkanoates (PHAs) with a novel antimicrobial hydroxyapatite (HA) containing selenium and strontium. Strontium was chosen for its well-known osteoinductive properties, while selenium is an emerging element investigated for its multi-functional activity as an antimicrobial and anticancer agent. Successful incorporation of such ions in the HA structure was obtained. Antibacterial activity against Staphylococcus aureus 6538P and Escherichia coli 8739 was confirmed for co-substituted HA in the powder form. Polymer-matrix composites based on two types of PHAs, P(3HB) and P(3HO-co-3HD-co-3HDD), were prepared by the incorporation of the developed antibacterial HA. An in-depth characterization of the composite materials was conducted to evaluate the effect of the filler on the physicochemical, thermal, and mechanical properties of the films. In vitro antibacterial testing showed that the composite samples induce a high reduction of the number of S. aureus 6538P and E. coli 8739 bacterial cells cultured on the surface of the materials. The films are also capable of releasing active ions which inhibited the growth of both Gram-positive and Gram-negative bacteria.

Bioinspired mineral–organic hybridization strategy to produce a green high performance soybean meal based adhesive

Soybean meal-based adhesives have been applied in many fields due to the abundant source and eco-friendly property. However, the preparation of high-performance soybean meal-based adhesives was still challenging. Inspired by the mineral-organic hybridization structure of nacre, hydroxyapatite and tannic acid complex was used as rigid nanofiller and cross-linker to improve the properties of soybean meal adhesives. Tannic acid was bonded with hydroxyapatite through coordination bonds and could promote the hydrogen bond between soybean meal and hydroxyapatite. Owing to enhanced crosslinking density, the wet shear strength of the adhesive increased from 0.66 to 1.70 MPa and the toughness was also clearly improved. The residual ratio increased to 85.8% and the moisture absorption reduced to 16.5%, indicating better water resistance. The high chemical reactivity of catechol and pyrogallol groups on tannic acid endowed the adhesive with better mildew resistance and antibacterial ability. Besides, the addition of hydroxyapatite and tannic acid complex could restrict the heat transfer and quench the oxygen free radicals, which enhanced the flame resistance of the adhesives. This study provided a new strategy for the preparation of green soybean meal-based adhesives with high performance.

Understanding Electrodeposition of Chitosan-Hydroxyapatite Structures for Regeneration of Tubular-Shaped Tissues and Organs.

Tubular-shaped hydrogel structures were obtained in the process of cathodic electrodeposition from a chitosan–hydroxyapatite solution carried out in a cylindrical geometry. The impact of the initial concentration of solution components (i.e., chitosan, hydroxyapatite, and lactic acid) and process parameters (i.e., time and voltage) on the mass and structural properties of deposit was examined. Commercially available chitosan differs in average molecular weight and deacetylation degree; therefore, these parameters were also studied. The application of Fourier-transform infrared spectroscopy, scanning electron microscopy, and time-of-flight secondary ion mass spectrometry allowed obtaining fundamental information about the type of bonds and interactions created in electrodeposited structures. Biocompatible tubular implants are highly desired in the field of regeneration or replacement of tubular-shaped tissues and organs; therefore, the possibility of obtaining deposits with the desired structural properties is highly anticipated.

ВЛИЯНИЕ СОСТАВА КРИСТАЛЛОХИМИЧЕСКОЙ СТРУКТУРЫ КАЛЬЦИЙ-ФОСФАТНОГО НАНОКОМПОЗИТА НА ФОРМИРОВАНИЕ ЭЛЕКТРОПОВЕРХНОСТНЫХ И КИСЛОТНО-ОСНОВНЫХ СВОЙСТВ

The single-phase modified nanostructured hydroxyapatites and biomimetic calcium-phosphate nanocomposite (BMHAP) doped by silicate and carbonate anions are synthesized by chemical precipitation in aqueous solutions. The chemical composition of the obtained samples is studied by energy dispersive X-ray spectroscopy using a scanning electron microscope. It is shown that the obtained molar ratios are close to the design values in all samples. The influence of different modifying ions in the crystal-chemical structure of hydroxyapatite (HAp) on the electrosurface properties of the synthesized products has been studied. Unmodified hydroxyapatite, silicate-substituted hydroxyapatite, and BMHAP particles are found to carry a negative charge in an aqueous suspension at pH = 7, while carbonate-substituted HAp particles had a positive charge. It is revealed that the introduction of silicate and carbonate anions into the HAp structure is accompanied by an increase in negative values of the zeta-potential from -1.05 to -4.29 mV. The change in the distribution of active centers on the surface of modified nanostructured hydroxyapatites is studied by the adsorption of acid-base indicators method with pKax in the range from -0.3 to +12.8. In contrast to stoichiometric hydroxyapatite, in BMHAP the neutral Bronsted centers prevails, and their concentration is 48.38 mmol-eq/g

Influences of strontium on the phase composition and lattice structure of biphasic calcium phosphate

Hydroxyapatite (HAp) and β-tricalcium phosphate (β-TCP) are widely used in bone graft materials, because they have excellent biocompatibility. However, the degradation rates of HAp and β-TCP do not match the rate of osteogenesis, which limits their clinical applications. Therefore, forming biphasic calcium phosphate (BCP) is a promising method to control the biodegradation rate of the material. In addition, strontium (Sr) is an important element that promotes osteogenesis and inhibits bone absorption. Therefore, this study focused on the effects of Sr in the as-synthesized BCP with varied Sr concentrations of 1, 5, and 15 mol%, which are synthesized by chemical precipitation and a high-temperature calcination method. In this study, we assume that Sr is doped into Ca(5) of β-TCP and Ca(1) & Ca(2) of HAp during the Rietveld refinement. On the basis of the Rietveld refinement results obtained from X-ray diffraction (XRD) patterns, with increasing Sr concentration, the mass percentage of HAp decreases first, which is due to the distortion of the HAp structure, resulting in a decrease in HAp stability and phase variation from HAp to β-TCP. However, when the concentration of Sr reaches 15 mol%, the mass percentage of HAp increases, which may be because of the phase transformation from β-TCP to calcium-deficient apatite by the diffusion of Ca. In addition, the increase in the lattice constants and volumes indicates that Sr has been successfully doped into the crystal lattices of both β-TCP and HAp, since the ion radius of Sr2+ (0.113 nm) is larger than the ion radius of Ca2+ (0.099 nm). As shown in the X-ray photoelectron spectroscopy (XPS) results, the intensities of Sr3d and Sr3p increase with increasing Sr concentrations, which indicates that Sr is not only on the surface of the sample but also in the crystalline structures of both β-TCP and HAp.

Development of Iron-Doped Hydroxyapatite Coatings

It is known that iron is found as a trace element in bone tissue, the main inorganic constituent of which is hydroxyapatite. Therefore, iron-doped hydroxyapatite (HApFe) materials could be new alternatives for many biomedical applications. A facile dip coating process was used to elaborate the iron-doped hydroxyapatite (HApFe) nanocomposite coatings. The HApFe suspension used to prepare the coatings was achieved using a co-precipitation method, which was adapted in the laboratory. The quality of the HApFe suspension was assessed through dynamic light scattering (DLS), ultrasonic measurements, and zeta potential values. The hydroxyapatite XRD patterns were observed in the HApFe nanocomposite with no significant shifting of peak positions, thus suggesting that the incorporation of iron did not significantly modify the hydroxyapatite structure. The morphology of the HApFe nanoparticles was evaluated using transmission electron microscopy (TEM). Scanning electron microscopy (SEM) was used in order to investigate the morphologies of HApFe particles and coatings, while their chemical compositions were assessed using energy-dispersive X-ray spectroscopy (EDS). The SEM results suggested that the HApFe consists mainly of spherical nanometric particles and that the surfaces of the coatings are continuous and homogeneous. Additionally, the EDS spectra highlighted the purity of the samples and confirmed the presence of calcium, phosphorous, and iron in the analyzed sample. The in vitro cytotoxicity of the HApFe suspensions and coatings was evidenced using osteoblast cells. The MTT assay showed that both the HApFe suspensions and coatings exhibited biocompatible properties.

Influence of magnesium and strontium substitutions in the structure of hydroxyapatite lattice on the deposition rate and properties of the CaP coatings formed via RF-sputtering of the powder targets

This work is dedicated to studying of the properties of the calcium phosphate (CaP) coatings deposited on Ti substrates by radio-frequency magnetron sputtering (RFMS) of three hydroxyapatite-based powder targets: pure hydroxyapatite (HA), Mg-substituted HA (Mg-HA, Mg = 0.93 ± 0.13 at.%) and Sr-substituted HA (Sr-HA, Sr ∼ 0.47 at.%). The influence of ionic substitutions in the structure of the sputtered targets on the surface morphology, physicochemical properties of the coatings and their wettability were studied. It is revealed that Mg and Sr ionic substitutions in the crystal lattice of HA at these concentrations don’t affect deposition rate, however, it influences morphology, wettability and elemental and phase composition of deposited coatings.

Defect structures of sodium and chloride co-substituted hydroxyapatite and its osseointegration capacity

A defect structure and osseointegration capacity of sodium and chloride co-substituted hydroxyapatite (NaClAp) were newly studied. The NaClAp was prepared by reacting H3PO4 and Ca(OH)2 with NaNO3 and NH4Cl followed by sintering; pure hydroxyapatite (HAp) was synthesized as a control. After sintering, the co-substitution of Ca and OH with Na and Cl, respectively, produced charged point defects at Ca and PO4 sites. Also, OH molecules partially adopted a head-on structure. The calculated total system energy of NaClAp was higher, whereas the binding energies between each constituent elements and system were lower than those of HAp. These results suggest that NaClAp was less stable than HAp, due to the formation of various defects by co-substitution of Na and Cl. Indeed, NaClAp exhibited higher dissolution behavior in simulated body fluid (SBF) compared with HAp. Accordingly, this increased the capability to produce low crystalline hydroxyl carbonate apatite, likely due to the increasing degree of apatite supersaturation in SBF. Besides, the NaClAp granules showed noticeable improvements in osseointegration capacity four weeks after in vivo test compared with HAp. Collectively, these results imply that the defects made by multiple ion substitutions are useful to increase osseointegration capacity of hydroxyapatite.

АНАЛИЗ СОСТАВА И СТРУКТУРЫ БИВНЯ МАМОНТА MAMMUTHUS PRIMIGENIUS МЕТОДАМИ ТЕРМОГРАВИМЕТРИЧЕСКОГО И РЕНТГЕНОФАЗОВОГО АНАЛИЗА

The article represents the results of the research of the chemical composition of mammoth tusk Mammuthus Primigenius and its phase transformation using thermogrammetric (TGA) and X-ray spectroscopy analysis (XRD). The elemental analysis of mammoth tusk showed, that besides basic elements in the structure of hydroxyapatite (HAP) contains magnesium ions, i.e. hydroxyapatite in the studied samples is presented in magnesium-substituted form. The thermal decomposition of mammoth tusk components occurs in wide temperature range with a change in the structure of the mineral part from hydroxyapatite to whitlockite. It was found that this process is caused by the presence of magnesium ions.

Efficient antibacterial activity of hydroxyapatite through ROS generation motivated by trace Mn(iii) coupled H vacancies.

Hydroxyapatite (HA) has attracted wide attention for medical application due to its biocompatibility and bioactivity. However, the infection problems of HA remain among the leading reasons for implantation failure. Thus, it is urgent to endow HA biomaterials with antibacterial activity. Herein, the high antibacterial activity was achieved by introducing trace Mn3+ and H vacancy couples in HA through a facile heat-treatment strategy in air. The theoretical results indicated that Mn3+ was preferentially substituted for the Ca(2) site in the HA structure with a charge-compensating H vacancy appearing at the adjacent OH- site. The antibacterial tests showed that Mn-HA possessed antibacterial activity towards both E. coli and S. aureus with trace Mn content at the ppm level, and implied that Mn3+ and centers may play an important role in the antibacterial process. The Mn3+ and couples in Mn-HA, serving as oxidative and reductive centers respectively, could then collectively participate in the CoQ/CoQH2 redox cycling and synergistically facilitate the accumulation of CoQ˙- and ROS radicals. This enhanced ROS production was the main factor to endow Mn-HA with efficient antibacterial activity. Moreover, the in vitro bioactivity assay showed that Mn-HA materials exhibited enhanced osteogenic activity and good biocompatibility. Therefore, this work not only provides a feasible method to control the oxidation state of Mn elements in HA, but also proposes a novel trace Mn3+-doped HA for potential applications in tissue engineering.

Nanofibers of polycaprolactone containing hydroxyapatite doped with aluminum/vanadate ions for wound healing applications

The combined doping of aluminum and vanadate ions into the structure of hydroxyapatite encapsulated in polycaprolactone nanofibers might represent a simple approach for wound dressing design.