Synthesis of multifunctional Fe3O4 core/hydroxyapatite shell nanocomposites by biomineralization

Superparamagnetic nanoparticles with surface functional groups (-OH, -COOH and -NH(2)) were modified by in situ deposition of hydroxyapatite (HA) on the materials' surface through the biomineralization process to form Fe(3)O(4) core/hydroxyapatite shell nanocomposites. They possess potential applications as targeted carriers for antitumor drugs and as bone tissue engineering scaffolds by integrating multiple functions into a single nanosystem.     

Effect of pH and temperature on the morphology and phases of co-precipitated hydroxyapatite

This paper reports a high-yield process to fabricate biomimetic hydroxyapatite nano-particles or nano-plates. Hydroxyapatite is obtained by simultaneous dripping of calcium chloride and ammonium hydrogen phosphate solutions into a reaction vessel. Reactions were carried out under various pH and temperature conditions. The morphology and phase composition of the precipitates were investigated using scanning electron microscope and X-ray diffraction. The analyses showed that large plates of calcium hydrophosphate are formed at neutral or acidic pH condition. Nanoparticles of hydroxyapatite were obtained in precipitates prepared at pH 9–11. Hydroxyapatite plates akin to seashell nacre were obtained at 40 °C and pH 9. This material holds promise to improve the strength of hydroxyapatite containing composites for bone implant or bone cement used in orthopaedic surgeries. The thermodynamics of the crystal growth under these conditions was discussed. An assembly mechanism of the hydroxyapatite plates was proposed according to the nanostructure observations.     

非化学计量羟基磷灰石骨水泥的制备及性能研究

采用磷酸四钙和磷酸氢钙混合粉末制备了nCa/nP比为1.58的非化学计量羟基磷灰石骨水泥(n-HAC)及其多孔支架材料。结果表明:与nCa/nP=1.67的化学计量羟基磷灰石骨水泥(HAC)相比,n-HAC的凝结时间和抗压强度没有明显的区别。XRD和IR显示:n-HAC与HAC都为羟基磷灰石结构,但n-HAC在Tris-HCl缓冲溶液的降解性明显大于HAC。细胞培养结果表明:成骨细胞在n-HAC和HAC两种材料上的粘附和细胞形态没有明显的区别,但细胞在n-HAC上的增殖率明显高于HAC。将多孔n-HAC支架材料植入兔股骨缺损处,观察其修复骨缺损情况,组织学分析结果表明:新生骨在多孔支架的表面形成,并长入其内部;n-HAC在体内的降解比HAC快,能明显地促进新骨生成。     

Hydroxyapatite-poly(d,l-lactide) Nanografts. Synthesis and Characterization as Bone Cement Additives

This paper reports the creation of hydroxyapatite/polyester nanografts by “graft-from” polymerization of d,l-lactide with [Ca₅(OH)(PO₄)₃]₂ as the initiator and tin(II)-2-ethylhexanoate as the catalyst. Model polymerizations were performed with cyclooctanol as initiator to confirm the grafting on the surface of the hydroxyapatite nanocrystals. Polymers with the highest molecular mass (M_n) between 4250 Da (cyclooctanol) and 6100 Da (hydroxyapatite) were produced. In both cases the molecular mass distributions of the polymers formed were monomodal. The materials obtained were characterized by size-exclusion chromatography, NMR and FT-IR spectroscopy, and thermal methods. Their suitability as additives for commercial bone cement (Simplex P Speedset, Stryker Orthopaedics) has been confirmed by thermal analysis techniques and mechanical testing. The results obtained show that addition of the hydroxyapatite/ polyester nanografts improved both thermal and mechanical properties of the bone cement.     

Hydroxyapatite Obtained via the Wet Precipitation Method and PVP/PVA Matrix as Components of Polymer-Ceramic Composites for Biomedical Applications

The aspect of drug delivery is significant in many biomedical subareas including tissue engineering. Many studies are being performed to develop composites with application potential for bone tissue regeneration which at the same provide adequate conditions for osteointegration and deliver the active substance conducive to the healing process. Hydroxyapatite shows a great potential in this field due to its osteoinductive and osteoconductive properties. In the paper, hydroxyapatite synthesis via the wet precipitation method and its further use as a ceramic phase of polymer–ceramic composites based on PVP/PVA have been presented. Firstly, the sedimentation rate of hydroxyapatite in PVP solutions has been determined, which allowed us to select a 15% PVP solution (sedimentation rate was 0.0292 mm/min) as adequate for preparation of homogenous reaction mixture treated subsequently with UV radiation. Both FT-IR spectroscopy and EDS analysis allowed us to confirm the presence of both polymer and ceramic phase in composites. Materials containing hydroxyapatite showed corrugated and well-developed surface. Composites exhibited swelling properties (hydroxyapatite reduced this property by 25%) in simulated physiological fluids, which make them useful in drug delivery (swelling proceeds parallel to the drug release). The short synthesis time, possibility of preparation of composites with desired shapes and sizes and determined physicochemical properties make the composites very promising for biomedical purposes.     

Élaboration de ciments apatitiques composites pour la rétention du césium et de l’iode

A composite apatitic cement made of hydroxyapatite loaded with β-tricalcic phosphate, zirconium phosphate and activated carbon has been elaborated and its ability to block cesium and iodine tested. It could be used as a buffer material in order to prevent the rapid release of soluble fission products (cesium and iodine) in aqueous solutions leaching the spent fuel, in the case of direct disposal of spent fuel.     

Preparation of nanostructure hydroxyapatite scaffold for tissue engineering applications

Hydroxyapatite due to its good biocompatibility and similar chemical composition to the mineral part of bone has found various applications in tissue engineering. Porous hydroxyapatite has high surface area, which leads to excellent osteoconductivity and resorbability, providing fast bone ingrowth. In this study, highly porous body of nanostructure hydroxyapatite was successfully fabricated via gelcasting method. The pure phase of hydroxyapatite was confirmed by X-ray diffraction. The result of scanning electron microscopy analysis showed that the prepared scaffold has highly interconnected spherical pores with a size in the range 100–400 μm. The crystallite size of the hydroxyapatite scaffold was measured in the range 30–42 nm. The mean values of true (total) and apparent (interconnected) porosity were calculated in the range 84–91 and 70–78%, respectively. The maximum values of compressive strength and elastic modulus of the prepared scaffold were found to be about 1.5 MPa and 167 MPa, respectively, which were achieved after sintering at 1,000 °C for 4 h. Transmission electron microscopy analysis showed that the particle sizes are smaller than 80 nm. In vitro test showed good bioactivity of the prepared scaffold. The mentioned properties could make the hydroxyapatite scaffold a good candidate for tissue engineering applications, especially applications that did not need to stand any loading.     

Preparation of a biphasic calcium phosphate from Ca(H2PO4)2·H2O AND CaCO3

Sintered hydroxyapatite (HAp) and β-tricalcium phosphate (β-TCP) are the two most common bio-ceramics for bone substitute. Although their composition are analogous to the constituent of human hard tissue, but some disadvantages are always exist till now, such as they need a high temperature sintering process, and this would lose the functional groups for bioactivity and closed the micro- pores without any interconnections, that hamper the body fluid transportation and angiogenesis during regeneration. Furthermore, the sintered ceramics with block and fixed size is difficult to fit non-regular defect area. In this study, the mixtures of Ca(H₂PO₄)₂·H₂O and CaCO₃ were adjusted firstly, then distilled water were introduced in wet chemical method, and a biphasic ceramic of HAp/β-TCP will be obtained after drying and sintering, then the result product that prepared by wet chemical method will be the sample in this investigation. The physical properties of result powders were characterized by DTA/TG, XRD and SEM, respectively, the particle size of two bio-ceramics that after heat treatment were found under 5 μm in SEM examination. Powder type calcium phosphate ceramics with the Ca/P molar ratio of 1.67 can be as bone cement by mixing with polymeric binder, the fine particle product of the setting cement will possess micro-pores and macro-pores that after suitable heat treatment process, and this is good for fluid transportation and tissue regeneration.     

Biocomposites of nanohydroxyapatite with collagen and poly(vinyl alcohol)

Biocomposites of hydroxyapatite, HAp, in conjunction with various binders including poly(vinyl alcohol), PVA, and collagen have the potential of serving in various tissue engineering applications, such as in bone repair and reconstruction tasks, especially if the nanoparticles of hydroxyapatite are used. Here, hydroxyapatite nanoparticles (n-HAp) were synthesized at the ultimate size range of 10-50 nm and then incorporated into PVA or in situ synthesized in collagen/PVA. The biocomposites of HAp with PVA exhibited relatively high elasticity (as revealed by the linear viscoelastic material functions, characterized upon small-amplitude oscillatory shear) especially upon cryogenic treatment. The incorporation of the collagen into the PVA/HAp biocomposite provided internal porosity to the biocomposite with the pores in the 50-100 nm range for collagen/HAp and 50-500 nm for the collagen/HAp/PVA.     

Valorization of Bone Waste of Saudi Arabia by Synthesizing Hydroxyapatite

At present, hydroxyapatite is being frequently used for diverse biomedical applications as it possesses excellent biocompatibility, osteoconductivity, and non-immunogenic characteristics. The aim of the present work was to recycle bone waste for synthesis of hydroxyapatite nanoparticles to be used as bone extracellular matrix. For this reason, we for the first time utilized bio-waste of cow bones of Albaha city. The residual bones were utilized for the extraction of natural bone precursor hydroxyapatite. A facile scientific technique has been used to synthesize hydroxyapatite nanoparticles through calcinations of wasted cow bones without further supplementation of chemicals/compounds. The obtained hydroxyapatite powder was ascertained using physicochemical techniques such as XRD, SEM, FTIR, and EDX. These analyses clearly show that hydroxyapatite from native cow bone wastes is biologically and physicochemically comparable to standard hydroxyapatite, commonly used for biomedical functions. The cell viability and proliferation over the prepared hydroxyapatite was confirmed with CCk-8 colorimetric assay. The morphology of the cells growing over the nano-hydroxyapatite shows that natural hydroxyapatite promotes cellular attachment and proliferation. Hence, the as-prepared nano-hydroxyapatite can be considered as cost-effective source of bone precursor hydroxyapatite for bone tissue engineering. Taking into account the projected demand for reliable bone implants, the present research work suggested using environment friendly methods to convert waste of Albaha city into nano-hydroxyapatite scaffolds. Therefore, besides being an initial step towards accomplishment of projected demands of bone implants in Saudi Arabia, our study will also help in reducing the environmental burden by recycling of bone wastes of Albaha city.     

Influence of process parameters on the sol–gel synthesis of nano hydroxyapatite using various phosphorus precursors

Hydroxyapatite Ca₁₀(PO₄)₆(OH)₂ has attracted widespread interest from both orthopedic and dental fields due to its excellent biocompatibility and tissue bioactivity properties. Since nanophase materials can mimic the dimensions of constituent components of natural tissues, the implants developed from nanophase material could serve as a successful alternative. However, the defects of hydroxyapatite ceramics, mainly brittleness and low fracture toughness, have been overcome by the use of nanophase hydroxyapatite coatings on the implant surfaces that integrate the good mechanical properties of metals and the bioactivity of hydroxyapatite. In the present investigation, Sol?Cgel hydroxyapatite was prepared from two different phosphorus precursors such as triethyl phosphate and phosphorus pentoxide respectively with calcium nitrate tetrahydrate as a calcium precursor. The effects of pH and liquid P³¹ Nuclear Magnetic Resonance spectroscopy for the solution aged at different periods were investigated and the synthesized hydroxyapatite powder was characterized by Transmission electron microscopy, X-ray Powder Diffraction, Fourier transform infrared spectroscopy and thermal analysis respectively. In order to fully understand the bioactivity of the synthesized materials, they were coated on 316L Stainless Steel implant surface by spin coating method at the spin speed of 2,000 Revolutions per minute. The effect of nanoparticles on the surface of 316L Stainless Steel implant was studied by adhesive strength measurements. The corrosion resistance property of the hydroxyapatite coatings was evaluated by electrochemical impedance analysis. From the results, it was observed that the hydroxyapatite coatings obtained from different precursors have very high resistance to corrosion with higher adhesive strength.     

Specific features of sorption of bovine serum albumin on hydroxyapatite doped with zinc ions,and the possibilities of its use as an intermediate binding protein for heterocyclic ligands

Russian Chemical Bulletin - In order to characterize hydroxyapatite (HAP) as a possible carrier of medicinal drugs and radionuclides, the possibility of using HAP modified with zinc ions (HAP-Zn)...     

Hydroxyapatite grown on a native extracellular matrix: initial interactions with human fibroblasts

Proteins are known to modulate the physical properties of minerals, and thus we anticipate that they will strongly influence the structure and the biological properties of biomimetically prepared carbonate-containing hydroxyapatite. This study was designed to learn more about the main morphological characteristics of hydroxyapatite layer grown on different substrates coated with an extracellular matrix, a biological matrix that was produced by cultured osteoblast-like cells. The hydroxyapatite growth was carried out in a simulated body fluid, a solution that resembles the human blood plasma. It was found that the extracellular matrix may serve as a template for the mineralization of biomimetic hydroxyapatite on the surface of materials like stainless steel, silicon, and silica glass, leading to the formation of a homogeneous layer. The latter was consisting of nanometer-sized hydroxyapatite crystals grouped in particles with regular sphere shape and with a significantly higher average diameter in comparison to samples without extracellular matrix coating. Subsequent in vitro studies with living fibroblasts showed that the cellular behavior depended on the type of underlying substrate used for the hydroxyapatite growth, as well as on the immersion time of the samples in the simulated body fluid. Increasing the thickness of the hydroxyapatite layer altered visibly the cellular response, and the fibroblasts developed stellate morphology on the samples with a hydroxyapatite-extracellular matrix coating. Preadsorption with fibronectin significantly improved the initial cell adhesion and spreading to all surfaces. Thus, such an approach may contribute to the development of surfaces with better tissue compatibility.     

Adsorption of citrate ions on hydroxyapatite synthetized by various methods

The specific adsorption of citric acid ions at hydroxyapatite interface was investigated by the means of radioisotope method (¹⁴C) as a function of citric acid ions concentration, NaCl concentration and pH. Application of the hydroxyapatite has become wide in the biomaterial field as the Ca₁₀(OH)₂(PO₄)₆ possess biocompatibility with human hard tissue. Hydroxyapatite was synthesized using three different methods. The physical properties of the resulting powder were characterized by DTA/TG, XRD, AFM and SEM microscopy. Physicochemical qualities characterizing the electrical double layer of the hydroxyapatite/NaCl solution interface were determined. The zeta potential and the adsorption of citric acid molecule were studied as a function of pH. The point of zero charge and the isoelectric point of samples were determined. Electrical double layer parameters of hydroxyapatite/NaCl interface are influenced by a synthesis method. The points pH_pzc and pH_IEP for sample 1 are pH_pzc 7.5 and pH_IEP 3; for sample 2 pH_pzc 7.05 and pH_IEP 3, for smaple 3 pH_pzc 6.7 and pH_IEP 3. Temperature has weak influence both on pure substance and with citric acid adsorbed, as derivatographic analysis has shown, and characterization of hydroxyapatite structure may be carried out by this thermal analysis. Two phenomena are responsible for citric acid adsorption: phosphate group’s replacement at hydroxyapatite surface by citric ions parallel to intraspherical complexes formation.     

Preparation and Characterization for the Electrodeposited Hybrid Coating of Calcium Phosphate/Chitosan on Ti Alloy Surface

Hydroxyapatite (HA) formulated as Ca₁₀(PO₄)₆(OH)₂ becomes a favorable material for implants because of its chemical similarity to the calcium phosphate minerals present in biological hard tissue. Many efforts have been made in recent years in the development of processing methods for depositing hydroxyapatite on implant alloy substrate in order to have high strength, good processability, suitable specific density, excellent corrosion resistance in the physiological environment and good affinity to the living body. The plasma spray technique is commonly used in the HA coating on implants. The major problem for the plasma spray, however, is the decomposition and phase transformation of hydroxyapatite during the spray coating process. Electrochemical techniques including electrophretic deposition and electro-deposition are being developed as an alternative method for producing hydroyapatite coated composite material. It is very desirable at present to further strengthen the coating and bond it to the metal substrate, and to increase the bioactivity of hydroxyapatite coatings as well, which is very important for forming a strong chemical bond with natural bone as an implant material.     

Effects of PCL,PEG and PLGA polymers on curcumin release from calcium phosphate matrix for in vitro and in vivo bone regeneration

Calcium phosphate materials are widely used as bone-like scaffolds or coating for metallic hip and knee implants due to their excellent biocompatibility, compositional similarity to natural bone and controllable bioresorbability. Local delivery of drugs or osteogenic factors from scaffolds and implants are required over a desired period of time for an effectual treatment of various musculoskeletal disorders. Curcumin, an antioxidant and anti-inflammatory molecule, enhances osteoblastic activity in addition to its anti-osteoclastic activity. However, due to its poor solubility and high intestinal liver metabolism, it showed limited oral efficacy in various preclinical and clinical studies. To enhance its bioavailability and to provide higher release, we have used poly (ε-caprolactone) (PCL), poly ethylene glycol (PEG) and poly lactide co glycolide (PLGA) as the polymeric system to enable continuous release of curcumin from the hydroxyapatite matrix for 22 days. Additionally, curcumin was incorporated in plasma sprayed hydroxyapatite coated Ti6Al4V substrate to study in vitro cell material interaction using human fetal osteoblast (hFOB) cells for load bearing implants. MTT cell viability assay and morphological characterization by FESEM showed highest cell viability with samples coated with curcumin-PCL-PEG. Finally, 3D printed interconnected macro porous β-TCP scaffolds were prepared and curcumin-PCL-PEG was loaded to assess the effects of curcumin on in vivo bone regeneration. The presence of curcumin in TCP results in enhanced bone formation after 6 weeks. Complete mineralized bone formation increased from 29.6% to 44.9% in curcumin-coated scaffolds compared to pure TCP. Results show that local release of curcumin can be designed for both load bearing or non-load bearing implants with the aid of polymers, which can be considered an excellent candidate for wound healing and tissue regeneration applications in bone tissue engineering.     

Improved antibacterial activity of HAP garlanded PLGA ultrafine fibers incorporated with CuO: synthesis and characterization

Well-organized nanocrystalline hydroxyapatite nanoparticles garlanded poly(dl-lactide-co-glycolide) (PLGA) ultrafine fibers with efficient antibacterial properties are of great interest in the development of new products. In the present study, hydroxyapatite doped PLGA ultrafine fibers incorporated with copper oxide nanocrystals were fabricated via two step methodology. Primarily; copper oxide nanocrystals were synthesized using wet chemical method. Then the as-synthesized nanocrystals were used for the preparation of composite fibers using electrospinning technique. The properties of pure and composite ultrafine fibers were characterized using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, and electron probe mapping analysis. The in vitro antimicrobial activity of synthesized pure and hydroxyapatite doped PLGA ultrafine fibers was investigated against model organism Escherichia coli (gram negative) using optical density method and morphological damage was observed by TEM. Ultrafine fibers with average diameter ranges from 1.0 to 1.2 μm were obtained. Uniform distribution of hydroxyapatite was observed. Admirable antimicrobial activity against E. coli was achieved which could be attributed by the synergy between hydroxyapatite and copper oxide. In contrast to pristine PLGA, lower concentrations of hydroxyapatite–copper oxide doped PLGA nanocomposite were needed to strongly inhibit the growth of E. coli. Our results report successful preparation of hydroxyapatite–copper oxide based novel nanocomposite. The developed hybrid nanocomposite possess exceptionally good antibacterial activity against E. coli due to the synergistic effect of hydroxyapatite and copper oxide. The antimicrobial nanocomposite can be utilized for a range of bio-functional purposes such as a good candidate for water purification, antibiofouling, wound dressings and bone tissue engineering etc.     

In situ mineralization of hydroxyapatite on poly(vinyl alcohol) monolithic scaffolds for tissue engineering

A poly(vinyl alcohol) (PVA)/hydroxyapatite (HAp) composite monolithic scaffold is prepared via thermally impacted non-solvent induced phase separation method, successively followed by an alternate soaking process. The morphology of the resulting composite monolith is observed by scanning electron microscopy (SEM). The formation of hydroxyapatite is confirmed by X-ray diffraction, SEM in combination with energy dispersive X-ray analysis, and Fourier transform infrared spectroscopy. The effects of soaking cycle and soaking time upon the formation of hydroxyapatite on the monolith surface are systematically investigated. With the increase of soaking cycle and soaking time, the amount of the formed hydroxyapatite increases. As the soaking cycle increases, the water uptake of the composite monolith decreases. The PVA/HAp composite monolith greatly has a promising application as scaffold of bone tissue engineering.     

羟基磷灰石在磺化聚醚苯并咪唑薄膜表面的生长

以聚[2,2′-(对氧基联苯)-5,5′-苯并咪唑](OPBI)及其磺化产物磺化聚[2,2′-(对氧基联苯)-5,5′-苯并咪唑](SOPBI)薄膜作为基体, 采用交替沉积和模拟体液(SBF)浸泡相结合的方法快速在薄膜表面沉积羟基磷灰石层. 采用选区电子衍射(SAED)和衰减全反射傅里叶变换红外光谱(ATR-FTIR)对羟基磷灰石(HA)的晶体结构进行了分析. 用扫描电子显微镜(SEM)对整个沉积过程中羟基磷灰石的形态变化进行了跟踪. 实验结果表明, SOPBI薄膜诱导HA沉积的速率明显快于OPBI薄膜. SOPBI的磺酸基团不但提供了固定Ca²⁺的负电表面, 而且还有助于咪唑基团对Ca²⁺的固定. 而缺失磺酸基团的OPBI在不同pH值的交替沉积溶液中的电离形式阻碍了咪唑基团对Ca²⁺和HPO₄^2-的作用, 且未能在SBF浸泡过程中得到改善.     

Apparent solubility distributions of hydroxyapatite and enamel apatite

Samples of human dental enamel and hydroxyapatite were equilibrated at 5 mg/40 ml for 9 days at 37 degrees C with acetate buffers adjusted to a range of saturations with respect to hydroxyapatite. Sigmoidal apparent solubility distributions, in which the fraction dissolved was plotted against--log(ion activity product for hydroxyapatite) (pIHA), were constructed. About 10% of the hydroxyapatite and 14% of the enamel was very soluble, dissolving even at pIHA 55. The apparent solubility distributions for both solids were invariant with pH (4.5, 5.0, 5.5), within experimental error, showing that solubility was controlled by a phase with the stoichiometry of hydroxyapatite, probably in the form of a surface layer or complex on the crystals, in agreement with other studies on carbonate-apatites and bone mineral. The pIHA at 50% dissolution was employed as an average value. The pIHA (50%) values for pooled data (58.76 for enamel and 60.17 for hydroxyapatite) were lower than the respective pIHA previously measured by conventional equilibration techniques. However, the average pIHA measured for enamel was higher than that obtained by the same technique in another study, possibly because of differences in specimen preparation and equilibration time. The possible implications of the findings for understanding the process of dental caries are discussed.