Surface modification of hydroxyapatite nanocrystals by grafting polymers containing phosphonic acid groups

A novel approach for the surface modification of hydroxyapatite (HAp) nanocrystals is described by grafting polymerization of vinyl phosphonic acid (VPA) using a redox initiating system in an aqueous media. Fourier transform infrared (FT-IR) and XRD analyses confirmed the modification reaction on HAp surfaces. Inductively coupled plasma mass spectroscopy (ICP MS) showed that the Ca/P molar ratio decreased from 1.67 to 1.36 with increasing the feed VPA amount. Zeta potentials of unmodified HAp and modified HAp in phosphate-buffered saline (PBS) solutions (pH 7.4, ionic strength = 10 mM) were negative and decreased with increasing the amount of grafted PVPA. Transmission electron microscopy (TEM) measurements and time-dependent phase monitoring indicated that the colloidal stability of modified HAp over unmodified HAp in water dramatically increased and tended to exist as single nanocrystals without aggregation.     

Fabrication of platy apatite nanocrystals loaded with TiO2 nanoparticles by two-step emulsion method and their photocatalytic activity

Nanometer-sized TiO(2) island structure on the platy hydroxyapatite nanocrystals (HAp) has been accomplished by two-step emulsion process. At the first step, platy HAp nanocrystals, of which size was in the range of 70-200 nm after heat-treatment at 1078 K for 1 h, were prepared using the W/O emulsion system. Before the second step, HAp nanocrystals were immersed in NaH(2)PO(4) solution for the formation of hydroxyl group on their surface. In the following, titanium tetraisopropoxide reacted with the hydroxyl group of HAp surface to form TiO(2) nanoparticles on the surface of HAp nanocrystals, which were dispersed in the micrometer-sized methanol droplets of polyethylene cetylether-cyclohexane mixture (methanol/oil emulsion). The resulting hydroxyapatite nanocrystals loaded with TiO(2) nanoparticles showed the high photocatalytic activity comparing to the commercial TiO(2) catalyst.     

The Surface Structure of Hydroxyapatite Single Crystal and the Accumulation of Arachidic Acid

Single crystals of hydroxyapatite (HAp) were grown by a flux method using beta-tricalcium phosphate and Ca(OH)(2) under hot isostatic pressure. After chemical etching by 0.05 N HCl aqueous solution, the HAp crystal surfaces were observed by an atomic force microscope (AFM) and shown dominantly to consist of steps with heights corresponding to a lattice distance d(100) or its 2/3. Arachidic acid films were accumulated on the etched HAp crystal by a Langmuir-Blodgett method. From section analyses by AFM, a distance between the carboxyl groups of arachidic acid and the HAp surface was estimated to be approximately 0.04 nm, sufficiently adjacent for a chemical interaction to take place. Copyright 2000 Academic Press.     

磷酸氢钙水解法合成羟基磷灰石纳米晶

采用磷酸氢钙水解法和水热处理技术在模拟体液(SBF)介质中合成HA纳米晶,利用XRD研究了pH值、水热处理温度等制备工艺对合成HA纳米晶的影响。TEM、EDS和FTIR表征结果表明磷酸钙产物为长100 nm、直径10 nm的棒状含碳酸根羟基磷灰石纳米晶,其Ca/P比为1.69,这表明本工作获得的HA在组成与形态上与骨骼中的HA十分相似。     

Growth of hydroxyapatite nanocrystals on polymer particle surface

In the present paper, we describe the preparation of hybrid particles consisting of polymeric core with deposited hydroxyapatite (HAp) nanocrystals. Polystyrene submicron particles modified by β-diketone groups have been used as templates for the growth of HAp. Hybrid particles with HAp nanocrystal content between 7 and 50 wt% have been prepared. Microscopy studies indicate that hybrid particles exhibit “raspberry” morphology, and HAp nanoparticles are not homogeneously distributed on the polymer particle surface. The increase in the HAp content on the polymer particle surface reduces the colloidal stability of the hybrid particles because of the vanishing of the surface charge.     

Nanocrystalline hydroxyapatite powders by a chitosan–polymer complex solution route: Synthesis and characterization

Nanocrystalline hydroxyapatite (HAp) powders were successfully synthesized by a simple method using chitosan–polymer complex solution. To obtain HAp nanopowders, the prepared precursor was calcined in air at 400–800 °C for 2 h. The phase composition of the calcined samples was studied by X-ray diffraction (XRD) technique. The XRD results confirmed the formation of HAp phase with a small trace of monotite phase. With increasing calcination temperature, the crystallinity of the HAp increased, showing the hexagonal structure of HAp with the lattice parameter a in a range of 0.94030–0.94308 nm and c of 0.68817–0.68948 nm. The particle sizes of the powder were found to be 55.02–73.36 nm as evaluated by the XRD line broadening method. The chemical composition of the calcined powders was characterized by FTIR spectroscopy. The peaks of the phosphate carbonate and hydroxyl vibration modes were observed in the FTIR spectra for all the calcined powders. TEM investigation revealed that the prepared HAP samples consisted of rod-like nanoparticles having the particle size in the range of 100–300 nm. The corresponding selected-area electron diffraction (SAED) analysis further confirmed the formation of hexagonal structure of HAp.     

Adsorption of a statherin peptide fragment on the surface of nanocrystallites of hydroxyapatite

Statherin is an active inhibitor of calcium phosphate precipitation in the oral cavity. For many studies of the interaction between statherin and hydroxyapatite (HAp), the samples are prepared by a direct mixing of statherin or its fragment with well-crystalline HAp crystals. In this work, the HAp sample is precipitated in the presence of peptide fragment derived from the N-terminal 15 amino acids of statherin (SN-15). The in situ prepared HAp crystallites are nanosized, leading to a significant increase of the peptide amount adsorbed on the HAp surface. The enhancement in NMR sensitivity allows, for the first time, the measurement of a two-dimensional 13C-13C correlation spectrum for a 13C uniformly labeled peptide sample adsorbed on mineral surface. The measurement time is about 18.5 h at a field strength of 7.05 T. Preliminary results suggest that there may exist two different mechanisms for the interaction between SN-15 and HAp. In addition to the one which will cause a conformational change near the N-terminal, SN-15 may also be absorbed on the HAp surface by simple electrostatic interaction, without any significant conformational changes of the peptides.     

A new glance at ruthenium sorption mechanism on hydroxy, carbonate, and fluor apatites: Analytical and structural studies

The sorption mechanism of Ru3+ ions on hydroxy (HAp), carbonate (CO3HAp), and fluor apatites (FAp) has been studied in detail. Ru apatites were obtained by reaction of the apatites with RuCl3 in aqueous solution. The structure and composition of the ruthenium-modified apatites were studied by several techniques: elemental analysis, XRD, EXAFS, IR, NMR, SEM-EDS, TEM, and thermal analysis. The amount of Ru in the modified apatite varies from 7.8 to 10.5 wt% and is not related to the initial composition or the specific surface area of the apatite. The different characterization techniques show that in the Ru-modified apatites Ru is surrounded by six oxygen atoms and do not contain any chlorine. For Ru-HAp and Ru-CO3HAp the new phase is amorphous whereas it is crystalline for FAp. The catalytic oxidation ability is higher for Ru-HAp and Ru-CO3HAp compared to Ru-FAp apatite in the oxidation of benzylic alcohol.     

X‐ray diffraction study of low‐energy carbon‐ion implanted Si(001)

In the search for Si‐ and C‐based crystalline phases in low‐energy ion implanted and electron‐beam annealed Si surface layers, X‐ray diffraction (XRD) measurements were performed at grazing incidence on samples of large SiC nanocrystals grown on a 90 nm thick Si layer containing C atoms. Diffraction patterns and reciprocal space maps did not reveal XRD patterns originating from the nanocrystals or the implanted layer, but did show that distortions of the Si crystal structure were introduced into the implanted layer. After annealing, the strain in the implanted layer is reduced, possibly by carbon atoms that have moved to locations close to dislocations and dislocation loops. This investigation underpins the growth theory of the SiC nanocrystals on Si, with carbon atoms migrating to form the nanostructures. Copyright © 2007 John Wiley & Sons, Ltd.     

Solid-state P-31 NMR study of the formation of hydroxyapatite in the presence of glutaric acid

We demonstrate that glutaric acid can be used to prepare nanorods of hydroxyapatite under hydrothermal condition at 100 degrees C with a Ca(2+):glutaric acid molar ratio of 1:4. Frequency-switched Lee-Goldburg irradiation is employed to obtain high-resolution (31)P{(1)H} correlation spectra of the reaction mixture at two different reaction periods, from which it is shown that octacalcium phosphate is the precursor phase of the final hydroxyapatite product. In addition, the spectra show that a substantial amount of water molecules is trapped between the glutaric acid and the hydroxyapatite surface, indicating that water molecules may play a prominent role in the noncovalent interaction of the glutaric acid and the HAp surface.     

Surface modification of P(EMA-co-HEA)/SiO2 nanohybrids for faster hydroxyapatite deposition in simulated body fluid?

P(EMA-co-HEA)/SiO₂ nanocomposites with 0, 15 and 30 wt% of silica were obtained by copolymerization of ethyl methacrylate, EMA, and hydroxyethyl acrylate, HEA, during the simultaneous acid-catalyzed sol–gel polymerization of tetraethoxysilane, TEOS. A surface modification treatment was applied in order to reduce the induction time for hydroxyapatite (HAp) nucleation, combining a previous NaOH attack to increase the number of surface nucleating sites, and an alternate soaking process in Ca and P solutions to form apatite precursors, prior to the immersion in a simulated body fluid (SBF). The NaOH treatment was not effective by itself in shortening the HAp induction time. It introduced sodium carboxylates in the copolymer but hydrolyzed the silica network excessively, thus reducing the surface nucleating potential of its boundary silanols. Therefore, bioactivity was only due to the surface carboxylate groups of the organic phase. Maybe a controlled dissolution extent of the silica network so as to improve bioactivity could be attained by reducing the duration of the NaOH-treatment. This would be interesting in the hybrid with 30 wt% of silica, because its dense silica network is not able to hydrolyze in SBF without any previous treatment, whereas the silica network in the hybrid with 15 wt% of silica hydrolyzes at the surface promoting the deposition of HAp. The CaP treatment was able to coat the surfaces of the samples with a calcium phosphate layer within minutes. This amorphous calcium phosphate acted as HAp precursor, skipping the induction period in SBF.     

Synthesis of high surface area hydroxyapatite nanoparticles by mixed surfactant-mediated approach

A new surfactant-mediated approach was developed to synthesize hydroxyapatite (HAp) nanoparticles with high surface areas by calcination of their precursors encapsulated with calcium stearate using mixed surfactant-containing reaction mixtures. Acidic aqueous solution of calcium phosphate was mixed with both or either nonaoxyethylene dodecyl ether (C12EO9) and polyoxyethylene(20) sorbitan monostearate (Tween 60) and then was treated with aqueous ammonium at 25 degrees C. The C12EO9-based single surfactant system yielded an aggregate of platy HAp nanoparticles 20-40 nm in size, whereas the Tween 60-based single and mixed systems led to lath-shaped HAp nanoparticles 2-8 nm wide and encapsulated with calcium stearate. On calcination at 500 degrees C, the stearate-encapsulated HAp nanoparticles in the latter two systems were deorganized into high surface area HAp nanoparticles. Particularly, the HAp nanoparticles in the mixed system exhibited a specific surface area as high as 364 m2 g(-1) that is roughly 3 times larger than 160 m2 g(-1) for those in the single system. The significantly high surface area for the former is attributed to much less adhesion of decapsulated HAp nanoparticles, which originated from the particle-separating effect of the C12EO9 molecules adsorbed on the outer surface of the stearate-encapsulated HAp nanoparticles to inhibit their agglomeration or interfacial coordination. The present results demonstrate that the mixed use of two different surfactants as a source of encapsulating and templating agent and a particle-separating agent is specifically effective for the synthesis of high surface area HAp nanoparticles.     

Preparation and applications of novel fluoroalkyl end‐capped vinyltrimethoxysilane oligomer/hydroxyapatite nanocomposites

Novel fluoroalkyl end‐capped vinyltrimethoxysilane oligomer/hydroxyapatite (HAp) nanocomposites were prepared by the reaction of calcium nitrate tetrahydrate and phosphoric acid in the presence of the corresponding oligomer. These fluorinated oligomer/HAp composites thus obtained are nanometer size‐controlled fine particles (83–173 nm), and were found to exhibit good dispersibility in methanol, ethanol, and isopropyl alcohol. These fluorinated HAp nanocomposites were applied to the surface modification of glass and poly(methyl methacrylate) (PMMA) to exhibit good hydro‐ and oleophobic characteristics imparted by fluorine on their surface. In addition, the surface structural changes of the modified polyethylene terephtalate and PMMA films treated with these fluorinated nanocomposites before and after soaking in a simulated body fluid (SBF) were analyzed by using SEM, XRD, and EDX to observe the formation of spherical HAp deposits on the surface. Copyright © 2009 John Wiley & Sons, Ltd.     

Aqueous microgels for the growth of hydroxyapatite nanocrystals

In present article, we demonstrate that aqueous microgels can be used as containers for the in-situ synthesis of hydroxyapatite. The hydroxyapatite nanocrystals (HAp NCs) become integrated into microgels forming hybrid colloids. The HAp NCs loaded in the microgel can be varied over a broad range. The HAp NCs are localized within the microgel corona. The deposition of the inorganic nanocrystals decreases the colloidal stability of the microgels and leads to particle aggregation at high HAp NCs loading. Because of the strong interactions between HAp NCs and polymer chains, the swelling degree of microgels decreases, and temperature-sensitive properties disappear at high loading of the inorganic component. We demonstrate that hybrid colloids can be used as building blocks for the preparation of nanostructured films on solid substrates.     

Preparation and applications of a variety of fluoroalkyl end-capped oligomer/hydroxyapatite composites

A variety of fluoroalkyl end-capped oligomers were applied to the preparation of fluorinated oligomer/hydroxyapatite (HAp) composites (particle size: 38-356 nm), which exhibit a good dispersibility in water and traditional organic solvents. These fluoroalkyl end-capped oligomer/HAp composites were easily prepared by the reactions of disodium hydrogen phosphate and calcium chloride in the presence of self-assembled molecular aggregates formed by fluoroalkyl end-capped oligomers in aqueous solutions. In these fluorinated HAp composites thus obtained, fluoroalkyl end-capped acrylic acid oligomers and 2-methacryloyloxyethanesulfonic acid oligomer/HAp nanocomposites afforded transparent colorless solutions toward water; however, fluoroalkyl end-capped N,N-dimethylacrylamide oligomer and acryloylmorpholine oligomer were found to afford transparent colorless solutions with trace amounts of white-colored HAp precipitants under similar conditions. HAp could be encapsulated more effectively into fluorinated 2-methacryloyloxyethanesulfonic acid oligomeric aggregate cores to afford colloidal stable fluorinated oligomer/HAp composites, compared to that of fluorinated acrylic acid oligomers. These fluorinated oligomer/HAp composites were applied to the surface modification of glass and PVA to exhibit a good oleophobicity imparted by fluorine. HAp formation was newly observed on the modified polyethylene terephthalate film surface treated with fluorinated 2-methacryloyloxyethanesulfonic acid oligomers and acrylic acid oligomer/HAp composites by soaking these films into the simulated body fluid.     

Fabrication and properties of mineralized collagen‐chitosan/hydroxyapatite scaffolds

A hydroxyapatite (HAp)/biopolymer composite scaffold was fabricated by mineralizing a crosslinked collagen/chitosan, which was pre‐mineralized with Ca²⁺ and phosphate salts, in simulated body fluid (SBF) for only 24 hr. A self‐organized structure similar to bone is expected. Microstructures of the crosslinked collagen/chitosan scaffold, the pre‐mineralized collagen–chitosan scaffold (CCS), and the mineralized collagen‐chitosan/HAp scaffolds (MCCHS) were characterized by scanning electron microscopy (SEM), revealing non‐alteration of the porous structure and formation of the HAp particles. X‐ray diffractometer (XRD) confirmed the crystalline structure of the HAp. Thermal gravimetric analysis found that more HAp particles were formed when the CCSs were pre‐mineralized in a higher concentration of Ca²⁺. Water‐uptake ratio of the crosslinked CCS was ～160, decreased to ～120 after incubating in Ca²⁺ solution, and further decreased to ～20 after mineralization. Mechanical strength of the CCS was improved significantly after the in situ mineralization too. The method introduced here may be potentially applied to obtain other biopolymer/HAp composite in a short period. Copyright © 2008 John Wiley & Sons, Ltd.     

Micro-PIXE analysis of bioconductive hydroxyapatite coatings on titanium alloy

Bioconductive materials and in particular implants using Ti alloy (Ti6–Al4–V) coated with hydroxyapatite (HAp) have proved to be a suitable surgical procedure. However, experience has shown that these implants not always have the required reliability to guarantee their expected life-span of approximate 15 years. In this research, experimental Ti alloy-implants coated with HAp and incubated in a simulated body fluid (r-SBF) under controlled physiological conditions were studied by nuclear microprobe (NMP). Selected HAp coatings, were analysed by micro-PIXE using protons of 1.5 MeV at the iThemba LABS NMP facility. Major elements (Ti, Al, V, Ca and P) as well as trace elements (Si, K, Fe, Zn and Sr) were determined. The effect of longer incubation time was of particular interest. Results confirmed that secondary Ca-deficient defect hydroxyapatite precipitated from the simulated body solution onto the HAp coating surface after prolonged incubation. This newly formed layer is thought to be of vital importance for bonding of implants with living bone tissue.     

铒镱共掺磷酸镧纳晶的合成和近红外荧光性质

以磷酸三丁酯作为配体,使用高温溶液法合成了掺铒磷酸镧纳米晶体,高分辨电镜和XRD结果表明产物尺寸均一,直径4nm左右,具有高度的结晶性,在甲苯等有机溶剂中分散性良好.近红外发光光谱表明,产物在1535 nm处有发光峰,半高全宽为50 nm,高于目前掺铒光纤放大器(EDFA)的增益带宽.通过IR、元素分析研究发现,使用真空干燥等方法不能有效去除纳晶表面的羟基.为了进一步消除表面缺陷和猝灭基团对纳晶发光性质的影响,我们尝试在其外围生长一层LaPO₄壳做成核壳粒子以消除表面缺陷和隔离猝灭基团,结果表明,新的纳晶的发光强度得到了显著提高.     

Synthesis and Characterization of Copolymercore-Silvershell Composite Microspheres

Composite microspheres composed of monodispersed poly（St-co-MAA） latices with diameter about 260 nm as core and Ag nanocrystals as shell were prepared by an in situ reduction method. The shell thickness could be controlled in the range of 15--45 nm by this coating process. The structure and the composition of the core-shell microspheres were characterized by transmission electron microscopy （TEM）, X-ray diffractometry （XRD）, X-ray photoelectron spectroscopy （XPS）, and thermogravimetric analysis （TG）. The formation of the composite microspheres is explained by the nucleation of silver on the surface of the latices followed by growth of the silver shell.     

Self‐Assembly of Nano Hydroxyapatite or Aragonite Induced by Molecular Recognition to Soy Globulin 7S or 11S

Molecular self‐assembly is emerging as a viable ‘bottom‐up’ approach to build stable organic/inorganic nanometer‐scale blocks. Herein, under the conditions of appropriate pH and ionic strength, soy globulin 7S or 11S were coprecipitated with hydroxyapatite (HAp) or aragonite (Arag), respectively, to fabricate two organic/inorganic hybrids: 7S/HAp and 11S/Arag. Results from high‐resolution transmission electron microscopy show that the hybrids exhibit a nanosized core–shell structure with globulin monomer 7S or 11S as core and HAp or Arag as shells. 7S/HAp and 11S/Arag present a disk and hexagon shape, respectively. After calcinations, monodispersed HAp without support from globulins existed as nanospheres. It was revealed that the globulin as host induces the self‐assembly and growth layer by layer of HAp or Arag nanocrystals. The factors of molecular recognition and surface potential definitely affected the size and shape of the hierarchical blocks. This work provided a novel pathway to controllably synthesize a wide variety of precise plant protein/biomineral hybrid biomaterials.