Surface modification of calcium hydroxyapatite with pyrophosphoric acid

The surface of synthetic colloidal calcium hydroxyapatite (Ca(10)(PO(4))(6)(OH)(2); CaHap) was treated with pyrophosphoric acid (H(4)P(2)O(7); PP) in acetone and the materials were characterized by XRD, thermal analysis, N(2) adsorption, TEM, and FTIR. No remarkable change in XRD patterns or in particle morphology by the modification was observed. The additional amount of PO(4) of CaHap was increased with an increase in PP concentration. The Ca/P molar ratio of CaHap was decreased from 1.62 to 1.35 by the modification. IR results indicated that the PP reacts with surface P-OH groups of CaHap to form additional surface P-OH groups as follows: surface P-OH+H(4)P(2)O(7)--> surface P-O-PO(OH)(2) + H(3)PO(4). When the modified CaHap with Ca/P molar ratio less than 1.50 was treated at 850 degrees C in air, the materials transformed into beta-Ca(3)(PO(4))(2).     

Protein adsorption characteristics of calcium hydroxyapatites modified with pyrophosphoric acids

Protein adsorption characteristics of calcium hydroxyapatite (Hap) modified with pyrophosphoric acids (PP(a)) were examined. The PP(a) modified Hap particles (abbreviated as PP-Hap) possessed anchored polyphosphate (PP: P-{O-PO(OH)}(n)-OH) branches on their surfaces. The proteins of bovine serum albumin (BSA: isoelectric point (iep)=4.7, molecular mass (M(s))=67,200 Da, acidic protein), myoglobin (MGB: iep=7.0, M(s)=17,800 Da, neutral protein), and lysozyme (LSZ: iep=11.1, M(s)=14,600 Da, basic protein) were examined. The zeta potential (zp) of PP-Hap particles as a function of pH overlapped; zp-pH curves were independent of the concentration of pyrophosphoric acids (abbreviated as [PP(a)]) used for modifying Hap surface. The saturated amounts of adsorbed BSA (Delta n(ads)(BSA)) were increased three-fold by the surface modification with PP(a) though they were independent of the [PP(a)]. Furthermore, the fraction of BSA desorption was independent of the [PP(a)]. This enhancement of BSA adsorption onto the PP-Hap is due to the hydrogen bonding between oxygen and OH groups of the PP-branches and functional groups of BSA molecules. In the case of LSZ, a more higher adsorption enhancement was observed; the saturated amount of adsorbed LSZ (Delta n(ads)(LSZ)) for Hap modified at [PP(a)]=6 mmol/dm(3) was nine-fold than that for Hap unmodified. This remarkable adsorption enhancement was explained by a three-dimensional binding mechanism; LSZ molecules were trapped inside of the PP-branches. Hence, a fraction of LSZ desorption was decreased with an increase in the [PP(a)]; as more PP-branches are presented on the surface the higher retardation of LSZ desorption was induced. It was expected from their small size that MGB adsorb between the PP-branches as well as LSZ. However, the amounts of adsorbed MGB (Delta n(ads)(MGB)) did not vary and were independent of the [PP(a)] due to the small numbers of functional groups of MGB. In addition, no dependence of the fraction of MGB desorption on the [PP(a)] was observed. The results of zp for all the protein systems supported the mode of protein adsorption discussed. The anchored structure of the PP-branches developed on the Hap surface to provide three-dimensional protein adsorption spaces was proved by a comparative experiment that was elucidating the effect of pyrophosphate ions for BSA adsorption onto Hap.     

Adsorption of immunogamma globulin onto various synthetic calcium hydroxyapatite particles

This paper presents data on adsorption of immunogamma globulin (IgG) onto synthetic rodlike calcium hydroxyapatite particles (CaHaps) with various particle lengths and calcium/phosphate (Ca/P) atomic ratios ranging from 1.54 to 1.65 and compares the obtained results to those of acidic (bovine serum albumin, BSA), neutral (myoglobin, MGB), and basic (lysozyme, LSZ) proteins reported before. The effect of electrolyte concentration on IgG adsorption was also examined. The initial rate of IgG adsorption was similar to that of BSA and was slower than that of MGB and LSZ. This fact was interpreted by the difference in the structural stability and molecular weight of these proteins. The isotherms of IgG adsorption onto the CaHap particles were of pseudo-Langmuir type. The saturated amount of adsorbed IgG values (nsIgG) for the particles with mean particle length less than 70 nm decreased with increasing Ca/P ratio. The adsorption behavior of IgG molecules was very similar to that of basic LSZ, though IgG has zero net charge. The nsIgG value was increased with increased mean particle length of CaHaps; the relationship was less significant than that for BSA but similar to those for MGB and LSZ. The similar adsorption behavior of IgG and LSZ suggested that the Fab parts of IgG molecules preferentially adsorb onto CaHap to provide the reversed Y-shaped conformation of IgG. The change of the adsorption mode of IgG molecules from the reversed Y-shaped conformation to side-on by "spreading" the Fc part of IgG molecules onto the particle surface over a longer adsorption time was suggested. The nsIgG value was increased with increasing electrolyte concentration by screening the intra- and intermolecular electrostatic interactions of proteins.     

Effects of acetonitrile on adsorption behavior of bovine serum albumin onto synthetic calcium hydroxyapatite particles

The objective of this study was to examine the effects of acetonitrile (AN) on the adsorption behavior of bovine serum albumin (BSA) onto calcium hydroxyapatite [Ca10(PO4)6(OH)2 Ca10, Hap] materials by combining the ultraviolet (UV) and circular dichroism (CD) measurements of BSA solution. The structural change of BSA molecules with addition of AN was investigated by UV and CD spectroscopy measurements prior to studying adsorption behavior of BSA onto Hap. The CD spectra revealed that the fraction of alpha-helical content of BSA is remarkably decreased at AN concentrations above 30 vol.%, while beta-sheet content is increased. On the other hand, the percentages of random coil and turn contents were decreased only slightly. In addition to this secondary structural change of BSA, the UV spectra suggested that the tertiary structure of protein molecules was also changed by the addition of large amounts of AN; BSA molecules associate to form molecular aggregates at [AN]> or =40 vol.%. From the adsorption of BSA onto Hap particles (ca. 30 nm in the particle length) from a water-AN mixed solution, it was revealed that the adsorption behavior of BSA strongly depends on the change of secondary and tertiary structures of BSA by addition of AN. The contraction of BSA molecules at low AN concentrations (10-20 vol.%) gave their small cross-sectional area, providing a large amount of adsorption (n(BSA)), although n(BSA) was decreased above 30 vol.% AN by enlargement of BSA molecules with solvation and unfolding some alpha-helix domains. The n(BSA) values of the systems with AN exhibited a maximum; n(BSA) was increased at a lower BSA concentration region, although it was decreased at a higher BSA concentration due to self-association. Accompanying the change of n(BSA) with AN addition, the maxima of electrophoretic mobility (em) of the Hap particles were observed for the systems with AN, although the em of Hap particles was normally increased and saturated with increase in protein coverage for the native structure on the system without AN. On the other hand, because the aggregated BSA molecules could be cooperatively bound, the adsorption of BSA onto the Hap particles with large size (108 nm in the particle length) was enhanced in the presence of AN.     

Preparation and characterization of hydrophobic calcium hydroxyapatite particles grafting oleylphosphate groups

Grafting of oleylphosphate (OP) molecules to the surface of calcium hydroxyapatite particles (HAP) was carried out by a coprecipitation method with a Ca(OH)₂–H₃PO₄ system in the presence of disodium oleylphosphate (DSOP). All the particles exhibited a single-crystal nature with rod-like shape and were elongated along c-axis from 36 to 122 nm in particle length with an increase in the concentration of DSOP. It was suggested that 084% of the phosphate ions exposed on the ac or bc faces of the HAP particles are exchanged with phosphate ions of DSOP molecules directing oleyl groups outward. The hydrophobicity of OP-grafted HAP particles was enhanced with an increase in the DSOP concentration. This high surface hydrophobicity was further confirmed by water adsorption experiments. The materials with the surface oleyl groups adsorbed much less water than the HAP particles produced without DSOP.     

Formation of 2D calcium hydroxyapatite on stainless steel modified with a TiN sublayer

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Adsorption of nicotinic acid on the surface of nanosized hydroxyapatite and structurally modified hydroxyapatite

In the present paper, hydroxyapatite and structurally modified hydroxyapatite were investigated to establish the best material for nicotinic acid adsorption. Structurally modified hydroxyapatite wa prepared by adding sodium silicate in the reaction medium. The influence of silica concentration, presence of small amounts of metal ions, temperature and initial concentrations of nicotinic acid solutions on the adsorption capacity, were studied. Results indicated that structurally modified hydroxyapatite doped with copper adsorbed the highest amount of nicotinic acid. For this material the adsorption capacity was 0.232 mg nicotinic acid / g material, at an initial concentration of 10⁻⁴ M nicotinic acid. For all types of materials, best results were obtained at 15°C. The amount of nicotinic acid adsorbed increases with the decrease in temperature and with the increase in the initial concentration of nicotinic acid. Adsorption kinetics data were modeled using pseudo-first and pseudo-second order models while the interference due to diffusion was analyzed with intraparticle diffusion model. The results indicate that pseudo-second order model best describes the adsorption kinetics data, indicating the formation of chemical bonding.     

Studies on removal of cobalt from an alkaline waste using synthetic calcium hydroxyapatite

The removal of cobalt from an alkaline waste solutions containing sodium was carried out using a radiotracer in a batch method using synthetic calcium hydroxyapatite (HAP). The influence of different parameters such as solution pH, contact time, cobalt concentration, and presence of other ions like sodium on cobalt removal was studied. The sorption process followed pseudo-second-order kinetics with necessary time of around 23–25 h to reach equilibrium and the cobalt uptake was quantitatively evaluated using the Freundlich model. The results indicated that the mechanism of cobalt removal by HAP was mainly due to chemisorption on a heterogeneous surface. In the presence of sodium, the sorption of cobalt on HAP was not affected. The sorption of cobalt on HAP was pH independent in the range from 4 to 8, because of its buffering properties. The adsorption of cobalt on HAP was fast and the percentage of cobalt sorption was >97 % during the first 30–40 min of the contact time.     

Protein adsorption behaviors onto photocatalytic Ti(IV)-doped calcium hydroxyapatite particles

The fundamental experiments on the adsorption behaviors of proteins onto photocatalytic Ti(4+)-doped calcium hydroxyapatite (TiHap) particles were examined comparing to those onto the calcium hydroxyapatite (CaHap) and commercially available typical titanium oxide (TiO(2)) photocatalyst (TKP-101). The heat treated TiHap and CaHap particles were also used after treated these particles at 650°C for 1h (abbreviated as TiHap650 and CaHap650, respectively). All the adsorption isotherms of bovine serum albumin (BSA), myoglobin (MGB) and lysozyme (LSZ) from 1×10(-4)mol/dm(3) KCl solution were the Langmuirian type. The saturated amounts of adsorbed BSA (n(s)(BSA)) for the CaHap650 particles was higher than that for CaHap. Similar results were observed for TiHap and TiHap650. The adsorption of LSZ exhibited the same result of BSA, while the saturated amounts of adsorbed LSZ (n(s)(LSZ)) value on the TiHap were much higher than CaHap. However, the saturated amounts of adsorbed MGB (n(s)(MGB)) are almost equal to those for the CaHap and TiHap nevertheless whether these particles were heat treated at 650°C or not. The TKP-101 exhibited extremely small adsorption capacity of all proteins due to its small particle size of ca. 4nm in diameter. The independence of the n(s)(MGB) value on the zeta potential (zp) of the particles was explained by the electrostatical neutrality of MGB molecules. On the other hand, the n(s)(LSZ) values were increased with increase in the negative zp of the particles. This fact was explained by increasing the electrostatic attractive forces between negatively charged particles and positively charged LSZ. However, the n(s)(BSA) values exhibit maxima for the heat treated TiHap650 and CaHap650 particles. This result was interpreted to the formation of β-TCP crystal phase by the heat treatment. The produced Ca(2+) ions by dissolution from β-TCP phase may exert as binders between BSA and surfaces of the heat treated particles.     

Heterogeneous reactions of gaseous methanesulfonic acid with calcium carbonate and kaolinite particles

Heterogeneous reactions of gaseous methanesulfonic acid (MSA) with calcium carbonate (CaCO₃) and kaolinite particles at room temperature were investigated using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and ion chromatography (IC). Methanesulfonate (MS^?) was identified as the product in the condensed phase, in accordance with the product of the reaction of gaseous MSA with NaCl and sea salt particles. When the concentration of gaseous MSA was 1.34 × 10¹³ molecules cm^?3, the uptake coefficient was (1.21 ± 0.06) × 10^?8 (1σ) for the reaction of gaseous MSA with CaCO₃ and (4.10 ± 0.65) × 10^?10 (1σ) for the reaction with kaolinite. Both uptake coefficients were significantly smaller than those of the reactions of gaseous MSA with NaCl and sea salt particles.     

Transport of ions of pyrophosphoric acid through chemically different anion-exchange membranes

Characteristics of mass transport of the anions of pyrophosphoric acid are investigated during electrodialysis through MA-40 and MA-41 anion-exchange membranes. It is established that the rate of mass transport for counterions is greater through the MA-41 membrane than the MA-40 membrane, and thus the former can be used for demineralizing solutions with salts of pyrophosphoric acid. Higher selectivity to pyrophosphate ions is found for the MA-40 membrane compared to the MA-41 membrane in the electrodialysis of mixtures of pyrophosphate and hydropyrophosphate ions, and thus the MA-40 membrane can be regarded as promising for the separation of such mixtures.     

Size-dependent defluoridation properties of synthetic hydroxyapatite

Batch adsorption experiments were conducted to investigate the removal of fluoride from aqueous solution by the addition of synthetic hydroxyapatites (HAps) with different particle sizes. Results showed that size-dependent defluoridation properties of HAps. Better performances were obtained with smaller particle sized HAps, which presented higher adsorption efficiency. Bulk HAp, the HAp sample with the largest particle size, presented the lowest percentage of fluoride removal. The isotherm studies showed that the Freundlich model was the best choice to describe the adsorption behaviors of nanosized HAps. However, the adsorption pattern of the bulk sample followed both Langmuir and Freundlich isotherms. All parameters that might influence the defluoridation process were assessed, which included the effect of adsorbent dose, initial fluoride concentration, contact time and the effect of temperature. The removal efficiency of fluoride increased with increasing adsorbent dose. Decrease of the initial fluoride concentration resulted in the increase of fluoride removal efficiency. The percentage of fluoride removal increased as the ambient pH decreased. Thermodynamic parameters suggested that the adsorption of fluoride onto HAp samples was physisorption and endothermic in nature. Moreover, adsorption kinetic study revealed that the adsorption process followed pseudo-second-order kinetics. This work indicated that synthetic hydroxyapatites, especially the smaller particle sized HAps, were efficient defluoridation materials.     

Structure and properties of chitosan derivatives modified calcium polyphosphate scaffolds

Organic and inorganic composite material is becoming a solution on making the mechanical and degradation properties of biomaterial more suited. Porous calcium polyphosphate was immersed into different concentrations of carboxymethyl chitosan before immersing 10% alginate dialdegyde. After freeze-drying, the scaffolds were performed in physiologic saline. At stated day, the weightloss, Ca²⁺ concentration, pH value and morphology were measured. The biocompatibility of the composite was demonstrated by extract and direct contact tests. As the results showed, the degradation rates of composites were faster, and the compressive strength became bigger because of the cross-linked network formed by Carboxymethyl chitosan (CMC) and alginate dialdehyde (ADA). The pH value of composite was higher than that of calcium polyphosphate (CPP) due to the organic part of composite’s pH was in slight alkaline. From the SEM, the cross-linked network structure could be observed clearly. Because the glycosaminoglycans-like chains in CMC molecules, which are typically presented in extracellular matrix (ECM), extractions of composite material gave the cells good adhesion and growth condition. All the results testified the composite scaffold was a good candidate for bone repair.     

Ion exchange of strontium on synthetic hydroxyapatite

Adsorption of strontium ions on synthetic hydroxyapatite was examined using both batch and column methods. The apatite was prepared from aqueous solutions and characterized by standard analytical methods. The sample obtained had characteristics of well crystallized stoichiometric hydroxyapatite. The experimental data for sorption of strontium can be very well fitted with Langmuir's adsorption isotherm. It was found that sorption occurs by an ion exchange reaction between strontium ions in solution and calcium ions in apatite.     

Sorption of aqueous palladium onto synthetic hydroxyapatite

The sorption of Pd(II) on hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) has been studied at 25 °C as a function of pH, in 0.01 M NaClO₄, and 0.01 and 0.025 M Ca(ClO₄)₂ aqueous background electrolytes and Pd(II) concentration (9.3 to 47 ??M), trying to minimize some types of reactions, such as solid dissolution of and metal precipitation. The radiotracer palladium, ¹⁰⁹Pd, obtained by neutron irradiation, has been used to calculate the palladium??s distribution coefficients K _d between aqueous and solid phase. A mathematical treatment of results has been made by ion-exchange theory in order to interpret palladium sorption onto treated solid. For this, we take into account the existence of active sites at the hydroxyapatite surface, and the aqueous solution chemistry of palladium as well as the effect of phosphate anions from solid dissolution. The results can be explained as evidence of sorption of the species PdOH⁺, and of a mixed hydroxo complex of Pd²⁺ like (XCaO^?)?CPdOH⁺·nH₂O fixed onto {??Ca?COH} surface sites of the hydroxyapatite.     

Selective decomposition of proteins by photocatalytic Ti(IV)-doped calcium hydroxyapatite particles from mixed-protein systems

The decomposition of protein molecules from a mixed-protein solution on the surface of calcium hydroxyapatite (CaHap) and Ti(IV)-doped CaHap (TiHap) particles with a Ti/(Ca + Ti) atomic ratio (X _Ti) of 0.10 and 0.20 under UV irradiation of 365 nm in wavelength was investigated. Acidic bovine serum albumin (BSA) and basic lysozyme (LSZ) were employed as a model of pathogenic proteins. The photocatalytic activities of TiHap particles were estimated from the decomposition of BSA and LSZ from the BSA (2.5 mg/cm³)–LSZ(1.0 mg/cm³) mixture under 1 mW/cm² UV irradiation dispersed in a 10-mL quartz tube. No change in BSA concentration by UV irradiation was observed for all the unheated original CaHap and TiHap particles without and with low photocatalytic activities, respectively. Similar results were observed for the systems that employed heat-treated particles endowed a high photocatalytic activity by heat treatment at 650 °C for 1 h. On the other hand, a selective photocatalytic decomposition was observed for the LSZ, i.e., only LSZ molecules were decomposed completely from the BSA (2.5 mg/cm³)–LSZ(1.0 mg/cm³) mixture by using heat-treated TiHap particles with X _Ti?=?0.10 and 0.20. This selective decomposition by TiHap particles was interpreted by higher adsorption affinity of positively charged LSZ to highly negatively charged TiHap together with low molecular weight and rigid structure of LSZ molecules.     

Thermal analysis of hydroxyapatite with adsorbed oxalic acid

Journal of Thermal Analysis and Calorimetry - The specific adsorption of oxalic acid ions at the hydroxyapatite interface was investigated by means of the radioisotope method (14C) as a function of...     

Morphology of synthetic goethite particles

The specific surface area of synthetic goethite depends on the preparation: the Fe(III):OH ratio, the rate of base titration of Fe salt, and the temperature and time of crystallization. The crystals also have different morphologies as determined by SEM or TEM. Carbon coating is used to improve the quality of SEM images of nonconducting specimens. We show here that needle-like goethite particles become substantially thicker in the course of standard carbon coating, and the length-to-width ratio obtained for carbon-coated particles is lower than that for the original goethite particles. The morphology of the goethite particles was also studied by tapping mode AFM.     

Bioadhesive hydrocaffeic acid modified chitosan colloidal particles using as particulate emulsifiers

A kind of bioadhesive hydrocaffeic acid modified chitosan colloidal particles (HCA-CS/TPP CPs) containing synthetic catecholamine groups was prepared via amidation reaction and ionic gelation. The formation process and property of the HCA-CS/TPP CPs were characterized by ultraviolet visible spectrophotometry and Zeta PALS instruments. The prepared HCA-CS/TPP CPs were then used as particulate emulsifier to stabilize Pickering emulsions. The stability of the Pickering emulsion droplet was characterized by digital camera and optical microscope. The results revealed that HCA-CS/TPP CPs exhibited good emulsifying property at a wide pH value range, which will endow the potential application of the Pickering emulsions stabilized by HCA-CS/TPP CPs in various fields.     

Peroxo derivatives of hydroxyapatite and calcium hydrophosphate

Hydroxyapatite and calcium hydrophosphate peroxo solvates were synthesized and characterized by IR spectroscopy, powder X-ray diffraction, and TGA to be used as biocompatible and antibacterial medicaments in manufacturing calcium phosphate bioceramics for implantations in orthopedics and dentistry. A wide range of hydrogen peroxide percentages in stable mixtures of mCa₅(PO₄)₃(OH) + nCaHPO₄ · H₂O₂ · H₂O (ranging from 0.5 to 18%) allows composites to be prepared with a tailored active oxygen content.