Influence of Crystallite Size On the Surface-properties of Calcium-deficient Hydroxyapatites

The surface properties of calcium-deficient hydroxyapatites (HAps) prepared under different synthesis conditions (e.g. by precipitation at pH 10, or by hydrolysis of dicalcium phosphate at pH 6.5) were studied. All the products tested were pure, well crystallized calcium-deficient HAps. The samples prepared under slightly acidic conditions exhibit larger crystallite sizes and higher calcium deficiency compared with those prepared under alkaline conditions. Electrophoretic mobilities were measured as a function of pH in 1.0 x 10(-3) M KNO3 aqueous solutions. The isoelectric points (iep) of HAp appear to depend strongly on the synthesis conditions; iep values of 4 were found for samples prepared under more acidic conditions, while values ranging from 5.5 to 7.2 were found for solids precipitated from alkaline solutions. The adsorption of hen egg-white lysozyme was measured at ambient temperature, in 1.0 x 10(-3) M KNO3 aqueous solutions buffered at pH 6.8 with 2.0 x 10(-3) M phosphate buffer. The parameters of the Langmuir-type adsorption isotherms were found to depend significantly on the specific surface of the samples; the monolayer coverage goes through a maximum of 40 x 10(-9) mol m-2 at S(BET) = 80 m2 g-1, while the affinity constant culminates at 355 mM-1 at the same value of S(BET). The decay of both monolayer coverage and affinity constant beyond S(BET) = 80 m2 g-1 can be ascribed partly to the lower accessibility of smaller pores to lysozyme molecules, particularly when electrostatic repulsion exists between the lysozyme molecules and the HAp surface. It is thought that specific bonds between lysozyme and the hydroxyapatite surface must exist, which are very sensitive to the nature and the relative amounts of crystallographic planes exposed on the solid surface

Adsorption of succinylated lysozyme on hydroxyapatite

Hen egg white lysozyme has been succinylated, the isoelectric point being shifted thereby from about 11 to 4.5-4.7. Its adsorption on a chromatography grade hydroxyapatite has been investigated at 20 degrees C and in the pH range from 5.9 to 7.4. Adsorption takes place despite an electrical repulsion between the surface and the adsorbate; consequently, it is favored by a decrease of pH and phosphate concentration and an increase of calcium concentration and ionic strength. While adsorption of native lysozyme is driven by electrostatic attraction to the surface, adsorption of succinylated lysozyme is controlled by hydrophobic interactions. This may be attributed to a different structure of modified lysozyme, compared to native lysozyme, or to a greater tendency to undergo conformational changes. (C) 1997 Academic Press

Hybrid Nanomaterials Based on Anionic Clays for Application to Water Dichlorophenoxyacetate and-Purification: Cases of 2,4 chlorobenzenesulfonate-4

The elimination of the herbicide 2,4dichlorophenoxycetic acid (2,4D) and the surfactant 4chlorobenzenesulfonic acid (4CBS) from aqueous solutions by the layered double hydroxides (LDHs) through anion exchange and/or adsorption proved to be effective. The interaction of LDHs with these pollutants was investigated by a combination of spectroscopic and physico-chemical methods. Treatment of solutions containing variable concentrations of 2,4D and 4CBS led to their elimination with an uptake ratio of up to 98% for 2,4D and 95% for 4CBS. Infrared spectroscopy and X-ray diffraction indicated that this maximum of retention corresponds to an elimination of the pollutants by exchange reactions, leading to their intercalation between the LDH layers, in addition to adsorption. Thermal decomposition of LDHs samples used in water purification experiments, coupled with mass spectrometry analysis of the evolved gases, allowed to confirm the organic-inorganic hybrid character of the materials.The elimination of the herbicide 2,4dichlorophenoxycetic acid (2,4D) and the surfactant 4chlorobenzenesulfonic acid (4CBS) from aqueous solutions by the layered double hydroxides (LDHs) through anion exchange and/or adsorption proved to be effective. The interaction of LDHs with these pollutants was investigated by a combination of spectroscopic and physico-chemical methods. Treatment of solutions containing variable concentrations of 2,4D and 4CBS led to their elimination with an uptake ratio of up to 98% for 2,4D and 95% for 4CBS. Infrared spectroscopy and X-ray diffraction indicated that this maximum of retention corresponds to an elimination of the pollutants by exchange reactions, leading to their intercalation between the LDH layers, in addition to adsorption. Thermal decomposition of LDHs samples used in water purification experiments, coupled with mass spectrometry analysis of the evolved gases, allowed to confirm the organic-inorganic hybrid character of the materials

Adsorption of catalase on hydroxyapatite

The adsorption of catalase on calcium hydroxyapatite is reported in this study. In all the solutions investigated, catalase adsorption takes place under conditions where the adsorbent and the adorbate are both negatively charged and is accompanied by the release of phosphate ions. This suggests that electrostatic attraction does not play a leading role in the adsorption process. However, electrostatic repulsion does play a role as evidenced by the influence of the solution composition on the maximum amount adsorbed. In fact, the amount adsorbed increases when the surface charge tends to be less negative (decrease of pH and phosphate concentration, presence of calcium) or when the electrical charges are screened as a result of the ionic strength increase. This was confirmed by the electrophoretic mobility which becomes more negative after protein adsorption. The rate of catalase adsorption is extremely low; the time required to reach a stationary concentration is 60 and 125 h in potassium nitrate and phosphate solution, respectively. The reversibility of catalase was examined with respect to changes in the bulk solution concentration. No significant desorption was obtained after several days of observation. The adsorption, desorption, and kinetic aspects have been discussed in relation to changes in the the protein structure upon interaction and to the microstructural characteristics of the mineral. (C) 1998 Academic Press

Removal of Pesticides from Water by Anionic Clays

The exchange of chloride ions by ions from the pesticide family 2.4-dichlorophe- noxyacetate (2.4D) in ?Zn-Al-Cl? anionic clay was investigated by X-ray diffraction and infrared spectroscopy. The effects of 2.4D concentration in solution and temperature on the ion exchange were studied. The best sample in terms of crystallinity, was obtained at 100 °C with a 2.4D concentration corresponding to the solubility limit of the ion in water. This sample was further characterised by chemical analyses and scanning electron microscopy. The anion intercalation was effected without degradation of the pesticide anion

Mechanical behavior of hydroxyapatite-chitosan composite: Effect of processing parameters

International audienceThree-dimensional hydroxyapatite-chitosan (HA-CS) composites were formulated via solid-liquid technic and freeze-drying. The prepared composites had an apatitic nature, which was demonstrated by X-ray diffraction and Infrared spectroscopy analyses. The impact of the solid/liquid (S/L) ratio and the content and the molecular weight of the polymer on the composite mechanical strength was investigated. An increase in the S/L ratio from 0.5 to 1 resulted in an increase in the compressive strength for HA-CSL (CS low molecular weight: CSL) from 0.08 ± 0.02 to 1.95 ± 0.39 MPa and from 0.3 ± 0.06 to 2.40 ± 0.51 MPa for the HA-CSM (CS medium molecular weight: CSM). Moreover, the increase in the amount (1 to 5 wt%) and the molecular weight of the polymer increased the mechanical strength of the composite. The highest compressive strength value (up to 2.40 ± 0.51 MPa) was obtained for HA-CSM (5 wt% of CS) formulated at an S/L of 1. The dissolution tests of the HA-CS composites confirmed their cohesion and mechanical stability in an aqueous solution. Both polymer and apatite are assumed to work together, giving the synergism needed to make effective cylindrical composites, and could serve as a promising candidate for bone repair in the orthopedic field. © 2021 by the authors. Licensee MDPI, Basel, Switzerland

The effect of bioactive glass particle size and liquid phase on the physical-chemical and mechanical properties of carbonated apatite cement

International audienceThis study reports for the first time the effect of particle size of bioactive glass 46S6 on the physico-chemical and mechanical properties of carbonated apatite cement (CPC) composed of brushite (CaHPO4. H2O) and vaterite (CaCO3). Three particle size ranges were investigated: coarse (BGc: 100–200 μm), medium (BGm: 40–100 μm), and fine (BGfandlt;40 μm). For the composite formulations, three liquid phases were used: distilled water as a simple setting solution, sodium alginate hydrogel as a cohesion and injectability enhancer, and sodium alginate solubilized in a setting accelerator (Na2HPO4) solution (Alg-NaP) to control the setting time. The changes in the bioglass particle size and the liquid phase lead to clear modifications in the setting, rheological, and mechanical properties of the prepared cements. The optimization of the different parameters reveals that the formulation with BGc and Alg-NaP as a liquid phase provides the best properties: good injectability of 95%, excellent cohesion, a setting time of 10 min that meets the range required by clinicians, and mechanical strength of 10.5 MPa comparable to that of cancellous bone. © 2022 Elsevier Ltd and Techna Group S.r.l