Mechanosynthesis of carbonate and lithium co-substituted hydroxyfluorapatite

International audienceThe presence of fluoride, lithium and carbonate group within hydroxyapatite occurring naturally within the body provides the basis for investigating the sintering ability of co-substituted hydroxyfluorapatites nanopowders for use as biomaterials. Ca10-xLix(PO4)6-x(CO3)x(OH)F nanopowders, with x equal to 0, 0.5, 1, 1.5, 2 and 2.5 were prepared using mechanosynthesis and their extensive characterization was realized. Substitution causes contraction of the unit hexagonal cell along the a-axis and elongation along the c-axis, as well as a decrease in the degree of crystallinity of the powders, and an increase of the amounts of unreacted calcium and lithium carbonates. Crystallite sizes and strains, determined by the Halder & Wagner method, remain the same whatever x. Spectroscopic analyses show that B-type carbonated apatite is formed. Annealing at 500°C improves the crystallinity of the apatite phase with low percentages of calcite and lithium phosphate as secondary phases (x<=2). Transmission electron microscopy observations show that untreated and calcined powders consist mainly of spherical nanoparticles. As-mechanosynthesized Ca9Li(PO4)5(CO3)(OH)F powder, sintered by Spark Plasma 2 Sintering, densifies in the temperature range of 580 to 650 °C. The crystallite size remains the same than that of the untreated-powder (about 15 nm)

Kinematic modelisation and parametric study of mechanosynthesis of hydroxyfluorapatite

International audienceThe nanocrystalline hydroxyfluorapatite (HFA) was synthesized by mechanosynthesis with a planetary ball mill (PM200). The disc to jar speed ratio was constant (equal to 0.5). The effect of different milling parameters such as grinding duration, balls number's, initial powder mass and disc rotation speed were studied to apprehend their effects on both the process of grinding/mechanosynthesis and the synthesis of nanocrystalline HFA. Unlike previous studies in which milling parameters have been independently studied, the effects of these parameters on the phase contents were simultaneously studied. Abdellaoui's model was also introduced to analyse the physical milling parameters effect such as the injected shock power, the shock kinetic energy, the shock frequency and the cumulated kinetic energy on the microstructural properties and synthesized phases contents. The results predicted by the model were compared to experimental ones. This study showed that the optimal conditions for the synthesis of nanocrystalline HFA were reached when the mechanosynthesis was carried out with a speed of 450 rpm, 6 balls, 1.2 g of starting material and 24 h of grinding duration. X-ray diffraction characterization confirmed the purity phase of HFA nanocrystalline powders

Critically ill infants with SARS-COV-2 delta variant infection

Background: SARS-CoV-2 is described to cause mild to moderate symptoms in children. To date, clinical data and symptoms of the Delta variant in pediatric patients are lacking. Aim: To describe clinical characteristics and outcomes of infants admitted in the pediatric intensive care unit (PICU) during the period of Delta variant predominance. Methods: We performed a retrospective study, between June 23, 2021 and August 16, 2021. We included children aged under 15 years, admitted to PICU with severe and critical form of SARS-CoV-2 infection as confirmed by RT-PCR. We reviewed medical records for all patients. Results: During the study period, 20 infants were included. The median age was 47 days (IQR: 26.5–77). The sex ratio was 0.8 (9 males). No underlying medical conditions were noted. Parents were not vaccinated. Respiratory involvement was the main feature to be observed in our cohort. Eleven patients had pediatric acute respiratory distress (PARDS) with a median oxygen saturation index (OSI) of 9 (IQR: 7–11). PARDS was mild in 4 cases, moderate in 5 cases and severe in 2 cases. Hemodynamic instability was observed in 4 cases. The main radiological finding was ground glass opacities in 11 cases. Seventeen patients were mechanically ventilated and 3 of them were escalated to high-frequency oscillatory ventilation. The median duration of mechanical ventilation was 6 days (IQR 2.5–12.5). The remaining patients were managed with high flow nasal cannula. Four patients died. Conclusion: We report herein a case series of very young infants, with no comorbidities, and with a life-threatening illness due to SARS-CoV-2 Delta variant

Structural, physicochemical and antioxidant properties of sodium alginate isolated from a Tunisian brown seaweed

An original sodium alginate from Tunisian seaweed (Cystoseira barbata) was purified and characterized by circular dichroism (CD) and ATR-FTIR spectroscopies. ATR-FTIR spectrum of C. barbata sodium alginate (CBSA) showed the characteristic bands of mannuronic (M) and guluronic acids (G). The M/G ratio was estimated by CD (M/G = 0.59) indicating that CBSA was composed of 37% mannuronic acid and 63% guluronic acid. The analysis of viscosity of CBSA showed evidence of pseudoplastic fluid behaviour. The emulsifying capacity of CBSA was evaluated at different concentrations (0.25–3%), temperatures (25–100 °C) and pH (3.0–11.0). Compared to most commercial emulsifiers, the emulsion formulated by CBSA was found to be less sensitive to temperature changes and more stable at acidic pH. CBSA was examined for antioxidant properties using various antioxidant assays. CBSA exhibited important DPPH radical-scavenging activity (74% inhibition at a concentration of 0.5 mg/ml) and considerable ferric reducing potential. Effective hydroxyl-radical scavenging activity (82% at a concentration of 5 mg/ml) and potent protection activity against DNA breakage were also recorded for CBSA. However, in the linoleate-β-carotene system, CBSA exerted moderate antioxidant activity (60% at a concentration of 1.5 mg/ml). Therefore, CBSA can be used as a natural ingredient in food industry or in the pharmaceutical field

Structural, physicochemical and antioxidant properties of sodium alginate isolated from a Tunisian brown seaweed

International audienceAn original sodium alginate from Tunisian seaweed (Cystoseira barbata) was purified and characterized by circular dichroism (CD) and ATR-FTIR spectroscopies. ATR-FTIR spectrum of C. barbata sodium alginate (CBSA) showed the characteristic bands of mannuronic (M) and guluronic acids (G). The M/G ratio was estimated by CD (M/G = 0.59) indicating that CBSA was composed of 37% mannuronic acid and 63% guluronic acid. The analysis of viscosity of CBSA showed evidence of pseudoplastic fluid behaviour. The emulsifying capacity of CBSA was evaluated at different concentrations (0.25–3%), temperatures (25–100 °C) and pH (3.0–11.0). Compared to most commercial emulsifiers, the emulsion formulated by CBSA was found to be less sensitive to temperature changes and more stable at acidic pH. CBSA was examined for antioxidant properties using various antioxidant assays. CBSA exhibited important DPPH radical-scavenging activity (74% inhibition at a concentration of 0.5 mg/ml) and considerable ferric reducing potential. Effective hydroxyl-radical scavenging activity (82% at a concentration of 5 mg/ml) and potent protection activity against DNA breakage were also recorded for CBSA. However, in the linoleate-β-carotene system, CBSA exerted moderate antioxidant activity (60% at a concentration of 1.5 mg/ml). Therefore, CBSA can be used as a natural ingredient in food industry or in the pharmaceutical field