Contribution of hydrogen to intergranular corrosion of 2024 aluminum alloy

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Colloidal and monocrystalline Ln3+ doped apatite calcium phosphate as biocompatible fluorescent probes

Ultrafine individualised mono crystalline Ca102x(PO4)62x-(HPO4)x(OH)22x deficient calcium hydroxyapatite nanocrystals displaying fluorescence under visible excitation are proposed for utilisation as biocompatible biological probes

Strontium-loaded mineral bone cements as sustained release systems : Compositions, release properties, and effects on human osteoprogenitor cells

This study aims to evaluate in vitro the release properties and biological behavior of original compositions of strontium (Sr)-loaded bone mineral cements. Strontium was introduced into vaterite CaCO3-dicalcium phosphate dihydrate cement via two routes: as SrCO3 in the solid phase (SrS cements), and as SrCl2 dissolved in the liquid phase (SrL cements), leading to different cement compositions after setting. Complementary analytical techniques implemented to thoroughly investigate the release/dissolution mechanism of Sr-loaded cements at pH 7.4 and 37°C during 3 weeks revealed a sustained release of Sr and a centripetal dissolution of the more soluble phase (vaterite) limited by a diffusion process. In all cases, the initial burst of the Ca and Sr release (highest for the SrL cements) that occurred over 48 h did not have a significant effect on the expression of bone markers (alkaline phosphatase, osteocalcin), the levels of which remained overexpressed after 15 days of culture with human osteoprogenitor (HOP) cells. At the same time, proliferation of HOP cells was significantly higher on SrS cements. Interestingly, this study shows that we can optimize the sustained release of Sr2þ, the cement biodegradation and biological activity by controlling the route of introduction of strontium in the cement paste

Evidences for liquid encapsulation in PMMA ultra-thin film grown by liquid injection Photo-CVD

This paper deals with the characterization of ultra-thin films of PMMA grown by an original photoassisted Chemical Vapor Deposition process equipped with a pulsed liquid injection system to deliver the monomer. The nanometric thick films showed a good ability to encapsulate a liquid phase as microdroplets protected by a thin polymeric tight membrane in the form of blisters. Techniques that are capable to analyze these heterogeneous structures at micro- and nanoscopic scale such as Raman Confocal Spectroscopy and Atomic Force Microscopy were used to characterize these polymer films. The liquid droplets were found to be monomer encapsulated by a PMMA film. The specific properties of these ultra-thin films exhibit self-healing capabilities at microscopic scale making them attractive for functionalization of surfaces and interfaces

Rheological properties of calcium carbonate self-setting injectable paste

With the development of minimally invasive surgical techniques, there is growing interest in the research and development of injectable biomaterials with controlled rheological properties. In this context, the rheological properties and injectability characteristics of an original CaCO3 self-setting paste have been investigated. Two complementary rheometrical procedures have been established using a controlled stress rheometer to follow the structure build-up at rest or during gentle mixing and/or handling on the one hand, and the likely shear-induced breakdown of this structure at 25 or 35 C on the other. The data obtained clearly show the influence of temperature on the development of a cement microstructure during setting, in all cases leading to a microporous cement made of an entangled network of aragonite-CaCO3 needle-like crystals. Linear viscoelastic measurements arriving from an oscillatory shear at low deformation showed a progressive increase in the viscous modulus (G0 0) during paste setting, which is enhanced by an increase in temperature. In addition, steady shear measurements revealed the shear-thinning behaviour of this self-setting paste over an extended period after paste preparation and its ability to re-build through progressive paste setting at rest. The shear-thinning behaviour of this self-setting system was confirmed using the injectability system and a procedure we designed. The force needed to extrude a homogeneous and continuous column of paste decreases strongly upon injection and reaches a weight level to apply on the syringe piston around 2.5 kg, revealing the ease of injection of this CaCO3 self-setting paste

Crystal structure of monoclinic calcium pyrophosphate dihydrate (m-CPPD) involved in inflammatory reactions and osteoarthritis

Pure monoclinic calcium pyrophosphate dihydrate (m-CPPD) has been synthesized and characterized by synchrotron powder X-ray diffraction and neutron diffraction. Rietveld refinement of complementary diffraction data has, for the first time, allowed the crystal structure of m-CPPD to be solved. The monoclinic system P21/n was confirmed and unit-cell parameters determined: a = 12.60842 (4), b = 9.24278 (4), c = 6.74885 (2) Å and β = 104.9916 (3)°. Neutron diffraction data especially have allowed the precise determination of the position of H atoms in the structure. The relationship between the m-CPPD crystal structure and that of the triclinic calcium pyrophosphate dihydrate (t-CPPD) phase as well as other pyrophosphate phases involving other divalent cations are discussed by considering the inflammatory potential of these phases and/or their involvement in different diseases. These original structural data represent a key step in the understanding of the mechanisms of crystal formation involved in different types of arthritis and to improve early detection of calcium pyrophosphate (CPP) phases in vivo

Conversion of snail shells (Achatina achatina) acclimatized in Benin to calcium phosphate for medical and engineering use

Most methods for producing calcium phosphates involve synthetic calcium and phosphates sources. However, it has recently been proposed that calcium phosphate can be produced with bio-based calcium sources such as nacre, coral, and cuttlefish bones. One specific source of bio-based calcium is found in the Achatina snail shell, which becomes a waste product after flesh consumption. The present work aimed to assess the effectiveness of Achatina snail shells and to study the conversion kinetics in both acid and alkaline environment rich in phosphate ions. It was observed that in acidic conditions, the calcium released by the dissolution of the aragonite precipitates with the phosphate ions of reaction medium induces brushite formation which is rapidly converted into monetite. In alkaline conditions, calcium released from aragonite reacts with surrounding phosphates and carbonate ions and induces carbonated apatite precipitation. Regardless of the source of calcium used in the presence of phosphate, the conversion is carried out according to complex phenomena that involve topotactic transformation or dissolution-precipitation mechanisms

Crystallisation of a highly metastable hydrated calcium pyrophosphate phase

A simple and fast synthesis method was set up to obtain pure hydrated calcium pyrophosphate (CPP)phases of biological interest. This work focused on a specific phase synthesised at 25 uC and pH 4.5 in a stirred tank reactor. Powder X-ray diffraction, FTIR spectroscopy, scanning electron microscopy and thermogravimetric analyses revealed that the phase is unknown but presents similarities with a monoclinic tetrahydrated CPP phase (Ca2P2O7?4H2O, m-CPPT b phase) synthesised under the same conditions of pH and temperature. Characterisation of the unreferenced phase (u-CPP) has been performed, especially to better identify its composition, structure and stability, as well as its possible relation to the m-CPPT b phase or to other hydrated CPP phases

A Kelvin probe force microscopy study of hydrogen insertion and desorption into 2024 aluminum alloy

Hydrogen was inserted into 2024 aluminum alloy by cathodic polarization in sulfuric acid at 25 °C. Scanning Kelvin Probe Force Microscopy (SKPFM) measurements performed perpendicularly to the charging side revealed a potential gradient and confirmed the insertion of hydrogen over hundreds of microns. A hydrogen diffusion coefficient of 1.7 x 10-9 cm2 s-1 was calculated from SKPFM measurements of H-charged samples for different durations. The evolution of the potential gradient during desorption of hydrogen in air, at room temperature and at 130 °C was investigated. Additional experiments performed at a corrosion defect showed that SKPFM could detect both reversibly and irreversibly bounded hydrogen. These results show that SKPFM is a cutting-edge technique for hydrogen detection and localization at a local scal

Biomimetic nanocrystalline apatites: Emerging perspectives in cancer diagnosis and treatment

Nanocrystalline calcium phosphate apatites constitute the mineral part of hard tissues, and the synthesis of biomimetic analogs is now wellmastered at the labscale. Recent advances in the fine physicochemical characterization of these phases enable one to envision original applications in the medical field along with a better understanding of the underlying chemistry and related pharmacological features. In this contribution, we specifically focused on applications of biomimetic apatites in the field of cancer diagnosis or treatment. We first report on the production and first biological evaluations (cytotoxicity, proinflammatory potential, internalization by ZR751 breast cancer cells) of individualized luminescent nanoparticles based on Eudoped apatites, eventually associated with folic acid, for medical imaging purposes. We then detail, in a first approach, the preparation of tridimensional constructs associating nanocrystalline apatite aqueous gels and drugloaded pectin microspheres. Sustained releases of a fluorescein analog (erythrosin) used as model molecule were obtained over 7 days, in comparison with the ceramic or microsphere reference compounds. Such systems could constitute original bonefilling materials for in situ delivery of anticancer drug