Agglomeration of stoichiometric hydroxyapatite: Impact on particle size distribution and purity in the precipitation and maturation steps

Stoichiometric hydroxyapatite (HAP) is a prominent biomaterial, notably used as coating on metal bone prostheses. High chemical purity and a specific particle size distribution are the main properties for such an application. Based on industrial practice, a reference synthesis was first performed in a lab-scale stirred reactor. Improvements were then suggested by varying the physicochemical and hydrodynamic conditions. The shear rate within the reactor, characterized by the mean Kolmogorov micro-scale, has a strong impact on the final agglomerate size distribution. By maintaining a rather high mixing rate and a high temperature, the duration of the synthesis can be reduced considerably without affecting the HAP purity provided the pH is properly regulated. This consists of imposing acidic conditions during a short period just after the initial formation of large aggregates and then setting the pH at above 7.5 to ensure the production of pure stoichiometric HAP

Nanocrystalline apatites: The fundamental role of water

Bone is a natural nanocomposite. Its mineral component is nanocrystalline calcium phosphate apatite, whose synthetic biomimetic analogs can be prepared by wet chemistry. The initially formed crystals, whether biological or synthetic, exhibit very peculiar physicochemical features. In particular, they are nanocrystalline, nonstoichiometric, and hydrated. The surface of the nanocrystals is covered by a non-apatitic hydrated layer containing mobile ions, which may explain their exceptional surface reactivity. For their precipitation in vivo or in vitro, for their evolution in solution, for the 3D organization of the nanocrystals, and for their consolidation to obtain bulk ceramic materials, water appears to be a central component that has not received much attention. In this mini-review, we explore these key roles of water on the basis of physicochemical and thermodynamic data obtained by complementary tools including FTIR, XRD, ion titrations, oxide melt solution calorimetry, and cryo-FEG-SEM. We also report new data obtained by DSC, aiming to explore the types of water molecules associated with the nanocrystals. These data support the existence of two main types of water molecules associated with the nanocrystals, with different characteristics and probably different roles and functions. These findings improve our understanding of the behavior of bioinspired apatite-based systems for biomedi- cine and also of biomineralization processes taking place in vivo, at present and in the geologic past. This paper is thus intended to give an overview of the specificities of apatite nanocrystals and their close relationship with water

Glycation des protéines et dysfonction endothéliale

Les produits de glycation avancée ou AGE font partie d'une famille de molécules hétérogènes, retrouvées en excès au cours du diabète, de l'insuffisance rénale et du vieillissement. Les lésions vasculaires sont corrélées avec leur accumulation, comme au cours de la rétinopathie ou la glomérulosclérose. La glycation des protéines des matrices extracellulaires est corrélée avec la sévérité des angiopathies diabétiques. L'activation du récepteur aux AGE (RAGE) est impliquée dans leurs effets délétères. La cellule endothéliale exprime alors un phénotype pro-inflammatoire associé à l'expression de molécules d'adhésion, de cytokines, de facteurs chimioattractants ou encore de facteur tissulaire. Les effets délétères de l'interaction AGE-RAGE font intervenir la production d'espèces réactives de l'oxygène via notamment la NADPH oxydase. Les agents inhibiteurs de la formation d'AGE, qui augmentent leur dégradation ou qui neutralisent leur activité, représentent une perspective thérapeutique pour protéger des atteintes vasculaires chez les diabétiques

Diverses demandes de congés lors de la séance du 28 décembre 1789

Démeunier Jean Nicolas, Lebrun François, Grossin de Bouville Louis Jacques, comte de, Upac de Badens Gabriel, marquis d'. Diverses demandes de congés lors de la séance du 28 décembre 1789. In: Archives Parlementaires de 1787 à 1860 - Première série (1787-1799) Tome XI - Du 24 décembre 1789 au 1er mars 1790. Paris : Librairie Administrative P. Dupont, 1880. p. 27

Dietary CML-enriched protein induces functional arterial aging in a RAGE-dependent manner in mice

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3D printed triply periodic minimal surfaces calcium phosphate bone substitute: The effect of porosity design on mechanical properties

peer reviewedTriply periodic minimal surfaces (TPMSs) are relevant structures for building synthetic bone grafts due to their tortuosity and interconnected pores. In order to investigate their porosity and mechanical properties, three different hydroxyapatite-based TPMSs were printed by vat polymerization: the Schwartz diamond, Schwartz primitive, and gyroid scaffolds. Each structure was designed with three levels of porosity, two different pore sizes, and two different wall thicknesses so as to gain an understanding of the effect of pore size and wall thickness on the mechanical properties. The results highlighted the importance of cleaning in the manufacturing process and its impact on the final porosity, especially for small pore sizes. This article intends to be among the first to discuss mechanical testing with macro spherical indentation. Bending and macro spherical indentation resistance tests revealed differences in the mechanical properties between the different structures, with a strong sensitivity of bending strength to the presence of cracks after thermal treatment. Notably, increasing the wall thickness was shown to increase the risk of damage to the solid parts of the scaffolds, therefore lowering the bending strength

Influence of aging in the modulation of epigenetic biomarkers of carcinogenesis after exposure to air pollution

International audienceBackgroundClassified as carcinogenic to humans by the IARC in 2013, fine air particulate matter (PM2.5) can be inhaled and retained into the lung or reach the systemic circulation. This can cause or exacerbate numerous pathologies to which the elderly are often more sensitive.MethodsIn order to estimate the influence of age on the development of early cellular epigenetic alterations involved in carcinogenesis, peripheral blood mononuclear cells sampled from 90 patients from three age classes (25–30, 50–55 and 75–80 years old) were ex vivo exposed to urban PM2.5.ResultsParticles exposure led to variations in telomerase activity and telomeres length in all age groups without any influence of age. Conversely, P16INK4A gene expression increased significantly with age after exposure to PM2.5. Age could enhance MGMT gene expression after exposure to particles, by decreasing the level of promoter methylation in the oldest people.ConclusionHence, our results demonstrated several tendencies in cells modification depending on age, even if all epigenetic assays were carried out after a limited exposure time allowing only one or two cell cycles. Since lung cancer symptoms appear only at an advanced stage, our results underline the needs for further investigation on the studied biomarkers for early diagnosis of carcinogenesis to improve survival

Effets du diabète de type 1 sans complication sur le métabolisme du monoxyde d’azote, le stress oxydant et l’hémodynamique musculaire à l’exercice

International audienceIntroduction : La dysfonction endothéliale précoce constitue un des facteurs de risques dans le développement des complications micro- et macrovasculaires dans le diabète de type 1 (DT1). Les mécanismes sous-jacents à cette dysfonction endothéliale restent peu connus et ce, particulièrement à l’exercice, stimulus physiologique de la vie quotidienne. Notre objectif était d’élucider les mécanismes impliqués dans les troubles de la vasoréactivité musculaire lors d’un exercice maximal chez des adultes DT1 indemnes de complications. Méthodes : Vingt-trois adultes DT1 (HbA1c:7,8±1,5%) appariés (notamment sur niveau d’activité physique) à 23 adultes non diabétiques réalisaient une épreuve d’effort maximale sur ergocycle. Lors de celle-ci, nous mesurions la vasoréactivité musculaire (NIRS) et des molécules impliquées dans le métabolisme du monoxyde d’azote (NO) (L-Arginine, ADMA, nitrites, nitrates, RXNO) et le stress oxydant (malondyaldéhyde, 8-F2-Isoprostane, produits d’oxydation fluorés, carboxyméthyl-lysine, protéines, superoxyde dismutase, glutathion péroxydase et réductase, statut antioxydant total, acide urique, Vitamines C et E, thiols libres totaux) (prélèvements sanguins avant, à l’arrêt immédiat de l’effort et après 15 min de récupération). Résultats : Une hypoperfusion relative musculaire, reflétée par une moindre augmentation de l'hémoglobine totale, est notable au cours de l’exercice maximal à partir de 50%VO2max chez les patients vs. contrôles (P<0,001). La concentration en L-arginine, substrat de la synthèse du NO est significativement diminuée chez les patients au cours de l’exercice (effet groupe, P<0,05). Les marqueurs du stress oxydant étudiés ne sont pas différents entre les groupes, mis à part pour l’antioxydant, acide urique, qui est diminué chez les patients vs. contrôles (38,42±8,00 vs. 46,61±9,95mg/L, effet groupe, P<0.01). Discussion : Les patients présentent une réduction du volume sanguin musculaire à l’exercice. Cette altération s’accompagne, dès le début de l’exercice, d’une moindre disponibilité en L-arginine et en acide urique, qui pourraient refléter respectivement une moindre production de NO et une inactivation accrue du NO produi