AIM: In vitro and in vivo studies were conducted to test a new carvacrol-based product designed to delay the carvacrol release so that it could reach the caeca of broiler chickens in order to control Campylobacter jejuni.METHODS AND RESULTS: Antimicrobial activity of carvacrol, a constituent of oregano and thyme essential oil, has been demonstrated against C. jejuni in vitro, and this compound was found beneficial for broiler growth. Here, we tested a new liquid formulation that did not change the antibacterial efficacy of carvacrol against C. jejuni in vitro, as assessed by broth microdilution. The mode of action of carvacrol also remained unchanged as illustrated by electronic microscopy. A pharmacokinetic assay monitored carvacrol of the solid galenic formulation in the avian digestive tract and this showed that this compound was mainly found in the last part (caeca, large intestine) and in the droppings. Extremely low concentrations of free carvacrol were present in blood plasma, with larger amounts of carvacrol metabolites: carvacrol glucuronide and sulphate. A qPCR analysis showed that the solid galenic form of carvacrol added at 5 kg per tonne of food (i.e. 9·5 mg of carvacrol per kg of bodyweight per day) significantly decreased the C. jejuni caecal load by 1·5 log.CONCLUSIONS: The new liquid formulation was as effective as unformulated carvacrol in vitro. In vivo the solid galenic form seems to delay the carvacrol release into the caeca and presented interesting results on C. jejuni load after 35 days.SIGNIFICANCE AND IMPACT OF THE STUDY: Results suggested that this product could be promising to control Campylobacter contamination of broilers.

The present invention relates to the field of optical devices, and more specifically to the field of active optical devices

One of the problems largely commented in the sol-gel science is how to make large bodies, because gels tend to crack during drying. The drying stresses are attributed to capillary phenomena and differential strain which result from a pressure gradient in the pore liquid. By the supercritical drying (SCD), the capillary stresses are eliminated and monolithic aerogel can be obtained. This chapter focuses on silica aerogel, the most studied aerogel. It presents an overview of the supercritical drying techniques, but also some of the remarkable aerogel properties (optical, mechanical, thermal and acoustical, etc.) with respect to its peculiar microstructure. The chapter briefly presents other kinds of aerogels (oxides and chalcogenideaerogels, composite aerogels, organic aerogels, etc.) and a panel of potential applications.

Aerogels are generally described in terms of brittle and elastic materials, like glasses or ceramics with poor and not predictable mechanical properties. We propose the synthesis of a nanocomposite aerogels with improved mechanical properties by addition of silica particles (aerosil; 20–100 nm) in the monomer solution. The elastic modulus and rupture strength increase, stiffening and strengthening the structure by a factor 5–8. The toughness, the critical flaw size, and the fracture energy increase also versus the silica particle concentration. Moreover, the mechanical strength distribution and the Weibull modulus, m, characterizing the statistical nature of flaw size in brittle materials show a more homogeneous flaw size distribution. Pores are considered as integral part of flaws, and small angle X-ray scattering shows that the usual fractal structure observed in aerogel disappears with the silica particle addition. The fractal structure in aerogel is characteristic of a large pore size distribution, but also of a large flaw size distribution. If nanocomposites behave as brittle material under a tension stress, they exhibit a different response when the structure is submitted to a compression: densification and plastic hardening. These opposite behaviors (brittle and plastic) are surprisingly related to the same kinds of gel features: pore volume, silanol content, and the pore size distribution. Because of improved mechanical properties, these nanocomposites aerogels could be used as host matrices for the synthesis of glass ceramics, doped glasses, and composites.

Different kinds of structure in alcogels and aerogels (fractal or not fractal) can be synthesized by a control of the chemical parameters and also by different steps in the preparation such as sintering and plastic compaction. The porosity of the gelsis affected either by the adjustment of the gelifying concentration, by a precise control of the viscous flow sintering process, or by an isostatic pressure deformation. The different kinds of gels cover the whole range of porosity between 99% and 0%, and their mechanical properties (elastic modulus, strength, toughness) are strongly dependent on the porosity but also on their structure. We follow the mechanical properties of the over the whole process alcogel–aerogel–glass. They vary by five orders of magnitude as a function of the density, and for the same relative density, the elastic modulus and strength can increase by one order of magnitude due to a change in connectivity. The influence of the sintering process compared to isostatic pressure on the mechanical properties is explained by the associated structural changes.