The study of the pseudo-polyrotaxane architecture as a route for mild surface functionalization by click chemistry of poly(ε-caprolactone)-based electrospun fibers.

Polycaprolactone (PCL) electrospun fibers are widely developed for biomedical applications. However, their hydrophobicity and passivity towards cell growth is an important limitation. An original method to functionalize PCL nanofibers, making them reactive for bioconjugation of proteins or other molecules of interest in water under mild conditions, is reported here. This method involves the preparation of pseudo-polyrotaxanes (pPRs) of cyclodextrin (CD) and PCL. Core:shell PCL:pPR fibers were then prepared by coaxial electrospinning in order to bring available reactive hydroxyl groups from the CD to the fiber surface. Different pPR architectures (star, miktoarm and block-copolymer-like) were synthesized to study the effect of the pPR structure on fiber morphology and surface reactivity by grafting fluorescein isothiocyanate (FITC). Finally, bicyclononyne groups were grafted onto the star-pPR based fibers allowing the conjugation of a fluorescent dye by click chemistry in water without any copper catalyst proving the potential of the method for the biofunctionalization of PCL-based fibers.

Fungal Fermentation of Lignocellulosic Biomass for Itaconic and Fumaric Acid Production.

The production of high-value chemicals from natural resources as an alternative for petroleum-based products is currently expanding in parallel with biorefinery. The use of lignocellulosic biomass as raw material is promising to achieve economic and environmental sustainability. Filamentous fungi, particularly Aspergillus species, are already used industrially to produce organic acid as well as many enzymes. The production of lignocellulose-degrading enzymes opens the possibility for direct fungal fermentation towards organic acids such as itaconic acid (IA) and fumaric acid (FA). These acids have wide-range applications and potentially addressable markets as platform chemicals. However, current technologies for the production of these compounds are mostly based on submerged fermentation. This work showed the capacity of two Aspergillus species (A. terreus and A. oryzae) to yield both acids by solid-state fermentation and simultaneous saccharification and fermentation. FA was optimally produced at by A. oryzae in simultaneous saccharification and fermentation (0.54 mg/g wheat bran). The yield of 0.11 mg IA/g biomass by A. oryzae is the highest reported in the literature for simultaneous solid-state fermentation without sugar supplements.

Sepiolite as a promising nanoclay for nano-biocomposites based on starch and biodegradable polyester.

The effects of sepiolite addition (0, 1, 3 and 5wt%) were evaluated on dynamic-mechanical behaviour, water uptake, thermal and optical properties of thermoplastic starch (TPS)/poly (butylene adipate-co-terephthalate) (PBAT) nano-biocomposites, with different TPS/PBAT (w/w) ratios and nanofiller contents. The results highlighted the improvement of the dynamic-mechanical behaviour with the addition of sepiolite, producing high performance materials. An increase of 25°C in the Tg of TPS was recorded by DMTA analysis at sepiolite content of 5wt%. The sepiolite influenced the crystallisation of nano-biocomposites, without causing interference in the crystal organisation, evidenced by DSC analysis. The addition of sepiolite nanoclay decreased the water adsorption rate and water adsorption capacity of the corresponding nano-biocomposites. For such multiphase systems, the successful use of natural sepiolite brought a clear benefit, without the need of any modifications or additional processes to produce advanced nano-biocomposites.

Elaboration, morphology and properties of starch/polyester nano-biocomposites based on sepiolite clay.

The incorporation of nano-sized sepiolite clays into thermoplastic starch/poly(butylene adipate-co-terephthalate) (TPS/PBAT) blends has been investigated with the goal of improving the matrix properties. TPS/PBAT nano-biocomposites were elaborated with two different proportions of the polymeric phases. The influence of the sepiolite nanoclays on the mechanical, thermal and structural properties of the corresponding blends was evaluated. SEM images confirmed the good dispersion of the sepiolite clay, with a low occurrence of small aggregates in the polymeric matrix. Wide-angle X-ray diffraction showed no significant alteration of the crystalline structures of PBAT and starch induced by the sepiolite clay. The addition of sepiolite slightly affected the thermal degradation of the nano-biocomposites; however, the mechanical tests revealed an increase in some mechanical properties, demonstrating that sepiolite is a promising nanofiller for TPS-based materials.

Mixed culture polyhydroxyalkanoate (PHA) production from volatile fatty acid (VFA)-rich streams: effect of substrate composition and feeding regime on PHA productivity, composition and properties.

In this study, the possibility of manipulating biopolymer composition in mixed culture polyhydroxyalkanoate (PHA) production from fermented molasses was assessed by studying the effects of substrate volatile fatty acid (VFA) composition and feeding regime (pulse wise versus continuous). It was found that the use of a continuous feeding strategy rather than a pulse feeding strategy can not only help mitigate the process constraints of the pulse-feeding strategy (resulting in higher specific and volumetric productivities) but also be used as means to broaden the range of polymer structures. Continuous feeding increased the hydroxyvalerate content by 8% relatively to that obtained from the same feedstock using pulse wise feeding. Therefore, the feeding strategy can be used to manipulate polymer composition. Furthermore, the range of PHA compositions, copolymers of P(HB-co-HV) with HV fraction ranging from 15 to 39%, obtained subsequently resulted in different polymer properties. Increasing HV content resulted in a decrease of the average molecular weight, the glass transition and melting temperatures and also in a reduction in the crystallinity degree from a semi-crystalline material to an amorphous matrix.

[Progression of diabetic retinopathy during pregnancy]. / Progression de la rétinopathie diabétique durant la grossesse.

Diabetic retinopathy should be carefully monitored during certain risk situations. Indeed, diabetic retinopathy in pregnant type 1 diabetic patients can rapidly progress and threaten vision, as in other situations such as puberty, glycemic equilibration, or ocular surgery. During pregnancy, five major risk factors for progression have been identified: pregnancy itself, diabetic retinopathy grade at baseline, duration of diabetes, important glycated hemoglobin reduction, and high blood pressure. These factors must be taken into account when planning pregnancy in diabetic patients and during the follow-up of their diabetic retinopathy. Diabetic women should be counseled about the risks of progression of their disease before planning pregnancy. Careful eye examination before and during the first trimester should be done in these patients, in order to detect severe non-proliferative diabetic retinopathy and/or high-risk diabetic retinopathy and perform rapid laser treatment if needed. Follow-up visit frequency should be adapted to the severity of the diabetic retinopathy. Very few authors have studied diabetic macular edema during pregnancy. This complication can spontaneously regress postpartum and should not be treated too rapidly.

Micromechanically-based formulation of the cooperative model for the yield behavior of starch-based nano-biocomposites.

The tensile yield stress of plasticized starch filled with montmorillonite has been studied as a function of the temperature and the strain rate and has been compared to the yield behavior of the original matrix. Aggregated/intercalated and exfoliated nano-biocomposites, obtained from different nanofillers, have been produced and tested under uniaxial tension (tensile test). To model the nanocomposite tensile yield stress behavior, a preexisting micro-mechanically based cooperative model, which describes properly the yield of semi-crystalline polymers has been modified. According to our development, the yield behavior of nano-biocomposites is strongly dependant on the clay concentration and exfoliation ratio. Based on the thermodynamics properties, an effective activation volume and effective activation energy are computed through the Takayanagi homogenization model. The predicted results for the yield stress at low strain rates and at different temperatures are in agreement with our experimental results.