Flow simulations of rectal evacuation: towards a quantitative evaluation from video defaecography.

Mechanistic understanding of anorectal (patho)physiology is missing to improve the medical care of patients suffering from defaecation disorders. Our objective is to show that complex fluid dynamics modelling of video defaecography may open new perspectives in the diagnosis of defaecation disorders. Based on standard X-ray video defaecographies, we developed a bi-dimensional patient-specific simulation of the expulsion of soft materials, the faeces, by the rectum. The model quantified velocity, pressure and stress fields during the defaecation of a neostool with soft stool-like rheology for patients showing normal and pathological defaecatory function. In normal defaecation, the proximal-distal pressure gradient resulted from both the anorectal junction which formed a converging channel and the anal canal. The flow of the neostool through these anatomical parts was dominated by its shear-thinning viscous properties, rather than its yield stress. Consequently, the evacuation flow rate was significantly affected by variations in pressure applied by the rectum, and much less by the geometry of the anorectal junction. Lastly, we simulated impaired defaecations in the absence of obvious obstructive phenomena. Comparison with normal defaecation allowed us to discuss critical elements which should lead to effective medical management.

Towards an assessment of rectal function by coupling X-ray defecography and fluid mechanical modelling.

Despite the numerous available clinical investi-gation tests, the associated alteration of quality of life and the socio-economic cost, it remains difficult for physicians to identify the pathophysiological origins of defecation disorders and therefore to provide the appropriate clinical care. Based on standardized dynamic X-ray defecography, we developed a 2D patient-specific computational fluid dynamic model of rectal evacuation. X-ray defecography was carried out in a sitting position with a standardized paste whose yield stress matched that of soft human feces. The flow was simulated with lattice-Boltzmann methods for yield stress fluids and moving boundary conditions. The model was applied for a patient with a normal recto-anal function. We deduced from the flow field that the main flow resistance during the defecation was due to the extrusion of the paste through the anal canal. We calculated also from pressure and stress fields the spatio-temporal evolution of the wall normal stress. This latter highlighted a gradient from the proximal to the distal part of the rectum. We discussed how this new set of hydrodynamical and biome-chanical parameters could be interpreted to gain new insights on the physiology of defecation and to diagnose underlying evacuation disorders. Clinical relevance - If confirmed, our approach should allow clinicians to obtain other parameters from a classic clinical examination and thus better adapt the response of clinicians to the defecation disorders observed in patients.

Biobased nucleation agents for poly-L-(lactic acid) - Effect on crystallization, rheological and mechanical properties.

In the present work, the nucleating aptitude for poly-L-(lactic acid) (PLLA) of several biobased nanoparticles (NPs) with different morphologies and surface properties, including cellulose nanofibrils with and without lignin (LCNFs and CNFs) as well as cellulose, chitin and starch nanocrystals (CNCs, ChNCs and SNCs), was investigated. A single melt-processing step using a small amount of poly(ethylene glycol) (PEG) as carrier for the NPs was adopted to prepare films with the same nanofiller content of 1 wt%. The nucleation efficiency was investigated by differential scanning calorimetry using Avrami's and Lauritzen-Hoffman's secondary nucleation theory. The crystallization half-time was found to change considerably according to the morphology and surface properties of the NPs, with the lowest time observed for CNFs and CNCs, followed by ChNCs, SNCs and LCNFs. Comparing the surface energy components of the different nucleating agents, it was found that the nanofiller with the highest γp had the lowest t1/2 and demonstrated the most effective nucleating aptitude. The evolution of the melt rheological properties of the different compositions, and the mechanical and optical properties of the films with and without a short annealing treatment were also studied.

Twin-screw extrusion for the production of nanocellulose-PVA gels with a high solid content.

Twin-screw extrusion (TSE) is a recent strategy used to prepare nanocelluloses at high solid contents. However, various aspects of the mechanism of disintegration and the role of fiber pretreatment remain to be elucidated. Oxidized cellulose fibers with carboxyl contents between 300 and 700 µmol·g-1 were extruded in the presence of polyvinyl alcohol (PVA) at a 80/20 (w/w) ratio, to produce high-consistency nanocellulose gels at 15 wt% solid content, ready for use in multiple applications. The influence of the origin of the pulps and the oxidation treatment on the efficiency of fiber disintegration was evaluated by porosity measurement. The rheological properties of the nanocellulose-PVA gels and the mechanical properties and transparency of the resulting nanopapers were studied as well. Combining TSE and rotor-stator dispersion or short sonication homogenization contributed to enhancing the fibrillation during extrusion, providing a method to increase the fraction of nanocellulose in a much less energy-consuming manner.

Honeycomb Organization of Chitin Nanocrystals (ChNCs) in Nanocomposite Films of UV-Cured Waterborne Acrylated Epoxidized Soybean Oil Emulsified with ChNCs.

Stable biobased waterborne Pickering dispersions of acrylated epoxidized soybean oil (AESO) were developed using chitin nanocrystals (ChNCs) as sole emulsifier without any additives. Thin AESO-ChNC nanocomposite films were produced by UV-curing thin-coated layers of the AESO emulsion after water evaporation. The kinetics of photopolymerization were assessed by monitoring the consumption of the AESO acrylate groups by infrared spectroscopy (Fourier transform infrared (FTIR)). The curing was faster in the presence of ChNCs, with a disappearance of the induction period observed for neat AESO. The coating of AESO droplets with a thin layer of ChNCs was confirmed by scanning electron microscopy (SEM) observation. SEM and transmission electron microscopy (TEM) images revealed the honeycomb organization of ChNCs inside the cured AESO-ChNC films. The mechanical, thermal, and optical properties of the nanocomposite films were studied by dynamic mechanical analysis (DMA), tensile testing, differential scanning calorimetry (DSC), and transmittance measurement, as a function of ChNC content. The inclusion of ChNCs is strongly beneficial to increase the stiffness and strength of the cured films, without compromising its optical transparency. The ability of ChNCs to act as an emulsifier for AESO in replacement of synthetic surfactants and their strong reinforcing effect in UV-cured films offer new opportunities to produce waterborne stable dispersions from AESO for application in biobased coatings and adhesives.

Chitin nanocrystals as Pickering stabilizer for O/W emulsions: Effect of the oil chemical structure on the emulsion properties.

Chitin nanocrystals (ChNCs) produced by hydrochloric acid hydrolysis of chitin were used as stabilizing agent for oil-in-water (O/W) emulsification of soybean oil (SO), acrylated soybean oil (ASO), and epoxidized soybean oil (ESO). The emulsion stability, droplet size, and rheology of the emulsion were found to be significantly affected by the oil chemical structure. Strong interaction between ChNCs and the oil droplets enhanced the stabilizing efficiency of ChNCs through a Pickering effect, resulting in emulsions with low droplet size and long-term stability. The use of ChNCs as stabilizer for O/W emulsions in replacement of synthetic surfactants opens new avenues to produce emulsions for a wide variety of applications, including cosmetic products, coating, inks and adhesives.

Vinyltriethoxysilane-functionalized starch nanocrystals as Pickering stabilizer in emulsion polymerization of acrylic monomers. Application in nanocomposites and pressure-sensitive adhesives.

Emulsion polymerization provides a sustainable way to produce latex polymers for coatings and adhesives thanks to the use of water as a dispersion medium. This synthesis approach can be even more attractive if synthetic surfactant can be replaced by biobased solid particles as a stabilizer, through what is known as a "Pickering effect". Herein, latex dispersions with solid content up to 35 wt% were successfully produced by emulsion polymerization using starch nanocrystals (SNCs) as a sole stabilizer and H2O2/citric acid as a redox-initiator. The effect of the SNC modification with vinyltriethoxysilane (VTES) on the colloidal properties of the polymer dispersion and performance of the resulting nanocomposite film were investigated. As an application of this approach, pressure-sensitive adhesive (PSA) dispersions have been prepared via Pickering emulsion polymerization in the presence of 8 wt% SNCs. The use of VTES-SNCs has a beneficial impact on the performance of PSAs with improved peel strength and wettability. The possibility to use SNCs as a stabilizer to replace synthetic surfactants in emulsion polymerization opens new avenues for the application of SNCs as biobased Pickering stabilizers to produce latex for coatings, adhesives, inks, and textiles.

Cellulose nanofibrils prepared by twin-screw extrusion: Effect of the fiber pretreatment on the fibrillation efficiency.

Twin-screw extrusion (TSE) is a rather recent method to produce cellulose nanofibrils (CNFs) at a high solid content under continuous feeding. Here, never-dried commercial eucalyptus pulp was used as starting material to produce CNFs by TSE after a chemical pretreatment to introduce carboxylic groups via TEMPO-mediated oxidation and carboxymethylation. Five samples with a carboxyl content ranging from 800 to 1300 µmol.g-1 were produced to explore how the carboxyl content affects the aptitude of cellulose fibers to be broken down to nanoscale. The properties of the resulting CNFs in terms of nanosized fraction, morphology and rheological properties were investigated. A critical carboxyl content of 700 µmol.g-1was a prerequisite for the successful conversion of cellulose fibers into a CNF gel by TSE, regardless the pretreatment method. The degree of swelling of the fibers was put forward to account for this critical parameter.

One-step processing of plasticized starch/cellulose nanofibrils nanocomposites via twin-screw extrusion of starch and cellulose fibers.

Nanocomposites based on thermoplasticized starch filled with cellulose nanofibrils (CNFs) were produced in a single step by twin-screw extrusion of corn starch granules, glycerol as a plasticizer, and oxidized cellulose fibers. The objective was to demonstrate the possibility to produce CNFs in situ during the processing of the nanocomposite when a hydrophilic polymer matrix was used. For comparison purpose, nanocomposites were also prepared by extrusion of a previously prepared CNF suspension, corn starch granules and glycerol. The nanocomposites were characterized in terms of mechanical properties, morphology, crystallinity, and transparency. The nanocomposites prepared via in situ fibrillation displayed a higher strength than those produced by incorporating readily prepared CNFs. In addition, the transparency degree up to a 15 wt% CNF content was similar for the two processing routes, confirming the effective breakdown of pretreated cellulose fibers into CNFs during the extrusion process.

Hybrid nanocellulose decorated with silver nanoparticles as reinforcing filler with antibacterial properties.

Cellulose (Cel) nanofibrils (CNFs) produced by periodate oxidation of native cellulose fibers were functionalized with silver (Ag) nanoparticles (NPs) using Tollens' reaction. The morphology and chemical composition of the resulting Cel-Aghybrid nanofibrils were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), as well as Fourier-transform infrared (FTIR) and UV-Vis spectroscopies. To check whether the hybridization with Ag affected the reinforcing potential of the CNFs, nanocomposite films based on an acrylic matrix filled with the as-prepared Cel-Ag nanofibrils at different contents were processed by film casting. Their mechanical properties were investigated by dynamic thermomechanical analysis (DMTA). The hybrid Cel-Ag nanofibrils exhibited good bactericidal properties against Gram+ and Gram- bacteria. Interestingly, the presence of Ag NPs did not seem to affect the reinforcing potential of the nanocellulose, and the amount of Ag leached out from films was below the permissible limit of 12 ppb. Nanocomposites based on this hybrid Cel-Ag nanofiller thus have a great potential in the field of active packaging films, coating and adhesives with enhanced antibacterial activity.

Surfactant-free emulsion Pickering polymerization stabilized by aldehyde-functionalized cellulose nanocrystals.

Aldehyde-functionalized cellulose nanocrystals (CN) with two aldehyde contents were produced by periodate oxidation and gentle sonication. The aldehyde-functionalized CNCs were shown to be an effective stabilizer in the Pickering emulsion polymerization of acrylate monomers using potassium persulfate (KPS)/metabisulfite redox initiation system at 50 °C without any added surfactant. The effect of CNC content on the particle size, zeta-potential, colloidal stability and film properties were discussed. CNCs with the highest aldehyde content impart better colloidal stability to the polymer dispersion and lower particle size. The stabilization process was explained by the reaction of bisulfite with aldehyde groups borne by CNC, forming an adduct that contributes to the initiation of the polymerization and nucleation of polymer particles. This favors the effective attachment of CNCs onto the polymer particle, which is prerequisite for the effective Pickering stabilization process. The optical and mechanical properties of the nanocomposite films obtained by simple casting of the polymer dispersion and water evaporation were also investigated by transmittance and dynamic mechanical analysis (DMA). Better transparency was observed for films prepared in the presence of CNCs with the highest aldehyde content, while a reverse trend was noted for the mechanical properties.

CNFs from twin screw extrusion and high pressure homogenization: A comparative study.

Cellulose nanofibrils (CNFs) from oxidized never dried Eucalyptus pulps have been produced by using twin screw extrusion (TSE) and high pressure homogenizer (HPH), and their properties were compared. CNFs from TSE are produced at 10% solid content and then diluted to 1% for purpose of comparison against HPH. The nanosized fraction (NF) was around 90% for CNFs from HPH compared to 70% when TSE was used. Difference in the fibrillation extent has led to a higher transparency degree for CNFs gel from HPH. However, the rheological properties of two CNFs gels are quite similar with a solid-like aspect. The elastic modulus is one order of magnitude higher than viscous modulus and nearly frequency-independent. Analysis of the nanosized fraction with AFM has revealed long nanosized fibrils 3-4 nm in width for both CNFs types. When mixed with waterborne polymer dispersion, transparent to translucide nanocomposite films were obtained. However, the reinforcing potential of CNFs from HPH has been shown to be stronger than that from TSE.

An experimental model to investigate the biomechanical determinants of pharyngeal mucosa coating during swallowing.

The development of innovative experimental approaches is necessary to gain insights in the complex biomechanics of swallowing. In particular, unraveling the mechanisms of formation of the thin film of bolus coating the pharyngeal mucosa after the ingestion of liquid or semi-liquid food products is an important challenge, with implication in dysphagia treatment and sensory perceptions. The aim here is to propose an original experimental model of swallowing (i) to simulate the peristaltic motions driving the bolus from the oral cavity to the esophagus, (ii) to mimic and vary complex physiological variables of the pharyngeal mucosa (lubrication, deformability and velocity) and (iii) to measure the thickness and the composition of the coatings resulting from bolus flow. Three Newtonian glucose solutions were considered as model food boli, through sets of experiments covering different ranges of each physiological parameter mimicked. The properties of the coatings (thickness and dilution in saliva film) were shown to depend significantly on the physical properties of food products considered (viscosity and density), but also on physiological variables such as lubrication by saliva, velocity of the peristaltic wave, and to a lesser extent, the deformability of the pharyngeal mucosa. The biomechanical peristalsis simulator developed here can contribute to unravel the determinants of bolus adhesion on pharyngeal mucosa, necessary both for the design of alternative food products for people affected by swallowing disorders, and for a better understanding of the dynamic mechanisms of aroma perception.

Impact of TEMPO-oxidization strength on the properties of cellulose nanofibril reinforced polyvinyl acetate nanocomposites.

Nanocomposites of polyvinyl acetate (PVAc) reinforced with two different TEMPO-oxidized cellulose nanofibrils (CNF) were prepared by casting/evaporation method. These two sets of CNF, designed as CNF-O-5min (5min of oxidation) and CNF-O-120min (120min of oxidation), are different by their surface charge, geometrical characteristics and crystallinity index. The weight fraction of CNF was changed from 1 to 10wt%. The mechanical and thermal properties of the nanocomposite films were studied by dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and tensile tests, and their morphology was investigated by scanning electron microscopy (SEM). For all nanocomposites, increasing amounts of CNF led to a significant increase in the mechanical properties (increase in Young's modulus and tensile strength) and in the water uptake. On the other hand, the lost of transparency became very significant when the weight fraction of CNF exceeded 3wt%. The comparison between the two sets of CNF showed that PVAc/CNF-O-5min nanocomposite films had a tendency to display higher tensile strength and elastic modulus than those of PVAc/CNF-O-120min films. In addition, the water uptake is higher for PVAc/CNF-O-120min. Finally, the thermal stability analyses for PVAc/CNF films show that shorter and more charged fibrils (CNF-O-120min) appear to slightly increase the thermal stability compared to other larger and less charged fibrils (CNF-O-5min). All these results are discussed in connection with the CNFs characteristics.

Ultrasonic assisted production of starch nanoparticles: Structural characterization and mechanism of disintegration.

In this paper, the disintegration of starch (waxy and standard starch) granules into nanosized particles under the sole effect of high power ultrasonication treatment in water/isopropanol is investigated, by using wide methods of analysis. The present work aims at a fully characterization of the starch nanoparticles produced by ultrasonication, in terms of size, morphology and structural properties, and the proposition of a possible mechanism explaining the top-down generation of starch nanoparticles (SNPs) via high intensity ultrasonication. Dynamic light scattering measurements have indicated a leveling of the particle size to about 40nm after 75min of ultrasonication. The WAXD, DSC and Raman have revealed the amorphous character of the SNPs. FE-SEM. AFM observations have confirmed the size measured by DLS and suggested that SNPs exhibited 2D morphology of platelet-like shapes. This morphology is further supported by SAXS. On the basis of data collected from the different characterization techniques, a possible mechanism explaining the disintegration process of starch granules into NPs is proposed.

Starch nanocrystals and starch nanoparticles from waxy maize as nanoreinforcement: A comparative study.

The morphological, structural and thermal behavior of starch nanocrystals (SNCs) extracted from waxy maize starch through an acid hydrolysis were compared with those of starch nanoparticles (SNPs) obtained through an ultrasound treatment starting from the same waxy maize starch. The SNPs were found to be completely amorphous, slightly smaller and had no surface charge, whereas the SNCs had the expected platelet-like morphology with a negative surface charge introduced as a result of the use of sulphuric acid in the acid hydrolysis step. SNCs also showed better thermal stability than SNPs in the presence of water. As a result of their platelet-like morphology, the SNCs performed better in reinforcing a polymer film. On the other hand, SNPs reduced the transparency of the nanocomposite films to a lesser extent than the SNCs due to their smaller size.

Bio-based polyurethane reinforced with cellulose nanofibers: a comprehensive investigation on the effect of interface.

Novel bio-based polyurethane (PU) nanocomposites composed of cellulose nanofiller extracted from the rachis of date palm tree and polycaprolactone (PCL) diol based PU were prepared by casting/evaporation. Two types of nanofiber were used: cellulose nanofibrils (CNFs) and cellulose nanocrystals (CNCs). The mechanical and thermal properties of the nanocomposite films were studied by DMA, DSC, and tensile tests and the morphology was investigated by SEM. Bionanocomposites presented good mechanical properties in comparison to neat PU. While comparing both nanofillers, the improvement in mechanical and thermal properties was more pronounced for the nanocomposites based on CNF which could be explained, not only by the higher aspect ratio of CNF, but also by their better dispersion in the PU matrix. Calculation of the solubility parameters of the nanofiller surface polymers and of the PU segments portend a better interfacial adhesion for CNF based nanocomposites compared to CNC.

Starch nanocrystal stabilized Pickering emulsion polymerization for nanocomposites with improved performance.

Latex/starch nanocrystal (SNC) nanocomposite dispersions were successfully synthesized via a one-step surfactant-free Pickering emulsion polymerization route using SNC as the sole stabilizer. The effect of the SNC content, initiator type and comonomer on the particle size, colloidal stability, and film properties were investigated. Both HCl and H2SO4-hydrolysed starch nanocrystals, each bearing different surface charges, were used as Pickering emulsion stabilizing nanoparticles. SNCs from HCl hydrolysis were found to provide a better stabilization effect, giving rise to a polymer dispersion with a lower average particle size. The mechanistic aspects of the Pickering emulsion polymerization were also discussed. Nanocomposites formed by film-casting the polymer Pickering emulsions showed better mechanical properties and optical transparency than those obtained by blending the polymer emulsion with a nanocrystal dispersion, showing the one-pot route to nanocomposite precursors to be doubly advantageous. Therefore, this in situ polymerization technique not only facilitates the use of SNC nanoparticles, it also provides a valuable nanocomposite with enhanced mechanical properties and high transparency level.

Electric field alignment of nanofibrillated cellulose (NFC) in silicone oil: impact on electrical properties.

This work aims to study how the magnitude, frequency, and duration of an AC electric field affect the orientation of two kinds of nanofibrillated cellulose (NFC) dispersed in silicone oil that differ by their surface charge density and aspect ratio. In both cases, the electric field alignment occurs in two steps: first, the NFC makes a gyratory motion oriented by the electric field; second, NFC interacts with itself to form chains parallel to the electric field lines. It was also observed that NFC chains become thicker and longer when the duration of application of the electric field is increased. In-situ dielectric properties have shown that the dielectric constant of the medium increases in comparison to the randomly dispersed NFC (when no electric field is applied). The optimal parameters of alignment were found to be 5000 Vpp/mm and 10 kHz for a duration of 20 min for both kinds of NFC. The highest increase in dielectric constant was achieved with NFC oxidized for 5 min (NFC-O-5 min) at the optimum conditions mentioned above.

Control of size and viscoelastic properties of nanofibrillated cellulose from palm tree by varying the TEMPO-mediated oxidation time.

The main objective of the present study was to control and optimize the preparation of nanofibrillated cellulose (NFC) from the date palm tree by monitoring the oxidation time (degree of oxidation) of the pristine cellulose and the number of cycles through the homogenizer. The oxidation was monitored by TEMPO (1-oxo-2,2,6,6-tétraméthylpipyridine 1-oxyle) mediated oxidation. Evidence of the successful isolation of NFC was given by FE-SEM observation revealing fibrils with a width in the range 20-30nm, depending of the oxidation time. The evolution of the transparency of the aqueous NFC suspension and carboxylic content according to the degree of oxidation and number of cycles were also analyzed by UV-vis transmittance, Fourier-transform infrared spectroscopy (FT-IR), conductimetry, and X-ray diffraction analysis. A significant NFC length reduction occurred during the TEMPO-mediated oxidation. The rheological properties of NFC suspensions were characterized as function of the oxidation time. Dynamic rheology showed that the aqueous suspension behavior changed from liquid to gel depending on the concentration. The highest concentration studied was 1wt% and the modulus reached 1MPa which was higher than for non-oxidized NFC. An explanation of the gel structure evolution with the oxidation time applied to the NFC (NFC length) was proposed. The gel structure evolves from an entanglement-governed gel structure to an immobilized water molecule-governed one.