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.

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.

Structural characterization of the interfacial self-assembly of chitosan with oppositely charged surfactant.

Controlling the assembly of polyelectrolytes and surfactant at liquid-liquid interfaces offers new ways to fabricate soft materials with specific physical properties. However, little is known of the relationships between the kinetics of interfacial assembly, structural and rheological properties of such interfaces. We studied the kinetics at water-oil interface of the assembly of a positively charged biopolymer, chitosan, with an anionic fatty acid using a multi-scale approach.

Dynamics of a Gel-Based Artificial Tear Film with an Emphasis on Dry Disease Treatment Applications.

This paper discusses the spreading of gel-based ophthalmic formulation on the cornea surface assumed to be flat. We show that gel-based formulations exhibit rheological behaviors that the Herschel-Bulkley model can describe. The continuity and momentum equations are solved numerically using the monofluid formulation and the volume-of-fluid (VOF) method.

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.

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.

Interfacial rheological properties of self-assembling biopolymer microcapsules.

Tuning the mechanical properties of microcapsules through a cost-efficient route of fabrication is still a challenge. The traditional method of layer-by-layer assembly of microcapsules allows building a tailored composite multi-layer membrane but is technically complex as it requires numerous steps. The objective of this article is to characterize the interfacial rheological properties of self-assembling biopolymer microcapsules that were obtained in one single facile step.

Ex vivo motility in the base of the rabbit caecum and its associated structures: an electrophysiological and spatiotemporal analysis.

We examined the coordination between contractile events at different sites in the basal portion of the rabbit caecum and its associated structures that were identified by electrophysiological recordings with simultaneous one-dimensional, and a novel two-dimensional, spatiotemporal mapping technique. The findings of this work provide evidence that the caecum and proximal colon/ampulla coli act reflexly to augment colonic outflow when the caecum is distended and mass peristalsis instituted, the action of the latter overriding the inherent rhythm and direction of haustral propagation in the adjacent portion of the proximal colon but not in the terminal ileum. Further, the findings suggest that the action of the sacculus rotundus may result from its distension with chyme by ileal peristalsis and that the subsequent propagation of contraction along the basal wall of the caecum towards the colon may be augmented by this local distension.

Determination of villous rigidity in the distal ileum of the possum (Trichosurus vulpecula).

We investigated the passive mechanical properties of villi in ex vivo preparations of sections of the wall of the distal ileum from the brushtail possum (Trichosurus vulpecula) by using a flow cell to impose physiological and supra-physiological levels of shear stress on the tips of villi. We directly determined the stress applied from the magnitude of the local velocities in the stress inducing flow and additionally mapped the patterns of flow around isolated villi by tracking the trajectories of introduced 3 µm microbeads with bright field micro particle image velocimetry (mPIV). Ileal villi were relatively rigid along their entire length (mean 550 µm), and exhibited no noticeable bending even at flow rates that exceeded calculated normal physiological shear stress (>0.

Mechanical characterization of cross-linked serum albumin microcapsules.

Controlling the deformation of microcapsules and capsules is essential in numerous biomedical applications. The mechanical properties of the membrane of microcapsules made of cross-linked human serum albumin (HSA) are revealed by two complementary experiments in the linear elastic regime. The first provides the surfacic shear elastic modulus Gs by the study of small deformations of a single capsule trapped in an elongational flow: Gs varies from 0.

Characterisation of mixing in the proximal duodenum of the rat during longitudinal contractions and comparison with a fluid mechanical model based on spatiotemporal motility data.

The understanding of mixing and mass transfers of nutrients and drugs in the small intestine is of prime importance in creating formulations that manipulate absorption and digestibility. We characterised mixing using a dye tracer methodology during spontaneous longitudinal contractions, i.e.

Fluid mechanical consequences of pendular activity, segmentation and pyloric outflow in the proximal duodenum of the rat and the guinea pig.

We conducted numerical experiments to study the influence of non-propagating longitudinal and circular contractions, i.e. pendular activity and segmentation, respectively, on flow and mixing in the proximal duodenum.

Spatiotemporal mapping of ex vivo motility in the caecum of the rabbit.

We used high definition radial, strain rate and intensity spatiotemporal mapping to quantify contractile movements of the body and associated structures of the rabbit caecum when the terminal ileum was being perfused with saline at a constant rate. This perfusion caused gradual distension of the caecum as a result of relative restriction of outflow from the ampulla caecalis. The body of the caecum exhibited two patterns of motility that appeared autonomous, i.

A biomechanical model of swallowing for understanding the influence of saliva and food bolus viscosity on flavor release.

After swallowing a liquid or a semi-liquid food product, a thin film responsible for the dynamic profile of aroma release coats the pharyngeal mucosa. The objective of the present article was to understand and quantify physical mechanisms explaining pharyngeal mucosa coating. An elastohydrodynamic model of swallowing was developed for Newtonian liquids that focused on the most occluded region of the pharyngeal peristaltic wave.

Mechanistic model to understand in vivo salt release and perception during the consumption of dairy gels.

The objective of this study was to develop a model to simulate salt release during eating. Salt release kinetics during eating was measured for four model dairy products with different dynamic salty perceptions. A simple in vivo model of salt release was developed to differentiate between the contribution of the individual and of the product to salt release.

A lubrication analysis of pharyngeal peristalsis: application to flavour release.

After eating a liquid or a semi-liquid food product, a thin film responsible for the dynamic profile of aroma release coats the pharyngeal mucosa. The aim of this article was to analyse the fluid mechanics of pharyngeal peristalsis and to develop a simple biomechanical model in order to understand the role of saliva and food bolus viscosity on the coating of pharyngeal mucosa. We began by analysing the physiology and the biomechanics of swallowing in order to determine relevant model assumptions.