News

29/06/2022 - Flow induced by small intestine villi

The movement of villi in the small intestine generates a steady streaming flow to transport particles, such as those used to deliver drugs.

The popular science version of the paper is available on Sciligth.

16/11/2021 - TransportGut project is starting for 4 years!

funded by ANR

We are hiring one PhD student in experimental biofluid dynamics and one post-doc in computational fluid dynamics to understand and model flow in the small intestine at macro- and micro- scales.

01/11/2021 - New publication: Dynamics of a gel-based artificial tear film with an emphasis on dry disease treatment applications

by Mehdaoui et al., Gels, 2021, 7, 215

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. We investigated the influence of the rheological properties, namely the consistency, the yield stress, and the flow behavior index, on the spreading of a gel-based artificial tear over the cornea surface. We propose optimal values of these properties for efficient gel-based artificial tears.

25/03/2021 - New publication: Membrane emulsification for the production of suspensions of uniform microcapsules with tunable mechanical properties

by Maleki et al., Chemical Engineering Science, 2021, 237(29): 116567

A way forward for high throughput fabrication of microcapsules with uniform size and mechanical properties was reported irrespective of the kinetic process of shell assembly. Microcapsules were produced using lab-scale emulsification equipment with a micro-engineered membrane in the size range 10–100 µm. The shell of the microcapsules was assembled at the water-oil interface by complexation of polyelectrolytes or cross-linking of proteins providing two different kinetic processes. Elasticity of microcapsules was characterized with an automated extensional flow chamber.

Process parameters were optimized to obtain suspensions with size variations of 15%. Some strategies were developed to obtain uniform elastic properties according to the kinetics of shell assembly. If kinetics is limited by diffusion, membrane emulsification and shell assembly have to be split into two steps. If kinetics is limited by the quantity of reactants encapsulated in the droplet, variations of elastic properties result only from size variations.

01/01/2021 - Maturation of RheoSurf technology is starting

An automated rheometer for the characterisation of microcapsule mechanical properties

Various everyday products (eg. perfumes) are fabricated through a micro-encapsulation of an active substance that is further released upon a desired conditions. The design and fabrication of the microcapsules is often a tedious process by lack of appropriate characterization tools.

RheoSurf allows, through small deformations of capsules, the quantitative, precise and fully automated characterisation of their mechanical properties in terms of real physical properties.

01/09/2020 - Workshop on Transport in the digestive tract : experiments, modeling, applications to microbiology

22-23 Ocotober 2020, Paris, France

Organized by Claude Loverdo and Clément de Loubens

01/07/2020 - New publication: Kinetic and structural characterization of whey protein aggregation in a millifluidic continuous process

by Vilotte et al., Food Hydrocolloids, 2020, 106137

Whey protein isolates (WPI) can be aggregated upon heating to create new functional properties (e.g. texture), which depend on ag- gregate size and structural properties. In industrial conditions, aggregates are obtained in continuous processes at high temperature (≥ 75°C) in few minutes. When studying the kinetics of WPI aggregation at high temperature and under flow, one major issue is to develop a process in which heat transfer does not limit aggregation. To this end, we used a down-scaling approach in which a WPI solution flows in a heated capillary tube. We show that this process makes it possible to study both the kinetics of aggregation after few seconds and its dependence with the mean shear rate in isothermal conditions. The size and mass of aggregates and protein conformation were characterized by small-angle X-ray scattering and resonant mass measurement for a single physico-chemical condition (pH 7.0, 10 mM NaCl, 92°C, 4 % w/w WPI) which led to sub-micrometric aggregates. Firstly, we report that the size of aggregates were three times larger than when produced in a test tube. Secondly, the size and mass of aggregates reached a steady-state value in a few seconds, whereas the kinetics of aggregation and denaturation had a characteristic time of few minutes. Thirdly, the shear rate had no significant effect on the size of the aggregates, or on the aggregation kinetics. We concluded that WPI aggregation at 92°C is limited by a step of nucleation, and that the fact that aggregates produced in test tube were smaller is due to a slower thermalization.

01/03/2020 - New publication: Rheology of human faeces and pathophysiology of defaecation

by de Loubens et al., Techniques in Coloproctology, 2020, 1-7

Rectal evacuation involves multiple mechanisms that are not completely understood. The aim of this study was to quantify the rheologic property, i.e. yield stress, that governs the ease of deformation of a range of faeces of differing consistency and understand its influence on the pathophysiology of defaecation. Yield stresses of faeces of differing consistencies and Bristol scores were determined by the Vane test. We then explored the effects of this property on ease of defecation using a simple static model of the recto-anal junction based on the laws of flow for yield stress pastes and checked the conclusions by X-ray defaecography experience. The yield stress of faeces increased exponentially with their solid content, from 20 to 8000 Pa. The static model of the recto-anal junction showed that evacuation of faeces of normal consistency and yield stress is possible with moderate dilatation of the anal canal, whilst the evacuation of faeces with higher yield stress requires greater dilatation of the anal canal. X-ray defaecography showed that such increases occurred in vivo. The diameter of the recto-anal junction is increased to enable the passage of feces with high yield stress. The finite limits to such dilation likely contribute to fecal impaction. Hence difficulties in defaecation may result either from unduly high yield stress or pathologies of reflex recto-anal dilatation or a combination of the two.