Laboratoire Matière et Systèmes Complexes

Flows and interfaces at micro scales : the gut and the microcapsule

Clément de Loubens

Laboratoire Rhéologie et Procédés, CNRS, Université Grenoble-Alpes

In this talk, I will present two different parts of my research activities. The first one concerns the flow at macro and micro scales generated by small intestine mucosa, an active biological interface. During the second part of my talk, I will present several experiments concerning the interfacial rheology, the dynamics and the stability (wrinkles, folds, and break-up) of microcapsules in flow.

Flow induces by active intestinal mucosa at macro- and micro- scales

Controlling the spatio-temporal delivery of drugs or nutrients in the gastro-intestinal tract is of prime importance to improve pharmaceutical treatments or to control the nutritional properties of food products. The major constraints to such mixing are the high viscosity and the non-Newtonian characteristics of the gastro-intestinal content and the low velocity of the active mucosa, which together result in low Reynolds numbers. It is most likely that transfers in the lumen should limit biochemical reactions. Hence, it is essential to understand and model the mixing strategies developed by the digestive tract.

To identify the relevant biomechanical and rheological factors that limit mixing and absorption in the small intestinal lumen, we have developed methods of high fidelity quantification of intestinal motility, coupled to realistic models of intestinal fluid dynamics as well at the scale of smooth muscle activity (1 mm), as at the one of villi, finger-like structures of around 500 μm length covering intestinal mucosa.

At macroscopic scale, we show that activity of smooth muscles are organised into domains of contractions. This activity is responsible for a process of shear dispersion of the luminal content in the longitudinal direction.

At microscopic scales, villous movement during longitudinal contractions is a major radial mixing mechanism that increases dispersion and absorption around the mucosa despite adverse rheological properties of the digesta.

Finally, we conclude that the intestinal mucosa can be considered as an active microfluidic mixer.

Microcapsules in flow : from interfacial rheology to wrinkling instability

Microcapsules are promising objects to control the spatio-temporal delivery of drugs, nutrients or chemicals. These substances are encapsulated in micro-drops, protected from the external fluid by a thin elastic membrane (typically less than few micrometres thick) and released by rupture, fusion or cyclic deformations of the membrane. These objects have the feature to be highly deformable under flow. In this talk, we will discuss about their dynamics in simple flow and the emergence of wrinkles when microcapsules are stretched.

Firstly, extensional flow is used to characterize the elastic properties of microcapsules up to the break-up. In the regime of large deformations, the microcapsules can present a non-linear elastic response or plastic deformations. Non-linear elastic constitutive law is deduced by comparison of the evolution of the shape of the microcapsule in the two main planes of deformation of the capsule with numerical simulations.

Secondly, in shear flow, the rotation of the membrane, i.e. the tank-treading, is visualised and quantified by decorating the membrane of microcapsules with particles. The tracking of the distance between two close microparticles showed membrane contraction at the tips and stretching on the sides. This dynamic of deformation induce viscous dissipation inside the membrane. The order of magnitude of membrane viscosity is determined by comparison with numerical simulations.

Finally, wrinkles instability is observed in extensional flow and studied by varying the interfacial properties of the microcapsules. In this way, the phase diagram of wrinkle instability for microcapsules has been deduced.

References :

Lim et al . 2015, Food & Function, 6 (6), 1787-1795

Lentle et de Loubens, 2015, Journal of Comparative Physiology B 185 (4), 369-387

de Loubens et al, 2014 Plos One, 9 (4), e95000

de Loubens et al. , 2013, Journal of the Royal Society Interface, 10 (83), 20130027

de Loubens et al. , 2014, Soft Matter, 10:25, 4561-4568

de Loubens et al. , 2015, J. Fluid. Mech., 767, R3

de Loubens et al. , 2016, J. Fluid. Mech., 789, 750-767

Xie et al., 2017 Soft Matter, 13:36, 6208-6217