RHEOLYMPH: studying the behaviour of lymph through experimental and computational microfluidics

All cells and body tissues are immersed in a fluid originating from the blood circulation called the interstitial liquid, which provides the cells with the necessary nutrients and in return, collects the metabolic excretes or wastes. When taken up from the interstitial space by lymph capillaries, this liquid is referred to as lymph. Lymph is conveyed through a network of lymphatic vessel towards specific glands where it is cleaned up and returned to the blood circulation. The lymphatic system has therefore an important function in the conservation of the plasma volume but also in the immune system: while it is mainly composed of plasma, it contains and transports lymphocytes (and other leucocytes), antigens, as well as waste products, cellular debris, and bacteria.

Troubles in lymph circulation, in particular valve defects in lymphatic capillaries, have been shown to underlie the pathogenesis of lymphatic distichiasis which affects over a hundred million people worldwide. In the present state of the art, computational and experimental studies are clearly needed for a deeper understanding of lymph flow.

Among the basic unresolved questions is the one of lymph rheology. Due to the important protein content of the plasma, and to the cellular or macromolecular content of lymph, both substantially affecting its rheology and viscoelastic properties, lymph cannot be considered as a Newtonian fluid.

This project proposes to develop a set of computational and experimental studies aimed at developing a thorough understanding of the complex flow behaviour of lymph that will be vital to appreciate lymph transport and its influence on immune cell/antigen migration.

The strategy of this project is to associate in situ observations thanks to a new in vivo approach where the lymphatic system is linked to the cardiovascular system through surgery, and micro-rheometric methods to capture the visco- elastic properties of lymph under close-to-real conditions (in terms of confinement or flow rate).

From the computational perspective, the main challenges lie in the modelling of a complex suspension, possibly a viscoelastic fluid with deformable suspended cells, in flows involving fluid- structure interactions.