Recruitment
Internship
Lymph transport: flow induced by active fluid-structure interactions
The lymphatic vascular system ensures the transport of interstitial fluid from the tissues to the cardiovascular system across the whole body of mammals. Contrary to blood, lymph is not transported via a central pump but via local actuations controlled by active feedback loops. Within collecting lymphatics, the combination of self-regulated contractions of muscles surrounding the lymphatic channels [1,2] and asymmetric protuberances (see Fig. 1), called leaflets, anchored along the channel generate unidirectional flows. This process appears to be the most robust way to control the transport of lymph across a very complex network of channels. Yet, the physical understanding of this process is very limited [3, 4]. During previous studies, a macroscopic model experiment of a lymphatic channel has been developed. Results show that the structure of the channel and the nature of the channel actuation (amplitude, frequency, etc.) are directly related to optimised fluid transport. One key parameter of lymph transport is the presence of feedback loops that trigger the deformation of the lymphatics upon local flow measurements.
The internship is focused on extending previous results toward the study of feedback loop based (i.e. active) deformations. The student will perform experiments on the previously developed setup on which deformation will not anymore be predetermined, but self-induced by fluid flow. He/She will then post-process the data (image analysis, flow measurement, etc.) and model how fluid transport emerges from active deformations. These results will then be compared with previously obtained in vivo measurements in order to conclude on the nature of active fluid-structure interaction leading to lymph transport.
Internship informations :
Duration : 5-6 months
Grant : 600 euros per month
Degree : from L3 to M2
Starting from February 2021.
Location : IRPHE, 49 Rue F. Joliot Curie 13013 Marseille
Contact: brandenbourger@irphe.univ-mrs.fr
References:
[1] Kunert, C., et al., Mechanobiological oscillators control lymph flow. Proceedings of the National Academy of Sciences, 2015. 112(35): p. 10938.
[2] Brandenbourger, M., et al., Tunable flow asymmetry and flow rectification with bio-inspired soft leaflets. Physical Review Fluids, 2020. 5(8): p. 084102.
[3] Moore, J.E. and C.D. Bertram, Lymphatic System Flows. Annual Review of Fluid Mechanics, 2018. 50(1): p. 459-482. [4] Scallan, J.P., et al., Lymphatic pumping: mechanics, mechanisms and malfunction. J Physiol, 2016. 594(20): p. 5749-5768.
Internship
Self-oscillation of bio-inspired active solids
Assemblies of active, dynamic, or driven elements, called active solids, can harbour unique largescale mechanical properties such as one-way transport, non-reciprocity, and self-oscillation. While self-oscillations are a prominent characteristic of large and complex living systems [1,2], little is known about the mechanisms that trigger them and their associated vibration modes. In a previous study [3], we showed, using theoretical and experimental models, how an elastic beam subject to local active body forces can self-oscillate. Fig. 1 describes the experimental setup. An elastic beam, in blue, is connected to 7 self-propelling robots (called HEXBUG, see Fig. 1B) that apply local active forces depicted as red arrows in Fig. 1A.
The internship is focused on extending previous results toward the study 2D structures built from the same principle as in Fig. 1. The student will devise various 2D shapes (from simple structures to bio-inspired ones) and study via image analysis the different modes of oscillation that emerge from this active solid. He/She will then model how the ratio between active forces and elasticity controls the amplitude and frequency of the oscillations. The results will be a primordial first step toward an overall better understanding of active deformations in active solids. These results will open the way to a better modelling of living systems and the development of soft robots and smart materials that are able to move in complex environments or to smartly interact with their surroundings.
Internship informations :
Duration : 5-6 months
Grant : 600 euros per month
Degree : from L3 to M2
Starting from February 2021.
Location : IRPHE, 49 Rue F. Joliot Curie 13013 Marseille
Contact: brandenbourger@irphe.univ-mrs.fr
References:
[1] Sekimoto, K., et al., Symmetry Breaking Instabilities of an In Vitro Biological System. Physical Review Letters, 75(1) 172-175 (1995).
[2] Lo, C.-J., et al., Mechanism and kinetics of a sodium-driven bacterial flagellar motor. Proceedings of the National Academy of Sciences, 110(28): E2544-E2551 (2013).
[3] E. Zheng, et al, Self-oscillation and Synchronisation Transitions in Elasto-Active Structures, arXiv preprint arXiv:2106.05721 (2021).