Bending and Stretching of Soft Pores Enable Passive Control of Fluid Flows

Abstract

Programmable valves and actuators are widely used in man-made systems to provide sophisticated control of fluid flows. In nature, however, this process is frequently achieved using passive soft materials. Here we study how elastic deformations of cylindrical pores embedded in a flexible membrane enable passive flow control. We develop biomimetic valves with variable pore radius, membrane radius, and thickness. Our experiments reveal a mechanism where small deformations bend the membrane and constrict the pore-thus reducing flow-while larger deformations stretch the membrane, expand the pore, and enhance flow. We develop a theory capturing this highly nonmonotonic behavior, and validate the scaling across a broad range of material and geometric parameters. Our results suggest that intercompartmental flow control in living systems can be encoded entirely in the physical attributes of soft materials. Moreover, this design could enable autonomous flow control in man-made systems.

Poroelastic plant-inspired structures & materials to sense, regulate flow, and move

“…soft robotics, surgery, or drug delivery. Other examples of plant-inspired designs leveraging poroelasticity have been used recently for biomimetic microrobotics [108,109], passive actuators [38,70,110,111], propulsion devices [112], morphing wings [113], car designs [114], and tactile sensors [115][116][117]. All of these examples translate multi-scale signaling and response to useful functionalities that will inspire exciting new designs across many scientific disciplines.…”

“…Inspired by this effect of pressure on the opening of a channel in a membrane, Louf et al [70] investigated how a simple hole in a membrane, a ubiquitous geometry in plants, also present in plants' plasmodesmata or fungi' septa (see figure 2(a)), can alter dramatically the flow rate depending only on the membrane's geometry and mechanical properties (see sketch in figure 2(b)).…”

“…The shrinking or expansion of a hole naturally has an effect on the flow characteristics and is the subject of this second step. If we assume a pressureinduced flow of an incompressible liquid at low Reynolds number in a long cylindrical pipe, also referred as Poiseuille flow [70,73], it is possible to use the new pore radius following bending or stretching of the membrane, to calculate the subsequent hydraulic resistance of the poroelastic membrane. By doing so, we observe that this variation in the hole diameter has a huge effect on the flow, increasing the hydraulic resistance at pressures lower than P e but reducing it at higher pressures.…”

The fluidic memristor as a collective phenomenon in elastohydrodynamic networks

“…Artificial and biologically-inspired microfluidic networks are rapidly evolving to incorporate nonlinear elements and more complex topologies [30][31][32][33][34][35][36][37][38][39][40][41][42] , including several examples of artificial valves, some of which exhibit NDR 14,33,35,36,[42][43][44][45][46][47][48] . Although connecting these nonlinear valves in fluid networks could be straightforward, we will show that complex phenomena emerges when: (i) the system is able to locally store volume and (ii) the local volume changes are coupled to the pressure distribution along the system.…”

Clogging of a Rectangular Slit by a Spherical Soft Particle

“…More extreme cases emerged in the case of air-liquid flows within flexible tubes, where surface tension led to a complete airway closure [8]. These effects of wall elasticity of the fluid flow have been used to explain sap flow in green plants [9] or to create soft valves for technological applications [10][11][12].…”