Soft channels: from bifurcation to wrinkling

  • Haolin Li

Student thesis: Phd


Soft channels, i.e. pathways with compliant boundaries, are ubiquitous in living systems like human blood vessels and airways. In order to understand the fluid-structure-interaction that drives the flow in such systems, we present two bench top models in this journal format thesis. We start with a Y-shaped elasto-rigid Hele-Shaw channel at macro-scale, and study experimentally the air finger propagation in this system. This allows us to model the role of elasticity and bifurcation in the problem of airway reopening. We observe steady finger propagation in the main channel, which is lost ahead of bifurcation and then recovered in the daughter channels. Despite minor differences in the channel geometry, the modes of finger propagation in the main and daughter channels are similar at low levels of initial collapse. However, at high levels of initial collapse, the dynamics of reopening becomes more complicated, and even reveals multiple fingering modes in the daughter channels developed from indistinguishable fingers in the main channel. We also characterise the recovery of steady states post-bifurcation and elucidate the underlying mechanism. Aiming to develop a multi-generational elasto-rigid network, then we propose a robust protocol for manufacturing PDMS microchannels topped with soft membranes as a scale-down but generation-inclusive model. While characterising its material properties, we investigate the swelling-induced wrinkling of its soft upper membrane. We find that if the membrane is pre-inflated using constant pressure before swelling, it experiences anisotropic stresses, which results in two distinct buckling instabilities as the swelling progresses. The membrane firstly buckles into small-amplitude varicose wrinkles, which develop into coarsened patterns of folds. The morphology of coarsened patterns depends on the pre-inflation degree. Using experimental and numerical techniques, we clarify the fundamental mechanism driving this buckling phenomenon and propose it as a method to reliably produce microchannels with versatile corrugated morphologies.
Date of Award1 Aug 2014
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorAnne Juel (Supervisor) & Draga Pihler-Puzovic (Supervisor)


  • Buckling instability
  • Microchannel
  • Swelling
  • Soft channel
  • Hele-shaw flow

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