Skip to main content

Complex Fluid Interfaces in Biomedical and Industrial Multiphase Flows

Final Report Summary - COMPFLIX (Complex Fluid Interfaces in Biomedical and Industrial Multiphase Flows)

COMPFLIX addresses the role of complex interfaces in multiphase flows of relevance to industrial and biomedical processes. Fluid interfaces in biomedical flows and industrial processing flows typically present complex microstructures due to adsorption of surfactant molecules or solid particles. The mechanical properties of these complex fluid interfaces have significant impact on the function and performance of the system. COMPFLIX investigates the emerging behaviors upon deformation of complex interfaces, and the link with their mechanical properties. Two types of complex interfaces are considered: fluid interfaces that are coated with solid particles, and cell membranes.

Particle-coated interfaces are common in food and cosmetic products, oil recovery, and catalysis. In this project, we have discovered that particle-stabilised bubbles can be used as delivery vehicles that release their cargo of particles with an ultrasound trigger. We have demonstrated complete particle release in under a millisecond. The attachment of particles onto drops and bubbles is typically considered to be irreversible because of the large energy barrier for particle detachment. Our method is programmable in time, and does not require any physicochemical modification of the fluids or the interface. This work addresses the emerging need for methods to recover interfacial particles from emulsions and foams in applications ranging from controlled release to interfacial catalysis and gas storage. In addition, we have developed a method to synthesize polymer-nanoparticle capsules with controlled internal microstructure and external shape, based on thermodynamics, phase inversion and directional solidification during solvent extraction. We have demonstrated a unique mechanism of delivery of nanoparticle clusters from these capsules by bursts, with implications for controlled release applications.

The deformation and rupture of cell membranes are of crucial importance for drug delivery, in which drug molecules need to enter the cell, and bioprocessing applications, in which products synthesized inside the cell need to be extracted. We have demonstrated that differences in lipid membrane and vesicle properties can enable selective flow-induced vesicle break-up. We obtained vesicle populations with different membrane properties by using different lipids and lipid:cholesterol mixtures. We subjected vesicles to large deformations in the acoustic microstreaming flow generated by ultrasound-driven microbubbles. By simultaneously deforming vesicles with different properties in the same flow, we determined the conditions in which rupture is selective with respect to the membrane stretching elasticity. Our work should enable new sorting mechanisms based on the difference in membrane composition and mechanical properties between different vesicles, capsules, or cells. We have further applied this method to the permeabilisation of microalgal cell membranes. Cell rupture induced by ultrasound is central to applications in biotechnology. For instance, cell disruption is required in the production of biofuels from microalgae. Ultrasound-induced cavitation, bubble collapse and jetting are exploited to induce sufficiently large viscous stresses to cause rupture of the cell membranes. However, our fundamental understanding of the conditions for rupture of microalgae in the complex flow fields generated by ultrasound-driven bubbles is still limited. We have performed a fluoresence uptake essay to visualize the miscroscale details of the interaction of Chlamydomonas reinhardtii with ultrasound-driven microbubbles. These measurements reveal permeabilisation of the cell wall even in the gentle microstreaming flow of oscillating microbubbles, without the occurrence of violent cavitation phenomena, contrary to previous expectations. This finding opens up the potential for energy-efficient biofuel production from microalgae.