Periodic Reporting for period 1 - Flow4Algae (Flows for Algae Growth: Uncovering the multi-scale dynamics of living suspensions)
Periodo di rendicontazione: 2023-01-01 al 2025-06-30
The urgent need to reduce greenhouse gas emissions has accelerated the search for sustainable alternatives to fossil fuels. Microalgae offer a promising solution due to their ability to capture CO2 and convert it into biofuels and valuable bioproducts. Unlike traditional crops, they have rapid harvesting cycles, can utilize wastewater as nutrients, and do not compete with food production. Despite these advantages, large-scale application faces significant technical challenges, particularly in optimizing bioreactor design, transport processes, and harvesting methods. A key obstacle lies in understanding the complex fluid dynamics of microalgae suspensions, where living cells behave as active particles in a multiphase flows and respond dynamically to environmental factors such as light, nutrients, and shear stress. Addressing this knowledge gap is crucial for improving the efficiency and scalability of microalgae-based technologies.
This project tackles these fundamental challenges by examining three critical aspects of microalgae fluid dynamics: (Objective 1) turbulence effects on large- and small-scale flow interactions, (Objective 2) behavior at solid and free interfaces, and (Objective 3) response to shear deformation. The interplay between fluid dynamics and cell physiology is a key factor influencing microalgae growth, motility, and distribution. Understanding these mechanisms is crucial for enhancing bioreactor performance, as inefficient mixing and nutrient distribution limit productivity. By leveraging advanced experimental techniques—including microfluidics, 3D cell tracking, and rheology tools—this project will generate new insights into microalgae transport and distribution. These findings will guide the design of next-generation bioreactors and optimizing biomass harvesting for industrial applications.
This project tackles these fundamental challenges by examining three critical aspects of microalgae fluid dynamics: (Objective 1) turbulence effects on large- and small-scale flow interactions, (Objective 2) behavior at solid and free interfaces, and (Objective 3) response to shear deformation. The interplay between fluid dynamics and cell physiology is a key factor influencing microalgae growth, motility, and distribution. Understanding these mechanisms is crucial for enhancing bioreactor performance, as inefficient mixing and nutrient distribution limit productivity. By leveraging advanced experimental techniques—including microfluidics, 3D cell tracking, and rheology tools—this project will generate new insights into microalgae transport and distribution. These findings will guide the design of next-generation bioreactors and optimizing biomass harvesting for industrial applications.
A shear flow cell was developed to study the transport of microswimmers in shear flows, enabling real-time observation of microalgae interactions with fluid dynamics. This optically accessible device generates flows ranging from laminar to turbulent regimes and accommodates multiple flow geometries, enhancing the ability to track cell behavior under various conditions. The system was integrated with a multi-camera microscope facility to obtain 3D positional tracking of individual microswimmers and analyze their movement patterns.
To investigate turbulence interactions (Objective 1), the shear flow cell was adapted into a Taylor-Couette (TC) setup, allowing exploration of microalgae behavior in a wide range of flow conditions and vortical structures. A Laser Induced Fluorescence (LIF) system was implemented to visualize microalgae distribution within vortical structures, revealing inhomogeneities in cell positioning and motility-induced vortex destabilization. High-density suspensions were also analyzed to assess their impact on large-scale turbulence using torque measurements in the TC system’s inner cylinder.
For understanding microalgae behavior at interfaces (Objective 2), a microfluidic platform was developed to generate and manipulate free surfaces and interfacial dynamics. The system enables precise manipulation of cells using only hydrodynamic forces, allowing real-time study of interactions at gas-liquid and liquid-liquid interfaces. Additionally, a microfabricated membrane platform was designed to trap cells, facilitating investigations into biofilm formation, flow generation, and flagellar coordination at solid interfaces. These tools are crucial for studying the ecological and industrial applications of microalgae.
Regarding microalgae rheology and response to shear (Objective 3), rheological studies on Chlamydomonas reinhardtii revealed a transition from Newtonian-like to Bingham-plastic behavior, determined by activity levels. This was a theoretically predicted effect but had not been previously observed experimentally. The study also demonstrated the emergence of collective dynamics within suspensions that enable this transition. Additionally, experiments showed that microswimmer suspension properties can be reversibly modulated by external stimuli such as temperature, revealing new possibilities for intelligent fluid systems with tunable properties.
To investigate turbulence interactions (Objective 1), the shear flow cell was adapted into a Taylor-Couette (TC) setup, allowing exploration of microalgae behavior in a wide range of flow conditions and vortical structures. A Laser Induced Fluorescence (LIF) system was implemented to visualize microalgae distribution within vortical structures, revealing inhomogeneities in cell positioning and motility-induced vortex destabilization. High-density suspensions were also analyzed to assess their impact on large-scale turbulence using torque measurements in the TC system’s inner cylinder.
For understanding microalgae behavior at interfaces (Objective 2), a microfluidic platform was developed to generate and manipulate free surfaces and interfacial dynamics. The system enables precise manipulation of cells using only hydrodynamic forces, allowing real-time study of interactions at gas-liquid and liquid-liquid interfaces. Additionally, a microfabricated membrane platform was designed to trap cells, facilitating investigations into biofilm formation, flow generation, and flagellar coordination at solid interfaces. These tools are crucial for studying the ecological and industrial applications of microalgae.
Regarding microalgae rheology and response to shear (Objective 3), rheological studies on Chlamydomonas reinhardtii revealed a transition from Newtonian-like to Bingham-plastic behavior, determined by activity levels. This was a theoretically predicted effect but had not been previously observed experimentally. The study also demonstrated the emergence of collective dynamics within suspensions that enable this transition. Additionally, experiments showed that microswimmer suspension properties can be reversibly modulated by external stimuli such as temperature, revealing new possibilities for intelligent fluid systems with tunable properties.
For objective 2, we developed a microfluidic platform that enables real-time particle and cell manipulation, providing insights into cell-flow interactions with implications for technology, medicine, and microbial ecology. Unexpectedly, we found that the system also facilitates flow manipulation for rheological measurements, overcoming limitations of conventional rheometers by dynamically shaping co-flow boundaries for precise viscosity and relaxation time assessments.
For objective 3, our rheology experiments revealed that microswimmer suspensions undergo a transition from Newtonian-like to Bingham-plastic behavior, driven by activity levels—an effect previously predicted but now observed experimentally for the first time. This transition appears linked to emergent collective dynamics and can be reversibly modulated by external stimuli such as temperature, demonstrating the potential for intelligent fluid systems with tunable properties.
For objective 3, our rheology experiments revealed that microswimmer suspensions undergo a transition from Newtonian-like to Bingham-plastic behavior, driven by activity levels—an effect previously predicted but now observed experimentally for the first time. This transition appears linked to emergent collective dynamics and can be reversibly modulated by external stimuli such as temperature, demonstrating the potential for intelligent fluid systems with tunable properties.