A new look at bubbles during biofilm inoculation reveals pronounced effects on growth and patterning

Microfluidic membraneless microbial fuel cells: new protocols for record power densities

The main hurdle in leveraging microfluidic advantages in membraneless MFCs is their low electrode area-normalized power. For nearly a decade, maximum power densities have remained stagnant, while at the same time macrosystems continue to gather pace. To bridge this growing gap, we showcase a strategy that focuses on (i) technology improvements, (ii) establishment of record areal power densities, and (iii) presentation of different normalization methods that complement areal power densities and enable direct comparisons across all MFC scales. Using a pure-culture Geobacter sulfurreducens electroactive biofilm (EAB) in a new membraneless MFC that adheres to the strategy above, we observed optimal anode colonization, resulting in the highest recorded electrode areal power density for a microfluidic MFC of 3.88 W m-2 (24.37 kW m-3). We also consider new power normalization methods that may be more appropriate for comparison to other works. Normalized by the wetted cross-section area between electrodes accounts for constraints in electrode/electrolyte contact, resulting in power densities as high as 8.08 W m-2. Alternatively, we present a method to normalize by the flow rate to account for acetate supply, obtaining normalized energy recovery values of 0.025 kW h m-3. With these results, the performance gap between micro- and macroscale MFCs is closed, and a road map to move forward is presented.

Versatile Microfluidic Platform for Automated Live-Cell Hyperspectral Imaging Applied to Cold Climate Cyanobacterial Biofilms

Microfluidic bioanalytical platforms are driving discoveries from synthetic biology to the health sciences. In this work, we present a platform for in vivo live-cell imaging and automated species detection in mixed cyanobacterial biofilms from cold climate environments. Using a multimodal microscope with custom optics applied to a chip with six parallel growth channels, we monitored biofilm dynamics via continuous imaging at natural irradiance levels. Machine learning algorithms were applied to the collected hyperspectral images for automatic segmentation of mixed-species biofilms into individual species of cyanobacteria with similar filamentous morphology. The coupling of microfluidic technology with modern multimodal imaging and computer vision systems provides a versatile platform for the study of cause-and-effect scenarios of cyanobacterial biofilms, which are important elements of many ecosystems, including lakes and rivers of the polar regions.

A surface spectroscopy study of a Pseudomonas fluorescens biofilm in the presence of an immobilized air bubble

A linear spectral mapping technique was applied to monitor the growth of biomolecular absorption bands at the bio-interface of a nascent Pseudomonas fluorescens biofilm during and after interaction with a surface-adhered air bubble. Attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectra were obtained in different locations in a microchannel with adequate spatial and temporal resolution to study the effect of a static bubble on the evolution of protein and lipid signals at the ATR crystal surface. The results reveal that the presence of a bubble during the lag phase modified levels of extracellular lipids and affected a surface restructuring process, many hours after the bubble's disappearance.

Removal of Bacteria from Solids by Bubbles: Effect of Solid Wettability, Interaction Geometry, and Liquid-Vapor Interface Velocity

Air bubbles are a promising means of controlling fouling for a range of applications, particularly delaying fouling in marine environments. This work investigates the mechanism by which the collision of an air bubble with a solid removes adsorbed bacteria. A key feature of the work is that the numbers of bacteria were monitored via video microscopy throughout the collision; so, we were able to explore the mechanism of bacteria removal. When a bubble collides with a solid, an air-liquid interface crosses the solid twice, and we were able to distinguish the effects of the first and second air-liquid interfaces. The bacterium Pseudomonas aeruginosa was allowed to adhere to smooth poly(dimethylsiloxane) and then a collision with a bubble was investigated for one of three different approach geometries: perpendicular, parallel, and oscillating parallel to the solid surface. Other factors examined were the speed of the bubble, the duration of bacterial adhesion on the solid surface, and the wettability of the solid. Surface wettability was identified as the most significant factor. When the solid dewet, almost all bacteria were removed from hydrophobic surfaces upon the passage of the first air-liquid interface. In contrast, when a thin liquid film remained between the solid and the bubble (a hydrophilic solid), variable amounts of bacteria remained. Although almost all bacteria were initially removed from hydrophobic solids, many bacteria were redeposited on hydrophobic surfaces upon the passage of the second air-liquid interface, especially when the first and second air-liquid interfaces moved in opposite directions. As described previously, a lower velocity of the bubble allows more time for the thin liquid film to drain and improved removal efficiency on hydrophilic solids. A rougher solid (8 μm diameter hemispherical protrusions) decreased the detachment efficiency because bacteria and liquid were able to shelter in concavities.

On the nature of "skeletal" biofilm patterns, "hidden" heterogeneity and the role of bubbles to reveal them

A short communication on the recent paper by Jang et al. discusses the role of “mushroom” structures and effects of nearly static bubbles on nascent biofilms.

Microfluidic bioanalytical flow cells for biofilm studies: a review

Bacterial biofilms are among the oldest and most prevalent multicellular life forms on Earth and are increasingly relevant in research areas related to industrial fouling, medicine and biotechnology. The main hurdles to obtaining definitive experimental results include time-varying biofilm properties, structural and chemical heterogeneity, and especially their strong sensitivity to environmental cues. Therefore, in addition to judicious choice of measurement tools, a well-designed biofilm study requires strict control over experimental conditions, more so than most chemical studies. Due to excellent control over a host of physiochemical parameters, microfluidic flow cells have become indispensable in microbiological studies. Not surprisingly, the number of lab-on-chip studies focusing on biofilms and other microbiological systems with expanded analytical capabilities has expanded rapidly in the past decade. In this paper, we comprehensively review the current state of microfluidic bioanalytical research applied to bacterial biofilms and offer a perspective on new approaches that are expected to drive continued advances in this field.