PEM in micro / nanofluidics for novel BioMEMS platforms

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering; and, (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 67-71).The overall goal of this thesis was to exploit the versatility of the polyelectrolyte multilayer (PEM) to fabricate a novel micro/nanofluidic device for patterning bacteria in BioMEMS. Nanofluidic channels offer new opportunities for advanced biomolecule manipulation and separation science because they provide unique capabilities such as ion-perm selectivity and nanometer-sized structures. In order to establish industrial applications for biotechnology and medicine, including separation of biomolecules, drug delivery, and single molecule detection, however, regular planar nanofluidic channels have limited fluidic conductance that results low throughput. Therefore, it would be important to develop a robust engineering platform with precise control of depth to the nanometer scale without channel collapse. Nanochannel-induced fluidic conduction can be enhanced by controlling the channel gap size for increasing electrical double layer (EDL) overlap as well as fabricating high-throughput vertical nanofluidic channels. We have fabricated a vertical nanofluidic channel by anisotropic etching of silicon. The gap size of the vertical nanochannel was as low as 50 nm, as obtained by layer-by-layer deposition of polyelectrolyte. Silicon-to-glass bonding was achieved by electrostatic interaction at lower temperature (180 'C) than conventional anodic bonding temperatures (300-400 C), and even at room temperature (25 C). The second part of this thesis focuses on patterning bacteria on polyelectrolyte multilayers. Patterns of bacteria are of growing interest in biofilm formation and the broader area of microbial ecology. A simple method to create functionalized surfaces for efficient micro-patterning of bacteria is presented, based on the use of micromolding in capillaries (MIMIC) of poly(ethylene glycol)-poly(lactide) diblock copolymer (PEG-PLA) onto polyelectrolyte multilayers. Two different implementations showed excellent selective antibiofouling results for micropatterning of bacteria.by Hongchul Jang.S.M

Resilience of bacterial quorum sensing against fluid flow

Quorum sensing (QS) is a population-density dependent chemical process that enables bacteria to communicate based on the production, secretion and sensing of small inducer molecules. While recombinant constructs have been widely used to decipher the molecular details of QS, how those findings translate to natural QS systems has remained an open question. Here, we compare the activation of natural and synthetic Pseudomonas aeruginosa LasI/R QS systems in bacteria exposed to quiescent conditions and controlled flows. Quantification of QS-dependent GFP expression in suspended cultures and in surface-attached microcolonies revealed that QS onset in both systems was similar under quiescent conditions but markedly differed under flow. Moderate flow (Pe > 25) was sufficient to suppress LasI/R QS recombinantly expressed in Escherichia coli, whereas only high flow (Pe > 102) suppressed QS in wild-type P. aeruginosa. We suggest that this difference stems from the differential production of extracellular matrix and that the matrix confers resilience against moderate flow to QS in wild-type organisms. These results suggest that the expression of a biofilm matrix extends the environmental conditions under which QS-based cell-cell communication is effective and that findings from synthetic QS circuits cannot be directly translated to natural systems

Temperature-evolution of spectral function and optical conductivity in heavy fermion compound Ce2_{2}IrIn8_{8} under crystalline electric field

We investigate the role of the crystalline electric field (CEF) in the temperature ($T$)-evolution of the Kondo resonance states and its effect on optical conductivity. We perform the combined first principles calculation of the density functional theory and dynamical mean field theory on Ce$_{2}$IrIn$_{8}$. The calculated spectral function reproduces the experimental observed CEF states at low $T$, while it shows a drastic change of the Fermi surface upon increasing $T$. The effect of the CEF states on the Fermi surface as a function of $T$ is elucidated through the first principles calculations as well as the analysis on the Anderson impurity model. Consequently, we suggest the importance of the CEF-driven orbital anisotropy in the low-energy states of optical experiments.Comment: 6 pages, 4 figure

The dynamics of surface detachment and quorum sensing in spatially controlled biofilm colonies of Pseudomonas aeruginosa

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2014.Cataloged from PDF version of thesis.Includes bibliographical references.Biofilms represent a highly successful life strategy of bacteria in a very broad range of environments and often have negative implications for industrial and clinical applications, as their removal from surfaces and the prevention of biofouling in the first place represent formidable and to date unmet challenges. At the same time, biofilms modulate important natural processes, including nutrient cycling in rivers and streams and the clogging of porous materials. Biofilm development is a dynamic process, dependent on a host of cellular and environmental parameters that include, among others, hydrodynamic environment and the communication among cells (QS). Here we used microfluidics and micro-contact printing, paired with video-microscopy and image analysis, to study several aspects relating to the temporal dynamics of bacterial biofilms. Beyond reporting on specific findings from these experiments, we demonstrate how these innovative technologies can aid in obtaining a new layer understanding on biofilm processes and biofilm removal, thanks to unprecedented control over the biofilm's microenvironment. In a first set of experiments (chapter 2), we cultured Pseudomonas aeruginosa biofilms in a microfluidic channel for different times, after which we used the passage of an air plug as a mechanical insult to drive detachment. We found that the adhesion properties of an early-stage biofilm have a strong correlation with the time of growth and that biofilm detachment can occur in a spatially heterogeneous manner characterized by a regular pattern of 'holes' in the original biofilm. The resulting spatial distribution of bacteria correlates with the distribution of the extra polymeric substance (EPS) matrix before the insult, indicating that the locations of the holes correspond to where there was the least EPS. These results demonstrate that the detachment mechanism is a competition between the shear force exerted by the external flow and the local adhesion force of a given patch of biofilm, in turn governed by the local amount of EPS. This mechanism, and the observed heterogeneity in the detachment, imply that even at rather high shear rates, where the bulk of the biofilm is removed, local strongholds survive detachment, and may represent seeds for the colony to reform. In a second set of experiments (chapter 3), we examined the effects of patch size and hydrodynamic environment on QS induction on spatially defined patches of Pseudomonas aeruginosa biofilm. We found that the smaller biofilm patches start QS earlier than those in the larger patches. However at later times the proportion of auto-induced bacteria (normalized by the surface area covered by the cells) is higher in the larger patches. We expanded on these findings by investigating the contribution of flow to QS induction on the patches. The effect of ambient fluid flow was to accelerate the induction of quorum sensing compared to static conditions at moderate flow rates, due to the increase in the convective supply of nutrients and to quench quorum sensing at high flow rates, due to the autoinducer signal being washed out by flow. These findings establish microfluidics as a new tool in the study of biofilms, which enables both accurate control over microenvironmental conditions and direct observation of the dynamics of biofilm formation and disruption. Chapter 4 deepens the exploration of the role of micro-spatial heterogeneity on microbial processes by presenting a numerical model of how heterogeneity and microbial behavior (chemotaxis) affect trophic in a microbial food web. Results show that the intensity of the trophic transfer strong depends on the motile behavior of the different trophic levels: trophic transfer is enhanced when directional motility towards resource patches outweighs the random component of motility inherent in all microbial locomotion. Finally, in the Appendices, we demonstrate how the methods developed in this thesis can help in the assessment of the antifouling capabilities of new-generation surfaces, designed to prevent fouling and in the assessment of the cell adhesion on surfaces, fabricated with an arrangement of spatially localized hydrophobic patterns. In summary, this thesis demonstrates that use of new micro-technology and associated mathematical modeling enables new insights into the colonial life form of microorganisms and may provide impetus for new approaches to prevent biofouling on surfaces or remove biofilms from surfaces.by Hongchul Jang.Ph. D

Biofilm disruption by an air bubble reveals heterogeneous age-dependent detachment patterns dictated by initial extracellular matrix distribution

Bacteria often adhere to surfaces, where they form communities known as biofilms. Recently, it has been shown that biofilm formation initiates with the microscopically heterogeneous deposition of a skeleton of extracellular polymeric substances (EPS) by individual cells crawling on the surface, followed by growth of the biofilm into a surface-covering continuum. Here we report microfluidic experiments with Pseudomonas aeruginosa biofilms showing that their “hidden” heterogeneity can affect the later dynamics of their disruption. Using controlled air bubbles as a model for mechanical insult, we demonstrate that biofilm disruption is strongly dependent on biofilm age, and that disruption to early-stage biofilms can take the shape of a semi-regular pattern of ~15 µm diameter holes from which bacteria have been removed. We explain hole formation in terms of the rupture and retreat of the thin liquid layer created by the long bubble, which scrapes bacteria off the surface and rearranges their distribution. We find that the resulting pattern correlates with the spatial distribution of EPS: holes form where there is less EPS, whereas regions with more EPS act as strongholds against the scraping liquid front. These results show that heterogeneity in the microscale EPS skeleton of biofilms has profound consequences for later dynamics, including disruption. Because few attached cells suffice to regrow a biofilm, these results point to the importance of considering microscale heterogeneity when designing and assessing the effectiveness of biofilm removal strategies by mechanical forces

Synergistic Prevention of Biofouling in Seawater Desalination by Zwitterionic Surfaces and Low-Level Chlorination

Smooth, durable, ultrathin antifouling layers are deposited onto commercial reverse osmosis membranes without damaging them and they exhibit a fouling reduction. A new synergistic approach to antifouling, by coupling surface modification and drinking-water-level chlorination is enabled by the films' unique resistance against chlorine degradation. This approach substantially enhances longer-term fouling resistance compared with surface modification or chlorination alone, and can reduce freshwater production cost and its collateral toxicity to marine biota.United States. Advanced Research Projects Agency-Energy (Award AR0000294)Center for Clean Water and Clean Energy at MIT and KFUPMNational Science Foundation (U.S.) (Grant OCE-6917641-CAREER)National Science Foundation (U.S.) (Grant CBET-6923975)National Institutes of Health (U.S.) (Grant 6917755)Samsung (Firm) (Fellowship

Polyphenols Coordinated with Cu (II) in an Aqueous System Build Ion-Channel Coatings on Hair Surfaces

Recently, developments in the field of cosmetics have led to a renewed interest in hair dyeing. However, damage to the hair during the dyeing process has increased hesitation in attempting hair dyeing. As a result, hair dyes with minimal side effects have been in constant demand, and are being developed. In this study, natural-extract polyphenols, pyrogallol, and gallic acid are coordinated by CuCl2 in a NaCl aqueous solution to form an oligomer, which creates an ion-channel coating on the hair surface to protect it. This work attempts to develop fast, simple, and damage-free hair-dye ingredients based on pyrogallol and gallic acid. The morphology and elements of polyphenols coated on hair are characterized. The results reveal that the hair is dyed with the polyphenol-based dye reagent successfully. Moreover, the thickness of the dyed hair continuously rises ten times after dyeing. The tensile strength of the dyed hair is also measured, showing an upward and downward trend. These results reflect the fact that pyrogallol and gallic acid are considered to be the essential and functional polyphenols, and can build ion blocks on hair, which can create new multifunctional coating materials

Orbital anisotropy of heavy fermion Ce2IrIn8 under crystalline electric field and its energy scale

© 2022 American Physical Society.We investigate the temperature (T) evolution of orbital anisotropy and its effect on spectral function and optical conductivity in Ce2IrIn8 using a first-principles dynamical mean-field theory combined with density functional theory. The orbital anisotropy develops by lowering T and it is intensified below a temperature corresponding to the crystalline-electric field (CEF) splitting size. Interestingly, the depopulation of CEF excited states leaves a spectroscopic signature, "shoulder,"in the T-dependent spectral function at the Fermi level. From the two-orbital Anderson impurity model, we demonstrate that CEF splitting size is the key ingredient influencing the emergence and the position of the "shoulder."Besides the two conventional temperature scales TK and T∗, we introduce an additional temperature scale to deal with the orbital anisotropy in heavy fermion systems.11Nsciescopu

Polyphenols Coordinated with Cu (II) in an Aqueous System Build ion-Channel Coatings on Hair Surfaces

Recently, developments in the field of cosmetics have led to a renewed interest in hair dyeing. However, damage to the hair during the dyeing process has increased hesitation in attempting hair dyeing. As a result, hair dyes with minimal side effects have been in constant demand, and are being developed. In this study, natural-extract polyphenols, pyrogallol, and gallic acid are coordinated by CuCl2 in a NaCl aqueous solution to form an oligomer, which creates an ion-channel coating on the hair surface to protect it. This work attempts to develop fast, simple, and damage-free hair-dye ingredients based on pyrogallol and gallic acid. The morphology and elements of polyphenols coated on hair are characterized. The results reveal that the hair is dyed with the polyphenol-based dye reagent successfully. Moreover, the thickness of the dyed hair continuously rises ten times after dyeing. The tensile strength of the dyed hair is also measured, showing an upward and downward trend. These results reflect the fact that pyrogallol and gallic acid are considered to be the essential and functional polyphenols, and can build ion blocks on hair, which can create new multifunctional coating materials