Session K01: Biological Fluid Dynamics: Biofilms (8:45am - 9:30am CST)

Microbial adhesion on Circular Obstacles: An Optimization Study

Microbial filtration has been revisited during the last years since numerical computation and experimental refinement are now available and possible, opening new questions and insights into microbes adhesion on complex surfaces and novel ways to control biofilm formation. In this work, we present a simple, non-hydro-dynamical model, using active Brownian particles with different swimming persistence, to study and enhance microbes adhesion on convex surfaces. By adding a short-range interaction between microswimmers and obstacle surface we can reproduce the experimental observed bacterial attachment and behavior over circular obstacles of different radius. Furthermore, by exploring different microswimmers activity and external flow we found a narrow velocity screen where microswimmers adhesion strongly changes and might determine microbes first adhesion to the surface, by changing the contact time between microbes and obstacle's surface. We expect that this detail study might help to improve in-vitro fertilization and bio-inspired chemical treatments in industry to optimize biofilm formation.   

Sustainable anti-biofouling and drag reduction of covalent mucilage coatings

Biofilms contaminate a wide variety of infrastructure elements, systems, and devices. Toxic paints containing biocides provide an effective antifouling tool. However, most of them have been banned internationally because of their unacceptable environmental impacts. To resolve this problem, the development of environmentally friendly coating method is necessary. Inspired by various functions of mucus or mucilage produced by algae and other marine organisms, we developed the multi-functional mucilage coating method with both drag reduction and anti-biofouling effect. In this study, carboxymethyl cellulose (CMC) was coated on the slide glass, and various functional polymers such as mPEG-amine, chitosan, and alginate were covalently attached on the CMC coated surfaces. We measured the slip length of CMC and mPEG coated surfaces with the best anti-biofouling effect. CMC coated surface had no slip effect, while the mPEG-amine coated surface showed slip effect. In this study, we demonstrated that our coating process generates a stable mucilage coating with anti-biofouling and drag reduction properties. The proposed covalent mucilage coating would be available in various industrial fields that require sustainable anti-biofouling and drag reduction.   

Monitoring biofilm deformation under laminar flow by a digital holography interferometry

Bacteria can grow and form biofilm on biotic and abiotic environments. Extra cellular polymetric substance (EPS) facilitates the attachment of bacteria upon contact to the surface and formation of biofilm. Biofilm after formation is subjected to mechanical forces. One of the major changes in a bacterium's environment when attachment to substrate occurs is the alteration in the mechanical characteristics of the environment. In this work, we have developed a technique to perform in-situ measurement of forces exerted on the bacteria cells causing the deformation of biofilm under flow sheer. The experiments are performed utilizing a uniquely designed fluidic platform containing a flexible mirror. The bottom layer of the mirror consists of Polydimethylsiloxane (PDMS) and is coated with agar gel. The flexible mirror is fabricated by sputter deposition of 50 nm aluminum thin film on 0.5 mm of PDMS that performs as a pressure sensitive substrate. The selection of agar gel as the topcoat for pressure sensitive substrate facilitates biofilm formation. The distinctive property of the flexible mirror is the sensitivity to weak forces that can be sensed by a digital holographic interferometer (DHI) or an interference reflection microscopy (IRM). The experimental setup consists of a closed loop microfluidic platform with the flexible mirror as the bottom layer, a reservoir, two pumps and connecting tubing to form two recirculating loops. The initial experiments are being performed under non-flow conditions to examine any elastic deformation. Funded by ARO, ONR   

Formation of Shear Resistant (SR-)Biofilm over chemically structured surfaces with self-assembled monolayer micro-patches in shear flows

Biofilm consisting of structured bacterial communities protected cells from environmental insults such as antibiotics, biocides, and mechanical abrasions. Recent studies on near surface bacterial motility and biofilm responses to flow shear leads to hypothesis that substrate landscape (e.g. surface hydrophobicity, roughness, and chemistry) and hydrodynamic conditions (e.g. flow and shear) substantially affect the fundamental formation processes and cause the film to evolve to diametrically different mature biofilms. In this study, we apply our newly developed \textit{Ecology-on-a-chip} (\textit{eChip}) microfluidic microcosm platform and surface-patterning technique with OTS self-assembled monolayer micro-patches to study the role of surficial energy landscape and flow shear on 3D biofilm structures. \textit{Pseudomonas} (PAO1) biofilm will be formed in-situ in t\textit{eChip} platform with a SMA patterned bottom surface. The formation processes (e.g. attachment, proliferation, dispersal, regrowth) and the evolution of 3D film structures will be measured in the real-time as well as their capability of resisting shear will also be assessed and quantified. Funded by ONR   

How do bacteria `feel' their environment?

Bacteria sense and respond to the surfaces they grow on. When a bacteria cell makes contact with a surface, it initiates a program of gene expression that promotes colonization and biofilm formation; yet, the precise mechanisms by which bacteria `feel' their environment remains unclear. To understand this process, we have developed synthetic hydrogels with tunable stiffness and controllable pore size to assess the effects of substrate mechanics on biofilm development. We use time lapse microscopy to track the growth and form of expanding Serratia marcescens colonies and traction force microscopy to measure forces the bacteria exert on the surface. We find a specific regime in which biofilm expansion increases with substrate stiffness, unlike what is seen on conventional agar substrates. Our results suggest that the transport and spread of bacteria can be independently modified and controlled by substrate stiffness and new models of biofilm growth based on the contribution of substrate mechanics are needed.