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1. Shaving and breaking bacterial chains with a viscous flow

   https://doi.org/10.1039/D0SM00292E  

   Gomand, Faustine; Mitchell, William H.; Burgain, Jennifer; Petit, Jérémy; Borges, Frédéric; Spagnolie, Saverio E.; Gaiani, Claire (October 2020, Soft Matter)

   null (Ed.)

   Some food and ferment manufacturing steps such as spray-drying result in the application of viscous stresses to bacteria. This study explores how a viscous flow impacts both bacterial adhesion functionality and bacterial cell organization using a combined experimental and modeling approach. As a model organism we study Lactobacillus rhamnosus GG (LGG) “wild type” (WT), known to feature strong adhesive affinities towards beta-lactoglobulin thanks to pili produced by the bacteria on cell surfaces, along with three cell-surface mutant strains. Applying repeated flows with high shear-rates reduces bacterial adhesive abilities up to 20% for LGG WT. Bacterial chains are also broken by this process, into 2-cell chains at low industrial shear rates, and into single cells at very high shear rates. To rationalize the experimental observations we study numerically and analytically the Stokes equations describing viscous fluid flow around a chain of elastically connected spheroidal cell bodies. In this model setting we examine qualitatively the relationship between surface traction (force per unit area), a proxy for pili removal rate, and bacterial chain length (number of cells). Longer chains result in higher maximal surface tractions, particularly at the chain extremities, while inner cells enjoy a small protection from surface tractions due to hydrodynamic interactions with their neighbors. Chain rupture therefore may act as a mechanism to preserve surface adhesive functionality in bacteria. 

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2. Adhesion-based high-throughput label-free cell sorting using ridged microfluidic channels

   https://doi.org/10.1039/D3SM01117H  

   Chrit, Fatima Ezahra; Li, Peiru; Sulchek, Todd; Alexeev, Alexander (February 2024, Soft Matter)

   Numerous applications in medical diagnostics, cell engineering therapy, and biotechnology require the identification and sorting of cells that express desired molecular surface markers. We developed a microfluidic method for high-throughput and label-free sorting of biological cells by their affinity of molecular surface markers to target ligands. Our approach consists of a microfluidic channel decorated with periodic skewed ridges and coated with adhesive molecules. The periodic ridges form gaps with the opposing channel wall that are smaller than the cell diameter, thereby ensuring cell contact with the adhesive surfaces. Using three-dimensional computer simulations, we examine trajectories of adhesive cells in the ridged microchannels. The simulations reveal that cell trajectories are sensitive to the cell adhesion strength. Thus, the differential cell trajectories can be leveraged for adhesion-based cell separation. We probe the effect of cell elasticity on the adhesion-based sorting and show that cell elasticity can be utilized to enhance the resolution of the sorting. Furthermore, we investigate how the microchannel ridge angle can be tuned to achieve an efficient adhesion-based sorting of cells with different compliance. 

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3. Preconditioning Layers Affect Osteoblastic Cell Adhesion to Orthopedic Implant Surfaces

   https://doi.org/10.1007/978-3-031-17445-2_9  

   Boyd, James D; Grady, Martha E (November 2022, Springer International Publishing)

   Bacteria can proliferate orthopedic implants, resulting in infection rates as high as 5%. A consistent problem across implantology is the development of surfaces which successfully promote the adhesion and propagation of healthy fibroblast and osteoblast cells while deterring formation of bacterial biofilms. Selecting surface configurations which favor cell adhesion will lead to decreased infection rates. Progress in identifying appropriate surface configurations is hindered by the lack of quantitative adhesion techniques capable of comparing adhesion of cells and biofilms directly. Recent advancements in adhesion techniques have allowed for quantitatively measured adhesion strengths of both bacterial biofilms and cell monolayers using the laser spallation technique. The quantified stress-based adhesion values allow surface and environmental factors that modulate both bacterial and cell adhesion to implant surfaces to be evaluated. During implantation, blood propagates wound sites completely coating implant surfaces. Quantitatively determining the impact of preconditioning layers that accumulate on the implant surface on cell adhesion is vital to predict implant behavior. Previous work has demonstrated that these preconditioning layers either negatively or neutrally impact bacterial adhesion to titanium implant surfaces. This study focuses on the impact that blood plasma and fibronectin coatings have on the adhesion of osteoblastic (MG 63) cells and fibroblasts to the same titanium surfaces. Adhesion results indicate that preconditioning layers and increased surface roughness positively impact cell adhesion. Incorporating the increased adhesion values for cell adhesion into the Adhesion Index demonstrates that increased surface roughness, coupled with natural wound healing preconditioning of surfaces, yields positive biocompatibility. 

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4. Distribution of Gaps and Adhesive Interaction Between Contacting Rough Surfaces

   https://doi.org/10.1007/s11249-021-01454-6  

   Monti, Joseph M.; Sanner, Antoine; Pastewka, Lars (May 2021, Tribology Letters)

   Abstract Understanding the distribution of interfacial separations between contacting rough surfaces is integral for providing quantitative estimates for adhesive forces between them. Assuming non-adhesive, frictionless contact of self-affine surfaces, we derive the distribution of separations between surfaces near the contact edge. The distribution exhibits a power-law divergence for small gaps, and we use numerical simulations with fine resolution to confirm the scaling. The characteristic length scale over which the power-law regime persists is given by the product of the rms surface slope and the mean diameter of contacting regions. We show that these results remain valid for weakly adhesive contacts and connect these observations to recent theories for adhesion between rough surfaces. 

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5. Tunable Adhesion of Shape Memory Polymer Dry Adhesive Soft Robotic Gripper via Stiffness Control

   https://doi.org/10.3390/robotics12020059  

   Son, ChangHee; Jeong, Subin; Lee, Sangyeop; Ferreira, Placid M; Kim, Seok (April 2023, Robotics)

   A shape memory polymer (SMP) has been intensively researched in terms of its exceptional reversible dry adhesive characteristics and related smart adhesive applications over the last decade. However, its unique adhesive properties have rarely been taken into account for other potential applications, such as robotic pick-and-place, which might otherwise improve robotic manipulation and contribute to the related fields. This work explores the use of an SMP to design an adhesive gripper that picks and places a target solid object employing the reversible dry adhesion of an SMP. The numerical and experimental results reveal that an ideal compositional and topological SMP adhesive design can significantly improve its adhesion strength and reversibility, leading to a strong grip force and a minimal release force. Next, a radially averaged power spectrum density (RAPSD) analysis proves that active heating and cooling with a thermoelectric Peltier module (TEC) substantially enhances the conformal adhesive contact of an SMP. Based on these findings, an adhesive gripper is designed, fabricated, and tested. Remarkably, the SMP adhesive gripper interacts not only with flat and smooth dry surfaces, but also moderately rough and even wet surfaces for pick-and-place, showing high adhesion strength (>2 standard atmospheres) which is comparable to or exceeds those of other single-surface contact grippers, such as vacuum, electromagnetic, electroadhesion, and gecko grippers. Lastly, the versatility and utility of the SMP adhesive gripper are highlighted through diverse pick-and-place demonstrations. Associated studies on physical mechanisms, SMP adhesive mechanics, and thermal conditions are also presented. 

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