Time-dependent plastic behavior of bacteria leading to rupture.

A study of the mechanical response of bacteria is essential in designing an antibacterial surface for implants and food packaging applications. This research evaluated the mechanical response of Escherichia coli under different loading conditions. Indentation and prolonged creep tests were performed to understand their viscoelastic-plastic response. The results indicate that varying loading rates from 1 µm/s to 5 µm/s show an increase in modulus of 182% and 90%, calculated in the loading and unloading cycles, respectively, and a decrease in adhesion force by 42%. However, on varying loads from 5 nN to 25 nN, nominal change is observed in both modulus and adhesion force. The rupture curve at 100 nN load shows elastic and a small plastic deformation accompanied by a sharp peak indicating the cell wall rupture. The rupture force at the peak was found to be 34.38 ± 5.15 nN, irrespective of the loading rate, making it a failure criterion for bacteria rupture. The creep response of bacteria increases (for 6 s) and then remains constant (for 15 s) with time, indicating that a standard linear solid (SLS) model applies to this behavior. This work attempts to evaluate the mechanical properties of E. coli bacteria focusing on its rupture by contact killing mechanism.

A lab-on-chip solution for the detection and suppression of COVID-19 severity.

At present, the conventional method for detecting COVID-19 infection is reverse transcription-polymerase chain reaction (RT-PCR) performed on nasopharyngeal and pharyngeal swabs. In addition, other detection techniques such as isothermal nucleic acid amplification, enzyme-linked immunosorbent assay (ELISA) have also been proposed and are being used. However, these techniques are limited to central hospitals and pathologies. Point-of-care solutions may play an important role in rapid and timely detection by an individual at their doorstep. In addition, the disease adversely affects the functioning of various constituents of human blood. For example, it reduces the platelets count, increases production of proinflammatory cytokine which results in cytokine storm, and increases level of various plasma proteins with the severity of the disease. Therefore, monitoring and transfusion of blood plasma and platelets may play an essential role in detection and suppression of severity of COVID-19 infection. In this regard, we propose evolution of our existing microdevice for the detection and suppression of severity of COVID-19 infection. We propose modification of our microdevice in the following ways (i) as a platelet-rich plasma separation unit, (ii) as an on-chip device to study inter-cellular properties of platelets, and (iii) for on-chip detection of infection by separating plasma. The integration of these microdevices with lateral flow assays, flow-virometry reader (FVR), direct serological biosensor assay along with proprietary technology based on plasmonic, place these microdevices in an advantageous position. Moreover, coupling of the microdevices with machine leaning application for rapid detection of the severity of COVID-19 and platelets related disorders makes these microdevices as a complete unit for point-of-care application.

Anti-Biofouling Properties of Femtosecond Laser-Induced Submicron Topographies on Elastomeric Surfaces.

Antibacterial coatings are often employed to elastomer surfaces to inhibit bacterial attachment. However, such approaches could lead to increased antibiotic resistance. Surface micro-/nanotexturing is gaining significant attention recently, as it is a passive approach to reduce bacterial adhesion to surfaces. To this end, this work aims to assess the anti-biofouling functionality of femtosecond laser-induced submicron topographies on biomedical elastomer surfaces. Femtosecond laser processing was employed to produce two types of topographies on stainless-steel substrates. The first one was highly regular and single scale submicron laser-induced periodic surface structures (LIPSS) while the second one was multiscale structures (MSs) containing both submicron- and micron-scale features. Subsequently, these topographies were replicated on polydimethylsiloxane (PDMS) and polyurethane (PU) elastomers to evaluate their bacterial retention characteristics. The submicron textured PDMS and PU surfaces exhibited long-term hydrophobic durability up to 100 h under immersed conditions. Both LIPSS and MS topographies on PDMS and PU elastomeric surfaces were shown to substantially reduce (>89%) the adhesion of Gram-negative Escherichia coli bacteria. At the same time, the anti-biofouling performance of LIPSS and MS topographies was found to be comparable with that of lubricant-impregnated surfaces. The influence of physical defects on textured surfaces on the adhesion behavior of bacteria was also elucidated. The results presented here are significant because the polymeric biomedical components that can be produced by replication cost effectively, while their biocompatibility can be improved through femtosecond surface modification of the respective replication masters.

Surface Alterations to Impart Antiviral Properties to Combat COVID-19 Transmission.

A global epidemic caused by highly transmittable COVID-19 is causing severe loss of human life. In this study, two aspects of reducing transmission of COVID-19 virus, due to surface contact, are discussed: first refers to the effect of nanocarbon fullerene C60 coating on surface, that causes lipid peroxidation on the phospholipid layer present in the outer envelope of COVID-19; the second aspect refers to creating hydrophobic surfaces by texturing them, so that the contact area between virus and surface is minimized due to the presence of entrapped air between the topographies. These can be similar to micro-/nano-multiscale textured surfaces that have anti-biofouling properties. Fullerene-coated surfaces can be seen as a possible solution to decrease the adhesion of virus on the surface, as they will be hydrophobic as well as toxic to the envelope.

Microdevice for plasma separation from whole human blood using bio-physical and geometrical effects.

In this research work, we present a simple and efficient passive microfluidic device for plasma separation from pure blood. The microdevice has been fabricated using conventional photolithography technique on a single layer of polydimethylsiloxane, and has been extensively tested on whole blood and enhanced (upto 62%) hematocrit levels of human blood. The microdevice employs elevated dimensions of about 100 µm; such elevated dimensions ensure clog-free operation of the microdevice and is relatively easy to fabricate. We show that our microdevice achieves almost 100% separation efficiency on undiluted blood in the flow rate range of 0.3 to 0.5 ml/min. Detailed biological characterization of the plasma obtained from the microdevice is carried out by testing: proteins by ultra-violet spectrophotometric method, hCG (human chorionic gonadotropin) hormone, and conducting random blood glucose test. Additionally, flow cytometry study has also been carried on the separated plasma. These tests attest to the high quality of plasma recovered. The microdevice developed in this work is an outcome of extensive experimental research on understanding the flow behavior and separation phenomenon of blood in microchannels. The microdevice is compact, economical and effective, and is particularly suited in continuous flow operations.

Utilization of Cavity Vortex To Delay the Wetting Transition in One-Dimensional Structured Microchannels.

Frictional resistance across rough surfaces depends on the existence of slip on the liquid-gas interface; therefore, prolonging the existence of liquid-gas interface becomes relevant. In this work, we explore manipulation of the cavity shape in order to delay the wetting transition. We propose that liquid-driven vortices generated in the air cavity dissipate sufficient energy to delay the Cassie-Wenzel transition. Toward this, we fabricated cavities on the side walls of a polydimethylsiloxane-based microchannel for easy visualization and analysis of the dynamics of the liquid-gas interface. Two distinct flow regimes are identified in the experimental envelope. In the first regime, the liquid-gas interface is found to be protruding into the flow field, thus increasing the pressure drop at low Reynolds number. In the second regime, flow rate and geometry-based wetting transitions are established at moderate to high Reynolds numbers. We then investigate the effect of different cavity shapes (square, trapezoidal, and U-shape) in delaying the wetting transition by manipulating liquid-driven vortices. Out of the shapes considered in this study, trapezoidal cavities perform better than cavities with vertical walls in delaying the wetting transition due to geometrical squeezing of vortices toward the liquid-gas interface. Numerical simulations corroborate the experimental findings in that cavities with inclined walls exert more force on the liquid-gas interface, thus delaying their wetting transition. The proposed method being passive in nature appears more attractive than previous active methods.

Modelling and simulation of effect of ultrasonic vibrations on machining of Ti6Al4V.

The titanium alloys cause high machining heat generation and consequent rapid wear of cutting tool edges during machining. The ultrasonic assisted turning (UAT) has been found to be very effective in machining of various materials; especially in the machining of "difficult-to-cut" material like Ti6Al4V. The present work is a comprehensive study involving 2D FE transient simulation of UAT in DEFORM framework and their experimental characterization. The simulation shows that UAT reduces the stress level on cutting tool during machining as compared to that of in continuous turning (CT) barring the penetration stage, wherein both tools are subjected to identical stress levels. There is a 40-45% reduction in cutting forces and about 48% reduction in cutting temperature in UAT over that of in CT. However, the reduction magnitude reduces with an increase in the cutting speed. The experimental analysis of UAT process shows that the surface roughness in UAT is lower than in CT, and the UATed surfaces have matte finish as against the glossy finish on the CTed surfaces. Microstructural observations of the chips and machined surfaces in both processes reveal that the intensity of thermal softening and shear band formation is reduced in UAT over that of in CT.