Department of Applied Mechanics

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

<a href="https://www.sciencedirect.com/topics/chemistry/endotoxin">Bacterial endotoxins</a> such as <a href="https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/lipopolysaccharide">lipopolysaccharides</a> (LPS) are major contaminants of most pharmaceutical and consumer products. We report an antibiotic-mediated <a href="https://www.sciencedirect.com/topics/engineering/plasmonics">plasmonic</a> <a href="https://www.sciencedirect.com/topics/engineering/biosensors">biosensor</a> for LPS detection based on a facile U-bent <a href="https://www.sciencedirect.com/topics/engineering/fiber-optic-probe">fiber optic probe</a> (UFOP) technology. <a href="https://www.sciencedirect.com/topics/engineering/biomimetics">Biomimetic</a> self-assembled layer of <a href="https://www.sciencedirect.com/topics/engineering/octadecyltrichlorosilane">octadecyltrichlorosilanes</a> (OTS) were functionalized on the surface of <a href="https://www.sciencedirect.com/topics/engineering/optical-fibers">optical fiber</a> probes to hydrophobically entrap LPS from aqueous solutions. The binding of LPS molecules was monitored in real-time by measuring the change in <a href="https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/refraction-index">refractive index</a> (RI) in the <a href="https://www.sciencedirect.com/topics/engineering/evanescent">evanescent</a> layer. To add specificity and <a href="https://www.sciencedirect.com/topics/engineering/signal-amplification">signal amplification</a>, the bound LPS molecules were further tagged with antimicrobial polymyxin-B conjugated <a href="https://www.sciencedirect.com/topics/chemistry/gold-nanoparticle">gold nanoparticles</a> (PMB-AuNPs) in a sandwich format. The assay was extensively optimized by investigating the role of experimental parameters like OTS concentration, <a href="https://www.sciencedirect.com/topics/engineering/incubation-time">incubation time</a> and addition of a silver reduction step at the end of the assay. The lower limit of detection (LOD) for LPS was found to be 0.4 ng/mL with a 36-fold improved sensitivity upon silver enhancement. The total assay time was 1 h. The assay was also found to be highly specific in the presence of common biopharmaceutical components and could thus serve as an efficient endotoxin detection platform for quality control testing during therapeutic development.

World University root node

Fulltext

Biosensors and Bioelectronics

Plasmonic biosensors for bacterial endotoxin detection on biomimetic C-18 supported fiber optic probes

The two-dimensional (2D) inclined stroke plane kinematics of insect wing is studied for various stroke plane angles using the Immersed Boundary (IB) solver. The numerical results revealed the dominant lift enhancement mechanisms for this class of flows. The generated dipole was analyzed to find the maximum velocity, inclination and spread. The analysis of these dipole characteristics for the different stroke plane angles exposed the alternate method to study the vertical force variation with the stroke plane angles. Lift enhancement mechanisms and dipole characteristics complement the high vertical force coefficient for the stroke plane angle of 60˚ commonly used by dragonflies during hover. The location of the dipole identified a region of influence around the wing and demonstrated the role of the dipole jet in multi-body dynamics and wall effects. © 2020, Jilin University.

Journal of Bionic Engineering

Role of Dipole Jet in Inclined Stroke Plane Kinematics of Insect Flight

Flexoelectricity is the development of an electric field under an applied strain gradient. This effect is highly size-dependent and is significant at nanoscales. Unsymmetric magnetoelectric (ME) composites undergo bending deformations under a magnetic field that results in non-zero strain gradients. Hence, it is important to give due consideration to flexoelectricity, along with direct piezoelectricity in these composites. This article presents a finite-element model that predicts the static and dynamic behavior of ME nanobeams subjected to magnetic fields. The effect of material nonlinearity of the ferromagnetic phase and flexoelectricity in the ferroelectric phase on the ME coupling are determined, and the obtained results show agreement with the literature. It is found that flexoelectricity results in substantially higher static ME coefficients. However, the resonant ME response is weakened by flexoelectricity. The effect of surface elasticity on the ME coupling coefficient is also investigated by making use of the Gurtin-Murdoch theory. The surface effects are found to improve the ME coefficient at bending resonance, while its effect is trivial at static and axial resonant conditions. Furthermore, the effect of load resistance on the ME voltage and charge coefficients is determined. The results indicate clear changes in the trend between short-circuit and open-circuit conditions. © 1965-2012 IEEE.

IEEE Transactions on Magnetics

Effects of Flexoelectricity and Surface Elasticity on the Nonlinear Magnetoelectric Coupling in Unsymmetric Composites

Measurement of the viscoelastic properties of a cell using microscopic tracer particles has been complicated given that the medium viscosity is dependent upon the size of the measurement probe leading to reliability issues. Further, a technique for direct calibration of optically trapped particles in vivo has been elusive due to the frequency dependence and spatial inhomogeneity of the cytoplasmic viscosity, and the requirement of accurate knowledge of the medium refractive index. Here, we employ a recent extension of Jeffery's model of viscoelasticity in the microscopic domain to fit the passive motional power spectra of micrometer-sized optically trapped particles embedded in a viscoelastic medium. We find excellent agreement between the 0 Hz viscosity in MCF7 cells and the typical values of viscosity in literature, between 2 to 16 mPa sec expected for the typical concentration of proteins inside the cytoplasmic solvent. This bypasses the dependence on probe size by relying upon small thermal displacements. Our measurements of the relaxation time also match values reported with magnetic tweezers, at about 0.1 s. Finally, we calibrate the optical tweezers and demonstrate the efficacy of the technique to the study of in vivo translational motion. © 2020 IOP Publishing Ltd.

Department Of Physics

Journal of Physics Condensed Matter

Measurement of viscoelastic properties of the cellular cytoplasm using optically trapped Brownian probes

In this paper, the effect of porosity on the ductility of as-cast AA7075 (a commercial highstrength aluminum alloy) was investigated. The as-cast material was processed through hot upsetting, and specimens with different porosity content were achieved. These were then subjected to tensile and compression tests. It was shown that the tensile ductility exhibited a near sigmoidal dependence on the porosity content. Compressive ductility, on the other hand, was not affected by the initial porosity content. In addition, direct observations, on an X-ray microscope (XRM), enabled 3-dimensional imaging of the porosity evolution during plastic deformation. Numerical simulations using a homogenized damage model, the Gurson-Tvergaard-Needleman (GTN) approach, was used for predicting the mechanical responses. The continuum model, which accounted for the growth and coalescence of spherical voids, captured the overall experimental patterns reasonably well. © 2020 by ASME.

Department of Aerospace Engineering

Journal of Engineering Materials and Technology, Transactions of the ASME

Relating porosity with ductility in a commercial AA7075 alloy: A combined experimental and numerical study

This paper aims to estimate the enhancement in the energy absorption characteristics of the glass fiber reinforced composites (GFRP) by embedding prestrained pseudo-elastic shape memory alloy (SMA) that was used as a secondary reinforcement. The pseudo-elastic SMA (PE-SMA) embedded were in the form of wires and have an equiatomic composition (i.e., 50%-50%) of nickel (Ni) and titanium (Ti). These specimens are fabricated using a vacuum-assisted resin infusion process. The estimation is done for the GFRP and SMA/GFRP specimens at four different impact velocities (65, 75, 85, and 103 m/s) using a gas-gun impact set-up. At all different impact velocities, the failure modes change as we switch from GFRP to SMA/GFRP specimen. In the SMA/GFRP specimen, the failure mode changed from delamination in the primary region to SMA-pull out and SMA deformation. This leads to an increase in the ballistic limit. It is observed that energy absorbed by SMA/GFRP specimens is higher than the GFRP specimens subjected to the same levels of impact energy. To understand the damping capabilities of SMA embedment, vibration signals are captured, and the damping ratio is calculated. SMA dampens the vibrations imparted by the projectile to the specimen. The damping ratio of the SMA/GFRP specimens is higher than the GFRP specimens. The damping effect is more prominent below the ballistic limit when the projectile got rebounded (65 m/s).

Department of Engineering Design

Molecules (Basel, Switzerland)

Ballistic Impact Behaviour of Glass/Epoxy Composite Laminates Embedded with Shape Memory Alloy (SMA) Wires

Colour transfer methodology is used in the field of image processing to transfer colour characteristics between images. In this study, colour transfer employing principal component analysis (PCA) is explored to circumvent the colour mismatch between application and calibration images in twelve fringe photoelasticity. For this, the images are considered as 3-D pixel clouds in RGB colour space. © Society for Experimental Mechanics, Inc. 2020.

Conference Proceedings of the Society for Experimental Mechanics Series

Colour Transfer in Twelve Fringe Photoelasticity (TFP)

High performance thermoresponsive soft, controllable and reversible actuators are highly desirable for diverse applications. The practical implementation of the existing poly(N-isopropylacrylamide) (pNipam) based soft thermoresponsive actuators faces serious limitations due to their functional requirement of proximal bulk solvent medium. In this work, addressing this issue, we report the development of a bilayer based actuator composed of a solvent responsive biodegradable polymer and temperature responsive pNipam. The designed bilayer is capable of achieving reversible and irreversible actuation as needed when exposed to a physiological range of body temperature, without any solvent bath around. The solvent or water supplied by the pNipam layer at its lower critical solution temperature (LCST) builds a concentration gradient across the thickness of the polymer layer. The concentration gradient results in a strain gradient, causing an out-of-plane folding of the bilayer. The underlying coupled diffusion-deformation interaction during folding and unfolding is incorporated in the reported finite element model, capable of predicting actuation characteristics under different initial conditions. The combined experimental and modelling effort in this work highlights the possibility of engineering 2-dimensional films into complex 3-dimensional shapes, which could have potential applications in soft machines and robotics. © The Royal Society of Chemistry 2020.

Department of Mechanical Engineering

Soft Matter

Controlled shape morphing of solvent free thermoresponsive soft actuators

This work reports the growth of stable TiO2 nanotube arrays on flexible Kapton substrates by electrochemical anodization of a sputtered Ti (titanium) film. Although such nanotubes are conventionally fabricated on Ti foils, obtaining these on polymer-based flexible substrates remained a challenge because of higher annealing temperature not compatible with thermal stability of the substrates. Here, we demonstrate the fabrication of TiO2 nanotubes (1.5 μm long and 80 nm diameter) by anodization of the Ti film deposited using the RF sputtering technique at two different substrate temperatures (room temperature and 300 °C). Nanoindentation and nanoscratch techniques reveal better adhesion of the Ti film with an underlying Kapton substrate for 300 °C deposition temperature. Such investigations reveal a more than twofold enhancement of the "rear pileup"for the Ti film deposited at elevated temperature compared to that at room temperature. The amorphous TiO2 nanotubes are crystallized at 220 °C for 3 h using a solvothermal technique that allows crystallization at temperatures much lower than the annealing temperature. Application of these nanotubes for photo-electrochemical water splitting reveals a photocurrent density of 18 μA/cm2 under AM 1.5 G conditions. Furthermore, the charge density and flat band potential (VFB) are calculated from Mott-Schottky analysis, showing features comparable to the TiO2 nanotubes on the Ti foil crystallized through thermal annealing. The present work establishes a scalable approach for developing TiO2 nanotube arrays on the flexible substrate and its use for photo-electrochemical solar energy conversion. © 2020 American Chemical Society. All rights reserved.

ACS Applied Nano Materials

TiO2Nanotube Arrays on Flexible Kapton Substrates for Photo-Electrochemical Solar Energy Conversion

Polymer bi-layer systems are often exposed to different environmental service conditions which can potentially alter the mechanical properties as it approaches the glass transition temperature of an inaccessible substrate. However, since the substrate is inaccessible, it is difficult to measure or quantify the changes in these properties while in use. A methodology has been proposed in this work for prediction of glass transition temperature and Young's modulus of an inaccessible substrate in a bilayer system. The composite mechanical property of a bi-layer system is a function of the mechanical properties of coating, substrate and the depth at which it is measured. In the present work, poly-Methylmethacrylate (PMMA) coating of 900 nm is deposited on epoxy substrate. Nanoindentation experiments are conducted at different temperatures on the bi-layer system as well as on bulk PMMA. Finite element analysis has been used to obtain the material dependency of stress distribution coefficient (α) for deconvoluting the modulus of the substrate. The methodology developed by the present authors can predict the glass transition temperature as well the magnitudes of Young's modulus of an inaccessible substrate reasonably well. © 2020