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Hypothesis Dried blood droplet morphology may potentially serve as an alternative biomarker for several patho-physiological conditions. The deviant properties of the red blood cells and the abnormal composition of diseased samples are hypothesized to manifest through unique cell-cell and cell-substrate interactions leading to different morphological patterns. Identifying distinctive morphological trait from a large sample size and proposing confirmatory explanations are necessary to establish the signatory pattern as a potential biomarker to differentiate healthy and diseased samples. Experiments Comprehensive experimental investigation was undertaken to identify the signatory dried blood droplet patterns. The corresponding image based analysis was in turn used to differentiate the blood samples with a specific haematological disorder “Thalassaemia” from healthy ones. Relevant theoretical analysis explored the role of cell-surface and cell-cell interactions pertinent to the formation of the distinct dried patterns. Findings The differences observed in the dried blood patterns, specifically the radial crack lengths, were found to eventuate from the differences in the overall interaction energies of the system. A first-generation theoretical analysis, with the mean field approximation, also confirmed similar outcome and justified the role of the different physico-chemical properties of red blood cells in diseased samples resulting in shorter radial cracks.

Diabetes, a chronic condition, is one of the prevalent afflictions of the 21st century, and if left unchecked, this ailment could lead to severe life-threatening complications. A widely accepted methodology for monitoring diabetes is the estimation of the glucose and ketone contents in the body-fluids, viz. blood, urine, etc. Additionally, certain conditions such as starvation, and following a protein rich diet (e.g., keto-diet) could also lead to significant changes in the ketone content, thereby resulting in false-positive diagnosis. Hence, a precise, portable, and on-demand procedure for the rapid and combined estimation of glucose and ketone in the bodily-fluids is of utmost importance. To that end, paper-based analytical devices (μPADs) are promising tools, owing to their multitudinous advantages, and compatibility with biofluids. Although, numerous researchers have contributed substantially in the fundamental investigation, design, and fabrication of μPADs for various applications, a combined platform capable of rapid, accurate and on-demand glucose and ketone detection, that is easy to fabricate, is still relatively unexplored. Moreover, the flow dynamics of an analyte, in combination with enzyme-catalysed (for glucose) and uncatalyzed reactions (for ketone), within a porous paper matrix is also vaguely understood. Herein, we present a facile laser-printing based fabrication of colorimetric sensors on a filter paper, for rapid, and non-invasive estimation of glucose and ketone contents in urine. The urine sample, upon being deposited in a particular expanse, is wicked through the paper matrix, and reacts with specific reagents in the designated zone(s), giving rise to a final color, concomitant with the glucose or ketone content in the sample. The device design enables the liquid to be wicked into the porous matrix in a way that would concentrate the colored product in a dedicated detection zone, thereby augmenting the feasibility for accurate colorimetric detection. Furthermore, we present for the first time, a detailed dynamic model of the flow-field in a variable cross-section paper device using the Richards’ equation, while also considering the species transport and reaction kinetics within the porous media. The results of the numerical simulation agree well with those observed experimentally, thereby validating the present model. Finally, we also developed a web and desktop-based application that would enable the user to upload the images of the colored zones to provide an accurate estimate of the glucose and ketone content in the sample. We believe that our model, in combination with the proposed fabrication methodology, and the in-house developed app., would enable rapid and reliable fabrication of μPADs for various fundamental investigations, and applications pertaining to affordable health-care monitoring.Graphical Abstract

A Rose petal is well known for a unique form of hydrophobicity, exhibiting simultaneously high apparent equilibrium contact angle (θ*) as well as high adhesion that hinders the rolling off of droplets. This behaviour is fundamentally different than that commonly encountered in other bio-mimetic superhydrophobic surfaces (like a lotus leaf) that have air entrapped in the solid-liquid contact zone (Cassie Baxter wetting state), thereby exhibiting low adhesion. Based on laser scanning confocal microscopy as well as underwater in-situ atomic force microscopy, we obtain high resolution image of the water-substrate contact region (∼0.9–20 μm) which is significantly higher than that reported so far in the literature. We clearly demonstrate that this unique "Petal effect" can indeed be attributed to the Cassie impregnating wetting state, thereby resolving the prevailing ambiguity on this topic. We have also replicated the structure of the actual rose petals using soft lithography on cross-linked polydimethylsiloxane (PDMS, Sylgard 184) and show that both θ* as well as the adhesive properties of the replicated surface to be nearly identical to that of an actual petal. This implies that the force of adhesion depends on the wetting state and the area of contact. Incidentally, the negative replica of the petal, which is obtained as an intermediate during the replication process, exhibits slightly higher adhesion and identical θ*, as compared to the actual rose petal and its positive replica. However, the prevalent wetting state on the negative replica turns out to be Cassie like due to the presence of entrapped air. Both the negative and the positive replica of the Rose petal can potentially be used as biomimetically fabricated sticky hydrophobic surface.

Hypothesis Viscoelastic liquids could be used as potential substrates in the microfluidics paradigm. The theoretical and experimental investigation of an evaporating aqueous droplet, over a viscoelastic liquid substrate, could provide a fundamental perspective of the complex interplay amongst capillarity, viscosity, and elasticity, resulting in a wide array of intriguing dynamics, which could be important in several microscale processes. Experiments The evaporation dynamics of a water droplet atop an un-crosslinked polydimethylsiloxane film (polymeric liquid substrate) are examined using an optical goniometer and a laser scanning confocal microscopy, to discern the interfaces. The recorded videos were analyzed to estimate the contact angles, velocities, and other parameters of relevance. Findings The viscoelasticity of the film, in conjunction with evaporation, triggered a self-propulsion in the droplet, leading to crumpling of the polymeric film, and finally culminating in the encapsulation of the water drop by the polymer. The evaporation caused a dynamic variation in both the radius and contact angle of the droplet. The physics of the hitherto unreported phenomena is explained via the development of a semi-analytical model, considering all the relevant forces. We postulate that this symbiotic and self-sustained dynamics would pave the path towards the comprehension of micro-swimmers and surface encapsulation, to name a few.

Pattern formation during evaporation of biofluids has numerous biomedical applications, e.g., in disease identification. The drying of a bidisperse colloidal droplet involves formation of coffee ring patterns owing to the deposition of constituent particles. In the present study, we examine the distinctly different pattern formations during the drying of a colloidal solution depending on the nature of the constituent proteins. The pattern formations of two oppositely charged proteins, namely HSA and lysozyme, have been studied in the presence of fluorescence polystyrene beads of two different sizes (providing better image contrast for further analysis). The variation of pattern formation has been studied by varying the concentrations of the proteins as well as the particles. Furthermore, using image analysis, the patterns are segmented into different regions for quantification. To explain the variations in the patterns, we delve into the interplay of the interactions, especially the capillary and the DLVO forces (between the particles and the substrate). The developed methodology based on the coffee ring effect may be used to identify individual proteins.

The formation of specific patterns during evaporation of biofluids e.g. blood, serum etc. can be analyzed for quick identification of several diseases. Human Serum Albumin (HSA) is frequently used as the model protein to study amyloid fibril formation that is responsible for numerous neurodegenerative diseases like Parkinson’s disease, Alzheimer’s disease etc. In the present study the fibril growth of HSA is characterized by analyzing the drying patterns of the protein solution. The fibril formation of HSA is confirmed by spectrofluorimetry and the β-sheet content is quantified by far-UV Circular Dichroism spectrometry. Examinations of the drying patterns of HSA, in presence of fluorescent nanoparticles, reveals distinctive pattern transformations with increase in the β-sheet content visualized through fluorescence microscopy and FESEM. The fluorescence images of the dried droplet are analyzed using image processing by the color thresholding method. A rapid quantification methodology of the β-sheet content of HSA and the fraction of unfolded protein has been developed by comparing the results of the image analysis with those of the far-UV CD data.

Microscopic investigations of any abnormality associated with erythrocyte/red blood cell morphology constitute an important segment of the age-old peripheral smear test. Though the test is conducted on a glass slide, the effect of glass and similar other solid substrates on erythrocyte morphology remained majorly unexplored. In the first of its kind investigation, we have outlined the effect of varying the substrate surface potential on erythrocyte morphology. Such a substrate induced phenomenon has been quantified for two distinctly different drying configurations (droplets and film) upon systematically varying the cell concentration. Experimental results and supporting theoretical analysis unambiguously show the surface potential of the solid substrate to be the most influential parameter in the process of morphological alteration. The findings of the present investigation may be utilized to formulate an error-free protocol for the baseline peripheral smear test of hematological diagnosis.

Understanding the dynamics of blood flow in physiologically relevant confinements turns out to be an outstanding proposition in biomedical research. Despite the large number of studies being reported to theoretically elucidate the dynamics of red blood cells (RBCs) in confined geometries, in vitro experimental studies unveiling the implications of the collective dynamics of red blood cells in physiologically relevant bio-mimetic microfluidic channels remain elusive. Here, we investigate the implications of complex dynamvic interactions between the whole blood and a deformable channel wall fabricated using a hydrogel matrix. For a range of flow rates, we map the trajectories of the RBCs for varying levels of softness of the microchannel wall. We compare these scenarios with the reference cases of rigid polydimethylsiloxane (PDMS) channels. Our results reveal that the smallest channels investigated herein exhibit the most intricate interactions between the collective dynamics of the RBC and the wall flexibility, attributable to confinement-induced hydrodynamic interactions in the presence of spatially varying shear rates. These results may open up new paradigms in conceptual understanding of in vivo dynamics of blood flow through simple in vitro experiments on a simple microfluidic platform.

In order to demonstrate the influence of the surface chirality of the nanoparticles on amyloid fibrillation, the inhibiting effectiveness of the chiral gold nanoparticles, synthesized using the two enantiomeric forms (i.e., d- and l-) of glutamic acid, toward the fibrillation of human serum albumin (HSA) has been investigated. Here the enantiomers of glutamic acid are used as both reducing and stabilizing/capping agents. It is found that the surface chirality is the only major difference between the d-glutamic acid mediated gold (DGAu) and l-glutamic acid mediated gold (LGAu) nanoparticles. The fibrillation process has been monitored using various biophysical techniques, e.g., turbidity assay, Thioflavin T fluorescence kinetics, Congo red binding study, circular dichroism spectroscopy, fluorescence microscopy, and transmission electron microscopy. The experimental results illustrate that DGAu is more effective in inhibiting the formation of HSA fibrils than LGAu. Furthermore, the differential inhibiting e...

The effect of oscillation induced by a frequency-dependent alternating current (AC) electric field to dissociate preformed amyloid fibrils has been investigated. An electrowetting-on-dielectric type setup has been used to apply the AC field of varying frequencies on preformed fibrils of human serum albumin (HSA). The disintegration potency has been monitored by a combination of spectroscopic and microscopic techniques. The experimental results suggest that the frequency of the applied AC field plays a crucial role in the disruption of preformed HSA fibrils. The extent of stress generated inside the droplet due to the application of the AC field at different frequencies has been monitored as a function of the input frequency of the applied AC voltage. This has been accomplished by assessing the morphology deformation of the oscillating HSA fibril droplets. The shape deformation of the oscillating droplets is characterized using image analysis by measuring the dynamic changes in the shape dependent parameters such as contact angle and droplet footprint radius and the amplitude. It is suggested that the cumulative effects of the stress generated inside the HSA fibril droplets due to the shape deformation induced hydrodynamic flows and the torque induced by the intrinsic electric dipoles of protein due to their continuous periodic realignment in presence of the AC electric field results in the destruction of the fibrillar species.

The formation and deposition of amyloid fibrils have been linked to the pathogenesis of numerous debilitating neurodegenerative disorders. Serum albumins serve as good model proteins for understanding the molecular mechanisms of protein aggregation and fibril formation. Graphene-based nanotherapeutics appear to be promising candidates for designing inhibitors of protein fibrillation. The inhibitory effect of graphene oxide (GO) nanoparticles on the fibrillation of human serum albumin (HSA) in an in vitro mixed solvent system has been investigated. The methods used include ThT fluorescence, ANS binding, Trp fluorescence, circular dichroism, fluorescence microscopy, field-emission scanning electron microscopy, and high-resolution transmission electron microscopy. It was observed that GO inhibits HSA fibrillation and forms agglomerates with β-sheet rich prefibrillar species. Binding of GO prevents the formation of mature fibrils with characteristic cross-β sheet but does not promote refolding to the native state.

The amyloid β-peptide fragment comprising residues 25-35 (Aβ25-35 ) is known to be the most toxic fragment of the full length Aβ peptide which undergoes fibrillation very rapidly. In the present work, we have investigated the effects of the micellar environment (cationic, anionic, and nonionic) on preformed Aβ25-35 fibrils. The amyloid fibrils have been prepared and characterized by several biophysical and microscopic techniques. Effects of cationic dodecyl trimethyl ammonium bromide (DTAB), cetyl trimethylammonium bromide (CTAB), anionic sodium dodecyl sulfate (SDS), and nonionic polyoxyethyleneoctyl phenyl ether (Triton X-100 or TX) on fibrils have been studied by Thioflavin T fluorescence, UV-vis spectroscopy based turbidity assay and microscopic analyses. Interestingly, DTAB and SDS micelles were observed to disintegrate prepared fibrils to some extent irrespective of their charges. CTAB micelles were found to break down the fibrillar assembly to a greater extent. On the other hand, the nonionic surfactant TX was found to trigger the fibrillation process. The presence of a longer hydrophobic tail in case of CTAB is assumed to be a reason for its higher fibril disaggregating efficacy, the premise of their formation being largely attributed to hydrophobic interactions. Proteins 2016; 84:1213-1223. © 2016 Wiley Periodicals, Inc.

Protein and peptide aggregation/fibrillation is reported to be responsible for several neurological disorders. Fibrillation of the amyloid β-peptide fragment (25–35) which is a biologically active region of the full length peptide, has been observed to be significantly inhibited in presence of the two dimensional nanomaterial graphene oxide (GO). Fibrillation and inhibition of the Aβ25–35 peptide by GO has been performed at 37 °C at physiological pH (pH 7.4). The inhibition process is monitored by ThioflavinT fluorescence (ThT), circular dichroism spectroscopy, matrix assisted laser desorption/ionization mass spectrometry, dynamic light scattering experiments etc. The soluble fraction of the protein is quantified by the BCA assay. Microscopic techniques are used to study the morphology of the fibrils formed. GO is observed to inhibit the fibrillation even at very low concentrations and is amplified with increase in concentration of GO. ThT kinetic data fitted well with a sigmoidal curve and shows that GO is able to lengthen the lag phase of the fibrillation process. It appears that surface adsorption of protein on the nanomaterial prevents the monomers to come together. It is speculated that the presence of both polar and non-polar moieties in GO interact strongly with the hydrophobic and hydrophilic residues of the Aβ25–35 peptide monomer units, thus preventing further aggregation.

To understand the pharmacokinetics of administered nanomaterials, it is essential to examine the stability and biological activity of proteins by investigating the physicochemical characteristics of the protein–nanoparticle bioconjugate. In this work, the mechanistic detail of the interaction between human serum albumin (HSA) and silver nanoparticles synthesized using nontoxic and biodegradable chitosan as a reducing and stabilizing agent, have been investigated at the nanobio interface. A combination of spectroscopic, calorimetric, and microscopic techniques have been employed to monitor the interaction process. The results illustrate that the chitosan-mediated silver nanoparticles spontaneously bind to HSA without appreciable conformational changes of the protein. Furthermore the potential of the nanoparticles to inhibit the formation of HSA amyloid-like fibrils, in vitro, has been analyzed using thioflavin T fluorescence, circular dichroism, fluorescence microscopy, and transmission electron microscopy. The experimental observations indicate that interactions between HSA and chitosan-based silver nanoparticles have led to appreciable reduction in amyloid fibril formation. Additionally, cytotoxicity and hemolytic assays are performed to ensure the biocompatibility of the nanoparticles within the application limit.

We bring out unique aspects of the pulsatile flow of a blood analog fluid (Xanthan gum solution) in a biomimetic microfluidic channel. Pressure waveforms that mimic biologically consistent pulsations are applied on physiologically relevant cylindrical microchannels fabricated using polydimethylsiloxane. The in vivo features of the relevant waveforms like peak amplitude and dicrotic notch are reproduced in vitro. The deformation profiles exhibit viscoelastic behavior toward the end of each cycle. Further, the time-varying velocity profiles are critically analyzed. The local hydrodynamics within the microchannel is found to be more significantly affected by pressure waveform rather than the actual wall deformation and the velocity profile. These results are likely to bear far-reaching implications for assessing micro-circulatory dynamics in lab on a chip based microfluidic platforms that to a large extent replicate physiologically relevant conditions.

Droplet motion on a surface with chemical energy induced wettability gradient has been simulated using molecular dynamics (MD) simulation to highlight the underlying physics of molecular movement near the solid-liquid interface including the contact line friction. The simulations mimic experiments in a comprehensive manner wherein microsized droplets are propelled by the surface wettability gradient against forces opposed to motion. The liquid-wall Lennard-Jones interaction parameter and the substrate temperature are varied to explore their effects on the three-phase contact line friction coefficient. The contact line friction is observed to be a strong function of temperature at atomistic scales, confirming their experimentally observed inverse functionality. Additionally, the MD simulation results are successfully compared with those from an analytical model for self-propelled droplet motion on gradient surfaces.

The effect of axial flow variation on the hydrodynamic (Taylor–Aris) dispersion in a patterned microchannel consisting of periodic pillars and gaps is characterized for limiting Cassie–Baxter and Wenzel state configurations. The entry effects of flow for subsequent gaps and pillars are crucial as the flow tends towards plug flow over the gaps due to free slip at the air–liquid interface for the Cassie state or increased cross section for the Wenzel state and fully-developed parabolic flow over the pillars. The study includes analyzing the solute concentration distribution as a function of Peclet number based on the gap length, using CFD simulation and quantifying the dispersion based on Aris method of moments. For the Cassie State, simulations predict a narrower solute concentration distribution compared to flow in smooth channels. Detailed analysis reveal varied dispersion characteristics with Peclet number: similar dispersion with a time lag for low Peclet numbers and a reduced dispersion for high Peclet Number due to enhanced effect of slip. For the Wenzel state, a considerable loss of solute occurs due to the presence of dead zones within the gaps resulting in a significant increase in dispersion. The changed dispersion characteristics may have profound implications in microfluidic applications involving mixing and separation e.g., in liquid chromatography.

Significant enhancements in the instantaneous speed of a water droplet on a silicon surface with a chemically induced hydrophilicity gradient are observed with moderate increases in substrate temperature. The instantaneous droplet velocities and the contact angles are measured by a frame by frame analysis of the droplet motion using a goniometer with a high speed camera. A force balance based model captures the underlying experimental trends in a precise quantitative sense. The relevant forces are the chemically induced surface tension gradient inspired driving force and the resistive forces namely, the three-phase contact line, hydrodynamic and the drag force. The variation in the values of the coefficient of contact line friction and its effect on the overall droplet transport has been evaluated. This study points to the enhanced cooling potential of speciality surfaces where the dissipated heat may be utilized as a natural advantage for faster movement of droplets towards the hot spot.

We investigate electroosmotic flow of two immiscible viscoelastic fluids in a parallel plate microchannel. Contrary to traditional analysis, the effect of the depletion layer is incorporated near the walls, thereby capturing the complex coupling between rheology and electrokinetics. Toward ensuring realistic prediction, we show the dependence of electroosmotic flow rate on the solution pH and polymer concentration of the complex fluid. In order to assess our theoretical predictions, we have further performed experiments on electroosmosis of an aqueous solution of polyacrylamide (PAAm). Our analysis reveals that neglecting the existence of a depletion layer would result in grossly incorrect predictions of the electroosmotic transport of such fluids. These findings are likely to be of importance in understanding electroosmotically driven transport of complex fluids, including biological fluids, in confined microfluidic environments.

A novel low-voltage technique employing electrohydrodynamic (EHD) flow for micropumping oil-in-water emulsions through microchannels is presented. The concept of EHD flow reported at microscopic scale during colloidal aggregation is extended to larger scales, for actuation of bulk motion of emulsion. The experiments involve immersing two vertical parallel electrodes in an oil-in-water emulsion and applying AC fields (15–40 V p-p ; 5–500 Hz) across the electrodes. Liquid flow along the electrode gap is analyzed by microscopically tracking the motion of the suspended oil drops on the free surface. Experimental results confirm an EHD mechanism of flow through field distortions caused by the dispersed oil drops leading to tangential electric field on the charge polarization layer. Comparison of the scheme with conventional EOF scheme shows a drastic reduction in the actuation voltage required for attaining identical velocities. Additional advantage of EHD over EOF includes the independence of the actuation voltage on the microchannel length.

The rapid oscillation of a micro-litre sized droplet on application of a periodic DC electric field in an EWOD (electrowetting on dielectric) configuration, consisting of an ITO (Indium Tin Oxide – In2O3/SnO2) coated glass substrate coated with polydimethylsiloxane (PDMS) and Teflon, has been studied. The physics of the wetting and dewetting phenomena during the oscillation process is analyzed extensively as a function of the time dependent applied voltage. DC pulse functions with voltages ranging from 150 V to 300 V and delay time from 25 ms to 200 ms are imposed on the droplet and the subsequent amplitude, frequency of oscillation, contact angle change and hysteresis are measured. It has been demonstrated that the oscillation and the ensuing mixing inside the droplet result in the augmentation of the transport process. The enhancement of the cooling rate of a hot spot on a substrate due to droplet oscillation and its variation with droplet volume and delay time are evaluated experimentally. The increase is a result of oscillation induced internal circulation inside the evaporating droplet and can be used as a tool for specific micro-cooling applications; e.g., cooling of a hot-spot.

Exercising control over the evaporation of colloidal suspensions is pivotal to modulate the coating characteristics for specific uses, wherein the interactions among the liquid, the particles, and the substrate control the process. In the present study, the contact line dynamics of a receding colloidal liquid film consisting of particles of distinctly different sizes (nominal diameters 0.055 and 1 μm and surface unmodified) during evaporation is analyzed. The role of the liquid polarity is also investigated by replacing the polar liquid (water) with a relatively nonpolar liquid (isopropyl alcohol) in the colloidal suspension. The characteristics of the evaporating receding meniscus, namely, the film thickness and the curvature are experimentally evaluated using an image-analyzing interferometry technique. The experimental results are assessed in conjunction with the augmented Young-Laplace equation, highlighting the roles of the relevant components of the disjoining pressure and the polarity of the liquid involved in the colloidal suspension.

The favorable effects of air sparging to reduce deposition on the membrane and consequent fouling during membrane separation are studied, first with a model solute (pectin), followed by degreasing effluent from a tannery. Directly injecting air into the feed stream enhances the permeate flux and the performance of the separation process in a rectangular flat sheet tangential flow membrane module. The effects of various operating parameters, namely, gas velocity, membrane surface orientations with respect to the flow direction, transmembrane pressure, cross-flow velocity, and model solute concentration, are quantified. The concentrations of pectin solutions used herein are chosen such that they behave similar to the degreasing effluent in terms of gel layer-type deposition on the membrane surface. Also, there are significant changes in the permeate quality (80 mg/l) by using air sparging in the flow channel which is below Indian discharge standards (250 mg/l). There are appreciable changes in the p...

A heat transfer cell is specifically designed to analyze the heat spreading capacity of a microgrooved surface. V-shaped microgrooves are etched on silicon wafers using standard lithographic process. The shapes of the liquid menisci in the microgrooves are accurately measured using image analyzing interferometry as functions of heat input and opposing body force (angle of inclination). The relevant parameters that govern the spreading and cooling process of an evaporating curved microfilm, e.g., the adsorbed film thickness, contact angle, and curvature at the thicker end of the meniscus are accurately measured. The trends in these values are found to be consistent with the physics of the process. The temperature profiles are measured for the microgrooved and non-grooved silicon substrates under identical conditions of heat input and inclination and the enhanced spreading of the film in presence of microgrooves toward the hot region is quantified. The axially average values of a dimensionless temperature, defined for this study, are used to quantify the enhanced cooling and temperature homogenization potentials of microgrooved surfaces along with the effect of opposing body forces. The study clearly indicates the beneficial effects of change-of-phase heat transfer from an evaporating microfilm on microgrooved surfaces and its potential use in a miniature passive cooling device.

Argon–oxygen (Ar–O 2 ) plasma treatment of polyethersulfone (PES) membranes is carried out to enhance hydrophilicity of the membranes leading to less deposition of solute particles and subsequent flux enhancement. The membranes are exposed to plasma of Ar–O 2 mixtures and the effects of exposure time and concentration of oxygen have been studied in detail. The membrane is characterized by Fourier transform infrared (FTIR) spectrum analysis and the hydrophilicity and flux enhancement of the plasma treated membranes are quantified by contact angle measurements, SEM and experiments with polyethylene glycol (PEG) of molecular weight 20,000, in a continuous flow cylindrical cell. The deposition thicknesses of PEG on the membrane surfaces are optically quantified using image analyzing microscopy. The results clearly demonstrate that a plasma treated PES membrane is more hydrophilic and resists fouling leading to significant enhancement of permeate flux.

Electric field enhanced cross-flow ultrafiltration has been carried out for fractionation of aqueous solution of two proteins, e.g., bovine serum albumin (BSA) and Lysozyme using a 30 kg/mol molecular weight cut-off membrane. A detailed parametric study has been carried out to investigate the effect of system parameter such as electric field, solution pH, feed concentration ratio, cross-flow velocity and pressure difference on the permeate flux and observed retention of Lysozyme. A theoretical model based on film theory is developed to predict permeate flux and observed retention of Lysozyme under laminar flow regime including the effects of external d.c. electric field for osmotic pressure governed ultrafiltration. The governing equations of the concentration profile in the developed mass transfer boundary layer in a rectangular channel are solved numerically. The model parameters such as real retention ( R r2 ) of the Lysozyme and protein–protein interaction parameter ( B ) are evaluated by optimizing the experimental values of steady state permeate flux and permeate concentration. The experimental results reveal that there is a significant effect of electric field on both permeate flux and observed retention.

The thermodynamics of cloud point extraction (CPE) of three different dyes are investigated. Dyes used are congo red, eosin and chrysoidine. Iso-octyl phenoxy polyethoxy ethanol (TX-100) and octyl phenol poly ethylene glycol ether (TX-114) are used as non-ionic surfactant. The effects of different operating conditions (e.g., temperature and concentrations of surfactants and dyes) on various thermodynamic parameters such as change in Gibbs free energy (Δ G 0 ), change in enthalpy (Δ H 0 ) and change in entropy (Δ S 0 ) are observed and presented in detail. It is found that the values of Δ G 0 increase with temperature but decreases with the concentrations of surfactant and dye. The values of Δ H 0 and Δ S 0 increase with surfactant concentration but decrease with dye concentration. Comparisons of all the thermodynamic parameters are made for chrysoidine–TX-100 and chrysoidine–TX-114 systems. Negative values of Δ G 0 of all three dyes dictate that the solubilizations are spontaneous phenomena. Endothermic nature of the solubilization process of all dye is governed by the positive value of Δ H 0 . On the other hand, positive values of Δ S 0 prove that dye molecules are organized on the mantle of aqueous hydrophilic chains in a more random fashion.

The effect of alteration in hydrodynamic conditions and external electric field on the permeate flux during ultrafiltration of synthetic and mosambi juice in a cross flow channel has been studied. The hydrodynamic conditions inside the cross flow channel were altered by imposing laminar flow, laminar flow with turbulent promoters, flow in the transition (in case of synthetic juice) and turbulent (in case of actual juice) regime. The steady state permeate flux was in the range of 17.5 to 18.5 L/m2h (at Re = 657, laminar flow) for operating pressures (276 to 552 kPa). This range was in between 18 and 22.5 L/m2h using turbulent promoters at the same Reynolds number and in between 35 and 43 L/m2h in the transition flow regime at the same operating pressure. In the third case, the effects of external electric field (a body force) on the flux enhancement were explored. The steady state flux of the synthetic juice increased by about 20% when the external electric field was applied gradually up to 1,600 v/m. For actual depectinized mosambi juice, about 50% enhancement of steady state flux was achieved with an external electric field of strength 500 v/m. PRACTICAL APPLICATIONS The application of membrane technology to fruit juice processing is one of the emerging areas in food industry. Ultrafiltration (UF) and microfiltration (MF) processes are valid approaches for the clarification of fruit juices. The traditional method of fruit juice clarification involves a number of steps involving centrifugation to remove suspended solid, enzymatic treatment for depectinization, fining agents such as bentonite, gelatin to remove haze and finally filtration by the diatomaceous earth to remove the fining agents. The major problem during juice clarification is the pectin present in juice even after the enzyme treatment, leading to a drastic flux decline during UF and MF. In this study, two methods, namely, alteration of hydrodynamic conditions in the flow channel and application of external electric field for improving the permeate flux during UF of synthetic as well as depectinized mosambi juice, are investigated.

Removal of dye from aqueous solution using electric field assisted micellar enhanced ultrafiltration (MEUF) has been studied in a rectangular cross-flow channel over a wide range of operating conditions. Sodium dodecyl sulfate (SDS) and methylene blue (MB) have been taken as anionic surfactant and cationic dye, respectively. An ultrafiltration membrane (polyphenylene ethersulfone) of molecular weight cut-off (MWCO) 10 kDa, has been used in the experiment. The effects of operating conditions, e.g., electric field, surfactant to dye concentration ratio, transmembrane pressure and cross-flow velocity on the permeate flux and retention of MB have been investigated in detail. Experimental results confirm that by applying d.c. electric field (1000 V m −1 ), permeate flux increases by about 33% with approximately 99% removal of MB. An expression for the prediction of limiting flux in ultrafiltration is developed in this study. The predictions of permeate flux are in good agreement with the experimental results.

Electric field-assisted cross-flow ultrafiltration of mosambi ( Citrus sinensis (L.) Osbeck) juice has been carried out using a 50 kDa molecular weight cut-off membrane. Electric field is applied in both constant as well as pulse mode. The effect of process parameters, e.g., electric field, pulse ratio, cross-flow velocity and transmembrane pressure on the permeate flux and energy consumption are studied. Application of dc electric field has resulted in significant improvement of permeate flux. Application of pulsed electric field is found to be more beneficial in terms of energy consumption, and equally effective in terms of flux augmentation as compared to constant field. An already developed resistance-in-series model based on gel layer theory is used incorporating the effect of constant as well as pulsed electric field and numerically solved to quantify the flux decline and gel layer deposition. The predictions from the numerical solution of the model are successfully compared with experimental results under various operating conditions.

Electric field enhanced cross flow ultrafiltration of aqueous solution of bovine serum albumin (BSA) has been carried out in a thin rectangular channel using 30,000 molecular weight cut-off membrane over a wide range of operating conditions. Detailed parametric study has been performed to observe the effect of feed concentration, electric field, cross flow velocity and pressure on permeate flux. An artificial neural network approach with single hidden layer has been systematically developed to predict permeate flux using some of the experimental results. The rest of the experimental results are successfully compared with the model predictions with less than 1% average error. The analysis reveals significant beneficial effect of electric field on permeate flux. In this work, emphasis has been given on random selection of training data and small network. The developed trained network is also able to capture the non-linear prediction of permeate flux with new operating conditions which has not been used in the training process and enhances the physical understanding of the process.

The shelf life of filtered juice is extremely important to make the clarification process successful. Ultrafiltered mosambi juice was collected under aseptic condition in sterilized vials in a laminar flow chamber. The collected filtered juice was stored in amber-colored and transparent vials for 1 month, and its quality parameters (total soluble solid, pH, clarity, color and ascorbic acid) were studied at 5-day intervals. The juice, stored at room temperature, was spoiled in 3 days. The soluble solid and pH of the juice stored at refrigerated temperature in both vials remained unchanged during the storage period. The degradation kinetics of ascorbic acid and nonenzymatic browning for both the storage vials was established. The clarity of juice decreases with time marginally. Ascorbic acid decreases, and nonenzymatic browning increases in both vials to some extent at the end of storage time (30 days). PRACTICAL APPLICATIONS The study of the shelf life of ultrafiltered mosambi juice is of utmost importance from the point of view of industrial applications. Production of clarified juice is meaningful only if it can be stored for a prolonged period without being fermented. This renders availability of processed juice round the year and the places where the fruits are not available. The clarified mosambi juice produced by ultrafiltration is free of any additives and preservatives. Therefore, a proper storage study over an adequate period of time is necessary. Monitoring of various parameters of the juice, degradation kinetics of the clarity and ascorbic acid will dictate the longevity of the treated juice, which in turn will indicate the expiry time of the juice from the day of processing.

An experimental investigation of electric field assisted clarification of synthetic juice (a mixture of pectin and sucrose) and mosambi ( Citrus Sinensis ( L .) Osbeck ) juice using a 30 kDa molecular weight cut-off membrane in cross-flow ultrafiltration mode under laminar flow regime is reported herein. Electric field is applied in both continuous as well as pulse mode. Application of d.c. electric field has resulted in significant enhancement of permeate flux. It has been found that use of pulsed electric field is more advantageous in terms of less energy consumption, no property variations of the permeate and retentate streams and equally effective in terms of flux enhancement as compared to continuous field. A gel polarization model is proposed incorporating continuous as well as pulsed electric field and numerically solved to quantify the permeate flux. Experimental flux values are successfully compared with results from the numerical solution of the model under various operating conditions.

An experimental investigation has been undertaken to observe the effect of external electric field on the enhancement of permeate flux during clarification of mosambi (Citrus sinensis (L.) Osbeck) juice by ultrafiltration. A detailed study has been carried out using a 50 kDa molecular weight cut-off flat sheet polyethersulfone membrane in cross-flow ultrafiltration under laminar flow conditions for a wide range of operating conditions. Use of d.c. electric field resulted in a 32% enhancement of permeate flux. A steady state gel polarization model has been applied to evaluate the gel layer concentration, effective diffusivity and effective viscosity of the juice within the concentration boundary layer, by optimizing the experimental flux data.

A two-step membrane separation process, namely, nanofiltration (NF), followed by reverse osmosis (RO), is proposed to treat the soaking effluent collected from a tannery. Solution diffusion and osmotic pressure model are combined to predict the steady-state permeate flux and permeate concentration for continuous, cross flow membrane separation operations. Three flow regimes, namely, laminar, laminar with promoters, and turbulent flow are considered. The extent of polarization on the membrane surface is quantified. For both NF and RO, the extent of polarization increases with increasing transmembrane pressure and decreases with cross flow rate. The model parameters are optimized by comparing the calculated results with the experimental data. © 2008 American Institute of Chemical Engineers Environ Prog, 2008

Aqueous solution containing copper (cation) and potassium permanganate (anion) was treated by ultrafiltration using mixed micellar system comprising of sodium dodecyl sulfate and cetylpyridinium chloride. Simultaneous separation characteristics of both cation and anion, as well as permeate flux were studied for various operating conditions, namely, transmembrane pressure drop and cross-flow rate. The study was carried over a wide concentration range of both solutes. In the mixture, copper concentration was in the range from 0.05 to 4.0 kg/m3 and that of potassium permanganate was 0.05 to 0.25 kg/m3. Retention of copper was in the range of 90–100% and that of potassium permanganate was 96–99%. Permeate flux was found to be less in the mixed micellar system compared to single surfactant system. A four step chemical treatment process was proposed to recover and reuse the surfactants.

Ultrafiltration of synthetic fruit juice (mixture of pectin and sucrose) is performed in continuous cross flow mode with an organic ultrafiltration membrane (PPE 30, poly phenylene ethersulfone) of 30 K molecular weight cut off. The permeate fluxes are measured under various operating conditions, namely, transmembrane pressure and cross flow velocity. Significant enhancement of permeate flux is achieved by incorporation of cylindrical promoters placed perpendicular to the flow. Image analyzing video microscopy is used to quantify the deposition profile of pectin on the membrane surface. The consistency of these measurements in relation to enhancement of permeate flux are examined. The coupled fluid flow and mass transfer processes including the effects of the promoters are modeled and solved using FLUENT. The geometry of the system is constructed using GAMBIT and special attentions are given to mesh sizes in the different zones of flow, e.g., finer mesh is used near the membrane surface. The calculated values of permeate flux under various operating conditions agree well with the experimental data.

Flux decline mechanism during microfiltration of watermelon juice was studied in detail. Identification of the flux decline mechanism was carried out by conducting experiments in an unstirred batch cell. Using the identified mechanism, flux decline was predicted during stirred microfiltration in a continuous mode. The operating pressure range was from 137 to 276 kPa and that of Reynolds number was 1.40 × 105 to 1.87 × 105. Cake formation was identified as the main reason for flux decline. Prediction of flux decline during stirred continuous microfiltration using this mechanism was found adequate.

Experiments were carried out for removal of copper and calcium ions (single component as well as binary mixture) from aqueous solution using micellar-enhanced ultrafiltration (MEUF) in a cross-flow system. Micelles of anionic surfactant, sodium dodecyl sulfate (SDS) were used. The permeate flux was predicted using gel layer controlling model. The effects of concentration of cations on the gel concentration of SDS micelles were quantified. The model was extended to the prediction of permeate flux of the binary mixture of Cu2+ and Ca2+, as well. The extent of counterion binding of the single component as well as the mixture was quantified using localized adsorption model. The parameters of the adsorption isotherms were estimated using non-linear regression analysis of the experimental data.

Removal of arsenate (As(V)) ions by adsorption on natural laterite (NL) is investigated in the present study. Both equilibrium and kinetic study over a wide range of operating conditions are tested to evaluate the effectiveness of NL to remove As(V) from water. In the batch study, the effects of adsorbent dose, initial pH, ionic strength of solution, initial arsenate concentration, temperature, and contact time are examined. Batch study reveals that the uptake of arsenate is effective in the pH range of 5.5 to 7.5. The isotherm data is fitted well in the Langmuir isotherm model, and adsorption capacity is found to be 0.565 mg g-1. The effective intraparticle diffusion coefficient of arsenate ions in NL is observed to be in the range of 7.4 to 9.4 × 10-10 cm2 s-1. Continuous column study using a fixed bed is also carried out. The Adams−Bohart model is applied for the predicting breakthrough curve for column study.

Electric field enhanced ultrafiltration of pectin–sucrose mixture (synthetic juice) and mosambi ( Citrus sinensis (L.) Osbeck) fruit juice using 50,000 (MWCO) polyerthersulfon membrane is studied in a cross-flow cell. Pectin, completely rejected by the membrane, forms a gel type layer over the membrane surface. Under the application of an external dc electric field across the membrane, gel-layer formation is restricted leading to an enhancement of permeate flux. During ultrafiltration of synthetic juice, application of dc electric field (800 V/m) increases the permeate flux to almost threefold compared to that with zero electric field. A theoretical model based on integral method assuming suitable concentration profile in the boundary layer is developed. The proposed model is used to predict the permeate flux in gel-layer governed electric field enhanced ultrafiltration. Predictions of the model are successfully compared with the experimental results under a wide range of operating conditions. Experiments with fruit juice also demonstrated significant increase in flux with the application of a suitable electric field.

Separation characteristics of two systems of binary mixtures, namely, (i) copper and calcium; (ii) copper and beta naphthol were studied using micellar‐enhanced ultrafiltration (MEUF). Sodium dodecyl sulfate (SDS) was taken as the anionic surfactant. An organic polyamide membrane of molecular weight cut‐off 5 kDa was used in cross flow MEUF experiments. Suitable feed surfactant concentration was found to be about 25 kg/m3. The effects of the feed composition, the transmembrane pressure drop, and the cross flow rate on the permeate flux and observed retention of each solute were studied. For single solute systems, the observed retention of both copper and calcium were about 99% for a solute concentration up to 1.0 kg/m3 but the retention reduced to 90% to 92% when solute concentration was increased to about 3 to 4 kg/m3. Retention of copper and calcium was in the range of 88 to 97% for various compositions in their binary mixture. Retention of beta naphthol was in between 82 to 84% in its mixture ...

Ultrafiltration studies of synthetic sucrose and pectin mixture and enzymatically treated mosambi juice have been performed in a stirred continuous cell. A model based on gel layer theory is developed to predict the flux decline during filtration for both synthetic and actual juice. From the steady state flux data, the mass transfer coefficient is observed to vary with operating pressure only and a modified Sherwood number relationship is proposed for such a system. The permeate of the filtered juice contains almost all the nutritional values of the original juice with significant improvement in clarity.

Treatment of a dyeing bath of a tannery was carried out using a hybrid membrane-based separation scheme consisting of Nanofiltration (NF) followed by Reverse Osmosis (RO). Experiments were conducted using a cross-flow cell in continuous mode. The performance criteria of the separation scheme were evaluated in terms of dye concentration, Chemical Oxygen Demand (COD), Biological Oxygen Demand (BOD), Total Dissolved Solids (TDS), Total Solids (TS), pH, Cl− concentration, chromium (III) concentration, etc. Effects of different operating conditions, namely operating pressure and cross-flow velocity, on the system performance were investigated. Complete retention of dye was obtained in NF step itself. NF-treated solution was further subjected to RO to bring down the BOD and COD values of the treated effluent below the permissible level. Possibility of flux enhancement using turbulent promoter in laminar flow regime and imposing turbulent flow regime itself was also investigated both in NF as well as RO.

Arsenite removal capacity of natural laterite (NL), collected from Kharagpur, in the district of Midnapore, West Bengal, India, has been investigated. Effects of adsorbent dose, operating pH, contact time, initial arsenite concentration, adsorbent particle size, etc. on the removal of arsenite are examined. Kinetic study in agitated baffled vessel reveals that uptake of As(III) ions is rapid in the first two hours and slows down thereafter. Maximum removal efficiency of As(III) achieved is 98% at an adsorbent dose of 40 g/l with initial As(III) concentration of 1000 μg/l in batch studies and 94% at 20 g/l absorbent dose under the same conditions. Equilibrium time is almost independent of initial arsenite concentration. Equilibrium studies show that As(III) ions have high affinity towards NL even at very low concentration of arsenite. In speciation study, about 20% conversion to As(V) from As(III) is observed, with initial As(III) concentration of 1000 μg/l and at 20 g/l adsorbent dose. Thermodynamic parameters depicted the endothermic nature of adsorption. The results suggest that NL could be used as effective filter medium for removal of As(III) ions.

Activated carbon is used for the removal of colored toxic congo red dye. The effects of different operating conditions like, initial dye concentration, contact time, pH and temperature are studied for adsorption of congo red by a known amount of activated carbon (1.0g/L) under stirred batch condition. The zero point of charge of the activated carbon is found about 6.6. About 90% dye is removed for initial concentration of 50 and 100mg/L, it is about 80% at pH 7.0. Maximum adsorption (about 100%) of dye is observed at pH 2.0 for the concentration range studied here. Freundlich isotherm is found to fit the equilibrium data more adequately. Pseudo second order kinetic model explain successfully the kinetic data. The surfactant enhanced carbon regeneration (SECR) technique using both cationic and anionic surfactants is adopted for the regeneration of spent carbon by desorbing the dye. A kinetic model for dye desorption from the commercial activated carbon (CAC) is also proposed. Anionic surfactants show better performance than the cationic ones. Efficiency of dye desorption using surfactants is also compared with the desorption using pH change.

A treatment method of liming effluent of a tannery is tested using hybrid membrane separation processes. The effluent after gravity settling and alum coagulation is subjected to ultrafiltration followed by nanofiltration. The optimum alum dose is obtained by analyzing the effluent using various concentrations of alum. The membrane separation processes are conducted in a continuous cross flow mode. The effects of operating conditions e.g., transmembrane pressure difference, and cross flow velocity (Reynolds number) on the permeate flux are analyzed. Effects of change in hydrodynamic conditions in various flow regimes, e.g., laminar, laminar with turbulent promoter, and turbulent flow on flux improvement have been studied. A resistance‐in‐series model for flux decline during the filtration process is proposed. COD, BOD, TDS, TS, pH, Ca2+ concentration, Cl− concentration and conductivity are measured before and after each operation. The potential of the dried sludge as organic fertilizer is also exp...

Attenuated total internal reflection Fourier transform infra-red (ATR-FT-IR) spectrum analysis is done to characterize a thin film composite (TFC) nanofiltration (NF) membrane. The chemical compositions of the skin layer (composite polyamide) and the support substrate (polysulfone) are evaluated. Using a high-resolution optical microscope, the thickness of the different layers of the composite membrane is measured. The deposition and penetration of crystal violet molecules on and inside the composite membrane during nanofiltration at different operating conditions are optically measured. The deposition and penetration as a function of location on the membrane are also measured. The experimental results are found to be consistent with the basic physics of the process.

Flux decline during ultrafiltration (UF) of depectinized mosambi juice was quantified by a resistance-in-series model. Resistance against the solvent flux was assumed to be comprised of four components, namely, membrane hydraulic, adsorption, pore plugging and fouling resistance. Apart from the membrane hydraulic resistance, evolution of each of these resistances with time was determined from separate set of experiments independently. The experiments were conducted in a stirred continuous mode both under low as well as high polarization conditions. The range of operating transmembrane pressure drop in the experiments was 276–552 kPa and that of Reynolds number was 1.4–2.1 × 10 5 . Correlations were proposed to quantify the growth kinetics of the resistances, separately. Finally, the profile of total resistance and corresponding flux decline were calculated and compared with the experimental data. The adsorption resistance was found to be about 60% of membrane hydraulic resistance. The pore blocking resistance was about the same as that of membrane resistance at higher Reynolds number and was about four times at lower Reynolds number. The fouling resistance was about six to ten times the membrane resistance in the range of operating conditions, studied herein.

A systematic method is outlined to design cloud point extraction process. The aim is to calculate the concentration of non-ionic surfactant required for a desired extraction of dye at various operating conditions (feed dye concentration and temperature). In the course of design calculations, information about the following two characteristics of this system are required: (1) the solubilization isotherm of the dye in the surfactant solution at various operating temperatures and (2) quantification of the variation of the fractional coacervate phase volume with the feed surfactant, dye concentration and the operating temperature. In case of TX-100 and the dye system (congo red and eosin), a Langmuir type solubilization isotherm is fitted using the experimental data. Correlations are developed for the variation of isotherm parameters with temperature. A simple correlation of fractional coacervate phase volume with feed surfactant concentration is proposed in the form of a c s b . From the experimental data, the variations of a and b with feed dye concentration and temperature are evaluated. Using the developed correlations and proposed design method, the concentration of feed surfactant required to achieve 1 ppm dye concentration in the dilute phase is calculated for the two dyes at typical operating temperatures and feed dye concentrations. The developed method will be of immense help for scale up of cloud point extraction process.