Welcome To Ashis Research Group

Research

Dynamics of deformable objects at immiscible fluid-fluid interface:

Here, we reported continuous splitting of aqueous droplets at the interface between two co-flowing immiscible oil streams in a microchannel and demonstrated splitting of droplets encapsulating microbeads and cells

(Soft Matter,2018)


We studied the migration behavior of rigid polystyrene microparticles at an interface of co-flowing streams of primary CP1 (aqueous) and secondary CP2 (oils) immiscible phases at low Reynolds numbers in a microchannel. Rigid microparticles in a low flow do not experience any lateral force and move along the streamlines passing through their center of mass. The behavior of the particles at the interface is governed by the spreading parameter, S and is also influenced by the presence of surfactants at the interface

(J Colloid and Interface Science,2017)


We presented the dynamics of aqueous droplets of different size and viscosity at an interface between concurrent streams of immiscible continuous phases. Also we discussed the interplay between the competing non-inertial lift and interfacial tension forces, which govern the interfacial migration of the droplets

(Langmuir,2016)


We studied the ultra-low voltage based electro coalescence phenomenon for the demulsification of aqueous droplets with an aqueous stream. In the absence of electric field, due to the disjoining pressure resulting from the tail-tail interaction between the surfactant molecules present on the aqueous droplets and interface, coalescence of aqueous droplets with the aqueous stream is prevented. However, above a critical electric field, the electrical stress overcomes the disjoining pressure thus leading to the droplet coalescence

(Langmuir,2017)


Wetting and elasto-capillarity:

We demonstrated the flotation of a denser liquid (water) drop on a lighter liquid in a pair that does not satisfy the Neumann triangle. We attribute this newly studied phenomenon to the role of line tension which prevents the water droplet from complete engulfment. We establish line tension values for different liquids with water and show possible heterogeneous nucleation that contributes toward the variance of line tension values

(Langmuir,2016)


We report the dynamics of compound droplets with a denser liquid (water) droplet over a less dense sessile droplet (mineral oil) that satisfies the Neumann condition.For a water droplet-to-oil droplet at volume ratio 0.05 stable axisymmetric configuration is achieved ; for migration of water droplet is observed.Also, we demostrated the coalescence of water droplets of size above the critical size at the axisymmetric position.

(Langmuir,2017)


Manipulation of liquid plug inside the microchannel by a driving liquid

(Appl. Phys. Lett., 2015)


At present, we are working on transport of liquid using PDMS membranes by elastocapillarity

When liquid comes in contact with flexible membrane, due to surface tension force it deforms which results in Laplace pressure gradient which governs the flow

(Soft Matter, 2017)



Super hydrophobic surfaces that exhibit a very high water contact angle (>150°) as well as a very low sliding angle (<10°), have remained a buzz topic in recent times due to their significant applications. Super hydrophobic surfaces are of special interest due to several distinctive characteristics such as self-cleaning, anti-icing, anticontamination, and anticorrosion. Due to these properties, such surfaces have found a wide variety of applications in antibiofouling paints for boats, anti-sticking of snow for antennas and windows, self-cleaning windshields for automobiles, stain resistant textiles, open surface digital microfluidics, blood plasma separation, drop guiding systems, and oil−water separation. Also, large contact angles and small liquid−solid contact areas in super hydrophobic surfaces lead to significant reduction in the drag force

(ACS Appl. Matter. & Interfaces, 2017)



Elastocapillarity is the study of interest, where capillary force can overcome the bending rigidity of the material. This phenomenon is mostly observed in micro scales. This is known to cause stiction of slender structures in MEMS, coalescence of wet hairs and thin membranes wrapping liquid droplets. In the past, we have used this principle to manipulate fluids in microchannel.

One of the wall as deformable membrane for increasing the capillary velocity

Fluid flow in primary channel can be manipulated by a fluid flow in secondary channel with a PDMS membrane separating them as a flexible wall

(Phys Rev E., 2015)

(Appl. Phys. Lett., 2016)


Magnetofluidics:

Magnetofluidics handles micro scale fluid mechanics with an additional volumetric force. Recently it has acquired immense attention due to its contact free manipulations. Using magnetic fluids along with magnetic field capillary manipulation is demonstrated. A sharp increase in meniscus velocity is found using this configuration. Further control of meniscus inside the microchannel has been demonstrated extensively

(Sensors and Actuators B Chemical,2016)


Digital Magnetofluidics talks about handling discrete magnetic drops on engineered surfaces. Manipulation of tiny droplets enables coalescence, splitting etc. Here we have studied the dynamics of ferrofluid droplets on PDMS surface under the influence of a permanent magnet. Wetting dynamics and splitting characterizations have been studied and explained in detail.

 

(Soft Matter,2018)


Acoustofluidics:

 
 
 
 

Acoustofluidics, handling of fluids, microparticles and cells using ultrasonic waves has emerged as a power tool in the past few decades due to its inherent nature of precise and contactless manipulation. Two types of waves namely bulk and surface acoustic waves are employed here to perform manipulations

(Appl. Phys. Lett., 2016)

We demonstrated on-chip blood plasma separation in a continuous stream of whole blood using bulk acoustic waves. We also developed a model to predict the concentration profile of the focused RBCs which is extremely useful for the design of microchannel for the blood plasma separation application

We demonstrated the focusing of microparticles using surface acoustic waves. The same concept is adopted to perform on-chip blood plasma separation of diluted human blood samples, where the blood cells are focused at the center leaving plasma at the periphery


Blood-Plasma Separation:

Capillary Flow with Hydrophobic Patch Filtration
 
 
 

Plasma is the major component of human blood, constituting ~ 55% by volume, and consisting of numerous proteins, antigens, antibodies etc., which serve as disease biomarkers. Often, these biomarkers are present in very low quantities, and detecting them against a huge background of red and white blood cells requires using efficient separation techniques. To address issues with the recovery of high-purity plasma, we employ the hydrophobic patch filtration mechanism and acoustophoresis. While the patch filtration device enables batch processing for the detection of glucose in recovered plasma, the acoustophoretic microchannel provides means to continuously process the patient sample. We have also developed models to predict flow profile within the patch filtration device and the concentration profile of the focused RBC’s inside the acoustophoretic microchannel.

Biomicrofluidics,2016

Scientific Reports, 2017


Prediction of Sepsis:


Early detection of systemic inflammatory response syndrome (SIRS) helps in managing sepsis and minimizing its adverse effects in patients. Gaseous signaling molecules, also referred to as gasotransmitters, play a vital role in the process of inflammation. The concentration of these compounds gives crucial information about the state of inflammation. Thus, the change in the level of such gasotransmitters in patients’ blood is a prognostic marker of sepsis. We have fabricated a microfluidic device that utilizes fluorimetry for the continuous monitoring of the concentration of H2S, a gasotransmitter, in patients’ blood. We plan to integrate our device with a microfluidic plasma separation unit for on-chip blood cell separation and sepsis detection for use in clinical settings.


CTC Isolation and Genomic Analysis:


Circulating tumor cells (CTC’s) occur in very low frequency in whole blood, i.e. 1 mL human blood could contain 1-100 CTC’s among few million white blood cells (WBC’s) and a billion red blood cells (RBC’s). Quantification of CTC’s have high clinical value as these cells usually indicate tumor metastasis and facilitate real-time monitoring of systemic therapy by sequential peripheral blood sampling. Molecular characterization of CTC’s helps to understand the mechanism of metastasis, enables identifying therapeutic targets and contributes to personalized, anti-metastatic therapies.


Dengue Diagnostics via Colorimetry and Localized Surface Plasmon Resonance:

Colorimetry Analysis
Localized Surface Plasmon Resonance (LSPR)
 

Dengue is an infectious disease that is transmitted by the adult Aedes aegypti mosquito and affects more than 100 million people annually. Its symptoms are usually mild, and hence in its early stages, patients are often treated for other febrile diseases. Among the numerous dengue biomarkers, the non-structural protein (NS1) antigen appears in plasma as early as the onset of infection, and hence has high diagnostic value. We employ two highly-sensitive techniques, namely colorimetry and localized surface plasmon resonance, to accomplish rapid detection of NS1 antigen via microfluidics. For real-world applications, we will integrate these techniques with inexpensive microfluidic architectures.


Mechanophenotyping:

Size and stiffness of cells can be considered as biomarkers for the detection of various diseases including malaria, cancer, sickle cell and sepsis. We have found that hydrodynamic resistance of cells is related to cell size and stiffness

(Biomicrofluidics, 2014).

The cell stiffness was also characterized using AFM

(RSC Advances, 2016).


We have also observed that the entry and transit behavior of cells from a wider channel into a narrow constriction is dependent on the cell size and stiffness. The entry and transit behavior can be utilized to extract various biophysical properties such as cytoplasmic viscosity, Young’s Modulus and induced hydrodynamic resistance offered by the cell.

(Lab Chip, 2017)


Incubation :

In order to take some of the technologies developed in our lab towards product development and possible commercialization, we have incubated Ariken Labs Pvt. Ltd. Please visit the link for more details.