A. Sudeepthi

Bio: A. Sudeepthi is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Circulating tumor cell & Microfluidics. The author has an hindex of 3, co-authored 6 publications receiving 37 citations.

Cassie-Wenzel wetting transition on nanostructured superhydrophobic surfaces induced by surface acoustic waves

Abstract: We report irreversible Cassie–Wenzel wetting transition on a nanostructured superhydrophobic surface employing surface acoustic wave (SAW) vibration. The transition is achieved upon penetration of the liquid into the nanogrooves driven by the inertial energy of the drop imparted by the SAW. However, the filling up of nanopores imposes an energy barrier ( E b) to the transition, which requires the displacement of the initial solid–air interface inside the pores with a solid–liquid interface. We unravel that the relative magnitudes of the input acoustic energy ( E a c), and this energy barrier, hence, dictate the occurrence of the wetting transition, with the irreversibility in the transition, therefore, being explained from energy minimization of the system following the transition. In addition, observing the dynamics of the wetting front allowed the different regimes of the wetting transition process to be identified.

Aggregation of a dense suspension of particles in a microwell using surface acoustic wave microcentrifugation

Abstract: We investigate the aggregation of a dense suspension of particles (volume fraction, $$\varphi \sim 0.1$$ ) in a PDMS microwell by employing surface acoustic wave (SAW) microcentrifugation. In spite of acoustic attenuation at the LiNbO3–PDMS interface, a significant portion of the energy (> 80%) is available for driving fluid actuation, and, in particular, microcentrifugation in the microwell via acoustic streaming. Rapid particle aggregation can then be affected in the microcentrifugation flow, arising as a consequence of the interplay between the hydrodynamic pressure gradient force $$F_{\text{p}}$$ responsible for the migration of particles to the center of the microwell and shear-induced diffusion force $$F_{\text{SID}}$$ that opposes their aggregation. Herein, we experimentally investigated the combined effect of the particle size $$a$$ and sample concentration $$c$$ on these microcentrifugation flows. The experimental results show that particles of smaller size and lower sample concentration (such that $$F_{\text{p}} > F_{\text{SID}}$$ ) are concentrated efficiently into an equilibrium spot, whose diameter scales with the initial particle volume fraction as $$d_{\text{cs}} \sim \varphi^{0.3}$$ . In contrast, we found that as the local particle volume fraction at the center of the microwell approaches $$\varphi \sim 0.1$$ such that $$F_{\text{SID}} \ge F_{\text{p}}$$ , the particle aggregation fails. Additionally, we also investigate the effects of the well diameter, and the height, lateral positioning of microwell and the liquid volume on the microcentrifugation.

Substrate stiffness affects particle distribution pattern in a drying suspension droplet

Abstract: The complexities involved in achieving a tailor-made evaporative deposition pattern have remained a challenge. Here, we show that the morphological pattern of drying suspension droplets can be altered by varying substrate elastic modulus E . We find that the particle spot diameter and spacing between the particles scale with substrate stiffness as d s ∼ E − 0.15 and s ∼ E − 1.23 , respectively. We show that the larger spot diameter and spacing between particles on a softer substrate are attributed to a higher energy barrier U associated with stronger pinning of the contact line. The particle deposition pattern is characterized in terms of deposition index, I d , whose value is 0.75 for centralized (multilayer) and uniform (monolayer) deposition patterns observed for stiffer and softer substrates, respectively. The outcome of the present study may find applications in biochemical characterization and analysis of micro-/nanoparticles.

Continuous electrical lysis of cancer cells in a microfluidic device with passivated interdigitated electrodes.

Abstract: Cell lysis is a critical step in genomics for the extraction of cellular components of downstream assays. Electrical lysis (EL) offers key advantages in terms of speed and non-interference. Here, we report a simple, chemical-free, and automated technique based on a microfluidic device with passivated interdigitated electrodes with DC fields for continuous EL of cancer cells. We show that the critical problems in EL, bubble formation and electrode erosion that occur at high electric fields, can be circumvented by passivating the electrodes with a thin layer (∼18 μm) of polydimethylsiloxane. We present a numerical model for the prediction of the transmembrane potential (TMP) at different coating thicknesses and voltages to verify the critical TMP criterion for EL. Our simulations showed that the passivation layer results in a uniform electric field in the electrode region and offers a TMP in the range of 5–7 V at an applied voltage of 800 V, which is well above the critical TMP (∼1 V) required for EL. Experiments revealed that lysis efficiency increases with an increase in the electric field (E) and residence time (tr): a minimum E ∼ 105 V/m and tr ∼ 1.0 s are required for efficient lysis. EL of cancer cells is demonstrated and characterized using immunochemical staining and compared with chemical lysis. The lysis efficiency is found to be ∼98% at E = 4 × 105 V/m and tr = 0.72 s. The efficient recovery of genomic DNA via EL is demonstrated using agarose gel electrophoresis, proving the suitability of our method for integration with downstream on-chip assays.

Microfluidics Technology for Label-Free Isolation of Circulating Tumor Cells

Abstract: Circulating tumor cells (CTCs) are the tumor cells that get detached from a primary tumor site and enter bloodstream circulation that promotes the metastasis condition of cancer. The detection and analysis of CTCs hold significant clinical and research value in terms of cancer diagnosis, prognosis, treatment, and drug development research. Isolation and analysis of CTCs are already proven as a promising tool for effective drug screening. CTCs in the circulation can be considered as biomarkers for the early-stage detection of cancer. CTCs also offer the opportunity to study, monitor, and ultimately gain insights into the process of cancer metastasis. Among the existing approaches, microfluidic technology has become a hot spot in CTC detection and isolation due to their promising features such as automation, high precision, accuracy and sensitivity, portability, that are amenable to the development of point-of-care devices. CTCs can be isolated from the blood by labeling the cells with tumor-specific biomarkers, but the use of chemicals for labeling may interfere with the downstream assay. This paper aims to review the label-free microfluidic techniques for the detection and isolation of CTCs that have the potential to preserve phenotypic and genotypic characteristics of isolated cells. The principle of operation, methodology, application, advantages, and limitations of the different techniques are discussed. The performance of the different techniques is assessed based on several parameters such as capture efficiency, throughput, purity, sensitivity, and cell viability. Finally, a brief discussion on the challenges, commercialization aspects, and future perspectives is presented.

Rapid Deceleration-Driven Wetting Transition during Pendant Drop Deposition on Superhydrophobic Surfaces

Abstract: A hitherto unknown mechanism for wetting transition is reported. When a pendant drop settles upon deposition, there is a virtual "collision" where its center of gravity undergoes rapid deceleration. This induces a high water hammer-type pressure that causes wetting transition. A new phase diagram shows that both large and small droplets can transition to wetted states due to the new deceleration driven and the previously known Laplace mechanisms, respectively. It is explained how the attainment of a nonwetted Cassie-Baxter state is more restrictive than previously known.

Effect of surface energy and roughness on cell adhesion and growth – facile surface modification for enhanced cell culture

Abstract: In vitro, cellular processing on polymeric surfaces is fundamental to the development of biosensors, scaffolds for tissue engineering and transplantation. However, the effect of surface energy and roughness on the cell–surface interaction remains inconclusive, indicating a lack of complete understanding of the phenomenon. Here, we study the effect of surface energy (Es) and roughness ratio (r) of a polydimethylsiloxane (PDMS) substrate on cell attachment, growth, and proliferation. We considered two different cell lines, HeLa and MDA MB 231, and rough PDMS surfaces of different surface energy in the range Es = 21–100 mJ m−2, corresponding to WCA 161°–1°, and roughness ratio in the range r = 1.05–3, corresponding to roughness 5–150 nm. We find that the cell attachment process proceeds through three different stages marked by an increase in the number of attached cells with time (stage I), flattening of cells (stage II), and elongation of cells (III) on the surface. Our study reveals that moderate surface energy (Es ≈ 70 mJ m−2) and intermediate roughness ratio (r ≈ 2) constitute the most favourable conditions for efficient cell adhesion, growth, and proliferation. A theoretical model based on the minimization of the total free energy of the cell–substrate system is presented and is used to predict the spread length of cells that compares well with the corresponding experimental data within 10%. The performance and reusability of the rough PDMS surface of moderate energy and roughness prepared via facile surface modification are compared with standard T-25 cell culture plates for cell growth and proliferation, which shows that the proposed surface is an attractive choice for efficient cell culture.

High Frequency Sonoprocessing: A New Field of Cavitation-Free Acoustic Materials Synthesis, Processing, and Manipulation.

Abstract: Ultrasound constitutes a powerful means for materials processing. Similarly, a new field has emerged demonstrating the possibility for harnessing sound energy sources at considerably higher frequencies (10 MHz to 1 GHz) compared to conventional ultrasound (⩽3 MHz) for synthesizing and manipulating a variety of bulk, nanoscale, and biological materials. At these frequencies and the typical acoustic intensities employed, cavitation-which underpins most sonochemical or, more broadly, ultrasound-mediated processes-is largely absent, suggesting that altogether fundamentally different mechanisms are at play. Examples include the crystallization of novel morphologies or highly oriented structures; exfoliation of 2D quantum dots and nanosheets; polymer nanoparticle synthesis and encapsulation; and the possibility for manipulating the bandgap of 2D semiconducting materials or the lipid structure that makes up the cell membrane, the latter resulting in the ability to enhance intracellular molecular uptake. These fascinating examples reveal how the highly nonlinear electromechanical coupling associated with such high-frequency surface vibration gives rise to a variety of static and dynamic charge generation and transfer effects, in addition to molecular ordering, polarization, and assembly-remarkably, given the vast dimensional separation between the acoustic wavelength and characteristic molecular length scales, or between the MHz-order excitation frequencies and typical THz-order molecular vibration frequencies.

Robust and durable liquid-repellent surfaces.

Abstract: Liquid-repellent surfaces, such as superhydrophobic surfaces, superoleophobic surfaces, and slippery liquid-infused surfaces, have drawn keen research interest from the communities engaged in chemical synthesis, interfacial chemistry, surface engineering, bionic manufacturing and micro-nano machining. This is due to their great potential applications in liquid-proofing, self-cleaning, chemical resistance, anti-icing, water/oil remediation, biomedicine, etc. However, poor robustness and durability that notably hinders the real-world applications of such surfaces remains their Achilles heel. The past few years have witnessed rapidly increasing publications that address the robustness and durability of liquid-repellent surfaces, and many breakthroughs have been achieved. This review provides an overview of the recent progress made towards robust and durable liquid-repellent surfaces. First, we discuss the wetting of solid surface and its generally-adopted characterisation methods, and introduce typical liquid-repellent surfaces. Second, we focus on various evaluation methods of the robustness and durability of liquid-repellent surfaces. Third, the recent advances in design and fabrication of robust and durable liquid-repellent surfaces are reviewed in detail. Fourth, we present the applications where these surfaces have been employed in fields like chemistry, engineering, biology and in daily life. Finally, we discuss the possible research perspectives in robust and durable liquid-repellent surfaces. By presenting such state-of-the-art of this significant and fast-developing area, we believe that this review will inspire multidisciplinary scientific communities and industrial circles to develop novel liquid-repellent surfaces that can meet the requirements of various real-world applications.

Submicron Particle and Cell Concentration in a Closed Chamber Surface Acoustic Wave Microcentrifuge.

Abstract: The preconcentration of particulate and cellular matter for their isolation or detection is often a necessary and critical sample preparation or purification step in many lab-on-a-chip diagnostic d...