Ankur Gupta

High-Throughput Contact Flow Lithography

High‐throughput fabrication of graphically encoded hydrogel microparticles is achieved by combining flow contact lithography in a multichannel microfluidic device and a high capacity 25 mm LED UV source. Production rates of chemically homogeneous particles are improved by two orders of magnitude. Additionally, the custom‐built contact lithography instrument provides an affordable solution for patterning complex microstructures on surfaces.

Sensitive and Multiplexed On‐chip microRNA Profiling in Oil‐Isolated Hydrogel Chambers

Although microRNAs (miRNAs) have been shown to be excellent indicators of disease state, current profiling platforms are insufficient for clinical translation. Here, we demonstrate a versatile hydrogel-based microfluidic approach and novel amplification scheme for entirely on-chip, sensitive, and highly specific miRNA detection without the risk of sequence bias. A simulation-driven approach is used to engineer the hydrogel geometry and the gel-reaction environment is chemically optimized for robust detection performance. The assay provides 22.6u2005fM sensitivity over a three log range, demonstrates multiplexing across at least four targets, and requires just 10.3u2005ng of total RNA input in a 2u2005hour and 15u2005minutes assay.

A General Route for Nanoemulsion Synthesis using Low Energy Methods at Constant Temperature

The central dogma of nanoemulsion formation using low-energy methods at constant temperature-popularly known as the emulsion inversion point (EIP) method-is that to create O/W nanoemulsions, water should be added to a mixture of an oil and surfactant. Here, we demonstrate that the above order of mixing is not universal and a reverse order of mixing could be superior, depending on the choice of surfactant and liquid phases. We propose a more general methodology to make O/W as well as W/O nanoemulsions by studying the variation of droplet size with the surfactant hydrophilic-lypophilic balance for several model systems. Our analysis shows that surfactant migration from the initial phase to the interface is the critical step for successful nanoemulsion synthesis of both O/W and W/O nanoemulsions. On the basis of our understanding and experimental results, we utilize the reverse order of mixing for two applications: (1) crystallization and formulation of pharmaceutical drugs with faster dissolution rates and (2) synthesis of alginate-based nanogels. The general route provides insights into nanoemulsion formation through low-energy methods and also opens up possibilities that were previously overlooked in the field.

Low Energy Nanoemulsions as Templates for the Formulation of Hydrophobic Drugs

Most small molecule active pharmaceutical ingredients (APIs) are hydrophobic which poses formulation challenges due to their poor water solubility. Current approaches are energy intensive and involve presenting the API in a nanoparticle form that is then combined with other additives into a stable formulation. Here, a bottom‐up and scalable method that formulates nanoparticles (crystalline or amorphous) of poorly water‐soluble APIs directly embedded in composite hydrogel beads is presented. Using nanoemulsions prepared from a low energy method as templates, the flexible approach allows to vary the embedded API nanoparticle size from 100 to 500 nm and the hydrogel bead size from 100 to 1200 µm, and subsequently achieve control over the dissolution kinetics. To better understand the dissolution process, a physical model is build that allows to collapse the kinetic data onto a master curve and predict the dependence of release rates on size of both API nanoparticles and hydrogel beads. Lastly, it is demonstrated that the dissolution kinetics of multiple drugs embedded in the same hydrogel matrix can be tuned simultaneously, an attractive property for commercial multi‐drug dosage applications. The new approach not only leads to process intensification, but also improved performance.

Oil Recovery from Micropatterned Triangular Troughs during a Surfactant Flood

We study the recovery of oil trapped inside micropatterned triangular troughs after injecting a surfactant solution. In our experiments, we track the trapped oil volume with duration of surfactant flood for different capillary numbers. We observe that the capillary number affects the amount of oil recovered as the well as the rate of oil recovery. We employ multiphase flow simulations to analyze our system and show a qualitative agreement between the simulations and experimental results. We also discover that beyond a capillary number, the volume of oil recovered plateaus, and no additional oil is released with an increase in capillary number. We develop a theoretical model to predict the dependence of maximum oil recovery on geometrical features and find that the theoretical predictions compare favorably with the trends obtained from our simulations. Though approximate, theoretical relation provides insights into the efficiency of oil recovery and can be utilized to understand the effect of sharp bends and dead ends in enhanced oil recovery and soil remediation.

Electrical Double Layers: Effects of Asymmetry in Electrolyte Valence on Steric Effects, Dielectric Decrement, and Ion–Ion Correlations

We study the effects of asymmetry in electrolyte valence (i.e., non z: z electrolytes) on mean field theory of the electrical double layer. Specifically, we study the effect of valence asymmetry on finite ion-size effects, the dielectric decrement, and ion-ion correlations. For a model configuration of an electrolyte near a charged surface in equilibrium, we present comprehensive analytical and numerical results for the potential distribution, electrode charge density, capacitance, and dimensionless salt uptake. We emphasize that the asymmetry in electrolyte valence significantly influences the diffuse-charge relations, and prior results reported in the literature are readily extended to non z: z electrolytes. We develop scaling relations and invoke physical arguments to examine the importance of asymmetry in electrolyte valence on the aforementioned effects. We conclude by providing implications of our findings on diffuse-charge dynamics and other electrokinetic phenomena.