Browsing by Author "Patel, Panchami"

This article describes two sets of experiments designed to enhance the understanding of colloidal systems. These experiments were designed as a part of the theme “Colloids: Where Science Meets Engineering” taught in the Department of Chemical Engineering and additionally offered to physics, chemistry, and materials science departments as an advanced course at IIT Gandhinagar, India. Through this article, we describe experiments planned and conducted simultaneously with the course content to improve the student interaction with the subject matter and enhance their learning. The first set of experiments deals with preparing and characterizing gold nanoparticle sol and observing phenomena such as the Tyndall effect and aggregation with the addition of salt by UV analysis, DLS sizing, and zeta potential measurements. The second set of experiments deals with understanding interfaces, including contact angle, surface tension, critical micellar concentration of surfactants, and surface energy. The students are not only able to visualize course content but also exposed to the lab environment, learn basic preparation protocols, and handle or observe the application of high-tech equipment. Thus, this article aims to help develop further teaching protocols for instructors with similar course plans by suggesting key experiments that are easy to perform along with the course and facilitate student learning.

Hydrogels, a 3D network structure of polymer chains with significant water content, can be formed of either natural or synthetic polymers; biopolymers are highly preferred for their biocompatibility, biodegradability, and cell response. For targeted applications such as wound dressing, 3D printing, packaging, implants, drug delivery, cell imaging and targeting, biopolymer hydrogels can be formed across multiple scales of macro to nano size. To achieve the desired gel utility at any scale, the properties can be controlled by modifying the structural characteristics such as crosslink density, mesh size, polymer conformation, and microstructure. This review aspires to give a perspective assessment of the preparation methods, characterization techniques, and targeted applications of biopolymer-based hydrogels at macro and micro/nano scales. Additionally innovative coupling of characterization modes can provide both quantitative and qualitative insight into gel structure, property, and functionality.

The current manuscript reports the development of free-standing nanomaterial-modified hydrogels that can be explored for sensing applications. Most of the nanomaterial-hydrogel systems developed till now rely on the modification of an electrode as the supporting substrate on which the electrochemical reactions can take place. These substrates can be pencil electrodes and or screen-printed electrodes. This widely limits the use of hydrogels which can be used as scaffolds and can be explored for the fabrication of free-standing electrodes. Since the functionality of only hydrogel is quite limited the current manuscript reports the loading of gold nanoparticles inside the hydrogel matrix which makes it functionally active. The successful synthesis of the modified hydrogel was confirmed with Scanning Electron Microscopy (SEM) and elemental analysis. The rheological data confirmed the positive effect of gold loading on the hydrogel storage modulus. As a proof of concept, the work reports the non-enzymatic electrochemical detection of glucose using gold nanoparticle loaded carrageenan hydrogel. The sensor showed a linear response towards varying glucose concentrations (0 to 2.5 mM). The hydrogel systems can be incorporated into wearables and implantable sensors and can be extended for the detection of other biomarkers in bodily fluids.

Surfactants in water and both alcohol-water mixed solutions are used extensively in a host of industrial applications. This work presents the solution behavior and micellar transition of a cationic gemini surfactant (GS): N,N′-dihexadecyl-N,N,N′,N′-tetramethyl-N,N′-ethanediyl-diammonium dibromide (16-2-16) in water and mixed water-ethanol media. Phase behavior for 16-2-16 in the ethanol–water system was investigated at ambient temperature. The rheological data obtained for these systems at varying alcohol concentrations showed that the system viscosity (η) decreased with as the ethanol concentration increased. Small-angle neutron scattering (SANS) was used to probe the structural details of the cationic micelles as a function of ethanol concentration and temperature. The scattering data inferred a structural transition from unilamellar vesicles (ULV) through rod-like micelles to ellipsoidal micelles occurs that is dependent on the solvent composition and temperature indicating the behavior of ethanol molecules as a cosolvent in the process of micelle breaking. The plausible physicochemical interactions in the 16-2-16-ethanol mixed system were further investigated using a computational simulation study employing density functional theory (DFT)/B3LYP (Gauss View 5.0.9) utilizing a 3-21G basis set.

Hydrogel beads are emerging as alternate adsorbent material for the batch or continuous column treatment of dye wastewater. Polysaccharide-based gel beads are preferred for their uniform shape and size, large specific surface area, and easy separation by filtration and subsequent reuse. In this work, we prepare and rheologically characterize UV-active κ-carrageenan/TiO2 beads for the adsorption and degradation of dyes. The 3–4 mm sized nanocomposite beads are formed by the extrusion of κ-carrageenan/TiO2 gel solution in salt solutions. The maximum increase in modulus was observed with the addition of 1% w/v TiO2 to κ-carrageenan and subsequent crosslinking with mixed salt of KCl and CaCl2. κ-carrageenan/TiO2 beads crosslinked by mixed salt of KCl and CaCl2 have higher adsorption capacity, as compared to beads crosslinked with single salt of KCl. The kinetic study indicated the chemisorption of Methylene Blue on the bead surface. κ-carrageenan/TiO2 beads showed higher degradation for Methylene Blue and Nile Blue A than Rhodamine B in 5 and 50 ppm each multicomponent dye systems under UV irradiation. The κ-carrageenan/TiO2 beads could form a porous column for the selective adsorption of positively charged dyes from a multicomponent dye system.

In this work, κ-carrageenan and olive oil at different oil to κ-carrageenan ratios (OCR) are homogenized to create emulsion gels. Interestingly, confocal imaging shows that the oil droplets are stabilized in the κ-carrageenan-structured gel matrix without using any surfactants. Rheological studies show that the oil droplets enhanced the oscillatory yield stress and the maximum printable height of the emulsion gels. The creation of the emulsion gels with an OCR of 1:9-3:7 led to an improvement in the structural integrity of extrusion printed structures. The emulsion gel with an OCR of 3:7 efficiently encapsulates vitamin C in the aqueous phase and curcumin in the hydrophobic oil phase, enabling the extrusion 3D printing of tablets with varying surface area to volume (SA/V) ratios. The release of vitamin C and curcumin is influenced by the preparation method of printing versus casting and the SA/V ratio of the tablets. The hollow cylinder with the highest SA/V ratio was observed to have the highest vitamin C release, whereas for curcumin, the printed tablets had a higher release compared to the cast tablet. Additionally, through rheo-dissolution experiments, we observe a lower modulus and higher vitamin C release from the 3D-printed disc versus the higher modulus and lower vitamin C release from the cast disc tablet.

κ-carrageenan is a seaweed-derived polysaccharide commonly used in the food and pharmaceutical industry as a thickening agent and rheological modifier. The biopolymer has shown promising potential as a gel-based ink for 3D printing applications. However, its application is limited due to its poor structural stability and mechanical strength. In this work, we propose to overcome the printing limitation by optimizing the ink formulation of salt-induced κ-carrageenan gels. The gelation of 0.25–2% w/v κ-carrageenan with gelling agents of potassium chloride (KCl), calcium chloride (CaCl2), and a combination of KCl and CaCl2 salts was studied using rheological and SANS measurements, and SEM and AFM imaging. A state diagram for the κ-carrageenan-salt samples reveals that the sol-gel transformation shifts to lower κ-carrageenan concentrations with the 25 mM salts. The rheological measurements show a synergistic increase in the storage modulus of κ-carrageenan by the addition of equimolar mixed salts of KCl and CaCl2. The addition of 25 mM KCl or CaCl2 significantly improved the printability of 1% w/v κ-carrageenan to form thin and continuous filaments. However, complex shapes consisting of cylinders, polygons, and multilayer structures could successfully be 3D printed with only the 1% w/v κ-carrageenan with 25 mM KCl gel ink. Live/dead assay of human lung cancer A549 cells seeded on the printed structures show the excellent biocompatibility of these gels.

Quantitative, accurate, and standardized metrics are important for reliable shear wave elastography (SWE)-based biomarkers. For over two decades, the linear-elastic material assumption has been employed in SWE modes. In recent years, viscoelasticity estimation methods have been adopted in a few clinical systems. The current study aims to systematically quantify differences in SWE estimates obtained using linear-elastic and viscoelastic material assumptions. An acousto-mechanical simulation framework of acoustic radiation force impulse-based SWE was created to elucidate the effect of material viscosity and shear modulus on SWE estimates. Shear modulus estimates exhibited errors up to 72% when a numerical viscoelastic phantom was assessed as linearly elastic. Shear modulus estimates of polyvinyl alcohol phantoms between rheometry and SWE following the Kelvin-Voigt viscoelastic model assumptions were not significantly different. However, the percentage difference in shear modulus estimates between rheometry and SWE using the linear-elastic assumption was 50.1%-62.1%. In ex vivo liver, the percentage difference in shear modulus estimates between linear-elastic and viscoelastic methods was 76.1%. These findings provide a direct and systematic quantification of the potential error introduced when viscoelastic tissues are imaged with SWE following the linear-elastic assumption. This work emphasizes the need to utilize viscoelasticity estimation methods for developing robust quantitative imaging biomarkers.

This study uniquely reveals the hierarchical self-assembly and complex micellar transitions in a selective zwitterionic-anionic mix surfactant system in aqueous solution and the presence of varied salts. A combination of tensiometry, rheology, and small-angle neutron scattering (SANS) experiments was used to investigate these nanoscale transitions in a selective mixed micellar system. The critical micelle concentration (CMC) for single and mixed systems was determined at ambient temperature, and the interaction parameter (β), depicting favorable synergism at a specific mole fraction, was calculated using Rubingh’s regular solution theory (RST). Again, various thermodynamic parameters, such as Maeda’s free energy of micellization (ΔGMaeda), the free energy of micellization (ΔGM), and the free energy of adsorption (ΔGads), were calculated. Density functional theory (DFT) calculations were carried out employing the Gaussian 09W software package and visualized using Gauss View 6.0, which yielded varied quantum chemical descriptors that supported the marked influence of the anionic surfactant in favoring the micellization of the zwitterionic surfactant in the examined system. Also, the obtained reduced density gradient (RDG) and noncovalent interactions (NCI) enabled the understanding of the synergistic interactions involved therein, which is affirmed by Two-Dimensional Nuclear Overhauser Enhancement Spectroscopy (2D-NOESY) that explored the self-assembly mechanism in the examined micellar solution. The rheological parameters, such as the modulus of elasticity (G′) and modulus of viscosity (G″), described varied solution behavior covering fluidic, viscous, and gel formation, thus attributing viscoelasticity, particularly in the presence of salts. The SANS approach inferred micellar growth with various morphology transitions ranging from spheres, ellipsoids, and cylinders. Interestingly, it also displayed a fractal dimension (Dm) in the examined system, not previously reported for this class of surfactant mixtures, making this study very novel, giving an account of the specific binding of anions and cations from the added electrolyte.