arXiv subjects

Namrata Gundiah

Publications and source records attributed to Namrata Gundiah.

4 recordsLinked to original sources

arXiv2026

Viscous Dissipation Governs Bubble Morphology and Failure in Soft Matter

Cavitation, the growth of bubbles in fluids and soft matter, plays a central role in tissue damage, ultrasound therapies, and material failure, yet the influence of viscoelastic dissipation on bubble dynamics remains unclear. Here, we investigate cavitation in polyacrylamide hydrogels with identical elastic moduli but different viscous dissipation. We observe a striking symmetry breaking transition: elastic gels rapidly develop ellipsoidal cavities before rupture, whereas viscoelastic gels sustain large, nearly spherical bubbles. A modified Rayleigh Plesset framework shows that viscous stresses suppress shape instabilities and delay symmetry breaking, whereas elastic stresses accelerate cavity deformation. Finite element simulations independently validate these findings. The Deborah number (De) further captures the competition between material relaxation and cavity growth, with higher De associated with predominantly elastic growth and lower De with greater relaxation. Together, our results establish viscous dissipation as a key stabilizing mechanism that governs bubble morphology and failure in soft materials. These results have direct implications for understanding cavitation-mediated damage in biological tissues, optimizing therapeutic ultrasound, and advancing mechanical characterization of hydrogels for engineering and food processing applications.

cond-mat.soft↗

arXiv2022

Crosslinks increase the elastic modulus and fracture toughness of gelatin hydrogels

Hydrogels have the ability to undergo large deformations and yet fail like brittle materials. The development of biocompatible hydrogels with high strength and toughness is an ongoing challenge in many applications. We crosslinked bovine gelatin using glutaraldehyde (control) and methylglyoxal (MGO) and assessed changes in their fracture toughness. Swelling experiments show ~710% retention of water in MGO hydrogels as compared to ~450% in control specimens. We used FTIR to identify the presence of chemical groups that may be involved in the crosslinking of gelatin gels. Scanning electron micrographs of lyophilized MGO hydrogels show large pores with plate-like intact walls that help retain water as compared to control specimens. Monotonic compression tests demonstrate nonlinear stress-strain behaviors for both hydrogel groups. MGO samples had 96% higher moduli as compared to control hydrogels that had moduli of 4.77+-0.73 kPa (n=4). A first order Ogden model fit the stress-strain data well as compared to Mooney-Rivlin and neo-Hookean models. We used cavitation rheology to quantify the maximum pressure for bubble failure in the hydrogels using blunt needles with inner radii of 75, 150, 230, and 320 μm respectively. Pressures inside the bubbles increased linearly with time and dropped sharply following a critical value. Bubbles in MGO gels were small and penny-shaped as compared to large spherical bubbles in control samples. We used the critical pressures to quantify the fracture energies of the hydrogels. MGO treatment increased the fracture energy by 187% from 13.09 J/m2 for control gels. Finally, we discuss the challenges in using the Ogden and Mooney-Rivlin models to compute the failure energy for gelatin hydrogels.

physics.bio-ph↗

arXiv2021

Density fluctuations and border forces direct leader cell plasticity during collective epithelial migrations

Epithelial cell monolayers expand on substrates by forming finger-like protrusions, created by leader cells, in the monolayer boundary. Information transmission and communication between individual entities in the cohesive collective lead to long-range order, vortical structures, and disorder to ordered phase transitions. We ask the following questions: what makes a leader? What is the role of followers in leader cell formation? We used a particle-based model to simulate epithelial cell migrations on substrates of 9.4 kPa, 21 kPa and 33 kPa stiffness. The dynamics of cellular motion in the ensemble are governed by orientational Vicsek and inter-cellular interactions between neighboring particles. The model also includes bending, curvature-based motility, and acto-myosin contractile cable forces on the contour, in addition to density dependent noise and cell proliferations. We show that border forces are essential in the leader cell formation and the overall areal expansions of epithelial monolayers on substrates. Radial velocities and areal expansions of the monolayer agree with experiments reported for epithelial cells on substrates of varied stiffness. Ordering in follower cells within a specific region of the monolayer was apparent on substrates of higher stiffness and occurred prior to the emergence of leader cells. We demonstrate that regions of increased cell density occur behind the leader cell edge on all three substrates. Finally, we assessed the role of cell divisions on the ordering of velocities in the monolayer. These results demonstrate that monolayer heterogeneities, caused by density instabilities in the interior regions, correlate with leader cell formation during epithelial migrations.

physics.bio-ph↗

arXiv2019

Mechanics of bioinspired fiber reinforced elastomers

Fiber reinforcement is a crucial attribute of soft bodied muscular hydrostats that have the ability to undergo large deformations and maintain their posture. Helically wound fibers around the cylindrical worm body help control the tube diameter and length. Geometric considerations show that a fiber winding angle of 54.7 degrees, called the magic angle, results in a maximum enclosed volume. Few studies have explored the effects of differential fiber winding on the large deformation mechanics of fiber reinforced elastomers (FRE). We fabricated FRE materials in transversely isotropic layouts varying from 0-90 degrees using a custom filament winding technique and characterized the nonlinear stress-strain relationships using uniaxial and equibiaxial experiments. We used these data within a continuum mechanical framework to propose a novel constitutive model for incompressible FRE materials with embedded extensible fibers. The model includes individual contributions from the matrix and fibers in addition to coupled terms in strain invariants, I1 and I4. The deviatoric stress components show inversion at fiber orientation angles near the magic angle in the FRE composites. These results are useful in soft robotic applications and in the biomechanics of fiber reinforced tissues such as the myocardium, arteries and skin.

cond-mat.soft↗