Chordocytes, in early zebrafish, pack in a small number of stereotyped patterns. Disruptions of the WT pattern are associated with developmental defects, including scoliosis. The dominant WT "staircase" pattern is the only regular pattern with transverse eccentricity. Morphometry and pattern analysis have established a length ratio governing which patterns will be observed. Physical models of...
Metachrony is often found throughout nature in many locomotory and fluid transport systems. Gossamer worms, also known tomopterids, are a soft-bodied, pelagic polychaete that employ metachronal paddling, with flexible parabodia on both sides of their body that navigate the midwater ecosystem which they inhabit. In the following study, we introduce a three-dimensional, computational,...
In the oocyte of the common fruit fly, large scale cytoplasmic flows appear in the mid-to-late stages of oogenesis. Proteins, synthesized in adjoining nurse cells, and yolk, endocytosed through the cell cortex, are transported and mixed throughout the oocyte, presumably accelerated by the cytoplasmic flows. While a biophysical mechanism has been proposed which explains the onset of cytoplasmic...
Micro-swimmer dynamics in heterogeneous media is receiving increased interest in fluid dynamics and biological physics due to the pervasiveness of microorganisms in complex environments [1]. We present a model for a microswimmer moving in a porous medium. One such a porous medium consisting of with impurities immersed in fluid, is the Brinkman fluid which approximates a sparse matrix of...
Viscoelastic behavior in biological fluid arises from the stretching of polymeric structures. Capturing finite extensibility is essential for predicting phenomena like strain hardening and elastic instabilities. This work develops a multiscale framework linking the statistical mechanics of freely jointed chains, expressed through the inverse Langevin function (ILF), to stochastic microscale...
We investigate the coupled dynamics of centrosomes and the cell nucleus under microtubule-mediated pulling within a viscous cytoplasmic environment. A coarse-grained, stoichiometric framework [1] is developed to capture the interactions between microtubules and force generators (FGs) distributed on the nuclear envelope and cortex. The model integrates hydrodynamic coupling, nuclear envelope...
Microfiltration is a water purification method used by municipal facilities to produce potable water that relies primarily on a size-exclusion mechanism. When a contaminated solvent passes through a membrane filter, unwanted contaminants with diameter larger than that of the membranes pores, such as suspended solids, large bacteria, and proteins, are retained on the membrane. This foulant...
Euglenids are flagellated microorganisms whose elongated, flexible bodies enable rich swimming dynamics in confined environments. Focusing on their flagellated mode of locomotion rather than body shape deformations, we construct a simplified hydrodynamic model in which the euglenid is represented as a rigid prolate spheroid and surface slip velocities are imposed over a portion of the body to...
A swimming microorganism stirs the surrounding fluid, creating a flow field that governs not only its locomotion and nutrient uptake, but also its interactions with other microorganisms and the environment. Despite its fundamental importance, capturing this flow field and unraveling its biological implications remains a challenge. Here, we report the first direct, time-resolved measurements of...
Liquid crystals serve as model systems for structured environments and represent a broader class of anisotropic, non-Newtonian fluids encountered by bacteria, such as host mucus [1] and extracellular polymeric substances involved in biofilm formation [2]. In this study, we investigated the collective swimming of fluorescently labelled Escherichia coli in nematic liquid crystals and observed...
The Method of Regularized Stokeslets (MRS) provides a robust, mesh-free framework for resolving the fluid-structure interactions of these filaments [1]. It has two critical bottlenecks: the spatial complexity of pairwise hydrodynamic calculations and the temporal stiffness arising from the material properties of the rod. To address these challenges, we first discuss a parallel-in-time approach...
Flagellated bacteria navigate complex environments by modulating flagellar rotation. The properties of the flagella, together with the cell body shape, govern the dynamics of bacterial motion and resulting swimming strategies. While the motility of many flagellated bacteria is well understood, comparatively little is known about bipolar flagellated species. In this talk, we present a...
From research to clinical development and production, Mycoplasma are well-recognized and widespread contaminants in biopharmaceutical manufacturing. Their successful proliferation despite the ultrafiltration performed to eliminate them has been attributed in part to the flexibility of their cell walls.
How does this bacterium manage to squeeze through pores that are, in some cases,...
Collective cell migration is ubiquitous amongst multicellular communities and contributes to many phenomena, e.g., morphogenesis and cancer metastasis. Nonetheless, it is still poorly understood how cells coordinate to control the emergent collective motion of cell groups (or swarms). Recent experimental data suggests that physical interactions between cells within the swarms can result in...
The Immersed Boundary (IB) method is widely used for problems that involve fluid-structure interactions or complex geometries. However, when adapted to flows with rigid objects, the IB method typically involves either using penalty forces, which only approximately satisfy boundary conditions, or they are formulated as constraint problems that suffer from the need to solve a linear system that...
The Immersed Boundary Method (IBM) is widely used in the simulation of systems involving fluid-structure interaction [1]. The ability to simulate problems involving complex, moving geometry using a simple, Eulerian grid has led to the use of the IBM for the study of many biomechanical and biophysical systems. However, the study of chemical systems often necessitates the ability to impose...
Elongated microswimmers such as E. coli exhibit run-and-tumble dynamics that bias motion in response to chemical gradients. In confined pressure-driven flows, elongated swimmers also reorient along Jeffery orbits, spending extended periods oriented near the upstream or downstream direction. Near boundaries, this alignment leads to upstream swimming, contributing to contamination and surface...
Contact lenses are worn by millions of people worldwide to correct vision impairments. The mechanical interactions between the lens and the ocular surface are difficult to access in the clinic. We developed a mathematical model of the mechanical interactions between the lens and the eye to predict the ocular stress load due to contact lens wear.
The lens is modeled as a thin, axially...
The mammalian ear has a remarkable ability to distinguish sounds that differ only slightly in frequency, while at the same time amplifying these signals so that they can be converted into neural impulses. This fine-frequency tuning phenomenon is commonly attributed to some form of mechanical resonance within the fluid-filled cochlea (or inner ear), and more specifically to resonant...
Microtubule astersโdynamic microtubules anchored at a centrosomeโform the spindle poles during cell division. Utilizing the method of regularized Stokeslets, we prescribe the motion of microtubule asters in a confined geometry and compute the resulting hydrodynamic drag on the aster. Moving beyond classical asymptotic approximations, we characterize the drag on a single aster inside a...
Malignant gliomas are devastating, aggressive tumours that frequently kill patients with a low survival rate (1 year after diagnosis). Diffuse invasion of glioma cells after surgical resection in brain tissue is a major obstacle for effective therapy. Glioma cells use the tortuous extracellular routes of migration, using blood vessels as guides. These cells manipulate ion channels in the local...
Mathematical and computational modeling plays an important role in understanding biological fluid mechanics. Even though the fluid motion is governed by partial differential equations, there are many projects in this field that can be made accessible to undergraduate students. The Method of Regularized Stokeslets (MRS) [1] is a popular technique used in modeling low Reynolds number flows. In...
Biological fluidโstructure interactions arise in environments ranging from Newtonian liquids to complex non-Newtonian media such as mucus, cytoplasm, and extracellular matrices. This minisymposium focuses on Newtonian and non-Newtonian biofluid mechanics, integrating theoretical analysis, experimental observations, mathematical modeling, and numerical simulations. Topics include microscale...
