705 research outputs found
Hierarchical biomechanics: student engagement activities with a focus on biological physics
Hierarchical structure and mechanics are crucial in biological systems as they allow for smaller molecules, such as proteins and sugars, to be used in the construction of large scale biological structures exhibiting properties such as structural support functionality. By exploring the fundamental principles of structure and mechanics at the macroscale, this general theme provides a clear insight into how physics can be applied to the complex questions of biology. With a focus on biopolymer networks and hydrogels, we present a series of interactive activities which cover a range of biophysical concepts at an introductory level, such as viscoelasticity, biological networks and ultimately, hierarchical biomechanics. These activities enable us to discuss multidisciplinary science with a general audience and, given the current trends of research science, this conceptualisation of science is vital for the next generation of scientists
Localized energy absorbers in Hertzian chains
Energy absorbers and energy-harvesting devices have been under the scope of
scientists and engineers for decades to fulfill specific technological needs,
mainly concerned with sound and vibration absorbers, and efficient mechanical
energy converters. In this paper, as a proof of concept, we build a
mass-in-mass device to study the response of a linear absorber immersed in one
of the spheres composing a linear array of equal elastic spheres. Spheres
barely touch one another and can thus sustain nonlinear solitary wave
propagation only. The linear intruder absorbs a given amount of energy
depending on the frequency content of the incident solitary wave. A numerical
simulation is developed to account for the experimental finding. The validation
of the numerical model allows for the theoretical study of the energy absorbed
by any number of intruders, and to demonstrate that the former increases
exponentially with the latter, indicating that only ten of the intruders is
enough to absorb the system energy. A detailed study of the transmitted energy
from an external source into the chain reveals that, due to nonlinearity, the
array of spheres is able to convert almost any mechanical shock to a well
defined solitary or trains of solitary waves, whose frequency content is nearly
independent on the excitation amplitude. This property leads to the design of a
device, which is optimized to absorb energy over a broad frequency range
Shaken Baby Syndrome: Retinal Hemorrhaging. A Biomechanical Approach to Understanding the Mechanism of Causation
Shaken Baby Syndrome (SBS) is a form of abuse where typically an infant, age six months or less, is held and shaken. There may or may not be direct impact associated with this action. Further, there is very little agreement on the actual mechanism of SBS. Clinical studies are limited in showing the exact mechanism of injury and only offer postulations and qualitative descriptions. SBS has received much attention in the media, has resulted in a great deal of litigation and can be the source of unfounded accusations. Therefore, it is necessary to try to quantify the forces that may cause injury due to SBS.
The physiology of infants makes injury due to SBS more likely. Infants have relatively large heads supported by weak necks that simply act as tethers (Prange et al., 2003). Therefore, there is minimal resistance to shaking. In addition, the cerebrospinal fluid (CSF) layer surrounding the infant\u27s brain is up to 10 mm thick as opposed to 1–2 mm in older children and adults (Morison, 2002). This thick layer reduces the resistance in rotation of the brain and can cause shearing injuries to the brain tissue. In addition, retinal hemorrhaging has been reported in SBS. The infant\u27s eyes have a vitreous that is typically more gelatinous and with a higher viscosity than in adult eyes. In addition, this vitreous is firmly attached to the retina and is difficult to remove (Levin, 2000).
A preliminary parametric model of an infant eye will be presented so that resultant nodal retinal force of the posterior retina can be investigated and compared with a documented shaking frequency and a documented impact pulse. Retinal forces are then compared with various studies that investigate retinal detachment or adhesive strength. This eye model is built using a variety of material properties that have been reported for the sclero-cornea shell, choroids, retina, vitreous, aqueous, lens, ciliary, optic nerve, tendons, extra ocular muscles, optic nerve, and orbital fatty tissue. The geometry of the eye has been carefully optimized for this parametric model based on scaling to an infant from an adult using idealized eye globe geometry and transverse slice tracings of The Visible Human Project.
This model shows promise in investigating the forces and kinematics of the infant eye exposed to harmonic shaking and further bolsters some of the few biomechanical studies investigating SBS. However, improvements are necessary to complete the eye model presented. Specifically, improvements on the mechanical properties for the components of the eye and especially the infant eye are needed. There is currently a deficit of biomechanical studies of the materials needed for the infant eye that is specifically geared for use in an explicit finite element code package. Conversions and adaptations of available materials are used in this first version of the infant eye model presented here and are in fair agreement with some of the clinical studies concerning SBS
Modeling electrospinning process and a numerical scheme using Lattice Boltzmann method to simulate viscoelastic fluid flows
In the recent years, researchers have discovered a multitude of applications
using nanofibers in fields like composites, biotechnology, environmental engineering,
defense, optics and electronics. This increase in nanofiber applications needs
a higher rate of nanofiber production. Electrospinning has proven to be the best
nanofiber manufacturing process because of simplicity and material compatibility.
Study of effects of various electrospinning parameters is important to improve the
rate of nanofiber processing. In addition, several applications demand well-oriented
nanofibers. Researchers have experimentally tried to control the nanofibers using
secondary external electric field. In the first study, the electrospinning process is
modeled and the bending instability of a viscoelastic jet is simulated. For this, the
existing discrete bead model is modified and the results are compared, qualitatively,
with previous works in literature. In this study, an attempt is also made to simulate
the effect of secondary electric field on electrospinning process and whipping instability.
It is observed that the external secondary field unwinds the jet spirals, reduces
the whipping instability and increases the tension in the fiber. Lattice Boltzmann method (LBM) has gained popularity in the past decade as
the method is easy implement and can also be parallelized. In the second part of this
thesis, a hybrid numerical scheme which couples lattice Boltzmann method with finite
difference method for a Oldroyd-B viscoelastic solution is proposed. In this scheme,
the polymer viscoelastic stress tensor is included in the equilibrium distribution function
and the distribution function is updated using SRT-LBE model. Then, the local
velocities from the distribution function are evaluated. These local velocities are used
to evaluate local velocity gradients using a central difference method in space. Next,
a forward difference scheme in time is used on the Maxwell Upper Convected model
and the viscoelastic stress tensor is updated. Finally, using the proposed numerical
method start-up Couette flow problem for Re = 0.5 and We = 1.1, is simulated. The
velocity and stress results from these simulations agree very well with the analytical
solutions
Microrheology to explore protein and cell dynamics
In this thesis, I explore the applications of optical tweezers and passive video particle tracking
microrheology for bioanalytical applications.
Microrheology is a branch of rheology that has the same principles as conventional bulk rheology,
but which works on micron length scales. Microrheological techniques relate the free or the driven
motion of micron-sized tracer particles suspended in the fluid under investigation to the ‘elastic’
and ‘viscous’ components of the material. These components can be related to the dynamics of the
molecules that make up the fluid, and thus microrheology has the potential to reveal new
information about the microscopic properties of complex materials.
Optical tweezers are sensitive instruments that have been used to apply forces on the order of pN
and to measure the displacements down to nm of objects ranging in size from 10 nm to over
100μm, making them an essential tool for microrheology. Here, we have developed a new set of
analytical methods for microrheological measurements of biological and bio-analytical systems. In
particular, we have developed two new self-consistent procedures for measuring the linear
viscoelastic properties of materials across the widest frequency range achievable with optical
tweezers (Phys.Review E. (2010) 81:2, and J. Optics (2011) 13:4). Furthermore, we present a
straightforward procedure for measuring the in vivo linear viscoelastic properties of single cells via
passive video particle tracking microrheology of single beads attached to the cells’ exterior.
Notably, the procedure presented here represents an alternative methodology that can be extended
to many experimental formats and provides a simple addition to existing cellular physiology
studies.
In addition, we introduce new methodologies for deriving the concentration scaling laws of
polymer and biopolymer solutions from microrheological measurements carried out with optical
tweezers. These methods have been adopted to investigate the concentration scaling laws of in vitro
reconstituted actin solutions and actin/myosin solution
Biplanar High-Speed Fluoroscopy of Pony Superficial Digital Flexor Tendon (SDFT)-An In Vivo Pilot Study.
The superficial digital flexor tendon (SDFT) is the most frequently injured structure of the musculoskeletal system in sport horses and a common cause for early retirement. This project's aim was to visualize and measure the strain of the sound, injured, and healing SDFTs in a pony during walk and trot. For this purpose, biplanar high-speed fluoroscopic kinematography (FluoKin), as a high precision X-ray movement analysis tool, was used for the first time in vivo with equine tendons. The strain in the metacarpal region of the sound SDFT was 2.86% during walk and 6.78% during trot. When injured, the strain increased to 3.38% during walk and decreased to 5.96% during trot. The baseline strain in the mid-metacarpal region was 3.13% during walk and 6.06% during trot and, when injured, decreased to 2.98% and increased to 7.61%, respectively. Following tendon injury, the mid-metacarpal region contributed less to the overall strain during walk but showed increased contribution during trot. Using this marker-based FluoKin technique, direct, high-precision, and long-term strain measurements in the same individual are possible. We conclude that FluoKin is a powerful tool for gaining deeper insight into equine tendon biomechanics
A comparison between the FENE-P and sPTT constitutive models in Large Amplitude Oscillatory Shear (LAOS)
The FENE-P and sPTT viscoelastic models are widely used for modelling of
complex fluids. Although they are derived from distinct micro-structural
theories, these models can become mathematically identical in steady and
homogeneous flows with a particular choice of the value of the model
parameters. However, even with this choice of parameter values, the model
responses are known to differ from each other in transient flows. In this work,
we investigate the responses of the FENE-P and sPTT constitutive models in
Large Amplitude Oscillatory Shear (LAOS). In steady-shear, the shear stress
scales with the non-dimensional group for the
FENE-P (sPTT) model, where is the Weissenberg number, is the limit
of extensibility in the FENE-P model ( being ) and
is the extensibility parameter in the sPTT model. Our numerical and analytical
results show that, in LAOS, the FENE-P model only shows this universality for
large values of whereas the sPTT model shows this universality for all
values of. In the strongly non-linear region, there is a drastic
difference between the responses of the two models, with the FENE-P model
exhibiting strong shear stress overshoots which manifest as self-intersecting
secondary loops in the viscous Lissajous curves. We quantify the non-linearity
exhibited by each constitutive model using the Sequence of Physical Processes
framework. Despite the high degree of non-linearity exhibited by the FENE-P
model, we also show using fully non-linear 1D simulations that it does not
shear band in LAOS within the range of conditions studied.Comment: Submitted to Journal of Fluid Mechanic
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