227 research outputs found
Organic slug control using Phasmarhabditis hermaphrodita
Phasmarhabditis hermaphrodita is a lethal slug parasitic nematode that has been formulated into an effective biological control agent called Nemaslug®. We investigated the possibility of using different application methods of P. hermaphrodita to reduce cost and the number of nematodes applied. We also compared P. hermaphrodita with a new slug pellet called Ferramol®, which is available for use on organic farms
Microscale Mechanics of Plug-and-Play In Vitro Cytoskeleton Networks
This chapter describes recent techniques that have been developed to reconstitute and characterize well-controlled, tunable networks of actin and microtubules outside of cells. It describes optical tweezers microrheology techniques to characterize the linear and nonlinear mechanics of these plug-and-play in vitro networks from the molecular-level to mesoscopic scales. It also details fluorescence microscopy and single-molecule tracking methods to determine macromolecular transport properties and stress propagation through cytoskeleton networks. Throughout the chapter the intriguing results that this body of work has revealed are highlighted—including how the macromolecular constituents of cytoskeleton networks map to their signature responses to stress or strain; and the elegant couplings between network structure, macromolecular mobility, and stress response that cytoskeleton networks exhibit
Polymer threadings and rigidity dictate the viscoelasticity and nonlinear relaxation dynamics of entangled ring-linear blends and their composites with rigid rod microtubules
Mixtures of polymers of varying topologies and stiffnesses display complex
emergent rheological properties that often cannot be predicted from their
single-component counterparts. For example, entangled blends of ring and linear
polymers have been shown to exhibit enhanced shear thinning and viscosity, as
well as prolonged relaxation timescales, compared to pure solutions of rings or
linear chains. These emergent properties arise in part from the synergistic
threading of rings by linear polymers. Topology has also been shown to play an
important role in composites of flexible (e.g., DNA) and stiff (e.g.,
microtubules) polymers, whereby rings promote mixing while linear polymers
induce de-mixing and flocculation of stiff polymers, with these
topology-dependent interactions giving rise to highly distinct rheological
signatures. To shed light on these intriguing phenomena, we use optical
tweezers microrheology to measure the linear and nonlinear rheological
properties of entangled ring-linear DNA blends and their composites with rigid
microtubules. We show that the linear viscoelasticity is primarily dictated by
the microtubules at lower frequencies, but their contributions become frozen
out at frequencies above the DNA entanglement rate. In the nonlinear regime, we
reveal that mechanical response features, such as shear thinning, stress
softening and multi-modal relaxation dynamics are mediated by entropic
stretching, threading, and flow alignment of entangled DNA, as well as forced
de-threading, disentanglement, and clustering. The contributions of each of
these mechanisms depend on the strain rate as well as the entanglement density
and stiffness of the polymers, leading to non-monotonic rate dependences of
mechanical properties that are most pronounced for highly concentrated
ring-linear blends rather than DNA-MT composites.Comment: 22 pages, 8 figure
OpTiDDM (Optical Tweezers integrating Differential Dynamic Microscopy) maps the spatiotemporal propagation of nonlinear stresses in polymer blends and composites
How local stresses propagate through polymeric fluids, and, more generally,
how macromolecular dynamics give rise to viscoelasticity are open questions
vital to wide-ranging scientific and industrial fields. Here, to unambiguously
connect polymer dynamics to force response, and map stress propagation in
macromolecular materials, we present a powerful approach-Optical Tweezers
integrating Differential Dynamic Microscopy (OpTiDMM)-that simultaneously
imposes local strains, measures resistive forces, and analyzes the motion of
the surrounding polymers. Our measurements with blends of ring and linear
polymers (DNA) and their composites with stiff polymers (microtubules) uncover
a surprising resonant response, in which affine alignment, superdiffusivity,
and elastic memory are maximized when the strain rate is comparable to the
entanglement rate. Microtubules suppress this resonance, while substantially
increasing elastic force and memory, due to varying degrees to which the
polymers buildup, stretch and flow along the strain path, and configurationally
dissipate stress. More broadly, the rich multi-scale coupling of mechanics and
dynamics afforded by OpTiDDM, empowers its interdisciplinary use to elucidate
non-trivial phenomena that sculpt stress propagation dynamics-critical to
commercial applications and cell mechanics alike.Comment: 32 pages, 10 figure
Direct measurement of the intermolecular forces confining a single molecule in an entangled polymer solution
We use optical tweezers to directly measure the intermolecular forces acting
on a single polymer imposed by surrounding entangled polymers (115 kbp DNA, 1
mg/ml). A tube-like confining field was measured in accord with the key
assumption of reptation models. A time-dependent harmonic potential opposed
transverse displacement, in accord with recent simulation findings. A tube
radius of 0.8 microns was determined, close to the predicted value (0.5
microns). Three relaxation modes (~0.4, 5 and 30 s) were measured following
transverse displacement, consistent with predicted relaxation mechanisms.Comment: 11 pages, 3 figure
Active restructuring of cytoskeleton composites leads to increased mechanical stiffness, memory, and heterogeneity
The composite cytoskeleton, comprising interacting networks of semiflexible
actin and rigid microtubules, actively generates forces and restructures using
motor proteins such as myosins to enable key mechanical processes including
cell motility and mitosis. Yet, how motor-driven activity alters the mechanics
of cytoskeleton composites remains an open challenge. Here, we perform optical
tweezers microrheology on actin-microtubule composites driven by myosin II
motors to show that motor activity increases the linear viscoelasticity and
elastic storage of the composite by active restructuring to a network of
tightly-packed filament clusters and bundles. Our nonlinear microrheology
measurements performed hours after cessation of activity show that the
motor-contracted structure is stable and robust to nonlinear forcing. Unique
features of the nonlinear response include increased mechanical stiffness,
memory and heterogeneity, coupled with suppressed filament bending following
motor-driven restructuring. Our results shed important new light onto the
interplay between viscoelasticity and non-equilibrium dynamics in active
polymer composites such as the cytoskeleton
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