32 research outputs found
Autonomous Motility of Active Filaments due to Spontaneous Flow-Symmetry Breaking
We simulate the nonlocal Stokesian hydrodynamics of an elastic filament which
is active due a permanent distribution of stresslets along its contour. A
bending instability of an initially straight filament spontaneously breaks flow
symmetry and leads to autonomous filament motion which, depending on
conformational symmetry, can be translational or rotational. At high ratios of
activity to elasticity, the linear instability develops into nonlinear
fluctuating states with large amplitude deformations. The dynamics of these
states can be qualitatively understood as a superposition of translational and
rotational motion associated with filament conformational modes of opposite
symmetry. Our results can be tested in molecular-motor filament mixtures,
synthetic chains of autocatalytic particles, or other linearly connected
systems where chemical energy is converted to mechanical energy in a fluid
environment.Comment: 7 pages, 3 figures; contains supplemental text; movies at
http://proofideas.org/rjoy/gallery; published in Physical Review Letter
Ultrafast reversible self-assembly of living tangled matter
Tangled active filaments are ubiquitous in nature, from chromosomal DNA and
cilia carpets to root networks and worm blobs. How activity and elasticity
facilitate collective topological transformations in living tangled matter is
not well understood. Here, we report an experimental and theoretical study of
California blackworms (Lumbriculus variegatus), which slowly form tangles over
minutes but can untangle in milliseconds. Combining ultrasound imaging,
theoretical analysis and simulations, we develop and validate a mechanistic
model that explains how the kinematics of individual active filaments
determines their emergent collective topological dynamics. The model reveals
that resonantly alternating helical waves enable both tangle formation and
ultrafast untangling. By identifying generic dynamical principles of
topological self-transformations, our results can provide guidance for
designing new classes of topologically tunable active materials
Directional takeoff, aerial righting, and adhesion landing of semiaquatic springtails
Springtails (Collembola) have been traditionally portrayed as explosive
jumpers with incipient directional takeoff and uncontrolled landing. However,
for these collembolans who live near the water, such skills are crucial for
evading a host of voracious aquatic and terrestrial predators. We discover that
semiaquatic springtails Isotomurus retardatus can perform directional jumps,
rapid aerial righting, and near-perfect landing on the water surface. They
achieve these locomotive controls by adjusting their body attitude and impulse
during takeoff, deforming their body in mid-air, and exploiting the
hydrophilicity of their ventral tube, known as collophore. Experiments and
mathematical modeling indicate that directional-impulse control during takeoff
is driven by the collophores adhesion force, the body angle, and the stroke
duration produced by their jumping organ, the furcula. In mid-air, springtails
curve their bodies to form a U-shape pose, which leverages aerodynamic forces
to right themselves in less than 20 ms, the fastest ever measured in animals. A
stable equilibrium is facilitated by the water adhered to the collophore.
Aerial righting was confirmed by placing springtails in a vertical wind tunnel
and through physical models. Due to these aerial responses, springtails land on
their ventral side 85% of the time while anchoring via the collophore on the
water surface to avoid bouncing. We validated the springtail biophysical
principles in a bioinspired jumping robot that reduces in-flight rotation and
lands upright 75% of the time. Thus, contrary to common belief, these wingless
hexapods can jump, skydive and land with outstanding control that can be
fundamental for survival.Comment: 12 pages, 8 figure
Conservation Tools: The Next Generation of Engineering--Biology Collaborations
The recent increase in public and academic interest in preserving
biodiversity has led to the growth of the field of conservation technology.
This field involves designing and constructing tools that utilize technology to
aid in the conservation of wildlife. In this article, we will use case studies
to demonstrate the importance of designing conservation tools with
human-wildlife interaction in mind and provide a framework for creating
successful tools. These case studies include a range of complexities, from
simple cat collars to machine learning and game theory methodologies. Our goal
is to introduce and inform current and future researchers in the field of
conservation technology and provide references for educating the next
generation of conservation technologists. Conservation technology not only has
the potential to benefit biodiversity but also has broader impacts on fields
such as sustainability and environmental protection. By using innovative
technologies to address conservation challenges, we can find more effective and
efficient solutions to protect and preserve our planet's resources
Amorphous Entangled Active Matter
The design of amorphous entangled systems, specifically from soft and active
materials, has the potential to open exciting new classes of active,
shape-shifting, and task-capable 'smart' materials. However, the global
emergent mechanics that arises from the local interactions of individual
particles are not well understood. In this study, we examine the emergent
properties of amorphous entangled systems in three different examples: an
in-silico "smarticle" collection, its robophysical chain, and living entangled
aggregate of worm blobs (L. variegatus). In simulations, we examine how
material properties change for a collective composed of dynamic three-link
robots. We compare three methods of controlling entanglement in a collective:
externally oscillations, shape-changes, and internal oscillations. We find that
large-amplitude changes of the particle's shape using the shape-change
procedure produced the highest average number of entanglements, with respect to
the aspect ratio (l/w), improving the tensile strength of the collective. We
demonstrate application of these simulations in two experimental systems:
robotic chains and entangled worm blobs. In the robophysical models, we find
emergent auxeticity behavior upon straining the confined collective. And
finally, we show how the individual worm activity in a blob can be controlled
through the ambient dissolved oxygen in water, leading to complex emergent
properties of the living entangled collective, such as solid-like entanglement
and tumbling. Taken together, our work reveals principles by which future
shape-modulating, potentially soft robotic systems may dynamically alter their
material properties, advancing our understanding of living entangled materials,
while inspiring new classes of synthetic emergent super-materials.Comment: 15 pages, 19 figures, W.S. and H.T. contributed equally to this wor
Droplet superpropulsion in an energetically constrained insect
Abstract Food consumption and waste elimination are vital functions for living systems. Although how feeding impacts animal form and function has been studied for more than a century since Darwin, how its obligate partner, excretion, controls and constrains animal behavior, size, and energetics remains largely unexplored. Here we study millimeter-scale sharpshooter insects (Cicadellidae) that feed exclusively on a plant’s xylem sap, a nutrient-deficit source (95% water). To eliminate their high-volume excreta, these insects exploit droplet superpropulsion, a phenomenon in which an elastic projectile can achieve higher velocity than the underlying actuator through temporal tuning. We combine coupled-oscillator models, computational fluid dynamics, and biophysical experiments to show that these insects temporally tune the frequency of their anal stylus to the Rayleigh frequency of their surface tension-dominated elastic drops as a single-shot resonance mechanism. Our model predicts that for these tiny insects, the superpropulsion of droplets is energetically cheaper than forming jets, enabling them to survive on an extreme energy-constrained xylem-sap diet. The principles and limits of superpropulsion outlined here can inform designs of energy-efficient self-cleaning structures and soft engines to generate ballistic motions
A 3D-printed hand-powered centrifuge for molecular biology.
The centrifuge is an essential tool for many aspects of research and medical diagnostics. However, conventional centrifuges are often inaccessible outside of standard laboratory settings, such as remote field sites, because they require a constant external power source and can be prohibitively costly in resource-limited settings and Science, technology, engineering, and mathematics (STEM)-focused programs. Here we present the 3D-Fuge, a 3D-printed hand-powered centrifuge, as a novel alternative to standard benchtop centrifuges. Based on the design principles of a paper-based centrifuge, this 3D-printed instrument increases the volume capacity to 2 mL and can reach hand-powered centrifugation speeds up to 6,000 rpm. The 3D-Fuge devices presented here are capable of centrifugation of a wide variety of different solutions such as spinning down samples for biomarker applications and performing nucleotide extractions as part of a portable molecular lab setup. We introduce the design and proof-of-principle trials that demonstrate the utility of low-cost 3D-printed centrifuges for use in remote field biology and educational settings