27 research outputs found
High-Performance Multiresponsive Paper Actuators
There is an increasing
demand for soft actuators because of their
importance in soft robotics, artificial muscles, biomimetic devices,
and beyond. However, the development of soft actuators capable of
low-voltage operation, powerful actuation, and programmable shape-changing
is still challenging. In this work, we propose programmable bilayer
actuators that operate based on the large hygroscopic contraction
of the copy paper and simultaneously large thermal expansion of the
polypropylene film upon increasing the temperature. The electrothermally
activated bending actuators can function with low voltages (≤ 8
V), low input electric power per area (<i>P</i> ≤
0.14 W cm<sup>–2</sup>), and low temperature changes (≤ 35
°C). They exhibit reversible shape-changing behavior with curvature
radii up to 1.07 cm<sup>–1</sup> and bending angle of 360°,
accompanied by powerful actuation. Besides the electrical activation,
they can be powered by humidity or light irradiation. We finally demonstrate
the use of our paper actuators as a soft gripper robot and a lightweight
paper wing for aerial robotics
Mechanics of Load–Drag–Unload Contact Cleaning of Gecko-Inspired Fibrillar Adhesives
Contact
self-cleaning of gecko-inspired synthetic adhesives with
mushroom-shaped tips has been demonstrated recently using load–drag–unload
cleaning procedures similar to that of the natural animal. However,
the underlying mechanics of contact cleaning has yet to be fully understood.
In this work, we present a detailed experiment of contact self-cleaning
that shows that rolling is the dominant mechanism of cleaning for
spherical microparticle contaminants, during the load–drag–unload
procedure. We also study the effect of dragging rate and normal load
on the particle rolling friction. A model of spherical particle rolling
on an elastomer fibrillar adhesive interface is developed and agrees
well with the experimental results. This study takes us closer to
determining design parameters for achieving self-cleaning fibrillar
adhesives
Supporting video SV1 from Soiled adhesive pads shear clean by slipping: a robust self-cleaning mechanism in climbing beetles
Beetle climbing glass with 45-micron bead
Parallel Microcracks-based Ultrasensitive and Highly Stretchable Strain Sensors
There is an increasing demand for
flexible, skin-attachable, and wearable strain sensors due to their
various potential applications. However, achieving strain sensors
with both high sensitivity and high stretchability is still a grand
challenge. Here, we propose highly sensitive and stretchable strain
sensors based on the reversible microcrack formation in composite
thin films. Controllable parallel microcracks are generated in graphite
thin films coated on elastomer films. Sensors made of graphite thin
films with short microcracks possess high gauge factors (maximum value
of 522.6) and stretchability (ε ≥ 50%), whereas sensors
with long microcracks show ultrahigh sensitivity (maximum value of
11 344) with limited stretchability (ε ≤ 50%).
We demonstrate the high performance strain sensing of our sensors
in both small and large strain sensing applications such as human
physiological activity recognition, human body large motion capturing,
vibration detection, pressure sensing, and soft robotics
Multifunctional Bacteria-Driven Microswimmers for Targeted Active Drug Delivery
High-performance,
multifunctional bacteria-driven microswimmers
are introduced using an optimized design and fabrication method for
targeted drug delivery applications. These microswimmers are made
of mostly single <i>Escherichia coli</i> bacterium attached
to the surface of drug-loaded polyelectrolyte multilayer (PEM) microparticles
with embedded magnetic nanoparticles. The PEM drug carriers are 1
μm in diameter and are intentionally fabricated with a more
viscoelastic material than the particles previously studied in the
literature. The resulting stochastic microswimmers are able to swim
at mean speeds of up to 22.5 μm/s. They can be guided and targeted
to specific cells, because they exhibit biased and directional motion
under a chemoattractant gradient and a magnetic field, respectively.
Moreover, we demonstrate the microswimmers delivering doxorubicin
anticancer drug molecules, encapsulated in the polyelectrolyte multilayers,
to 4T1 breast cancer cells under magnetic guidance <i>in vitro</i>. The results reveal the feasibility of using these active multifunctional
bacteria-driven microswimmers to perform targeted drug delivery with
significantly enhanced drug transfer, when compared with the passive
PEM microparticles
Wrinkling Instability and Adhesion of a Highly Bendable Gallium Oxide Nanofilm Encapsulating a Liquid-Gallium Droplet
The
wrinkling and interfacial adhesion mechanics of a gallium-oxide
nanofilm encapsulating a liquid-gallium droplet are presented. The
native oxide nanofilm provides mechanical stability by preventing
the flow of the liquid metal. We show how a crumpled oxide skin a
few nanometers thick behaves akin to a highly bendable elastic nanofilm
under ambient conditions. Upon compression, a wrinkling instability
emerges at the contact interface to relieve the applied stress. As
the load is further increased, radial wrinkles evolve, and, eventually,
the oxide nanofilm ruptures. The observed wrinkling closely resembles
the instability experienced by nanofilms under axisymmetric loading,
thus providing further insights into the behaviors of elastic nanofilms.
Moreover, the mechanical attributes of the oxide skin enable high
surface conformation by exhibiting liquid-like behavior. We measured
an adhesion energy of 0.238 ± 0.008 J m<sup>–2</sup> between
a liquid-gallium droplet and smooth flat glass, which is close to
the measurements of thin-sheet nanomaterials such as graphene on silicon
dioxide
Wrinkling Instability and Adhesion of a Highly Bendable Gallium Oxide Nanofilm Encapsulating a Liquid-Gallium Droplet
The
wrinkling and interfacial adhesion mechanics of a gallium-oxide
nanofilm encapsulating a liquid-gallium droplet are presented. The
native oxide nanofilm provides mechanical stability by preventing
the flow of the liquid metal. We show how a crumpled oxide skin a
few nanometers thick behaves akin to a highly bendable elastic nanofilm
under ambient conditions. Upon compression, a wrinkling instability
emerges at the contact interface to relieve the applied stress. As
the load is further increased, radial wrinkles evolve, and, eventually,
the oxide nanofilm ruptures. The observed wrinkling closely resembles
the instability experienced by nanofilms under axisymmetric loading,
thus providing further insights into the behaviors of elastic nanofilms.
Moreover, the mechanical attributes of the oxide skin enable high
surface conformation by exhibiting liquid-like behavior. We measured
an adhesion energy of 0.238 ± 0.008 J m<sup>–2</sup> between
a liquid-gallium droplet and smooth flat glass, which is close to
the measurements of thin-sheet nanomaterials such as graphene on silicon
dioxide
Wrinkling Instability and Adhesion of a Highly Bendable Gallium Oxide Nanofilm Encapsulating a Liquid-Gallium Droplet
The
wrinkling and interfacial adhesion mechanics of a gallium-oxide
nanofilm encapsulating a liquid-gallium droplet are presented. The
native oxide nanofilm provides mechanical stability by preventing
the flow of the liquid metal. We show how a crumpled oxide skin a
few nanometers thick behaves akin to a highly bendable elastic nanofilm
under ambient conditions. Upon compression, a wrinkling instability
emerges at the contact interface to relieve the applied stress. As
the load is further increased, radial wrinkles evolve, and, eventually,
the oxide nanofilm ruptures. The observed wrinkling closely resembles
the instability experienced by nanofilms under axisymmetric loading,
thus providing further insights into the behaviors of elastic nanofilms.
Moreover, the mechanical attributes of the oxide skin enable high
surface conformation by exhibiting liquid-like behavior. We measured
an adhesion energy of 0.238 ± 0.008 J m<sup>–2</sup> between
a liquid-gallium droplet and smooth flat glass, which is close to
the measurements of thin-sheet nanomaterials such as graphene on silicon
dioxide
Microemulsion-Based Soft Bacteria-Driven Microswimmers for Active Cargo Delivery
Biohybrid
cell-driven microsystems offer unparalleled possibilities
for realization of soft microrobots at the micron scale. Here, we
introduce a bacteria-driven microswimmer that combines the active
locomotion and sensing capabilities of bacteria with the desirable
encapsulation and viscoelastic properties of a soft double-micelle
microemulsion for active transport and delivery of cargo (<i>e</i>.<i>g</i>., imaging agents, genes, and drugs)
to living cells. Quasi-monodisperse double emulsions were synthesized
with an aqueous core that encapsulated the fluorescence imaging agents,
as a proof-of-concept cargo in this study, and an outer oil shell
that was functionalized with streptavidin for specific and stable
attachment of biotin-conjugated <i>Escherichia coli</i>.
Motile bacteria effectively propelled the soft microswimmers across
a Transwell membrane, actively delivering imaging agents (<i>i</i>.<i>e</i>., dyes) encapsulated inside of the
micelles to a monolayer of cultured MCF7 breast cancer and J744A.1
macrophage cells, which enabled real-time, live-cell imaging of cell
organelles, namely mitochondria, endoplasmic reticulum, and Golgi
body. This <i>in vitro</i> model demonstrates the proof-of-concept
feasibility of the proposed soft microswimmers and offers promise
for potential biomedical applications in active and/or targeted transport
and delivery of imaging agents, drugs, stem cells, siRNA, and therapeutic
genes to live tissue in <i>in vitro</i> disease models (<i>e</i>.<i>g</i>., organ-on-a-chip devices) and stagnant
or low-flow-velocity fluidic regions of the human body
Comparison of wettability analysis of Cu whiskers versus control flat Cu thin films.
<p>Dynamic contact angle hysteresis (CAH) analysis via advancing (A-C) versus receding (D-F) contact angle of whisker and flat samples. (G-I) Mean contact versus step number surface profiles of whisker against the control flat surfaces.</p