5 research outputs found
Mimicking Neuromuscular Junctions Using Controlled Crystallization of Solvents: A Surface and Interface Engineering Technique for Polymers
Recently,
crystallization engineering has become a novel processing
technique for various materials, including ceramics, polymers, and
composites. Herein, a novel processing technology of polymers based
on controlled directional crystallization was developed for biomimetic
surfaces and interfaces. Solvent was allowed to come into contact
with a polymer surface for a limited time, followed by controlled
crystallization of the solvent along a temperature gradient perpendicular
to the surface. As a result, perpendicular pores of well-defined patterns
were successfully prepared, as well as adhesive-free strong interfaces
mimicking neuromuscular junctions. By increasing the temperature of
the polymer or solvent contact time, the pore depth and contact angle
increased. Highly hydrophobic surfaces of polycarbonate were efficiently
prepared, and interfacial adhesion with polydimethylsiloxane was improved
by more than 4-fold. This novel processing technique based on crystal
engineering could open completely new application possibilities, particularly
for biomedical devices, soft lithography, microfabrication, soft sensors,
and flexible and stretchable electronics
3D Cocontinuous Composites of Hydrophilic and Hydrophobic Soft Materials: High Modulus and Fast Actuation Time
Hydrogels
in nature seldom form a single phase, more often forming
structured phases with other soft phases, allowing nature to develop
responsive and adaptive strategies. Based on knowledge of how hydrogels
are utilized in nature, we developed novel 3D cocontinuous composites
from soft materials with extremely different properties, a hydrogel
and a silicone. These were successfully prepared by infiltrating liquid
polydimethylsiloxane (PDMS) into polyÂ(<i>N</i>-isopropylacrylamide)
(PNIPAm) frameworks of aligned pores prepared by directional melt
crystallization. The composites had outstanding modulus and swelling
ratio compared to other mechanically strong hydrogels. More interestingly,
the deswelling kinetics were dramatically accelerated (by a factor
of 1000), possibly due to the aligned microchannels and the hydrophobic
nature of PDMS. As a result, an actuator movement mimicking flowering
could be completed in less than 20 s. This novel and versatile cocontinuous
composite strategy could overcome the current limitations of soft
materials
Biaxial Stretchability and Transparency of Ag Nanowire 2D Mass-Spring Networks Prepared by Floating Compression
Networks
of silver nanowires (Ag NWs) have been considered as promising materials
for stretchable and transparent conductors. Despite various improvements
of their optoelectronic and electromechanical properties over the
past few years, Ag NW networks with a sufficient stretchability in
multiple directions that is essential for the accommodation of the
multidirectional strains of human movement have seldom been reported.
For this paper, biaxially stretchable, transparent conductors were
developed based on 2D mass-spring networks of wavy Ag NWs. Inspired
by the traditional papermaking process, the 2D wavy networks were
produced by floating Ag NW networks on the surface of water and subsequently
applying biaxial compression to them. It was demonstrated that this
floating-compression process can reduce the friction between the Ag
NW–water interfaces, providing a uniform and isotropic in-plane
waviness for the networks without buckling or cracking. The resulting
Ag NW networks that were transferred onto elastomeric substrates successfully
acted as conductors with an excellent transparency, conductivity,
and electromechanical stability under a biaxial strain of 30%. The
strain sensors that are based on the prepared conductors demonstrated
a great potential for the enhanced performances of future wearable
devices
Reversibly Stretchable, Optically Transparent Radio-Frequency Antennas Based on Wavy Ag Nanowire Networks
We report a facile approach for producing
reversibly stretchable, optically transparent radio-frequency antennas
based on wavy Ag nanowire (NW) networks. The wavy configuration of
Ag NWs is obtained by floating the NW networks on the surface of water,
followed by compression. Stretchable antennas are prepared by transferring
the compressed NW networks onto elastomeric substrates. The resulting
antennas show excellent performance under mechanical deformation due
to the wavy configuration, which allows the release of stress applied
to the NWs and an increase in the contact area between NWs. The antennas
formed from the wavy NW networks exhibit a smaller return loss and
a higher radiation efficiency when strained than the antennas formed
from the straight NW networks, as well as an improved stability in
cyclic deformation tests. Moreover, the wavy NW antennas require a
relatively small quantity of NWs, which leads to low production costs
and provides an optical transparency. These results demonstrate the
potential of these wavy Ag NW antennas in applications of wireless
communications for wearable systems
Active Antioxidizing Particles for On-Demand Pressure-Driven Molecular Release
Overproduced reactive
oxygen species (ROS) are closely related to various health problems
including inflammation, infection, and cancer. Abnormally high ROS
levels can cause serious oxidative damage to biomolecules, cells,
and tissues. A series of nano- or microsized particles has been developed
to reduce the oxidative stress level by delivering antioxidant drugs.
However, most systems are often plagued by slow molecular discharge,
driven by diffusion. Herein, this study demonstrates the polymeric
particles whose internal pressure can increase upon exposure to H<sub>2</sub>O<sub>2</sub>, one of the ROS, and in turn, discharge antioxidants
actively. The on-demand pressurized particles are assembled by simultaneously
encapsulating water-dispersible manganese oxide (MnO<sub>2</sub>)
nanosheets and green tea derived epigallocatechin gallate (EGCG) molecules
into a polyÂ(lactic-<i>co</i>-glycolic acid) (PLGA) spherical
shell. In the presence of H<sub>2</sub>O<sub>2</sub>, the MnO<sub>2</sub> nanosheets in the PLGA particle generate oxygen gas by decomposing
H<sub>2</sub>O<sub>2</sub> and increase the internal pressure. The
pressurized PLGA particles release antioxidative EGCG actively and,
in turn, protect vascular and brain tissues from oxidative damage
more effectively than the particles without MnO<sub>2</sub> nanosheets.
This H<sub>2</sub>O<sub>2</sub> responsive, self-pressurizing particle
system would be useful to deliver a wide array of molecular cargos
in response to the oxidation level