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 poly­(<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 H₂O₂, one of the ROS, and in turn, discharge antioxidants actively. The on-demand pressurized particles are assembled by simultaneously encapsulating water-dispersible manganese oxide (MnO₂) nanosheets and green tea derived epigallocatechin gallate (EGCG) molecules into a poly­(lactic-<i>co</i>-glycolic acid) (PLGA) spherical shell. In the presence of H₂O₂, the MnO₂ nanosheets in the PLGA particle generate oxygen gas by decomposing H₂O₂ 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 MnO₂ nanosheets. This H₂O₂ responsive, self-pressurizing particle system would be useful to deliver a wide array of molecular cargos in response to the oxidation level