A “Sticky” Mucin‐Inspired DNA‐Polysaccharide Binder for Silicon and Silicon–Graphite Blended Anodes in Lithium‐Ion Batteries

New binder concepts have lately demonstrated improvements in the cycle life of high‐capacity silicon anodes. Those binder designs adopt adhesive functional groups to enhance affinity with silicon particles and 3D network conformation to secure electrode integrity. However, homogeneous distribution of silicon particles in the presence of a substantial volumetric content of carbonaceous components (i.e., conductive agent, graphite, etc.) is still difficult to achieve while the binder maintains its desired 3D network. Inspired by mucin, the amphiphilic macromolecular lubricant, secreted on the hydrophobic surface of gastrointestine to interface aqueous serous fluid, here, a renatured DNA‐alginate amphiphilic binder for silicon and silicon–graphite blended electrodes is reported. Mimicking mucin's structure comprised of a hydrophobic protein backbone and hydrophilic oligosaccharide branches, the renatured DNA‐alginate binder offers amphiphilicity from both components, along with a 3D fractal network structure. The DNA‐alginate binder facilitates homogeneous distribution of electrode components in the electrode as well as its enhanced adhesion onto a current collector, leading to improved cyclability in both silicon and silicon–graphite blended electrodes.     

Monolithic Flexible Vertical GaN Light‐Emitting Diodes for a Transparent Wireless Brain Optical Stimulator

Flexible inorganic‐based micro light‐emitting diodes (µLEDs) are emerging as a significant technology for flexible displays, which is an important area for bilateral visual communication in the upcoming Internet of Things era. Conventional flexible lateral µLEDs have been investigated by several researchers, but still have significant issues of power consumption, thermal stability, lifetime, and light‐extraction efficiency on plastics. Here, high‐performance flexible vertical GaN light‐emitting diodes (LEDs) are demonstrated by silver nanowire networks and monolithic fabrication. Transparent, ultrathin GaN LED arrays adhere to a human fingernail and stably glow without any mechanical deformation. Experimental studies provide outstanding characteristics of the flexible vertical μLEDs (f‐VLEDs) with high optical power (30 mW mm^?2), long lifetime (≈12 years), and good thermal/mechanical stability (100 000 bending/unbending cycles). The wireless light‐emitting system on the human skin is successfully realized by transferring the electrical power f‐VLED. Finally, the high‐density GaN f‐VLED arrays are inserted onto a living mouse cortex and operated without significant histological damage of brain.     

Transient SHG Imaging on Ultrafast Carrier Dynamics of MoS2 Nanosheets

Understanding the collaborative behaviors of the excitons and phonons that result from light–matter interactions is important for interpreting and optimizing the underlying fundamental physics at work in devices made from atomically thin materials. In this study, the generation of exciton‐coupled phonon vibration from molybdenum disulfide (MoS₂) nanosheets in a pre‐excitonic resonance condition is reported. A strong rise‐to‐decay profile for the transient second‐harmonic generation (TSHG) of the probe pulse is achieved by applying substantial (20%) beam polarization normal to the nanosheet plane, and tuning the wavelength of the pump beam to the absorption of the A‐exciton. The time‐dependent TSHG signals clearly exhibit acoustic phonon generation at vibration modes below 10 cm^?1 (close to the Γ point) after the photoinduced energy is transferred from exciton to phonon in a nonradiative fashion. Interestingly, by observing the TSHG signal oscillation period from MoS₂ samples of varying thicknesses, the speed of the supersonic waves generated in the out‐of‐plane direction (Mach 8.6) is generated. Additionally, TSHG microscopy reveals critical information about the phase and amplitude of the acoustic phonons from different edge chiralities (armchair and zigzag) of the MoS₂ monolayers. This suggests that the technique could be used more broadly to study ultrafast physics and chemistry in low‐dimensional materials and their hybrids with ultrahigh fidelity.     

Efficient Hydrogen Evolution Reaction Catalysis in Alkaline Media by All‐in‐One MoS2 with Multifunctional Active Sites

MoS₂ becomes an efficient and durable nonprecious‐metal electrocatalyst for the hydrogen evolution reaction (HER) when it contains multifunctional active sites for water splitting derived from 1T‐phase, defects, S vacancies, exposed Mo edges with expanded interlayer spacings. In contrast to previously reported MoS₂‐based catalysts targeting only a single or few of these characteristics, the all‐in‐one MoS₂ catalyst prepared herein features all of the above active site types. During synthesis, the intercalation of in situ generated NH₃ molecules into MoS₂ sheets affords ammoniated MoS₂ (A‐MoS₂) that predominantly comprises 1T‐MoS₂ and exhibits an expanded interlayer spacing. The subsequent reduction of A‐MoS₂ results in the removal of intercalated NH₃ and H₂S to form an all‐in‐one MoS₂ with multifunctional active sites mentioned above (R‐MoS₂) that exhibits electrocatalytic HER performance in alkaline media superior to those of all previously reported MoS₂‐based electrocatalysts. In particular, a hybrid MoS₂/nickel foam catalyst outperforms commercial Pt/C in the practically meaningful high‐current region (>25 mA cm^?2), demonstrating that R‐MoS₂‐based materials can potentially replace Pt catalysts in practical alkaline HER systems.     

True Low‐Power Self‐Locking Soft Actuators

Natural double‐layered structures observed in living organisms are known to exhibit asymmetric volume changes with environmental triggers. Typical examples are natural roots of plants, which show unique self‐organized bending behavior in response to environmental stimuli. Herein, light‐ and electro‐active polymer (LEAP) based actuators with a double‐layered structure are reported. The LEAP actuators exhibit an improvement of 250% in displacement and hold an object three times heavier as compared to that in the case of conventional electro‐active polymer actuators. Most interestingly, the bending motion of the LEAP actuators can be effectively locked for a few tens of minutes even in the absence of a power supply. Further, the self‐locking LEAP actuators show a large and reversible bending strain of more than 2.0% and require only 6.2 mW h cm^?2 of energy to hold an object for 15 min at an operating voltage of 3 V. These novel self‐locking soft actuators should find wide applicability in artificial muscles, biomedical microdevices, and various innovative soft robot technologies.     

Nondestructive Real‐Time Monitoring of Enhanced Stem Cell Differentiation Using a Graphene‐Au Hybrid Nanoelectrode Array

Stem cells have attracted increasing research interest in the field of regenerative medicine because of their unique ability to differentiate into multiple cell lineages. However, controlling stem cell differentiation efficiently and improving the current destructive characterization methods for monitoring stem cell differentiation are the critical issues. To this end, multifunctional graphene–gold (Au) hybrid nanoelectrode arrays (NEAs) to: (i) investigate the effects of combinatorial physicochemical cues on stem cell differentiation, (ii) enhance stem cell differentiation efficiency through biophysical cues, and (iii) characterize stem cell differentiation in a nondestructive real‐time manner are developed. Through the synergistic effects of physiochemical properties of graphene and biophysical cues from nanoarrays, the graphene‐Au hybrid NEAs facilitate highly enhanced cell adhesion and spreading behaviors. In addition, by varying the dimensions of the graphene‐Au hybrid NEAs, improved stem cell differentiation efficiency, resulting from the increased focal adhesion signal, is shown. Furthermore, graphene‐Au hybrid NEAs are utilized to monitor osteogenic differentiation of stem cells electrochemically in a nondestructive real‐time manner. Collectively, it is believed the unique multifunctional graphene‐Au hybrid NEAs can significantly advance stem‐cell‐based biomedical applications.     

Synthesis Process of CoSeO3 Microspheres for Unordinary Li‐ion Storage Performances and Mechanism of Their Conversion Reaction with Li ions

Multicomponent materials with various double cations have been studied as anode materials of lithium‐ion batteries (LIBs). Heterostructures formed by coupling different‐bandgap nanocrystals enhance the surface reaction kinetics and facilitate charge transport because of the internal electric field at the heterointerface. Accordingly, metal selenites can be considered efficient anode materials of LIBs because they transform into metal selenide and oxide nanocrystals in the first cycle. However, few studies have reported synthesis of uniquely structured metal selenite microspheres. Herein, synthesis of high‐porosity CoSeO₃ microspheres is reported. Through one‐pot oxidation at 400 °C, CoSe_x–C microspheres formed by spray pyrolysis transform into CoSeO₃ microspheres showing unordinary cycling and rate performances. The conversion mechanism of CoSeO₃ microspheres for lithium‐ion storage is systematically studied by cyclic voltammetry, in situ X‐ray diffraction and electrochemical impedance spectroscopy, and transmission electron microscopy. The reversible reaction mechanism of the CoSeO₃ phase from the second cycle onward is evaluated as CoO + xSeO₂ + (1 ? x)Se + 4(x + 1)Li⁺+ 4( x + 1)e^? ? Co + (2x + 1)Li₂O + Li₂Se. The CoSeO₃ microspheres show a high reversible capacity of 709 mA h g^?1 for the 1400th cycle at a current density of 3 A g^?1 and a high reversible capacity of 526 mA h g^?1 even at an extremely high current density of 30 A g^?1.     

A desirability function method for optimizing mean and variability of multiple responses using a posterior preference articulation approach

A desirability function approach has been widely used in multi‐response optimization due to its simplicity. Most of the existing desirability function‐based methods assume that the variability of the response variables is stable; thus, they focus mainly on the optimization of the mean of multiple responses. However, this stable variability assumption often does not apply in practical situations; thus, the quality of the product or process can be severely degraded due to the high variability of multiple responses. In this regard, we propose a new desirability function method to simultaneously optimize both the mean and variability of multiple responses. In particular, the proposed method uses a posterior preference articulation approach, which has an advantage in investigating tradeoffs between the mean and variability of multiple responses. It is expected that process engineers can use this method to better understand the tradeoffs, thereby obtaining a satisfactory compromise solution.