Hybrid Bilayer Research Articles

Formation of mixed hybrid bilayer lipid membrane on transparent thin film oxide electrodes

In this work, we attempted to design phospholipid bilayers tethered to semiconducting metal oxide films. The phospholipid layers assembled on compact monocomponent self-assembled monolayers (SAM) on oxide films were accomplished earlier; however, previous studies indicated a poor ability of these layers to functionally reconstitute transmembrane proteins. Commercially available fluorine doped tin oxide (FTO) sheet glass was chosen as a model solid support. FTO surface was functionalised utilising by the mixture of the long and short chain hydrophobic silanes. Specifically, octadecyltrichlorosilane (OTS) and vinyltrimethoxysilane (VTS) were used to assemble mixed silane-based SAMs on FTO. Exposure of mixed SAMs to a solution of multilamellar vesicles of 1,2-dioleoylsn- glycero-3-phosphocholine (DOPC) and 40% cholesterol triggered the changes of electrochemical parameters commensurate with the formation of additional dielectric layers of phospholipids.

Planar aggregation of the influenza viral fusion peptide alters membrane structure and hydration, promoting poration

To infect, enveloped viruses employ spike protein, spearheaded by its amphipathic fusion peptide (FP), that upon activation extends out from the viral surface to embed into the target cellular membrane. Here we report that synthesized influenza virus FPs are membrane active, generating pores in giant unilamellar vesicles (GUV), and thus potentially explain both influenza virus’ hemolytic activity and the liposome poration seen in cryo-electron tomography. Experimentally, FPs are heterogeneously distributed on the GUV at the time of poration. Consistent with this heterogeneous distribution, molecular dynamics (MD) simulations of asymmetric bilayers with different numbers of FPs in one leaflet show FP aggregation. At the center of FP aggregates, a profound change in the membrane structure results in thinning, higher water permeability, and curvature. Ultimately, a hybrid bilayer nanodomain forms with one lipidic leaflet and one peptidic leaflet. Membrane elastic theory predicts a reduced barrier to water pore formation when even a dimer of FPs thins the membrane as above, and the FPs of that dimer tilt, to continue the leaflet bending initiated by the hydrophobic mismatch between the FP dimer and the surrounding lipid.

Ferroelectric van der Waals heterostructures of CuInP2S6 for non-volatile memory device applications

Two-dimensional (2D) ferroelectric materials are providing promising platforms for creating future nano- and opto-electronics. Here we propose new hybrid van der Waals heterostructures, in which the 2D ferroelectric material CuInP2S6 (CIPS) is layered on a 2D semiconductor for near-infrared (NIR) memory device applications. Using density functional theory, we show that the band gap of the hybrid bilayers formed with CIPS can be tuned and that the optical and electronic properties can be successfully modulated via ferroelectric switching. Of the 3712 heterostructures considered, we identified 19 structures that have a type II band alignment and commensurate lattice matches. Of this set, both the CuInP2S6/PbSe and CuInP2S6/Ge2H2 heterostructures possess absorption peaks in the NIR region that change position and intensity with switching polarisation, making them suitable for NIR memory devices. The CuInP2S6/ISSb, CuInP2S6/ISbSe, CuInP2S6/ClSbSe and CuInP2S6/ZnI2 heterostructures had band gaps which can be switched from direct to indirect with changing the polarisation of CIPS making them suitable for optoelectronics and sensors. The heterostructures formed with CIPS are exciting candidates for stable ferroelectric devices, opening a pathway for tuning the band alignment of van der Waal heterostructures and the creation of modern memory applications that use less energy.

Multiple plasmon-induced transparency based on black phosphorus and graphene for high-sensitivity refractive index sensing.

A hybrid bilayer black phosphorus (BP) and graphene structure with high sensitivity is proposed for obtaining plasmon-induced transparency (PIT). By means of surface plasmon resonance in the rectangular-ring BP structure and ribbon graphene structure, a PIT effect with high refractive index sensitivity is achieved, and the surface plasmon hybridization between graphene and anisotropic BP is analyzed theoretically. Meanwhile, the PIT effect is quantitatively described using the coupled oscillator model and the strong coherent coupling phenomena are analyzed by adjusting the coupling distance between BP and graphene, the Fermi level of graphene, and the crystal orientation of BP, respectively. The simulation results show that the refractive index sensitivity S = 7.343 THz/RIU has been achieved. More importantly, this is the first report of tunable PIT effects that can produce up to quintuple PIT windows by using the BP and graphene hybrid structure. The high refractive index sensitivity of the quintuple PIT system for each peak is 3.467 THz/RIU, 3.467 THz/RIU, 3.600 THz/RIU, 4.267 THz/RIU, 4.733 THz/RIU and 6.133 THz/RIU, respectively, which can be used for multiple refractive index sensing function.

Fabrication and Modeling of Flexible High-Performance Resistive Switching Devices With Biomaterial Gelatin/Ultrathin HfOx Hybrid Bilayer

Flexible resistive random access memory (RRAM) devices with biomaterial gelatin and ultrathin HfOx hybrid bilayer dielectric exhibiting excellent resistive switching (RS) behavior are demonstrated. The fabricated devices show a very high memory window of greater than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{{5}}$ </tex-math></inline-formula> and data retention of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{{4}}$ </tex-math></inline-formula> s without any degradation in a pristine state. Moreover, to investigate the mechanical stability of the hybrid bilayer film and variation in switching performance upon bending was studied by bending the devices at a 12-mm radius followed by 7 mm. Even after this extreme bending, the device maintained the memory window of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{{5}}$ </tex-math></inline-formula> without any degradation in data retention, indicating excellent electromechanical stability of the device. Furthermore, a simple mathematical model of the RRAM device was used to simulate these devices with the help of our experimental data and the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}$ </tex-math></inline-formula> equations. The developed model shows excellent accuracy with a relative root mean square (RMS) error of less than 5%, which can prove to be an excellent tool for the simulation of circuits and systems based on these RRAMs.

On the use of negative thermal expansion engineered structures in flexural-mode solid-state thermoacoustics

Recent numerical studies have shown evidence of self-sustained oscillations in solids due to externally-applied spatial thermal gradients. In analogy with its acoustic counterpart in gases, this phenomenon was dubbed solid-state thermoacoustics (SSTA). Such heat-driven oscillation can give rise to either longitudinal or flexural motion, depending on the specific design of the system. Although an experimental proof of self-sustained motion in flexural-mode SSTA (F-SSTA) devices has yet to be produced, previous experimental studies pointed to the reduction of the effective damping as a clear indicator of the thermo-mechanical energy conversion process at the core of the F-SSTA mechanism. The F-SSTA theory suggested that negative thermal expansion (NTE), which is not a common property in natural materials, offers a remarkable opportunity to enhance the F-SSTA instability. The present study explores a design approach that leverages the unique features afforded by the solid state design in order to improve the overall performance of F-SSTA’s devices and reduce the technological gap to achieve, in a near future, a successful experimental validation. The proposed design approach leverages a hybrid bilayer beam concept where one of the two layers is designed to exhibit NTE properties. More specifically, the NTE layer is composed of a bi-material octet truss that contracts in the axial direction upon heating. This axial contraction is particularly beneficial to induce a strong thermal bending moment that ultimately enhances the F-SSTA instability. In addition, this work also furthers the conceptual understanding of the F-SSTA process by presenting an analytical perturbation energy budget developed on the basis of a simplified discrete model. These theoretical considerations provide new important insights in the energy conversion mechanism at the basis of the F-SSTA process, hence helping reducing the gap of knowledge towards a successful experimental realization of the F-SSTA effect. • Improved performance of F-SSTA systems via architectured NTE materials. • Identification of parameters controlling the flexural thermoacoustic instability. • A simplified analytical energy budget to understand the energy conversion mechanism.

Hybrid bilayer membranes as platforms for biomimicry and catalysis.

Hybrid bilayer membrane (HBM) platforms represent an emerging nanoscale bio-inspired interface that has broad implications in energy catalysis and smart molecular devices. An HBM contains multiple modular components that include an underlying inorganic surface with a biological layer appended on top. The inorganic interface serves as a support with robust mechanical properties that can also be decorated with functional moieties, sensing units and catalytic active sites. The biological layer contains lipids and membrane-bound entities that facilitate or alter the activity and selectivity of the embedded functional motifs. With their structural complexity and functional flexibility, HBMs have been demonstrated to enhance catalytic turnover frequency and regulate product selectivity of the O2 and CO2 reduction reactions, which have applications in fuel cells and electrolysers. HBMs can also steer the mechanistic pathways of proton-coupled electron transfer (PCET) reactions of quinones and metal complexes by tuning electron and proton delivery rates. Beyond energy catalysis, HBMs have been equipped with enzyme mimics and membrane-bound redox agents to recapitulate natural energy transport chains. With channels and carriers incorporated, HBM sensors can quantify transmembrane events. This Review serves to summarize the major accomplishments achieved using HBMs in the past decade.

Redox-Induced Lipid Vesicle Fusion Onto Electroactive Self-Assembled Monolayers

Supported lipid bilayers (SLBs) are popular model systems to study cell membrane functionalities and various biomolecular interaction forces. A key advantage of SLBs on metallic surfaces, is the application of spectroscopic, electrochemical, and surface plasmon resonance techniques for biomolecular recognition studies. The most common method for forming SLBs is vesicle fusion, which involves the adsorption, deformation, and rupture of small unilamellar vesicles (SUVs) of lipids from aqueous suspension to the substrate surface.1 The formation of continuous single bilayers by vesicle fusion can be problematic due to the many experimental parameters influencing vesicle rupture and bilayer spreading (i.e., lipid and vesicle properties, physicochemical characteristics of the surface, temperature, and solvent environment)1. Vesicle fusion typically works only with smooth hydrophilic surfaces, such as glass, silica, and mica. Although approaches have been developed to form bilayers on technologically relevant surfaces such gold (e.g., surface functionalization with hydrophilic organic films,2 solvent-assisted lipid bilayer formation3 or the addition of a vesicle-destabilizing agent4), there remains a need for active strategies that are fast, versatile, and scalable.We present a redox-induced approach for the formation of single bilayers on gold functionalized with electroactive self-assembled monolayers (SAMs) of ferrocenylalkanethiolates. The electrochemical oxidation of the SAM-bound ferrocene (Fc) to ferrocenium (Fc+) involves coupled electron transfer and ion pairing reactions. Counteranions from solution pair with the ferroceniums to stabilize the oxidized cations and neutralize the excess positive charge at the SAM/aqueous interface. The surface-confined redox reaction triggers the formation of single bilayer membranes from SUVs of anionic or zwitterionic phospholipids onto gold surfaces modified with the electroactive SAM. The ion pairing association of the charged lipid head groups with the electrogenerated ferroceniums drives the assembly of the phospholipids on the SAM surface to produce solid-supported bilayers of high surface coverage (≳ 90%) from gel- or fluid-phase forming phospholipids within minutes at room temperature. The redox-mediated strategy reported in this work is a conceptual advance in the preparation of solid-supported lipid bilayers. It is fast, insensitive to the phase state of the phospholipid in the vesicle precursor, and not limited to hydrophilic surfaces. References Richter, R. P.; Bérat, R.; Brisson, A. R., Formation of Solid-Supported Lipid Bilayers: An Integrated View. Langmuir 2006, 22 (8), 3497-3505.Silin, V. I.; Wider, H.; Woodward, J. T.; Valincius, G.; Offenhausser, A.; Plant, A. L., The Role of Surface Energy on the Formation of Hybrid Bilayer Membranes. J. Am. Chem. Soc. 2002, 124, 14676-14683.Ferhan, A. R.; Yoon, B. K.; Park, S.; Sut, T. N.; Chin, H.; Park, J. H.; Jackman, J. A.; Cho, N.-J., Solvent-Assisted Preparation of Supported Lipid Bilayers. Nat. Protoc. 2019, 14 (7), 2091-2118.Cho, N.-J.; Cho, S.-J.; Cheong, K. H.; Glenn, J. S.; Frank, C. W., Employing an Amphipathic Viral Peptide to Create a Lipid Bilayer on Au and TiO2. J. Am. Chem. Soc. 2007, 129 (33), 10050-10051. Figure 1

Highly Reliable Synaptic Cell Array Based on Organic–Inorganic Hybrid Bilayer Stack toward Precise Offline Learning

Offline LearningIn article number 2200018, Sung-Yool Choi and co-workers demonstrate an organic–inorganic hybrid bilayer stack for highly reliable synaptic cells toward precise offline learning. This study provides a practical approach to using ECM-based memristors for inference-only neural network accelerators through the guided formation of conductive filaments. The cover image shows that 5-bit multilevel states are achieved with striking retention characteristics due to high conductance-level stability.

Highly Reliable Synaptic Cell Array Based on Organic–Inorganic Hybrid Bilayer Stack toward Precise Offline Learning

As the use of artificial intelligence (AI) soars, the development of novel neuromorphic computing is demanding because of the disadvantages of the von Neumann architecture. Furthermore, extensive research on electrochemical metallization (ECM) memristors as synaptic cells have been carried out toward a linear conductance update for online learning applications. In most cases, however, a conductance distribution change over time has not been studied as a major issue, giving less consideration to inference‐only computing accelerators based on offline learning. Herein, organic–inorganic bilayer stacking for synaptic unit cells using poly(1,3,5‐trivinyl‐1,3,5‐trimethyl cyclotrisiloxane) (pV3D3) and Al2O3 thin films is suggested, showing highly enhanced reliability for offline learning. The bilayer structure achieves better reliability and control of the analog resistive switching and synaptic functions, respectively, through the guided formation of conductive filaments via tip‐enhanced electric fields. In addition, 5‐bit multilevel states achieve long‐term stability (&gt;104 s) following an in‐depth study on conductance‐level stability. Finally, a device‐to‐system‐level simulation is performed by building a convolutional neural network (CNN) based on the hybrid devices. This highlighted the significance of multilevel states in fully connected layers. It is believed that the study provides a practical approach to using ECM‐based memristors for inference‐only neural network accelerators.

Electrografting a Hybrid Bilayer Membrane via Diazonium Chemistry for Electrochemical Impedance Spectroscopy of Amyloid-β Aggregation.

Herein, a novel hybrid bilayer membrane is introduced as a platform to study the aggregation of amyloid-β1–42 (Aβ1–42) peptide on surfaces. The first layer was covalently attached to a glassy carbon electrode (GCE) via diazonium electrodeposition, which provided a highly stable template for the hybrid bilayer formation. To prepare the long-chain hybrid bilayer membrane (lcHBLM)-modified electrodes, GCE surfaces were modified with 4-dodecylbenzenediazonium (DDAN) followed by the modification with dihexadecyl phosphate (DHP) as the second layer. For the preparation of short-chain hybrid bilayer membrane (scHBLM)-modified electrodes, GCE surfaces were modified with 4-ethyldiazonium (EDAN) as the first layer and bis(2-ethylhexyl) phosphate (BEHP) was utilized as the second layer. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were used to characterize the bilayer formation. Both positively charged [Ru(NH3)6]3+ and negatively charged ([Fe(CN)6]3-/4-) redox probes were used for electrochemical characterization of the modified surfaces using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). EIS results showed a decrease in charge transfer resistance (Rct) upon incubation of Aβ1–42 on the hybrid bilayer-modified surfaces. This framework provides a promising electrochemical platform for designing hybrid bilayers with various physicochemical properties to study the interaction of membrane-bound receptors and biomolecules on surfaces.

Isolated and hybrid bilayer graphene quantum rings

Using the continuum model, we investigate the electronic properties of two types of bilayer graphene (BLG) quantum ring (QR) geometries: (i) an isolated BLG QR and (ii) a monolayer graphene (MLG) with a QR put on top of an infinite graphene sheet (hybrid BLG QR). Solving the Dirac-Weyl equation in the presence of a perpendicular magnetic field and applying the infinite-mass boundary condition at the ring boundaries, we obtain analytical results for the energy levels and corresponding wave spinors for both structures. In the case of isolated BLG QR, we observe a sizeable and magnetically tunable band gap which agrees with the tight-binding transport simulations. Our analytical results also show the intervalley symmetry $ E^K_e (m) = -E^{K'}_h(m) $ between the electron (e) and hole (h) states ($ m $ being the angular momentum quantum number) for the energy spectrum of the isolated BLG QR. The presence of interface boundary in a hybrid BLG QR modifies drastically the energy levels as compared to that of an isolated BLG QR. Its energy levels are tunable from MLG dot, to isolated BLG QR, and to MLG Landau energy levels as magnetic field is varied. Our predictions can be verified experimentally using different techniques such as by magnetotransport measurements.

Tethered Bilayer Membrane Formation on Silanized Fluorine Doped Tin Oxide Surface

Silane compound was synthesized via click chemistry and a mixture of synthesis products without purification was used to form the self-assembled monolayers on metal oxide conducting films of fluorine doped tin oxide (FTO). Silanized FTO surfaces triggered rupture of multilamellar vesicles and formed electrically insulating tethered bilayer membranes (tBLMs). In contrast to well-known hybrid bilayer membranes on silane monolayers such as ones formed from octadecyltrichlorosilane, tBLMs on FTO contained water-ion reservoir between solid surface and phospholipid bilayer sheet. They demonstrated biological relevance and ability to reconstitute the pore-forming protein channels such as α-hemolysin from Staphylococcus aureus and melittin. The addition of cholesterol to tBLMs decreased the membrane-damaging effect of melittin, while the opposite was observed in the case of α-hemolysin. The tBLMs can be regenerated multiple times without losing their functionality. The described methodology (both synthesis and formation of anchor monolayer) can be extended to any oxide film surface by properly adjusting chemical composition of molecular anchor and silanization conditions. This makes the proposed biomimetic membrane system attractive for various applications including biomedical sensors for the detection of pore-forming toxins.

Exchange bias at the organic/ferromagnet interface may not be a spinterface effect

Exchange bias is a physical effect that is used in many spintronic devices like magnetic read heads, magnetic random access memories, and most kinds of magnetic sensors. For the next generation of fully organic devices, molecular exchange bias, if existing, could have a huge impact for developing mechanically soft and environment friendly devices. The observation of molecular exchange bias has been reported recently in hybrid systems where a metallic ferromagnet is exchanged biased by an organic film, and it is considered to be a spinterface effect. To understand this effect, we investigate if the molecular exchange bias exists in Co/metal tetra-phenyl porphyrin hybrid bilayer systems. The molecular exchange bias is never observed when the samples are properly encapsulated, and when the exchange bias is eventually observed, it is not a spinterface effect, but it results from air-driven partial oxidation of the cobalt film transforming part of the metallic cobalt into a cobalt oxide that is well known to induce exchange bias effects. Surprisingly, oxidation is very difficult to prevent even by using very thick metallic encapsulating layers. A similar effect is observed in the Co/metal-phthalocyanine bilayer system, showing that the molecular exchange bias is not a spinterface effect also in the hybrid system in which this effect was originally discovered.

A cascade bilayer electron transport layer toward efficient and stable Ruddlesden‐Popper perovskite solar cells

Optimal interfaces play a key role in charge transport/recombination characteristics and minimized potential loss of perovskite solar cells (PSCs). Currently, n-type oxide semiconductors are the most common electron transport layer (ETL) material, but the imperfect electronic structure, unfavorable band alignment, and corresponding poor interface of ETL/perovskite absorber remain a great challenge for achieving a high photovoltaic performance of PSCs. Here, we combine a fullerene derivative or a non-fullerene organic semiconductor with tin(IV) oxide (SnO2) to promise much-improved surface and electronic structure of ETL interface in Ruddlesden-Popper perovskites (RPPs)-based photovoltaic devices. The organic semiconductors fill a bumpy surface of SnO2 to make the surface smoother, which effectively avoids the shunt pathways at the interface of the ETL/RPP absorber layer, and thereby suppresses unintended electron-hole recombination. The organic-inorganic bilayered ETLs also improve the electronic structure of the SnO2 surface, which provides favorable optoelectronic properties such as quick electron extraction and elongated carrier lifetime in the device. Moreover, the hydrophobic organic semiconductor is helpful in not only growing a uniform, compact, and largely grained RPP absorber layer but also improving the stability of the perovskite absorber layer. Benefiting from the optimized bilayer ETLs, the power conversion efficiency is obviously enhanced up to 10.17% in the RPP-based photovoltaic devices. More importantly, the bilayer ETLs allow improved long-term stability in ambient storage of the devices, providing a viable path to design practical interfaces of efficient and stable RPP-based PSCs. Highlights Hybrid bilayer electron transport layer is designed to enhance the efficiency of Ruddlesden-Popper perovskite solar cells. Phenyl-C61-butyric acid methyl ester and ITIC are inserted as n-type organic semiconductors onto SnO2 film for the bilayer electron transport layer. Tailored optoelectronic properties of the bilayer electron transport layers deliver 10.17% efficiency of Ruddlesden-Popper perovskite solar cells.

Influence of hydrophilic polymers on mechanical property and wound recovery of hybrid bilayer wound dressing system for delivering thermally unstable probiotic

In this study, a novel hybrid bilayer wound dressing (HBD) has been developed for delivering a thermally unstable probiotic, Lactobacillus brevis. The HBD was composed of two layer, a hydrocolloid layer and a Lactobacillus brevis-loaded hydrogel layer as a block supporter and drug carrier, respectively. Moreover, various probiotic-loaded hydrogel layers in HBD were prepared with polyvinyl alcohol (PVA) and numerous hydrophilic polymers via a freezing and thawing method, and their mechanical property, release and wound recovery were assessed. Among the hydrophilic polymers investigated, copovidone most improved the mechanical strength, swelling ability, and release properties; and thus, copovidone/PVA (ratio of 1.0/10) was determined as an appropriate composition of hydrogel layer in HBD. The selected HBD exhibited superior stability than conventional dressing, maintaining approximately 90% of Lactobacillus brevis (9.0 × 108 CFU) during the preparation and storage process. Moreover, the HBD had about 5- and 4-fold better swelling ability and elasticity compared to the conventional dressing. Additionally, it exhibited superior recovery efficacy than the commercial dressing in the animal study. Therefore, this HBD system for delivering a thermally unstable Lactobacillus brevis would be a promising wound dressing with excellent mechanical property and wound recovery.

Insight into the stacking and the species-ordering dependences of interlayer bonding in SiC/GeC polar heterostructures

Two-dimensional (2D) polar materials experience an in-plane charge transfer between different elements due to their electron negativities. When they form vertical heterostructures, the electrostatic force triggered by such charge transfer plays an important role in the interlayer bonding beyond van der Waals (vdW) interaction. Our comprehensive first principle study on the structural stability of the 2D SiC/GeC hybrid bilayer heterostructure has found that the electrostatic interlayer interaction can induce the π–π orbital hybridization between adjacent layers under different stacking and out-of-plane species ordering, with strong hybridization in the cases of Si–C and C–Ge species orderings but weak hybridization in the case of the C–C ordering. In particular, the attractive electrostatic interlayer interaction in the cases of Si–C and C–Ge species orderings mainly controls the equilibrium interlayer distance and the vdW interaction makes the system attain a lower binding energy. On the contrary, the vdW interaction mostly controls the equilibrium interlayer distance in the case of the C–C species ordering and the repulsive electrostatic interlayer force has less effect. Interesting finding is that the band structure of the SiC/GeC hybrid bilayer is sensitive to the layer-layer stacking and the out-of-plane species ordering. An indirect band gap of 2.76 eV (or 2.48 eV) was found under the AA stacking with Si–C ordering (or under the AB stacking with C–C ordering). While a direct band gap of 2.00–2.88 eV was found under other stacking and species orderings, demonstrating its band gap tunable feature. Furthermore, there is a charge redistribution in the interfacial region leading to a built-in electric field. Such field will separate the photo-generated charge carriers in different layers and is expected to reduce the probability of carrier recombination, and eventually give rise to the electron tunneling between layers.

A programmable bilayer hydrogel actuator based on the asymmetric distribution of crystalline regions.

A novel strategy to fabricate bilayer hydrogel actuators based on the asymmetric distribution of crystalline regions across the bilayer structures was proposed. By employing PVA polymer chains into an alkali solvent-derived chitosan hydrogel matrix, chitosan/PVA hybrid bilayer hydrogels with both excellent responsive bending and mechanical properties were obtained as pH-controlled manipulators. In the design, the chitosan/PVA hydrogels upon treatment with freeze-thawing cycles were taken as the first monolayer, where excessive crystalline regions appeared. The original chitosan/PVA hydrogel as the second monolayer was then integrated into one bilayer device through the chemical-crosslinking of epichlorohydrin at the interface. The results showed that the resultant chitosan/PVA bilayer hydrogel actuator with a weight ratio of 3 : 1 displayed better sensitivity upon exposure to stimuli. The actuation behaviors are strongly dependent on experimental parameters such as the pH, PVA content and the chemical-crosslinking density. It is proposed that the driving force originates from the asymmetric distribution of crystalline regions, thus resulting in differential swelling ratios between the monolayers. In addition, programmable 3D shape transformations were achieved by using the bilayer hydrogel with designed 2D geometric patterns, and the tailored gripper-like hydrogel actuator can successfully capture and transport the cargo. Moreover, this actuation behavior can be erased and re-written on demand under certain conditions. Taking advantage of this universal strategy, more attractive actuators derived from synthetic or natural polymers in combination with PVA are highly expected, which can be used as smart soft robots in various fields such as manipulators, grippers, and cantilever sensors.

Functionalized Fluoropolymer-Compatibilized Elastomeric Bilayer Composites for Osteochondral Repair: Unraveling the Role of Substrate Stiffness and Functionalities

The osteochondral lesions and osteoarthritis-related complications continue to be clinically relevant challenges to be addressed by the biomaterials community. Hydrogel-based scaffolds have been widely investigated to enhance osteochondral regeneration, but the inferior mechanical properties together with poor functional stability are the major constraints in their clinical translation. The development of osteochondral implants with natural tissue-mimicking mechanical properties remains largely unexplored. In this perspective, the present study demonstrates a strategy to develop a bilayer osteochondral implant with an elastically stiff composite (poly(vinylidene difluoride)-reinforced BaTiO3, PVDF/BT) and elastically compliant composite (maleic anhydride-functionalized PVDF/thermoplastic polyurethane/BaTiO3, m-PVDF/TPU/BT). The compositional variation in polymer composites allowed the elastic modulus of the hybrid bilayer construct to vary from ∼2 GPa to ∼90 MPa, which enabled a better understanding of the substrate-stiffness-dependent cellular behavior and maturation of preosteoblasts and chondrocytes. The cellular functionalities on PVDF-based polymer matrices have been benchmarked against ultrahigh-molecular-weight polyethylene (UHMWPE), which is clinically used for a wide spectrum of orthopedic applications. The increased alkaline phosphatase (ALP) activity, collagen synthesis, and matrix mineralization confirmed the early differentiation of preosteoblasts on the PVDF/BT matrix with subchondral bone-like mechanical properties. On the contrary, the upregulated chondrogenic functionalities were recorded on m-PVDF/TPU/BT with an elevated level of collagen content, glycosaminoglycans, and proteoglycans. Emphasis has been laid on probing the regulation of the osteochondral behavior using tailored substrate stiffness and functionalities using compatibilized fluoropolymer-based elastomeric composites. Taken together, the results of this work conclusively establish the efficacy of the hybrid bilayer composite with natural tissue-mimicking mechanical properties for the functional repair of osteochondral defects.

Bipolar Resistive Switching Behavior of PVP-GQD/HfOx/ITO/Graphene Hybrid Flexible Resistive Random Access Memory.

We have investigated highly flexible memristive devices using reduced graphene oxide (RGO) nanosheet nanocomposites with an embedded GQD Layer. Resistive switching behavior of poly (4-vinylphenol):graphene quantum dot (PVP:GQD) composite and HfOx hybrid bilayer was explored for developing flexible resistive random access memory (RRAM) devices. A composite active layer was designed based on graphene quantum dots, which is a low-dimensional structure, and a heterogeneous active layer of graphene quantum dots was applied to the interfacial defect structure to overcome the limitations. Increasing to 0.3–0.6 wt % PVP-GQD, Vf changed from 2.27–2.74 V. When negative deflection is applied to the lower electrode, electrons travel through the HfOx/ITO interface. In addition, as the PVP-GQD concentration increased, the depth of the interfacial defect decreased, and confirmed the repetition of appropriate electrical properties through Al and HfOx/ITO. The low interfacial defects help electrophoresis of Al+ ions to the PVP GQD layer and the HfOx thin film. A local electric field increase occurred, resulting in the breakage of the conductive filament in the defect.