Network of Inorganic Nanocrystals Can Swell: Study of Swelling-Induced Surface Instability.

A unique organic-inorganic hybrid network composed of inorganic nanocores (ranging from semiconductors to metallic ones) interconnected through organic molecules can be produced by crosslinking the organic ligands of colloidal inorganic nanocrystals in assemblies. This work reports that this network, which is conventionally considered an inorganic film, can swell when exposed to a solvent because of the interaction between the solvent and the organic linkage within the network. Intriguingly, this work discovers that drying the solvent of the swollen organic-inorganic hybrid network can significantly affect the morphology owing to the swelling-induced compress stress, which is widely observed in various organic network systems. This work studies the surface instability of crosslinked organic-inorganic hybrid networks swollen by various organic solvents, which led to buckling delamination. Specifically, this work investigates the effects of the i) solvent-network interaction, ii) crosslinking density of the network, and iii) thickness of the film on the delamination behavior of the crosslinked network.

Extending the Operational Lifetime of Electrochemiluminescence Devices by Installing a Floating Bipolar Electrode.

Electrochemiluminescence (ECL) holds significant promise for the development of cost-effective light-emitting devices because of its simple structure. However, conventional ECL devices (ECLDs) have a major limitation of short operational lifetimes, rendering them impractical for real-world applications. Typically, the luminescence of these devices lasts no longer than a few minutes during operation. In the current study, a novel architecture is provided for ECLDs that addresses this luminescence lifespan issue. The device architecture features an ECL active layer between two coplanar driving electrodes and a third floating bipolar electrode. The inclusion of the floating bipolar electrode enables modulating the electrical-field distribution within the active layer when a bias is applied between the driving electrodes. This, in turn, enables the use of opaque yet electrochemically stable noble metals as the driving electrodes while allowing ECL light to escape through the transparent floating bipolar electrode. A significant extension on operational lifetime is achieved, defined as the time required for the initial luminance (>100 cd m-2) to decrease by 50%, surpassing 1 h. This starkly contrasts the short lifetime (<1 min) attained by ECLDs in a conventional sandwich-type architecture with two transparent electrodes. These results provide simple strategies for developing durable ECL-based light-emitting devices.

Recent Advances in Marine Biomaterials Tailored and Primed for the Treatment of Damaged Soft Tissues.

The inherent self-repair abilities of the body often fall short when it comes to addressing injuries in soft tissues like skin, nerves, and cartilage. Tissue engineering and regenerative medicine have concentrated their research efforts on creating natural biomaterials to overcome this intrinsic healing limitation. This comprehensive review delves into the advancement of such biomaterials using substances and components sourced from marine origins. These marine-derived materials offer a sustainable alternative to traditional mammal-derived sources, harnessing their advantageous biological traits including sustainability, scalability, reduced zoonotic disease risks, and fewer religious restrictions. The use of diverse engineering methodologies, ranging from nanoparticle engineering and decellularization to 3D bioprinting and electrospinning, has been employed to fabricate scaffolds based on marine biomaterials. Additionally, this review assesses the most promising aspects in this field while acknowledging existing constraints and outlining necessary future steps for advancement.

Differential Toxicity of Graphene Family Nanomaterials Concerning Morphology.

Graphene family nanomaterials (GFNs) are well-known carbonaceous materials, which find application in several fields like optoelectronics, photocatalysis, nanomedicine, and tissue regeneration. Despite possessing many advantages in biomedical applications, GFNs exhibited toxicity depending on various parameters including dosage, size, exposure time, and kinds of administration. GFNS are majorly classified into nanosheets, quantum dots, nanoplatelets, and nanoribbons based on morphology. Understanding the toxic effects of GFNs would provide new suggestions as to how the materials can be utilized effectively. Hence, we are summarizing here some of the recent findings in cellular and animal level toxicity studies of GFNs on the perspective of their different morphologies. Notwithstanding, we highlight progress, challenges, and new toxicological approaches to ensure biosafety of GFNs for future directions.

Functional Graphene Nanomaterials-Based Hybrid Scaffolds for Osteogenesis and Chondrogenesis.

With the emerging trends and recent advances in nanotechnology, it has become increasingly possible to overcome current hurdles for bone and cartilage regeneration. Among the wide type of nanomaterials, graphene (G) and its derivatives (graphene-based materials, GBMs) have been highlighted due to the specific physicochemical and biological properties. In this review, we present the recent development of GBM-based scaffolds for bone and cartilage engineering, focusing on the formulation/shape/size-dependent characteristics, types of scaffold and modification, biocompatibility, bioactivity and underlying mechanism, drawback and prospect of each study. From the findings described herein, mechanical property, biocompatibility, osteogenic and chondrogenic property of GBM-based scaffolds could be significantly enhanced through various scaffold fabrication methods and conjugation with polymers/nanomaterials/drugs. In conclusion, the results presented in this review support the promising prospect of using GBM-based scaffolds for improved bone and cartilage tissue engineering. Although GBM-based scaffolds have some limitations to be overcome by future research, we expect further developments to provide innovative results and improve their clinical potential for bone and cartilage regeneration.

Role of Graphene Family Nanomaterials in Skin Wound Healing and Regeneration.

Owing to astonishing properties such as the large surface area to volume ratio, mechanical stability, antimicrobial property, and collagen crosslinking, graphene family nanomaterials (GFNs) have been widely used in various biomedical applications including tissue regeneration. Many review literatures are available to compile the role of GFNs in cardiac, bone, and neuronal tissue regeneration. However, the contribution of GFNs in skin wound healing and tissue regeneration was not yet discussed. In the present review, we have highlighted the properties of GFNs and their application in skin wound healing. In addition, we have included challenges and future directions of GFNs in skin tissue regeneration in the portion of conclusion and perspectives.

Bipolar Membranes to Promote Formation of Tight Ice-Like Water for Efficient and Sustainable Water Splitting.

Bipolar membranes (BPMs) have recently received much attention for their potential to improve the water dissociation reaction (WDR) at their junction by utilizing catalysts. Herein, composite catalysts (Fe2 O3 @GO) comprising hematite nanoparticles (α-Fe2 O3 ) grown on 2D graphene oxide (GO) nanosheets are reported, which show unprecedentedly high water dissociation performance in the BPM. Furthermore, new catalytic roles in facilitating WDR at the catalyst-water interface are mechanistically elucidated. It is demonstrated that the partially dissociated bound water, formed by the strongly Lewis-acidic Fe atoms of the Fe2 O3 @GO catalyst, helps the "ice-like water" to become tighter, consequently resulting in weaker intramolecular OH bonds, which reduces activation barriers and thus significantly improves the WDR rate. Notably, Fe2 O3 @GO-incorporated BPM shows an extremely low water dissociation potential (0.89 V), compared to commercially available BPM (BP-1E, 1.13 V) at 100 mA cm-2 , and it is quite close to the theoretical potential required for WDR (0.83 V). This performance reduces the required electrical energy consumption for water splitting by ≈40%, as compared to monopolar (Nafion 212 and Selemion AMV) membranes. These results can provide a new approach for the development of water dissociation catalysts and BPMs for realizing highly efficient water splitting systems.

Continuous Preparation of Water-Dispersible Magnetite Nanoparticles by Electrochemical Synthesis.

Highly water-dispersible magnetic nanoparticles were synthesized by convenient electrochemical techniques using a continuous flow reactor. The surface properties of the magnetic nanoparticles (MNPs) were modified with hydrophilic organic ligands during the electrochemical synthesis process to control the degree of dispersion in water. The kind of hydrophilic low-molecular weight polymers or surfactants influenced the sizes of the particles ranged between 25-40 nm (in diameter) and their size distribution. Chitosan-modified MNPs exhibited the most uniform particle size distribution among the MNPs synthesized in this study as well as excellent dispersion stability and magnetic properties in water after the crosslinking of the amino groups in chitosan. Especially, the dispersion stability of the MNPs in water was systematically investigated via a light scattering analysis.

Nanocomposite Membranes Comprising Crosslinked Polymer Blends of Poly(vinyl alcohol)/Poly(styrene sulfonic acid-co-maleic acid) and Fumed Silica Nanoparticles.

Nanocomposite polymer electrolyte membranes comprising a crosslinked polymer blend of poly(vinyl alcohol)/poly(styrene sulfonic acid-co-maleic acid) (PVA/PSSA-co-MA) and fumed silica nanoparticles were prepared for direct methanol fuel cell (DMFC) applications. Silica nanoparticles could be incorporated well uniformly in the completely miscible system, which can form a three-dimensional network structure to achieve the enhancement of mechanical properties as well as the additional reduction of methanol permeability. The optimized proton conductivities and methanol permeability of the PVA/PSSA-co-MA membrane with silica nanoparticles of 10 wt.% were 0.0482 S cm-1 at room temperature and 5.78 × 10-7 cm2 s-1 at the methanol concentration of 40% (w/w), respectively.

Large-Area CVD-Grown Sub-2 V ReS2 Transistors and Logic Gates.

We demonstrated the fabrication of large-area ReS2 transistors and logic gates composed of a chemical vapor deposition (CVD)-grown multilayer ReS2 semiconductor channel and graphene electrodes. Single-layer graphene was used as the source/drain and coplanar gate electrodes. An ion gel with an ultrahigh capacitance effectively gated the ReS2 channel at a low voltage, below 2 V, through a coplanar gate. The contact resistance of the ion gel-gated ReS2 transistors with graphene electrodes decreased dramatically compared with the SiO2-devices prepared with Cr electrodes. The resulting transistors exhibited good device performances, including a maximum electron mobility of 0.9 cm2/(V s) and an on/off current ratio exceeding 104. NMOS logic devices, such as NOT, NAND, and NOR gates, were assembled using the resulting transistors as a proof of concept demonstration of the applicability of the devices to complex logic circuits. The large-area synthesis of ReS2 semiconductors and graphene electrodes and their applications in logic devices open up new opportunities for realizing future flexible electronics based on 2D nanomaterials.

Assemblies of Colloidal CdSe Tetrapod Nanocrystals with Lengthy Arms for Flexible Thin-Film Transistors.

Herein, we report unique features of the assemblies of tetrapod-shaped colloidal nanocrystals (TpNCs) with lengthy arms applicable to flexible thin-film transistors. Due to the extended nature of tetrapod geometry, films made of the TpNC assemblies require reduced numbers of inter-NC hopping for the transport of charge carriers along a given channel length; thus, enhanced conductivity can be achieved compared to those made of typical spherical NCs without arms. Moreover, electrical conduction through the assemblies is tolerant against mechanical bending because interconnections between TpNCs can be well-preserved under bending. Interestingly, both the conductivity of the assemblies and their mechanical tolerance against bending are improved with an increase in the length of tetrapod arms. The arm length-dependency was demonstrated in a series of CdSe TpNC assemblies with different arm lengths (l = 0-90 nm), whose electrical conduction was modulated through electrolyte gating. From the TpNCs with the longest arm length included in the study (l = 90 nm), the film conductivity as high as 20 S/cm was attained at 3 V of gate voltage, corresponding to electron mobility of >10 cm2/(V s) even when evaluated conservatively. The high channel conductivity was retained (∼90% of the value obtained from the flat geometry) even under high bending (bending radius = 5 mm). The results of the present study provide new insights and guidelines for the use of colloidal nanocrystals in solution-processed flexible electronic device applications.

Self-organization of nanorods into ultra-long range two-dimensional monolayer end-to-end network.

Highly uniform large-scale assembly of nanoscale building blocks can enable unique collective properties for practical electronic and photonic devices. We present a two-dimensional (2-D), millimeter-scale network of colloidal CdSe nanorods (NRs) in monolayer thickness through end-to-end linking. The colloidal CdSe NRs are sterically stabilized with tetradecylphosphonic acid (TDPA), and their tips are partially etched in the presence of gold chloride (AuCl3) and didecyldimethylammonium bromide (DDAB), which make them unwetted in toluene. This change in surface wetting property leads to spontaneous adsorption at the 2-D air/toluene interface. Anisotropy in both the geometry and the surface property of the CdSe NRs causes deformation of the NR/toluene/air interface, which derives capillary attraction between tips of neighboring NRs inward. As a result, the NRs confined at the interface spontaneously form a 2-D network composed of end-to-end linkages. We employ a vertical-deposition approach to maintain a consistent rate of NR supply to the interface during the assembly. The rate control turns out to be pivotal in the preparation of a highly uniform large scale 2-D network without aggregation. In addition, unprecedented control of the NR density in the network was possible by adjusting either the lift-up speed of the immersed substrate or the relative concentration of AuCl3 to DDAB. Our findings provide important design criteria for 2-D assembly of anisotropic nanobuilding blocks.

Thin Films of Highly Planar Semiconductor Polymers Exhibiting Band-like Transport at Room Temperature.

We report the observation of band-like transport from printed polymer thin films at room temperature. This was achieved from donor-acceptor type thiophene-thiazole copolymer that was carefully designed to enhance the planarity of the backbone and the resulting transfer integral between the macromolecules. Due to the strong molecular interaction, the printed polymer film exhibited extremely low trap density comparable to that of molecular single crystals. Moreover, the energy barrier height for charge transport could be readily reduced with the aid of electric field, which led formation of extended electron states for band-like charge transport at room temperature.

Solid-phase flexibility in Ag2Se semiconductor nanocrystals.

Nanocrystals are known to alter the relative stability of bulk solid phases. Here we test the limits of this effect on Ag2Se nanocrystals, a promising new electronic and infrared material. In the bulk, Ag2Se exhibits a solid-solid phase transition to a superionic conducting phase at moderate temperatures. We map this phase transition as a function of size, temperature, and surface treatment in Ag2Se core-only and core-shell nanocrystals. We show that the transition can be tuned not just below but also above the bulk phase-transition temperature. This phase flexibility has implications for applications in optoelectronic and phase-memory devices.

Water-gel for gating graphene transistors.

Water, the primary electrolyte in biology, attracts significant interest as an electrolyte-type dielectric material for transistors compatible with biological systems. Unfortunately, the fluidic nature and low ionic conductivity of water prevents its practical usage in such applications. Here, we describe the development of a solid state, megahertz-operating, water-based gate dielectric system for operating graphene transistors. The new electrolyte systems were prepared by dissolving metal-substituted DNA polyelectrolytes into water. The addition of these biocompatible polyelectrolytes induced hydrogelation to provide solid-state integrity to the system. They also enhanced the ionic conductivities of the electrolytes, which in turn led to the quick formation of an electric double layer at the graphene/electrolyte interface that is beneficial for modulating currents in graphene transistors at high frequencies. At the optimized conditions, the Na-DNA water-gel-gated flexible transistors and inverters were operated at frequencies above 1 MHz and 100 kHz, respectively.

Studies on cytocompatibility of human dermal fibroblasts on carbon nanofiber nanoparticle-containing bioprinted constructs.

Functional nanocomposite-based printable inks impart strength, mechanical stability, and bioactivity to the printed matrix due to the presence of nanomaterials or nanostructures. Carbonaceous nanomaterials are known to improve the electrical conductivity, osteoconductivity, mechanical, and thermal properties of printed materials. In the current work, we have incorporated carbon nanofiber nanoparticles (CNF NPs) into methacrylated gelatin (GelMA) to investigate whether the resulting nanocomposite printable ink constructs (GelMA-CNF NPs) promote cell proliferation. Two kinds of printable constructs, cell-laden bioink and biomaterial ink, were prepared by incorporating various concentrations of CNF NPs (50, 100, and 150 µg/mL). The CNF NPs improved the mechanical strength and dielectric properties of the printed constructs. The in vitro cell line studies using normal human dermal fibroblasts (nHDF) demonstrated that CNF NPs are involved in cell-material interaction without affecting cellular morphology. Though the presence of NPs did not affect cellular viability on the initial days of treatment, it caused cytotoxicity to the cells on days 4 and 7 of the treatment. A significant level of cytotoxicity was observed in the highly CNF-concentrated bioink scaffolds (100 and 150 µg/mL). The unfavorable outcomes of the current work necessitate further study of employing functionalized CNF NPs to achieve enhanced cell proliferation in GelMA-CNF NPs-based bioprinted constructs and advance the application of skin tissue regeneration.

Regulated Behavior in Living Cells with Highly Aligned Configurations on Nanowrinkled Graphene Oxide Substrates: Deep Learning Based on Interplay of Cellular Contact Guidance.

Micro-/nanotopographical cues have emerged as a practical and promising strategy for controlling cell fate and reprogramming, which play a key role as biophysical regulators in diverse cellular processes and behaviors. Extracellular biophysical factors can trigger intracellular physiological signaling via mechanotransduction and promote cellular responses such as cell adhesion, migration, proliferation, gene/protein expression, and differentiation. Here, we engineered a highly ordered nanowrinkled graphene oxide (GO) surface via the mechanical deformation of an ultrathin GO film on an elastomeric substrate to observe specific cellular responses based on surface-mediated topographical cues. The ultrathin GO film on the uniaxially prestrained elastomeric substrate through self-assembly and subsequent compressive force produced GO nanowrinkles with periodic amplitude. To examine the acute cellular behaviors on the GO-based cell interface with nanostructured arrays of wrinkles, we cultured L929 fibroblasts and HT22 hippocampal neuronal cells. As a result, our developed cell-culture substrate obviously provided a directional guidance effect. In addition, based on the observed results, we adapted a deep learning (DL)-based data processing technique to precisely interpret the cell behaviors on the nanowrinkled GO surfaces. According to the learning/transfer learning protocol of the DL network, we detected cell boundaries, elongation, and orientation and quantitatively evaluated cell velocity, traveling distance, displacement, and orientation. The presented experimental results have intriguing implications such that the nanotopographical microenvironment could engineer the living cells' morphological polarization to assemble them into useful tissue chips consisting of multiple cell types.

Harnessing 3D printed highly porous Ti-6Al-4V scaffolds coated with graphene oxide to promote osteogenesis.

Bone tissue engineering (BTE) strategies have been developed to address challenges in orthopedic and dental therapy by expediting osseointegration and new bone formation. In this study, we developed irregular porous Ti-6Al-4V scaffolds coated with reduced graphene oxide (rGO), specifically rGO-pTi, and investigated their ability to stimulate osseointegration in vivo. The rGO-pTi scaffolds exhibited unique irregular micropores and high hydrophilicity, facilitating protein adsorption and cell growth. In vitro assays revealed that the rGO-pTi scaffolds increased alkaline phosphatase (ALP) activity, mineralization nodule formation, and osteogenic gene upregulation in MC3T3-E1 preosteoblasts. Moreover, in vivo transplantation of rGO-pTi scaffolds in rabbit calvarial bone defects showed improved bone matrix formation and osseointegration without hemorrhage. These findings highlight the potential of combining rGO with irregular micropores as a promising BTE scaffold for bone regeneration.

Quantum Dot-Based Three-Stack Tandem Near-Infrared-to-Visible Optoelectric Upconversion Devices.

Quantum dots (QDs) exhibit size-tunable optical properties, making them suitable for efficient light-sensing and light-emitting devices. Tandem devices that can convert near-infrared (NIR) to visible (Vis) signals can be fabricated by integrating an NIR-sensing QD device with a Vis electroluminescence (EL) QD device. However, these devices require delicate control of the QD layer during processing to prevent damage to the predeposited QD layers in tandem devices during the subsequent deposition of other functional layers. This has restricted attainable device structures for QD-based upconversion devices. Herein, we present a modular approach for fabricating QD-based optoelectric upconversion devices. This approach involves using NIR QD-absorbing (Abs) and Vis QD-EL units as building modules, both of which feature cross-linked functional layers that exhibit structural tolerance to dissolution during subsequent solution-based processes. Tandem devices are fabricated in both normal (EL unit on Abs unit) and inverted (Abs unit on EL unit) structures using the same set of NIR QD-Abs and Vis QD-EL units stacked in opposite sequences. The tandem device in the normal structure exhibits a high NIR photon-to-Vis-photon conversion efficiency of up to 1.9% in a practical transmissive mode. By extending our modular approach, we also demonstrate a three-stack tandem device that incorporates a single NIR-absorbing unit coupled with two EL units, achieving an even higher conversion efficiency of up to 3.2%.

Skeletal muscle regeneration with 3D bioprinted hyaluronate/gelatin hydrogels incorporating MXene nanoparticles.

There has been significant progress in the field of three-dimensional (3D) bioprinting technology, leading to active research on creating bioinks capable of producing structurally and functionally tissue-mimetic constructs. Ti3C2Tx MXene nanoparticles (NPs), promising two-dimensional nanomaterials, are being investigated for their potential in muscle regeneration due to their unique physicochemical properties. In this study, we integrated MXene NPs into composite hydrogels made of gelatin methacryloyl (GelMA) and hyaluronic acid methacryloyl (HAMA) to develop bioinks (namely, GHM bioink) that promote myogenesis. The prepared GHM bioinks were found to offer excellent printability with structural integrity, cytocompatibility, and microporosity. Additionally, MXene NPs within the 3D bioprinted constructs encouraged the differentiation of C2C12 cells into skeletal muscle cells without additional support of myogenic agents. Genetic analysis indicated that representative myogenic markers both for early and late myogenesis were significantly up-regulated. Moreover, animal studies demonstrated that GHM bioinks contributed to enhanced regeneration of skeletal muscle while reducing immune responses in mice models with volumetric muscle loss (VML). Our results suggest that the GHM hydrogel can be exploited to craft a range of strategies for the development of a novel bioink to facilitate skeletal muscle regeneration because these MXene-incorporated composite materials have the potential to promote myogenesis.