Verifiable Delay Function and Its Blockchain-Related Application: A Survey.

The concept of verifiable delay functions has received attention from researchers since it was first proposed in 2018. The applications of verifiable delay are also widespread in blockchain research, such as: computational timestamping, public random beacons, resource-efficient blockchains, and proofs of data replication. This paper introduces the concept of verifiable delay functions and systematically summarizes the types of verifiable delay functions. Firstly, the description and characteristics of verifiable delay functions are given, and weak verifiable delay functions, incremental verifiable delay functions, decodable verifiable delay functions, and trapdoor verifiable delay functions are introduced respectively. The construction of verifiable delay functions generally relies on two security assumptions: algebraic assumption or structural assumption. Then, the security assumptions of two different verifiable delay functions are described based on cryptography theory. Secondly, a post-quantum verifiable delay function based on super-singular isogeny is introduced. Finally, the paper summarizes the blockchain-related applications of verifiable delay functions.

Multilayer 3D Chiral Folding Polymers and Their Asymmetric Catalytic Assembly.

A novel class of polymers and oligomers of chiral folding chirality has been designed and synthesized, showing structurally compacted triple-column/multiple-layer frameworks. Both uniformed and differentiated aromatic chromophoric units were successfully constructed between naphthyl piers of this framework. Screening monomers, catalysts, and catalytic systems led to the success of asymmetric catalytic Suzuki-Miyaura polycouplings. Enantio- and diastereochemistry were unambiguously determined by X-ray structural analysis and concurrently by comparison with a similar asymmetric induction by the same catalyst in the asymmetric synthesis of a chiral three-layered product. The resulting chiral polymers exhibit intense fluorescence activity in a solid form and solution under specific wavelength irradiation.

Cost-Effective Yarn-Shaped Lithium-Ion Battery with High Wearability.

Because of flexibility, compactness, weavability, and ergonomic design, yarn-shaped lithium-ion batteries (LIBs) have enormous potential applications in wearable electronics. Still, the yarn-shaped LIB with the ability to meet commercialization requirements has never been reported, owing to the current challenge in complex material synthesis technologies, expensive raw material costs, poor safety performance, and nonstandard manufacturing equipment. Herein, we propose a yarn-shaped LIB that meets the aforementioned requirements. With a highly conductive and flexible stainless-steel yarn acting as the current collector, the electrode active materials and the gel electrolyte, which are commercially available at low cost, are uniformly coated onto the stainless-steel yarn by a simple and facile dipping-drying method. Even at different deformation conditions (i.e., bending or knotting), the specific capacity of the yarn-shaped LIB (7 cm long, <2 mm in diameter) assembled from graphite and lithium iron phosphate electrodes is maintained >85%. After charged treatment, it can successfully power up an electronic watch and an electronic thermo-hygrometer. Thanks to the simple preparation process, low cost of raw materials, and good safety performance, this work can promote the commercialization of wearable energy storage devices.

In vitro study of transportation of porphyrin immobilized graphene oxide through blood brain barrier.

Blood brain barrier (BBB), a barrier formed by endothelial cells, separates the brain from the circulatory system and protects the stability of central neural system normally, however, it also results in low permeability of vast majority of drugs for brain disease therapy. In this work, the cytotoxicity, uptake and transportation of 2D graphene nanosheet through BBB were investigated in in vitro models of BBB constructed by human brain microvascular endothelia cells (hBMECs). Permeability of two types of graphene nanosheet, including graphene oxide (GO) and porphyrin conjugated graphene oxide (PGO) through BBB were studied. With hydrophobic chemicals conjugation on its surface, permeability of PGO was greatly improved compared to GO. Furthermore, transportation behavior of assorted sizes of PGO obtained by differential velocity centrifugation through BBB was also explored, revealing that PGO with larger size has higher permeability than smaller-size PGO. The significant improved permeability of 2D graphene nanosheet through BBB compared to traditional drugs provides promising applications in drug delivery and disease therapy for brain disease in the near future.

Thermal-Recoverable Tough Hydrogels Enhanced by Porphyrin Decorated Graphene Oxide.

Artificial tissue materials usually suffer properties and structure loss over time. As a usual strategy, a new substitution is required to replace the worn one to maintain the functions. Although several approaches have been developed to restore the mechanical properties of hydrogels, they require direct heating or touching, which cannot be processed within the body. In this manuscript, a photothermal method was developed to restore the mechanical properties of the tough hydrogels by using near infrared (NIR) laser irradiation. By adding the porphyrin decorated graphene oxide (PGO) as the nanoreinforcer and photothermal agent into carrageenan/polyacrylamide double network hydrogels (PDN), the compressive strength of the PDN was greatly improved by 104%. Under a short time of NIR laser irradiation, the PGO effectively converts light energy to thermal energy to heat the PDN hydrogels. The damaged carrageenan network was rebuilt, and a 90% compressive strength recovery was achieved. The PGO not only significantly improves the mechanical performance of PDN, but also restores the compressive property of PDN via a photothermal method. These tough hydrogels with superior photothermal recovery may work as promising substitutes for load-bearing tissues.

Three-Dimensional Hierarchically Porous Graphene Fiber-Shaped Supercapacitors with High Specific Capacitance and Rate Capability.

Chemically converted graphene fiber-shaped supercapacitors (FSSCs) are highly promising flexible energy storage devices for wearable electronics. However, the ultralow specific capacitance and poor rate performance severely hamper their practical applications. They are caused by severe stacking of graphene nanosheets and tortuous ion diffusion path in graphene-based electrodes; thus, the ultralow utilization of graphene has been rarely carefully considered to date. Here, we address these issues by developing three-dimensional hierarchically porous graphene fiber with the incorporation of holey graphene for efficient utilization of graphene to achieve fast charge diffusion and good charge storage capability. Without deterioration in electrical but robust mechanical properties, the optimal graphene fiber shows ultrahigh specific capacitance of 220.1 F cm-3 at current density of 0.1 A cm-3 and boosted specific capacitance of 254.3 F cm-3 at 0.1 A cm-3 after nitrogen doping. Moreover, the nitrogen-doped 40% holey graphene hybrid fiber-assembled FSSC exhibits ultrahigh rate capability (96, 91, and 87% at current density of 0.5, 1.0, and 2.0 A cm-3, respectively, and 67% even at ultrahigh current density of 10.0 A cm-3) and excellent cycle stability (95.65% capacitance retention after 10 000 cycles). The contribution of three-dimensional interconnected hierarchically porous network to the enhanced electrochemical (EC) performance is semiquantitatively elucidated by Brunauer-Emmett-Teller and energy dispersive spectroscopy mapping. Our work gives insights into the importance of fully utilizing graphene and provides an efficient strategy for high EC performance in chemically converted graphene-based FSSCs.

Modeling-Based Assessment of 3D Printing-Enabled Meniscus Transplantation.

3D printing technology is able to produce personalized artificial substitutes for patients with damaged menisci. However, there is a lack of thorough understanding of 3D printing-enabled (3DP-enabled) meniscus transplantation and its long-term advantages over traditional transplantation. To help health care stakeholders and patients assess the value of 3DP-enabled meniscus transplantation, this study compares the long-term cost and risk of this new paradigm with traditional transplantation by simulation. Pathway models are developed to simulate patients' treatment process during a 20-year period, and a Markov process is used to model the state transitions of patients after transplantation. A sensitivity analysis is also conducted to show the effect of quality of 3D-printed meniscus on model outputs. The simulation results suggest that the performance of 3DP-enabled meniscus transplantation depends on quality of 3D-printed meniscus. The conclusion of this study is that 3DP-enabled meniscus transplantation has many advantages over traditional meniscus transplantation, including a minimal waiting time, perfect size and shape match, and potentially lower cost and risk in the long term.

Exceptional thermoelectric properties of flexible organic-inorganic hybrids with monodispersed and periodic nanophase.

Flexible organic-inorganic hybrids are promising thermoelectric materials to recycle waste heat in versatile formats. However, current organic/inorganic hybrids suffer from inferior thermoelectric properties due to aggregate nanostructures. Here we demonstrate flexible organic-inorganic hybrids where size-tunable Bi2Te3 nanoparticles are discontinuously monodispersed in the continuous conductive polymer phase, completely distinct from traditional bi-continuous hybrids. Periodic nanofillers significantly scatter phonons while continuous conducting polymer phase provides favored electronic transport, resulting in ultrahigh power factor of ~1350 µW m-1 K-2 and ultralow in-plane thermal conductivity of ~0.7 W m-1 K-1. Consequently, figure-of-merit (ZT) of 0.58 is obtained at room temperature, outperforming all reported organic materials and organic-inorganic hybrids. Thermoelectric properties of as-fabricated hybrids show negligible change for bending 100 cycles, indicating superior mechanical flexibility. These findings provide significant scientific foundation for shaping flexible thermoelectric functionality via synergistic integration of organic and inorganic components.

Enhancing Electrochemical Performance of Graphene Fiber-Based Supercapacitors by Plasma Treatment.

Graphene fiber-based supercapacitors (GFSCs) hold high power density, fast charge-discharge rate, ultralong cycling life, exceptional mechanical/electrical properties, and safe operation conditions, making them very promising to power small wearable electronics. However, the electrochemical performance is still limited by the severe stacking of graphene sheets, hydrophobicity of graphene fibers, and complex preparation process. In this work, we develop a facile but robust strategy to easily enhance electrochemical properties of all-solid-state GFSCs by simple plasma treatment. We find that 1 min plasma treatment under an ambient condition results in 33.1% enhancement of areal specific capacitance (36.25 mF/cm2) in comparison to the as-prepared GFSC. The energy density reaches 0.80 µW h/cm2 in polyvinyl alcohol/H2SO4 gel electrolyte and 18.12 µW h/cm2 in poly(vinylidene difluoride)/ethyl-3-methylimidazolium tetrafluoroborate electrolyte, which are 22 times of that of as-prepared ones. The plasma-treated GFSCs also exhibit ultrahigh rate capability (69.13% for 40 s plasma-treated ones) and superior cycle stability (96.14% capacitance retention after 20 000 cycles for 1 min plasma-treated ones). This plasma strategy can be extended to mass-manufacture high-performance carbonaceous fiber-based supercapacitors, such as graphene and carbon nanotube-based ones.

Bio-inspired bioactive glasses for efficient microRNA and drug delivery.

Bio-inspired pinecone-like bioactive glasses consisting of ordered thin-layers separated by consistent cavities were synthesized using a sol-gel process. The short diameter of the as-produced particles was as short as 161 nm, and the surface area was as high as 280 m2 g-1. The pore volume, ranging from ∼0.74 cm3 g-1 to ∼0.67 cm3 g-1, could be modulated by the aqueous ammonia concentration. The surface was further tailored for positive charges by amino grafting. The as-produced nanoparticles could successfully enter cells via endocytosis. The microRNA delivery of the bioactive glass particles was further investigated by fluorescence microscopy and flow cytometry, indicating a loading efficiency and transfection efficiency greater than 90%. The potential of such particles as drug carriers was also studied. CCK8, live-dead cell staining and PI/annexinV double staining analyses confirmed that the bioactive glass particles loaded with antitumour doxorubicin (DOX) significantly accelerated the apoptosis of tumour cells. These bio-inspired bioactive glasses are promising as novel vectors for drug and microRNA delivery with high efficiency.

Thermoelectric properties of PEDOT nanowire/PEDOT hybrids.

Freestanding poly(3,4-ethylenedioxythiophene) (PEDOT) nanowires were synthesized by template-confined in situ polymerization, and then integrated into polystyrene sulfonate (PSS)-doped PEDOT and tosylate-doped PEDOT hosts, respectively. The hybrid morphologies were characterized by atomic force microscopy, indicating the homogeneous dispersion of PEDOT nanowires. The thermoelectric properties of the resultant hybrids were measured, and the power factor was found to be enhanced by 9-fold in comparison with PEDOT: PSS mixed with 5 vol% dimethyl sulfoxide while the low thermal conductivity was still maintained. Such a significant improvement could be attributed to the synergistic effects of interfacial energy filtering, component contributions, and changes of carrier concentrations in the host materials. Upon addition of 0.2 wt% PEDOT nanowires, the resultant composites demonstrated a power factor as high as 446.6 µW m(-1) K(-2) and the thermoelectric figure of merit could reach 0.44 at room temperature. The thermoelectric devices were investigated by using the PEDOT nanowire/PEDOT hybrid as a p-type leg and nitrogen-doped graphene as an n-type leg. The normalized power output was as high as ∼0.5 mW m(-2) for a temperature gradient of ΔT = 10.1 °C, indicating great potential for practical applications. These findings open up a new route towards high-performance organic thermoelectric materials and devices.

Porphyrin Immobilized Nanographene Oxide for Enhanced and Targeted Photothermal Therapy of Brain Cancer.

Brain cancer is a fatal disease that is difficult to treat because of poor targeting and low permeability of chemotherapeutic drugs through the blood brain barrier. In a comparison to current treatments, such as surgery followed by chemotherapy and/or radiotherapy, photothermal therapy is a remarkable noninvasive therapy developed in recent years. In this work, porphyrin immobilized nanographene oxide (PNG) was synthesized and bioconjugated with a peptide to achieve enhanced and targeted photothermal therapy for brain cancer. PNG was dispersed into the agar based artificial tissue model and demonstrated a photo-to-thermal conversion efficiency of 19.93% at a PNG concentration of only 0.5 wt %, with a heating rate of 0.6 °C/s at the beginning of irradiation. In comparison, 0.5 wt % graphene oxide (GO) indicated a photo-to-thermal conversion efficiency of 12.20% and a heating rate of 0.3 °C/s. To actively target brain tumor cells without harming healthy cells and tissues surrounding the laser path, a tripeptide l-arginyl-glycyl-l-aspartic (RGD) was further grafted to PNG. The photothermal therapy effects of PNG-RGD completely eliminated the tumor in vivo, indicating its excellent therapeutic effect for the treatment of brain cancer.

Tough and fully recoverable hydrogels.

In natural cartilage, collagen fibers form the extracellular matrix, while aggrecan entangles with these fibers and provides cartilage with its osmotic properties, which are critical to resist cyclic compressive loads. In this paper, a hydrogel was fabricated via the entanglement of a bio-inspired nanostructure (chondroitin sulfate-coated vinyl silica nanoparticles, CS-SNP) within an agar/poly(acrylamide) double network hydrogel. The highly charged chondroitin sulfate groups provide additional compression resistance within the macromolecular chains, while the solid silica cores anchor these entanglements. The presence of the CS-SNP not only improved the compressive modulus, compressive strength, fracture toughness, and fatigue resistance of this hydrogel, but also ensured the full recovery of all these properties after thermal heating. This tough, fully recoverable, and robust hydrogel is a promising material for applications with strong mechanical requirements.

Large-area preparation of high-quality and uniform three-dimensional graphene networks through thermal degradation of graphene oxide-nitrocellulose composites.

We demonstrate a simple method to prepare high-quality and uniform three-dimensional (3D) graphene networks through thermal degradation of graphene oxide (GO)-nitrocellulose composites over a large area. The nitrocellulose simultaneously acts as a support and aids in the reduction of GO by exothermic decomposition. The graphene networks have tunable porous morphology where the pore size can be controlled by adjusting the concentration of GO in the composite. This new technique is a very simple method to obtain 3D graphene networks and has the potential to produce 3D graphene-modified substrates for use in energy storage and conversion applications, in supporting frameworks of catalyst, and in sensors. In this report, the prepared 3D graphene networks were directly used as the electrodes of supercapacitors without using a binding agent and/or conducting additive with a high specific capacitance of 162.5 F g(-1) at 0.5 A g(-1) current density.

Enhancing thermoelectric properties of organic composites through hierarchical nanostructures.

Organic thermoelectric (TE) materials are very attractive due to easy processing, material abundance, and environmentally-benign characteristics, but their potential is significantly restricted by the inferior thermoelectric properties. In this work, noncovalently functionalized graphene with fullerene by π-π stacking in a liquid-liquid interface was integrated into poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate). Graphene helps to improve electrical conductivity while fullerene enhances the Seebeck coefficient and hinders thermal conductivity, resulting in the synergistic effect on enhancing thermoelectric properties. With the integration of nanohybrids, the electrical conductivity increased from ~10,000 to ~70,000 S/m, the thermal conductivity changed from 0.2 to 2 W·K(-1)m(-1) while the Seebeck coefficient was enhanced by around 4-fold. As a result, nanohybrids-based polymer composites demonstrated the figure of merit (ZT) as high as 6.7 × 10(-2), indicating an enhancement of more than one order of magnitude in comparison to single-phase filler-based polymer composites with ZT at the level of 10(-3).

Shape memory polymer nanocomposites for application of multiple-field active disassembly: experiment and simulation.

Active disassembly (AD) uses innovative materials that can perform a designed disassembly action by the application of an external field. AD provides improvements over current disassembly processes by limiting machine or manual labor and enabling batch processing for end-of-life products. With improved disassembly operations, more reuse of components and purer recycling streams may be seen. One problem with AD, however, has been with the single-field actuation because of the probability of accidental disassembly. This presentation will discuss the application of shape memory polymer (SMP) nanocomposites in a new AD process. This novel AD process requires multiple-field actuation of the SMP nanocomposite fastener. In the analysis of this AD process, thermal and magnetic field tests were performed on the SMP nanocomposite. From these tests, finite-element analysis was performed to model and simulate the multiple-field AD process. The results of the simulations provide performance variables for the AD process and show a better performance time for the SMP nanocomposite fastener than for a comparable SMP fastener.

Thermoelectric properties of porous multi-walled carbon nanotube/polyaniline core/shell nanocomposites.

Porous polyaniline (PANI)-coated multi-walled carbon nanotube (MWNT) core/shell nanohybrids were fabricated through in situ polymerization and subsequently assembled into macroscopic composites. N(2) adsorption/desorption analysis indicated that the volume of nanopores increased significantly, which could make a significant contribution to phonon scattering. Thermal annealing was also carried out to improve the Seebeck coefficient of the as-produced nanocomposites. The optimal sample showed electrical conductivity of 14.1 S cm(-1), a Seebeck coefficient of 79.8 µV K(-1) and thermal conductivity of 0.27 W mK(-1), resulting in a highest figure of merit (ZT) of 0.01 at a very low loading of MWNTs (<1 wt%). These results will provide a potential direction to enhance thermoelectric performance of organic materials and also facilitate the application of organic materials in thermal energy harvesting or cooling.

A reduced graphene oxide based electrochemical biosensor for tyrosine detection.

In this paper, a 'green' and safe hydrothermal method has been used to reduce graphene oxide and produce hemin modified graphene nanosheet (HGN) based electrochemical biosensors for the determination of l-tyrosine levels. The as-fabricated HGN biosensors were characterized by UV-visible absorption spectra, fluorescence spectra, Fourier transform infrared spectroscopy (FTIR) spectra and thermogravimetric analysis (TGA). The experimental results indicated that hemin was successfully immobilized on the reduced graphene oxide nanosheet (rGO) through π-π interaction. TEM images and EDX results further confirmed the attachment of hemin on the rGO nanosheet. Cyclic voltammetry tests were carried out for the bare glass carbon electrode (GCE), the rGO electrode (rGO/GCE), and the hemin-rGO electrode (HGN/GCE). The HGN/GCE based biosensor exhibits a tyrosine detection linear range from 5 × 10(-7) M to 2 × 10(-5) M with a detection limitation of 7.5 × 10(-8) M at a signal-to-noise ratio of 3. The sensitivity of this biosensor is 133 times higher than that of the bare GCE. In comparison with other works, electroactive biosensors are easily fabricated, easily controlled and cost-effective. Moreover, the hemin-rGO based biosensors demonstrate higher stability, a broader detection linear range and better detection sensitivity. Study of the oxidation scheme reveals that the rGO enhances the electron transfer between the electrode and the hemin, and the existence of hemin groups effectively electrocatalyzes the oxidation of tyrosine. This study contributes to a widespread clinical application of nanomaterial based biosensor devices with a broader detection linear range, improved stability, enhanced sensitivity and reduced costs.

The synergistic effect of nanocrystal integration and process optimization on solar cell efficiency.

This paper investigates the roles of semiconducting single-walled carbon nanotubes (SWNTs) and metallic SWNTs in the SWNT/poly(3-hexylthiophene) (P3HT)-based photovoltaic conversion system. SWNTs containing different fractions of semiconducting nanotubes were conjugated with P3HT by virtue of π-π interaction. The energy transfer and carrier transport mechanisms in the photovoltaic composites were experimentally investigated by optical absorption spectroscopy, photoluminescence spectroscopy and carrier mobility measurements. At low loading of SWNTs, a high percentage of semiconducting nanotubes result in diminished non-radiative decay of exciton and lower carrier mobility, causing higher open circuit voltage and lower photocurrent. At an optimized morphology, SWNT/P3HT/phenyl-C61-butyric acid methyl ester (PCBM) hybrid-based solar cells demonstrated much higher photocurrent than a reference solar cell (P3HT:PCBM) due to the improved carrier mobility. Further thermal annealing of the devices significantly increased the open circuit voltage to 610 mV, resulting in an 80% increase of power conversion efficiency in comparison to the reference solar cell. These results are expected to lay a foundation for the integration of various nanocrystals into solar cells for efficient photovoltaic conversion.