ResearchPad - nanotechnology https://www.researchpad.co Default RSS Feed en-us © 2020 Newgen KnowledgeWorks <![CDATA[A novel dry-blending method to reduce the coefficient of thermal expansion of polymer templates for OTFT electrodes]]> https://www.researchpad.co/article/elastic_article_11241 Among the patterning technologies for organic thin-film transistors (OTFTs), the fabrication of OTFT electrodes using polymer templates has attracted much attention. However, deviations in the electrode alignment occur because the coefficient of thermal expansion (CTE) of the polymer template is much higher than the CTE of the dielectric layer. Here, a novel dry-blending method is described in which SiO2 nanoparticles are filled into a grooved silicon template, followed by permeation of polydimethylsiloxane (PDMS) into the SiO2 nanoparticle gaps. The SiO2 nanoparticles in the groove are extracted by curing and peeling off PDMS to prepare a PDMS/SiO2 composite template with a nanoparticle content of 83.8 wt %. The composite template has a CTE of 96 ppm/°C, which is a reduction by 69.23% compared with the original PDMS template. Finally, we achieved the alignment of OTFT electrodes using the composite template.

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<![CDATA[Electromigration-induced directional steps towards the formation of single atomic Ag contacts]]> https://www.researchpad.co/article/elastic_article_11240 Even though there have been many experimental attempts and theoretical approaches to understand the process of electromigration (EM), it has not been quantitatively understood for ultrathin structures and at grain boundaries. Nevertheless, we showed recently that it can be used reliably for the formation of single atomic point contacts after careful pre-structuring of the initial Ag nanostructures. The process of formation of nanocontacts by EM down to a single-atom point contact was investigated for ultrathin (5 nm) Ag structures at 100 K by measuring the conductance as a function of the time during EM. In this paper, we compare the process of thinning by EM of structures with constrictions below the average grain size of Ag layers (15 nm) with that of structures with much larger initial constrictions of around 150 nm having multiple grains at the centre constriction prior to the formation of a point contact. Even though clear morphological differences exist between both types of structures, quantized conductance plateaus showing the formation of single point contacts have been observed for both. Here we put emphasis on the thinning process by EM, just before a point contact is formed. To understand this thinning process, the semi-classical regime before the contact reaches the quantum regime was analyzed in detail. For this purpose, we used experimental conductance histograms in the range between 2G0 and 15G0 and their corresponding Fourier transforms (FTs). The FT analysis of the conductance histograms exhibits a clear preference for thinning along the [100] direction. Using well-established models, both atom-by-atom steps and ranges of stability, presumably caused by electronic shell effects, can be discriminated. Although the directional motion of atoms during EM leads to specific properties such as the instabilities mentioned, similarities to mechanically opened contacts with respect to cross-sectional stability were found.

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<![CDATA[Effect of substitutional defects on resonant tunneling diodes based on armchair graphene and boron nitride nanoribbons lateral heterojunctions]]> https://www.researchpad.co/article/elastic_article_11239 A nanometer-scaled resonant tunneling diode based on lateral heterojunctions of armchair graphene and boron nitride nanoribbons, exhibiting negative differential resistance is proposed. Low-bandgap armchair graphene nanoribbons and high-bandgap armchair boron nitride nanoribbons are used to design the well and the barrier region, respectively. The effect of all possible substitutional defects (including BC, NC, CB, and CN) at the interface of graphene and boron nitride nanoribbons on the negative differential resistance behavior of the proposed resonant tunneling diode is investigated. Transport simulations are carried out in the framework of tight-binding Hamiltonians and non-equilibrium Green’s functions. The results show that a single substitutional defect at the interface of armchair graphene and boron nitride nanoribbons can dramatically affect the negative differential resistance behavior depending on its type and location in the structure.

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<![CDATA[Quantitative determination of the interaction potential between two surfaces using frequency-modulated atomic force microscopy]]> https://www.researchpad.co/article/elastic_article_7817 The interaction potential between two surfaces determines the adhesive and repulsive forces between them. It also determines interfacial properties, such as adhesion and friction, and is a key input into mechanics models and atomistic simulations of contacts. We have developed a novel methodology to experimentally determine interaction potential parameters, given a particular potential form, using frequency-modulated atomic force microscopy (AFM). Furthermore, this technique can be extended to the experimental verification of potential forms for any given material pair. Specifically, interaction forces are determined between an AFM tip apex and a nominally flat substrate using dynamic force spectroscopy measurements in an ultrahigh vacuum (UHV) environment. The tip geometry, which is initially unknown and potentially irregularly shaped, is determined using transmission electron microscopy (TEM) imaging. It is then used to generate theoretical interaction force–displacement relations, which are then compared to experimental results. The method is demonstrated here using a silicon AFM probe with its native oxide and a diamond sample. Assuming the 6-12 Lennard-Jones potential form, best-fit values for the work of adhesion (Wadh) and range of adhesion (z0) parameters were determined to be 80 ± 20 mJ/m2 and 0.6 ± 0.2 nm, respectively. Furthermore, the shape of the experimentally extracted force curves was shown to deviate from that calculated using the 6-12 Lennard-Jones potential, having weaker attraction at larger tip–sample separation distances and weaker repulsion at smaller tip–sample separation distances. This methodology represents the first experimental technique in which material interaction potential parameters were verified over a range of tip–sample separation distances for a tip apex of arbitrary geometry.

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<![CDATA[Stochastic excitation for high-resolution atomic force acoustic microscopy imaging: a system theory approach]]> https://www.researchpad.co/article/elastic_article_8468 In this work, a high-resolution atomic force acoustic microscopy imaging technique is developed in order to obtain the local indentation modulus at the nanoscale level. The technique uses a model that gives a qualitative relationship between a set of contact resonance frequencies and the indentation modulus. It is based on white-noise excitation of the tip–sample interaction and uses system theory for the extraction of the resonance modes. During conventional scanning, for each pixel, the tip–sample interaction is excited with a white-noise signal. Then, a fast Fourier transform is applied to the deflection signal that comes from the photodiodes of the atomic force microscopy (AFM) equipment. This approach allows for the measurement of several vibrational modes in a single step with high frequency resolution, with less computational cost and at a faster speed than other similar techniques. This technique is referred to as stochastic atomic force acoustic microscopy (S-AFAM), and the frequency shifts of the free resonance frequencies of an AFM cantilever are used to determine the mechanical properties of a material. S-AFAM is implemented and compared with a conventional technique (resonance tracking-atomic force acoustic microscopy, RT-AFAM). A sample of a graphite film on a glass substrate is analyzed. S-AFAM can be implemented in any AFM system due to its reduced instrumentation requirements compared to conventional techniques.

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<![CDATA[Effect of Ag loading position on the photocatalytic performance of TiO<sub>2</sub> nanocolumn arrays]]> https://www.researchpad.co/article/elastic_article_8467 Plasmonic metal/semiconductor composites have attracted great attention for efficient solar energy harvesting in photovoltaic and photocatalytic applications owing to their extremely high visible-light absorption and tuned effective band gap. In this work, Ag-loaded TiO2 nanocolumn (Ag-TNC) arrays were fabricated based on anodic aluminum oxide (AAO) template by combining atomic layer deposition (ALD) and vacuum evaporation. The effects of the Ag loading position and deposition thickness, and the morphology, structure and composition of Ag-deposited TNC arrays on its optical and photocatalytic properties were studied. The Ag-filled TiO2 (AFT) nanocolumn arrays exhibited higher removal efficiency of methylene blue (MB) compared with Ag-coated TiO2 (ACT) nanocolumn arrays and pure TiO2 nanocolumns arrays. Both experimental and theoretical simulation results demonstrated that the enhanced photocatalytic performance of AFT nanocolumn arrays was attributed to the surface plasmon resonance (SPR) of Ag and the absorption of light by TiO2. These results represent a promising step forward to the development of high-performance photocatalysts for energy conversion and storage.

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<![CDATA[Hexagonal boron nitride: a review of the emerging material platform for single-photon sources and the spin–photon interface]]> https://www.researchpad.co/article/elastic_article_7804 Single-photon sources and their optical spin readout are at the core of applications in quantum communication, quantum computation, and quantum sensing. Their integration in photonic structures such as photonic crystals, microdisks, microring resonators, and nanopillars is essential for their deployment in quantum technologies. While there are currently only two material platforms (diamond and silicon carbide) with proven single-photon emission from the visible to infrared, a quantum spin–photon interface, and ancilla qubits, it is expected that other material platforms could emerge with similar characteristics in the near future. These two materials also naturally lead to monolithic integrated photonics as both are good photonic materials. While so far the verification of single-photon sources was based on discovery, assignment and then assessment and control of their quantum properties for applications, a better approach could be to identify applications and then search for the material that could address the requirements of the application in terms of quantum properties of the defects. This approach is quite difficult as it is based mostly on the reliability of modeling and predicting of color center properties in various materials, and their experimental verification is challenging. In this paper, we review some recent advances in an emerging material, low-dimensional (2D, 1D, 0D) hexagonal boron nitride (h-BN), which could lead to establishing such a platform. We highlight the recent achievements of the specific material for the expected applications in quantum technologies, indicating complementary outstanding properties compared to the other 3D bulk materials.

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<![CDATA[Structural optical and electrical properties of a transparent conductive ITO/Al–Ag/ITO multilayer contact]]> https://www.researchpad.co/article/elastic_article_7788 Indium tin oxide (ITO) is a widely used material for transparent conductive oxide (TCO) films due to its good optical and electrical properties. Improving the optoelectronic properties of ITO films with reduced thickness is crucial and quite challenging. ITO-based multilayer films with an aluminium–silver (Al–Ag) interlayer (ITO/Al–Ag/ITO) and a pure ITO layer (as reference) were prepared by RF and DC sputtering. The microstructural, optical and electrical properties of the ITO/Al–Ag/ITO (IAAI) films were investigated before and after annealing at 400 °C. X-ray diffraction measurements show that the insertion of the Al–Ag intermediate bilayer led to the crystallization of an Ag interlayer even at the as-deposited stage. Peaks attributed to ITO(222), Ag(111) and Al(200) were observed after annealing, indicating an enhancement in crystallinity of the multilayer films. The annealed IAAI film exhibited a remarkable improvement in optical transmittance (86.1%) with a very low sheet resistance of 2.93 Ω/sq. The carrier concentration increased more than twice when the Al–Ag layer was inserted between the ITO layers. The figure of merit of the IAAI multilayer contact has been found to be high at 76.4 × 10−3 Ω−1 compared to a pure ITO contact (69.4 × 10−3 Ω−1). These highly conductive and transparent ITO films with Al–Ag interlayer can be a promising contact for low-resistance optoelectronics devices.

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<![CDATA[Application of co-culture technology of epithelial type cells and mesenchymal type cells using nanopatterned structures]]> https://www.researchpad.co/article/elastic_article_7654 Various nanopatterning techniques have been developed to improve cell proliferation and differentiation efficiency. As we previously reported, nanopillars and pores are able to sustain human pluripotent stem cells and differentiate pancreatic cells. From this, the nanoscale patterns would be effective environment for the co-culturing of epithelial and mesenchymal cell types. Interestingly, the nanopatterning selectively reduced the proliferative rate of mesenchymal cells while increasing the expression of adhesion protein in epithelial type cells. Additionally, co-cultured cells on the nanopatterning were not negatively affected in terms of cell function metabolic ability or cell survival. This is in contrast to conventional co-culturing methods such as ultraviolet or chemical treatments. The nanopatterning appears to be an effective environment for mesenchymal co-cultures with typically low proliferative rates cells such as astrocytes, neurons, melanocytes, and fibroblasts without using potentially damaging treatments.

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<![CDATA[Imaging dataset of fresh hydrous plants obtained by field-emission scanning electron microscopy conducted using a protective NanoSuit]]> https://www.researchpad.co/article/elastic_article_7644 Although scanning electron microscopy (SEM) can generate high-resolution images of nanosized objects, it requires a high vacuum to do so, which precludes direct observations of living organisms and often produces unwanted structural changes. It has previously been reported that a simple surface modification gives rise to a nanoscale layer, termed the “NanoSuit”, which can keep small animals alive under the high vacuum required for field-emission scanning electron microscopy (FE-SEM). We have previously applied this technique to plants, and successfully observed healthy petals in a fully hydrated state using SEM. The flower petals protected with the NanoSuit appeared intact, although we still lack a fundamental understanding of the images of other plants observed using FE-SEM. This report presents and evaluates a rich set of images, acquired using the NanoSuit, for a taxonomically diverse set of plant species. This dataset of images allows the surface features of various plants to be analyzed and thus provides a further complementary morphological profile. Image data can be accessed and viewed through Figshare (https://doi.org/10.6084/m9.figshare.c.4446026.v1).

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<![CDATA[Some Peculiarities in the Dose Dependence of Separate and Combined In Vitro Cardiotoxicity Effects Induced by CdS and PbS Nanoparticles With Special Attention to Hormesis Manifestations]]> https://www.researchpad.co/article/N31b29e51-2c7e-43de-a7b2-c38e099b1209

Spherical nanoparticles (NPs) of cadmium and lead sulfides (diameter 37 ± 5 and 24 ± 4 nm, respectively) have been found to be cytotoxic for HL-1 cardiomyocytes as evidenced by decrease in adenosine triphosphate–dependent luminescence. Cadmium sulfide (CdS)-NPs were discovered to produce a much greater cytotoxic impact than lead sulphide (PbS)-NP. Given the same dose range, CdS-NP reduced the number of calcium spikes. A similar effect was observed for small doses of PbS-NP. In addition to cell hypertrophy under the impact of certain doses of CdS-NP and PbS-NP, doses causing cardiomyocyte size reduction were identified. For these 3 outcomes, we obtained both monotonic “dose–response” functions (well approximated by the hyperbolic function) and different variants of non-monotonic ones for which we found adequate mathematical expressions by modifying certain models of hormesis available in the literature. Data analysis using a response surface linear model with a cross-term provided new support to the previously established postulate that a diversity of types of joint action characteristic of one and the same pair of damaging agents is one of the important assertions of the general theory of combined toxicity.

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<![CDATA[Chitosan-propolis nanoparticle formulation demonstrates anti-bacterial activity against Enterococcus faecalis biofilms]]> https://www.researchpad.co/article/5989db50ab0ee8fa60bdc122

Propolis obtained from bee hives is a natural substance with antimicrobial properties. It is limited by its insolubility in aqueous solutions; hence ethanol and ethyl acetate extracts of Malaysian propolis were prepared. Both the extracts displayed antimicrobial and anti-biofilm properties against Enterococcus faecalis, a common bacterium associated with hospital-acquired infections. High performance liquid chromatography (HPLC) analysis of propolis revealed the presence of flavonoids like kaempferol and pinocembrin. This study investigated the role of propolis developed into nanoparticles with chitosan for its antimicrobial and anti-biofilm properties against E. faecalis. Bacteria that grow in a slimy layer of biofilm are resistant to penetration by antibacterial agents. The use of nanoparticles in medicine has received attention recently due to better bioavailability, enhanced penetrative capacity and improved efficacy. A chitosan-propolis nanoformulation was chosen based on ideal physicochemical properties such as particle size, zeta potential, polydispersity index, encapsulation efficiency and the rate of release of the active ingredients. This formulation inhibited E. faecalis biofilm formation and reduced the number of bacteria in the biofilm by ~90% at 200 μg/ml concentration. When tested on pre-formed biofilms, the formulation reduced bacterial number in the biofilm by ~40% and ~75% at 200 and 300 μg/ml, respectively. The formulation not only reduced bacterial numbers, but also physically disrupted the biofilm structure as observed by scanning electron microscopy. Treatment of biofilms with chitosan-propolis nanoparticles altered the expression of biofilm-associated genes in E. faecalis. The results of this study revealed that chitosan-propolis nanoformulation can be deemed as a potential anti-biofilm agent in resisting infections involving biofilm formation like chronic wounds and surgical site infections.

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<![CDATA[Nanoparticles based on the zwitterionic pillar[5]arene and Ag+: synthesis, self-assembly and cytotoxicity in the human lung cancer cell line A549]]> https://www.researchpad.co/article/N06f88fbe-3e18-4938-bcf5-cf21717415bf

For the first time, stable pillar[5]arene/Ag+ nanoparticles, consisting of water-soluble pillar[5]arene containing γ-sulfobetaine fragments and Ag+ ions without Ag–Ag bonds, were synthesized and characterized. The pillar[5]arene/Ag+ (ratio 1:10) nanoparticles obtained were cubic with a rib length of 100 nm and are less cytotoxic than Ag+ ions. The survival of the A549 model cells in the presence of pillar[5]arene/Ag+ (1:10) nanoparticles at a concentration of 30 and 40 μM was 76% and 55%, while in the absence of pillar[5]arene, the cell survival for free Ag+ ions at the same concentration was 30% and 10%, respectively. The results can be used to create new antibacterial materials and 2D biomedical coatings.

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<![CDATA[Electrochemically derived functionalized graphene for bulk production of hydrogen peroxide]]> https://www.researchpad.co/article/N29cf17f4-3138-48b3-8437-82e758fc894c

On-site peroxide generation via electrochemical reduction is gaining tremendous attention due to its importance in many fields, including water treatment technologies. Oxidized graphitic carbon-based materials have been recently proposed as an alternative to metal-based catalysts in the electrochemical oxygen reduction reaction (ORR), and in this work we unravel the role of C=O groups in graphene towards sustainable peroxide formation. We demonstrate a versatile single-step electrochemical exfoliation of graphite to graphene with a controllable degree of oxygen functionalities and thickness, leading to the formation of large quantities of functionalized graphene with tunable rate parameters, such as the rate constant and exchange current density. Higher oxygen-containing exfoliated graphene is known to undergo a two-electron reduction path in ORR having an efficiency of about 80 ± 2% even at high overpotential. Bulk production of H2O2 via electrolysis was also demonstrated at low potential (0.358 mV vs RHE), yielding ≈34 mg/L peroxide with highly functionalized (≈23 atom %) graphene and ≈16 g/L with low functionalized (≈13 atom %) graphene, which is on par with the peroxide production using state-of-the-art precious-metal-based catalysts. Hence this method opens a new scheme for the single-step large-scale production of functionalized carbon-based catalysts (yield ≈45% by weight) that have varying functionalities and can deliver peroxide via the electrochemical ORR process.

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<![CDATA[High dynamic resistance elements based on a Josephson junction array]]> https://www.researchpad.co/article/Nd873b370-3389-45cd-8183-0952bc673cb4

A chain of superconductor–insulator–superconductor junctions based on Al–AlOx–Al nanostructures and fabricated using conventional lift-off lithography techniques was measured at ultra-low temperatures. At zero magnetic field, the low current bias dynamic resistance can reach values of ≈1011 Ω. It was demonstrated that the system can provide a decent quality current biasing circuit, enabling the observation of Coulomb blockade and Bloch oscillations in ultra-narrow Ti nanowires associated with the quantum phase-slip effect.

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<![CDATA[Synthesis and enhanced photocatalytic performance of 0D/2D CuO/tourmaline composite photocatalysts]]> https://www.researchpad.co/article/N9d541b99-337e-4b3e-a1ef-462e829df591

Photocatalysis is considered to be a green and promising technology for transforming organic contaminants into nontoxic products. In this work, a CuO/tourmaline composite with zero-dimensional/two-dimensional (0D/2D) CuO architecture was successfully obtained via a facile hydrothermal process, and its photocatalytic activity was evaluated by the degradation of methylene blue (MB). Surface element valence state and molecular vibration characterization revealed that CuO chemically interacted with tourmaline via Si–O–Cu bonds. The specific surface area of the CuO/tourmaline composite (23.60 m2 g−1) was larger than that of the pristine CuO sample (3.41 m2 g−1). The CuO/tourmaline composite exhibited excellent photocatalytic activity for the degradation of MB, which was ascribed to the increase in the quantity of the adsorption-photoreactive sites and the efficient utilization of the photoinduced charge carriers. This study provides a facile strategy for the construction of 0D/2D CuO structures and the design of tourmaline-based functional composite photocatalysts for the treatment of organic contaminants in water.

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<![CDATA[Atomic-resolution imaging of rutile TiO2(110)-(1 × 2) reconstructed surface by non-contact atomic force microscopy]]> https://www.researchpad.co/article/N6017abf4-5426-4e6c-985e-31396050bc82

The structure of the rutile TiO2(110)-(1 × 2) reconstructed surface is a phase induced by oxygen reduction. There is ongoing debate about the (1 × 2) reconstruction, because it cannot be clarified whether the (1 × 2) structure is formed over a wide area or only locally using macroscopic analysis methods such as diffraction. We used non-contact atomic force microscopy, scanning tunneling microscopy, and low-energy electron diffraction at room temperature to characterize the surface. Ti2O3 rows appeared as bright spots in both NC-AFM and STM images observed in the same area. High-resolution NC-AFM images revealed that the rutile TiO2(110)-(1 × 2) reconstructed surface is composed of two domains with different types of asymmetric rows.

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<![CDATA[Nanoarchitectonics: bottom-up creation of functional materials and systems]]> https://www.researchpad.co/article/N2288b092-02f6-4d59-9ab9-44d8f1385395 ]]> <![CDATA[Current measurements in the intermittent-contact mode of atomic force microscopy using the Fourier method: a feasibility analysis]]> https://www.researchpad.co/article/N58b1921a-e577-4faf-81a8-ea229cede187

Atomic force microscopy (AFM) is an important tool for measuring a variety of nanoscale surface properties, such as topography, viscoelasticity, electrical potential and conductivity. Some of these properties are measured using contact methods (static contact or intermittent contact), while others are measured using noncontact methods. Some properties can be measured using different approaches. Conductivity, in particular, is mapped using the contact-mode method. However, this modality can be destructive to delicate samples, since it involves continuously dragging the cantilever tip on the surface during the raster scan, while a constant tip–sample force is applied. In this paper we discuss a possible approach to develop an intermittent-contact conductive AFM mode based on Fourier analysis, whereby the measured current response consists of higher harmonics of the cantilever oscillation frequency. Such an approach may enable the characterization of soft samples with less damage than contact-mode imaging. To explore its feasibility, we derive the analytical form of the tip–sample current that would be obtained for attractive (noncontact) and repulsive (intermittent-contact) dynamic AFM characterization, and compare it with results obtained from numerical simulations. Although significant instrumentation challenges are anticipated, the modelling results are promising and suggest that Fourier-based higher-harmonics current measurement may enable the development of a reliable intermittent-contact conductive AFM method.

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<![CDATA[Effect of 3-Aminobenzamide on the Ultrastructure of Astrocytes and Microvessels After Focal Cerebral Ischemia in Rats]]> https://www.researchpad.co/article/N8b07f23f-2b81-4b53-b73a-d324468089b0

The disruption of blood–brain barrier (BBB) is a critical event in the formation of brain edema during early phases of ischemic brain injury. Poly(ADP-ribose) polymerase (PARP) activation, which contributes to BBB damage, has been reported in ischemia–reperfusion and traumatic brain injury. Here, we investigated the effect of 3-aminobenzamide (3-AB), a PARP-1 inhibitor, on the ultrastructure of BBB. Male Sprague Dawley rats were suffered from 90 minutes of middle cerebral artery occlusion, followed by 4.5 hours or 22.5 hours of reperfusion (R). The vehicle or 3-AB (10 mg/kg) was administered intraperitoneally (ip) 60 minutes after lacking of blood. Tissue Evans Blue (EB) levels, ultrastructures of astrocytes and microvessels, and areas of perivascular edema were examined in penumbra and core, at I 1.5 hours /R 4.5 hours and I 1.5 hours /R 22.5 hours, respectively. The severity of ultrastructural changes was graded with a scoring system in each group. We showed that 3-AB treatment significantly decreased tissue EB levels and ultrastructural scores, attenuated damages in astrocytes and microvessels, and reduced areas of perivascular edema. In conclusion, PARP inhibition may provide a novel therapeutic approach to ischemic brain injury.

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