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Nanomaterials, Volume 9, Issue 4 (April 2019)

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Cover Story (view full-size image) Thermal transport in nanolayered thin films is investigated by Time-Domain X-ray Thermal [...] Read more.
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Open AccessArticle
Effect of Ultrasonic Surface Rolling Process on the Hot Compression Behavior of Inconel 718 Superalloy at 700 °C
Nanomaterials 2019, 9(4), 658; https://doi.org/10.3390/nano9040658
Received: 28 March 2019 / Revised: 14 April 2019 / Accepted: 23 April 2019 / Published: 25 April 2019
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Abstract
A series of hot compression tests at the temperature of 700 °C were applied to study the effect of the ultrasonic surface rolling process (USRP) on the hot compression behavior of Inconel 718 superalloy. The results indicated that the USRP-treated samples exhibited a [...] Read more.
A series of hot compression tests at the temperature of 700 °C were applied to study the effect of the ultrasonic surface rolling process (USRP) on the hot compression behavior of Inconel 718 superalloy. The results indicated that the USRP-treated samples exhibited a better ability to withstand axial hot compression than the untreated samples. After the hot compression process, the size of the matrix grains was slightly decreased, and the volume fraction of ultra-fine recrystallized grains in the near-surface regions was increased for the USRP-treated samples. In addition, for USRP-treated samples, a large number of γ″ phases with size less than 100 nm were precipitated within the broadened grain boundaries in the near-surface regions rather than the inner grains. The enhanced ability to withstand axial compression at 700 °C for USRP-treated samples was related to the ultra-fine microstructure induced by USRP, combined with the precipitation of nano-γ″ phases within broadened grain boundaries and the increase of ultra-fine recrystallized grains in the near-surface regions during the hot compression process. Full article
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Open AccessArticle
Short-Chain Modified SiO2 with High Absorption of Organic PCM for Thermal Protection
Nanomaterials 2019, 9(4), 657; https://doi.org/10.3390/nano9040657
Received: 2 April 2019 / Revised: 18 April 2019 / Accepted: 19 April 2019 / Published: 25 April 2019
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Abstract
Organic phase change materials (PCMs) have great potential in thermal protection applications but they suffer from high volumetric change and easy leakage, which require “leak-proof” packaging materials with low thermal conductivity. Herein, we successfully modify SiO2 through a simple 2-step method consisting [...] Read more.
Organic phase change materials (PCMs) have great potential in thermal protection applications but they suffer from high volumetric change and easy leakage, which require “leak-proof” packaging materials with low thermal conductivity. Herein, we successfully modify SiO2 through a simple 2-step method consisting of n-hexane activation followed by short-chain alkane silanization. The modified SiO2 (M-SiO2) exhibits superior hydrophobic property while maintaining the intrinsic high porosity of SiO2. The surface modification significantly improves the absorption rate of RT60 in SiO2 by 38%. The M-SiO2/RT60 composite shows high latent heat of 180 J·g−1, low thermal conductivity of 0.178 W·m−1·K−1, and great heat capacity behavior in a high-power thermal circuit with low penetrated heating flow. Our results provide a simple approach for preparing hydrophobic SiO2 with high absorption of organic PCM for thermal protection applications. Full article
(This article belongs to the Special Issue Thermal Transport in Nanostructures and Nanomaterials)
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Open AccessReview
Electrospun Nanofibers: Recent Applications in Drug Delivery and Cancer Therapy
Nanomaterials 2019, 9(4), 656; https://doi.org/10.3390/nano9040656
Received: 11 March 2019 / Revised: 18 April 2019 / Accepted: 19 April 2019 / Published: 24 April 2019
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Abstract
Polymeric nanofibers (NFs) have been extensively reported as a biocompatible scaffold to be specifically applied in several researching fields, including biomedical applications. The principal researching lines cover the encapsulation of antitumor drugs for controlled drug delivery applications, scaffolds structures for tissue engineering and [...] Read more.
Polymeric nanofibers (NFs) have been extensively reported as a biocompatible scaffold to be specifically applied in several researching fields, including biomedical applications. The principal researching lines cover the encapsulation of antitumor drugs for controlled drug delivery applications, scaffolds structures for tissue engineering and regenerative medicine, as well as magnetic or plasmonic hyperthermia to be applied in the reduction of cancer tumors. This makes NFs useful as therapeutic implantable patches or mats to be implemented in numerous biomedical researching fields. In this context, several biocompatible polymers with excellent biocompatibility and biodegradability including poly lactic-co-glycolic acid (PLGA), poly butylcyanoacrylate (PBCA), poly ethylenglycol (PEG), poly (ε-caprolactone) (PCL) or poly lactic acid (PLA) have been widely used for the synthesis of NFs using the electrospun technique. Indeed, other types of polymers with stimuli-responsive capabilities has have recently reported for the fabrication of polymeric NFs scaffolds with relevant biomedical applications. Importantly, colloidal nanoparticles used as nanocarriers and non-biodegradable structures have been also incorporated by electrospinning into polymeric NFs for drug delivery applications and cancer treatments. In this review, we focus on the incorporation of drugs into polymeric NFs for drug delivery and cancer treatment applications. However, the principal novelty compared with previously reported publications is that we also focus on recent investigations concerning new strategies that increase drug delivery and cancer treatments efficiencies, such as the incorporation of colloidal nanoparticles into polymeric NFs, the possibility to fabricate NFs with the capability to respond to external environments, and finally, the synthesis of hybrid polymeric NFs containing carbon nanotubes, magnetic and gold nanoparticles, with magnetic and plasmonic hyperthermia applicability. Full article
(This article belongs to the Special Issue Electrospun Nanofibers for Biomedical Applications)
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Open AccessArticle
Tailoring of Aqueous-Based Carbon Nanotube–Nanocellulose Films as Self-Standing Flexible Anodes for Lithium-Ion Storage
Nanomaterials 2019, 9(4), 655; https://doi.org/10.3390/nano9040655
Received: 19 March 2019 / Revised: 18 April 2019 / Accepted: 22 April 2019 / Published: 24 April 2019
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Abstract
An easy and environmentally friendly method was developed for the preparation of a stabilized carbon nanotube–crystalline nanocellulose (CNT–CNC) dispersion and for its deposition to generate self-standing CNT–CNC composite films. The composite films were carbonized at different temperatures of 70 °C, 800 °C, and [...] Read more.
An easy and environmentally friendly method was developed for the preparation of a stabilized carbon nanotube–crystalline nanocellulose (CNT–CNC) dispersion and for its deposition to generate self-standing CNT–CNC composite films. The composite films were carbonized at different temperatures of 70 °C, 800 °C, and 1300 °C. Structural and morphological characteristics of the CNT–CNC films were investigated by X-ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM), which revealed that the sample annealed at 800 °C (CNT–CNC800) formed nano-tree networks of CNTs with a high surface area (1180 m2·g−1) and generated a conductive CNC matrix due to the effective carbonization. The carbonized composite films were applied as anodes for lithium-ion batteries, and the battery performance was evaluated in terms of initial voltage profile, cyclic voltammetry, capacity, cycling stability, and current rate efficiency. Among them, the CNT–CNC800 anode exhibited impressive electrochemical performance by showing a reversible capacity of 443 mAh·g−1 at a current density of 232 mA·g−1 after 120 cycles with the capacity retention of 89% and high rate capability. Full article
(This article belongs to the Special Issue Application of Nanomaterials in Ion Batteries)
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Open AccessArticle
Inkjet Printing Functionalization of SOFC LSCF Cathodes
Nanomaterials 2019, 9(4), 654; https://doi.org/10.3390/nano9040654
Received: 26 March 2019 / Revised: 15 April 2019 / Accepted: 19 April 2019 / Published: 24 April 2019
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Abstract
An important segment of the future renewable energy economy is the implementation of novel energy generation systems. Such electrochemical systems are solid oxide fuel cells, which have the advantage of direct conversion of the chemical energy stored in the fuel to electrical energy [...] Read more.
An important segment of the future renewable energy economy is the implementation of novel energy generation systems. Such electrochemical systems are solid oxide fuel cells, which have the advantage of direct conversion of the chemical energy stored in the fuel to electrical energy with high efficiency. Improving the performance and lowering the cost of solid oxide fuel cells (SOFCs) are strongly dependent on finding commercially viable methods for nano-functionalization of their electrodes via infiltration. Inkjet printing technology was proven to be a feasible method providing scalability and high-resolution ink delivery. LaxSr1−xCoyFe1−yO3−δ cathodes were modified using inkjet printing for infiltration with two different materials: Gd-doped ceria (CGO) commonly used as ion-conductor and La0.6Sr0.4CoO3–δ (LCO) commonly used as a mixed ionic electronic conductor. As-modified surface structures promoted the extension of the three-phase boundary (TPB) and enhanced the mechanisms of the oxygen reduction reaction. Electrochemical impedance measurements revealed significantly lowered polarization resistances (between 2.7 and 3.7 times) and maximum power output enhancement of 24% for CGO infiltrated electrodes and 40% for LCO infiltrated electrodes. Full article
(This article belongs to the Special Issue Inkjet Printing of Nanomaterials)
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Open AccessArticle
Measuring Device and Material ZT in a Thin-Film Si-Based Thermoelectric Microgenerator
Nanomaterials 2019, 9(4), 653; https://doi.org/10.3390/nano9040653
Received: 31 March 2019 / Revised: 13 April 2019 / Accepted: 17 April 2019 / Published: 24 April 2019
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Abstract
Thermoelectricity (TE) is proving to be a promising way to harvest energy for small applications and to produce a new range of thermal sensors. Recently, several thermoelectric generators (TEGs) based on nanomaterials have been developed, outperforming the efficiencies of many previous bulk generators. [...] Read more.
Thermoelectricity (TE) is proving to be a promising way to harvest energy for small applications and to produce a new range of thermal sensors. Recently, several thermoelectric generators (TEGs) based on nanomaterials have been developed, outperforming the efficiencies of many previous bulk generators. Here, we presented the thermoelectric characterization at different temperatures (from 50 to 350 K) of the Si thin-film based on Phosphorous (n) and Boron (p) doped thermocouples that conform to a planar micro TEG. The thermocouples were defined through selective doping by ion implantation, using boron and phosphorous, on a 100 nm thin Si film. The thermal conductivity, the Seebeck coefficient, and the electrical resistivity of each Si thermocouple was experimentally determined using the in-built heater/sensor probes and the resulting values were refined with the aid of finite element modeling (FEM). The results showed a thermoelectric figure of merit for the Si thin films of z T = 0.0093, at room temperature, which was about 12% higher than the bulk Si. In addition, we tested the thermoelectric performance of the TEG by measuring its own figure of merit, yielding a result of ZT = 0.0046 at room temperature. Full article
(This article belongs to the Special Issue Nanostructured Materials for Thermoelectrics)
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Open AccessArticle
Nanocarriers for Protein Delivery to the Cytosol: Assessing the Endosomal Escape of Poly(Lactide-co-Glycolide)-Poly(Ethylene Imine) Nanoparticles
Nanomaterials 2019, 9(4), 652; https://doi.org/10.3390/nano9040652
Received: 15 March 2019 / Revised: 15 April 2019 / Accepted: 21 April 2019 / Published: 23 April 2019
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Abstract
Therapeutic proteins and enzymes are a group of interesting candidates for the treatment of numerous diseases, but they often require a carrier to avoid degradation and rapid clearance in vivo. To this end, organic nanoparticles (NPs) represent an excellent choice due to their [...] Read more.
Therapeutic proteins and enzymes are a group of interesting candidates for the treatment of numerous diseases, but they often require a carrier to avoid degradation and rapid clearance in vivo. To this end, organic nanoparticles (NPs) represent an excellent choice due to their biocompatibility, and cross-linked enzyme aggregates (CLEAs)-loaded poly (lactide-co-glycolide) (PLGA) NPs have recently attracted attention as versatile tools for targeted enzyme delivery. However, PLGA NPs are taken up by cells via endocytosis and are typically trafficked into lysosomes, while many therapeutic proteins and enzymes should reach the cellular cytosol to perform their activity. Here, we designed a CLEAs-based system implemented with a cationic endosomal escape agent (poly(ethylene imine), PEI) to extend the use of CLEA NPs also to cytosolic enzymes. We demonstrated that our system can deliver protein payloads at cytoplasm level by two different mechanisms: Endosomal escape and direct translocation. Finally, we applied this system to the cytoplasmic delivery of a therapeutically relevant enzyme (superoxide dismutase, SOD) in vitro. Full article
(This article belongs to the Special Issue Organic Nanomaterials in Biomedicine: Applications and Perspectives)
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Open AccessArticle
Titania Photonic Crystals with Precise Photonic Band Gap Position via Anodizing with Voltage versus Optical Path Length Modulation
Nanomaterials 2019, 9(4), 651; https://doi.org/10.3390/nano9040651
Received: 25 March 2019 / Revised: 20 April 2019 / Accepted: 20 April 2019 / Published: 23 April 2019
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Abstract
Photonic crystals based on titanium oxide are promising for optoelectronic applications, for example as components of solar cells and photodetectors. These materials attract great research attention because of the high refractive index of TiO2. One of the promising routes to prepare [...] Read more.
Photonic crystals based on titanium oxide are promising for optoelectronic applications, for example as components of solar cells and photodetectors. These materials attract great research attention because of the high refractive index of TiO2. One of the promising routes to prepare photonic crystals based on titanium oxide is titanium anodizing at periodically changing voltage or current. However, precise control of the photonic band gap position in anodic titania films is a challenge. To solve this problem, systematic data on the effective refractive index of the porous anodic titanium oxide are required. In this research, we determine quantitatively the dependence of the effective refractive index of porous anodic titanium oxide on the anodizing regime and develop a model which allows one to predict and, therefore, control photonic band gap position in the visible spectrum range with an accuracy better than 98.5%. The prospects of anodic titania photonic crystals implementation as refractive index sensors are demonstrated. Full article
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Open AccessArticle
Dual Carbonaceous Materials Synergetic Protection Silicon as a High-Performance Free-Standing Anode for Lithium-Ion Battery
Nanomaterials 2019, 9(4), 650; https://doi.org/10.3390/nano9040650
Received: 13 February 2019 / Revised: 27 March 2019 / Accepted: 15 April 2019 / Published: 23 April 2019
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Abstract
Silicon is the one of the most promising anode material alternatives for next-generation lithium-ion batteries. However, the low electronic conductivity, unstable formation of solid electrolyte interphase, and the extremely high volume expansion (up to 300%) which results in pulverization of Si and rapid [...] Read more.
Silicon is the one of the most promising anode material alternatives for next-generation lithium-ion batteries. However, the low electronic conductivity, unstable formation of solid electrolyte interphase, and the extremely high volume expansion (up to 300%) which results in pulverization of Si and rapid fading of its capacity have been identified as primary reasons for hindering its application. In this work, we put forward to introduce dual carbonaceous materials synergetic protection to overcome the drawbacks of the silicon anode. The silicon nanoparticle was coated by pyrolysed carbon, and meanwhile anchored on the surface of reduced graphene oxide, to form a self-standing film composite ([email protected]/rGO). The [email protected]/rGO film electrode displays high flexibility and an ordered porous structure, which could not only buffer the Si nanoparticle expansion during lithiation/delithiation processes, but also provides the channels for fast electron transfer and lithium ion transport. Therefore, the self-standing [email protected]/rGO film electrode shows a high reversible capacity of 1002 mAh g−1 over 100 cycles and exhibits much better rate capability, validating it as a promising anode for constructing high performance lithium-ion batteries. Full article
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Open AccessArticle
Preparation of Fe3O4@polyoxometalates Nanocomposites and Their Efficient Adsorption of Cationic Dyes from Aqueous Solution
Nanomaterials 2019, 9(4), 649; https://doi.org/10.3390/nano9040649
Received: 10 March 2019 / Revised: 15 April 2019 / Accepted: 16 April 2019 / Published: 23 April 2019
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Abstract
In this work, two magnetic adsorbents Fe3O4@1 and Fe3O4@2 were prepared by combining Fe3O4 nanoparticles and polyoxometalate hybrids [Ni(HL)2]2H2[P2Mo5O23 [...] Read more.
In this work, two magnetic adsorbents Fe3O4@1 and Fe3O4@2 were prepared by combining Fe3O4 nanoparticles and polyoxometalate hybrids [Ni(HL)2]2H2[P2Mo5O23]·4H2O (1), [H2L]5H[P2Mo5O23]·12H2O (2) (HL = 2-acetylpyridine-thiosemicarbazone). The temperature-dependent zero-field-cooled (ZFC) and field-cooled (FC) measurements indicated the blocking temperature at 160 K and 180 K, respectively. The Brunauer–Emmett–Teller (BET) surface area of Fe3O4@1 and Fe3O4@2 is 8.106 m2/g and 1.787 m2/g, respectively. Cationic dye methylene blue (MB) and anionic dye methyl orange (MO) were investigated for selective dye adsorption on Fe3O4@1 and Fe3O4@2. The two adsorbents were beneficial for selective adsorption of cationic dyes. The adsorption efficiency of MB was 94.8% for Fe3O4@1, 97.67% for Fe3O4@2. Furthermore, the two adsorbents almost maintained the same adsorption efficiency after seven runs. The maximum MB adsorption capacity of Fe3O4@1 and Fe3O4@2 is 72.07 and 73.25 mg/g, respectively. The fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) spectra of the adsorbents collected after adsorption of MB are very similar to the initial as-synthesized Fe3O4@polyoxometalates indicating the high stability of the two adsorbents. The adsorption kinetics indicated that the MB removal followed the pseudo-second-order model. These results showed that the two adsorbents had a potential application in treating wastewater. Full article
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Open AccessArticle
Small-Angle Scattering from Weakly Correlated Nanoscale Mass Fractal Aggregates
Nanomaterials 2019, 9(4), 648; https://doi.org/10.3390/nano9040648
Received: 2 April 2019 / Revised: 17 April 2019 / Accepted: 18 April 2019 / Published: 22 April 2019
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Abstract
Formation of fractal aggregates is generally an undesired effect which may lead to end products with worse properties as compared to those of the individual components, especially in nanocomposite materials. Although several methods exist to overcome this issue, such as inclusion of additives, [...] Read more.
Formation of fractal aggregates is generally an undesired effect which may lead to end products with worse properties as compared to those of the individual components, especially in nanocomposite materials. Although several methods exist to overcome this issue, such as inclusion of additives, irradiation grafting or sonication, their effectiveness relies on a detailed knowledge of the structural properties of the aggregates. Here, small-angle scattering (SAS) technique is used and a theoretical model based on a unified Guinier–Porod approach with weak correlations is developed for investigating the structural properties of nanoscale fractal aggregates. It is shown how one can extract information concerning the correlation length/degree between aggregates, their fractal dimension and the overall size. These parameters can be used for development of various types of novel nanomaterials with pre-determined properties and functions. Full article
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Open AccessReview
New Developments in Material Preparation Using a Combination of Ionic Liquids and Microwave Irradiation
Nanomaterials 2019, 9(4), 647; https://doi.org/10.3390/nano9040647
Received: 8 March 2019 / Revised: 11 April 2019 / Accepted: 16 April 2019 / Published: 22 April 2019
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Abstract
During recent years, synthetic methods combining microwaves and ionic liquids became accepted as a promising methodology for various materials preparations because of their high efficiency and low energy consumption. Ionic liquids with high polarity are heated rapidly, volumetrically and simultaneously under microwave irradiation. [...] Read more.
During recent years, synthetic methods combining microwaves and ionic liquids became accepted as a promising methodology for various materials preparations because of their high efficiency and low energy consumption. Ionic liquids with high polarity are heated rapidly, volumetrically and simultaneously under microwave irradiation. Hence, combination of microwave irradiation as a heating source with ionic liquids with various roles (e.g., solvent, additive, template or reactant) opened a completely new technique in the last twenty years for nanomaterials and polymers preparation for applications in various materials science fields including polymer science. This review summarizes recent developments of some common materials syntheses using microwave-assisted ionic liquid method with a focus on inorganic nanomaterials, polymers, carbon-derived composites and biomass-based composites. After that, the mechanisms involved in microwave-assisted ionic-liquid (MAIL) are discussed briefly. This review also highlights the role of ionic liquids in the reaction and crucial issues that should be addressed in future research involving this synthesis technique. Full article
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Open AccessArticle
Eu3+, Tb3+- and Er3+, Yb3+-Doped α-MoO3 Nanosheets for Optical Luminescent Thermometry
Nanomaterials 2019, 9(4), 646; https://doi.org/10.3390/nano9040646
Received: 17 March 2019 / Revised: 5 April 2019 / Accepted: 17 April 2019 / Published: 21 April 2019
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Abstract
Here we report a novel synthesis approach for the preparation of α-MoO3:Ln3+ materials employing a two-step synthesis. Additionally, in this work the α-MoO3:Ln3+ materials are reported as potential optical thermometers for the first time. In this synthesis [...] Read more.
Here we report a novel synthesis approach for the preparation of α-MoO3:Ln3+ materials employing a two-step synthesis. Additionally, in this work the α-MoO3:Ln3+ materials are reported as potential optical thermometers for the first time. In this synthesis approach, first MoS2 2D nanosheets were prepared, which were further heat treated to obtain α-MoO3. These materials were fully characterized by powder X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray fluorescence (XRF), thermogravimetry (TG) and differential thermal analysis (DTA), transmission electron microscopy (TEM), and luminescence spectroscopy. Temperature-dependent luminescence measurements were carried out to determine the optical thermometric properties of two different types of α-MoO3:Ln3+ materials (Eu3+/Tb3+ downshifting and Er3+/Yb3+ upconversion luminescence systems). We demonstrate in this study that this class of material could be a potential candidate for temperature-sensing applications. Full article
(This article belongs to the Special Issue Luminescent Rare-Earth Based Nanomaterials)
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Open AccessArticle
Boron Nitride Doped Polyhydroxyalkanoate/Chitosan Nanocomposite for Antibacterial and Biological Applications
Nanomaterials 2019, 9(4), 645; https://doi.org/10.3390/nano9040645
Received: 14 March 2019 / Revised: 6 April 2019 / Accepted: 10 April 2019 / Published: 21 April 2019
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Abstract
The present research focused on the fabrication of biocompatible polyhydroxyalkanoate, chitosan, and hexagonal boron nitride incorporated (PHA/Ch-hBN) nanocomposites through a simple solvent casting technique. The fabricated nanocomposites were comprehensively characterized by Fourier transform infrared spectroscope (FT-IR), field emission scanning electroscope (FESEM), and elemental [...] Read more.
The present research focused on the fabrication of biocompatible polyhydroxyalkanoate, chitosan, and hexagonal boron nitride incorporated (PHA/Ch-hBN) nanocomposites through a simple solvent casting technique. The fabricated nanocomposites were comprehensively characterized by Fourier transform infrared spectroscope (FT-IR), field emission scanning electroscope (FESEM), and elemental mapping and thermogravimetric analysis (TGA). The antibacterial activity of nanocomposites were investigated through time-kill method against multi drug resistant (MDR) microbes such as methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli (E. coli) K1 strains. In addition, nanocomposites have examined for their host cytotoxicity abilities using a Lactate dehydrogenase (LDH) assay against spontaneously immortalized human keratinocytes (HaCaT) cell lines. The results demonstrated highly significant antibacterial activity against MDR organisms and also significant cell viability as compared to the positive control. The fabricated PHA/Ch-hBN nanocomposite demonstrated effective antimicrobial and biocompatibility properties that would feasibly suit antibacterial and biomedical applications. Full article
(This article belongs to the Special Issue Recent Progress in Antimicrobial Nanomaterials)
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Open AccessArticle
Effect of Electrospun Fiber Mat Thickness and Support Method on Cell Morphology
Nanomaterials 2019, 9(4), 644; https://doi.org/10.3390/nano9040644
Received: 13 March 2019 / Revised: 3 April 2019 / Accepted: 10 April 2019 / Published: 20 April 2019
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Abstract
Electrospun fiber mats (EFMs) are highly versatile biomaterials used in a myriad of biomedical applications. Whereas some facets of EFMs are well studied and can be highly tuned (e.g., pore size, fiber diameter, etc.), other features are under characterized. For example, although substrate [...] Read more.
Electrospun fiber mats (EFMs) are highly versatile biomaterials used in a myriad of biomedical applications. Whereas some facets of EFMs are well studied and can be highly tuned (e.g., pore size, fiber diameter, etc.), other features are under characterized. For example, although substrate mechanics have been explored by several groups, most studies rely on Young’s modulus alone as a characterization variable. The influence of fiber mat thickness and the effect of supports are variables that are often not considered when evaluating cell-mechanical response. To assay the role of these features in EFM scaffold design and to improve understanding of scaffold mechanical properties, we designed EFM scaffolds with varying thickness (50–200 µm) and supporting methodologies. EFM scaffolds were comprised of polycaprolactone and were either electrospun directly onto a support, suspended across an annulus (3 or 10 mm inner diameter), or “tension-released” and then suspended across an annulus. Then, single cell spreading (i.e., Feret diameter) was measured in the presence of these different features. Cells were sensitive to EFM thickness and suspended gap diameter. Overall, cell spreading was greatest for 50 µm thick EFMs suspended over a 3 mm gap, which was the smallest thickness and gap investigated. These results are counterintuitive to conventional understanding in mechanobiology, which suggests that stiffer materials, such as thicker, supported EFMs, should elicit greater cell polarization. Additional experiments with 50 µm thick EFMs on polystyrene and polydimethylsiloxane (PDMS) supports demonstrated that cells can “feel” the support underlying the EFM if it is rigid, similar to previous results in hydrogels. These results also suggest that EFM curvature may play a role in cell response, separate from Young’s modulus, possibly because of internal tension generated. These parameters are not often considered in EFM design and could improve scaffold performance and ultimately patient outcomes. Full article
(This article belongs to the Special Issue Electrospun Nanofibers for Biomedical Applications)
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Open AccessArticle
Highly Optimized Nitrogen-Doped MWCNTs through In-Depth Parametric Study Using Design of Experiments
Nanomaterials 2019, 9(4), 643; https://doi.org/10.3390/nano9040643
Received: 2 March 2019 / Revised: 13 April 2019 / Accepted: 16 April 2019 / Published: 20 April 2019
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Abstract
The in-situ nitrogen doping of multiwalled carbon nanotubes via chemical vapor deposition is investigated employing design of experiments (DoE). The establishment of empirical DoE models allowed for the prediction of product features as a function of process conditions in order to systematically synthesize [...] Read more.
The in-situ nitrogen doping of multiwalled carbon nanotubes via chemical vapor deposition is investigated employing design of experiments (DoE). The establishment of empirical DoE models allowed for the prediction of product features as a function of process conditions in order to systematically synthesize tailor-made nitrogen-doped carbon nanotubes. The high informative content of this approach revealed effects of individual parameters and their interaction with each other. Hence, new valuable insights into the effect of temperature, injection rate, and carrier gas flow on the doping level were obtained which give motivation to approach further theoretical studies on the doping mechanism. Ultimately, competitive nitrogen-doped carbon nanotube features were optimized and yielded promising combinations of achieved doping level, graphitization, and aspect ratios in comparison to present literature values. Full article
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Open AccessArticle
Electrochemical Adsorption on Pt Nanoparticles in Alkaline Solution Observed Using In Situ High Energy Resolution X-ray Absorption Spectroscopy
Nanomaterials 2019, 9(4), 642; https://doi.org/10.3390/nano9040642
Received: 1 March 2019 / Revised: 12 April 2019 / Accepted: 15 April 2019 / Published: 20 April 2019
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Abstract
The oxygen reduction reaction (ORR) on Pt/C in alkaline solution was studied by in situ high energy resolution X-ray absorption spectroscopy. To discuss the X-ray absorption near-edge structure (XANES), this paper introduced the rate of change of the Δμ (RCD), which is [...] Read more.
The oxygen reduction reaction (ORR) on Pt/C in alkaline solution was studied by in situ high energy resolution X-ray absorption spectroscopy. To discuss the X-ray absorption near-edge structure (XANES), this paper introduced the rate of change of the Δμ (RCD), which is an analysis method that is sensitive to surface adsorption. The surface adsorptions as hydrogen (below 0.34 V), superoxide anion (from 0.34 V to 0.74 V), hydroxyl species (from 0.44 V to 0.74 V), atomic oxygen (above 0.74 V), and α-PtO2 (above 0.94 V) were distinguished. It is clarified that the catalytic activity in an alkaline solution is enhanced by the stability of atomic oxygen and the low stability of superoxide anion/peroxide adsorption on the platinum surface. Full article
(This article belongs to the Special Issue Nanomaterials in Environmental Friendly Fuel Cell)
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Open AccessArticle
Fe-Nanoporous Carbon Derived from MIL-53(Fe): A Heterogeneous Catalyst for Mineralization of Organic Pollutants
Nanomaterials 2019, 9(4), 641; https://doi.org/10.3390/nano9040641
Received: 9 March 2019 / Revised: 12 April 2019 / Accepted: 15 April 2019 / Published: 19 April 2019
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Abstract
Catalytic electrodes were prepared via carbonization of MIL-53(Fe) on the surface of porous carbon felt electrodes (CF) for use in wastewater treatment by the heterogeneous electro-Fenton (EF) process. The best results were obtained when the carbon felt was pretreated with nitric acid, enhancing [...] Read more.
Catalytic electrodes were prepared via carbonization of MIL-53(Fe) on the surface of porous carbon felt electrodes (CF) for use in wastewater treatment by the heterogeneous electro-Fenton (EF) process. The best results were obtained when the carbon felt was pretreated with nitric acid, enhancing the affinity of the MIL-53(Fe) for the surface. Following a series of optimization experiments, carbonization conditions of 800 °C for 5 h were used to form Fe-nanoporous carbon ([email protected]). The as-prepared electrodes were used as both cathode and heterogeneous catalyst in the EF process for the mineralization of exemplar dye Acid Orange 7 (AO7). Total organic carbon (TOC) removal of 46.1% was obtained within 8 h of electrolysis at around neutral pH (6.5) and the electrode retained over 80% of its original efficiency over five treatment cycles. Full article
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Open AccessArticle
Nonlinear Optical Response of Graphene Oxide Langmuir-Blodgett Film as Saturable Absorbers
Nanomaterials 2019, 9(4), 640; https://doi.org/10.3390/nano9040640
Received: 28 March 2019 / Revised: 12 April 2019 / Accepted: 16 April 2019 / Published: 19 April 2019
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Abstract
Two-dimensional (2D) materials as saturable absorbers (SAs) have attracted intense interest for applications in pulsed laser generation because of their distinguishing optical properties. However, the existing methods of preparing SAs were insufficient. Here, we fabricated graphene oxide (GO) SAs by Langmuir-Blodgett (LB) methods [...] Read more.
Two-dimensional (2D) materials as saturable absorbers (SAs) have attracted intense interest for applications in pulsed laser generation because of their distinguishing optical properties. However, the existing methods of preparing SAs were insufficient. Here, we fabricated graphene oxide (GO) SAs by Langmuir-Blodgett (LB) methods for passively Q-switched Nd:YAG laser. The GO sheets were deposited on a quartz plate using the LB method. Two different LB-GO SAs grown under the surface pressure of 22 and 38 mN/m were obtained. Compared with the drop coating method, LB-GO SA exhibited more excellent uniformity, larger nonlinear performance and higher optical transparency. By inserting LB-GO SA into the Nd:YAG laser linear cavity, the short pulse duration of 156 ns and the average output power of 1.313 W were obtained. The slope efficiency was as high as 43.7%, due to low loss of the LB-GO SA. Our results illustrated a new way for preparing the SA using the LB technique. Full article
(This article belongs to the Special Issue Non-Linear Optical Effects in Nanomaterials)
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Open AccessArticle
Investigation of the Impact of Cross-Polymerization on the Structural and Frictional Properties of Alkylsilane Monolayers Using Molecular Simulation
Nanomaterials 2019, 9(4), 639; https://doi.org/10.3390/nano9040639
Received: 15 March 2019 / Revised: 5 April 2019 / Accepted: 12 April 2019 / Published: 19 April 2019
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Abstract
Cross-linked chemisorbed n-alkylsilane (CH3(CH2)n−1Si(OH)3) monolayers on amorphous silica surfaces have been studied and their structural properties and frictional performance were compared to those of equivalent monolayers without cross-linkages. The simulations isolated for the [...] Read more.
Cross-linked chemisorbed n-alkylsilane (CH3(CH2)n−1Si(OH)3) monolayers on amorphous silica surfaces have been studied and their structural properties and frictional performance were compared to those of equivalent monolayers without cross-linkages. The simulations isolated for the first time the effects of both siloxane cross-linkages and the fraction of chains chemisorbed to the surface, providing insight into a longstanding fundamental question in the literature regarding molecular-level structure. The results demonstrate that both cross-linkages and the fraction of chemisorbed chains affect monolayer structure in small but measurable ways, particularly for monolayers constructed from short chains; however, these changes do not appear to have a significant impact on frictional performance. Full article
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Open AccessReview
Lipid-Based Nanoparticles: Application and Recent Advances in Cancer Treatment
Nanomaterials 2019, 9(4), 638; https://doi.org/10.3390/nano9040638
Received: 11 March 2019 / Revised: 10 April 2019 / Accepted: 15 April 2019 / Published: 19 April 2019
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Abstract
Many therapeutically active molecules are non-soluble in aqueous systems, chemically and biologically fragile or present severe side effects. Lipid-based nanoparticle (LBNP) systems represent one of the most promising colloidal carriers for bioactive organic molecules. Their current application in oncology has revolutionized cancer treatment [...] Read more.
Many therapeutically active molecules are non-soluble in aqueous systems, chemically and biologically fragile or present severe side effects. Lipid-based nanoparticle (LBNP) systems represent one of the most promising colloidal carriers for bioactive organic molecules. Their current application in oncology has revolutionized cancer treatment by improving the antitumor activity of several chemotherapeutic agents. LBNPs advantages include high temporal and thermal stability, high loading capacity, ease of preparation, low production costs, and large-scale industrial production since they can be prepared from natural sources. Moreover, the association of chemotherapeutic agents with lipid nanoparticles reduces active therapeutic dose and toxicity, decreases drug resistance and increases drug levels in tumor tissue by decreasing them in healthy tissue. LBNPs have been extensively assayed in in vitro cancer therapy but also in vivo, with promising results in some clinical trials. This review summarizes the types of LBNPs that have been developed in recent years and the main results when applied in cancer treatment, including essential assays in patients. Full article
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Open AccessArticle
Plasma-Coated Polycaprolactone Nanofibers with Covalently Bonded Platelet-Rich Plasma Enhance Adhesion and Growth of Human Fibroblasts
Nanomaterials 2019, 9(4), 637; https://doi.org/10.3390/nano9040637
Received: 11 March 2019 / Revised: 11 April 2019 / Accepted: 15 April 2019 / Published: 19 April 2019
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Abstract
Biodegradable nanofibers are extensively employed in different areas of biology and medicine, particularly in tissue engineering. The electrospun polycaprolactone (PCL) nanofibers are attracting growing interest due to their good mechanical properties and a low-cost structure similar to the extracellular matrix. However, the unmodified [...] Read more.
Biodegradable nanofibers are extensively employed in different areas of biology and medicine, particularly in tissue engineering. The electrospun polycaprolactone (PCL) nanofibers are attracting growing interest due to their good mechanical properties and a low-cost structure similar to the extracellular matrix. However, the unmodified PCL nanofibers exhibit an inert surface, hindering cell adhesion and negatively affecting their further fate. The employment of PCL nanofibrous scaffolds for wound healing requires a certain modification of the PCL surface. In this work, the morphology of PCL nanofibers is optimized by the careful tuning of electrospinning parameters. It is shown that the modification of the PCL nanofibers with the COOH plasma polymers and the subsequent binding of NH2 groups of protein molecules is a rather simple and technologically accessible procedure allowing the adhesion, early spreading, and growth of human fibroblasts to be boosted. The behavior of fibroblasts on the modified PCL surface was found to be very different when compared to the previously studied cultivation of mesenchymal stem cells on the PCL nanofibrous meshes. It is demonstrated by X-ray photoelectron spectroscopy (XPS) that the freeze–thawed platelet-rich plasma (PRP) immobilization can be performed via covalent and non-covalent bonding and that it does not affect biological activity. The covalently bound components of PRP considerably reduce the fibroblast apoptosis and increase the cell proliferation in comparison to the unmodified PCL nanofibers or the PCL nanofibers with non-covalent bonding of PRP. The reported research findings reveal the potential of PCL matrices for application in tissue engineering, while the plasma modification with COOH groups and their subsequent covalent binding with proteins expand this potential even further. The use of such matrices with covalently immobilized PRP for wound healing leads to prolonged biological activity of the immobilized molecules and protects these biomolecules from the aggressive media of the wound. Full article
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Open AccessArticle
Lipidic Liquid Crystalline Cubic Phases and Magnetocubosomes as Methotrexate Carriers
Nanomaterials 2019, 9(4), 636; https://doi.org/10.3390/nano9040636
Received: 21 March 2019 / Revised: 9 April 2019 / Accepted: 16 April 2019 / Published: 19 April 2019
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Abstract
The release profiles of methotrexate, an anticancer drug, from the monoolein liquid crystalline cubic phases were studied. The cubic phases were used either in the form of a lipidic film deposited onto a glassy carbon electrode surface or in the dispersed form of [...] Read more.
The release profiles of methotrexate, an anticancer drug, from the monoolein liquid crystalline cubic phases were studied. The cubic phases were used either in the form of a lipidic film deposited onto a glassy carbon electrode surface or in the dispersed form of magnetocubosomes, which are considered a prospective hybrid drug delivery system. Commonly, cubosomes or liposomes are employed, but not in the case of toxic methotrexate, known to block the receptors responsible for folate transport into the cells. The release profiles of the drug from the lipidic films were monitored electrochemically and described using the Higuchi model. They were also modified via changes in temperature; the release was faster, although it deviated from the model when the temperature was increased. Cubic phase nanoparticles (magnetocubosomes) containing hydrophobic magnetic nanoparticles placed in an alternating magnetic field of low frequency and amplitude, stimulated drug release from the suspension, which was monitored spectroscopically. These new biocompatible hybrid nanomaterials in the dispersed form allow to control the release of the drug at the appropriate sites, can be easily separated or relocated under external magnetic field and await further investigations of their in vitro cytotoxicity and in vivo biodistribution. Full article
(This article belongs to the Special Issue Soft, Biological and Composite Nanomaterials)
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Open AccessArticle
Neutron Radiography Study of Laboratory Ageing and Treatment Applications with Stone Consolidants
Nanomaterials 2019, 9(4), 635; https://doi.org/10.3390/nano9040635
Received: 11 March 2019 / Revised: 9 April 2019 / Accepted: 11 April 2019 / Published: 19 April 2019
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Abstract
A nano-silica consolidant and nano-titania modified tetraethyl-orthosilicate were applied on two building stones, a carbonate and a silicate, by brush, poultice or capillary absorption. Neutron radiography was used to monitor capillary water absorption, and to analyse changes in physical properties caused by heat [...] Read more.
A nano-silica consolidant and nano-titania modified tetraethyl-orthosilicate were applied on two building stones, a carbonate and a silicate, by brush, poultice or capillary absorption. Neutron radiography was used to monitor capillary water absorption, and to analyse changes in physical properties caused by heat treatment of specimens for the purposes of artificially ageing and different treatment applications with stone consolidants. Moreover, ultrasonic pulse velocity and gravimetrically determined water absorption were analysed to cross-validate neutron radiography. The results reveal that reactive systems like tetraethyl-orthosilicates need an unknown period for polymerisation, which makes nano-silica consolidants more favourable for construction follow-up work. While polymerisation is incomplete, hydrophobic behaviour, water trapping and pore clogging are evident. Within the tetraethyl-orthosilicate treatment, poultice and brushing are strongly influenced by the applicant, which results in wide ranging amounts of water absorbed and anomalous water distributions and kinetics. The carbonate lithotype displays polymerisation initiated in the core of the specimen, while the lateral surfaces are still mostly hydrophobic. Reaction time differences can be attributed to the different amounts of consolidants applied, which is a result of the chosen application settings. Artificial ageing of stone specimens is a prerequisite when mechanical strength gain is studied, as demonstrated by sound speed propagation. Full article
(This article belongs to the Special Issue Nanotechnologies in Cultural Heritage Conservation)
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Open AccessReview
Carbon Dots and Graphene Quantum Dots in Electrochemical Biosensing
Nanomaterials 2019, 9(4), 634; https://doi.org/10.3390/nano9040634
Received: 30 March 2019 / Revised: 16 April 2019 / Accepted: 17 April 2019 / Published: 19 April 2019
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Abstract
Graphene quantum dots (GQDs) and carbon dots (CDs) are among the latest research frontiers in carbon-based nanomaterials. They provide interesting attributes to current electrochemical biosensing due to their intrinsic low toxicity, high solubility in many solvents, excellent electronic properties, robust chemical inertness, large [...] Read more.
Graphene quantum dots (GQDs) and carbon dots (CDs) are among the latest research frontiers in carbon-based nanomaterials. They provide interesting attributes to current electrochemical biosensing due to their intrinsic low toxicity, high solubility in many solvents, excellent electronic properties, robust chemical inertness, large specific surface area, abundant edge sites for functionalization, great biocompatibility, low cost, and versatility, as well as their ability for modification with attractive surface chemistries and other modifiers/nanomaterials. In this review article, the use of GQDs and CDs as signal tags or electrode surface modifiers to develop electrochemical biosensing strategies is critically discussed through the consideration of representative approaches reported in the last five years. The advantages and disadvantages arising from the use of GQDs and CDs in this context are outlined together with the still required work to fulfil the characteristics needed to achieve suitable electrochemical enzymatic and affinity biosensors with applications in the real world. Full article
(This article belongs to the Special Issue Nanostructured Biosensors)
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Open AccessArticle
Nanoscale Characterization of V-Defect in InGaN/GaN QWs LEDs Using Near-Field Scanning Optical Microscopy
Nanomaterials 2019, 9(4), 633; https://doi.org/10.3390/nano9040633
Received: 27 March 2019 / Revised: 14 April 2019 / Accepted: 15 April 2019 / Published: 18 April 2019
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Abstract
The size of the V-defects in the GaN/InGaN-based quantum wells blue light-emitting diode (LED) was intentionally modified from 50 nm to 300 nm. High resolution photoluminescence and electroluminescence of a single large V-defect were investigated by near-field scanning optical microscopy. The current distribution [...] Read more.
The size of the V-defects in the GaN/InGaN-based quantum wells blue light-emitting diode (LED) was intentionally modified from 50 nm to 300 nm. High resolution photoluminescence and electroluminescence of a single large V-defect were investigated by near-field scanning optical microscopy. The current distribution along the {10-11} facets of the large defect was measured by conductive atomic force microscopy. Nearly 20 times the current injection and dominant emission from bottom quantum wells were found in the V-defect compared to its vicinity. Such enhanced current injection into the bottom part of quantum wells through V-defect results in higher light output power. Reduced external quantum efficiency droops were achieved due to more uniform carrier distribution. The un-encapsulated fabricated chip shows light output power of 172.5 mW and 201.7 mW at 400 mA, and external quantum efficiency drop of 22.3% and 15.4% for the sample without and with large V-defects, respectively. Modified V-defects provide a simple and effective approach to suppress the efficiency droop problem that occurs at high current injection, while improving overall quantum efficiency. Full article
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Open AccessArticle
Trastuzumab-Modified Gold Nanoparticles Labeled with 211At as a Prospective Tool for Local Treatment of HER2-Positive Breast Cancer
Nanomaterials 2019, 9(4), 632; https://doi.org/10.3390/nano9040632
Received: 13 March 2019 / Revised: 12 April 2019 / Accepted: 15 April 2019 / Published: 18 April 2019
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Abstract
Highly localized radiotherapy with radionuclides is a commonly used treatment modality for patients with unresectable solid tumors. Herein, we propose a novel α-nanobrachytherapy approach for selective therapy of human epidermal growth factor receptor 2 (HER2)-positive breast cancer. This uses local intratumoral injection of [...] Read more.
Highly localized radiotherapy with radionuclides is a commonly used treatment modality for patients with unresectable solid tumors. Herein, we propose a novel α-nanobrachytherapy approach for selective therapy of human epidermal growth factor receptor 2 (HER2)-positive breast cancer. This uses local intratumoral injection of 5-nm-diameter gold nanoparticles (AuNPs) labeled with an α-emitter (211At), modified with polyethylene glycol (PEG) chains and attached to HER2-specific monoclonal antibody (trastuzumab). The size, shape, morphology, and zeta potential of the 5 nm synthesized AuNPs were characterized by TEM (Transmission Electron Microscopy) and DLS (Dynamic Light Scattering) techniques. The gold nanoparticle surface was modified by PEG and subsequently used for antibody immobilization. Utilizing the high affinity of gold for heavy halogens, the bioconjugate was labelled with 211At obtained by α irradiation of the bismuth target. The labeling yield of 211At was greater than 99%. 211At bioconjugates were stable in human serum. Additionally, in vitro biological studies indicated that 211At-AuNP-PEG-trastuzumab exhibited higher affinity and cytotoxicity towards the HER2-overexpressing human ovarian SKOV-3 cell line than unmodified nanoparticles. Confocal and dark field microscopy studies revealed that 211At-AuNP-PEG-trastuzumab was effectively internalized and deposited near the nucleus. These findings show promising potential for the 211At-AuNP-PEG-trastuzumab radiobioconjugate as a perspective therapeutic agent in the treatment of unresectable solid cancers expressing HER2 receptors. Full article
(This article belongs to the Special Issue Nanocarriers and Targeted Drug Delivery)
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Open AccessArticle
MMP-9 Downregulation with Lipid Nanoparticles for Inhibiting Corneal Neovascularization by Gene Silencing
Nanomaterials 2019, 9(4), 631; https://doi.org/10.3390/nano9040631
Received: 25 March 2019 / Revised: 12 April 2019 / Accepted: 16 April 2019 / Published: 18 April 2019
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Abstract
Gene silencing targeting proangiogenic factors have been shown to be a useful strategy in the treatment of corneal neovascularization (CNV). Among interference RNA (RNAi) molecules, short-hairpin RNA (shRNA) is a plasmid-coded RNA able to down-regulate the expression of the desired gene. It is [...] Read more.
Gene silencing targeting proangiogenic factors have been shown to be a useful strategy in the treatment of corneal neovascularization (CNV). Among interference RNA (RNAi) molecules, short-hairpin RNA (shRNA) is a plasmid-coded RNA able to down-regulate the expression of the desired gene. It is continuously produced in the host cell, inducing a durable gene silencing effect. The aim of this work was to develop a solid lipid nanoparticle (SLN)-based shRNA delivery system to downregulate metalloproteinase 9 (MMP-9), a proangiogenic factor, in corneal cells for the treatment of CNV associated with inflammation. The nanovectors were prepared using a solvent emulsification-evaporation technique, and after physicochemical evaluation, they were evaluated in different culture cell models. Transfection efficacy, cell internalization, cell viability, the effect on MMP-9 expression, and cell migration were evaluated in human corneal epithelial cells (HCE-2). The inhibition of tube formation using human umbilical vein endothelial cells (HUVEC) was also assayed. The non-viral vectors based on SLN were able to downregulate the MMP-9 expression in HCE-2 cells via gene silencing, and, consequently, to inhibit cell migration and tube formation. These results demonstrate the potential of lipid nanoparticles as gene delivery systems for the treatment of CNV-associated inflammation by RNAi technology. Full article
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Open AccessArticle
Interaction in [email protected] and Li+@Fullerenes: First Principle Insights to Li-Based Endohedral Fullerenes
Nanomaterials 2019, 9(4), 630; https://doi.org/10.3390/nano9040630
Received: 27 March 2019 / Revised: 10 April 2019 / Accepted: 10 April 2019 / Published: 18 April 2019
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Abstract
This work reveals first principle results of the endohedral fullerenes made from neutral or charged single atomic lithium (Li or Li+) encapsulated in fullerenes with various cage sizes. According to the calculated binding energies, it is found that the encapsulation of [...] Read more.
This work reveals first principle results of the endohedral fullerenes made from neutral or charged single atomic lithium (Li or Li+) encapsulated in fullerenes with various cage sizes. According to the calculated binding energies, it is found that the encapsulation of a single lithium atom is energetically more favorable than that of lithium cation. Lithium, in both atomic and cationic forms, exhibits a clear tendency to depart from the center in large cages. Interaction effects dominate the whole encapsulation process of lithium to carbon cages. Further, the nature of the interaction between Li (or Li+) and carbon cages is discussed based on reduced density gradient, energy decomposition analysis, and charge transfer. Full article
(This article belongs to the Special Issue Computational Materials Design for Renewable Energy Applications)
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Open AccessArticle
Unidirectional Enhanced Dipolar Emission with an Individual Dielectric Nanoantenna
Nanomaterials 2019, 9(4), 629; https://doi.org/10.3390/nano9040629
Received: 25 March 2019 / Revised: 8 April 2019 / Accepted: 16 April 2019 / Published: 18 April 2019
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Abstract
Light manipulation at the nanoscale is the vanguard of plasmonics. Controlling light radiation into a desired direction in parallel with high optical signal enhancement is still a challenge for designing ultracompact nanoantennas far below subwavelength dimensions. Here, we theoretically demonstrate the unidirectional emissions [...] Read more.
Light manipulation at the nanoscale is the vanguard of plasmonics. Controlling light radiation into a desired direction in parallel with high optical signal enhancement is still a challenge for designing ultracompact nanoantennas far below subwavelength dimensions. Here, we theoretically demonstrate the unidirectional emissions from a local nanoemitter coupled to a hybrid nanoantenna consisting of a plasmonic dipole antenna and an individual silicon nanorod. The emitter near-field was coupled to the dipolar antenna plasmon resonance to achieve a strong radiative decay rate modification, and the emitting plasmon pumped the multipoles within the silicon nanorod for efficient emission redirection. The hybrid antenna sustained a high forward directivity (i.e., a front-to-back ratio of 30 dB) with broadband operating wavelengths in the visible range (i.e., a spectral bandwidth of 240 nm). This facilitated a large library of plasmonic nanostructures to be incorporated, from single element dipole antennas to gap antennas. The proposed hybrid optical nanorouter with ultracompact structural dimensions of 0.08 λ2 was capable of spectrally sorting the emission from the local point source into distinct far-field directions, as well as possessing large emission gains introduced by the nanogap. The distinct features of antenna designs hold potential in the areas of novel nanoscale light sources, biosensing, and optical routing. Full article
(This article belongs to the Special Issue From Nanomaterials to Intelligent Nanosystems)
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