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1.
Adv Mater ; 32(28): e2001675, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32419262

RESUMO

Transparent ceramics are usually polycrystalline materials, which are wildly used in many optical applications, such as lasers. As of today, the fabrication of transparent ceramic structures is still limited to conventional fabrication methods, which do not enable the formation of complex structures. A new approach for 3D printing of micrometer-size, transparent ceramic structures is presented. By using a solution of metal salts that can undergo a sol-gel process and photopolymerization by two-photon printing, micrometer-sized yttrium aluminum garnet (YAG) structures doped with neodymium (Nd) are fabricated. The resulting structures are not only transparent in the visible spectrum but can also emit light at 1064 nm due to the doping with Nd. By using solution-based precursors, without any particles, the sintering can be performed under air at ambient pressure and at a relatively low temperature, compared to conventional processes for YAG. The crystalline structure is imaged at atomic resolution by ultrahigh-resolution scanning transmission electron microscopy (STEM), indicating that the doped Nd atoms are located at the yttrium positions. Such miniaturized structures can be used for diverse applications, e.g., optical components in high-intensity laser systems, which require heat resistance, or as light sources in optical circuits.

2.
Soft Robot ; 2020 Mar 10.
Artigo em Inglês | MEDLINE | ID: mdl-32160139

RESUMO

By designing an actuator composed of thin layers with different coefficients of thermal expansion (CTE) together with an electrically conductive layer, the CTE mismatch can be utilized to produce soft electrothermal actuators (ETAs). These actuators have been typically implemented using only two layers, commonly relying on Timoshenko's analytic model that correlates the temperature to the actuator's curvature. In this study, we extend the analytic model to include the thermoelectric relation present in ETAs, that is, the conductive layer's properties with respect to the operation temperature. By applying the thermoelectric relation, a minimal voltage optimization can be applied to the analytic model. Using dimensionless analysis, we optimize the ETAs performance for both bi- and tri-layer ETAs with and without the thermal modeling. The bi-layer optimization not only predicts the maximal value for the bi-layer performance but also provides the optimal thickness of each layer for any couple of materials. We validate the tri-layer analytic model experimentally by measuring the curvature for different third layer thicknesses. Finally, we optimize the tri-layer design based on the analytic model, which can achieve an improvement in curvature per voltage of >3000% over the optimal bi-layer ETA.

3.
Soft Robot ; 7(2): 123-129, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-31580782

RESUMO

Due to their high deformability, lightness, and safe interaction with the surrounding environment, flexible actuators are key ingredients in soft robotics technologies. Among these, electro-thermal actuators (ETAs), based on carbon nanotubes (CNTs), are used to generate agile movements when current is applied. The extent of movement is determined mostly by the coefficient of thermal expansion (CTE) of the materials arranged in a bi-/tri-layer structure. However, current CNT-based ETAs usually accomplish only simple actions with limited movements. In this work, we successfully developed novel ETAs that are capable of carrying out various controllable movements, such as extremely high bending curvature or unique actuations mimicking a wheel and a worm. These superior functionalities are achieved by adding a third layer or hinges composed of a thermo-responsive shape memory polymer (SMP) onto a bi-layer CNT-kapton ETA. To predict the unique movements of the "triangle" and "worm" actuators, finite element simulations were performed. The combination of SMP and electro-thermal behavior demonstrates its potential for applications in the field of soft actuators and robotics.

4.
ACS Omega ; 4(22): 19635-19640, 2019 Nov 26.
Artigo em Inglês | MEDLINE | ID: mdl-31788593

RESUMO

Vanadium dioxide, a well-known phase transition material with abrupt resistance change during its transition temperature, is herein used to fabricate the transparent mesh film onto a glass slide through self-assembly mesh printing. A record high ON/OFF ratio up to 104 is achieved together with high visible transmittance of 86% compared to the normal glass slide with visible transmittance at 88%. The high transparent properties make the resistive switches applicable for next-generation electronics, such as see-through computing device and beyond. A simple and scalable mesh printing approach-integrated phase change material may provide a promising way to fabricate transparent resistance switches for next-generation electronics.

5.
Chemistry ; 2019 Sep 25.
Artigo em Inglês | MEDLINE | ID: mdl-31556175

RESUMO

The electrophoretic deposition (EPD) of graphene-based materials on transparent substrates is highly potential for many applications. Several factors can determine the yield of the EPD process, such as applied voltage, deposition time and particularly the presence of dispersion additives (stabilisers) in the suspension solution. This study presents an additive-free EPD of graphene quantum dot (GQD) thin films on an indium tin oxide (ITO) glass substrate and studies the deposition mechanism with the variation of the applied voltage (10-50 V) and deposition time (5-25 min). It is found that due to the small size (≈3.9 nm) and high content of deprotonated carboxylic groups, the GQDs form a stable dispersion (zeta-potential of about -35 mV) without using additives. The GQD thin films can be deposited onto ITO with optimal surface morphology at 30 V in 5 min (surface roughness of approximately (3.1±1.3) nm). In addition, as-fabricated GQD thin films also possess some interesting physico-optical properties, such as a double-peak photoluminescence at about λ=417 and 439 nm, with approximately 98 % visible transmittance. This low-cost and eco-friendly GQD thin film is a promising material for various applications, for example, transparent conductors, supercapacitors and heat conductive films in smart windows.

6.
Nanoscale ; 11(23): 11209-11216, 2019 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-31157812

RESUMO

Semiconductor nanocrystals have been shown to have unique advantages over traditional organic photoinitiators for polymerization in solution. However, efficient photoinitiation with such nanoparticles in solvent-free and additive-free formulations so far has not been achieved. Herein, the ability to use semiconductor nanocrystals for efficient bulk polymerization as sole initiators is reported, operating under modern UV-blue-LED light sources found in 3D printers and other photocuring applications. Hybrid semiconductor-metal nanorods exhibit superior photoinitiation capability to their pristine semiconductor counterparts, attributed to the enhanced charge separation and oxygen consumption in such systems. Moreover, photoinitiation by semiconductor nanocrystals overcoated by inorganic ligands is reported, thus increasing the scope of possible applications and shedding light on the photoinitiation mechanism; in light of the results, two possible pathways are discussed - ligand-mediated and cation-coordinated oxidation. A demonstration of the unique attributes of the quantum photoinitiators is reported in their use for high-resolution two-photon printing of optically fluorescing microstructures, demonstrating a multi-functionality capability. The bulk polymerization demonstrated here can be advantageous over solvent based methods as it alleviates the need of post-polymerization drying and reduces waste and exposure to toxic solvents, as well as broadens the possible use of quantum photoinitiators for industrial and research uses.

7.
Sci Rep ; 9(1): 8566, 2019 06 12.
Artigo em Inglês | MEDLINE | ID: mdl-31189986

RESUMO

Localization of rectal tumors is a challenge in minimally invasive surgery due to the lack of tactile sensation. We had developed liposomal indocyanine green (Lip-ICG) for localization of rectal tumor. In this study we evaluated the effects of liposome size and lipid PEGylation on imaging. We used an endoscopically-guided orthotopic experimental rectal cancer model in which tumor fluorescence was determined at different time points after intravenous (i.v.) administration of Lip-ICG and PEGylated liposomes (PEG-Lip-ICG). Signal intensity was measured by tumor-to-background ratio (TBR), or normalized TBR (compared to TBR of free ICG). Fluorescence microscopy of tumor tissue was performed to determine fluorescence localization within the tissue and blood vessels. Liposomes of 60 nm showed an increased TBR compared with free ICG at 12 hours after i.v. injection: normalized TBR (nTBR) = 3.11 vs. 1, respectively (p = 0.006). Larger liposomes (100 nm and 140 nm) had comparable signal to free ICG (nTBR = 0.98 ± 0.02 and 0.78 ± 0.08, respectively), even when additional time points were examined (0.5, 3 and 24 hours). PEG-Lip- ICG were more efficient than Lip-ICG (TBR = 4.2 ± 0.18 vs. 2.5 ± 0.12, p < 0.01) presumably because of reduced uptake by the reticulo-endothelial system. ICG was found outside the capillaries in tumor margins. We conclude that size and lipid modification impact imaging intensity.

8.
Mikrochim Acta ; 186(6): 370, 2019 05 22.
Artigo em Inglês | MEDLINE | ID: mdl-31119470

RESUMO

Two kinds of carbon-based nanozymes were constructed from the same precursor of zeolitic imidazolate framework-8 (ZIF-8) for O2•- determination. Hollow carbon cubic nanomaterial (labelled as HCC) was obtained by chemically etching ZIF-8 with tannic acid and a subsequent calcination. A porous carbon cubic nanomaterial (labelled as PCC) was prepared by directly pyrolysis. Then HCC and PCC were immobilized on the surface of screen printed carbon electrodes (SPCE), fabricating HCC and PCC modified electrodes (denoted as HCC/SPCE and PCC/SPCE). HCC/SPCE, best operated at -0.5 V (vs. Ag/AgCl), has a sensitivity of 6.55 × 102 nA µM-1 cm-2 with a detection limit of 207 nM (at S/N = 3) for O2•- sensing. And PCC/SPCE, best operated at -0.4 V (vs. Ag/AgCl), exhibited a superior performance for O2•- detection with a sensitivity of 1.14 × 103 nA µM-1 cm-2 and a low detection limit of 140 nM (at S/N = 3). The two sensors possess excellent reproducibility and stability. They were used to sense O2•- released from HeLa cells. Graphical abstract Illustration of the synthesis of the hollow carbon cubic nanomaterial (HCC) and of the porous carbon cubic nanomaterial (PCC), and the scheme for detection of superoxide anions in HeLa cell.


Assuntos
Carbono/química , Técnicas Eletroquímicas/métodos , Nanoestruturas/química , Superóxidos/análise , Técnicas Eletroquímicas/instrumentação , Eletrodos , Células HeLa , Humanos , Limite de Detecção , Oxirredução , Reprodutibilidade dos Testes , Oxigênio Singlete/química , Superóxidos/metabolismo , Zeolitas/química , Zimosan/farmacologia
9.
Adv Mater ; 31(28): e1900514, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31081206

RESUMO

Local mechanical cues can affect crucial fate decisions of living cells. Transepithelial stress has been discussed in the context of epithelial monolayers, but the lack of appropriate experimental systems leads current studies to approximate it simply as an in-plane stress. To evaluate possible contribution of force vectors acting in other directions, double epithelium in a 3D-printed "GeminiChip" containing a sessile and a pendant channel is reconstituted. Intriguingly, the sessile epithelia is prone to apoptotic cell extrusion upon crowding, whereas the pendant counterpart favors live cell delamination. Transcriptome analyses show upregulation of RhoA, BMP2, and hypoxia-signaling genes in the pendant epithelium, consistent with the onset of an epithelial-mesenchymal transition program. HepG2 microtumor spheroids also display differential spreading patterns in the sessile and pendant configuration. Using this multilayered GeminiChip, these results uncover a progressive yet critical role of perpendicular force vectors in collective cell behaviors and point at fundamental importance of these forces in the biology of cancer.


Assuntos
Epitélio/metabolismo , Homeostase , Fenômenos Mecânicos , Impressão Tridimensional , Fenômenos Biomecânicos , Estresse Mecânico
10.
J Colloid Interface Sci ; 536: 701-709, 2019 Feb 15.
Artigo em Inglês | MEDLINE | ID: mdl-30408690

RESUMO

Directed-assembly by standing surface acoustic waves (SSAWs) only requires an acoustic contrast between particles and their surrounding medium. It is therefore highly attractive as this requirement is fulfilled by almost all dispersed systems. Previous studies utilizing SSAWs demonstrated mainly reversible microstructure arrangements from nanoparticles. The surface chemistry of colloids dramatically influences their tendency to aggregate and sinter; therefore, it should be possible to form permanent microstructures with intimate contact between nanoparticles by controlling this property. Dispersed silver nanoparticles in a microfluidic channel were exposed to SSAWs and reversibly accumulated at the pressure nodes. We show that addition of chloride ions that remove the polyacrylic capping of the nanoparticles trigger their sintering and the formation of stable conducting silver microstructures. Moreover, if the destabilizing ions are added prior to nanoparticle assembly while continuously streaming the dispersion through the acoustic aperture, the induced aggregation leads to formation of significantly thinner microstructures, which are (for the first time) unlimited in length by the acoustic apparatus. This new approach overcomes the discrepancy between the need for organic dispersants to prevent unwanted aggregation in the dispersion, and the end product's requirement for intimate contact between the colloidal particles.

11.
Chem Soc Rev ; 48(6): 1712-1740, 2019 Mar 18.
Artigo em Inglês | MEDLINE | ID: mdl-30569917

RESUMO

This review describes recent developments in the field of conductive nanomaterials and their application in 2D and 3D printed flexible electronics, with particular emphasis on inks based on metal nanoparticles and nanowires, carbon nanotubes, and graphene sheets. We present the basic properties of these nanomaterials, their stabilization in dispersions, formulation of conductive inks and formation of conductive patterns on flexible substrates (polymers, paper, textile) by using various printing technologies and post-printing processes. Applications of conductive nanomaterials for fabrication of various 2D and 3D electronic devices are also briefly discussed.

12.
Adv Sci (Weinh) ; 5(8): 1800061, 2018 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-30128232

RESUMO

Hybrid organic-inorganic sol gel inks that can undergo both condensation and radical polymerization are developed, enabling fabrication of complex objects by additive manufacturing technology, yielding 3D objects with superior properties. The 3D objects have very high silica content and are printed by digital light processing commercial printers. The printed lightweight objects are characterized by excellent mechanical strength compared to currently used high-performance polymers (139 MPa), very high stability at elevated temperatures (heat deflection temperature >270 °C), high transparency (89%), and lack of cracks, with glossiness similar to silica glasses. The new inks fill the gap in additive manufacturing of objects composed of ceramics only and organic materials only, thus enabling harnessing the advantages of both worlds of materials.

13.
ACS Appl Mater Interfaces ; 10(22): 18879-18885, 2018 Jun 06.
Artigo em Inglês | MEDLINE | ID: mdl-29741081

RESUMO

A sol, aqueous solution-based ink is presented for fabrication of 3D transparent silica glass objects with complex geometries, by a simple 3D printing process conducted at room temperature. The ink combines a hybrid ceramic precursor that can undergo both the photopolymerization reaction and a sol-gel process, both in the solution form, without any particles. The printing is conducted by localized photopolymerization with the use of a low-cost 3D printer. Following printing, upon aging and densifying, the resulting objects convert from a gel to a xerogel and then to a fused silica. The printed objects, which are composed of fused silica, are transparent and have tunable density and refractive indices.

14.
Adv Mater ; 30(41): e1706344, 2018 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-29756242

RESUMO

The field of 3D printing, also known as additive manufacturing (AM), is developing rapidly in both academic and industrial research environments. New materials and printing technologies, which enable rapid and multimaterial printing, have given rise to new applications and utilizations. However, the main bottleneck for achieving many more applications is the lack of materials with new physical properties. Here, some of the recent reports on novel materials in this field, such as ceramics, glass, shape-memory polymers, and electronics, are reviewed. Although new materials have been reported for all three main printing approaches-fused deposition modeling, binder jetting or laser sintering/melting, and photopolymerization-based approaches, apparently, most of the novel physicochemical properties are associated with materials printed by photopolymerization approaches. Furthermore, the high resolution that can be achieved using this type of 3D printing, together with the new properties, has resulted in new implementations such as microfluidic, biomedical devices, and soft robotics. Therefore, the focus here is on photopolymerization-based additive manufacturing including the recent development of new methods, novel monomers, and photoinitiators, which result in previously inaccessible applications such as complex ceramic structures, embedded electronics, and responsive 3D objects.

15.
Biosens Bioelectron ; 102: 365-371, 2018 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-29172145

RESUMO

Bioelectronics platforms are gaining widespread attention as they provide a template to study the interactions between biological species and electronics. Decoding the effect of the electrical signals on the cells and tissues holds the promise for treating the malignant tissue growth, regenerating organs and engineering new-age medical devices. This work is a step forward in this direction, where bio- and electronic materials co-exist on one platform without any need for post processing. We fabricate a freestanding and flexible hydrogel based platform using 3D bioprinting. The fabrication process is simple, easy and provides a flexible route to print materials with preferred shapes, size and spatial orientation. Through the design of interdigitated electrodes and heating coil, the platform can be tailored to print various circuits for different functionalities. The biocompatibility of the printed platform is tested using C2C12 murine myoblasts cell line. Furthermore, normal human dermal fibroblasts (primary cells) are also seeded on the platform to ascertain the compatibility.


Assuntos
Bioimpressão , Técnicas Biossensoriais , Impressão Tridimensional , Engenharia Tecidual , Linhagem Celular , Sobrevivência Celular , Fibroblastos/química , Fibroblastos/citologia , Humanos , Hidrogel de Polietilenoglicol-Dimetacrilato/química , Mioblastos/química , Mioblastos/citologia , Tecidos Suporte/química
16.
ACS Appl Mater Interfaces ; 10(3): 3082-3093, 2018 Jan 24.
Artigo em Inglês | MEDLINE | ID: mdl-29268600

RESUMO

Liquid drop evaporation on surfaces is present in many industrial and medical applications, e.g., printed electronics, spraying of pesticides, DNA mapping, etc. Despite this strong interest, a theoretical description of the dynamic of the evaporation of complex liquid mixtures and nanosuspensions is still lacking. Indeed, one of the aspects that have not been included in the current theoretical descriptions is the competition between the kinetics of evaporation and the adsorption of surfactants and/or particles at the liquid/vapor and liquid/solid interfaces. Materials formed by an electrically isolating solid on which a patterned conducting layer was formed by the deposits left after drop evaporation have been considered as very promising for building electrical circuits on flexible plastic substrates. In this work, we have done an exhaustive study of the evaporation of nanosuspensions of latex and hydrophobized silver nanoparticles on four substrates of different hydrophobicity. The advancing and receding contact angles as well as the time dependence of the volume of the droplets have been measured over a broad range of particle concentrations. Also, mixtures of silver particles and a surfactant, commonly used in industrial printing, have been examined. Furthermore, the adsorption kinetics at both the air/liquid and solid/liquid interfaces have been measured. Whereas the latex particles do not adsorb at the solid/liquid and only slightly reduce the surface tension, the silver particles strongly adsorb at both interfaces. The experimental results of the evaporation process were compared with the predictions of the theory of Semenov et al. (Evaporation of Sessile Water Droplets: Universal Behavior in the Presence of Contact Angle Hysteresis. Colloids Surf. Physicochem. Eng. Asp. 2011, 391 (1-3), 135-144) and showed surprisingly good agreement despite that the theory was developed for pure liquids. The morphology of the deposits left by the droplets after total evaporation was studied by scanning electronic microscopy, and the effects of the substrate, the particle nature, and their concentrations on these patterns are discussed.

17.
J Colloid Interface Sci ; 512: 529-535, 2018 Feb 15.
Artigo em Inglês | MEDLINE | ID: mdl-29096114

RESUMO

Surface engineering is an effective method to improve the thermochromic performance of VO2. In this paper, an acid-etching top down method was proposed to tailor the VO2 surface morphology from the continuous dense-packed surface to patterned structure, which exhibited the enhanced integrated visible transmittance (Tlum) and the enlarged solar modulating abilities (ΔTsol). Moreover, a self-patterning approach was also illustrated to improve the thermochromic properties. The proposed surface engineering methods represent a facile and cost-effective approach for enhancing thermochromic properties that could promote the application of VO2 thin films in smart windows.

18.
Surg Endosc ; 32(2): 963-970, 2018 02.
Artigo em Inglês | MEDLINE | ID: mdl-28779247

RESUMO

BACKGROUND: Iatrogenic ureteral injury is an increasing concern in the laparoscopic era, affecting both patient morbidity and costs. Current techniques enabling intraoperative ureteral identification require invasive procedures or radiations. Our aim was to develop a real-time, non-invasive, radiation-free method to visualize ureters, based on near-infrared (NIR) imaging. For this purpose, we interfered with the biliary excretion pathway of the indocyanine green (ICG) fluorophore by loading it into liposomes, enabling renal excretion. In this work, we studied various parameters influencing ureteral imaging. METHODS: Fluorescence intensity (FI) of various liposomal ICG sizes and doses were characterized in vitro and subsequently tested in vivo in mice and pigs. Quantification was performed by measuring FI in multiple points and applying the ureteral/retroperitoneum ratio (U/R). RESULTS: The optimal liposomal ICG loading dose was 20%, for the different liposomes' sizes tested (30, 60, 100 nm). Higher concentration of ICG decreased FI. In vivo, the optimal liposome size for ureteral imaging was 60 nm, which yielded a U/R of 5.2 ± 1.7 (p < 0.001 vs. free ICG). The optimal ICG dose was 8 mg/kg (U/R = 2.1 ± 0.4, p < 0.05 vs. 4 mg/kg). Only urine after liposomal ICG injection had a measurable FI, and not after free ICG injection. Using a NIR-optimized laparoscopic camera, ureters could be effectively imaged in pigs, from 10 min after injection and persisting for at least 90 min. Ureteral peristaltic waves could be clearly identified only after liposomal ICG injection. CONCLUSIONS: Optimization of liposomal ICG allowed to visualize enhanced ureters in animal models and seems a promising fluorophore engineering, which calls for further developments.


Assuntos
Corantes Fluorescentes/administração & dosagem , Verde de Indocianina/administração & dosagem , Imagem Óptica/métodos , Ureter/diagnóstico por imagem , Animais , Feminino , Lipossomos , Masculino , Camundongos , Espectroscopia de Luz Próxima ao Infravermelho , Suínos
19.
Small ; 14(1)2018 01.
Artigo em Inglês | MEDLINE | ID: mdl-29134772

RESUMO

The field of printed electronics is continually trying to reduce the dimensions of the electrical components. Here, a method of printing metallic lines with widths as small as 15 nm and up to a few micrometers using fountain pen nanolithography (FPN) is shown. The FPN technique is based on a bent nanopipette with atomic force feedback that acts similar to a nanopen. The geometry of the nanopen allows for rapid placement accuracy of the printing tip, on any desired location, with the highest of optical sub-micrometer resolution. Using this nanopen, investigations of various inks are undertaken together with instrumental and script-tool development that allows accurate printing of multiple layers. This has led to the printing of conductive lines using inks composed of silver nanoparticles and salt solutions of silver and copper. In addition, it is shown that the method can be applied to substrates of various materials with minimal effect on the dimension of the line. The line widths are varied by using nanopens with different orifices or by tailoring the wetting properties of the ink on the substrate. Metallic interconnections of conducting lines are reported.

20.
ACS Appl Mater Interfaces ; 9(50): 44214-44221, 2017 Dec 20.
Artigo em Inglês | MEDLINE | ID: mdl-29172418

RESUMO

The laser-induced microbubble technique (LIMBT) has recently been developed for micro-patterning of various materials. In this method, a laser beam is focused on a dispersion of nanoparticles leading to the formation of a microbubble due to laser heating. Convection currents around the microbubble carry nanoparticles so that they become pinned to the bubble/substrate interface. The major limitation of this technique is that for most materials, a noncontinuous deposition is formed. We show that continuous patterns can be formed by preventing the microbubble from being pinned to the deposited material. This is done by modulating the laser so that the construction and destruction of the microbubble are controlled. When the method is applied to a dispersion of Ag nanoparticles, continuous electrically conductive lines are formed. Furthermore, the line width is narrower than that achieved by the standard nonmodulated LIMBT. This approach can be applied to the direct-write fabrication of micron-size conductive patterns in electronic devices without the use of photolithography.

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