Restrained fingering

Nice Title..........

• Pep Pàmies

Nature Materials

 

11,

 

829

 

(2012)

 

doi:10.1038/nmat3446

Published online

 

24 September 2012

A flowing, low-viscosity fluid penetrating a thicker one tends to form elongated patterns, resembling fingers, in the direction of the flow. Such 'fingering instabilities' can cause inefficiencies in oil-recovery processes and in microfluidic set-ups; for instance, when air is used to flush a liquid out of a channel, traces may be left behind. Now, Talal Al-Housseiny and colleagues show that fingering instabilities can be easily avoided by creating a depth gradient in the direction of the flow. Using a Hele-Shaw cell (a shallow rectangular channel) with varying depth, the researchers demonstrated that finger-like patterns disappear when the capillary number — the ratio of viscous to surface-tension forces — is below a critical value, which depends on the viscosity ratio of the displaced and displacing fluids, the contact angle of the fluid interface with the cell's wall, and the gradient in fluid depth. With appropriate flow rates, microfluidic channels that are tapered should then be easier to clean perfectly with a flush.

Soft robotics: Bionic jellyfish

• Viola Vogel

Viola Vogel is in the Laboratory of Applied Mechanobiology in the Department of Health Sciences and Technology at the ETH Zurich, Wolfgang-Pauli-Strasse 10, HCI F443, 8093 Zurich, Switzerland

Nature Materials

 

11,

 

841–842

 

(2012)

 

doi:10.1038/nmat3438

Published online

 

24 September 2012

A polymeric tissue-engineered structure capable of swimming in a similar manner to a jellyfish is created by mimicking the structural design, stroke kinematics and fluid dynamics of the organism.

Near Infrared Light Triggered Release of Biomacromolecules from Hydrogels Loaded with Upconversion Nanoparticles

Bin Yan †, John-Christopher Boyer ‡, Damien Habault†, Neil R. Branda *‡, and Yue Zhao *†

^† Département de Chimie, Université de Sherbrooke, Sherbrooke, Québec, Canada J1K 2R1

^‡ 4D LABS, Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia, Canada V5A 1S6

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja308876j

Publication Date (Web): September 26, 2012

Copyright © 2012 American Chemical Society

Using a photosensitive hybrid hydrogel loaded with upconversion nanoparticles (UCNPs), we show that continuous-wave near-infrared (NIR) light (980 nm) can be used to induce the gel–sol transition and release large, inactive biomacromolecules (protein and enzyme) entrapped in the hydrogel into aqueous solution “on demand”, where their bioactivity is recovered. This study is a new demonstration and development in harnessing the unique multiphoton effect of UCNPs for photosensitive materials of biomedical interest.

Eggshell-Inspired Biomineralization Generates Vaccines that Do Not Require Refrigeration

1. Guangchuan Wang¹, 
2. Xiaofeng Li², 
3. Lijuan Mo³, 
4. Zhiyong Song¹, 
5. Wei Chen¹, 
6. Yongqiang Deng², 
7. Hui Zhao², 
8. Ede Qin², 
9. Prof. Dr. Chengfeng Qin^2,*, 
10. Prof. Dr. Ruikang Tang^1,*

Article first published online: 24 SEP 2012

DOI: 10.1002/anie.201206154

We’re not gonna bake it: In situ biomineralization creates an egg-like shell on vaccine particles to improve their thermostability. Different from the bare vaccine (squares), the biomineralized vaccine (red circles) can be stored at ambient temperature without refrigeration for up to a week and retain biological activity both in vitro (see graph), as well as in a mouse model.

Patterning: Nanopattern Fabrication of Gold on Hydrogels and Application to Tunable Photonic Crystal

1. Naonobu Shimamoto^1,2, 
2. Yoshito Tanaka²,
3. Hideyuki Mitomo^1,2, 
4. Ryuzo Kawamura¹,
5. Kuniharu Ijiro^1,2, 
6. Keiji Sasaki², 
7. Yoshihito Osada^1,*

Article first published online: 25 SEP 2012

DOI: 10.1002/adma.201290231

Nanopattern fabrication of metal dots on a water-swollen hydrogel is performed by transcribing metallic nanodots from a solid substrate to the hydrogel surface. This fabrication technique may stimulate advances in nanoscience using soft, wet matter, enabling development of new ion-based bio-related devices. Au nano-dots on a hydrogel can produce iridescent color, and its spectral response can be finely modulated by controlling the nanodot spacing, as reported by Yoshihito Osada and co-workers

Time-Resolved, Confocal Single-Molecule Tracking of Individual Organic Dyes and Fluorescent Proteins in Three Dimensions

Jason J. Han †, Csaba Kiss ‡, Andrew R. M. Bradbury‡, and James H. Werner †*

^†Center for Integrated Nanotechnologies and^‡Biosciences Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States

ACS Nano, Article ASAP

DOI: 10.1021/nn302912j

Publication Date (Web): September 8, 2012

Copyright © 2012 American Chemical Society

We demonstrate following individual fluorescent protein constructs and individual organic dyes as they diffuse in 3-D in solution at rates up to 1 μm²/s over distances of several micrometers in X, Y, and Z. Our 3-D tracking method is essentially a stage scanning confocal microscope that uses a unique spatial filter geometry and active feedback 200 times/s to follow fast 3-D motion. Here we detail simulations used to find optimal feedback parameters for following individual fluorescent proteins in 3-D and show that a wide range of parameters are capable of following individual proteins diffusing at 1 μm²/s rates. In addition, we experimentally show that through 3-D single-molecule tracking of a protein oligomer series (monomer, dimer, and tetramer) of the fluorescent protein Azami Green one can determine the protein oligomerization state. We also perform time-resolved spectroscopy (photon pair correlation measurements) during the measured 3-D trajectories. The photon pair correlation measurements show clear fluorescence photon antibunching, demonstrating that the trajectories are of single fluorescent molecules. We note that the rates of single-molecule diffusive motion we follow (approximately 1 μm²/s) are comparable to or faster than many intracellular transport processes.

The Role of Multiscale Roughness in the Lotus Effect: Is It Essential for Super-Hydrophobicity?

Eyal Bittoun and Abraham Marmur *

The Wolfson Department of Chemical Engineering Technion, Israel Institute of Technology, 32000 Haifa, Israel

Langmuir, Article ASAP

DOI: 10.1021/la3029512

Publication Date (Web): September 4, 2012

Copyright © 2012 American Chemical Society

The role of multiscale (hierarchical) roughness in optimizing the structure of nonwettable (superhydrophobic) solid surfaces was theoretically studied for 2D systems of a drop on three different types of surface topographies with up to four roughness scales. The surface models considered here were sinusoidal, flat-top pillars, and triadic Koch curves. Three criteria were used to compare between the various topographies and roughness scales. The first is the transition contact angle (CA) between the Wenzel (W) and Cassie–Baxter (CB) wetting states, above which the CB state is the thermodynamically stable one. The second is the solid–liquid (wetted) interfacial area, as an indicator for the ease of roll-off of a drop from the superhydrophobic surfaces. The third is the protrusion height that reflects the mechanical stability of the surface against breakage. The results indicate that multiscale roughness per se is not essential for superhydrophobicity; however, it mainly decreases the necessary protrusion height. Thus, multiscale roughness is beneficial for the Lotus effect mostly with regard to mechanical stability. The sinusoidal topography with three levels of roughness scales is best for nonwettability out of the topographies studied here. This observation may partially explain why Nature chose rounded-top protrusions, such as those on the Lotus leaf. The least useful topography is the flat-top pillars with three roughness scales. In the case of the triadic Koch topography, four roughness scales are required to have nonwettable surface.

Flexible Electronics: Materials and Designs for Wirelessly Powered Implantable Light-Emitting Systems

1. Rak-Hwan Kim^1,†, 
2. Hu Tao^2,†, 
3. Tae-il Kim^1,†,
4. Yihui Zhang³, 
5. Stanley Kim¹, 
6. Bruce Panilaitis², 
7. Miaomiao Yang², 
8. Dae-Hyeong Kim⁴, 
9. Yei Hwan Jung¹, 
10. Bong Hoon Kim^1,5,
11. Yuhang Li^3,6, 
12. Yonggang Huang³, 
13. Fiorenzo G. Omenetto^2,*, 
14. John A. Rogers^1,7,*

Article first published online: 17 SEP 2012

DOI: 10.1002/smll.201290099

A stretchable, microscale inorganic light-emitting diode (μ-ILED) with an integrated coil for wireless power delivery is described F. G. Omenetto, J. A. Rogers, and co-workers on page 2812. The ultrathin layout of the μ-ILED, the serpentine structures in the metal traces, and the rubber substrate combine to provide a system that can be deformed to large levels of strain. Detailed studies of the mechanics reveal the underlying design principles. The physical characteristics and constituent materials enable its use as an implantable light source, as illustrated through in vivo studies using animal models.

Nanocarbon-Based Photovoltaics

Marco Bernardi †, Jessica Lohrman ‡, Priyank V. Kumar †, Alec Kirkeminde ‡, Nicola Ferralis †, Jeffrey C. Grossman †*, and Shenqiang Ren ‡*

^† Department of Materials Science and Engineering,Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139-4307, United States

^‡ Department of Chemistry, University of Kansas, 1251 Wescoe Hall Drive, Lawrence, Kansas 66045, United States

ACS Nano, Article ASAP

DOI: 10.1021/nn302893p

Publication Date (Web): September 6, 2012

Copyright © 2012 American Chemical Society

Carbon materials are excellent candidates for photovoltaic solar cells: they are Earth-abundant, possess high optical absorption, and maintain superior thermal and photostability. Here we report on solar cells with active layers made solely of carbon nanomaterials that present the same advantages of conjugated polymer-based solar cells, namely, solution processable, potentially flexible, and chemically tunable, but with increased photostability and the possibility to revert photodegradation. The device active layer composition is optimized using ab initio density functional theory calculations to predict type-II band alignment and Schottky barrier formation. The best device fabricated is composed of PC₇₀BM fullerene, semiconducting single-walled carbon nanotubes, and reduced graphene oxide. This active-layer composition achieves a power conversion efficiency of 1.3%—a record for solar cells based on carbon as the active material—and we calculate efficiency limits of up to 13% for the devices fabricated in this work, comparable to those predicted for polymer solar cells employing PCBM as the acceptor. There is great promise for improving carbon-based solar cells considering the novelty of this type of device, the high photostability, and the availability of a large number of carbon materials with yet untapped potential for photovoltaics. Our results indicate a new strategy for efficient carbon-based, solution-processable, thin film, photostable solar cells.

Complex Stiffness Gradient Substrates for Studying Mechanotactic Cell Migration

1. Cheng-Hwa R. Kuo¹, 
2. Jian Xian², 
3. James D. Brenton², 
4. Kristian Franze^3,*, 
5. Easan Sivaniah^1,*

Article first published online: 18 SEP 2012

DOI: 10.1002/adma.201202520

Polyacrylamide gels are cast upon a stiff support with controlled topography, resulting in a thin gel layer of variable height. The topographical profiles project a stiffness map onto the gel, resulting in controlled linear and non-linear 2D stiffness gradients. Fibroblasts, which migrate towards stiffer substrates, accumulate in areas with a gel thickness below 15 μm.

Building Research Equipment with Free, Open-Source Hardware

Science 14 September 2012: 
Vol. 337 no. 6100 pp. 1303-1304 
DOI: 10.1126/science.1228183

1. Joshua M. Pearce

Most experimental research projects are executed with a combination of purchased hardware equipment, which may be modified in the laboratory and custom single-built equipment fabricated inhouse. However, the computer software that helps design and execute experiments and analyze data has an additional source: It can also be free and open-source software (FOSS) (1). FOSS has the advantage that the code is openly available for modification and is also often free of charge. In the past, customizing software has been much easier than custom-building equipment, which often can be quite costly because fabrication requires the skills of machinists, glassblowers, technicians, or outside suppliers. However, the open-source paradigm is now enabling creation of open-source scientific hardware by combining three-dimensional (3D) printing with open-source microcontrollers running on FOSS. These developments are illustrated below by several examples of equipment fabrication that can better meet particular specifications at substantially lower overall costs.

Solid Immersion Facilitates Fluorescence Microscopy with Nanometer Resolution and Sub-Ångström Emitter Localization

1. Dominik Wildanger^1,*, 
2. Brian R. Patton²,
3. Heiko Schill¹, 
4. Luca Marseglia², 
5. J. P. Hadden², 
6. Sebastian Knauer², 
7. Andreas Schönle¹, 
8. John G. Rarity², 
9. Jeremy L. O'Brien², 
10. Stefan W. Hell^1,*, 
11. Jason M. Smith³

Article first published online: 12 SEP 2012

DOI: 10.1002/adma.201203033

Exploring the maximum spatial resolution achievable in far-field optical imaging, we show that applying solid immersion lenses (SIL) in stimulated emission depletion (STED) microscopy addresses single spins with a resolution down to 2.4 ± 0.3 nm and with a localization precision of 0.09 nm.

Tiny Mechanical Scale Weighs Molecules One at a Time

• M. S. Hanay,
• S. Kelber,
• A. K. Naik,
• D. Chi,
• S. Hentz,
• E. C. Bullard,
• E. Colinet,
• L. Duraffourg
• & M. L. Roukes

Nature Nanotechnology

 

7,

 

602–608

 

(2012)

 

doi:10.1038/nnano.2012.119

Received

 

24 February 2012 

Accepted

 

15 June 2012 

Published online

 

26 August 2012

Nanoelectromechanical systems (NEMS) resonators can detect mass with exceptional sensitivity. Previously, mass spectra from several hundred adsorption events were assembled in NEMS-based mass spectrometry using statistical analysis. Here, we report the first realization of single-molecule NEMS-based mass spectrometry in real time. As each molecule in the sample adsorbs on the resonator, its mass and position of adsorption are determined by continuously tracking two driven vibrational modes of the device. We demonstrate the potential of multimode NEMS-based mass spectrometry by analysing IgM antibody complexes in real time. NEMS-based mass spectrometry is a unique and promising new form of mass spectrometry: it can resolve neutral species, provide a resolving power that increases markedly for very large masses, and allow the acquisition of spectra, molecule-by-molecule, in real time.