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15 Oct 2012

Volume 101, Issue 16, Articles (16xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 161105 (2012); http://dx.doi.org/10.1063/1.4744947 (4 pages)

Nan Niu, Tsung-Li Liu, Igor Aharonovich, Kasey J. Russell, Alexander Woolf, Thomas C. Sadler, Haitham A. R. El-Ella, Menno J. Kappers, Rachel A. Oliver, and Evelyn L. Hu
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Efficient active actuation to imitate locomotion of gecko's toes using an ionic polymer-metal composite actuator enhanced by carbon nanotubes

Min Yu, Qingsong He, Dingshan Yu, Xiaoqing Zhang, Aihong Ji, Hao Zhang, Ce Guo, and Zhendong Dai

Appl. Phys. Lett. 101, 163701 (2012); http://dx.doi.org/10.1063/1.4756999 (5 pages)

Online Publication Date: 15 October 2012

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Active actuation of the adhesive pads is important for a gecko-robot climbing on walls. We demonstrate the fabrication of an ionic polymer-metal composite (IPMC) actuator enhanced with carbon nanotubes (CNTs) and its use for actively actuating an adhesive array to imitate the locomotion of gecko's toes. The as-fabricated IPMC actuator doped with CNTs exhibits a maximum blocking force of 3.59 gf driven at a low voltage of 3 V. It can be easily controlled by voltage signals to actuate an artificial gecko's toe to attach and detach from a surface. This will allow active, distributed actuation in a gecko robot.
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85.35.Kt Nanotube devices
77.84.Lf Composite materials

Effect of pre-tension on the peeling behavior of a bio-inspired nano-film and a hierarchical adhesive structure

Zhilong Peng and Shaohua Chen

Appl. Phys. Lett. 101, 163702 (2012); http://dx.doi.org/10.1063/1.4758481 (5 pages)

Online Publication Date: 15 October 2012

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Inspired by the reversible adhesion behaviors of geckos, the effects of pre-tension in a bio-inspired nano-film and a hierarchical structure on adhesion are studied theoretically. In the case with a uniformly distributing pre-tension in a spatula-like nano-film under peeling, a closed-form solution to a critical peeling angle is derived, below or above which the peel-off force is enhanced or reduced, respectively, compared with the case without pre-tension. The effects of a non-uniformly distributing pre-tension on adhesion are further investigated for both a spatula-like nano-film and a hierarchical structure-like gecko's seta. Compared with the case without pre-tension, the pre-tension, no matter uniform or non-uniform, can increase the adhesion force not only for the spatula-like nano-film but also for the hierarchical structure at a small peeling angle, while decrease it at a relatively large peeling angle. Furthermore, if the pre-tension is large enough, the effective adhesion energy of a hierarchical structure tends to vanish at a critical peeling angle, which results in spontaneous detachment of the hierarchical structure from the substrate. The present theoretical predictions can not only give some explanations on the existing experimental observation that gecko's seta always detaches at a specific angle and no apparent adhesion force can be detected above the critical angle but also provide a deep understanding for the reversible adhesion mechanism of geckos and be helpful to the design of biomimetic reversible adhesives.
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81.90.+c Other topics in materials science (restricted to new topics in section 81)
68.35.Np Adhesion
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Ultrasound-induced release of micropallets with cells

Sijia Guo, Yuli Wang, Nancy Allbritton, and Xiaoning Jiang

Appl. Phys. Lett. 101, 163703 (2012); http://dx.doi.org/10.1063/1.4757648 (3 pages)

Online Publication Date: 16 October 2012

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Separation of selected adherent live cells attached on an array of microelements, termed micropallets, from a mixed population is an important process in biomedical research. We demonstrated that adherent cells can be safely, selectively, and rapidly released from the glass substrate together with micropallets using an ultrasound wave. A 3.3-MHz ultrasound transducer was used to release micropallets (500 μm × 500 μm × 300 μm) with attached HeLa cells, and a cell viability of 92% was obtained after ultrasound release. The ultrasound-induced release process was recorded by a high-speed camera, revealing a proximate velocity of ∼0.5 m/s.
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87.17.Rt Cell adhesion and cell mechanics

Characteristic microvessel relaxation timescales associated with ultrasound-activated microbubbles

Hong Chen, Andrew A. Brayman, and Thomas J. Matula

Appl. Phys. Lett. 101, 163704 (2012); http://dx.doi.org/10.1063/1.4761937 (4 pages)

Online Publication Date: 19 October 2012

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Ultrasound-activated microbubbles were used as actuators to deform microvessels for quantifying microvessel relaxation timescales at megahertz frequencies. Venules containing ultrasound contrast microbubbles were insonified by short 1 MHz ultrasound pulses. Vessel wall forced-deformations were on the same microsecond timescale as microbubble oscillations. The subsequent relaxation of the vessel was recorded by high-speed photomicrography. The tissue was modeled as a simple Voigt solid. Relaxation time constants were measured to be on the order of ∼10 μs. The correlation coefficients between the model and 38 data sets were never lower than 0.85, suggesting this model is sufficient for modeling tissue relaxation at these frequencies. The results place a bound on potential numerical values for viscosity and elasticity of venules.
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87.63.D- Ultrasonography
87.19.rd Elastic properties

Single molecule labeling of an atomic force microscope cantilever tip

Jianwei Liu and Manish J. Butte

Appl. Phys. Lett. 101, 163705 (2012); http://dx.doi.org/10.1063/1.4760283 (3 pages)

Online Publication Date: 19 October 2012

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In this paper, we present a method to functionalize the very apex of an atomic force microscope cantilever with a single or a few molecules. In force spectroscopy or interaction mapping, the cantilever must be functionalized with only a few molecules to avoid noise or spurious measurements. Here, we covalently attached single molecules to the cantilever by touching it to a paper wetted with a solution of quantum dots. The paper competes with wicking up the hydrophilic surface of the tip. This method has broad applications in scanning probe microscopy where small numbers of molecules are needed on the tip.
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68.37.Ps Atomic force microscopy (AFM)
68.08.Bc Wetting
68.65.Hb Quantum dots (patterned in quantum wells)
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