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Ultrasensitive mechanical crack-based sensor inspired by the spider sensory system
Kang, Daeshik,Pikhitsa, Peter V.,Choi, Yong Whan,Lee, Chanseok,Shin, Sung Soo,Piao, Linfeng,Park, Byeonghak,Suh, Kahp-Yang,Kim, Tae-il,Choi, Mansoo Nature Publishing Group, a division of Macmillan P 2014 Nature Vol.516 No.7530
Recently developed flexible mechanosensors based on inorganic silicon, organic semiconductors, carbon nanotubes, graphene platelets, pressure-sensitive rubber and self-powered devices are highly sensitive and can be applied to human skin. However, the development of a multifunctional sensor satisfying the requirements of ultrahigh mechanosensitivity, flexibility and durability remains a challenge. In nature, spiders sense extremely small variations in mechanical stress using crack-shaped slit organs near their leg joints. Here we demonstrate that sensors based on nanoscale crack junctions and inspired by the geometry of a spider’s slit organ can attain ultrahigh sensitivity and serve multiple purposes. The sensors are sensitive to strain (with a gauge factor of over 2,000 in the 0–2 per cent strain range) and vibration (with the ability to detect amplitudes of approximately 10 nanometres). The device is reversible, reproducible, durable and mechanically flexible, and can thus be easily mounted on human skin as an electronic multipixel array. The ultrahigh mechanosensitivity is attributed to the disconnection–reconnection process undergone by the zip-like nanoscale crack junctions under strain or vibration. The proposed theoretical model is consistent with experimental data that we report here. We also demonstrate that sensors based on nanoscale crack junctions are applicable to highly selective speech pattern recognition and the detection of physiological signals. The nanoscale crack junction-based sensory system could be useful in diverse applications requiring ultrahigh displacement sensitivity.
Shape‐Controllable Microlens Arrays via Direct Transfer of Photocurable Polymer Droplets
Kang, Daeshik,Pang, Changhyun,Kim, Sang Moon,Cho, Hye Sung,Um, Hyung Sik,Choi, Yong Whan,Suh, Kahp Y. WILEY‐VCH Verlag 2012 ADVANCED MATERIALS Vol.24 No.13
<P><B>A simple method is presented to form an array of shape‐controllable microlenses</B> by partial photocuring of an UV‐curable polymer and direct transfer. Using the transferred lens array, nanoscale metal patterns as small as 130‐nm gaps are detected under an optical microscope with a distinguishable resolution.</P>
Pang, Changhyun,Kang, Daeshik,Kim, Tae-il,Suh, Kahp-Yang American Chemical Society 2012 Langmuir Vol.28 No.4
<P>We report an analysis of preload-dependent reversibleinterlockingbetween regularly arrayed, high aspect ratio (AR) polymer micro- andnanofibers. Such a reversible interlocking is inspired from the wing-lockingdevice of a beetle where densely populated microhairs (termed microtrichia)on the cuticular surface form numerous hair-to-hair contacts to maximizelateral shear adhesion. To mimic this, we fabricate various high AR,vertical micro- and nanopillars on a flexible substrate and investigatethe shear locking force with different preloads (0.1–10 N/cm<SUP>2</SUP>). A simple theoretical model is developed based on the competitionbetween van der Waals (VdW) attraction and deflection forces of pillars,which can explain the preload-dependent maximum deflection, tiltingangle, and total shear adhesion force.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/langd5/2012/langd5.2012.28.issue-4/la203853r/production/images/medium/la-2011-03853r_0004.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/la203853r'>ACS Electronic Supporting Info</A></P>
Artificial Slanted Nanocilia Array as a Mechanotransducer for Controlling Cell Polarity
Kim, Hong Nam,Jang, Kyung-Jin,Shin, Jung-Youn,Kang, Daeshik,Kim, Sang Moon,Koh, Ilkyoo,Hong, Yoonmi,Jang, Segeun,Kim, Min Sung,Kim, Byung-Soo,Jeong, Hoon Eui,Jeon, Noo Li,Kim, Pilnam,Suh, Kahp-Yang American Chemical Society 2017 ACS NANO Vol.11 No.1
<P>We present a method to induce cell directional behavior using slanted nanocilia arrays. NIH-3T3 fibroblasts demonstrated bidirectional polarization in a rectangular arrangement on vertical nanocilia arrays and exhibited a transition from a bidirectional to a unidirectional polarization pattern when the angle of the nanocilia was decreased from 90 degrees to 30 degrees. The slanted nanocilia guided and facilitated spreading by allowing the cells to contact the sidewalls of the nanocilia, and the directional migration of the cells opposed the direction of the slant due to the anisotropic bending stiffness of the slanted nanocilia. Although the cells recognized the underlying anisotropic geometry when the nanocilia were coated with fibronectin, collagen type I, and Matrigel, the cells lost their directionality when the nanocilia were coated with poly-D-lysine and poly-L-lysine. Furthermore, although the cells recognized geometrical anisotropy on fibronectin coatings, pharmacological perturbation of PI3K-Rac signaling hindered the directional elongation of the cells on both the slanted and vertical nanocilia. Furthermore, myosin light chain II was required for the cells to obtain polarized morphologies. These results indicated that the slanted nanocilia array provided anisotropic contact guidance cues to the interacting cells. The polarization of cells was controlled through two steps: the recognition of underlying geometrical anisotropy and the subsequent directional spreading according to the guidance cues.</P>