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ABSTRACT: Osteocyte apoptosis is known to trigger targeted bone resorption. In the present study, we developed an osteocyte-viability-based trabecular bone remodeling (OVBR) model. This novel remodeling model, combined with recent advanced simulation methods and analysis techniques, such as the element-by-element 3D finite element method and the ITS technique, was used to quantitatively study the dynamic evolution of bone mass and trabecular microstructure in response to various loading and unloading conditions. Different levels of unloading simulated the disuse condition of bed rest or microgravity in space. The amount of bone loss and microstructural deterioration correlated with the magnitude of unloading. The restoration of bone mass upon the reloading condition was achieved by thickening the remaining trabecular architecture, while the lost trabecular plates and rods could not be recovered by reloading. Compared to previous models, the predictions of bone resorption of the OVBR model are more consistent with physiological values reported from previous experiments. Whereas osteocytes suffer a lack of loading during disuse, they may suffer overloading during the reloading phase, which hampers recovery. The OVBR model is promising for quantitative studies of trabecular bone loss and microstructural deterioration of patients or astronauts during long-term bed rest or space flight and thereafter bone recovery.
Biomechanics and Modeling in Mechanobiology 04/2013; · 3.19 Impact Factor
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ABSTRACT: Bone remodeling is a complex dynamic process, which modulates both bone mass and bone microstructure. In addition to bone mass, bone microstructure is an important contributor to bone quality in osteoporosis and fragility fractures. However, the quantitative knowledge of evolution of three-dimensional (3D) trabecular microstructure in adaptation to the external forces is currently limited. In this study, a new 3D simulation method of remodeling of human trabecular bone was developed to quantitatively study the dynamic evolution of bone mass and trabecular microstructure in response to different external loading conditions. The morphological features of trabecular plate and rod, such as thickness and number density in different orientations were monitored during the remodeling process using a novel imaging analysis technique, namely Individual Trabecula Segmentation (ITS). We showed that the volume fraction and microstructures of trabecular bone including, trabecular type and orientation, were determined by the applied mechanical load. Particularly, the morphological parameters of trabecular plates were more sensitive to the applied load, indicating that they played the major role in the mechanical properties of the trabecular bone. Reducing the applied load caused severe microstructural deteriorations of trabecular bone, such as trabecular plate perforation, rod breakage, and a conversion from plates to rods.
Journal of biomechanics 08/2012; 45(14):2417-25. · 2.66 Impact Factor
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ABSTRACT: Human immunodeficiency virus type 1 protease (HIV-1 PR) is one of the primary inhibition targets for chemotherapy of AIDS because of its critical role in the replication cycle of the HIV. In this work, a combinatory coarse-grained and atomistic simulation method was developed for dissecting molecular mechanisms and binding process of inhibitors to the active site of HIV-1 PR, in which 35 typical inhibitors were trialed. We found that the molecular size and stiffness of the inhibitors and the binding energy between the inhibitors and PR play important roles in regulating the binding process. Comparatively, the smaller and more flexible inhibitors have larger binding energy and higher binding rates; they even bind into PR without opening the flaps. In contrast, the larger and stiffer inhibitors have lower binding energy and lower binding rate, and their binding is subjected to the opening and gating of the PR flaps. Furthermore, the components of binding free energy were quantified and analyzed by their dependence on the molecular size, structures, and hydrogen bond networks of inhibitors. Our results also deduce significant dynamics descriptors for determining the quantitative structure and property relationship in potent drug ligands for HIV-1 PR inhibition.
Chemical Biology & Drug Design 05/2012; 80(3):440-54. · 2.28 Impact Factor
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ABSTRACT: The flow theory of mechanism-based strain gradient plasticity theory (MSG) developed by Qiu et al. (2003) is extended for
incompressible material. The MSG flow theory is used to predict the increase of plastic work hardening for plane strain tension
of surface-passivated Cu thin film. The theoretical predictions agree well with experiments for suitably chosen material parameters.
Science in China Series G Physics Mechanics and Astronomy 05/2012; 52(9):1375-1381. · 1.41 Impact Factor
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ABSTRACT: Stretchable electronics represents a direction of recent development in next-generation semiconductor devices. Such systems
have the potential to offer the performance of conventional wafer-based technologies, but they can be stretched like a rubber
band, twisted like a rope, bent over a pencil, and folded like a piece of paper. Isolating the active devices from strains
associated with such deformations is an important aspect of design. One strategy involves the shielding of the electronics
from deformation of the substrate through insertion of a compliant adhesive layer. This paper establishes a simple, analytical
model and validates the results by the finite element method. The results show that a relatively thick, compliant adhesive
is effective to reduce the strain in the electronics, as is a relatively short film.
KeywordsStrain isolation–Thin film–Substrate–Adhesive–Stretchable electronics
Acta Mechanica Sinica 04/2012; 26(6):881-888. · 0.86 Impact Factor
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ABSTRACT: To understand the underlying mechanisms of significant differences in dissociation rate constant among different inhibitors for HIV-1 protease, we performed steered molecular dynamics (SMD) simulations to analyze the entire dissociation processes of inhibitors from the binding pocket of protease at atomistic details. We found that the strength of hydrogen bond network between inhibitor and the protease takes crucial roles in the dissociation process. We showed that the hydrogen bond network in the cyclic urea inhibitors AHA001/XK263 is less stable than that of the approved inhibitor ABT538 because of their large differences in the structures of the networks. In the cyclic urea inhibitor bound complex, the hydrogen bonds often distribute at the flap tips and the active site. In contrast, there are additional accessorial hydrogen bonds formed at the lateral sides of the flaps and the active site in the ABT538 bound complex, which take crucial roles in stabilizing the hydrogen bond network. In addition, the water molecule W301 also plays important roles in stabilizing the hydrogen bond network through its flexible movement by acting as a collision buffer and helping the rebinding of hydrogen bonds at the flap tips. Because of its high stability, the hydrogen bond network of ABT538 complex can work together with the hydrophobic clusters to resist the dissociation, resulting in much lower dissociation rate constant than those of cyclic urea inhibitor complexes. This study may provide useful guidelines for design of novel potent inhibitors with optimized interactions.
PLoS ONE 01/2011; 6(4):e19268. · 4.09 Impact Factor
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ABSTRACT: The mechanics of wet adhesion between a water strider's legs and a water surface was studied. First, we showed that the nanoscale to microscale hierarchical surface structure on striders' legs is crucial to the stable water-repellent properties of the legs. The smallest structure is made for the sake of a stable Cassie state even under harsh environment conditions, which sets an upper limit for the dimension of the smallest structure. The maximum stress and the maximum deformation of the surface structures at the contact line are size-dependent because of the asymmetric surface tension, which sets a lower limit for the dimension of the smallest structure. The surface hierarchy can largely reduce the adhesion between the water and the legs by stabilizing the Cassie state, increasing the apparent contact angle, and reducing the contact area and the length of the contact line. Second, the processes of the legs pressing on and detaching from the water surface were analyzed with a 2D model. We found that the superhydrophobicity of the legs' surface is critically important to reducing the detaching force and detaching energy. Finally, the dynamic process of the legs striking the water surface, mimicking the maneuvering of water striders, was analyzed. We found that the large length of the legs not only reduces the energy dissipation in the quasi-static pressing and pulling processes but also enhances the efficiency of energy transfer from bioenergy to kinetic energy in the dynamic process during the maneuvering of the water striders. The mechanical principles found in this study may provide useful guidelines for the design of superior water-repellent surfaces and novel aquatic robots.
Langmuir 11/2010; 26(24):18926-37. · 4.19 Impact Factor
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Dae-Hyeong Kim,
Jonathan Viventi,
Jason J Amsden,
Jianliang Xiao,
Leif Vigeland,
Yun-Soung Kim,
Justin A Blanco,
Bruce Panilaitis,
Eric S Frechette,
Diego Contreras,
David L Kaplan,
Fiorenzo G Omenetto,
Yonggang Huang, Keh-Chih Hwang,
Mitchell R Zakin,
Brian Litt,
John A Rogers
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ABSTRACT: Electronics that are capable of intimate, non-invasive integration with the soft, curvilinear surfaces of biological tissues offer important opportunities for diagnosing and treating disease and for improving brain/machine interfaces. This article describes a material strategy for a type of bio-interfaced system that relies on ultrathin electronics supported by bioresorbable substrates of silk fibroin. Mounting such devices on tissue and then allowing the silk to dissolve and resorb initiates a spontaneous, conformal wrapping process driven by capillary forces at the biotic/abiotic interface. Specialized mesh designs and ultrathin forms for the electronics ensure minimal stresses on the tissue and highly conformal coverage, even for complex curvilinear surfaces, as confirmed by experimental and theoretical studies. In vivo, neural mapping experiments on feline animal models illustrate one mode of use for this class of technology. These concepts provide new capabilities for implantable and surgical devices.
Nature Material 06/2010; 9(6):511-7. · 32.84 Impact Factor
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Taeseup Song,
Jianliang Xia,
Jin-Hyon Lee,
Dong Hyun Lee,
Moon-Seok Kwon,
Jae-Man Choi,
Jian Wu,
Seok Kwang Doo,
Hyuk Chang,
Won Il Park,
Dong Sik Zang,
Hansu Kim,
Yonggang Huang, Keh-Chih Hwang,
John A Rogers,
Ungyu Paik
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ABSTRACT: Silicon is a promising candidate for electrodes in lithium ion batteries due to its large theoretical energy density. Poor capacity retention, caused by pulverization of Si during cycling, frustrates its practical application. We have developed a nanostructured form of silicon, consisting of arrays of sealed, tubular geometries that is capable of accommodating large volume changes associated with lithiation in battery applications. Such electrodes exhibit high initial Coulombic efficiencies (i.e., >85%) and stable capacity-retention (>80% after 50 cycles), due to an unusual, underlying mechanics that is dominated by free surfaces. This physics is manifested by a strongly anisotropic expansion in which 400% volumetric increases are accomplished with only relatively small (<35%) changes in the axial dimension. These experimental results and associated theoretical mechanics models demonstrate the extent to which nanoscale engineering of electrode geometry can be used to advantage in the design of rechargeable batteries with highly reversible capacity and long-term cycle stability.
Nano Letters 04/2010; 10(5):1710-6. · 13.20 Impact Factor
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Small 12/2009; 5(23). · 8.35 Impact Factor
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ABSTRACT: A simple analytical model is established for the development of hemisphere electronics, which has many important applications in electronic-eye cameras and related curvilinear systems. The photodetector arrays, made in planar mesh layouts with conventional techniques, are deformed and transferred onto a hemisphere. The model gives accurately the positions of photodetectors on the hemisphere, and has been validated by experiments and finite element analysis. The results also indicate very small residual strains in the photodetectors. The model provides a tool to define a pattern of photodetectors in the planar, as-fabricated layout to yield any desired spatial configuration on the hemisphere.
Applied Physics Letters 11/2009; 95(18):181912-181912-3. · 3.84 Impact Factor
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Jianliang Xiao,
Simon Dunham,
Ping Liu,
Yongwei Zhang,
Coskun Kocabas,
Lionel Moh,
Yonggang Huang, Keh-Chih Hwang,
Chun Lu,
Wei Huang,
John A Rogers
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ABSTRACT: Single-walled carbon nanotubes (SWNTs) possess extraordinary electrical properties, with many possible applications in electronics. Dense, horizontally aligned arrays of linearly configured SWNTs represent perhaps the most attractive and scalable way to implement this class of nanomaterial in practical systems. Recent work shows that templated growth of tubes on certain crystalline substrates yields arrays with the necessary levels of perfection, as demonstrated by the formation of devices and full systems on quartz. This paper examines advanced implementations of this process on crystalline quartz substrates with different orientations, to yield strategies for forming diverse, but well-defined horizontal configurations of SWNTs. Combined experimental and theoretical studies indicate that angle-dependent van der Waals interactions can account for nearly all aspects of alignment on quartz with X, Y, Z, and ST cuts, as well as quartz with disordered surface layers. These findings provide important insights into methods for guided growth of SWNTs, and possibly other classes of nanomaterials, for applications in electronics, sensing, photodetection, light emission, and other areas.
Nano Letters 11/2009; 9(12):4311-9. · 13.20 Impact Factor
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ABSTRACT: Materials and design strategies for stretchable silicon integrated circuits that use non-coplanar mesh layouts and elastomeric substrates are presented. Detailed experimental and theoretical studies reveal many of the key underlying aspects of these systems. The results shpw, as an example, optimized mechanics and materials for circuits that exhibit maximum principal strains less than 0.2% even for applied strains of up to approximately 90%. Simple circuits, including complementary metal-oxide-semiconductor inverters and n-type metal-oxide-semiconductor differential amplifiers, validate these designs. The results suggest practical routes to high-performance electronics with linear elastic responses to large strain deformations, suitable for diverse applications that are not readily addressed with conventional wafer-based technologies.
Small 10/2009; 5(24):2841-7. · 8.35 Impact Factor
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ABSTRACT: Materials and methods to achieve electronics intimately integrated on the surfaces of substrates with complex, curvilinear shapes are described. The approach exploits silicon membranes in circuit mesh structures that can be deformed in controlled ways using thin, elastomeric films. Experimental and theoretical studies of the micromechanics of such curvilinear electronics demonstrate the underlying concepts. Electrical measurements illustrate the high yields that can be obtained. The results represent significant experimental and theoretical advances over recently reported concepts for creating hemispherical photodetectors in electronic eye cameras and for using printable silicon nanoribbons/membranes in flexible electronics. The results might provide practical routes to the integration of high performance electronics with biological tissues and other systems of interest for new applications.
Small 10/2009; 5(23):2703-9. · 8.35 Impact Factor
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Sang-Il Park,
Yujie Xiong,
Rak-Hwan Kim,
Paulius Elvikis,
Matthew Meitl,
Dae-Hyeong Kim,
Jian Wu,
Jongseung Yoon,
Chang-Jae Yu,
Zhuangjian Liu,
Yonggang Huang, Keh-chih Hwang,
Placid Ferreira,
Xiuling Li,
Kent Choquette,
John A Rogers
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ABSTRACT: We have developed methods for creating microscale inorganic light-emitting diodes (LEDs) and for assembling and interconnecting them into unusual display and lighting systems. The LEDs use specialized epitaxial semiconductor layers that allow delineation and release of large collections of ultrathin devices. Diverse shapes are possible, with dimensions from micrometers to millimeters, in either flat or "wavy" configurations. Printing-based assembly methods can deposit these devices on substrates of glass, plastic, or rubber, in arbitrary spatial layouts and over areas that can be much larger than those of the growth wafer. The thin geometries of these LEDs enable them to be interconnected by conventional planar processing techniques. Displays, lighting elements, and related systems formed in this manner can offer interesting mechanical and optical properties.
Science 09/2009; 325(5943):977-81. · 31.20 Impact Factor
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Advanced Materials 07/2009; 21(36):3703 - 3707. · 13.88 Impact Factor
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ABSTRACT: The tensile deformations and fractures of super carbon nanotubes (STs) are investigated through the atomic-scale finite element method. STs generated from carbon nanotubes (CNTs) with different characteristic aspect-ratioed arms are found to have different nonlinear behaviors in the uniaxial tension process. Specifically, the ST with higher aspect-ratioed arms has three distinct stages: rotation, stretch and rupture, while the ST with lower aspect-ratioed arms has only two stages. Moreover, the local buckling can be only observed in the ST with higher aspect-ratioed arms. This information may lay the foundations for further explorations to the properties of STs in the near future.
Journal of Computational and Theoretical Nanoscience 12/2008; 6(1):41-45. · 0.91 Impact Factor
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ABSTRACT: Electronic systems that offer elastic mechanical responses to high-strain deformations are of growing interest because of their ability to enable new biomedical devices and other applications whose requirements are impossible to satisfy with conventional wafer-based technologies or even with those that offer simple bendability. This article introduces materials and mechanical design strategies for classes of electronic circuits that offer extremely high stretchability, enabling them to accommodate even demanding configurations such as corkscrew twists with tight pitch (e.g., 90 degrees in approximately 1 cm) and linear stretching to "rubber-band" levels of strain (e.g., up to approximately 140%). The use of single crystalline silicon nanomaterials for the semiconductor provides performance in stretchable complementary metal-oxide-semiconductor (CMOS) integrated circuits approaching that of conventional devices with comparable feature sizes formed on silicon wafers. Comprehensive theoretical studies of the mechanics reveal the way in which the structural designs enable these extreme mechanical properties without fracturing the intrinsically brittle active materials or even inducing significant changes in their electrical properties. The results, as demonstrated through electrical measurements of arrays of transistors, CMOS inverters, ring oscillators, and differential amplifiers, suggest a valuable route to high-performance stretchable electronics.
Proceedings of the National Academy of Sciences 12/2008; 105(48):18675-80. · 9.68 Impact Factor
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ABSTRACT: Nix and Gao established an important relation between the microindentation hardness and indentation depth. Such a relation
has been verified by many microindentation experiments (indentation depths in the micrometer range), but it does not always
hold in nanoindentation experiments (indentation depths approaching the nanometer range). Indenter tip radius effect has been
proposed by Qu et al. and others as possibly the main factor that causes the deviation from Nix and Gao's relationship. We
have developed an indentation model for micro- and nanoindentation, which accounts for two indenter shapes, a sharp, conical
indenter and a conical indenter with a spherical tip. The analysis is based on the conventional theory of mechanism-based
strain gradient plasticity established from the Taylor dislocation model to account for the effect of geometrically necessary
dislocations. The comparison between numerical result and Feng and Nix's experimental data shows that the indenter tip radius
effect indeed causes the deviation from Nix-Gao relation, but it seems not be the main factor.
Acta Mechanica Sinica 01/2006; 22(1):1-8. · 0.86 Impact Factor
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ABSTRACT: Due to the enormous difference in the scales involved in correlating the macroscopic properties with the micro- and nano-physical
mechanisms of carbon nanotube-reinforced composites, multiscale mechanics analysis is of considerable interest. A hybrid atomistic/continuum
mechanics method is established in the present paper to study the deformation and fracture behaviors of carbon nanotubes (CNTs)
in composites. The unit cell containing a CNT embedded in a matrix is divided in three regions, which are simulated by the
atomic-potential method, the continuum method based on the modified Cauchy–Born rule, and the classical continuum mechanics,
respectively. The effect of CNT interaction is taken into account via the Mori–Tanaka effective field method of micromechanics.
This method not only can predict the formation of Stone–Wales (5-7-7-5) defects, but also simulate the subsequent deformation
and fracture process of CNTs. It is found that the critical strain of defect nucleation in a CNT is sensitive to its chiral
angle but not to its diameter. The critical strain of Stone–Wales defect formation of zigzag CNTs is nearly twice that of
armchair CNTs. Due to the constraint effect of matrix, the CNTs embedded in a composite are easier to fracture in comparison
with those not embedded. With the increase in the Young’s modulus of the matrix, the critical breaking strain of CNTs decreases.
International Journal of Fracture 07/2005; 134(3):369-386. · 1.49 Impact Factor
