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Mechanical compression

Zhiqiang Zhao, Hang Yin, Kun Cai, Wanqi Zhou
The mechanical properties of black phosphorus (BP) are anisotropic. Correspondingly, the properties of the nanotubes formed by bending the same BP ribbon along different directions are different as well. When bending the ribbon along the [110] direction (i.e., stair direction), or along its perpendicular direction (i.e., ps-direction), s- or ps-BPNT can be obtained. The two types of BPNTs are investigated via molecular dynamics (MD) simulations on their thermal and mechanical properties. The results indicate that, for the thermal stability of the s-BPNTs with similar diameters, s-BPNT is weaker than a-BPNTs (armchair type) but stronger than ps-BPNT, and z-BPNT (zigzag type) is the weakest one...
January 15, 2018: Physical Chemistry Chemical Physics: PCCP
Khaja Moiduddin
The traditional methods of metallic bone implants are often dense and suffer from adverse reactions, biomechanical mismatch and lack of adequate space for new bone tissue to grow into the implant. The objective of this study is to evaluate the customized porous cranial implant with mechanical properties closer to that of bone and to improve the aesthetic outcome in cranial surgery with precision fitting for a better quality of life. Two custom cranial implants (bulk and porous) are digitally designed based on the Digital Imaging and Communications in Medicine files and fabricated using additive manufacturing...
January 1, 2018: Proceedings of the Institution of Mechanical Engineers. Part H, Journal of Engineering in Medicine
Yi Hua, Andrew P Voorhees, Ian A Sigal
Purpose: To model the sensitivity of the optic nerve head (ONH) biomechanical environment to acute variations in IOP, cerebrospinal fluid pressure (CSFP), and central retinal artery blood pressure (BP). Methods: We extended a previously published numerical model of the ONH to include 24 factors representing tissue anatomy and mechanical properties, all three pressures, and constraints on the optic nerve (CON). A total of 8340 models were studied to predict factor influences on 98 responses in a two-step process: a fractional factorial screening analysis to identify the 16 most influential factors, followed by a response surface methodology to predict factor effects in detail...
January 1, 2018: Investigative Ophthalmology & Visual Science
Xuhui Zhang, Xiyu Liu, Zedong Yan, Jing Cai, Fei Kang, Shuai Shan, Pan Wang, Mingming Zhai, X Edward Guo, Erping Luo, Da Jing
Repetitive fatigue loading can induce microdamage accumulation in bone matrix, which results in impaired mechanical properties and increased fracture susceptibility. However, the spatial distribution and time-variant process of microdamage accumulation in fatigue-loaded skeleton, especially for linear microcracks which are known to initiate bone remodeling, remain not fully understood. In this study, the time-varying process of the morphology and distribution of microcracks in rat ulnae subjected to uniaxial compressive fatigue loading was investigated...
January 10, 2018: Bone
Masoumeh Ozmaian, David Jasnow, Afshin Eskandari Nasrabad, Anton Zilman, Rob D Coalson
The effect of cohesive contacts or, equivalently, dynamical cross-linking on the equilibrium morphology of a polymer brush infiltrated by nanoparticles that are attracted to the polymer strands is studied for plane-grafted brushes using coarse-grained molecular dynamics and approximate statistical mechanical models. In particular, the Alexander-de Gennes (AdG) and Strong Stretching Theory (SST) mean-field theory (MFT) models are considered. It is found that for values of the MFT cross-link strength interaction parameter beyond a certain threshold, both AdG and SST models predict that the polymer brush will be in a compact state of nearly uniform density packed next to the grafting surface over a wide range of solution phase nanoparticle concentrations...
January 14, 2018: Journal of Chemical Physics
Shier Nee Saw, Jess Yi Ru Low, Citra Nurfarah Zaini Mattar, Arijit Biswas, Lujie Chen, Choon Hwai Yap
Intrauterine growth restriction is a prevalent disease in pregnancy in which placental insufficiency leads to 5 to 10 times higher mortality and lifelong morbidities. The current detection rate is poor, and recently, ultrasound strain elastography (USEL) was proposed as a new diagnostic technique. Currently, placental USEL uses maternal subcutaneous fat as the reference layer, but this is not ideal as fat tissue stiffness can vary widely between subjects. Current USEL also uses manual palpation, and under different compression depths and rates, viscoelastic tissues such as placenta can yield different stiffness results...
January 9, 2018: Ultrasound in Medicine & Biology
André D R Silva, Willian R Rigoli, Denise Osiro, Daphne C R Mello, Luana M R Vasconcellos, Anderson O Lobo, Eliria M J A Pallone
The modification of biomaterials approved by the Food and Drug Administration could be an alternative to reduce the period of use in humans. Porous bioceramics are widely used as support structures for bone formation and repair. This composite has essential characteristics for an implant, including good mechanical properties, high chemical stability, biocompatibility and adequate aesthetic appearance. Here, three-dimensional porous scaffolds of Al2 O3 containing 5% by volume of ZrO2 were produced by the replica method...
January 12, 2018: Journal of Biomedical Materials Research. Part B, Applied Biomaterials
Laetitia Vincent, Doriane Djomani, Mariam Fakhfakh, Charles Renard, Benoit Belier, Daniel Bouchier, Gilles Patriarche
We report on an unprecedented formation of allotrope heterostructured Si nanowires by plastic deformation based on applied radial compressive stresses inside a surrounding matrix. Si nanowires with standard diamond structure (3C) undergo a phase transformation toward the hexagonal 2H-allotrope. The transformation is thermally activated above 500°C and is clearly driven by a shear-stress relief occurring in parallel shear-bands lying on {115} planes. We have studied the influence of temperature and axial orientation of nanowires The observations are consistent with a martensitic phase transformation but the finding leads to a clear evidence of a different mechanism of deformation-induced phase transformation in Si nanowires with respect to their bulk counterpart...
January 12, 2018: Nanotechnology
Fernando Hallwass, Rubens R Teles, Erich Hellemann, Christian Griesinger, Roberto R Gil, Armando Navarro-Vázquez
Mechanical compression of polymer gels provides a simple way for the measurement of Residual Chemical Shift Anisotropies (RCSAs), which then can be employed, on its own, or in combination with Residual Dipolar Couplings (RDCs), for structural elucidation purposes. RCSAs measured using compression devices needed a posteriori correction to account for the increase of the polymer to solvent ratio inside the swollen gel. This correction has been cast before in terms of a single free parameter which, as shown here, can be simultaneously optimized along with the components of the alignment tensor while still retaining discriminating power of the different relative configurations as illustrated in the stereochemical analysis of α-santonin and 10-epi-8-deoxycumambrin B...
January 11, 2018: Magnetic Resonance in Chemistry: MRC
Pascal G Yot, Vibhav Yadav, Salem Ould Amara, Jean-Paul Itiè, Umit B Demirci, Guillaume Maurin
Crystalline B-N-H compounds of low molecular weight have been intensively investigated over the past two decades owing to their promises for chemical hydrogen storage. Hydrazine borane NH2-NH2-BH3 is one of the most recent examples of this family of materials. In the present work, we explored its structural behaviour under mechanical stimulus by synchrotron high pressure X-ray diffraction. It has been evidenced that hydrazine borane shows a gradual pressure-induced decrease of its unit cell dimension and the process is reversible when the applied pressure is released...
January 12, 2018: Physical Chemistry Chemical Physics: PCCP
Seong Soo Yoo, Gwan H Choi, Wooseop Lee, Juhyun Park, Gi-Ra Yi, Du Yeol Ryu, Pil J Yoo
Wrinkling is a well-known example of instability-driven surface deformation that occurs when the accumulated compressive stress exceeds the critical value in multilayered systems. A number of studies have investigated the instability conditions and the corresponding mechanisms of wrinkling deformation. Force balance analysis of bilayer systems, in which the thickness of the capping layer is importantly considered, has offered a useful approach for the quantitative understanding of wrinkling. However, it is inappropriate for multilayer wrinkling (layer number > 3) consisting of heterogeneous materials (e...
January 12, 2018: Soft Matter
Michael R Jones, Joshua Yue, Angela K Wilson
Improper signaling of the nuclear factor-κB (NF-κB) pathway plays a critical role in many inflammatory disease states including cancer, stroke, and viral infections. Although the signaling pathways are known, how these molecular mechanisms respond to changes in the intracellular microenvironment such as pH, ionic strength, and temperature, remains elusive. Molecular dynamics simulations were employed to differentiate the structural dynamics of the NF-kB Inducing Kinase (NIK), a protein kinase responsible for invoking the non-canonical NF-κB pathway, in its native and mutant form, and in the absence and presence of salt concentration in efforts to probe whether changes in the ionic environment stabilize or destabilize the NIK dimer...
January 8, 2018: Journal of Structural Biology
Xinjie Wu, Yingna Qi, Feng Yang, Mingsheng Tan, Jie Lin
BACKGROUND: Thymic carcinoid with spinal metastasis is an extremely rare entity. Clinically, the tumor presents either by its endocrine manifestations or by mechanical compression of surrounding structures. However, no previous studies reported a case with neck pain, and neurological deficit as initial presentation of an atypical thymic carcinoid. METHOD: A 56-year-old non-smoking man presented with 12-month history of intermittent neck pain and 1-month history of progressive numbness and weakness of the right upper limb...
January 8, 2018: World Neurosurgery
Yasar Ozturk, Ismail Bozkurt, Mesut Emre Yaman, Yahya Guvenc, Tolga Tolunay, Deniz Billur, Fatma Kubra Erbay, Salim Senturk, Gokhan Bozkurt
BACKGROUND: Epidural fibrosis is a challenging topic in spinal surgery. This phenomenon constitutes one of the the main reasons behind "post-laminectomy syndrome" or "failed-back surgery syndrome", which leads to persistent back and leg pain in association with compression and/or stretching the nerve root or the dura. The exact mechanism of action in epidural fibrosis is complex and remains uncertain. Excessive deposition of collagen, fibronectin, and dermatan sulfate known as "extracellular matrix", and decrease of tissue cellularity results in epidural fibrosis...
January 8, 2018: World Neurosurgery
Tapabrata Maity, Anushree Dutta, Parijat Pallab Jana, Konda Gokuldoss Prashanth, Jürgen Eckert, Jayanta Das
The present study demonstrates the evolution of eutectic microstructure in arc-melted (Zr0.76Fe0.24)100-xNbx (0 ≤ x ≤ 10 atom %) composites containing α-Zr//FeZr₂ nano-lamellae phases along with pro-eutectic Zr-rich intermetallic phase. The effects of Nb addition on the microstructural evolution and mechanical properties under compression, bulk hardness, elastic modulus, and indentation fracture toughness (IFT) were investigated. The Zr-Fe-(Nb) eutectic composites (ECs) exhibited excellent fracture strength up to ~1800 MPa...
January 11, 2018: Materials
Stuart A Young, Stephen E Sherman, Tyler T Cooper, Cody Brown, Fraz Anjum, David A Hess, Lauren E Flynn, Brian G Amsden
A promising strategy for treating peripheral ischemia involves the delivery of stem cells to promote angiogenesis through paracrine signaling. Treatment success depends on cell localization, retention, and survival within the mechanically dynamic intramuscular (IM) environment. Herein we describe an injectable, in situ-gelling hydrogel for the IM delivery of adipose-derived stem/stromal cells (ASCs), specifically designed to withstand the dynamic loading conditions of the lower limb and facilitate cytokine release from encapsulated cells...
January 4, 2018: Biomaterials
Kimberly Hamilton, Brandon Rocque, Nathaniel Brooks
BACKGROUND: Deer hunting is popular in much of the United States. In Wisconsin, use of tree stands for hunting is common. Spine surgeons at a Level 1 Trauma Center observed a high incidence of spine and spinal cord injury due to falls from tree stands while hunting. This study's purpose is to systematically characterize and classify those injuries. METHODS: We reviewed the University of Wisconsin Hospital and Clinics' trauma database for tree stand-related injuries from 1999 to 2013...
November 2017: WMJ: Official Publication of the State Medical Society of Wisconsin
Shin-Ichi Fujiwara
Deducing the scapular positions of extinct tetrapod skeletons remains difficult, because the scapulae and rib cage are connected with each other not directly by skeletal joint, but by thoracic muscles. In extant non-testudine quadrupedal tetrapods, the top positions of the scapulae/suprascapulae occur at the anterior portion of the rib cage, above the vertebral column and near the median plane. The adequacy of this position was tested using three-dimensional mechanical models of Felis, Rattus and Chamaeleo that assumed stances on a forelimb on a single side and the hindlimbs...
January 11, 2018: Journal of Anatomy
Anne-Marie Pobloth, Sara Checa, Hajar Razi, Ansgar Petersen, James C Weaver, Katharina Schmidt-Bleek, Markus Windolf, Andras Á Tatai, Claudia P Roth, Klaus-Dieter Schaser, Georg N Duda, Philipp Schwabe
Three-dimensional (3D) titanium-mesh scaffolds offer many advantages over autologous bone grafting for the regeneration of challenging large segmental bone defects. Our study supports the hypothesis that endogenous bone defect regeneration can be promoted by mechanobiologically optimized Ti-mesh scaffolds. Using finite element techniques, two mechanically distinct Ti-mesh scaffolds were designed in a honeycomb-like configuration to minimize stress shielding while ensuring resistance against mechanical failure...
January 10, 2018: Science Translational Medicine
Fiachra E Rowan, Amanda Wach, Timothy M Wright, Douglas E Padgett
Mechanically assisted crevice corrosion (MACC) is a mechanism for trunnion damage in total hip arthroplasties (THAs). Retrieval studies have shown reduced MACC-related damage for ceramic heads compared with cobalt-chromium (CoCr) heads. We propose that ceramic heads demonstrate fretting at higher cyclic compressive loads than CoCr heads on titanium alloy trunnions in a simulated corrosion model. A closed electrochemical chamber was used to measure fretting current onset loads for two modern titanium alloy trunnions (Zimmer 12/14 and Stryker V-40) in which trunnion failure has been reported...
January 10, 2018: Journal of Orthopaedic Research: Official Publication of the Orthopaedic Research Society
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