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Yafeng Zhang, Jing Zheng, Jiaxin Yu, Hongtu He
Human saliva consists of approximately 98% water and a variety of electrolytes and proteins. Those proteins can be selectively adsorbed onto the enamel surface. The cuticular material formed on the enamel surface is termed acquired salivary pellicle (ASP), which is critical for the health of oral mucosa and teeth. The ASP is composed of a inner layer and a outer layer. The lubricating properties of ASP are closely associated with the inner layer. The aim of this research is to characterize the structural and mechanical properties of the inner layer of ASP...
November 7, 2017: Journal of Biomechanics
Hariprasad Gopalan, Atul H Chokshi
Nacre achieves excellent mechanical properties with a relatively simple hierarchical structure. Analyses suggest that a significant gain in toughness is realized with a modest reduction in strength, with increasing levels of hierarchy. This study probes the role of different hierarchical length scales in governing the strength and modulus of nacre using a combination of bulk compression tests, microindentation and nanoindentation tests. The variability in the measured properties is assessed through Weibull analyses...
October 18, 2017: Journal of the Mechanical Behavior of Biomedical Materials
Furqan A Shah, Adrian Stoica, Carina Cardemil, Anders Palmquist
Cortical bone plays a vital role in determining overall bone strength. We investigate the structural, compositional, and nanomechanical properties of cortical bone following ovariectomy (OVX) of 12 week old Sprague Dawley rats, since this animal model is frequently employed to evaluate the performance of implantable biomaterials in compromised bone healing conditions. Morphological parameters and material properties of bone in the geometrical centre of the femoral cortex were investigated four and eight weeks post-OVX and in unoperated controls (Ctrl), using X-ray micro-computed tomography, backscattered electron scanning electron microscopy, Raman spectroscopy, and nanoindentation...
November 16, 2017: Journal of Biomedical Materials Research. Part A
Zhengzhi Wang, Kun Wang, Wanyin Xu, Xiaoyu Gong, Feiyu Zhang
OBJECTIVES: The local structures and mechanical properties within tooth dentin-enamel-junction (DEJ) regions have been focused for numerous studies. The reported results, however, remain inconsistent particularly on the functional width and gradient architecture of the DEJ. The current study aims at systematically determining the mechanical gradient of the DEJ at different intratooth locations such that a clearer understanding on the tooth properties and the potential correlations with the tooth function could be obtained...
November 11, 2017: Dental Materials: Official Publication of the Academy of Dental Materials
Hansol D Lee, Kamal K Ray, Alexei V Tivanski
Currently, the impact of various phase states of aerosols on the climate is not well understood, especially for submicrometer sized aerosol particles that typically have extended life time in the atmosphere. This is largely due to the inherent size-limitations present in current experimental techniques that aim to directly assess the phase states of fine aerosol particles. Here-in we present a technique that uses atomic force microscopy (AFM) to directly probe for the phase states of individual, submicrometer particles by using nanoindentation and nano-Wilhelmy methodologies as a function of relative humidity (RH) and ambient temperature conditions...
November 14, 2017: Analytical Chemistry
Alexandre Anesi, Marzia Ferretti, Francesco Cavani, Roberta Salvatori, Michele Bianchi, Alessandro Russo, Luigi Chiarini, Carla Palumbo
Clinical advantages of piezosurgery have been already proved. However, few investigations have focused on the dynamics of bone healing. The aim of this study was to evaluate, in adult rabbits, bone regeneration after cranial linear osteotomies with two piezoelectrical devices (Piezosurgery(®) Medical - PM and Piezosurgery(®) Plus - PP), comparing them with conventional rotary osteotomes (RO). PP was characterized by an output power three times higher than PM. Fifteen days after surgery, histomorphometric analyses showed that the osteotomy gap produced with PM and PP was about half the size of that produced by RO, and in a more advanced stage of recovery...
October 12, 2017: Journal of Cranio-maxillo-facial Surgery
Wu-Rong Jian, Liang Wang, Xiaohu Yao, Sheng-Nian Luo
Superplasticity can be achieved in nanoglasses but at the expense of strength, and such a loss can be mitigated via embedding stronger nanocrystals, i.e., forming nanoglass/nanocrystal composites. As an illustrative case, we investigate plastic deformation of Cu<sub>64</sub>Zr<sub>36</sub> nanoglass/nanocrystalline Cu composites during uniaxial tension and nanoindentation tests with molecular dynamics simulations. With increasing fraction of nanocrystalline grains, the tensile strength of the composite is enhanced, while its ductility decreases...
November 9, 2017: Nanotechnology
Michael T Barako, Scott G Isaacson, Feifei Lian, Eric Pop, Reinhold H Dauskardt, Kenneth E Goodson, Jesse Tice
Thermal interface materials (TIMs) are essential for managing heat in modern electronics, and nanocomposite TIMs can offer critical improvements. Here, we demonstrate thermally conductive, mechanically compliant TIMs based on dense, vertically aligned copper nanowires (CuNWs) embedded into polymer matrices. We evaluate the thermal and mechanical characteristics of 20-25% dense CuNW arrays with and without polydimethylsiloxane infiltration. The thermal resistance achieved is below 5 mm(2) K W(-1), over an order of magnitude lower than commercial heat sink compounds...
November 20, 2017: ACS Applied Materials & Interfaces
A Leitner, V Maier-Kiener, D Kiener
Modern nanoindentation devices are capable of dynamic experimentations, which allow us to exploit instrumented hardness tests extensively. Beside the assets of recording mechanical properties continuously over displacement, there are ongoing debates whether the superimposed force alters the material's hardness. We will show for a broad range of materials that significant hardness differences are noted between dynamic and static tests, even for large displacements. Those mainly result from a changing indentation strain-rate during the hold segment at peak load...
November 2017: Materials research letters
Shingo Urata, Yosuke Sato
Molecular dynamics (MD) simulations were applied to construct a plasticity model, which enables one to simulate deformations of soda-lime silica glass (SLSG) by using continuum methods. To model the plasticity, stress induced by uniaxial and a variety of biaxial deformations was measured by MD simulations. We found that the surfaces of yield and maximum stresses, which are evaluated from the equivalent stress-strain curves, are reasonably represented by the Mohr-Coulomb ellipsoid. Comparing a finite element model using the constructed plasticity model to a large scale atomistic model on a nanoindentation simulation of SLSG reveals that the empirical method is accurate enough to evaluate the SLSG mechanical responses...
November 7, 2017: Journal of Chemical Physics
Cheng Huang, Xianghe Peng, Bo Yang, Yinbo Zhao, Shayuan Weng, Tao Fu
In this work, the interaction between dislocation loop (DL) and coherent twin boundary (CTB) in a body-centered cubic (BCC) tantalum (Ta) film during nanoindentation was investigated with molecular dynamics (MD) simulation. The formation and propagation of <111> full DLs in the nanotwinned (nt) Ta film during the indentation was observed, and it was found that CTB can strongly affect the stress distribution in the Ta film, and thus change the motion and type of dislocations. There are three kinds of mechanisms for the interaction between DL and CTB in a twinned BCC Ta film: (i) dislocation absorption, (ii) dislocation desorption, and (iii) direct slip transmission...
November 6, 2017: Nanomaterials
Xiaofei Fu, Chao Liu, Xili Lu, Xianli Li, Jingwei Lv, Famei Wang, Liying Wang
The structure and nanoscale mechanical properties of Ni48.8Mn27.2Ga24 thin film fabricated by DC magnetron sputtering are investigated systematically. The thin film has the austenite state at room temperature with the L21 Hesuler structure. During nanoindentation, stress-induced martensitic transformation occurs on the nanoscale for the film annealed at 823 K for 1 hour and the shape recovery ratio is up to 85.3%. The associated mechanism is discussed.
2017: Scanning
X Ojanen, P Tanska, M K H Malo, H Isaksson, S P Väänänen, A P Koistinen, L Grassi, S P Magnusson, S M Ribel-Madsen, R K Korhonen, J S Jurvelin, J Töyräs
Trabecular bone is viscoelastic under dynamic loading. However, it is unclear how tissue viscoelasticity controls viscoelasticity at the apparent-level. In this study, viscoelasticity of cylindrical human trabecular bone samples (n=11, male, age 18-78 years) from 11 proximal femurs were characterized using dynamic and stress-relaxation testing at the apparent-level and with creep nanoindentation at the tissue-level. In addition, bone tissue elasticity was determined using scanning acoustic microscope (SAM)...
October 13, 2017: Journal of Biomechanics
Cesare Rovera, Carlo A Cozzolino, Masoud Ghaani, Davide Morrone, Richard T Olsson, Stefano Farris
Fundamental physical behaviors of materials at the nanoscale level are crucial when local aspects govern the macroscale performance of nanocomposites, e.g., interface and surface phenomena. Because of the increasing interest in biopolymer nanocomposite coatings for many different applications (e.g., optical devices, displays/screens, and packaging), this work investigates the potential of nanoindentation as a method for clarifying the interplay between distinct phases (i.e., organic and inorganic) at local level in thin biopolymer films loaded with nanoparticles...
October 31, 2017: Journal of Colloid and Interface Science
Przemysław Raczyński, Krzysztof Górny, Violetta Raczyńska, Mateusz Pabiszczak, Zbigniew Dendzik, Zygmunt Gburski
The influence of the single-walled carbon nanotubes on the phospholipid bilayer has been studied using steered molecular dynamics (SMD) simulations. The impact of different nanotubes on the phospholipid bilayer structure is discussed as well as the speed of indentation. Additionally, a series of simulations with pulling out of the nanotubes from the membrane were performed. The deflection of the membrane in both nanoindenation and extraction processes is also discussed. The self-sealing ability of membrane during this process is examined...
October 31, 2017: Biochimica et Biophysica Acta
Debashis Maji, Soumen Das
Crack free electrically continuous metal thin films over soft elastomeric substrates play an integral part in realization of modern day flexible bio-electronics and biosensors. Under non-optimized deposition conditions, delamination and/or cracking of the top film as well as the underlying soft substrate hinders optimal performance of these devices. Hence it is very important to understand and control not only the various deposition factors like power, time or deposition pressure but also investigate the various interfacial physics playing a critical role in assuring thin film adhesion and substrate compliancy...
November 1, 2017: Journal of Biomedical Materials Research. Part A
Huan Li, Jinshan Li, Bin Tang, Jiangkun Fan, Huang Yuan
The intergranular crack propagation of the lamellar structure β titanium alloys is investigated by using a modified Gurson-type damage model. The representative microstructure of the lamellar alloy, which consists of the soft α phase layer surrounding the hard grain interiors, is generated based on an advanced Voronoi algorithm. Both the normal fracture due to void growth and the shear fracture associated with void shearing are considered for the grain boundary α layer. The individual phase properties are determined according to the experimental nanoindentation result and the macroscopic stress-strain curve from a uni-axial tensile test...
October 30, 2017: Materials
Verena Maier-Kiener, Karsten Durst
Nanoindentation became a versatile tool for testing local mechanical properties beyond hardness and modulus. By adapting standard nanoindentation test methods, simple protocols capable of probing thermally activated deformation processes can be accomplished. Abrupt strain-rate changes within one indentation allow determining the strain-rate dependency of hardness at various indentation depths. For probing lower strain-rates and excluding thermal drift influences, long-term creep experiments can be performed by using the dynamic contact stiffness for determining the true contact area...
2017: JOM: the Journal of the Minerals, Metals & Materials Society
Zhixin Zeng, Jin-Chong Tan
The mechanical properties of individual nanocrystals and small micron-sized single crystals of metal-organic frameworks (MOFs), hitherto, cannot be measured directly by employing the conventional instrumented nanoindentation approach. Here we propose the application of atomic force microscopy (AFM)-based nanoindentation technique, equipped with a calibrated diamond cube-corner indenter tip to quantify the Young's modulus, hardness, adhesion energy, and interfacial and fracture strengths of a zeolitic imidazolate framework (ZIF-8) porous material...
November 2, 2017: ACS Applied Materials & Interfaces
Borislav Vasić, Aleksandar Matković, Radoš Gajić
We investigate the phase imaging of supported graphene using amplitude modulation atomic force microscopy (AFM), the so-called tapping mode. The phase contrast between graphene and the neighboring substrate grows in hard tapping conditions and the contrast is enhanced compared to the topographic one. Therefore, phase measurements could enable the high-contrast imaging of graphene and related two-dimensional materials and heterostructures, which is not achievable with conventional AFM based topographic measurements...
October 23, 2017: Nanotechnology
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