Nanomechanical Behavior Research Articles

Nanomechanical Deformation Behavior of Amyloid Fibrils

Amyloid fibrils playing a role in disease expression have recently been found to exhibit excellent mechanical properties, which are highly correlated with the biological functions of amyloid fibrils. It has not yet fully understood how amyloid fibrils formed by aggregation of mechanically weak protein chains can exhibit remarkable mechanical properties. In this work, we study the nanomechanical deformation behavior of amyloid fibrils using steered molecular dynamics simulations. It is shown that the length scale of amyloid fibrils is a key factor in determining the nanomechanical deformation mechanisms of amyloid fibrils and their resulting nanomechanical properties. It is attributed to the competition between shear and bending deformations, which depends on the length scale of amyloid fibrils. The length-dependent elastic property of amyloid fibrils has been elucidated based on Timoshenko beam model. Our study sheds light on the importance of the length scale of amyloid fibrils for understanding their nanomechanical properties.

Structure and Nano-Mechanics of DNA during the Initial Stages of Methyl-Directed Mismatch Repair

DNA undergoing replication is a mechanically complex system on which mismatch repair machinery must not only identify errors on a concurrently replicating / supercoiling DNA molecule but also signal the information along the crowded DNA molecule to excision / re-synthesis elements. In the methyl-directed (dam/mutH-dependent) mismatch repair pathway in E. coli, if errors in newly-replicated DNA are detected by MutS, MutH will nick transiently hemi-methylated d(GATC) sites on the daughter strand in response to activating signals from MutS and MutL to initiate repair. The nearest d(GATC) may be over 1000 base-pairs away from the error, and the mechanics of how MutH-activating signals are transmitted along DNA remain poorly understood-- most models focus on efforts by MutS/MutL complexes to contact latent MutH waiting on the DNA. Using a suite of single-molecule tools (atomic force microscopy, single molecule force spectroscopy, and tethered particle motion), we directly investigate the structure, forces, and nano-mechanical behavior of individual DNA undergoing the initial stages of repair. To understand how d(GATC) sites are identified after a replication error is found, we observe and biophysically characterize the looping of individual DNA molecules by MutS and the structure of MutS/MutL/MutH complexes on DNA, and record both the mechanical strength of interactions between complexes of MutS, MutL, and MutH and with DNA and the resulting structure of the DNA molecule. Potential application and extension of these biophysical techniques to MutH-independent and mammalian mismatch repair systems will also be discussed.

Nanomechanical behavior of 3D porous metal–ceramic nanocomposite Bi/Bi2O3 films

The nanomechanical properties of three-dimensional (3D) porous metal/metal oxide composite (Bi/Bi2O3) films grown by direct current electrodeposition have been studied by nanoindentation at two different loading rates. The synthesized films exhibit a mixture of crystallographic phases of metallic Bi and α-Bi2O3, as evidenced by X-ray diffraction. An in-situ compaction of the sample during the nanoindentation assays has been observed. This in-situ compaction has an influence over both the hardness and elastic modulus of the material, being more important on the latter and, therefore, on the determination of the degree of porosity of the composite film. The influence of the loading rate on the mechanical properties has been investigated. In addition, time-dependent deformation processes (creep tests) have been also performed, revealing an anelastic behavior irrespective of the loading rate. From these creep tests, a viscoelastic non-Newtonian behavior of the sample is evidenced, which is well-described by a three-element Voigt model.

Nanomechanical behavior of yttria stabilized zirconia (YSZ) based thermal barrier coating

In the present study, the detailed evaluation of nanomechanical properties in terms of hardness and Young׳s modulus of duplex and compositionally graded YSZ based thermal barrier coating (TBC) have been evaluated by nanoindentation technique. Duplex and compositionally graded TBCs have been fabricated by thermal spray deposition technique. As TBCs are commonly applied for high temperature protection, effect of isothermal treatment in air (at 900°C and 1000°C) on nanomechanical properties has also been evaluated. Finally, the mechanical properties have been correlated with characteristics of the coating. The hardness and Young׳s modulus of the TBCs are found to increase with increased duration of thermal exposure. Modulus of resilience and resistance to plastic deformation of the duplex and compositionally graded TBC have also been evaluated at room temperature and with thermal exposure and discussed in detail.

Effect of Indentation Size and Strain Rate on Nanomechanical Behavior of Ti-6Al-4VAlloy

Nanoindentation experiments were carried out at strain rates of 0.05, 0.10, 0.15 and 0.20/s at indentation depths of 1000, 1500 and 2000 nm to investigate the nanomechanical behaviour of Ti-6Al-4V alloy. The strain rate had little influence on nanohardness, however, nanohardness as well as Young’s modulus gradually decreased with the increase of indentation depth indicating strong indentation size effects. The relation between H2 and 1/h exhibited a good linear relationship, and it is observed that the effect of strain gradient on σ/σ0 is significant at high strain rates according to Nix and Gao strain gradient model. The analysis of plastic behaviour revealed that, strain rates had no significant effect on strain hardening exponent, but had little influence on yield stress.

Influence of temperature and hot corrosion on the micro–nanomechanical behavior of protective mullite EBCs

Materials for components installed in the hot section of gas turbines must endure highly aggressive conditions, such as elevated temperatures and corrosive environments. Under these scenarios, CVD mullite coatings enriched in alumina in the outer surface have demonstrated excellent thermal stability and protection to SiC against corrosion and recession. It is essential that, in addition to the excellent protective behavior exhibited by Al-rich mullite coatings, their structural integrity and mechanical properties can be retained after their exposure to such aggressive conditions. This investigation is devoted to the study of the effect of temperature and hot-corrosion on the main micro–nanomechanical properties and performance of mullite-based EBCs. Nanoindentation was conducted to determine coatings' hardness, stiffness and fracture toughness whereas nanoscratch tests allowed evaluating their intrinsic structural integrity. Temperature and corrosion were found to have a minor effect on the mechanical behavior of the studied coatings. Hardness and Young's modulus remained comparable after thermal treatments, and scratch tests show similar damage features. From these results it can be concluded that mullite-based coatings present a satisfactory structural integrity and reliability to be used as environmental barrier coatings for hot environments.

A Review On Tribology Of Surfaces And Interfaces

Tribological study includes surface interaction and mechanism involve between contacts. At contact points, surface forces affect the geometry and properties of material whereas stress concentration affects processes that involve during friction interactions. Nanomechanical behaviour of thin-film and surfaces has been largely studied during past years in the field of electronics industry such as microelectronics, optoelectronics application, aerospace industry, iron and steel industries and also adapted in the field of biological sector that likely to grow in near future extensively. High resolution microscope and computational techniques enable the material to investigate their interfacial problems at nanoscale. In this, we studied mechanism of tribology, with different deposition technique and their mechanical properties. Copyright © 2014 VBRI press.

Nanomechanical phenotype of chondroadherin-null murine articular cartilage

Chondroadherin (CHAD), a class IV small leucine rich proteoglycan/protein (SLRP), was hypothesized to play important roles in regulating chondrocyte signaling and cartilage homeostasis. However, its roles in cartilage development and function are not well understood, and no major osteoarthritis-like phenotype was found in the murine model with CHAD genetically deleted (CHAD−/−). In this study, we used atomic force microscopy (AFM)-based nanoindentation to quantify the effects of CHAD deletion on changes in the biomechanical function of murine cartilage. In comparison to wild-type (WT) mice, CHAD-deletion resulted in a significant ≈70–80% reduction in the indentation modulus, Eind, of the superficial zone knee cartilage of 11weeks, 4months and 1year old animals. This mechanical phenotype correlates well with observed increases in the heterogeneity collagen fibril diameters in the surface zone. The results suggest that CHAD mainly plays a major role in regulating the formation of the collagen fibrillar network during the early skeletal development. In contrast, CHAD-deletion had no appreciable effects on the indentation mechanics of middle/deep zone cartilage, likely due to the dominating role of aggrecan in the middle/deep zone. The presence of significant rate dependence of the indentation stiffness in both WT and CHAD−/− knee cartilage suggested the importance of both fluid flow induced poroelasticity and intrinsic viscoelasticity in murine cartilage biomechanical properties. Furthermore, the marked differences in the nanomechanical behavior of WT versus CHAD−/− cartilage contrasted sharply with the relative absence of overt differences in histological appearance. These observations highlight the sensitivity of nanomechanical tools in evaluating structural and mechanical phenotypes in transgenic mice.

Nano-mechanical behavior of a green ultra-high performance concrete

As a revolutionary construction material, ultra-high performance concrete (UHPC) has been extensively studied in the last two decades and one research interest has been focused on preparing UHPC with low-priced raw materials or industrial by-products. In this study, a green UHPC which used high volumes of fly ash and river sand as part of raw materials was prepared, and the objective is to investigate the nano-mechanical behavior of the UHPC using nanoindentation. The results show that the hydration products, which account for about half of the paste by volume, are mainly high-stiffness hydrate phases, and significant quantities of unreacted cement and fly ash have higher mechanical properties than the hydration products and can function as micro-aggregates to strengthen the UHPC paste. Moreover, the mechanical properties of the paste near aggregate or fiber surfaces are similar to those of the bulk paste, which indicates that the UHPC has a strong and efficient bond at the interfacial zone. The experimental findings at the nano-scale could help to understand the macro-performance of the green UHPC.

Nanomechanical behavior of (1 0 0) oriented titanium thin films

Titanium thin films were deposited on single crystal Si (3 1 1) and polycrystalline 316 LN nuclear grade stainless steel substrates by RF magnetron sputtering. X-ray diffraction revealed that, irrespective of substrate type, films exhibit preferential growth along the (1 0 0) plane. The microstructure of the films corresponds to the zone-I type in structure zone model on both substrates. The hardness and Young's modulus of the films were extracted from load-displacement curves. The maximum values of hardness and Young's modulus were 12 and 132 GPa respectively for 220 nm thin film on SS substrate. The electrical resistivity data revealed that the films are metallic in nature and the resistivity is lower in the case of the 220 nm thickness film, on both substrates. The observed changes in mechanical and electrical properties can be correlated with variations in the microstructure of Ti films.

A coupling atomistic–continuum approach for modeling mechanical behavior of nano-crystalline structures

In this article, a novel approach is presented for the concurrent coupling of continuum---atomistic model in the nano-mechanical behavior of atomic structures. The study is focused on the static concurrent multi-scale simulation, which is able to effectively capture the surface effects intrinsic in the molecular mechanics modeling. The Hamiltonian approach is applied to combine the continuum and molecular models with the same weight in the overlapping domain. A Lagrange-multiplier method is employed over the overlapping domain for coupling the continuum nodal displacement with the atomic lattice deformation. A multiple-step algorithm is developed to decouple the solution process in the atomic and continuum domains. The mass and stiffness matrices of continuum domain are computed based on the linear bridging map of the atomic lattice displacement, laid underneath the continuum grid to the element displacements. Numerical simulation results present that the stress and displacement contours of the presented coupling method are in good agreement with those obtained from the molecular mechanics simulation.

Hardness enhancement of PEO-treated Mg alloy for biodegradable implants

In recent times, magnesium alloys have emerged as a possible biodegradable implant material. Plasma electrolytic oxidation (PEO) has been used in the past as a useful surface treatment technique to improve wear resistance and corrosion resistance of magnesium alloys by forming protective coatings. This study focuses on the effect of electrolyte solution on the microstructural and nanomechanical behavior of PEO coatings for possible use in biodegradable implants. Microstructural characterization of the coating was carried out by X-ray diffraction (XRD), scanning electron microscopy followed by image analysis and energy dispersive X-ray spectroscopy. Furthermore, nanoindentation was used to evaluate nanohardness of the PEO coatings. The results show beneficial effects of the PEO coating to improve the hardness of the uncoated AZ31 magnesium alloy. The XRD pattern shows that the crystal structures of the film vary based on electrolyte solution and the effect that has on nanomechanical behavior. In conclusion, this article shows the possible benefit of PEO coating for biodegradable implant use.

A concurrent multi-scale modeling for dynamic behavior of nano-crystalline structures

In this paper, a new multi-scale technique is developed for concurrent coupling of atomistic-continuum domains in modeling nano-mechanical behavior of atomic structures. A Lagrange multiplier method is employed over an overlapping domain to coupling the continuum nodal velocities with atomic lattice velocities. The Hamiltonian method is applied to combine the continuum and molecular Hamiltonians with the same weight in the overlapping domain. The mass and stiffness matrices of the continuum domain are obtained using a linear bridging map of the atomic lattice displacement laid underneath the continuum grid to the element displacements. Numerical examples are performed by presenting the stress and displacement distributions over the continuum and molecular domains in both coupling and molecular dynamic methods where a good agreement is perceived. A comparison of two methods at the surface, demonstrates the capability of the coupling method to practically consider the surface effects. Also, an illustration of energy distribution along the time and domain approves the capability of the represented method to thoroughly eliminate the spurious wave reflection at the atomic-continuum interface.

Special Section on Mechanics of Nanocomposites and Nanostructures

This special section includes a selection of original research papers focused on the mechanics of nanocomposites and nanostructures. The September issue includes the first set of papers on the subject. Most of the papers were also presented at the Nanomechanics and Nanocomposites Symposium at the 2012 Conference of the Engineering Mechanics Institute of the American Society of Civil Engineers held at Notre Dame University in South Bend, Indiana. The Nanomechanics and Nanocomposites Symposium provided a unique venue for researchers exploring the intersections of applied and computational mechanics within the field of materials science at the nanoscale. In this area, there are both tremendous challenges and opportunities. It is humbling to consider the limitations of our current knowledge about the structures and properties of materials at the smaller scales. On the other hand, it is bewildering to consider all of the possibilities for breakthroughs in the engineering disciplines that might be achieved by understanding our world and employing that knowledge to make advances in the materials we use. Although this symposium featured papers on a wide variety of topics, mechanics of materials at the nanoscale was a dominant theme discussed. Indeed, four of the five papers in this first series were devoted entirely to nanomechanical behavior of materials, and a majority of the remaining papers also focused, at least in part, on aspects of nanomechanics. Accordingly, we are pleased to publish this collection of papers in the similarly themed Journal of Nanomechanics and Micromechanics. We believe these papers represent some of the wide scope seen in the field.

In-situ observation of nanomechanical behavior arising from critical-temperature-induced phase transformation in Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 thin film

In this Letter, we use the nanoindentation technique and vary the testing temperature to above and below critical values to study the nanomechanical features of a strong Pb-free piezoelectric Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 (BZT-0.5BCT) thin film across its piezoelectric-optimal morphotropic phase boundary. The mechanisms responsible for the Young's modulus and hardness evolution are then discussed. An X-ray diffraction method that can detect the d(110) variation associated with the change in the inclination angle ψ of the (110) plane was developed to quantify the residual stress in the BZT-0.5BCT films.

Morphological and Nanomechanical Behavior of Supported Lipid Bilayers on Addition of Cationic Surfactants

The addition of surfactants to lipid bilayers is important for the modulation of lipid bilayer properties (e.g., in protein reconstitution and development of nonviral gene delivery vehicles) and to provide insight on the properties of natural biomembranes. In this work, the thermal behavior, organization, and nanomechanical stability of model cationic lipid-surfactant bilayers have been investigated. Two different cationic surfactants, hexadecyltrimethylammonium bromide (CTAB) and a novel derivative of the amino acid serine (Ser16TFAc), have been added (up to 50 mol %) to both liposomes and supported lipid bilayers (SLBs) composed by the zwitterionic phospholipid DPPC. The thermal phase behavior of mixed liposomes has been probed by differential scanning calorimetry (DSC), and the morphology and nanomechanical properties of mixed SLBs by atomic force microscopy-based force spectroscopy (AFM-FS). Although DSC thermograms show different results for the two mixed liposomes, when both are deposited on mica substrates similar trends on the morphology and the mechanical response of the lipid-surfactant bilayers are observed. DSC thermograms indicate microdomain formation in both systems, but while CTAB decreases the degree of organization on the liposome bilayer, Ser16TFAc ultimately induces the opposite effect. Regarding the AFM-FS studies, they show that microphase segregation occurs for these systems and that the effect is dependent on the surfactant content. In both SLB systems, different microdomains characterized by their height and breakthrough force Fb are formed. The molecular organization and composition is critically discussed in the light of our experimental results and literature data on similar lipid-surfactant systems.

Nanomechanical and Wear Behavior of Microtextured Carbide-Coated CoCrMo Alloy Surfaces

The nanomechanical properties of a CoCrMo medical implant alloy and a novel microtextured carbide-coated CoCrMo alloy (MTCC) surface—hardness and elastic modulus—were examined using nanoindentation. The MTCC surfaces may be a successful alternative bearing material for artificial joints. Understanding the nanomechanical, material properties, and surface morphology of the MTCC–CoCrMo surface are important for designing wear resistant artificial joints. The microtextured carbide surfaces were created using a microwave plasma-assisted chemical vapor deposition reaction (MPCVD). Nanomechanical properties, volumetric wear properties, and surface morphology were measured and used to determine the performance of the conventional CoCrMo alloy and MTCC surfaces (processed for either 2 or 4 h) in static environments and under severe wear conditions. The hardness, elastic modulus, and surface parameters of the 4-h MTCC surfaces were always greater than the 2-h MTCC and CoCrMo alloy surfaces. The nanomechanical properties changed for the CoCrMo alloy and 2-h and 4-h MTCC surfaces after, in contrast to before, wear testing. This indicates that the wear mechanisms affect the nanomechanical results. Overall, the 4-h MTCC surfaces had greater wear resistance than the 2-h MTCC or CoCrMo alloy surfaces.

In situ biosensing of the nanomechanical property and electrochemical spectroscopy of Streptococcus mutans-containing biofilms

This work presents in situ biosensing approaches to study the nanomechanical and electrochemical behaviour of Streptococcus mutans biofilms under different cultivation conditions and microenvironments. The surface characteristics and sub-surface electrochemistry of the cell wall of S. mutans were measured by atomic force microscopy (AFM) based techniques to monitor the in situ biophysical status of biofilms under common anti-pathogenic procedures such as ultraviolet (UV) radiation and alcohol treatment. The AFM nanoindentation suggested a positive correlation between nanomechanical strength and the level of UV radiation of S. mutans; scanning impedance spectroscopy of dehydrated biofilms revealed reduced electrical resistance that is distinctive from that of living biofilms, which can be explained by the discharge of cytoplasm after alcohol treatment. Furthermore, the localized elastic moduli of four regions of the biofilm were studied: septum (Z-ring), cell wall, the interconnecting area between two cells and extracellular polymeric substance (EPS) area. The results indicated that cell walls exhibit the highest elastic modulus, followed by Z-ring, interconnect and EPS. Our approach provides an effective alternative for the characterization of the viability of living cells without the use of biochemical labelling tools such as fluorescence dyeing, and does not rely on surface binding or immobilization for detection. These AFM-based techniques can be very promising approaches when the conventional methods fall short.

Nanoscale Interfacial Interactions of Graphene with Polar and Nonpolar Liquids

While mechanical and frictional properties of graphene in air have been extensively studied, graphene's nanomechanical behavior in liquids, vital for its operation in rechargeable batteries, supercapacitors, and sensors, is still largely unexplored. In this paper, we investigate the nanomechanics of normal (adhesive and elastic) and tangential (friction) forces between a stationary, moving, and ultrasonically excited nanoscale atomic force microscope (AFM) tip and exfoliated few layer graphene (FLG) on SiO2 substrate as a function of surrounding media-air, polar (water), and nonpolar (dodecane) liquids. We find that, while the friction coefficient is significantly reduced in liquids, and is always lower for FLG than SiO2, it is higher for graphene in nonpolar dodecane than highly polar water. We also confirm that in ambient environment the water meniscus dominates high adhesion for both hydrophobic FLG and the more hydrophilic SiO2 surface, with the lowest adhesion observed in liquids, in particular for FLG in dodecane, reflecting the low interface energy of this system. By using nanomechanical probing via ultrasonic force microscopy (UFM), we observed a profound reduction of graphene rippling and increase of graphene-substrate contact area in liquid environment. Friction force dependence on ultrasonic modulation amplitude suggests that dodecane at the graphene interface produces a solid-like "cushion" of approximately 2 nm thickness, whereas, in water immersion, the same dependence shows a remarkable similarity with the ambient environment, confirming the presence of a water meniscus in air, and suggesting negligible thickness of a similar water "cushion" on graphene. Dependence of friction on local environment opens new pathways for friction management in microfluidic and micro- and nanoelectromechanical systems.

ZnO nanoparticles induced effects on nanomechanical behavior and cell viability of chitosan films

The aim of this paper is to develop novel chitosan–zinc oxide nanocomposite films for biomedical applications. The films were fabricated with 1, 5, 10 and 15% w/w of zinc oxide (ZnO) nanoparticles (NPs) incorporated with chitosan (CS) using a simple method. The prepared nanocomposite films were characterized using atomic force microscopy, Raman and X-ray diffraction studies. In addition, nano and micro mechanical properties were measured. It was found that the microhardness, nanohardness and its corresponding elastic modulus increased with the increase of ZnO NP percentage in the CS films. However, the ductility of films decreased as the percentage of ZnO NPs increased. Cell attachment and cytotoxicity of the prepared films at days two and five were evaluated in vitro using osteoblasts (OBs). It was observed that OB viability decreased in films with higher than 5% ZnO NPs. This result suggests that although ZnO NPs can improve the mechanical properties of pure CS films, only a low percentage of ZnO NPs can be applied for biomedical and bioengineering applications because of the cytotoxicity effects of these particles.