Nanomechanical Behavior Research Articles

Bacterial surface appendages strongly impact nanomechanical and electrokinetic properties of Escherichia coli cells subjected to osmotic stress.

The physicochemical properties and dynamics of bacterial envelope, play a major role in bacterial activity. In this study, the morphological, nanomechanical and electrohydrodynamic properties of Escherichia coli K-12 mutant cells were thoroughly investigated as a function of bulk medium ionic strength using atomic force microscopy (AFM) and electrokinetics (electrophoresis). Bacteria were differing according to genetic alterations controlling the production of different surface appendages (short and rigid Ag43 adhesins, longer and more flexible type 1 fimbriae and F pilus). From the analysis of the spatially resolved force curves, it is shown that cells elasticity and turgor pressure are not only depending on bulk salt concentration but also on the presence/absence and nature of surface appendage. In 1 mM KNO3, cells without appendages or cells surrounded by Ag43 exhibit large Young moduli and turgor pressures (∼700–900 kPa and ∼100–300 kPa respectively). Under similar ionic strength condition, a dramatic ∼50% to ∼70% decrease of these nanomechanical parameters was evidenced for cells with appendages. Qualitatively, such dependence of nanomechanical behavior on surface organization remains when increasing medium salt content to 100 mM, even though, quantitatively, differences are marked to a much smaller extent. Additionally, for a given surface appendage, the magnitude of the nanomechanical parameters decreases significantly when increasing bulk salt concentration. This effect is ascribed to a bacterial exoosmotic water loss resulting in a combined contraction of bacterial cytoplasm together with an electrostatically-driven shrinkage of the surface appendages. The former process is demonstrated upon AFM analysis, while the latter, inaccessible upon AFM imaging, is inferred from electrophoretic data interpreted according to advanced soft particle electrokinetic theory. Altogether, AFM and electrokinetic results clearly demonstrate the intimate relationship between structure/flexibility and charge of bacterial envelope and propensity of bacterium and surface appendages to contract under hypertonic conditions.

Nanomechanical characteristics of annealed Si/SiGe superlattices

In this study, the nanomechanical damage was investigated on the annealed Si/SiGe strained-layer superlattices (SLSs) deposited using an ultrahigh-vacuum chemical vapor deposition (UHVCVD). Nanoscratch, nanoindenter, atomic force microscopy (AFM), and transmission electron microscopy (TEM) techniques were used to determine the nanomechanical behavior of the SiGe films. With a constant force applied, greater hardness number and larger coefficients of friction ( μ) were observed on the samples that had been annealed at 600 °C, suggesting that annealing of the Si/SiGe SLSs can induce greater shear resistance. AFM morphological studies of the Si/SiGe SLSs revealed that pile-up phenomena occurred on both sides of each scratch, with the formation of some pellets and microparticles. The Si/SiGe SLSs that had been subjected to annealing under various conditions exhibited significantly different features in their indentation results. Indeed, the TEM images reveal slight dislocation propagation in the microstructures. Thus, the hardness and elastic modulus can be increased slightly after annealing treatment because the existence of comparatively unstable microstructures. It is suggested that cracking phenomena dominate the damage cause of Si/SiGe SLSs.

Effect of the beta‐sheet‐breaker peptide LPFFD on oriented network of amyloid β25‐35 fibrils

Amyloid fibrils are self-associating filamentous structures deposited in extracellular tissue in various neurodegenerative and protein misfolding disorders. It has been shown that beta-sheet-breaker (BSB) peptides may interfere with amyloid fibril assembly. Although BSB peptides are prospective therapeutic agents in amyloidosis, there is ambiguity about the mechanisms and generality of their action. In the present work we analyzed the effect of the BSB peptide LPFFD on the growth kinetics, morphologic, and mechanical properties of amyloid β25-35 (Aβ25-35) fibrils assembled in an oriented array on mica surface. Aβ25-35 is thought to represent the biologically active, toxic fragment of the full-length Aβ peptide. Growth kinetics and morphologic features were analyzed using in situ atomic force microscopy in the presence of various concentrations of LPFFD. We found that the addition of LPFFD only slightly altered the assembly kinetics of Aβ25-35 fibrils. Already formed fibrils did not disassemble in the presence of high concentrations of LPFFD. The mechanical stability of the fibrils was explored with force spectroscopy methods. The nanomechanical behavior of Aβ25-35 fibrils is characterized by the appearance of force staircases which correspond to the force-driven unzipping and dissociation of several protofilaments. In the presence of LPFFD single-plateau force traces dominated. The effects of LPFFD on Aβ25-35 fibril assembly and stability suggest that inter-protofilament interactions were slightly weakened. Complete disassembly of fibrils, however, was not observed. Thus, under the conditions explored here, LPFFD may not be considered as a BSB peptide with generalized beta-sheet breaking properties.

Hardness and Young's modulus distributions in atmospheric plasma sprayed WC–Co coatings using nanoindentation

A statistical indentation analysis of WC–Co coatings obtained by atmospheric plasma spray (APS) with two secondary plasma gases, H 2 and He, was investigated using an instrumented indentation technique with the aim of correlating the influence of the nanomechanical behaviour of each constituent phase with the micromechanical characteristics of these coatings. X-ray diffraction (XRD) and backscattered electron (BSE) analysis showed that H 2 gas produced a greater decarburisation of the WC phase. The dissolution and decomposition of the WC phase during the process produced a Co + W+C solid solution as binder phase and the formation of W 2C and W as secondary phases. The nanohardness ( H) and Young's modulus ( E) resulting from a grid of 300 indentations performed at 50 nm in depth identified the characteristics of each phase in the heterogeneous structure produced by decarburisation. Statistical study by a CDF fit and Gaussian simulated distributions showed that the mechanical properties of the coatings were governed by the binder phase content, which decreased the possible hardening effect of the arising hardest phases (W 2C and Co+W + C solid solution).

Surface and Nanomechanical Behavior of Human Molars Soaked in Sodium Fluoride

Surface and Nanomechanical Behavior of Human Molars Soaked in Sodium Fluoride

Structural Consequences of Epitaxial Assembly Constraints Imposed on Amyloid ß25-35 Fibrils

Amyloid fibrils are filamentous aggregates deposited in extracellular tissue in various neurodegenerative and protein misfolding disorders. Amyloid s (As) peptides form self-associating fibrillar structures in Alzheimer's disease. The As25-35 peptide is thought to represent the biologically active, toxic fragment of the full-length beta peptide.We have previously shown that As25-35 forms an oriented network on mica by epitaxial assembly mechanisms that significantly accelerate fibril growth. Whether the structure of the epitaxially grown fibrils is identical to that of the fibrils assembled under equilibrium conditions is not known. To explore these differences, we investigated fibril structure and dynamics with AFM, force spectroscopic, and fluorescence and absorption spectroscopic methods. To facilitate fluorescence labeling, we employed a mutant peptide, As25-35_N27C, which was labeled with TMRIA. The nanomechanical behavior of As25-35 fibrils was characterized by the appearance of force staircases which correspond to the force-driven unzipping and dissociation of protofilaments. The elementary plateau force was 30 pN for both the epitaxially-grown fibrils and for the fibrils assembled in solution. The average fibril height was 1-3 nm for the epitaxially-grown fibrils, whereas fibrils grown in solution were 3-15 nm thick. Unlike epitaxialy-grown fibrils, the fibrils assembled in solution displayed a helical structure with 30-50 nm periodicity. Whereas fibril assembly in solution occurred on a time scale of hours to days, on mica surface fibrils appeared within a few minutes. In the absorption spectra of TMRIA-labeled As25-35_N27C, a significant peak at 518 nm corresponding to rhodamine dimmers appeared rapidly, suggesting that peptide dimerization is a fast process, and the rate limiting step of fibril growth lies further along the assembly pathway.

Thermal annealing effect on the nanomechanical properties and structure of P3HT:PCBM thin films

Nanostructured polymer–fullerene thin films are among the most prominent materials for application in high efficient polymer solar cells. Specifically, poly(3-hexylthiophene) (P3HT) and fullerene derivatives (PCBM) blends are used as the donor/acceptor materials forming a bulk heterojunction. Although P3HT:PCBM properties have been extensively studied, less light has been set on its nanomechanical properties, which affect the device service life. In this work Atomic Force Acoustic Microscopy (AFAM), Atomic Force Spectroscopy and Nanoindentation were used to study the effect of the fullerene presence and the annealing on the P3HT:PCBM nanomechanical behavior. The P3HT:PCBM thin films were prepared by spin coating on glass substrates and then annealed at 100 °C and 145 °C for 30 min. Large phase separation was identified by optical and Atomic Force Microscopy (AFM) for the annealed samples. Needle-like PCBM crystals were formed and an increase of the polymer crystallinity degree with the increase of the annealing temperature was confirmed by X-ray diffraction. AFAM characterization revealed the presence of aggregates close to stiff PCBM crystals, possibly consisting of amorphous P3HT material. AFM force–distance curves showed a continuous change in stiffness in the vicinity of the PCBM crystals, due to the PCBM depletion near its crystals, and the AFM indentation provided qualitative results about the changes in P3HT nanomechanical response after annealing.

Finite element 3D modeling of mechanical behavior of mineralized collagen microfibrils

The aim of this work is to develop a 3D finite elements model to study the nanomechanical behaviour of mineralized collagen microfibrils, which consists of three phases, (i) collagen phase formed by five tropocollagen (TC) molecules linked together with cross links, (ii) a mineral phase (Hydroxyapatite) and (iii) impure mineral phase, and to investigate the important role of individual properties of every constituent. The mechanical and the geometrical properties (TC molecule diameter) of both tropocollagen and mineral were taken into consideration as well as cross-links, which was represented by spring elements with adjusted properties based on experimental data. In the present paper an equivalent homogenised model was developed to assess the whole microfibril mechanical properties (Young's modulus and Poisson's ratio) under varying mechanical properties of each phase. In this study both equivalent Young's modulus and Poisson's ratio which were expressed as functions of Young's modulus of each phase were obtained under tensile load with symmetric and periodic boundary conditions.

Nano mechanical properties of an automotive clear-coats containing nano silica particles with different surface chemistries

Different nano-silica particles were incorporated in an automotive OEM clear-coat based on acrylic-melamine chemistry. A neat and three silane-treated nano-silica particles were added to the clear-coat. Treated grades were coated by dimethyl dichloro silane, hexamethyl disilane and methacryl silane, respectively. The scratch/mar resistances of the heat-cured films were investigated using nano-indentation hardness measurements. It was found that there is a close relationship between the surface chemistry of silica nano-particles and nano mechanical behavior of the baked films. Adding the above-mentioned nano-silica particles to the clear coat resulted in higher elastic modulus and indentation hardness. The most significant effect was observed in samples containing silica particles coated with dimethyl dichloro silane and carrying acidic surface hydroxyl groups.

Influence of 8DSS Peptide on Nano-mechanical Behavior of Human Enamel

Aspartate-serine-serine (DSS) repeats are abundant in naturally occurring proteins that are critical for tooth formation. We recently developed octuplet repeats of aspartate-serine-serine (8DSS) peptides to promote the nucleation of calcium phosphate carbonate from free ions. In this paper, we report a possible role of 8DSS in promoting mineral deposition onto human enamel. Human enamel specimens were demineralized, exposed briefly to 8DSS solution, and then exposed to simulated body fluid that favors mineral deposition. At various stages of treatment, nano-mechanical behaviors, namely, hardness and elastic modulus, were determined by nano-indentation. Nano-indentation results showed that 8DSS treatment effectively improved the mechanical and elastic properties of demineralized enamel. The values of hardness and elastic modulus for the 8DSS-treated enamel were significantly higher than those of surfaces without 8DSS treatment. Furthermore, 8DSS peptides promoted the uniform deposition of nano-crystalline calcium phosphate carbonate over demineralized enamel surfaces and reduced surface roughness of demineralized enamel.

Nano-mechanical properties of individual mineralized collagen fibrils from bone tissue

Mineralized collagen fibrils (MCFs) are distinct building blocks for bone material and perform an important mechanical function. A novel experimental technique using combined atomic force microscopy and scanning electron microscopy is used to manipulate and measure the mechanical properties of individual MCFs from antler, which is a representative bone tissue. The recorded stress-strain response of individual MCFs under tension shows an initial linear deformation region for all fibrils, followed by inhomogeneous deformation above a critical strain. This inhomogeneous deformation is indicative of fibrils exhibiting either yield or strain hardening and suggests possible mineral compositional changes within each fibril. A phenomenological model is used to describe the fibril nano-mechanical behaviour.

Nanomechanical behaviour of Al-Ti layered composites produced by accumulative roll bonding

In this study Ti-foils were roll bonded together with commercially pure aluminium AA1050. The laminates were produced by using two 1 mm thick AA1050 sheets at the outer side of the stack combined with 100 μm thick Ti-foils as an intermediate layer for each accumulative roll bonding process. The samples were rolled up to 4 ARB cycles. Subsequently the sheets were post-process heat treated at 180°C, 400°C or 600°C, respectively, for 24 hours. The local mechanical behaviour of the Al/Ti intermetallic interfaces have been investigated using nanoindentation experiments. A strong dependence between annealing-temperature, – time and deformation grade is detected. While a heat treatment at 180°C only leads to a weak bonding between Al and Ti with a preservation of the UFG structure, temperatures up to 600°C are causing a complete recrystallisation of the microstructure and formation of diffusion layers with different Al and Ti concentrations.

Atomic force microscopy studies on the nanomechanical properties of Saccharomyces cerevisiae

In the past years atomic force microscopy (AFM) techniques have turned out to be a suitable and versatile tool for probing the physical properties of microbial cell surfaces. Besides interaction forces, nanomechanical properties can be obtained from force spectroscopic measurements. Analyzing the recorded force curves by applying appropriate models allows the extraction of cell mechanical parameters, e.g. the Young's modulus or the cellular spring constant. In the present work the nanomechanical properties of the baker's yeast Saccharomyces cerevisiae are extensively studied by force spectroscopy using an AFM. Single cells deform purely elastically so that a cellular spring constant can reliably be determined. It is presented, how this spring constant depends on the probing position on the cell, and how it depends on the extracellular osmotic conditions. Investigations aiming a statistically firm description of the nanomechanical behavior of the yeast cell population are conducted. Finally, the informative value of the cellular spring constant as a cell mechanical parameter is critically discussed.

A model-based approach to compensate for the dynamics convolution effect on nanomechanical property measurement

A model-based approach to compensate for the dynamics convolution effect on the measurement of nanomechanical properties is proposed. In indentation-based approach to measure nanomechanical properties of soft materials, an excitation force consisting of multiple frequencies needs to be accurately exerted (from the probe) to the sample material, and the indentation generated in the sample needs to be accurately measured. However, when the measurement frequency range becomes close to the bandwidth of the instrument hardware, the instrument dynamics along with the probe-sample interaction can be convoluted with the mechanical behavior of the soft material, resulting in distortions in both the applied force and the measured indentation, which, in turn, directly lead to errors in the measured nanomechanical properties of the material (e.g., the creep compliance). In this article, the dynamics involved in indentation-based nanomechanical property measurement is investigated to reveal that the convoluted dynamics effect can be described as the difference between the lightly damped probe-sample interaction and the overdamped nanomechanical behavior of the soft sample. Thus, these two different dynamics effects can be decoupled via numerical fitting based on the viscoelastic model of the soft material. The proposed approach is illustrated by implementing it to compensate for the dynamics convolution effect on a broadband viscoelasticity measurement of a polydimethylsiloxane sample using a scanning probe microscope.

Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin exposure on bone material properties

Dioxins are known to decrease bone strength, architecture and density. However, their detailed effects on bone material properties are unknown. Here we used nanoindentation methods to characterize the effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on nanomechanical behaviour of bone matrix. Pregnant rats were treated with a single intragastric dose of TCDD (1 μg/kg) or vehicle on gestational day 11. Tibias of female offspring were sampled on postnatal day (PND) 35 or 70, scanned at mid-diaphysis with pQCT, and evaluated by three-point bending and nanoindentation. TCDD treatment decreased bone mineralization ( p<0.05), tibial length ( p<0.01), cross-sectional geometry ( p<0.05) and bending strength ( p<0.05). Controls showed normal maturation pattern between PND 35 and 70 with decreased plasticity by 5.3% and increased dynamic hardness, storage and complex moduli by 26%, 13% and 12% respectively ( p<0.05), while similar maturation was not observed in TCDD-exposed pups. In conclusion, for the first time, we demonstrate retardation of bone matrix maturation process in TCDD-exposed animals. In addition, the study confirms that developmental TCDD exposure has adverse effects on bone size, strength and mineralization. The current results in conjunction with macromechanical behaviour suggest that reduced bone strength caused by TCDD is more associated with the mineralization and altered geometry of bones than with changes at the bone matrix level.

Nanoscopic mechanical anisotropy in hydrogel surfaces.

The bulk mechanical properties of soft materials have been studied widely, but it is unclear to what extent macroscopic behavior is reflected in nanomechanics. Using an atomic force microscopy (AFM) imaging method called force spectroscopy mapping (FSM), it is possible to map the nanoscopic spatial distribution of Young's modulus, i.e. "stiffness," and determine if soft or stiff polymer domains exist to correlate nano- and macro-mechanics. Two model hydrogel systems typically used in cell culture and polymerized by a free radical polymerization process, i.e. poly (vinyl pyrrolidone) (PVP) and poly(acrylamide) (PAam) hydrogels, were found to have significantly different nanomechanical behavior despite relatively similar bulk stiffness and roughness. PVP gels contained a large number of soft and stiff nanodomains, and their size was inversely related to crosslinking density and changes in crosslinking efficiency within the hydrogel. In contrast, PAam gels displayed small nanodomains occuring at low frequency, indicating relatively uniform polymerization. Given the responsiveness of cells to changes in gel stiffness, inhomogeneities found in the PVP network indicate that careful nanomechanical characterization of polymer substrates is necessary to appreciate complex cell behavior.

J0206-1-1 分子動力学法を用いたアクチンフィラメントの引張・ねじれ剛性評価([J0206-1]生命体統合シミュレーション(1))

It is essential to investigate the nanomechanical behavior of cytoskeletal actin filaments in order to understand their critical role as mechanical components in various cellular functional activities. These actin filaments consisting of monomeric molecules function in the thermal fluctuations. Hence, it is important to understand their mechanical behavior on the microscopic scale by comparing the stiffness based on thermal fluctuations with the one experimentally measured on the macroscopic scale. In this study, we perform a large-scale molecular dynamics (MD) simulation for a half-turn structure of an actin filament. We analyzed its longitudinal and twisting Brownian motions in equilibrium and evaluated its apparent extensional and torsional stiffness on the nanosecond scale. Upon increasing the sampling-window durations for analysis, the apparent stiffness gradually decreases and exhibits a trend to converge to a value that is close to the experimental value.

Scale-dependent nanomechanical behavior and anisotropic friction of nanotextured silicon surfaces

Nanoscale surface texturing of silicon was accomplished by oblique Ar+ ion beam irradiation. Atomic force microscope (AFM) imaging showed that nanotexturing produced an anisotropic morphology consisting of ordered nanometer-sized ripples. Surface force microscope (SFM) measurements showed that the nanotextured surface exhibited scale-dependent nanomechanical behavior during indentation loading/unloading and anisotropic sliding friction, significantly different from those of the original (untextured) surface. AFM and SFM results showed a strong dependence of the nanoindentation response and friction coefficient on the tip radius and sliding direction relative to the ripple orientation. The observed experimental trends are interpreted in terms of the applied normal load, real contact area, interfacial adhesion force, tip-ripple interaction scale, and ripple orientation.

Evaluation of the nanoindentation behaviors of SiGe epitaxial layer on Si substrate

In this paper, ultra-high vacuum chemical vapor deposition (UHV/CVD) was employed to synthesize silicon–germanium (SiGe), and sequence to endure annealing treatment. Morphological characterization, roughness, and microstructural morphology were observed by means of scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The elements distribution, crystallographic, and nanomechanical behavior were carried out using energy-dispersive X-ray spectroscopy (EDS) mapping technique, X-ray diffraction (XRD), and nanoindentation technique. The annealing treated SiGe leads to the 2D germanium segregation on the surface. The phenomenon is interpreted in terms of dislocation-induced structural changes in annealing treatment. Thus, the dislocation propagation in the microstructure was observed. Subsequently hardness and elastic modulus were increased because of a comparatively unstable microstructure after annealing treatment.

In Situ and Ex Situ Nanomechanical Analysis of Reactive Nanolayer Solder Joints

The nanomechanical behavior of NiAl derived from explosively RNLs in reactive solder joints is studied using in situ nanocompression and nanoindentation. We report the direct analysis of slip and discuss the role it plays in the much disputed ductility of NiAl. The hardness, modulus, and residual stress in the NiAl layer are studied by load-displacement curve analysis.