Abstract Atomic Force Microscopy Research Articles

Cryopreserved Cells Regeneration Monitored by Atomic Force Microscopy and Correlated With State of Cytoskeleton and Nuclear Membrane.

Atomic force microscopy (AFM) helps to describe and explain the mechanobiological properties of living cells on the nanoscale level under physiological conditions. The stiffness of cells is an important parameter reflecting cell physiology. Here, we have provided the first study of the stiffness of cryopreserved cells during post-thawing regeneration using AFM combined with confocal fluorescence microscopy. We demonstrated that the nonfrozen cell stiffness decreased proportionally to the cryoprotectant concentration in the medium. AFM allowed us to map cell surface reconstitution in real time after a freeze/thaw cycle and to monitor the regeneration processes at different depths of the cell and even different parts of the cell surface (nucleus and edge). Fluorescence microscopy showed that the cytoskeleton in fibroblasts, though damaged by the freeze/thaw cycle, is reconstructed after long-term plating. Confocal microscopy confirmed that structural changes affect the nuclear envelopes in cryopreserved cells. AFM nanoindentation analysis could be used as a noninvasive method to identify cells that have regenerated their surface mechanical properties with the proper dynamics and to a sufficient degree. This identification can be important particularly in the field of in vitro fertilization and in future cell-based regeneration strategies.

Modeling forces between the probe of atomic microscope and the scanning surface

Atomic force microscope (AFM) is usually used to study the properties and surface structure of nanoscale materials. AFMs have three major abilities: force measurement, imaging, and manipulation. In the force measurement, AFM can be used to measure the forces between the probe and the sample as a function of their mutual separation. AFM compared to scanning electron microscope has a single image scan size; also the scanning speed of AFM is also a limitation. AFM images can also be affected by nonlinearity, hysteresis, creep of the piezoelectric material, and cross talk between the x, y, and z axes that may require software enhancement and filtering. Due to the nature of AFM probes, they cannot normally measure steep walls or overhangs in surface. In this study, the force between the Probe of Atomic Microscope and the surface is simulated by using force measurement ability of AFM and artificial neural network. The experimental data are used for training of artificial neural networks. The best model was found to be a feed-forward backpropagation network, with Logsig, Tansig and Tansig transfer functions in successive layers, respectively, and 3 and 2 neurons in the first and second hidden layers. According to the results, the proposed neural network is well capable of modeling the behavior of AFM probes in noncontact mode.

Effect of environmental parameters on the nano mechanical properties of hyaluronic acid/poly(l-lysine) multilayers.

Atomic force microscopy (AFM) was used to determine the mechanical properties as the indentation modulus of native and crosslinked poly(l-lysine) (PLL)/hyaluronic acid (HA) multilayer films by static force measurements. The influence of the surrounding medium on the mechanical properties of the films after preparation is investigated. The indentation modulus of native and crosslinked film was measured at different pH values, ionic strengths and temperatures. The native HA/PLL films, which behave like a physical gel, show the highest values of the indentation modulus for an intermediate pH value and low ionic strength. Any changes in the pH or an increase in the ionic strength/temperature decreases the measured indentation modulus. In contrast, the crosslinked films show an increase by a factor of 80 in the indentation modulus but no response to changes in the pH, ionic strength or temperature; they behave like a chemical gel. The pH, ionic strength and temperature used in this work are close to the in vivo conditions and thus give a fundamental point of view on the nanomechanical response of the PLL/HA films. Furthermore, information about the mechanical properties can be used for the understanding and manipulation of cell adhesion.

The Effect of Anti-aging Peptides on Mechanical and Biological Properties of HaCaT Keratinocytes

Atomic force microscopy (AFM) and fluorescence microscopy was applied to determine the influence of the anti-aging peptides on the morphology and the mechanical properties of keratinocytes. Immortalized human keratinocytes (HaCaT) were treated with two anti-aging bioactive peptides: Acetyl Tetrapeptide-2 and Acetyl Hexapeptide-50 (Lipotec). The AFM measurement of the keratinocyte stiffness were carried after 48 h exposure at an indentation depth of 200 nm. AFM analysis showed increase of the cell stiffness for cells treated with Acetyl Tetrapeptide-2 (P1) in concentration range. Acetyl Hexapeptide-50 (P2) at concentration of 0.05 µg/ml also increased the stiffness of HaCaT cells but at higher concentrations 0.5 and 5 µg/ml cell stiffness was lower as compared to untreated control. Fluorescence microscopy revealed remodeling of actin filaments dependent on the concentration of P2 peptide. The mechanical response of HaCaT cells treated with P2 peptide corresponds to change of transcription level of ACTN1 and SOD2 which activity was expected to be modulated by P2 treatment.

Experimental analysis of rough surface topography and modifying the humidity effect in AFM images to improve the topography quality

Atomic force microscopy (AFM) is one of the most powerful tools for imaging surfaces at the nano-scale. The existence of disruptive forces in the output images that are obtained from AFM in a moist environment causes low-quality images at the nano-scale. Therefore, to enhance the quality of topography, eliminating the effect of these forces is of great importance. For this purpose, increasing accuracy in modeling and simulation of vibration behavior of AFM piezoelectric micro-cantilever (MC) and its comparison with experimental tests is important to improve the quality of images. Using modified couple stress (MCS) and classical theory, this article addresses inhomogeneous four-layered AFM MC considering Timoshenko and Euler-Bernoulli beam models in 2D modeling. In 3D modeling by using the COMSOL software, cantilever frequency and time responses were obtained and compared with different theories including classical and MCS. Laboratory tests were conducted not only to validate results but also to evaluate the effect of humidity on topography image quality in the amplitude mode. Furthermore, using simulation results based on the Timoshenko beam theory and MC behavior prediction, the capillary effect which causes noise in experimental images was filtered and the image quality which is taken by the AFM is improved.

The investigation of fly ash based asphalt binders using atomic force microscope

Atomic Force Microscope (AFM) is a relatively new technique for investigation of construction materials. In this study AFM was used to investigate the interaction of asphalt binder with fly ash. Fly ash is a coal combustion byproduct of electric power utilities having pozzolanic properties and commonly used in Portland cement concrete. In this study, an investigation was made by using different types of fly ash with two types of asphalt binders such as PG 58-28 and PG 64-28. Asphalt microstructure is divided into four subgroups such as Saturates, Aromatics, Resins and Asphaltenes (SARA). These four phases can be distinguished by the atomic force microscope. The interaction of these phases affected by introducing fly-ash was investigated and correlation with rheological properties was observed.

Atomic force microscopy investigation of phase morphology correlated with adhesive properties for modified telechelic natural rubber based-pressure sensitive adhesive

Atomic force microscopy (AFM) is a powerful technique to determine phase morphology and surface mechanical properties of materials. In this research natural rubber was degraded and grafted by malelic anhydride before modification with 3-amino-1,2,4-triazole to obtain modified telechelic natural rubber or modified TNR. It was then blended with cumarone-indene resin at 10, 30, and 50 phr, acting as tackifier. Phase morphology and surface topography were investigated by intermitted AFM. The results showed that tackifier enriched domains were clearly observed in modified TNR matrix after added 30 and 50 phr and the domain sizes were approximately to be the order of micrometer (5–10 µm) which it increased with increasing tackifier content. The intermolecular hydrogen bonding interaction between tackifier and modified TNR was observed by attenuated total reflectance Fourier transform infrared spectroscopy. The adhesive properties (loop tack, peel, and shear strength) were governed by the size of tackifier enriched domains, surface mean roughness and compatibility or interaction between modified TNR rubber and cumarone-indene tackifier resin.

NANOMECHANICS OF THE RUBBER–FILLER INTERFACE

ABSTRACT Atomic force microscope (AFM)–based nanomechanics is one of the most promising tools for accessing the rubber–filler interface while providing not only structural information but also mechanical–property evaluation. An AFM-based static modulus map is used to close in on the understanding of the filler reinforcement effect. As an example, a famous Guth–Gold equation is verified by comparing tensile testing and AFM. Two different novel methods are also introduced to visualize viscoelastic quantities such as storage and loss moduli, loss tangent, relaxation modulus, and viscosity. The difference in segmental dynamics between a rubber matrix and an interfacial region will be reviewed.

Influence of the samarium impurity on the structure and surface morphology of Se95Te5 chalcogenide glassy semiconductor

X-ray diffraction and atomic-force microscopy are used to study the structure and surface morphology of Se95Te5 chalcogenide glassy semiconductor films and the influence exerted on these films by doping with samarium. The parameters of the first sharp diffraction peak (FSDP), observed in X-ray diffraction patterns, are used to determine the numerical values of the local structure parameters, such as the “quasiperiod” of density fluctuations, correlation length [size of medium-range-order (MRO) regions], and nanovoid diameters. In addition, the numerical values of the roughness-amplitude parameters are determined. It is found that the disorder in the atomic structure and the irregularities on the surface of the films under study become more pronounced with increasing percentage content of the samarium impurity.

3D simulation of AFM non-uniform piezoelectric micro-cantilever with various geometries subjected to the tip-sample forces

Atomic force microscope (AFM) is a powerful instrument for investigation of surface topography at different workspaces. It is important to understand the dynamic behavior of AFM to improve its performance. 3D numerical method is suitable in order to simulate experimental conditions. This paper has investigated modeling and dynamic simulation of rectangular, Dagger and V-shaped geometries of AFM piezoelectric micro-cantilever (MC) with two electrode layers in the air environment. For a better understanding of the system dynamic, multi-layer MC dynamic equation has been derived. Euler-Bernoulli beam theory has been used for modeling the AFM cantilever. Hamilton’s principle has been used for the MC modeling and the finite element method (FEM) has been applied for its discretization. In 3D, with respect to the tip-sample forces piezoelectric MC has been simulated via the COMSOL software. The frequency and time responses have been also investigated. The topographies have been performed on different surfaces with various roughness’s types in the tapping and non-contact mode. The results of these two methods have been compared with experimental results. Moreover, the effects of MC geometrical parameters on surfaces topography and frequency responses have been studied and optimal dimensions of topographies have been obtained for each of the beam geometries. Simulations of various tip geometries have been performed in order to examine the effects of tip dimensions on the frequency and time responses. Furthermore, the effect of tip displacement on the frequency response has been investigated for different MC lengths.

Morphological changes induced in erythrocyte membrane by the antiepileptic treatment: An atomic force microscopy study.

Atomic force microscopy (AFM), a powerful characterization tool widely applied in problems in a large range of disciplines of the natural sciences, including cellular biology, was used to obtain information about the morphological changes induced in the erythrocyte membrane at the patients with epilepsy that undergo a long time treatment that operates upon one or several neuronal ionic channels, comparative with a healthy donor. This technique allowed non-invasive imaging of erythrocyte membrane, revealing details and specific characteristics down to the nanometer level with characterization of surface texture parameters, such as average height, average roughness and coefficient of kurtosis at micrometer/nanometer resolution. For the healthy donor the AFM morphology appears to have all the characteristics of a normal red blood cell membrane. Instead, the closer examination of the erythrocytes membrane surface morphology for the samples collected from the patients diagnosed with epilepsy and treated with specific drugs did not reveal similar structures with those obtained for the healthy donor. The nanostructure of the membrane was drastically damaged, depending on the administrated treatment, and probably in time will affect their functionality. Therefore, the anticomital drugs have influence not only at the neuronal level, but also at the red blood cell level.

The effect of surfaces type on vibration behavior of piezoelectric micro-cantilever close to sample surface in a humid environment based on MCS theory

Atomic force microscopy (AFM) has been known as an innovative tool in the fields of surface topography, determination of different mechanical properties and manipulation of particles at the micro- and nanoscales. This paper has been concerned with advanced modeling and dynamic simulation of AFM micro-cantilever (MC) in the amplitude mode in the air environment. To increase the accuracy of the governing equations, modified couple stress theory appropriate in micro- and nanoscales has been utilized based on Timoshenko beam theory in the air environment near the sample surface. Also, to discretize the equations, differential quadrature method has been recommended. In modeling, geometric discontinuities due to the presence of a piezoelectric layer enclosed between two electrode layers and the change in MC cross section when connected to the MC have been considered. In addition to the effect of MC modeling on the accuracy of modeling and vibration amplitude during surface topography, understanding and modeling the environmental forces in the air environment, including van der Waals, capillary and contact forces, are important. This paper has been provided more accurate environmental forces modeling and has been investigated the vibration behavior of piezoelectric MC in the humid environment. Moreover, this paper has been examined the maximum and minimum MC amplitude in the air environment close to the surface with different kinds of topography. The results illustrate that kind of surfaces has effect on the maximum and minimum amplitude due to the decrease or increase in equilibrium MC distance.

Prediction Surface Morphology of Nanostructure Fabricated by Nano-Oxidation Technology.

Atomic force microscopy (AFM) was used for visualization of a nano-oxidation technique performed on diamond-like carbon (DLC) thin film. Experiments of the nano-oxidation technique of the DLC thin film include those on nano-oxidation points and nano-oxidation lines. The feature sizes of the DLC thin film, including surface morphology, depth, and width, were explored after application of a nano-oxidation technique to the DLC thin film under different process parameters. A databank for process parameters and feature sizes of thin films was then established, and multiple regression analysis (MRA) and a back-propagation neural network (BPN) were used to carry out the algorithm. The algorithmic results are compared with the feature sizes acquired from experiments, thus obtaining a prediction model of the nano-oxidation technique of the DLC thin film. The comparative results show that the prediction accuracy of BPN is superior to that of MRA. When the BPN algorithm is used to predict nano-point machining, the mean absolute percentage errors (MAPE) of depth, left side, and right side are 8.02%, 9.68%, and 7.34%, respectively. When nano-line machining is being predicted, the MAPEs of depth, left side, and right side are 4.96%, 8.09%, and 6.77%, respectively. The obtained data can also be used to predict cross-sectional morphology in the DLC thin film treated with a nano-oxidation process.

Active Microcantilevers for High Material Contrast in Harmonic Atomic Force Microscopy

Atomic force microscope (AFM) probes are mechanical beams that can be used to simultaneously map topography and material properties. Upon contact of the tip with the sample surface at each cycle in the intermittent mode, higher harmonics are excited. The harmonics in the vicinity of higher eigenmodes are enhanced and present an amplified response, ultimately carrying information about the material properties. In this paper, active cantilevers with integrated actuation and sensing are used as a basis to create harmonic cantilevers for the signal-to-noise ratio improved measurement of time-varying forces. Focused ion beam milling is used to remove mass from specific areas in the cantilever such that the fundamental and higher eigenmodes are tuned toward each other. Two methods are tested, where the shape and location of mass removal is determined, first by simulation and second through an in situ approach. Higher harmonics of the harmonic cantilevers with piezoresistive deflection sensors indicate a significant response of up to 10% in respect to the first harmonic. The improved material contrast mapping abilities of the modified cantilevers are validated by characterization and AFM images. [2014-0260]

2D and 3D Analyses of Metal Oxide Thin Films Examined by Atomic Force Microscope

Atomic force microscope (AFM) is a useful tool to capture the two- and three-dimensional image of height and size of nanostructured thin film. It operate by measuring the forces between a sharp tip and surface of the measured sample. In addition, AFM is equipped with powerful software for image processing to interpret experimental results in detail. For example, by using the height and scanning length parameters of measured sample, average roughness and root mean square roughness can be evaluated. In the present works, the effect of image flattening process toward the surface roughness and surface fluctuations of metal oxide thin films will be presented. Set of samples were prepared by magnetron sputtering deposition and sol-gel coating techniques. In gas sensor industries using metal oxide thin film, surface roughness of metal oxide thin films are very important in order to improve the sensitivity and respond time of gas sensor. Therefore, optimization of thin film deposition and characterization are very important. The correlation between the three-dimensional image and thin film deposition and image processing parameters will also be presented.

Accurate and Traceable Calibration of the Stiffness of Various AFM Cantilevers

Atomic force microscope (AFM) is widely used to measure nanoforce in the analysis of nanomechanical and biomechanical properties. As the critical factor in the nanoforce measurement, the stiffness of the AFM cantilever must be determined properly. In this paper, an accurate and SI-traceable calibration method is presented to obtain the stiffness of the AFM cantilever in the normal direction. The calibration system consists of a homemade AFM head and an ultra-precision electromagnetic balance. The calibration is based on the Hooke's law i.e. the stiffness is equal to the force divided by the deflection of the cantilever. With this system, three kinds of cantilevers were calibrated. The relative standard deviation is better than 1%. The results of these experiments showed good accuracy and repeatability.

ANALYSIS OF A MECHANICAL STRUCTURE OF A MICROSCOPE SENSOR OF ATOMIC FORCE / ATOMINIŲ JĖGŲ MIKROSKOPO JUTIKLIO MECHANINĖS STRUKTŪROS ANALIZĖ

Atomic Force Microscopy (AFM) is a method that allows obtaining an image of the surface of the sample in high resolution. This article investigates the problems associated with modeling a mechanical structure of a microscope sensor of atomic force.The paper refers to the previous scientists’ works and describes most frequently used methods of modeling, basic equations and a variety of factors that have an influence on the dynamics of the system. Also, the obtained results of earlier works are discussed. Atominės jėgos mikroskopija (AJM) – metodas, leidžiantis gauti ypač didelės skiriamosios gebos tiriamojo bandinio paviršiaus vaizdą. Straipsnyje nagrinėjamos problemos, susijusios su atominių jėgų mikroskopo jutiklio mechaninės struktūros modeliavimu. Remiantis mokslininkų atliktais darbais aprašomi dažniausiai taikomi modeliavimo metodai, pateikiamos pagrindinės lygtys, nagrinėjama įvairių veiksnių įtaka sistemos dinaminėms charakteristikoms, aptariami atliktų tyrimų rezultatai.

Investigation of surface potential in the V-defect region of MBE Cd x Hg1 − x Te film

Atomic-force microscopy is used to investigate the distribution of the contact-potential difference (surface potential) in Cd x Hg1 − x Te epitaxial films grown by molecular-beam epitaxy. Modification of the solid-solution composition near the V-defect results in a variation in the contact-potential difference. It is shown that the solid-solution composition varies by ∼0.05 (2.5 at %) towards increasing mercury content in the V-defect region, and a region of mercury depletion by 0.36 at % is observed at the V-defect periphery. From analysis of the surface-potential distribution, it is shown that the Cd x Hg1 − x Te epitaxial film contains unform V-defects with a diameter less than 1 μm in addition to macroscopic V-defects.

Nano-Contact Force Calculation Method of Different Tip Radius of Curvature and the Specimen Surface of AFM

Atomic Force Microscope (AFM) works by the force between the probe tip and specimen surface. The nanocontact force between the probe tip and specimen surface has an important influence on the detection surface. Base on the analysis of the working principle of the AFM and nanocontact force calculation model, according to Hamaker assumptions, using continuum method established the theoretical contact force model of the AFM tip. the contact force calculation methods of contact pressure in process has been obtained. The variation of the force between the probe tip and specimen surface has been found by calculation model and programming calculation of Matlab. Provide the basis for improving the accuracy of an atomic force microscope surface inspection and error analysis

Effect of the Tip Size on AFM Cantilever Based Force Sensor

Atomic force microscopy (AFM) cantilever is a widely used end effector for precise force sensing and micro-nanomanipulation at small scale. However, in current researches, the effect of the cantilever tip on the force sensing and manipulation accuracy is rarely considered. In this paper, we investigate how the tip size of the end effector affects the measurement accuracy of the cell adhesion force. First, several end effectors with different tip sizes are fabricated from the same AFM cantilever via focused ion beam (FIB) etching. Then, the single cell detachment force is measured at the same experiment condition by these end effectors, respectively. The results indicate that the sensed adhesion force is susceptible to the tip size of the end effector obviously. In addition, the precision of cell manipulation is also regulated by the contact area between the cell and end effector greatly. These findings will benefit our in-depth understanding on the force interaction at small scale and will provide valid reference for the development of high-precision force sensor and manipulation.