Lamellar subcomponents of the cuticular cell membrane complex of mammalian keratin fibres show friction and hardness contrast by AFM

There is a substantial body of information indicating that 18‐methyleicosanoic acid (18‐MEA) is covalently linked to the outer surface of all mammalian keratin fibres and also forms the outer β‐layer of the cuticular cell membrane complex (CCMC) which separates the cuticle cells from each other. Low cohesive forces are expected between the lipid‐containing outer β‐layer and the δ‐layer of the CCMC, thus providing a weak point for cuticular delamination and presenting a fresh layer of 18‐MEA to the newly exposed surface. We have used lateral force microscopy and force modulation atomic force microscopy (AFM) to examine human hair fibres in which the non‐covalently linked fatty acids have been removed. Examination of the lateral force images of new cuticle surfaces revealed by the attrition of overlying cuticle layers showed three separate zones of clearly defined frictional contrast. These are thought to correspond with the δ‐layer, the proteinaceous epicuticle and outer β‐layers of the CCMC. The δ‐layer was found to have a thickness of 16 nm (SD = 1 nm, n = 25), comparable to the 18.0 nm thickness measured from transverse cross‐sections of fibres with transmission electron microscopy. Force modulation AFM showed that the outer β‐layer was softer than the epicuticle and the δ‐layer. The frictional contrast was removed following treatment with methanolic KOH (0.1 mol dm^?3) at 25 °C for 30 min, suggesting the hydrolysis of the thioester linkage and removal of 18‐MEA from the surface.     

Investigation of human hair fibers using lateral force microscopy

Atomic force microscopy (AFM) and lateral force microscopy (LFM) were used to investigate the morphologic and surface changes associated with various surface modifications to human hair. These included extraction with a series of solvents, bleaching, and treatment with a cationic copolymer. The study assessed the ability of these techniques to distinguish the changes in surface properties, including morphology and friction coefficient, as manifested in changes brought about by the indicated surface modifications. While topographic morphology can easily be investigated with contact AFM. LFM offers an additional tool for probing the surface distribution of oils and waxes. The removal of surface lipids from the fiber surface was accomplished using soxhlet extraction with t-butanol and n-hexane, while the free internal lipids (within the fiber structure) were removed by extraction with a mixture of chloroform and methanol (70:30, v/v). In addition, the surface of hair was modified with the cationic polymer, co(vinyl pyrrolidone-methacrylamidopropyl trimethylammonium chloride [PVP/MAPTAC]), and its distribution on the surface was monitored. Ambient AFM and LFM studies of surface modified and native fibers clearly indicate that when investigated as a function of tip loading force, the different modifications result in changes of the friction coefficient, which increase in this order: native, bleached, solvent extracted, and polymer-treated hair. Friction images show surface variations that are interpreted as areas of varying lipid film coverage. In addition, topographic images of the fibers show the presence of small pores, which become increasingly prevalent upon solvent extraction.     

Atomic force microscopy studies of conditioner thickness distribution and binding interactions on the hair surface

The way in which common hair care products, such as conditioner, deposit onto and change hair properties is of interest in beauty care science, as these properties are closely tied to product performance. The binding interaction between conditioner and the hair surface is one of the important factors in determining the conditioner thickness distribution and consequently the proper functions of conditioner. In this study, atomic force microscopy was used to obtain the local conditioner thickness distribution, adhesive forces and effective Young's modulus mapping of various hair surfaces. The conditioner thickness was extracted by measuring the forces on the atomic force microscopy tip as it approached, contacted and pushed through the conditioner layer. The effective Young's moduli of various hair surfaces were calculated from the force distance curves using Hertz analysis. The intrinsic binding interactions between different silicones and the hair surface on the microscopic scale, as well as their effect on the effective Young's modulus of the hair, are also discussed. It was found that the effective Young's modulus of the hair is strongly affected by the binding of conditioner molecules on the hair surface.     

Morphological, nanomechanical and cellular structural characterization of human hair and conditioner distribution using torsional resonance mode with an atomic force microscope

Characterization of the cellular structure and chemical and physical properties of hair are essential to develop better cosmetic products and advance the biological and cosmetic sciences. Although the morphology of the fine cellular structure of human hair has traditionally been investigated using scanning electron microscopy and transmission electron microscopy, atomic force microscopy can be used for characterization in ambient conditions without requiring specific sample preparations and surface treatment. In this study, the tapping and torsional resonance modes in an atomic force microscope are compared for measurements of stiffness and viscoelastic properties. The materials were mapped using amplitude and phase angle imaging. The torsional resonance mode showed advantages in resolving the in-plane (lateral) heterogeneity of materials. This mode was used for investigating and characterizing the fine cellular structure of human hair. Various cellular structures (such as the cortex and the cuticle) of human hair and fine sublamellar structures of the cuticle, such as the A-layer, the exocuticle, the endocuticle and the cell membrane complex were easily identified. The distribution and thickness of conditioner on the treated hair surface affects the tribological properties of hair. The thickness of the conditioner was estimated using force distance measurements with an atomic force microscope.     

Current-sensing scanning near-field optical microscopy using a metal probe for nanometre-scale observation of electrochromic films

A novel technique for scanning near‐field optical microscopy capable of point‐contact current‐sensing was developed in order to investigate the nanometre‐scale optical and electrical properties of electrochromic materials. An apertureless bent‐metal probe was fabricated in order to detect optical and current signals at a local point on the electrochromic films. The near‐field optical properties could be observed using the local field enhancement effect generated at the edge of the metal probe under p‐polarized laser illumination. With regard to electrical properties, current signal could be detected with the metal probe connected to a high‐sensitive current amplifier. Using the current‐sensing scanning near‐field optical microscopy, the surface topography, optical and current images of coloured WO₃ thin films were observed simultaneously. Furthermore, nanometre‐scale electrochromic modification of local bleaching could be performed using the current‐sensing scanning near‐field optical microscopy. The current‐sensing scanning near‐field optical microscopy has potential use in various fields of nanometre‐scale optoelectronics.     

Anisotropic stick-slip friction of highly oriented thin films of poly(tetrafluoroethylene) at the molecular level

Lateral force microscopy (LFM) studies of poly(tetrafluoroethylene) (PTFE) films with molecular resolution are reported. Thin PTFE layers with a high degree of orientation were obtained by pressing and sliding a block of polymer on a clean, heated muscovite mica substrate. LFM nanographs obtained on these films by scanning at directions between ca. 40 and 90° with respect to the film orientation direction, i.e. with respect to the direction of the polymer chains, showed a stick-slip type frictional motion of the LFM probe tip at the molecular level. The friction force observed at constant load decreased with decreasing scan angles. Chain-chain packing distances obtained by LFM and contact-mode atomic force microscopy were the same to within the experimental error and had a value of 5.8 Å. Dual-mode contact AFM/LFM imaging was also performed by scanning in the chain direction. Here LFM nanographs showed no distinct stick-slip phenomenon. The contact mode AFM images, however, exhibited clear molecular resolution with the expected chain-chain periodicity. The disappearance of the stick component in LFM scans performed in the chain direction was attributed to the smooth surface of PTFE on the molecular scale.     

A versatile multipurpose scanning probe microscope

A combined scanning probe microscope has been developed that allows simultaneous operation as a non‐contact/tapping mode atomic force microscope, a scattering near‐field optical microscope, and a scanning tunnelling microscope on conductive samples. The instrument is based on a commercial optical microscope. It operates with etched tungsten tips and exploits a tuning fork detection system for tip/sample distance control. The system has been tested on a p‐doped silicon substrate with aluminium depositions, being able to discriminate the two materials by the electrical and optical images with a lateral resolution of 130 nm.     

Characterization of the cutting edge of glass and diamond knives for ultramicrotomy by scanning force microscopy using cantilevers with a defined tip geometry. Part II

The cutting edge of glass as well as diamond knives was studied at high resolution using a scanning force microscope (SFM). The local shape of the cutting edge was estimated from single line profiles of the SFM topographs taking into account the exact shape of the probing tip estimated by a high‐resolution field emission scanning electron microscope (FESEM). The glass knives were prepared by ‘balanced breaking’. The radius of the investigated cutting edges was found to be 3.2–4.4 nm and 4.3–6.0 nm for the 35° and 45° diamond knife, respectively, and 3.4–4.3 nm for the glass knives. Besides the opening angle and the cutting edge radius, the friction of a knife during sectioning represents a significant factor influencing the quality of sections. Thus, the roughness of both the diamond clearance angle side and the back side was characterized as well. Corresponding RMS values of the roughness were found to be smaller on the back side (≈ 0.14 nm) than on the clearance angle side (≈ 0.26 nm).     

Different membrane modifications revealed by atomic force/lateral force microscopy after doping of human pancreatic cells with Cd, Zn, or Pb

The interaction of the cytotoxic metals cadmium, zinc, and lead with pancreatic cells was studied by atomic force/lateral Force microscopy (AFM/LFM), an approach that provides both topographic (with nanometer scale lateral resolution) and chemical information on the membrane. Different morphological modifications of the overall cell shape and roughness took place as consequence of 100 muM metal-dependent treatment. Furthermore, after exposure to Cd(Cl(2)) and Zn(Cl(2)), but not Pb(Cl(2)), the LFM images revealed several areas of the cell's surface showing lateral friction contrasts that have been interpreted as marker of different alterations of the cell physiology induced by the metal loading. Thus, the coupling of LFM detection to topographic AFM characterization allows to distinguish, through a nondestructive and surface characterising approach, between different metal-induced cytotoxic effects on cells. In this framework, the role of the LFM as an important tool to discriminate between different alteration of a biological system has to be highlighted.     

The effect of deformation on the lateral resolution of atomic force microscopy

A computer model based on the elastic properties of rubber is introduced for the evaluation of the lateral resolution in atomic force microscopy of deformable specimens. The computational results show that, if the full width at half-height can be defined as the lateral resolution, it is continuously improved at greater probe forces, at the expense of a reduced molecular height. In fact, even for a probe that is bigger than the molecule, the real size of the molecule can be 'recovered' at about 25% compression. This result demonstrates that for a better lateral resolution, a greater probe force can be beneficial, provided that the molecule is not moved or damaged and the response remains elastic. Measurements on isolated low-density lipoproteins (LDL) show that with 26% vertical compression, the lateral size measured in atomic force microscopy is only about 72% of the value predicted by a simple convolution, and is only slightly larger (≈ 13%) than the known size of LDL. Therefore, the results on LDL provide a direct support for the conclusions of the computational model.     

Characterization of the cutting edge of glass knives for ultramicrotomy by scanning force microscopy using cantilevers with a defined tip geometry

The geometry of glass knife edges for ultramicrotomy was studied with nanoscale resolution using scanning force microscopy (SFM) in the contact mode. The local shape of the cutting edge was estimated from single line profiles of the SFM topographic images by taking into account the exact radius of the ultrasharp silicon tip. The tip radius was estimated from secondary electron micrographs recorded at low voltage by field emission scanning electron microscopy (FESEM). The radius of the investigated cutting edges was found to be in range 5–20 nm. The results obtained illustrate that the combination of SFM and high resolution FESEM provides a unique means to determine precisely the radius of glass knives.     

Error analysis and regression mode of the V‐grooved sample in the atomic force microscope simulation measurement mode by the molecular mechanics

Based on the molecular mechanics, this study uses the two‐body potential energy function to construct a trapezoidal cantilever nano‐scale simulation measurement model of contact mode atomic force microscopy (AFM) under the constant force mode to simulate the measurement the nano‐scale V‐grooved standard sample. We investigate the error of offset distance of the cross‐section profile when using the probes with different trapezoidal cantilever probe tip radii (9.5, 8.5, and 7.5 Å) to scan the peak of the V‐grooved standard sample being reduced to one‐tenth (1/10) of its size, and use the offset error to inversely find out the regression equation. We analyze how the tip apex as well as the profile of the tip edge oblique angle and the oblique edge angle affects the offset distance. Furthermore, a probe with a larger radius of 9.5 nm is used to simulate and measure the offset error of scan curve, and acquire the regression equation. By the conversion proportion coefficient of size (ω), and revising the size‐reduced regression equation during the small size scale, a revised regression equation of a larger size scale can be acquired. The error is then reduced, further enhancing the accuracy of the AFM scanning and measurement. SCANNING 31: 147–159, 2009. © 2009 Wiley Periodicals, Inc.     

Macro- and nanotribological properties of organosilane monolayers prepared by a chemical vapor adsorption method on silicon substrates

Organosilane monolayers are novel ultrathin films used to control the physicochemical properties, such as friction and wear, of solid surfaces. In this study, the authors prepared alkylsilane and fluoroalkylsilane monolayers with a series of chain lengths by a chemical vapor adsorption method. The monolayers tribological properties were investigated by lateral force microscope (LFM) and friction tester. LFM nanoscale measurements of tribological properties showed that alkylsilane monolayer gave lower lateral force than the Si substrate surface. The lateral force decreased as the length of the alkyl chain increased. On the macroscale, friction test revealed that the organosilane monolayers gave lower dynamic friction coefficients than the Si substrate surface in air at room temperature. The longer the alkyl chain, the greater the wear resistance of the organosilane monolayers. Friction experiments using tetradecane as a lubricant showed better tribological properties than were obtained in air. Furthermore, microscopically line-patterned two-component organosilane monolayers were prepared and their macroscopic friction behavior was investigated. Even though the height difference between the two-components was less than 1 nm, friction force anisotropy between the parallel and perpendicular directions against the line pattern was observed.     

Bitumen morphologies by phase-detection atomic force microscopy

Bitumen is a complex mixture of hydrocarbons for which microstructural knowledge is incomplete. In an effort to detail this microstructure, 13 bitumens were analysed by phase‐detection atomic force microscopy. Based on morphology, the bitumens could be classified into three distinct groups. One group showed fine domains down to 0.1 µm, another showed domains of about 1 µm, and a third group showed up to four different domains or phases of different sizes and shapes. No correlation was found between the atomic force microscopy morphology and the composition based on asphaltenes, polar aromatics, naphthene aromatics and saturates. A high correlation was found between the area of the ‘bee‐like’ structures and the vanadium and nickel content in bitumen, and between the atomic force microscopy groups and the average size of molecular planes made of fused aromatics. The morphology and the molecular arrangements in bitumen thus appear to be partly governed by the molecular planes and the polarity defined by metallic cations.     

An integrated approach to the study of living cells by atomic force microscopy

We describe a technique for studying living cells with the atomic force microscope (AFM) in tapping mode using a thermostated, controlled-environment culture system. We also describe the integration of the AFM with bright field, epifluorescence and surface interference microscopy, achieving the highest level of integration for the AFM thus far described. We succeeded in the continuous, long-term imaging of relatively flat but very fragile cytoplasmic regions of COS cells at a lateral resolution of about 70 nm and a vertical resolution of about 3 nm. In addition, we demonstrate the applicability of our technology for continuous force volume imaging of cultured vertebrate cells.
The hybrid instrument we describe can be used to collect simultaneously a diverse variety of physical, chemical and morphological data on living vertebrate cells. The integration of light microscopy with AFM and steady-state culture methods for vertebrate cells represents a new approach for studies in cell biology and physiology.     

The effect of an Ni–Cr protective layer on cyclic oxidation of Ti3Al

The effect of an 80Ni?20Cr (at.%) metallic coating on the cyclic oxidation behaviour of a Ti₃Al‐based alloy with the composition Ti?25Al?11Nb (at.%) was investigated in this study. Cyclic oxidation tests were carried out in air at 600 °C and 900 °C for 120 h. For one cycle test, the specimens were held for 24 h at test temperature and then furnace‐cooled to room temperature. The oxidation rate was determined by plotting the mass gain per unit surface area of the specimen vs. exposure time. The morphology and composition of the oxidation products were characterized on the cross‐section of the specimens by scanning electron microscopy, energy‐dispersive X‐ray spectroscopy and atomic force microscopy. The oxidation scale forms during exposure at both 600 °C and 900 °C. TiO₂ is the main oxide component, whereas the Al₂O₃ layer appears only discontinuously. The remarkable improvement in oxidation resistance at 900 °C was attributed to the chemical composition and structure of the scale formed on the 80Ni?20Cr coating.     

Exploring the use of soft X‐ray microscopy for imaging subcellular structures of the inner ear1

The soft X‐ray microscope at the Lawrence Berkeley National Laboratory was developed for visualization of biological tissue. Soft X‐ray microscopy provides high‐resolution visualization of hydrated, non‐embedded and non‐sectioned cells and is thus potentially an alternative to transmission electron microscopy. Here we show for the first time soft X‐ray micrographs of structures isolated from the guinea‐pig inner ear. Sensory outer hair cells and supporting pillar cells are readily visualized. In the hair cells, individual stereocilia can easily be identified within the apical hair bundle. The underlying cuticular plate is, however, too densely composed or too thick to be clearly visualized, and thus appears very dark. The cytoplasmic structures protruding from the cuticular plates as well as the fibrillar material surrounding and projecting from the cell nuclei can be seen. In the pillar cells the images reveal individual microtubule bundles. Soft X‐ray images of the acellular tectorial membrane and thin two‐layered Reissner's membrane display a level of resolution comparable to low‐power electron microscopy.     

Characterization of human ovarian teratoma hair by using AFM, FT-IR, and Raman spectroscopy

The structural, physical, and chemical properties of hair taken from an ovarian teratoma (teratoma hair) was first examined by atomic force microscopy (AFM), Fourier transform infrared (FT-IR), and Raman spectroscopy. The similarities and differences between the teratoma hair and scalp hair were also investigated. Teratoma hair showed a similar morphology and chemical composition to scalp hair. Teratoma hair was covered with a cuticle in the same manner as scalp hair and showed the same amide bonding modes as scalp hair according to FT-IR and Raman spectroscopy. On the other hand, teratoma hair showed different physical properties and cysteic acid bands from scalp hair: the surface was rougher and the adhesive force was lower than the scalp hair. The cystine oxides modes did not change with the position unlike scalp hair. These differences can be understood by environmental effects not by the intrinsic properties of the teratoma hair.     

Calibration of the scanning (atomic) force microscope with gold particles

Scanning force microscopy (SFM) holds great promise for biological research. Two major problems that have confronted imaging with the scanning force microscope have been the distortion of the image and overestimation in measurements of lateral size due to the varying geometry and characteristics of the scanning tip. In this study, spherical colloidal gold particles (10, 20 and 40 nm in diameter) were used to determine (1) tip parameters (size, shape and semivertical angle); (2) the distortion of the image caused by the tip; and (3) the overestimation or broadening of lateral dimensions. These gold particles deviate little in size, are rigid and have a size similar to biological macromolecules. Images of the colloidal gold particles by SFM were compared with those obtained by electron microscopy (EM). The height of the gold particles as measured by SFM and EM was comparable and was little affected by the tip geometry. The measurements of the lateral dimensions of colloidal gold, however, showed substantial differences between SFM and EM in that SFM resulted in an overestimate of the lateral dimensions. Moreover, the distortion of images and broadening of lateral dimensions were specific to the SFM tip used. The calibration of the SFM tip with mica provided little clue as to the type of distortion and the amount of lateral broadening observed when the larger gold particles were scanned. The SFM image also depended on the orientation of the tip with respect to the specimen. Our results suggest that quantitative SFM imaging requires calibration to identify and account for both the distortions and the magnitude of lateral broadening caused by the cantilever tip. Calibration with gold particles is fast and nondestructive to the tip. The raw imaging data of the specimen can be corrected for the tip effect and true structural information can be derived. In summary, we present a simple and practical method for the calibration of the SFM tip using gold particles with a size in the range of biomacromolecules that allows: (1) selection of a cantilever tip that produces an image with minimal distortion; (2) quantitative determination of tip parameters; (3) reconstruction of the shape of the tip at different heights from the tip apex; (4) appreciation of the type of distortion that may be introduced by a specific tip and quantification of the overestimation of the lateral dimensions; and (5) calculation of the true structure of the specimen from the image data. The significance is that such calibration will permit quantitative and accurate imaging with SFM.