Surface Topographical Features Research Articles

Measuring Microtubule Supertwist and Defects by Three-Dimensional-Force-Clamp Tracking of Single Kinesin-1 Motors.

Three-dimensional (3D) nanometer tracking of single biomolecules provides important information about their biological function. However, existing microscopy approaches often have only limited spatial or temporal precision and do not allow the application of defined loads. Here, we developed and applied a high-precision 3D-optical-tweezers force clamp to track in vitro the 3D motion of single kinesin-1 motor proteins along microtubules. To provide the motors with unimpeded access to the whole microtubule lattice, we mounted the microtubules on topographic surface features generated by UV-nanoimprint lithography. Because kinesin-1 motors processively move along individual protofilaments, we could determine the number of protofilaments the microtubules were composed of by measuring the helical pitches of motor movement on supertwisted microtubules. Moreover, we were able to identify defects in microtubules, most likely arising from local changes in the protofilament number. While it is hypothesized that microtubule supertwist and defects can severely influence the function of motors and other microtubule-associated proteins, the presented method allows for the first time to fully map the microtubule lattice in situ. This mapping allows the correlation of motor-filament interactions with the microtubule fine-structure. With the additional ability to apply loads, we expect our 3D-optical-tweezers force clamp to become a valuable tool for obtaining a wide range of information from other biological systems, inaccessible by two-dimensional and/or ensemble measurements.

Restricted cell functions on micropillars are alleviated by surface-nanocoating with amino groups.

ABSTRACTThe topographical and chemical surface features of biomaterials are sensed by the cells, affecting their physiology at the interface. When placed on titanium, we recently discovered osteoblasts attempted caveolae-mediated phagocytosis of the sharp-edged microstructures. This active, energy-consuming process resulted in decreased osteoblastic cell functions (e.g. secretion of extracellular matrix proteins). However, chemical modification with plasma polymerized allylamine (PPAAm) was able to amplify osteoblast adhesion and spreading, resulting in better implant osseointegration in vivo. In the present in vitro study, we analyzed whether this plasma polymer nanocoating is able to attenuate the microtopography-induced changes of osteoblast physiology. On PPAAm, we found cells showed a higher cell interaction with the geometrical micropillars by 30 min, and a less distinct reduction in the mRNA expression of collagen type I, osteocalcin and fibronectin after 24 h of cell growth. Interestingly, the cells were more active and sensitive on PPAAm-coated micropillars, and react with a substantial Ca2+ ion mobilization after stimulation with ATP. These results highlight that it is important for osteoblasts to establish cell surface contact for them to perform their functions.

Photopolymerized Microfeatures Guide Adult Spiral Ganglion and Dorsal Root Ganglion Neurite Growth.

Microtopographical patterns generated by photopolymerization of methacrylate polymer systems will direct growth of neurites from adult neurons, including spiral ganglion neurons (SGNs). Cochlear implants (CIs) provide hearing perception to patients with severe to profound hearing loss. However, their ability to encode complex auditory stimuli is limited due, in part, to poor spatial resolution caused by spread of the electrical currents in the inner ear. Directing the regrowth of SGN peripheral processes towards stimulating electrodes could help reduce current spread and improve spatial resolution provided by the CI. Previous work has demonstrated that micro- and nano-scale patterned surfaces precisely guide the growth of neurites from a variety of neonatal neurons including SGNs. Here, we sought to determine the extent to which adult neurons likewise respond to these topographical surface features. Photopolymerization was used to fabricate methacrylate polymer substrates with micropatterned surfaces of varying amplitudes and periodicities. Dissociated adult dorsal root ganglion neurons (DRGNs) and SGNs were cultured on these surfaces and the alignment of the neurite processes to the micropatterns was determined. Neurites from both adult DRGNs and SGNs significantly aligned to the patterned surfaces similar to their neonatal counterparts. Further DRGN and SGN neurite alignment increased as the amplitude of the microfeatures increased. Decreased pattern periodicity also improved neurite alignment. Microscale surface topographic features direct the growth of adult SGN neurites. Topographical features could prove useful for guiding growth of SGN peripheral axons towards a CI electrode array.

Transparent superhydrophobic coating application to the interlocking clay block for the microbial growth mitigation

Interlocking clay block is of widespread use in many countries due to its less labor-intensive design. The block comprises of considerable amount of pore structures; therefore water can easily penetrate into it causing deterioration by natural weathering as well as the growth of microbes on its surface. In this present work, a transparent, superhydrophobic coating was applied onto the block’s surface to prevent water absorption. The coating which is a poly(methyl hydrogensiloxane) base containing fumed SiO2 nanoparticle was designed to possess surface topographic feature similar to that of the lotus leaf. After coating the block with the superhydrophobic compound, its water absorption decreased from 11.5 to 4.8% and porosity substantially decreased from 22.5 to 9.2%, while bulk and apparent densities did not change. Accelerated weathering test revealed that the coating had good stability. The coated samples exhibited growth inhibition of algae.

Diatom-Inspired Silica Nanostructure Coatings with Controllable Microroughness Using an Engineered Mussel Protein Glue to Accelerate Bone Growth on Titanium-Based Implants.

Silica nanoparticles (SiNPs) have been utilized to construct bioactive nanostructures comprising surface topographic features and bioactivity that enhances the activity of bone cells onto titanium-based implants. However, there have been no previous attempts to create microrough surfaces based on SiNP nanostructures even though microroughness is established as a characteristic that provides beneficial effects in improving the biomechanical interlocking of titanium implants. Herein, a protein-based SiNP coating is proposed as an osteopromotive surface functionalization approach to create microroughness on titanium implant surfaces. A bioengineered recombinant mussel adhesive protein fused with a silica-precipitating R5 peptide (R5-MAP) enables direct control of the microroughness of the surface through the multilayer assembly of SiNP nanostructures under mild conditions. The assembled SiNP nanostructure significantly enhances the in vitro osteogenic cellular behaviors of preosteoblasts in a roughness-dependent manner and promotes the in vivo bone tissue formation on a titanium implant within a calvarial defect site. Thus, the R5-MAP-based SiNP nanostructure assembly could be practically applied to accelerate bone-tissue growth to improve the stability and prolong the lifetime of medical implantable devices.

Micromorphology of AlN Epilayers on Sapphire Substrates

The purpose of this paper was to describe the 3D nano-scaled surface topography of the aluminum nitride on sapphire. The structures were prepared by magnetron sputtering with heating of the sapphire substrate. The dependence of the layers topography on the substrate temperature was presented. Surface appearance was studied by atomic force microscopy (AFM). The quantitative topography data from AFM were used for surface characterization by fractal analysis and statistical parameters. The results of fractal analysis show the correlation of fractal dimension and statistical characteristics of surface topography. The data may contribute to manufacture of AlN thin films with desired surface characteristics.

Sensing of micropillars by osteoblasts involves complex intracellular signaling

Topographical material surface features are sensed by cells and provoke a large range of cellular responses. We recognized earlier, that at micropillar topographies in the range of 5 µm, the osteoblasts attempt to phagocytize the pillars resulted in increased energy requirements and reduced osteoblast marker expression, e.g., collagen type I and osteocalcin. However, the precise cellular signaling transducing the topographic information into the cell and evoking phagocytic processes remained unknown. Here, we could show that the RhoA/ROCK signaling is involved in the transduction of the topography-mediated cellular reactions. After inhibition of ROCK-2 with Y27632 for 24 h, no caveolae-mediated micropillar assembly of the cell membrane domain component caveolin-1 (Cav-1) was found. ROCK inhibition was also able to attenuate the pillar-induced decrease in β-actin. Interestingly, phosphatidylinositol 3-kinase (PI3K) inhibition with LY294002 for 24 h did not influence the Cav-1 clustering on micropillars. Our results illustrate the importance of the integrin down-stream signaling of RhoA/ROCK in the recognition of and adaption to surface microtopographies by osteoblasts and extend our understanding about the complex mechanism of action inside the cells.Graphical abstract

Effect of Enamel Deproteinization in Primary Teeth.

To evaluate and compare the topographical features of enamel surface, etched with different materials. 10 extracted human primary molars were randomly selected and cut and trimmed to 1 mm2. Each group comprised of 10 blocks and the enamel was treated as follows: Group I-35% H3PO4; Group II-5.25% NaOCl + 35% H3PO4 ;Group III-5.25% NaOCl; Group IV no treatment was carried out. All the samples were prepared for Scanning electron microscope analysis. The images were obtained and evaluated for the quality type I-II etching of the enamel surface using Auto-CAD 2011 software. Wilcoxon Signed Ranks Test (p<0.001). The mean surface area of type I and II etching pattern values for Group- I was 39608.18 μm2 and Group- II was 45051.34 μm2. Deproteinization with 5.25% Sodium hypochlorite prior to acid etching could be used to increase the surface area of adhesion of composite material with the tooth surface.

Antibacterial properties of PEKK for orthopedic applications.

Orthopedic implant infections have been steadily increasing while, at the same time, antibiotics developed to kill such bacteria have proven less and less effective with every passing day. It is clear that new approaches that do not rely on the use of antibiotics are needed to decrease medical device infections. Inspired by cicada wing surface topographical features, nanostructured surfaces represent a new approach for imposing antibacterial properties to biomaterials without using drugs. Moreover, new chemistries with altered surface energetics may decrease bacterial attachment and growth. In this study, a nanostructured surface was fabricated on poly-ether-ketone-ketone (PEKK), a new orthopedic implant chemistry, comprised of nanopillars with random interpillar spacing. Specifically, after 5 days, when compared to the orthopedic industry standard poly-ether-ether-ketone (PEEK), more than 37% less Staphylococcus epidermidis were found on the PEKK surface. Pseudomonas aeruginosa attachment and growth also decreased 28% after one day of culture, with around a 50% decrease after 5 days of culture when compared to PEEK. Such decreases in bacteria function were achieved without using antibiotics. In this manner, this study demonstrated for the first time, the promise that nanostructured PEKK has for numerous anti-infection orthopedic implant applications.

Bioinspired Dip Catalysts for Suzuki–Miyaura Cross‐Coupling Reactions: Effect of Scaffold Architecture on the Performance of the Catalyst

AbstractDip catalysts suitable for catalyzing important chemical reactions are designed based on bioinspiration principles and are fabricated using a facile soft lithography technique. Specifically, in this work, leaves from two different plants, Gladiolus dalenii and Amaryllis belladonna are chosen, due to their contrasting surface topographical features. The surface microstructures of these two leaves are replicated on a polymer in order to prepare scaffolds for the fabrication of dip catalysts. The microstructures of these scaffolds are utilized to direct the self‐assembly of Pd nanoparticles according to the surface topographical features. A thin film of polyvinyl alcohol is used to lock the nanoparticles on the surface and prevent them from leaching. The fabricated bioinspired dip catalysts are thoroughly characterized and are demonstrated to be highly efficient for Suzuki–Miyaura cross‐coupling reactions, examined under different experimental conditions. These bioinspired dip catalysts' performance is evaluated based on the percentage yields of the reaction and is correlated with the corresponding surface topographical features to understand the effect of the scaffold architecture on the performance of the catalysts. The developed strategy can be easily adopted to fabricate many more dip catalysts, with intriguing surface features, suitable for catalyzing several other chemical reactions as well.

Relevant Properties for Immobilizing Short Peptides on Biosurfaces

Understanding protein and oligopeptide adsorption on biomaterial surfaces is important to develop new biomaterials with improved properties. The phenomenon of peptide adsorption is determined by many parameters such environmental pH, surface topographical features, surface polarity, peptide structure, and/or surface and peptide electric charges. We assessed the effect of surface and peptide net charges on oligopeptide adsorption on synthetic surfaces under different conditions. We have also assessed the ability of immobilizing peptides on the surface generating covalent bonds or electrostatic attraction. Direct relation between the amount of peptide adsorbed on the surface and the difference in net charge between surface and peptides was determined. No relation between the difference in net charge and the ability to promote covalent bonds between peptide and surface was found. Competitive adsorption experiments confirmed these findings. Understanding the specific interactions during adsorption of peptides onto synthetic surfaces improves our ability to develop strategies for the efficient immobilization of oligopeptides on biomaterial surfaces.

A comparative study on the wear resistance of electrical discharge machined surfaces

ABSTRACTThe properties of the surface were affected by many factors such as the pulse parameters, tool electrode material, and dielectric liquid in electrical discharge machining. Austenitic, dual-phase, and ferritic steel work materials were electrical discharge machined using graphite and copper tool electrodes in hydrocarbon- based oil and water dielectric liquids. Then the surfaces were analyzed regarding sliding friction wear responses on a comparative basis. The results revealed that the surface wear responses are sensitive to the type of the tool electrode material when machining in water dielectric liquid. However, the use of hydrocarbon-based dielectric liquid substantiality suppresses the influence of tool electrode on surface wear response due to excessive carbon release from the cracked dielectric. The machined surface topographical features were also affected due to the used electrical parameters regarding crater size, globular attachments, and microcracks that led significant alterations in sliding friction response. Primarily, weakly bounded globular attachments on the machined surface were dislodged at the initial stages of the friction tests and led higher sliding distances to the steady friction conditions. Finally, the results were compared with the subsurface microstructural properties to comprehend the wear responses.

Micromorphology investigation of GaAs solar cells: case study on statistical surface roughness parameters

The purpose of this work is surface characterization of GaAs solar cell using atomic force microscopy. The surface appearance influences the optical properties of the cells. It impacts light trapping and consequently affect the efficiency of the solar cells. In case of nano-structural surface, the properties are strongly depends on its geometrical characteristics. Surface appearance was studied by atomic force microscopy (AFM). Fractal analysis was done by the triangulation method and evaluation of statistical metrics was carrying out on the basis of AFM-data, before and after heating. The results of fractal analysis show the correlation of fractal dimension and statistical characteristics of surface topography. Characterization technique and data processing methodology are essential for description of the surface condition.

Surface topographical analysis of geomembranes and sands using a 3D optical profilometer

Understanding the stress-displacement response of granular materials and their interfaces with geosynthetics through surface topographical analysis is evolving as a new area of potential interest. Recent developments in optical techniques coupled with digital image recording have enabled the measurement of the surface topographical features of sand particles and geosynthetics, which can be applied to measure the shear-induced surface changes in geomembranes. This paper presents one of the latest, advanced surface measurement techniques based on coherence correlation interferometry using a 3D optical profilometer. An experimental technique was developed to measure the surface topography of sand particles, and the shear-induced surface changes in a smooth geomembrane caused by sand particles of different mean sizes, in interface direct shear tests. As the measured surfaces consisted of form and waviness along with roughness, appropriate filters were applied to remove form and waviness and measure the roughness of the surfaces. The selection of these filters for different cases and the spatial variability of surface roughness measurements are discussed. The results of the surface topographical analysis of sand particles of three different sizes, geomembranes sheared by sands of three different mean sizes, and their repeatability, are presented. The stress-displacement response of the sand–geomembrane interfaces is correlated to the surface changes on sheared geomembranes through visual observations and roughness quantifications.

Effects of surface pre-treatments on Mode I and Mode II interlaminar strength of CFRP/Mg laminates

In this work, three different surface modification techniques, including grit blasting, micro-arc oxidation (MAO) and laser ablation, were respectively carried out on magnesium alloy sheets, and then the treated surfaces were evaluated for surface topography and surface roughness characteristics. Besides, the interlaminar strength and the interface failure characteristics of the CFRP/Mg laminates were examined, in order to comprehensively analyze the effects of the various pre-treatment techniques on interlaminar strength and fracture mechanisms of the CFRP/Mg laminates under Mode I (peel) and Mode II (shear) loading. The results show that the MAO treatment resulted in a slight increase of shear strength when compared with grit blasted surfaces, yet it yields worse peel strength outcome due to the weak MAO coating/Mg substrate interface. The laser ablation effectively enhances the overall interlaminar strength of the CFRP/Mg laminates under peel and shear loading.

Topographical orientation effects on surface stresses influencing on wear in sliding DLC contacts, Part 2: Modelling and simulations

The effects of surface roughness and topographical orientation on surface stresses influencing wear have been investigated for diamond like carbon (DLC) coated steel surfaces with three levels of surface roughness in the range of 0.004–0.11μm Ra values, and with topographical groove orientations of 0°, 45° and 90°. A novel multiscale numerical finite element method (FEM) model was developed to integrate the layered and microstructural material features with the grooved topography. Fractal geometry and a surface voxelisation based approach were utilised to derive 3D surface topography. The surface texture representation includes: fractal signatures, which are sets of fractal dimensions calculated at individual scales in different directions, texture aspect ratio describing surface anisotropy, and texture direction signatures calculated by the variance orientation transform (VOT) method. The simulations show details of the main topographical orientation effects on local stresses affecting wear as they appear at a single scratch test with a spherical diamond ball and in a self-mated sliding situation of two rough surfaces. The 45° sliding direction in relation to grooves resulted in a mixed state of surface loading in the scratch test contact. In the complex state of stress-strain within the roughness peaks the overall tensile stress decreased, leading to greater surface resistance to cracking as compared to 0° and 90° directions. Model based calculations showed that the surface structure was about four times more rigid in the direction of grooves as compared to the more flexible behaviour in the perpendicular direction. This behaviour was empirically confirmed. The numerical calculations of rough vs rough sliding surface include real surface topographical features at various scales, material microstructural features down to nano-scale and topographical-microstructural interaction features. This approximation is thus more comprehensive than the classical approach. The real area of contact was 15–30% of the apparent contact area. The macro-topography dominated the tendency for surface cracking and plastic deformation, which is influencing on both wear and friction, while the micro-topographical features contributed to cracking and deformation by less than 40%.

Contact mechanics of the human finger pad under compressive loads.

The coefficient of friction of most solid objects is independent of the applied normal force because of surface roughness. This behaviour is observed for a finger pad except at long contact times (greater than 10 s) against smooth impermeable surfaces such as glass when the coefficient increases with decreasing normal force by about a factor of five for the load range investigated here. This is clearly an advantage for some precision manipulation and grip tasks. Such normal force dependence is characteristic of smooth curved elastic bodies. It has been argued that the occlusion of moisture in the form of sweat plasticises the surface topographical features and their increased compliance allows flattening under an applied normal force, so that the surfaces of the fingerprint ridges are effectively smooth. While the normal force dependence of the friction is consistent with the theory of elastic frictional contacts, the gross deformation behaviour is not and, for commonly reported values of the Young's modulus of stratum corneum, the deformation of the ridges should be negligible compared with the gross deformation of the finger pad even when fully occluded. This paper describes the development of a contact mechanics model that resolves these inconsistencies and is validated against experimental data.

Mixed morphology nanocrystalline cellulose from sugarcane bagasse fibers/poly(lactic acid) nanocomposite films: synthesis, fabrication and characterization

Fully green nanocomposite films with excellent mechanical properties were prepared using mixed morphology nanocrystalline cellulose obtained by the dual acid hydrolysis of sugarcane bagasse fibers as the reinforcing and poly(lactic acid) (PLA) as the matrix member. Sugarcane bagasse fibers were subjected to alkaline pretreatment and bleaching for de-lignification and partial acid hydrolysis resulting in the formation of microcrystalline cellulose (MCC). Nanocrystalline cellulose (NCC) was obtained by the dual acid hydrolysis of MCC using sulfuric acid and hydrochloric acid followed by ultrasonication. The nanocomposite films were solution cast from chloroform in varied compositions. Mixed morphology and surface topography characteristics of NCC and PLA/NCC films were established using microscopic studies. Changes in the functionality and molecular chemistry with subsequent treatments in the fibers were evaluated using FTIR. NCC exhibited better dispersion characteristics, increased crystallinity and rendered thermally stable from room temperature to 230 °C. Degradation profiles of samples were obtained from thermogravimetry, while the reinforcing effects of NCC in PLA were established by analyzing crystallization characteristics from X-ray diffraction studies. X-ray diffraction was utilized to estimate the increase in crystalline constituents and their state. The increase in tensile strength of the films confirmed the increased and effective positive interaction at the matrix–filler interfaces.

Approaches for Controlled Ag+ Ion Release: Influence of Surface Topography, Roughness, and Bactericide Content.

Silver is the most famous bactericidal element known from ancient times. Its antibacterial and antifungal effects are typically associated with the Ag ionization and concentration of Ag+ ions in a bacterial culture. Herein we thoroughly studied the influence of surface topography and roughness on the rate of Ag+ ion release. We considered two types of biocompatible and bioactive TiCaPCON-Ag films with 1 and 2 at. % of Ag and nine types of Ti surfaces with an average roughness varying in the range from 5.4 × 10-2 to 12.6 μm and different topographic features obtained through polishing, sandblasting, laser treatment, and pulsed electrospark deposition. It is demonstrated that the Ag+ ion release rates do not depend on the Ag content in the films as the main parameter, and it is other factors, such as the state of Ag agglomeration, surface topography and roughness, as well as kinetics of surface oxidation, that play a critical role. The obtained results clearly show a synergistic effect of the Ag content in the film and surface topography and roughness on Ag+ ion release. By changing the surface topographical features at a constant content of bactericidal element, we showed that the Ag+ ion release can be either accelerated by 2.5 times or almost completely suppressed. Despite low Ag+ ion concentration in physiological solution (<40 ppb), samples with specially fabricated surface reliefs (flakes or holes) showed a pronounced antibacterial effect already after 3 h of immersion in E. coli bacterial culture. Thus, our results open up new possibilities for the production of cost-effective, scalable, and biologically safe implants with pronounced antibacterial characteristics for future applications in the orthopedic field.

Influence of Surface Topography Characteristics on Mode Coupling Instability System

Influence of Surface Topography Characteristics on Mode Coupling Instability System