Increase In Adhesion Force Research Articles

Experimental study on the biocompatibility of keratoprosthesis with improved titanium implant.

To investigate whether hydroxyapatite (HAp) coating can improve keratoprosthesis (KPro) implant biointegration, ultimately to decrease the risk of implant-associated complications. The modified titanium implant was designed and prepared for artificial cornea. The titanium implant was treated with sandblasting and hydroxyapatite coating by acid-base two-step method. Surface was analyzed by scanning electron microscopy (SEM), KPro implants coated with HAp and KPro implant sandblasted were implanted in rabbits. Tissue adhesion to the implant was assessed and compared to an unmodified implant by histopathology (HE), transmission electron microscopy (TEM) and SEM. SEM demonstrated successful deposition of HAp on titanium implant sandblasted (HA/SB-Ti). The hydroxyapatite coatings caused enhancement of keratocyte proliferation compared with unmodified implant surfaces. HAp coating significantly increased adhesion forces. HAp coating of implants reduced the inflammatory response around the KPro implants in vivo. HAp-coated surfaces for use in titanium KPro implant greatly enhanced adherence of the titanium KPro implant in the rabbit cornea.

Experimental simulations of volcanic ash resuspension by wind under the effects of atmospheric humidity

Ash deposited during volcanic eruptions can be resuspended by wind and become hazardous for health and infrastructure hours to decades after an eruption. Accurate resuspension forecasting requires accurate modelling of the threshold friction velocity of the volcanic particles (Uth*), which is the key parameter controlling volcanic ash detachment by wind. Using an environmental wind tunnel facility this study provides much needed experimental data on volcanic particle resuspension, with the first systematic parameterization of Uth* for ash from the regions Campi Flegrei in Italy and also Eyjafjallajökull in Iceland. In this study atmospheric relative humidity (and related ash moisture content) was systematically varied, from <10% to >90%, which in the case of the Eyjafjallajökull fine ash (<63 μm) produced a twofold increase in Uth*. Using the Campi Flegrei fine ash (<63 μm) an increase in Uth* of only around a factor of 1.5 was observed. Reasonable agreement with force balance resuspension models was seen, which implied an increase in interparticle adhesion force of up to a factor of six due to high humidity. Our results imply that, contrary to dry conditions, one single modelling scheme may not satisfy the resuspension of volcanic ash from different eruptions under wet conditions.

Specific Ion Effects on the Interaction of Hydrophobic and Hydrophilic Self-Assembled Monolayers.

Interactions between mineral surfaces and organic molecules are fundamental to life processes. The presence of cations in natural environments can change the behavior of organic compounds and thus alter the mineral-organic interfaces. We investigated the influence of Na+, Mg2+, Ca2+, Sr2+, and Ba2+ on the interaction between two models, self-assembled monolayers, that were tailored to have hydrophobic -CH3 or hydrophilic -COO(H) terminations. Atomic force microscopy in chemical force mapping mode, where the tips were functionalized with the same terminations, was used to measure adhesion forces between the tip and substrate surfaces, to gather fundamental information about the role of these cations in the behavior of organic compounds and the surfaces where they adsorb. Adhesion force between hydrophobic surfaces in 0.5 M NaCl solutions that contained 0.012 M divalent cations did not change, regardless of the ionic potential, that is, the charge per unit radius, of the cation. For systems where one or the other surface was functionalized with carboxylate, -COO(H), mostly in its deprotonated form, -COO-, a reproducible change in the adhesion force was observed for each of the ions. The trend of increasing adhesion force followed the pattern: Na+ ≈ Mg2+ < Sr2+ < Ca2+ < Ba2+, suggesting that ionic potential, thus hydrated radius, controls the interaction. The presence of a -CH3 surface in the asymmetric system leads to lower adhesion forces than in the hydrophilic system, whereas the ionic trend remains the same. Although specific ion effects are felt in both systems, the lower adhesion force in the asymmetric system, compared with the hydrophilic system, implies that the -CH3 surface plays an important role.

Improved resistance to electromigration and acoustomigration of Al interdigital transducers by Ni underlayer

The structure and morphology of Al interdigital transducers as a function of Ni underlayer thickness were studied. The Al (111) texture intensity increases first and then decreases as Ni underlayer thickness increases. 6-nm Ni underlayer results in the strongest Al (111) texture with flattest surface, which exhibits almost 10 times longer life in electromigration measurement than those without Ni underlayer. 1.5 GHz surface acoustic wave filters fabricated with Al film on 6-nm Ni underlayer also have improved power durability compared with those without Ni underlayer from 29.0 to 32.5 dBm. It is observed that those fine grains in the 6-nm Ni underlayer greatly enhance Al (111) texture. Together with increased adhesion force, strong Al (111) texture accounts for the improved resistance to electromigration and acoustomigration via the reduction of gains boundaries, resistivity, and fine grains at the interface, which is promising for high power surface acoustic wave filters.

Effect of ampicillin on adhesive properties of bacteria examined by atomic force microscopy

Discovery of new antibacterial agents requires the development of novel techniques for bacteria surface characterization after treatment with antibiotics. In this study, we investigate the effect of ampicillin at MICs levels on adhesive properties of Gram-positive and Gram-negative bacteria, using atomic force microscopy (AFM). Our results revealed that the treatment leads to changes of bacterial surface properties, especially cell surface roughness. A nanomechanical alteration of the cells led to an increase of adhesive forces and rupture lengths. Changes in adhesive properties are determined not only by the modification of physicochemical cell properties but also by an increase in roughness, leading to an increase of the contact area with a cantilever tip. We discovered that the contribution of non-specific physicochemical interactions in the bacteria attachment to a substrate is not negligible and was significantly influenced by the presence of antibiotic. Ampicillin caused much greater change in the adhesion properties of Bacillus subtilis than Escherichia coli due to the mode of action of β-lactam antibiotic. Adhesion measurements may by a new way to investigate subtle changes of the bacterial surface properties caused by antibiotic, especially those targeting the bacterial cell wall. In contrast to nanoindentation assays, they provide information on adhesive properties of the bacteria surface.

Links between nanoscale and macroscale surface properties of natural root mucilage studied by atomic force microscopy and contact angle

Soil water repellency originating from organic coatings plays a crucial role for soil hydraulics and plant water uptake. Focussing on hydrophobicity in the rhizosphere induced by root-mucilage, this study aims to explore the link between macroscopic wettability and nano-microscopic surface properties. The existing knowledge of the nanostructures of organic soil compounds and its effect on wettability is limited by the lack of a method capable to assess the natural spatial heterogeneity of physical and chemical properties.In this contribution, this task is tackled by a geostatistical approach via variogram analysis of topography and adhesion force data acquired by atomic force microscopy and macroscopic sessile drop measurements on dried films of mucilage. The results are discussed following the wetting models given by Wenzel and Cassie-Baxter.Undiluted mucilage formed homogeneous films on the substrate with contact angles >90°. For diluted samples contact angles were smaller and incomplete mucilage surface coverage with hole-like structures frequently exhibited increased adhesion forces. Break-free distances of force curves indicated enhanced capillary forces due to adsorbed water films at atmospheric RH (35 ± 2%) that promote wettability. Variogram analysis enabled a description of complex surface structures exceeding the capability of comparative visual inspection.

Effect of the printing bed temperature on the adhesion of parts produced by fused filament fabrication

ABSTRACTFor parts produced by fused filament fabrication (FFF) the adhesion between the first printed layer and the printing bed is crucial, since it provides the foundation to the subsequent layers. Inadequate adhesion can result in poor printing quality or destroyed bed surfaces. This study aims at understanding and optimising the adhesion process for parts produced by FFF. The consequences of varying printing bed temperatures on the adhesion of two commonly used printing materials on two standard bed surfaces were investigated by means of an in-house built adhesion measurement device and complemented by contact angle measurements. This study shows a significant increase in adhesion forces, when printing parts at a bed temperature slightly above the glass transition temperature of the printing material.

Research into frictional interaction between the magnetized rolling elements

Results are presented of theoretical and experimental studies into effect of external magnetic field on the changes in adhesion parameters in a contact between magnetized steel rolling elements when they brought to each other to the level of atomic roughness. In theoretical studies, we calculated the interaction energy, adhesion force, friction and adhesion coefficient between magnetized steel rolling elements. The calculations are based on the general law of interaction between systems of charged particles, described by the Lennard-Jones potential, which takes into account both repulsion forces and attraction forces of these particles. A mathematical model was proposed for the calculation of force and coefficient of adhesion between steel rolling elements, taking into account magnetostrictive phenomena in the surface layers of a metal when magnetized by a constant magnetic field. The calculation of force and coefficient of adhesion was performed on the example of interaction between a wheel of a locomotive and a rail; the proposed model, however, could be applied to other elements of rolling friction. The technique and results of experimental studies are presented of the effect of external magnetic field on the coefficient of adhesion in the friction model of contact “wheel of a locomotive ‒ rail”. According to the results, magnetization of metal rolling elements leads to a significant, up to 36 %, increase in adhesion forces, which is important from the point of view of development and implementation of methods to control adhesion in similar tribological systems

Improvement of droplet speed and stability in electrowetting on dielectric devices by surface polishing

This paper reports on a technique that significantly improves the performance of open-plate electrowetting on dielectric (EWOD) devices by using chemical mechanical polishing (CMP) to achieve surface planarization. In EWOD devices, trenches are inevitably generated during fabrication, and these can have a considerable effect on droplet manipulation. Such artefacts lead to a local intensification in the electric field that not only hinders the droplet movement due to a partially increased adhesion force, but also limits the maximum applicable potential by increasing the likelihood of a dielectric breakdown. We conducted theoretical and experimental studies on the effect of trenches on the performance of both unpolished and polished EWOD devices. Various combinations of the droplet volume and electrode size were tested, and our proposed technique resulted in a notable improvement for all cases. For instance, when operating at 100 V, a 3.5 μL droplet could be translated at 70 mm/s on the polished EWOD device, which is twice as fast as that for its unpolished counterpart at the same voltage. Also, the maximum applicable potential resulting in a dielectric breakdown of the polished EWOD device was measured to be 27% higher than that of a conventional device.

Gecko Feet as a Bio Prototype for the Use of Dry Adhesion in Engineering Decisions

The focus of this review is to outline the remarkable ability of the gecko to climb surfaces vertically, at tremendous speed (over 1 m/s) using van der Waals forces (one of nature’s amazing “sticking and unsticking” directional dry adhesion design) as well as contact splitting mechanism. Further, the elasticity of the hairs conforming to the topology of the surface and hence contributing to an increased adhesion force is discussed, apart from the applications of gecko feet bio-inspired solutions. Such applications are in areas as diverse as, and not restricted to, climbing vertically and horizontally on glass surfaces; fitting televisions and computers on the walls; in robots for the inspection and maintenance of installations in space stations and self-cleaning surfaces. By this review, we hope to inspire and motivate the current generation of engineers to study, mimic and abstract the fundamental hierarchical structures as well as the incredible dry adhesion principles (as closely as is possible) objects of nature. This approach will help in improving upon the existing methods to produce gecko feet-like materials with dry adhesion as well as self-cleaning properties. Such refinement strategies can also include the development of hybrid structures utilizing a combination of designs found in other organisms in Mother Nature (for e.g., the mushroom-shaped structure found in the beetle). This requires improvements in the fundamental hierarchical arrangement of the gecko feet-like hairs and their inter-facial interactions with model substrata. Also, the mechanical deformations of the different gecko feet-like materials as well as how sliding velocity impacted adhesional and frictional phenomena should be studied and better understood. This will enable the engineer to develop better gecko feet-like adhesives.

Early Adhesion of Candida albicans onto Dental Acrylic Surfaces

Denture-associated stomatitis is a common candidal infection that may give rise to painful oral symptoms, as well as be a reservoir for infection at other sites of the body. As poly (methyl methacrylate) (PMMA) remains the main material employed in the fabrication of dentures, the aim of this research was to evaluate the adhesion of Candida albicans cells onto PMMA surfaces by employing an atomic force microscopy (AFM) single-cell force spectroscopy (SCFS) technique. For experiments, tipless AFM cantilevers were functionalized with PMMA microspheres and probed against C. albicans cells immobilized onto biopolymer-coated substrates. Both a laboratory strain and a clinical isolate of C. albicans were used for SCFS experiments. Scanning electron microscopy (SEM) and AFM imaging of C. albicans confirmed the polymorphic behavior of both strains, which was dependent on growth culture conditions. AFM force-spectroscopy results showed that the adhesion of C. albicans to PMMA is morphology dependent, as hyphal tubes had increased adhesion compared with yeast cells (P < 0.05). C. albicans budding mother cells were found to be nonadherent, which contrasts with the increased adhesion observed in the tube region. Comparison between strains demonstrated increased adhesion forces for a clinical isolate compared with the lab strain. The clinical isolate also had increased survival in blood and reduced sensitivity to complement opsonization, providing additional evidence of strain-dependent differences in Candida-host interactions that may affect virulence. In conclusion, PMMA-modified AFM probes have shown to be a reliable technique to characterize the adhesion of C. albicans to acrylic surfaces.

Adhesion of ligand-conjugated biosynthesized magnetite nanoparticles to triple negative breast cancer cells

This paper presents the results of an experimental study of the adhesion forces between components of model conjugated magnetite nanoparticle systems for improved selectivity in the specific targeting of triple negative breast cancer. Adhesion forces between chemically synthesized magnetite nanoparticles (CMNPs), biosynthesized magnetite nanoparticles (BMNPs), as well as their conjugated systems and triple negative breast cancer cells (MDA-MB-231) or normal breast cells (MCF 10A) are elucidated at a nanoscale. In all cases, the BMNPs had higher adhesion forces (to breast cancer cells and normal breast cells) than CMNPs. The adhesion of LHRH-conjugated BMNPs or BSA-conjugated BMNPs to cancer cells is shown to be about 6 times to that of normal breast cells. The increase in adhesion forces between luteinizing hormone-releasing hormone, LHRH- or EphA2, a breast specific antibody(BSA)-conjugated BMNPs to breast cancer cells is attributed to van der Waals interactions between the peptides/antibodies from the conjugated nanoparticles and the over-expressed receptors (revealed using immunofluorescence staining) on the surfaces of the breast cancer. The implications of the results are discussed for the selectivity and specificity of breast cancer targeting by ligand-conjugated BMNPs.

H2O2 Causes Improved Adhesion Between a Polysaccharide-based Membrane and Intestinal Serosa

In this work, hydrogen peroxide (H2O2) was employed to improve the adhesion of an alginate-based membrane to intestinal serosa: mechanical adhesion test and SEC-MALLS studies were performed to investigate the contribution of H2O2-induced modifications of both tissue and membrane to the adhesion enhancement. Adhesion tests confirmed that the formation of an adhesive gelatin layer on serosa plays a major role in increasing adhesion forces, while SEC-MALLS studies revealed a slight decrease of alginate molecular weight. However, the latter chain degradation does not seem to significantly impair the adhesion strength. Overall, this study describes a possible strategy to create adhesive interfaces between biomaterials and collagen-containing tissues.

Staphylococcal Adhesion, Detachment and Transmission on Nanopillared Si Surfaces

Nanostructured surfaces are extensively considered with respect to their potential impact on bacterial adhesion from aqueous suspensions or air, but in real-life bacteria are often transmitted between surfaces. Mechanistically, transmission involves detachment of adhering bacteria from a donor and adhesion to a receiver surface, controlled by the relative values of the adhesion forces exerted by both surfaces. We here relate staphylococcal adhesion, detachment and transmission to, from, and between smooth and nanopillared-Si surfaces with staphylococcal adhesion forces. Nanopillared-Si surfaces were prepared with pillar-to-pillar distances of 200, 400, and 800 nm. On smooth surfaces, staphylococcal adhesion forces, measured using bacterial-probe Atomic-Force-Microscopy, amounted to 4.4-6.8 and 1.8-2.1 nN (depending on the AFM-loading force) for extracellular-polymeric-substances (EPS) producing and non-EPS producing strains, respectively. Accordingly the EPS producing strain adhered in higher numbers than the non-EPS producing strain. Fractional adhesion forces on nanopillared-Si surfaces relative to the smooth surface ranged from 0.30 to 0.95, depending on AFM-loading force, strain and pillar-to-pillar distance. However, for each strain, the number of adhering bacteria remained similar on all nanopillared surfaces. Detachment of adhering staphylococci decreased significantly with increasing adhesion forces, while staphylococcal transmission to a receiver surface also decreased with increasing adhesion force exerted by the donor. In addition, the strain with ability to produce EPS was killed in high percentages and induced to produce EPS during transmission on nanopillared-Si surfaces, presumably by high local cell-wall stresses. This must be accounted for in applications of nanostructured surfaces: whereas killing may be favorable, EPS production may reduce antimicrobial efficacy.

Zero-Dimensional and Highly Oxygenated Graphene Oxide for Multifunctional Poly(lactic acid) Bionanocomposites

The unique strengths of 2D graphene oxide nanosheets (GONSs) in polymer composites are thwarted by nanosheet agglomeration due to strong intersheet attractions. Here, we reveal that shrinking the planar size to 0D graphene oxide quantum dots (GOQDs), together with the intercalation of rich oxygen functional groups, reduces filler aggregation and enhances interfacial interactions with the host polymer. With poly(lactic acid) (PLA) as a model matrix, atomic force microscopy colloidal probe measurements illustrated that a triple increase in adhesion force to PLA was achieved for GOQDs (234.8 nN) compared to GONSs (80.4 nN), accounting for the excellent exfoliation and dispersion of GOQDs in PLA, in contrast to the notable agglomeration of GONSs. Although present at trace amount (0.05 wt %), GOQDs made a significant contribution to nucleation activity, mechanical strength and ductility, and gas barrier properties of PLA, which contrasted the inferior efficacy of GONSs, accompanied by clear distinction in film...

Investigation of the μN level adhesion force characteristics of gold-coated materials in air

ABSTRACTThe typical adhesive phenomena of gold-coated contact material under cold switching conditions are observed using a micro-adhesion apparatus as a switch simulator. With repeated actuation, the recorded adhesion force results uniformly show a Gaussian-like distribution. Moreover, the effects of curvature radius of contact and contact force on adhesive force are investigated experimentally. For better understanding of the adhesion mechanism, the theoretical analysis model is built by introducing the Hamaker’s discussion about the interaction between a pair of neutral atoms or molecules. Data suggest that the substantial increase of adhesion force is correlated closely with the microscopic contact area.

The Effect of Multi-Directional Stimuli on the Stiction-Induced Failure Behavior of MEMS

The occurrence of adhesion-induced failures at microelectromechanical systems (MEMSs), also referred to as stiction, can be triggered by a variety of environmental, geometrical, and operational parameters, such as compressive contact forces acting in normal direction between two micromechanical surfaces. The knowledge of these parameters is essential for conducting and evaluating stiction-related reliability tests at MEMS. This paper investigates the operational parameter of tangential contact forces, which can occur in case of multi-directional overloads like shocks or vibrations during manufacturing, handling, or final application of MEMS inertial sensors. Tangential contact forces act in parallel to a contact area and are shown to affect the stiction-induced failure behavior of MEMS. For this purpose, three different types of test devices have been exposed to electrical as well as mechanical stimuli with and without cross-axes excitation contents, stimulating the occurrence of tangential forces during contact. The transient system responses of the test devices were calculated based on reduced-order impact models, allowing a detailed comparison of load conditions between different stimuli and test devices. The obtained results show that tangential contact forces lead to higher stiction rates, which indicates increased adhesion forces compared with excitations without tangential forces. [2015-0320]

低エネルギー電子線均質照射によるポリプロピレン(PP)とナイロン 6(PA6)積層シートの高速接着

2-layer laminated sheets (PP/PA6) with polypropylene (PP) and nylon 6(PA6) were prepared by applying low dose homogeneous low energy electron beam irradiation (HLEBI) prior to hot-press under 10 MPa, 403 K and 3 min. Although the adhesion of the PP/PA6 was often observed with a weak hot-press without HLEBI, the HLEBI (≦1.29 MGy) induced adhesion raised the bonding forces as evidenced by using the adhesive forces of peeling resistance (oFp). Based on the 3-parameter Weibull equation, the lowest oFp value at peeling probability (Pp) of zero (Fs) could be estimated. An increasing trend in Fs occurred by applying HLEBI up to 0.64 MGy reaching a maximum at 21.98 Nm−1, improving the safety level without radiation damage. When HLEBI cut the chemical bonds in PP polymer and generated not-terminated atoms having dangling bonds, they probably induced the chemical bonding. Thus, increasing adhesion force between the laminated sheets could be explained.

High Adhesive Force between Laminated Sheets of Titanium and Polyurethane Improved by Homogeneous Low Energy Electron Beam Irradiation Prior to Hot-Press

2-layer copper/polyurethane (Cu/PU) laminated sheets were prepared by a new adhesion method, a double-step treatment consisting of applying low dose (1⁄40.43MGy) homogeneous low energy electron beam irradiation (HLEBI) prior to hot-press under 5MPa and 413K. Although the weak hot-press adhesion of the Cu/PU was observed without HLEBI, the new adhesion raised the bonding forces as evidenced by the mean adhesive forces of peeling resistance (Fp). Based on the 3-parameter Weibull equation, the lowest Fp value at peeling probability (Pp) of zero (Fs) could be estimated. An increasing trend in Fs occurred by the double-step treatment applying HLEBI up to 0.13MGy reaching a maximum at 27.1Nm11, improving the safety level without radiation damage. When HLEBI cut the chemical bonds in PU polymer and generated terminated atoms with dangling bonds, they probably induced the chemical bonding and intermolecular coulomb attractive forces. Therefore, increasing adhesion force between the laminated sheets could be explained. [doi:10.2320/matertrans.MBW201312]

Influence of 4-vinylbenzylation on the rheological and swelling properties of photo-activated collagen hydrogels

ABSTRACTCovalent functionalisation of collagen has been shown to be a promising strategy to adjust the mechanical properties of highly swollen collagen hydrogels. At the same time, secondary interactions between for example, amino acidic terminations or introduced functional groups also play an important role and are often challenging to predict and control. To explore this challenge, 4-vinylbenzyl chloride (4VBC) and methacrylic anhydride (MA) were reacted with type I collagen, and the swelling and rheological properties of resulting photo-activated hydrogel systems investigated. 4VBC-based hydrogels showed significantly increased swelling ratio, in light of the lower degree of collagen functionalisation, with respect to methacrylated collagen networks, whilst rheological storage moduli were found to be comparable between the two systems. To explore the role of benzyl groups in the mechanical properties of the 4VBC-based collagen system, model chemical force microscopy (CFM) was carried out in aqueous environment with an aromatised probe against an aromatised gold-coated glass slide. A marked increase in adhesion force (F: 0.11±0.01 nN) was measured between aromatised samples, compared to the adhesion force observed between the non-modified probe and a glass substrate (F: 2.64±1.82 nN). These results suggest the formation of additional and reversible π-π stacking interactions in aromatic 4VBC-based networks and explain the remarkable rheological properties of this system in comparison to MA-based hydrogels.