Pull-off Force Research Articles

Shunt disconnection is less likely using a surgeon’s knot compared with a surgical constrictor knot

Introduction Ventriculo-peritoneal shunt malfunction is a common neurosurgical presentation, which may occur as a result of shunt disconnection at the level of the valve. Previous studies assessing ligatures have suggested that the constrictor knot is stronger in securing a ligature compared to the surgeon’s knot. Our study compared the ability of each knot to secure shunt tubing to the valve. Methods A medtronic shunt valve was secured to a peritoneal catheter using the surgeon’s knot versus constrictor’s knot. The weight and subsequent force (N) required to pull off the shunt tubing at the knot site were recorded. Results The mean pull-off force was 11.7 N for the surgeon knot, and 8.9 N for the constrictor knot. There was significant difference in favour for the surgeon’s knot compared to the constrictor knot. Conclusions The surgeon’s knot is significantly stronger than the constrictor knot for securing a peritoneal catheter to a CSF shunt valve.

Enhancement of the adhesive strength of antithrombogenic and hemocompatible a-C:H:SiOx films to polypropylene

Silicon- and oxygen-incorporated hydrogenated amorphous carbon films (a-C:H:SiOx) are deposited onto polypropylene substrates using plasma-assisted chemical vapor deposition to increase their antithrombogenicity and hemocompatibility. To increase the a-C:H:SiOx film adhesion to the polymer substrate, the latter is pretreated with argon or oxygen ions from the ion source with closed electron drift. The optimum conditions for the ion-beam treatment are determined by measurements of the surface wettability and chemical composition, the film morphology and adhesion. The adhesive properties are evaluated by the pull-off adhesion test. X-ray photoelectron spectroscopy shows the formation of new oxygen-containing functional groups after the exposure to both argon and oxygen ion beams. The highest film adhesion is observed for the substrate irradiated by oxygen ions, when the pull-off force increases from 3.4 to 24 kg/cm2. Various characterization techniques such as Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy are employed to study the a-C:H:SiOx film structure on a polymer substrate. In vitro investigation of platelet adhesion and cytotoxicity helps to evaluate the blood compatibility with the film. The a-C:H:SiOx film shows low thrombogenicity and no cytotoxic activity towards human leukocytes.

A Simplified Theory of Electroadhesion for Rough Interfaces

Electroadhesion is a very hot topic in tribology due to its implications in the science of surface haptics. Building on theories of Persson, we derive a simpler theory for electroadhesion between rough surfaces using BAM (Bearing Area Model) of Ciavarella. The theory is derived for both cases of conducting and insulating bodies and shows that pull-off forces depend mostly on the applied voltage, on the surface height rms and on the longest wavelength in the surface representation. However, real contact area and friction additionally depend on rms slopes and hence on truncation of the roughness spectrum. Two stickiness criteria have been derived based on the present theory and on the energy balance proposed by Persson and Tosatti. The coefficient of friction decays with normal pressure tending to a plateau in a manner which is consistent with existing experiments.

Do SiNx coatings bear the potential to reduce the risk of micromotion in modular taper junctions?

Fretting corrosion is one contributor to the clinical failure of modular joint arthroplasty. It is initiated by micromotion in metal junctions exposed to fluids. Omitting metal-on-metal contacts could help to reduce the corrosion risk. The coating of one metal taper partner with a ceramic-based silicon nitride (SiNx) coating might provide this separation. The aim of the study was to identify whether a SiNx coating of the male taper component influences the micromotion within a taper junction. Hip prosthesis heads made of CoCr29Mo6 (Aesculap) and Ti6Al4V (Peter Brehm) were assembled (2000 N) to SiNx-coated and uncoated stem tapers made of Ti6Al4V and CoCr29Mo6 (2×2×2 combinations, each n = 4). Consecutive sinusoidal loading representing three daily activities was applied. Contactless relative motion in six degrees of freedom was measured using six eddy-current sensors. Micromotion in the junction was determined by compensating for the elastic deformation derived from additional monoblock measurements. After pull-off, the taper surfaces were microscopically inspected. Micromotion magnitude reached up to 8.4 ± 0.8 µm during loading that represented stumbling. Ti6Al4V stems showed significantly higher micromotion than those made of CoCr29Mo6, while taper coating had no influence. Statistical differences in pull-off forces were found for none of the taper junctions. Microscopy revealed CoCr29Mo6 abrasion from the head taper surface if combined with coated stem tapers. Higher micromotion of Ti6Al4V tapers was probably caused by the lower Young's modulus. Even in the contact areas, the coating was not damaged during loading. The mechanics of coated tapers was similar to uncoated prostheses. Thus, the separation of the two metal surfaces with the objective to reduce in vivo corrosion appears to be achievable if the coating is able to withstand in vivo conditions. However, the hard ceramic-based stem coating lead to undesirable debris from the CoCr29Mo6 heads during loading.

Influence of Different Damage Patterns of the Stem Taper on Fixation and Fracture Strength of Ceramic Ball Heads for Total Hip Replacement.

Background Modularity finds frequent application in total hip replacement, allowing a preferable individual configuration and a simplified revision by retaining the femoral stem and replacing the prosthetic head. However, micromotions within the interface between the head and the stem taper can arise, resulting in the release of wear debris and corrosion products. The aim of our experimental study was to evaluate the influence of different taper damages on the fixation and fracture stability of ceramic femoral heads, after static and dynamic implant loading. Methods Ceramic ball heads (36 mm diameter) and 12/14 stem tapers made of titanium with various mild damage patterns (intact, scratched, and truncated) were tested. The heads were assembled on the taper with a quasistatic load of 2 kN and separated into a static and a dynamic group afterwards. The dynamic group (n = 18) was loaded over 1.5 million gait cycles in a hip wear simulator (ISO 14242-1). In contrast, the static group (n = 18) was not mechanically loaded after assembly. To determine the taper stability, all heads of the dynamic and static groups were either pulled off (ASTM 2009) or turned off (ISO 7206-16). A head fracture test (ISO 7206-10) was also performed. Subsequent to the fixation stability tests, the taper surface was visually evaluated in terms of any signs of wear or corrosion after the dynamic loading. Results In 10 of the 18 cases, discoloration of the taper was determined after the dynamic loading and subsequent cleaning, indicating the first signs of corrosion. Pull-off forces as well as turn-off moments were increased between 23% and 54% after the dynamic loading compared to the unloaded tapers. No significant influence of taper damage was determined in terms of taper fixation strength. However, the taper damage led to a decrease in fracture strength by approximately 20% (scratched) and 40% (truncated), respectively. Conclusion The results suggest that careful handling and accurate manufacturing of the stem taper are crucial for the ceramic head fracture strength, even though a mild damage showed no significant influence on taper stability. Moreover, our data indicate that a further seating of the prosthetic head may occur during daily activities, when the resulting hip force increases the assembly load.

An analytical solution to the adhesive cylindrical indentation of a compressible elastic thin layer

ABSTRACT A simple analytical method based on the Kerr-type model is proposed to extend the well-known Johnson-Kendall-Roberts (JKR) model to the adhesive contact between a rigid cylinder and a compressible elastic thin layer under plane strain. The Kerr-type model provides a linear differential relation between the contact pressure and the normal deflection of the upper surface of the layer, whose lower surface is either bonded or sliding on a rigid substrate. With the aid of Betti’s reciprocal theorem, several easy-to-use explicit formulas are obtained for the relations between the indentation force, the indentation depth and the contact width, and the pressure distribution inside the contact zone and the pull-off force are determined. Reasonable agreement of the predicted results with existing numerical results shows that the present analytical model can capture the adhesive effects on the cylindrical indentation of a compressible elastic thin layer on a rigid substrate.

Physical Variables Underlying Tactile Stickiness During Fingerpad Detachment.

One may notice a relatively wide range of tactile sensations even when touching the same hard, flat surface in similar ways. Little is known about the reasons for this variability, so we decided to investigate how the perceptual intensity of light stickiness relates to the physical interaction between the skin and the surface. We conducted a psychophysical experiment in which nine participants actively pressed their finger on a flat glass plate with a normal force close to 1.5 N and detached it after a few seconds. A custom-designed apparatus recorded the contact force vector and the finger contact area during each interaction as well as pre- and post-trial finger moisture. After detaching their finger, participants judged the stickiness of the glass using a nine-point scale. We explored how sixteen physical variables derived from the recorded data correlate with each other and with the stickiness judgments of each participant. These analyses indicate that stickiness perception mainly depends on the pre-detachment pressing duration, the time taken for the finger to detach, and the impulse in the normal direction after the normal force changes sign; finger-surface adhesion seems to build with pressing time, causing a larger normal impulse during detachment and thus a more intense stickiness sensation. We additionally found a strong between-subjects correlation between maximum real contact area and peak pull-off force, as well as between finger moisture and impulse.

Fretting corrosion of Si3 N4 vs CoCrMo femoral heads on Ti-6Al-V trunnions.

Fretting corrosion at the head-neck taper junction was compared between silicon nitride (Si3 N4 ) and commercially available cobalt chrome (CoCrMo) femoral heads on titanium (Ti-6Al-4V) trunnions. An electrochemical setup was used to capture the fretting currents (characterized by oxide abrasion and repassivation) during cyclic loading. Onset load, pull-off force (disassembly load), short term and long term (1 million cycles) fretting currents were used to compare the fretting corrosion performance between the test group (Si3 N4 /Ti-6Al-4V) and the control group (CoCrMo/Ti-6Al-4V). Incremental cyclic fretting corrosion tests showed that the Si3 N4 /Ti-6Al-4V combination had statistically lower (P < .05) average fretting current of 0.189 µA (SD = 0.114 µA) compared to 0.685 µA (SD = 0.630 µA) for CoCrMo/Ti-6Al-4V for cyclic load of 3200 N. Similarly, for the one million cycle fretting corrosion tests, the Si3 N4 /Ti-6Al-4V couples had statistically lower (P < .05) average current (0.048 µA, SD = 0.025 µA) vs CoCrMo/Ti-6Al-4V couples (0.366 µA, SD = 0.143 µA). The Si3 N4 heads also had higher onset loads (P < .05) for fretting (vs CoCrMo, 2200 N vs 1740 N) indicating a difference in surface contact mechanics between the two groups. Scanning electron microscopy with energy dispersive spectroscopy confirmed material transfer from the trunnions to the heads for both groups tested, and from head to trunnion for the CoCrMo heads. Minimal Si3 N4 transfer was noted. The electrochemical, mechanical, and microscopic inspection data supported the hypothesis that Si3 N4 /Ti-6Al-4Vcombination had better fretting corrosion performance compared to CoCrMo/Ti-6Al-4V.

Drawing-Based Manufacturing of Shear-Activated Reversible Adhesives.

Although biomimetic technologies for dry reversible adhesion seem to be maturing, the costs, complexity, and time expenditures associated with the current template-based molding techniques call for research on other fabrication methods. In this paper, we report a novel cost-effective, simple, and flexible drawing-based technique for manufacturing the soft elastomeric thin-film-based microstructures needed for successful implementation of the principles of biological shear-activated adhesion. Several different types of adhesive microstructures are fabricated, and the best of them demonstrate shear-driven amplification of pull-off force by a factor of 40, which significantly outperforms known molded analogues. A simple gripper based on a manual center-clamping vise is shown to enable pick-and-place manipulation of various flat and curved objects of everyday use.

Two-dimensional finite element analysis of elastic adhesive contact of a rough surface

Adhesive contact of a rigid flat surface with an elastic substrate having Weierstrass surface profile is numerically analyzed using the finite element method. In this work, we investigate the relationship between load and contact area spanning the limits of non-adhesive normal contact to adhesive contact for various substrate material properties, surface energy and roughness parameters. In the limit of non-adhesive normal contact, our results are consistent with published work. For the adhesive contact problem, we employ Lennard-Jones type local contact interaction model with numerical regularization to study the transition from partial to full contact including jump-to-contact instabilities as well as load-depth hysteresis. We have investigated evolution of bonded contact area and pull-off force for various surface roughness parameters, substrate material properties and surface energy. We have identified two non-dimensional parameters to adequately explain experimentally observed adhesion weakening and strengthening phenomena. A design chart of the relative pull-off force as function of non-dimensional parameters is also presented.

Roughness Effect on the Pull-Off Force between Two Surfaces with Water Adsorbed between Them. A Molecular Dynamics Simulation Perspective

Surface roughness has a high impact on the adhesion between particles and substrates. In the interaction of two surfaces in humid air, roughness usually controls the strength of the adhesion. In th...

AN INNOVATIVE TECHNOLOGY OF WAFFLES WITH FUNCTIONAL PROPERTIES

The high-priority tasks of today’s confectionery industry include the development and introduction of functional-purpose confections. These products are supposed to be of high technological qualities, be effective in production to the extent possible, and have physiological functional properties due to the physiologically valuable ingredients in their composition. These ingredients include the synbiotic complex composed of probiotics (bifidobacteria, lactobacilli) and prebiotics (inulin and lactulose). This complex has been studied in this research. The paper gives reasons why waffles with fatty fillings are the ones to which the synbiotic complex should be added. It has been established what mass fraction of the ingredients at what stage of fatty filling production should be added. It has been studied how the synbiotic complex affects the structural and mechanical properties of the fatty filling: its effective viscosity, adhesive strength, and critical shear stress. It has been found that the maximum shear rate that still allows obtaining a high-quality filling is 5.4 s-1. The specific pull-off force of the fatty filling with the synbiotic added becomes lower compared to that of the control sample. This helps reduce the energy consumed in the course of moulding waffles. An innovative manufacturing technology for waffles with synbiotic supplements has been developed and proved practical. It includes the stages of preparing microencapsulated microorganisms and adding prebiotics, and provides the technological parameters of fatty filling preparation. It has been established that the synbiotic included into the composition of the new fatty filling decreases the maturation of waffle blocks by 40–45%, and allows reducing the layer of filling to 1–1.5 mm. It has been proven that the synbiotic complex as an ingredient in the fatty filling of waffles will allow developing and manufacturing confections that improve human microflora. These new specialised products will be socially significant, as they will help solve a topical and important task of the confectionery industry: prevent gastrointestinal diseases.

Understanding the Interaction Mechanism between Elemental Selenium and Ferric Hydroxide in Wastewater Treatment

The conversion of selenium oxyanions to elemental selenium (Se0) of low solubility and bioavailability is an effective industrial approach for selenium management in wastewater treatment. The generated Se0 particles require further treatment with coagulants such as ferric ions to facilitate the precipitation of Se0 particles. In this work, the settling of Se0 particles in simulated wastewater was investigated with amorphous ferric hydroxide (Fe(OH)3) as a coagulant prepared from hydrolysis of ferric chloride. The effects of ferric ion dosage, water composition, and pH on the Se0 removal percentage were investigated. The surface properties, i.e., ζ potential and morphology, were characterized, which influenced the interactions between Se0 and Fe(OH)3. The forces acting between Se0 and Fe(OH)3 surfaces were directly measured, for the first time, using atomic force microscopy (AFM). The water composition and pH had a significant effect on the adhesion force. In simulated wastewater, the adhesion force generally increased with pH, suggesting that the adsorption of Ca2+ and Mg2+ on Fe(OH)3 surface increased with pH, which enhanced the adhesion. Interestingly, long-range pull-off forces and sawtooth patterns were observed on the retraction force–separation curves, which were attributed to the stretching of Fe(OH)3 particle aggregates or chains during separation. Bulk settling tests showed that the best Se0 removal performance of Fe(OH)3 was found to be around pH 8, which was because the largest amount of Fe(OH)3 precipitates was found around this pH. The results indicate that the Fe(OH)3 solubility as well as the related intermolecular and surface forces play the predominant role in determining the Se0 removal performance of the ferric coagulant. This work, for the first time, revealed the interaction mechanisms of Se0 particle and amorphous Fe(OH)3, providing useful insights on the performance of ferric coagulants on Se0 particle removal from wastewater under various solution conditions. The experimental approach used in this work can be readily extended to other water treatment systems and processes such as polymer flocculation.

Decohesion of a rigid flat punch from an elastic layer of finite thickness

Interfacial bond strength is a crucial mechanical property of solid adhesive joints that plays an important role in a wide range of applications. A common way of quantifying mechanical strength of an adhered interface is to measure the apparent adhesion strength by finding the maximum pulling force in a tensile bond test and dividing it by the area. Despite the simplicity of this method, there is growing evidence suggesting that the measured quantity is not necessarily an intrinsic attribute of the interface but depends on thickness of the adhesive film and size of the interface. In this work, the critical pull-off force of a flat rigid punch adhered to an elastic film of finite thickness is studied via asymptotic analysis as well as finite element (FE) simulations. The decohesion behavior is found to be governed by two dimensionless parameters η and φ: the former represents the deformation of the interface relative to the interaction distance of interfacial forces, while the latter denotes a correction factor due to finite thickness of the film. As η changes from 0 to infinity, the interface decohesion would take place from uniform detachment (DMT-like) to crack-like propagation (JKR-like). The transition behavior can be well described by an empirical solution, which suggests a new rational procedure to consistently characterize the intrinsic adhesion properties of an adhered interface from tensile bond tests. Finally, the general empirical solution and the adhesion characterization procedure are directly validated by a series of experiments via detaching a stainless-steel flat punch from adhesive Polydimethylsiloxane (PDMS) films. This work not only offers a clear and explicit solution to capture the transition behavior of interface decohesion but also provides a guideline for modulating adhesion performance via geometry rather than chemistry of the adhesives.

Sliding of adhesive nanoscale polymer contacts

The interaction between friction and adhesion is a defining factor of the macroscopic behavior of natural and synthetic soft materials. In this work, the interfacial normal and shear adhesion strength of contacts between nanoscale polymeric fibers were studied using novel experiments aided by micromachined devices by which the critical normal and tangential pull-off forces between individual polyacrylonitrile (PAN) nanofibers with diameters in the range 400 nm – 4 µm were measured in real-time. The work of adhesion under normal detachment, as computed using the Johnson-Kendall-Roberts (JKR) and the Maugis-Dugdale (M-D) models for elastic adhesive contact, was shown to be independent of the nanofiber diameter and comparable to twice the surface energy of bulk PAN. Under shear detachment, peeling of the contact area was calculated using the JKR and the M-D models combined with linear elastic fracture mechanics (LEFM). The M-D model combined with LEFM could predict the experimentally obtained tangential pull-off force instabilities. The interfacial shear adhesion strength is shown to be constant for a broad range of contact radii (25–140 nm) and approximately equal to the material shear stress at yielding. Thus, shear yielding is shown to be the controlling mechanism during shear detachment of individual polymer nanofibers interacting with strong van der Waals adhesion.

Vertical Fibrous Morphology and Structure-Function Relationship in Natural and Biomimetic Suction-Based Adhesion Discs

Summary Recent years have seen rapid development in bio-inspired materials for adhesion. However, it remains challenging to realize robust adhesion on rough aquatic surfaces. An inspiring natural model is the remora fish, which has evolved to retain powerful adhesion to hosts using a dorsal suction disc. We find that the remora suction disc has a unique fibrous architecture of vertically oriented collagen fibers that enable anisotropic mechanical properties and enhanced adhesion performance. In the engineered prototype, vertically oriented nylon fibers are embedded into the soft silicone matrix using electrostatic flocking. The anisotropic mechanical properties are validated in both natural and biomimetic suction discs. Furthermore, the biomimetic suction disc demonstrates an enhanced adhesion function with a maximum 62.5% increase in pull-off force and a 340% increase in attachment time compared with the silicone control. This work can shed light on natural adhesion mechanisms and inspire novel designs for aquatic soft adhesives and actuators.

Unbinding events of amino acids and peptides from water–pyrite interfaces: A case study of life’s origin on mineral surfaces

Selective binding of aqueous-phase amino acids to mineral surfaces is regarded as a plausible first step in oligopeptide formation on early Earth. To clarify the strength and underlying mechanism of amino acid binding to pyrite surfaces, we measured the unbinding (pull-off) force of ten amino acids and two oligo-peptides from water-pyrite interfaces using atomic force microscopy (AFM). The most probable unbinding force could be described by a linearly increasing function with the size of the amino acid and a characteristic offset. A good correlation was obtained between the most probable unbinding force and the residue volume, surface area and polarizability of samples suggesting at least a partial contribution of van der Waals (vdW) forces, especially the London dispersion force. These results are useful in analysis of adhesion phenomena of amino acids in the given environmental settings such as in this work.

Pull-off force modeling and experimental study of PDMS stamp considering preload in micro transfer printing

Micro transfer printing is an effective method for heterogeneous materials integration in soft micro device fabrication. In micro transfer printing, controllable adhesion force is an important and desired feature. In this paper, an accurate theoretical pull-off force model is established considering the influence of not only the pull-off velocity but also the preload in micro transfer printing, which reveals the relationships between the pull-off force and the pull-off velocity as well as preload. Experimental tests are carried out to investigate the influences of both pull-off velocity and preload on pull-off force and validate the theoretical model. The results show that the proposed pull-off force model matches well with the experiment data. The pull-off force of the stamp increases approximately linearly with the preload and the preload under large pull-off velocity has a greater influence on the pull-off force than that under small pull-off velocity. Therefore, the analytic model can not only provide an important understanding of micro transfer printing, but also support important information for the process optimization of micro transfer printing.

Effect of Various Surface Treatments on Ti-Base Coping Retention.

Mechanical surface roughening of the titanium-abutment base is necessary to increase the pull-off bond strength of the lithium disilicate abutment material. Additional chemical surface treatment may further increase the bond strength, but the effects are product specific.

Benefits of additive manufacturing and micro and nano surface texture modifications on mechanical strength and infection resistance of skin-implant interfaces in rats.

Patients find existing exo-prostheses utilizing traditional socket connections uncomfortable and irritating, as they do not provide the dexterity and proprioception which is often expected by active patients. Transcutaneous osseointegrated implants are a potential solution, but carry risk of infection at the skin–implant interface. Histological and observational studies previously demonstrated that textured implants have both improved epidermal ingrowth and decreased skin retraction. This study aimed to determine effects on mechanical integration, barrier to bacterial colonization, and infection of the skin–implant interface using additive manufacturing and post-manufactured surface modifications. In this study, titanium alloy implants were made by either computer numerical control machining (CNC) or electron beam melting (EBM). Implants in each group were left either unaltered (CNC-control and EBM-control), acid etched (CNC-micro and EBM-micro), or oxidatively treated (CNC-nano and EBM-nano) creating six distinct surface textures. This study was divided into two phases, each utilizing 10 rats. Six implants—one of each texture—randomized for position were placed in each rat. Phase 1 animals healed for three weeks and skin-implant mechanical pull-off strength was measured. Phase 2 animals were challenged by S. aureus inoculation during the three-week healing process and serial dilutions of the sonicated implants were performed to quantify bacterial colonization. The three EBM implant groups had 830% greater force at pull-off compared to the three CNC groups. Additionally, the pull-off force of EBM-micro implants was 101% and 83% stronger, respectively, than EBM-nano and EBM-control implants. There was negligible mechanical attachment of skin to any CNC implant. Bacterial colonization counts were collectively 63% ( P &lt; 0.05) lower for EBM implants relative to CNC implants. CNC-control implants exhibited 90% ( P &lt; 0.01) greater bacterial colonization than EBM-controls. No significant differences in bacterial colonization were noted between the other implant groups. Both manufacturing technique and post-manufacturing surface texture modification affected the skin-implant interface’s mechanical integration and effectiveness as a barrier to infection. EBM manufacturing produced markedly superior transcutaneous implants compared to machining.