Adhesion Research Articles

Application of validated size-exclusion chromatography method for physicochemical characterization of topical gel formulation of deferoxamine conjugated with PEGylated carbon nanoparticles

The focus of current research work was to develop and validate size-exclusion chromatography method and develop and evaluate gel formulation of deferoxamine conjugated with PEGylated carbon nanoparticles (DEF-PEG-CNP) for topical delivery. Size-exclusion chromatography-based method was validated as per ICH guidelines. Effect of Carbopol® 974P and Transcutol® on the nanoparticles’ permeation was studied by 3-level full factorial design of experiment. Gel formulations were characterized for viscosity, cohesive and adhesive force by texture analyzer, and drug permeation through pig ear and human skin. The analytical method was specific as no interference from solvent or excipients were observed and met preset criteria of validation with limit of quantification of 0.24 ± 0.00 μg/mL. The nanoparticles permeation, steady state flux, and retained drug were statistically (p < 0.05) affected by Carbopol® 974P and Transcutol® percentage in the gel formulations. The permeation, steady state flux, and retained nanoparticles from the gel formulations varied from 23.2 ± 2.5 % to 70.9 ± 113.3 %, 0.8 ± 0.3 to 6.6 ± 2.1 μg/cm2.h, and 5.6 ± 0.3 to 38.8 ± 8.8 µg/g, respectively. Permeation of the nanoparticles was 1.9 folds higher in pig skin compared to human skin. Immunofluorescence detected successful permeation of DEF-PEG-CNP particles into skin. In conclusion, the analytical method can quantify the nanoparticles from the gel formulation without interference, and gel formulation of the nanoparticles can permeate across the skin.

The bending of 3D-printed bio-inspired sandwich panels with wavy cylinder cores

Beetle Elytron Plates (BEPs) represent a new class of biomimetic sandwich cores with excellent mechanical properties inspired by the microstructure of the beetle elytra. The cores have a hexagonal centre-symmetric configuration with through-thickness cylinders in the unit cell. In this work, we describe the behaviour of sandwich panels with novel BEP core configurations possessing wavy cylinders under four-point bending tests. Full-scale simulations are also carried out to validate the experimental data. The results show that all the sandwich panels produced with face skins adhesively bonded have material failure earlier than the adhesive bond failure. BEPs with wavy cylinders have larger peak loads compared to those with straight cylinders, and all BEPs show higher peak loads than those of sandwich panels with classical hexagonal honeycombs. Additionally, all the BEPs exhibit an enhanced ductility compared to honeycomb sandwich panels.

APC orchestrates microtubule dynamics by acting as a positive regulator of KIF2A and a negative regulator of CLASPs

Tumor suppressor protein Adenomatous polyposis coli protein (APC) is an EB-binding and microtubule (MT) plus end-tracking protein; however, how exactly APC regulates MT dynamics remains elusive. Here, we show that in LLC-PK1 cells, APC and KIF2A, an MT depolymerase, form a complex clustering at the cell edge and destabilize MTs at the MT plus ends. Further biochemical characterization and mutational analysis reveal key residues for the APC-KIF2A interaction. In addition, APC counteracts the major MT-stabilizer CLASPs at MT plus ends and promotes directional cell migration via modulating cell adhesion force. Reconstitution experiments demonstrate that APC potentiates KIF2A-induced MT catastrophes and antagonizes the stabilizing effect of CLASP2 in vitro. In summary, APC functions as a positive regulator of MT-destabilizer and a negative regulator of MT-stabilizer to orchestrate MT dynamics.

Filled elastomers sliding over smooth obstacles: Experiments and modeling in large deformations

The objective of this paper is to shed light on the mechanical response of filled elastomers in sliding contact. Compared to situations encountered by tires in breaking conditions, the study only considers smooth obstacles in order to analyse the contribution of finite deformations and of the complex viscosity of filled elastomers without facing all the complexity of surface roughness. For this purpose, a new experiment is introduced that allows to measure the friction on the surface of a filled elastomer that is subjected to large local deformation through a cyclic contact loading applied by sliding indenters. The setup uses smooth spherical indenters sliding on the material of interest within a temperature controlled water tank. The relevance of adhesion forces is reduced by using Teflon as a dry lubricant and Sinnozon as a surfactant. To analyze the experimental results, full-field simulations of the experiments are carried out within the setting of finite viscoelastodynamics by making use of two types of viscoelastic constitutive models for the filled elastomer: (i) a classical viscoelastic model combining a Mooney–Rivlin equilibrium elasticity and Maxwell branches with constant viscosities and (ii) an internal-variable-based viscoelastic model that was introduced in (Kumar and Lopez-Pamies, Comptes Rendus Mecanique 344, 102-112) for unfilled elastomers and that is extended herein to account for the more complex viscous response of filled elastomers.

Schottky Diode Leakage Current Fluctuations: Electrostatically Induced Flexoelectricity in Silicon.

Nearly four decades have passed since IBM scientists pioneered atomic force microscopy (AFM) by merging the principles of a scanning tunneling microscope with the features of a stylus profilometer. Today, electrical AFM modes are an indispensable asset within the semiconductor and nanotechnology industries, enabling the characterization and manipulation of electrical properties at the nanoscale. However, electrical AFM measurements suffer from reproducibility issues caused, for example, by surface contaminations, Joule heating, and hard-to-minimize tip drift and tilt. Using as experimental system nanoscale Schottky diodes assembled on oxide-free silicon crystals of precisely defined surface chemistry, it is revealed that voltage-dependent adhesion forces lead to significant rotation of the AFM platinum tip. The electrostatics-driven tip rotation causes a strain gradient on the silicon surface, which induces a flexoelectric reverse bias term. This directional flexoelectric internal-bias term adds to the external (instrumental) bias, causing both an increased diode leakage as well as a shift of the diode knee voltage to larger forward biases. These findings will aid the design and characterization of silicon-based devices, especially those that are deliberately operated under large strain or shear, such as in emerging energy harvesting technologies including Schottky-based triboelectric nanogenerators (TENGs).

Mechanical and failure behaviors of adhesively bonded dissimilar materials joints incorporating bio-inspired morphological irregularities

Adhesive dissimilar material joints between stainless steel grade 316L and polyethylene terephthalate glycol (PETG) plastic were examined, in which irregular interface morphologies inspired by natural sutures were incorporated. The joint interfaces exhibited various teeth-like, non-repetitive zigzag patterns based on a pseudo-randomization method and sutural interdigitation index. Effects of their irregularities on mechanical and failure characteristics of adhesive butt joints were studied by means of experiments and FE simulations. The cohesive zone model, Drucker-Prager plasticity model and ductile failure criterion were applied for the interface and PETG, respectively. Predicted load-displacement curves of joints with different teeth profiles were well validated. The degree of irregularity became higher to 20%, 40%, and 60%, the joint strengths decreased by 1.47%, 5.39%, and 11.95%, while the total energies to failure increased by 110.74%, 129.33%, and 161.23%, accordingly. More inhomogeneous morphologies led to earlier local damage initiation, but enhanced damage evolution range by impeding abrupt joint separation. Smaller teeth angles provided higher joint strength, whereas significant declines of bonding strength were observed by too acute teeth angle due to excessive stress localization and resulting teeth breakage. The teeth angle of 45º enabled the superior joint performance owing to a proper combination of interlocking and large adhesive force under shear stress state. Finally, a key insight for designing an optimal dissimilar joint with morphological irregularities was provided.

High strength “breathable” glycosilicone/Aloe vera polysaccharide-based gel dressing for efficient wound repair

Medical wound dressings are effective in protecting wounds, maintaining moisture, creating an optimal healing environment and accelerating wound healing. However, their deficiencies in mechanical properties, adhesion and prevention of adhesion to the wound bed have been identified as limiting factors for their therapeutic efficacy in wound healing. To address these issues, we prepared glycosilicone gel dressings consisting of hydrophobic polysiloxanes and highly hydrophilic polysaccharides via ester exchange and silicone hydrogen addition reactions. Silicone gel dressings exhibit skin-like “respiratory” properties, with good permeability to O2 and CO2. Additionally, elongation and other important parameters are similar to those of the skin, which provides a foundation for the application of silicone gels in the field of wound dressings. The introduction of Aloe vera polysaccharide (AP) results in the glycosilicone gel exhibiting certain mechanical properties, including a tensile strength of 0.35 MPa and an adhesion force of 10 N/m. Furthermore, a mouse model of total skin defect demonstrated that the wound healing rate of the mice on the 12th day was 98 %, which effectively promotes wound healing. Consequently, the glycosilicone gel is anticipated to be an optimal wound dressing.

Factors Affecting the Adhesion of Flour Particles to Stainless-steel Surfaces and Vacuum Dry-cleaning

Recent outbreaks and recalls linked to flour-based products have highlighted the need for improved cleaning methods in low-moisture environments. The factors affecting adhesion forces of flour particles, and the vacuum cleaning methodologies to overcome these forces, need to be better understood. The objectives of this study were to: (1) Measure electrostatic charge build-up in flour under different environmental conditions (20, 40, 60% relative humidity at room temperature), (2) quantify how powder size (US standard No. 60–80 or 80–100 mesh), electrostatic charge (charged and uncharged), and relative humidity impact the force required to remove the powder from an electropolished 304 stainless steel coupon (8 × 8 × 0.2 cm), and (3) determine the most effective vacuum nozzle angle (0, 45, 90° relative to the surface) for cleaning. Chargeability (nC) of flour samples was assessed using Faraday cup electrometry, while the surface adhesion force of the flour particles was measured using a custom-built impact tester. The surface cleanliness after vacuum treatments was assessed using ATP (adenosine triphosphate) swabs and a luminometer. Charged flour samples at 20% relative humidity (RH) exhibited a significantly higher charge compared to those at 40 and 60% RH. Within the 60–80 mesh range, charged flour showed higher adhesion rates than uncharged samples at both 20 and 40% RH. However, in the 80–100 mesh range, charged flour did not show a significant difference in adhesion when compared to uncharged samples at any RH level. Additionally, at 60% RH, surface residues measured by ATP were significantly lower for a vacuum angle of 90° than for 0° across both 60–80 mesh and 80–100 mesh size ranges of wheat flour. The vacuum cleaning treatment proved capable of overcoming the increase in adhesion from triboelectric forces; however, trace flour residues were still detected on stainless steel surfaces postvacuuming, indicating that vacuuming alone may be insufficient.

Surface-engineered caterpillar-like silica nanocomposites for enhanced interparticle friction and interlock in shear thickening suspension

This study presents a novel method for fabricating surface-engineered caterpillar-like silica nanocomposites by combining rod-like nanorods with spherical nanoparticles to control aspect ratios and surface functionalization. This unique design facilitates functional assembly at the nanoscale. Additionally, we developed an innovative composite by encapsulating polyurethane elastomers within shear thickening fluid (STF)-impregnated Kevlar, significantly enhancing the flexibility and durability of the resulting STF/Kevlar/PU composite. Microstructural and chemical modifications were characterized, and detailed rheological analysis revealed a 165 % increase in viscosity and a substantial rise in storage modulus from 91.56 to 18,640 Pa, indicating improved surface morphology and roughness. These enhancements promoted stronger interparticle friction and rotational motion during flow. Impact resistance tests further demonstrated a 314 % increase in peak impact force, driven by frictional interactions between the dispersed caterpillar-like particles. The results confirmed that surface roughness and adhesive forces play a critical role in activating stress-dependent frictional contacts, a key mechanism behind the improved performance. These findings highlight the potential of these composites for mitigating penetration injuries and offer precise control over the shear-thickening transition in engineering applications, making them promising candidates for lightweight protective materials.

A Ni-Based Metal Hydroxide-Organic Framework Mesh Membrane with Ultra-Durable Underwater Superoleophobicity for High-Efficient Oil/Water Separation

Recently, MOF-based oil/water separation membranes with superwettability have attracted great attention in the treatment of oily wastewater due to their uniform chemical composition and intrinsic porosity. However, the real separation performance is still limited by broking the metal-ligand bonds of conventional MOF materials in extreme chemical and mechanical environments, such as acidic, alkaline, saline, organic, and abrasion. Herein, we provide a metal hydroxide-organic framework (MHOF) composite mesh membrane for high-efficient oil/water separation by simply growing Ni2(OH)2 clusters onto a polydopamine (PDA)-modified stainless-steel mesh (SSM). Compared with conventional MOF materials, our membrane possesses ultra-durable underwater superoleophobicity by taking advantages of its strong chemical bridging, rich hydrophilic groups, and rough surface morphology, which enables a 1 μL water droplet to spread to 0° contact angle within <100 ms and also obtains an ultra-low underwater oil adhesion force ∼1.9 μN. Separation of both oil/water mixtures and oil-in-water emulsions can be achieved by this Ni-based MHOF mesh membrane with high separation efficiency >99.7% and large permeate flux >57,000 L·m-2·h-1. Furthermore, the Ni2(OH)2@PDA-SSM mesh membrane exhibits excellent anti-oil-fouling, chemical stability and abrasion resistance, which shows a promising candidate for practical applications. This study provides a rational strategy to construct high-performance MHOF membranes for oil/water separation.

Low-temperature treatment optimization for diesel-contaminated kaolin: Mutual impacts of generated pyrolytic carbon and particle agglomeration

Efficiency improvement in low-temperature treatment for diesel-contaminated sites is urgent because changes in soil properties and the generation of new substance during the remediation process can influence the duration and energy utilization. This paper focuses on low-temperature treatment optimization based on the mutual impacts of pyrolytic carbon and kaolin aggregation. Results reveal that the peak mass loss rate occurred between 100–150°C, with minimal loss beyond 200°C. Samples thermally treated at 150–200°C exhibited darker colors, indicating pyrolytic carbon formation, corroborated by x-ray photoelectron spectroscopy (XPS), fourier transform infrared spectroscopy (FTIR), and three-dimensional fluorescence spectrum (3D-EEM) analyses. Additionally, diesel contamination influenced the fractal dimension of aggregates by influencing adhesion forces (<10000 mg/kg) and forming liquid bridges (≥10000 mg/kg) in untreated kaolin, resulting in an initial increase and subsequent fall in fractal dimension with increasing concentration. Decline rates of pollutant gas concentration were closely correlated with fractal dimension changes under thermal conditions due to pollutant volatilization and pyrolytic carbon formation. Based on the consistency between fractal dimension and decline rate, two critical remediation concentrations (C0) and temperatures (T0) indices were identified to optimize the low-temperature remediation.

Comparative Assessment of Adhesive Bond Strength of 25% and 50% Propolis-modified Glass Ionomer Cement to Human Dentin: An In Vitro Study

Comparative Assessment of Adhesive Bond Strength of 25% and 50% Propolis-modified Glass Ionomer Cement to Human Dentin: An In Vitro Study

Intercellular Adhesion Disorders In Tumorigenesis

The review discusses the problem of adhesion impairment in the course of tumorigenesis and aging. We hypothesize that impairment of homophilic intercellular adhesion in the target tissue results in developing conditions, which are favorable for malignancy, invasion, and metastases. Like a phoenix vanishing during the initiation of a primary tumor by breaking contacts between identical cells, adhesion molecules reappear with a new quality (the phoenix rising mechanism), thereby causing invasive and metastatic behavior of tumor cells. Due to this, primary tumor cells acquire motility and the ability to form metastases, which are the cause of most cancer deaths. At the same time, the provision of adhesive bonds between cancer cells and immune effector cells can also be controlled by one of the main neurotransmitters, dopamine (DA). The discovery of peripheral DA in lymphocytes gave grounds to the assumption that DA is involved in the infiltration of tumor leukocytes. DA receptors are found on cells of the adaptive (specific) immune response: T and B lymphocytes. Direct communication between brain DA and peripheral DA is crucial in modulating immune function. Peripheral DA mediates differentiation, binding to tumor cells, and cytotoxicity of CD8+ T cells. The review also confirms the need for the development of adhesion pharmaceutical agents. The disruption of intercellular adhesion in the target tissue and the general deficiency of immune surveillance can be controlled by central mechanisms involving brain DA, which is capable of regulating the active phase of immune responses against the tumor by means of adhesive interactions in the immune system, interfering with the process and thereby interrupting the development of a malignant neoplasm initiated by a local mutation in the tissue. The concept reveals the stress mechanism of cancer etiology and creates prospects for new methods of diagnostics, prevention and treatment of tumors, which can become another step towards solving the problem of malignant neoplasms.

Novel GSK-3 inhibitor based universal dentin bonding system: A comprehensive analysis of dentinal repair and improved bond strength

The aim of the study was to describe the formulation of a novel universal adhesive system, based on a GSK-3 (glycogen synthetase kinase-3) inhibitor (Tideglusib®), and to evaluate its bond strength and dentinal repair capability. Tideglusib® was added to Ultradent Peak Universal Dentin Bonding Agent to make experimental adhesives (0.5 %, 1 %, 2 % final concentration). They were applied to teeth which were sectioned, stored for 24 h, or 2 years then bond strengths measured. Baseline stiffness of bonded dentin beams was tested using the three-point bending test. Animal experiments were performed to provide specimens for microcomputed tomography imaging after adhesive application. Collagen matrix was evaluated using transmission electron microscopy. The cytotoxicity of the modified adhesives was determined using fibroblastic cells. Molecular modelling evaluated binding of the Tideglusib® molecule to active sites on collagen and the adhesive components. TGFβ-1/and BMP-2 in human dentin matrices were measured and interfaces were scanned using SkyScan 2211. Adhesives’ stability tests were done. ResultsRMSD (root mean square deviation) analysis indicated simulation has equilibrated with changes for globular proteins (p < 0.05). Specimens from 0.5 %, and 1 % Tideglusib® groups displayed adhesive penetration with Micro-CT imaging and a significant increase in dentin density was seen. Specimens from the same groups showed cells with large masses of cytoplasm with focal adhesion points. Bond strength decreased significantly (p < 0.05) with increased storage time. Gradual release (p < 0.05) of both TGFβ-1 and BMP-2 from hTDMs with 0.5 % and 1 % Tideglusib® groups occurred and higher elastic moduli (p < 0.05). Collagen-based amide and proline Raman bands were seen in the Tideglusib® groups. ConclusionIncorporation of Tideglusib® in experimental Universal Adhesive System at 1 % improved adhesive bond strength and promoted dentinal repair. Application of Tideglusib® based adhesive conserve mechanical properties of the tooth structure and promote regenerative capability so can be expected to extend the service life of adhesive restorations in clinical situations.

Multiscale revelation of asphalt morphology and adhesion performance evolution during stress relaxation process

The objective of this study is to investigate the evolution of asphalt morphology and adhesion properties during stress relaxation using atomic force microscopy (AFM) and molecular dynamics (MD) simulations. Changes in surface roughness, Derjaguin-Muller-Toporov (DMT) modulus, adhesion force, and force-distance curves were analyzed. Morphological and adhesion property evolution was assessed using correlation length and Lyapunov exponent. MD simulations provided insights into the internal stress-time relationship and free volume fraction of asphalt during relaxation. Results indicate that under constant tensile strain, the “bee structure” on the asphalt surface elongates, dark pits transform into light protrusions, microcracks heal, and surface roughness stabilizes after 10 h. Under compressive strain, similar changes occur but are more pronounced during tensile relaxation. The combined use of AFM and MD simulations offers a comprehensive understanding of the microscopic evolution mechanisms of asphalt under stress relaxation, providing valuable insights for optimizing asphalt pavement design and maintenance.

Adhesion of Meta-Aramid Coatings to Metal Substrates

The paper presents experimental investigations of the adhesive properties of meta-aramid coatings applied to metal substrates of different types. The increased adhesion ability of meta-aramid coatings to copper substrates was found in comparison with other metals and alloys used as structural materials. The dependence of the strength of the adhesive bond of the meta-aramid coating on the surface roughness at various concentrations of the polymer solution has been determined.

Investigation on the Adhesion Force between Tetrabutylammonium Bromide Hydrate Particles Using Atomic Force Microscopy.

This work investigates the adhesion force between tetrabutylammonium bromide (TBAB) hydrate particles dispersed in decane at different temperatures and TBAB concentrations using an atomic force microscopy. The thickness of the quasi-liquid layer (QLL) on the surface of the hydrate particles is calculated based on an adhesion force model. The results of force measurements indicate that the adhesion force between the hydrate particles increases with increasing temperature when TBAB concentration is 30 wt %. The increment of adhesion force between particles could be due to the increase in the QLL thickness on the particle surfaces. Furthermore, the force results also reveal that the adhesion force between hydrate particles(ice) at 253 K decreases when TBAB concentration increases from 0 to 30 wt %. The calculation indicates that QLL on the surface of formed hydrate particles becomes thinner at higher TBAB concentrations, which could be due to the conversion rate of water to hydrate within particles. The thickness of QLL is directly influenced by the temperature and TBAB concentration, which contributes to the adhesion force between hydrate particles.

Evaluation of the Flexural Behavior of One-Way Slabs by the Amount of Carbon Grid Manufactured by Adhesive Bonding

Fiber-reinforced polymers (FRPs), which are resistant to corrosion, are used as reinforcement material for concrete. However, the flexural behavior of concrete members reinforced with FRPs can vary depending on the properties of FRPs. In this study, the flexural behavior of one-way concrete slab specimens reinforced with a new grid-type carbon-fiber-reinforced polymer (CFRP) (carbon grid) manufactured by bonding pultruded CFRP strands to an adhesive was investigated. The experimental results indicated differences in the load–deflection relationships of the specimens depending on the carbon grid reinforcement amount. Specimens in which the carbon grids were over-reinforced or reinforced close to the balanced reinforcement ratio reached the maximum load due to concrete crushing and exhibited ductile failure. The specimen under-reinforced with the carbon grid exhibited brittle failure. Specimens with carbon grid reinforcement close to a balanced reinforcement ratio exhibited maximum loads ranging from 0.43 to 0.61 times the calculated flexural strength, which resulted in becoming 0.86–1.00 lower in the specimens with a wider width of the CFRP strands. This study proposes coefficients to estimate the stiffness of carbon-grid-reinforced concrete flexural members after cracking. Applying these coefficients resulted in stiffness calculations that reasonably simulated the behavior of the specimens reinforced with carbon grids after crack formation.

Polydopamine modification on dendritic porous silica surface for efficient adhesion of functional nanoparticles

The uniform and high-density immobilization of functional nanoparticles (NPs) on porous carriers is crucial to enhance various physicochemical properties and performances in diverse applications. However, there is a limited control towards the size and distribution of functional nanoparticles loaded on the carriers. In this work, the dendritic porous silica nanoparticles (DPSNs) featuring a three-dimensional center-radial porous structure were utilized as a nanocarrier, coated with a thin layer of polydopamine (PDA) to form DPSNs@PDA. The modified PDA exhibits strong adhesion and photothermal conversion properties. The pre-synthesized gold or platinum NPs (Au or Pt NPs) with tunable sizes were uniformly and densely loaded on the DPSNs@PDA, taking advantage of the strong adhesion properties of PDA. The resulting functional NPs-loaded DPSNs@PDA composites demonstrated excellent catalytic activity and recycling stability in heterogeneous catalysis, achieving over 95 % catalytic conversion efficiency of methylene blue (MB) after six cycles. Furthermore, due to the excellent photothermal effects of PDA and Au NPs, the apparent reaction rate increased by nearly threefold under 808 nm near-infrared (NIR) laser irradiation. The developed strategy of loading pre-synthesized NPs with tunable sizes by strong PDA adhesion force shows great potential for achieving efficient integration of various functional NPs, thereby facilitating the construction of advanced multifunctional materials.

A Gecko‐Inspired Robot Using Novel Variable‐Stiffness Adhesive Paw Can Climb on Rough/Smooth Surfaces in Microgravity

Space‐wall‐climbing robots face the challenge of stably attaching to and moving on spacecraft surfaces, which include smooth flat areas and rough intricate surfaces. Although adhesion‐based wall‐climbing robots demonstrate stable climbing on smooth surfaces in outer space, there is scarce research on their stable adhesion on rough surfaces within a microgravity environment. A novel adhesive material is developed inspired by the adhesion mechanism and locomotion of the Gekko gecko. This material exhibits exceptional adhesion across various materials and surface roughness. A variable‐stiffness gecko‐inspired paw is engineered, generating substantial adhesion forces while minimizing detachment forces. Impressively, this paw generates up to 180 N of adhesion force on smooth surfaces and achieves detachment without external forces. By integrating such variable‐stiffness paws with a wall‐climbing robot, a gecko‐inspired robot effectively operating in a microgravity environment is created. The robotic satellite surface climbing experiments and robotic satellite capture experiments are conducted using a simulated microgravity environment and a satellite model. The results unequivocally demonstrate the gecko‐inspired robot's proficiency in executing various functions, including stable motion and capture on both smooth and rough spacecraft surfaces within a microgravity environment. These experiments underscore the potential of adhesion‐based gecko‐inspired robots for in‐orbit services and spacecraft capture and recovery.