Adhesion Behavior Research Articles

Curing monitoring of adhesive layers between metal adherends by ultrasonic resonance technique

Abstract Layer resonance induced by ultrasonic wave incidence is applied to monitor the viscoelastic properties of a curing adhesive layer between metal plates. The theoretical analysis shows that when the adhesive layer is modeled as a linear viscoelastic material, the ultrasonic reflection spectrum takes local minima at the layer resonance frequencies depending on the wave velocity of the adhesive. On the other hand, the local minima of the reflection spectrum can be expressed as a function of the loss factor of the adhesive. Based on these results, a characterization technique for the wave velocity and the loss factor of a curing adhesive layer is proposed. This technique enables the evaluation of the viscoelastic properties even if the reflected waves from both faces of a bond layer cannot be separated. The proposed method is employed to investigate the curing behavior of bi-component epoxy adhesives. As a result, it is shown that the bonding condition affects the variation of the wave velocity and loss factor. The estimated wave velocity increases as the curing proceeds, while the loss factor sometimes takes a local maximum depending on the bonding condition and the frequency range. When the mixing ratio of the main and curing agents is imbalanced, the variation of the wave velocity becomes gradual. Furthermore, the increase in the curing temperature leads to fast changes in the wave velocity and loss factor. The proposed technique has the potential to provide insight into the curing behavior of the adhesive layer by incorporating it into other measurement methods and theories.

Research on Adhesion Pull-Off Behavior of Rigid Flat Punch and Viscoelastic Substrate

Interfacial adhesion is one of the key factors affecting the reliability of micro–nano systems. The adhesion contact mechanism is still unclear as the time-dependent viscoelasticity of soft materials. To clarify the adhesion interaction, the pull-off detachment between the rigid flat punch and viscoelastic substrate is explored considering the viscoelasticity of soft materials and rate-dependent adhesion. Taking the Lennard-Jones (L-J) potential characterizing interfacial adhesion and the Prony series defining the viscoelasticity of materials as references, the bilinear cohesion zone model (CZM) and standard Maxwell model are employed, and an adhesion analysis framework is established by combining finite element technology. The influence laws of the loading and unloading rates, material relaxation coefficients and size effect on adhesion pull-off behavior are revealed. The results show that the pull-off force is independent of the material relaxation effect and related to the unloading rate. When v^ ≥ 50 or v^ < 0.01, the pull-off force has nothing to do with the unloading rate, but when 0.01 < v^ < 50, the pull-off force increases with the increasing unloading rate. Also, it is controlled by the size effect, and the changing trend conforms to the MD-n model proposed by Jiang. The energy required for interfacial separation (i.e., effective adhesion work) is a result of the comprehensive influence of unloading rates, material properties and the relaxation effect, which is consistent with Papangelo1’s research results. In addition, we derive the critical contact radius of the transition from the Kendall solution to the strength control solution. This work not only provides a detailed solution for the interfacial adhesion behavior but also provides guidance for the application of adhesion in Micro-Electro-Mechanical Systems (MEMSs).

Unraveling a Molecular Adhesion Mechanism at Complex Polymer-Metal Interfaces.

Controlling polymer-metal adhesion is critical in ensuring that materials can be cleanly separated during production processes without residue, which is crucial for various industrial applications. Accurately characterizing adhesion on industrial-grade surfaces is complex due to factors like surface roughness and actual contact area between surfaces and the polymer. In this study, we quantified the adhesive behavior of stainless-steel samples with varying surface treatments against a polymer using the surface forces apparatus (SFA) in reflection geometry, as well as X-ray photoelectron spectroscopy (XPS). We compared adhesive properties with the penetration depth of oxygen and the hydroxide-to-oxide ratio, which were modified by plasma and thermal treatments. Our results indicate that both treatment types enhance the deadhesive properties of the materials compared to native passive films, due to decreasing hydroxide functionality on the surface. Thermal treatment reduces adhesion further, due to an even lower hydroxide content, which reduces hydrogen bonding between the surface and polymer. Furthermore, we show that van der Waals forces, which depend on the density, have marginal to no influence on the adhesive behavior. This study not only advances our understanding of the factors influencing polymer-metal adhesion but also demonstrates the application of the SFA in reflection geometry for characterizing industrially relevant rough surfaces.

Characterization of 3D printed composite for final dental restorations.

This study evaluated the mechanical, optical, microstructural, surface, and adhesive behavior of a 3D printing resin comparing it with a machinable resin composite. Specimens of different sizes and shapes were either printed (Vitality, Smart Dent) or machinable (Grandio Blocs, Voco GmbH) resin composites with similar composition were prepared. Surface and mechanical characterization were performed with Knoop hardness, flexural strength (three-point-bending), and elastic modulus tests. The wear of the tested materials was evaluated against steatite antagonists. The optical properties stability (color change, ΔE00, and translucency, TP00) were observed after staining in red wine. In addition, the bond strength of the resin composites to two resin cement protocols were investigated with microshear bond strength tests at baseline and after thermocycling. Scanning electron microscope (SEM) coupled with Energy-Dispersive X-ray Spectroscopy (EDS) was used for microstructural and chemical characterization. Statistical analyses were performed with t- and ANOVA tests. Hardness values (132.76 (16.32) KH- Machinable and 35.87 (2.78) KH - Printed), flexural strength (172.17 (26.99) MPa - Machinable and 88.69 (8.39) MPa - Printed), color and translucency change (1.86 (0.31)/0.06 - Machinable and 3.73 (0.36)/9,16- Printed), and wear depth (24.97mm (3.60)- Machinable and 7.16mm (2.84) - Printed) were statistically different. Average Regarding bond strength, mean values (MPa) for non-aged and aged groups were respectively 21.76 (6.64) / 31.9 (12.66) for Bifix cement (Voco GmbH, Cuxhaven, Germany) and 26.75 (5.14) / 24.36 (6.85) for Variolink cement (Ivoclar Vivadent, Schaan, Liechtenstein) in Printed and 17.79 (3.89) / 9.01 (3.36) ) for Bifix cement and 22.09 (6.55) / 11.01 (3.77) for Variolink cement in Machinable materials. The material and aging factors did affect bond strength but the cement factor did not (p = 0.202). No statistical differences were observed for mean roughness (Ra) between materials. The better dispersion and larger size of the inorganic particles in the Machinable resin were contrasted with the clustered smaller particles of printed resin, under SEM. The mechanical properties and color stability of the machinable resin were superior to those of the printed resin, probably due to the greater amount and dispersion of inorganic particles in the Mach resin, but bond strength after aging was stronger and more stable in the printed resin. 3D-printed resin composites with similar compositions to machinable resin composites do not necessarily exhibit the same properties, which can impact clinical performance. Understanding these differences can assist manufacturers in improving their materials and help clinicians distinguish between materials appropriate for provisional and final restorations.

A Microfluidic Design for Quantitative Measurements of Shear Stress-Dependent Adhesion and Motion of Dictyostelium discoideum Cells

Shear stress plays a crucial role in modulating cell adhesion and signaling. We present a microfluidic shear stress generator used to investigate the adhesion dynamics of Dictyostelium discoideum, an amoeba cell model organism with well-characterized adhesion properties. We applied shear stress and tracked cell adhesion, motility, and detachment using time-lapse videomicroscopy. In the precise shear conditions generated on-chip, our results show cell migration patterns are influenced by shear stress, with cells displaying an adaptive response to shear forces as they alter their adhesion and motility behavior. Additionally, we observed that DH1-10 wild-type D. discoideum cells exhibit stronger adhesion and resistance to shear-induced detachment compared to phg2 adhesion-defective mutant cells. We also highlight the influence of cell density on detachment kinetics.

Fabrication of Zinc(II) Mediated Poly(Acrylamide Co Acrylic Acid) Hydrogel with Thixotropic and Tribological Properties.

Hydrogels have emerged as promising candidates for biomedical applications, such as replacing natural articular cartilage, owing to their unique viscoelastic properties. However, sufficient mechanical properties, self-healing ability, and adhesive nature are some issues limiting its application window. Here, a facile one-pot synthesis of dual cross-linked zinc-coordinated copolymer hydrogels is presented. The network structure of the copolymer hydrogels is strategically developed via dynamic and reversible physical cross-linking by Zn2+ ions and simultaneous covalent cross-linking through a covalent cross-linker viz methylene bisacrylamide. Fourier-transform infrared (FTIR), X-ray diffraction (XRD) scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) analysis have thoroughly characterized the structure of the synthesized hydrogels. The introduction of Zn2+ offers dynamic and reversible complexation, leading to excellent mechanical properties and self-healing features. Moreover, the percentage of the equilibrium water content of zinc-coordinated copolymer hydrogel samples is comparable with that of natural articular cartilage. The Shear sliding study shows the dominant adhesive behavior of HGel-Zn(NO3)2 sample compared to the parent HGel sample. This facile dual cross-linked hydrogel, HGel-Zn(NO3)2, with a combination of good mechanical properties, efficient self-recovery, adequate water content, and favorable adhesive nature, seems very promising to mimic the articular cartilage.

Heat transfer origin of adhesion behaviors between liquid-aluminum and solid aluminum/silicon interfaces

Liquid-aluminum tends to adhere to some surfaces rather than others, and the underlying mechanism of the differences in adhesion of liquid-aluminum on different surfaces is still unclear. This manuscript takes liquid-aluminum/aluminum and liquid-aluminum/silicon interfaces as research objects, revealing that solid aluminum surface is aluminophilic but the solid silicon surface is aluminophobic, mainly due to differences in interfacial thermal conductance (ITC) between two interfaces. We also investigate effect of surface temperature on adhesion characteristics of liquid-aluminum on aluminum/silicon surfaces, and decode the reasons from lattice integrity and phonon spectra. It is shown that vibrational state with intact lattice excites fewer low frequency phonons with increasing surface temperature, resulting in a decrease in ITC and thus adhesion force. In diffusion state where lattice is fractured resulting from high temperature, interfacial adhesion is increased due to surface defects.

Prediction of mass adhesive damage based on the Rousselier model: Experimental and numerical analysis

The study of the mechanical strength of adhesives remains an important area of research for researchers. These adhesives must be prepared in the form of mass test pieces to characterize them under different mechanical stresses. However, during the preparation of the test pieces several defects are likely to be present, namely air bubbles, cavities, or impurities. The behavior of the adhesive differs depending on the presence of one of these defects and, in most cases, the real behavior of the adhesive is not precisely known. For this purpose, several tests are necessary to have a close estimate of the adhesive's behavior. To numerically model the behavior of the adhesive it is necessary to consider the presence of these types of defects. This paper proposes a damage criterion based on the Rousselier model, which describes the damage due to crack growth from the presence of cavities in an adhesive, assumed as a ductile material. The proposed damage model was developed and implemented in a user-defined subroutine in the ABAQUS finite element code. Other damage models integrated into ABAQUS were used. In addition, the extended finite element method (XFEM) was used in the numerical simulations to study automatic damage modelling by the appearance and propagation of cracks in highly stressed areas. The main objective of this work is an analysis by the finite element method to determine the elastoplastic behavior coupled with the damage in the mass adhesive, considering the size, position, and shape of the defect (porosities) by the proposed models. Initially, experimental tests were carried out on mass specimens of adhesive to characterize the tensile response and to determine their mechanical properties depending on the position and size of the defect, which may exist in the specimen following its fabrication. The numerical results were validated by uniaxial tensile tests on the mass adhesive. Comparisons with the damage models integrated into ABAQUS have proven their effectiveness in predicting the behavior of the adhesive in the presence of a cavity.

Ultrasonic-Assisted Marine Antifouling Strategy on Gel-like Epoxy Primer

Ultrasonic technology has drawn extensive interests for its great potential in marine antifouling applications. However, its effects on the adhesion behavior of marine fouling organisms on marine structures remain underexplored. This work investigated how ultrasonic treatment impacted the adhesion of Pseudoalteromonas on a gel-like marine epoxy primer. And the process parameters for ultrasonic treatment were optimized using response surface analysis with Design-Expert software 11. The results revealed that ultrasonic treatment disrupted the cellular structure of Pseudoalteromonas, causing the deformation and fragmentation of the cell membrane, leading to bacterial death. Additionally, ultrasonic treatment reduced the particle size and Zeta potential value of Pseudoalteromonas, which disrupted the stability of bacterial suspensions. It also increased the relative surface hydrophobicity of Pseudoalteromonas cells, resulting in a reduction in adhesion to the gel-like marine epoxy primer. This study demonstrated that ultrasonic treatment significantly disturbed the adhesion behavior of microorganisms like Pseudoalteromonas on the gel-like marine epoxy primer, which provided an effective approach for controlling marine biofouling.

Nanocasting synthesis of mesoporous CeO2 particle abrasives from mesoporous SiO2 hard templates for enhanced chemical mechanical polishing performance

Mesoporous abrasive particles exhibit superior chemical mechanical polishing/planarization (CMP) performance, as compared with the corresponding bulk materials. Nevertheless, the lack of control over the shape and particle size or distribution extremely restricts the development of mesoporous abrasives and their potential applications. To overwhelm these drawbacks, pure and ytterbium-doped mesoporous ceria (mCeO2 and mCeYbO2) spheres with well-defined morphology and good uniformity were synthesized via a straightforward nanocasting strategy using high-quality mesoporous silica spheres as hard templates and metal nitrates as precursors. The resulting samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, UV–vis diffuse reflectance spectroscopy, photoluminescence spectroscopy, Zeta potential, and N2 adsorption-desorption measurements. The as-prepared mCeO2 and mCeYbO2 products exhibited enriched surface defects (trivalent Ce, vacancy oxygen, hydroxyls) and polycrystalline porous frameworks with a surface area of up to 160 m2/g and pore size of 4–7 nm. Benefiting from these synergistic attributes, the flexible and defective particle abrasives enabled significant improvements in both surface quality and removal efficiency during oxide-CMP, as compared to commercial CeO2. A possible CMP mechanism was proposed on the basis of the physical contact state, adsorption and adhesion behavior, as well as tribochemical interaction occurred at CeO2–SiO2 interfaces. This work demonstrates highly promising abrasive materials advancement combining architecture and defect engineering towards high-performance oxide-CMP.

The role of nanomaterials in enhancing adhesion properties between bitumen and aggregate particles

During production and construction stages of asphalt mixtures, rheology of bitumen must be set at certain level. In addition, the adhesion strength between bitumen and the aggregate particles should be high enough so that during the service life of the pavement, asphalt mixture can resist various distresses. There are different methods of controlling rheological properties of bitumen binders and increasing adhesion properties of asphalt mixtures. One of the most effective methods of modifying bitumen binders of asphalt mixtures is using nanomaterials. In this research, two bitumen types of 60/70 and 85/100 penetration grades, three aggregate types (limestone, siliceous, and granite) and four nanomaterials types (nanohydrated lime NHL, nanosilica NSiO2, nanolime NCaCO3, and nanoclay bentonite NClay) were used at 2, 4, and 6% of the weight of bitumen. X-ray diffraction and X-ray fluorescence tests were performed and, microscopic images of thin-sections of aggregates and asphalt mixtures were taken with the aim of evaluating petrographic properties of aggregates and bonding characteristics of the bitumen binders with aggregate particles. Physical and rheological properties of the nano-modified bitumen binders were evaluated, performing dynamic shear rheometer and rotational viscometer tests. Boiling water and pull-off tests were also carried out in order to investigate the coating ability and the adhesion strength that is performed at the aggregate surface in the interface with the bitumen binders. Digital images were analyzed using Digimizer Software. The results indicated that the addition of nanomaterials at certain optimal percentage affected viscosity and improved rheological behavior of the bitumen binders at different temperatures, and increased adhesion properties of the bitumen coating the aggregate particles. Comparing the effects of different aggregates, it resulted that the binder coating the limestone aggregates performed better than the siliceous and the granite aggregates. The adhesion and the rheological properties of the 60/70 pen bitumen that was modified with nanomaterials were better than those of the 85/100 pen bitumen. Nano-modified binders at 4% NHL, or 2% NSiO2, or 4% NCaCO3, or 4% NClay exhibited the best behavior. Among these, the nano-modified binders containing 4% NHL resulted in better performance. Finally, the correlation between the adhesion and rheological behavior was suitable for nano-modified binders in order to improve the asphalt mixes' performance in operation and construction stages.

The effect of roughness and top layer in solid particle impingement erosion of multilayer nanostructured nitride PVD coatings

The effect of the surface roughness of the coating and the composition of the upper layer on the solid particle erosion of multilayer nanostructured coatings applied via cathodic arc evaporation (CAEPVD) method was investigated. CrN/TiN nanostructured multilayer coating (TiN as the upper layer) and TiN/CrN nanostructured multilayer coating (CrN as the upper layer) were applied on 410 stainless steel through the CAEPVD method with the following architecture. 1) a bottom layer of Cr and CrN deposited on the substrate, 2) nanolayers of TiN and CrN deposited on the bottom layer alternately and 3) an upper layer of CrN or TiN deposited on the nanolayers. After applying the coating, half of the samples were polished to obtain smooth surfaces, while the other half remained unpolished, resulting in rough surfaces. Surface morphology, phases identification, adhesion, mechanical, and erosion behavior of the coatings were characterized using SEM, XRD, Rockwell adhesion measurements, nanoindentation test, and solid particle impingement, respectively. The nano-scale indentation results demonstrated that the hardness, Young's modulus, H/E, and H3/E2 of the CrN/TiN coating were 5.57, 1.42, 3.86, and 85.39 times larger than those of the substrate. For the TiN/CrN coating, the values were 4.04, 1.13, 3.53 and 51.68 times greater than those of the substrate. The results of the erosion test showed that the erosion mass loss for the CrN/TiN and TiN/CrN coatings decreased up to 73% and 67%, respectively. Additionally, surface smoothing improved erosion resistance by 40% for both coatings. This shows that the smoothed CrN/TiN nanostructured multilayer coating is an excellent candidate for increasing the erosion resistance due to the higher ratios of H/E and H3/E2 and smoother surface.

Investigation of the Adhesion and Debonding Behaviors between Warm-Mix Recycled Asphalt and Aggregates Based on Molecular Dynamics Simulation

Investigation of the Adhesion and Debonding Behaviors between Warm-Mix Recycled Asphalt and Aggregates Based on Molecular Dynamics Simulation

Impact of Binder Selection on Functional Properties of Polymer Nanocomposite Featured with Metal Oxide Nanoparticle

The effectiveness of nanocomposite materials depends on the accuracy of the binder selection process. This process is crucial for ensuring compatibility, better adhesive behaviour, and stability during the synthesis of polymer composites with metal nanoparticles. An investigation was conducted to analyze the accuracy and efficiency of binder materials on metal nanoparticle (oxide) featured polymer composites. The investigation utilized Advanced Spectroscopic Computational Optimization Analysis (ASCOA) and high-throughput experimental methods to identify and optimize binders using computational modelling (ACM). The processes driving binder-nanoparticle interactions were unravelled by combining advanced characterization methods such as Transition Metal Oxide-based Materials (TMO-M), non-hydrolyzable sialic acid (N-HSIA), and oxygen reduction reaction process (ORR) investigations. In-depth simulation analyses were performed to verify the effectiveness of the proposed methods and gain further understanding. These simulations investigated alternative binding arrangements to maximize material performance while considering sustainability and economic factors. The results demonstrated how binder choice affects material properties, which can be valuable for designing better nanocomposite materials for specific purposes. Additionally, the ASCOA and ACM analyses revealed an accuracy ratio of more than 90% and efficiency ratios of 86% and 84% for ASCOA and ACM, respectively.

A membrane localized RTX-like protein mediates physiochemical properties of the Pantoea stewartii subsp. stewartii cell envelope that impact surface adhesion, cell surface hydrophobicity and plant colonization

Pantoea stewartii subsp. stewartii (Pnss), is the bacterial causal agent of Stewart’s wilt of sweet corn. Disease symptoms include systemic wilting and foliar, water-soaked lesions. A Repeat-in-toxin (RTX)-like protein, RTX2, causes cell leakage and collapse in the leaf apoplast of susceptible corn varieties and is a primary mediator of water-soaked lesion formation in the P. stewartii-sweet corn pathosystem. RTX toxins comprise a large family of proteins, which are widely distributed among Gram-negative bacteria. These proteins are generally categorized as cellulolysins, but the Biofilm-Associated Proteins (Bap) subfamily of RTX toxins are implicated in surface adhesion and other biofilm behaviors. The Pnss RTX2 is most phylogenetically related to other Bap proteins suggesting that Pnss RTX2 plays a dual role in adhesion to host surfaces in addition to mediating the host cell lysis that leads to water-soaked lesion formation. Here we demonstrated that RTX2 localizes to the bacterial cell envelope and influences physiochemical properties of the bacterial cell envelope that impact bacterial cell length, cell envelope integrity and overall cellular hydrophobicity. Interestingly, the role of RTX2 as an adhesin was only evident in absence of exopolysaccharide (EPS) production suggesting that RTX2 plays a role as an adhesin early in biofilm development before EPS production is fully induced. However, deletion of rtx2 severely impacted Pnss’ colonization of the xylem suggesting that the dual role of RTX2 as a cytolysin and adhesin is a mechanism that links the apoplastic water-soaked lesion phase of infection to the wilting phase of the infection in the xylem.

Effect of N2/Ar Ratio on Wear Behavior of Multi-Element Nitride Coatings on AISI H13 Tool Steel.

In this study, multi-element nitride coatings composed of (Ti, Cr, Cu, Al, Si)N were synthesized on H13 tool steel using cathodic arc deposition (CAD) technology. The N2/Ar flow ratio varied from 0 to 2 as the experimental parameter, and two targets, Ti-Cr-Cu and Al-Si alloys, were utilized simultaneously. The impact of the gas flow ratio on the coatings' abrasion properties was investigated, focusing on aspects, such as chemical composition, adhesion, hardness, and wear behavior. The experimental findings indicate that the coated specimens with a nitrogen reaction exhibit superior hardness and abrasion resistance compared to those without nitrogen use. While the surface roughness of the specimens tends to increase slightly with a higher N2/Ar ratio, the coating demonstrates improved hardness, adhesion, and abrasion resistance performance. In summary, the wear-resistant characteristics of H13 tool steel can be significantly enhanced when applying a CAD-(Ti, Cr, Cu, Al, Si)N film with a flow ratio of N2/Ar = 2.

Numerical Investigation of Fracture Behaviour of Polyurethane Adhesives under the Influence of Moisture.

The mechanical behaviour of polymer adhesives is influenced by the environmental conditions leading to ageing and affecting the integrity of the material. The polymer adhesives have hygroscopic behaviour and tend to absorb moisture from the environment, causing the material to swell without applying external load. The focus of the work is to investigate the viscoelastic material behaviour under ageing conditions. The constitutive equations and the governing equations to numerically investigate the fracture in swollen viscoelastic material are discussed to describe the numerical implementation. Phase-field damage modelling has been used in numerical studies of ductile and brittle materials for a long time. The finite-strain phase-field damage model is used to investigate the fracture behaviour in aged viscoelastic polymer adhesives. The finite-strain viscoelastic model is formulated based on the continuum rheological model by combining spring and Maxwell elements in parallel. Commercially available post-cured crosslinked polyurethane adhesives are used in the current investigation. Post-cured samples of crosslinked polyurethane adhesives are prepared for different humidity conditions under isothermal conditions. These aged samples are used to perform tensile and tear tests and the test data are used to identify the material parameters from the curve fitting process. The experiment and simulation are compared to relate the findings and are the first step forward to improve the method to model crosslinked polymers.

Adhesion of a rigid sphere to a freestanding elastic membrane with pre-tension

Abstract Adhesion between a solid sphere and a thin film is a common but crucial issue in the study of biological membranes and two-dimensional materials. To supplement quantitative knowledge of membrane adhesion, this work addresses the axisymmetric adhesive contact between a rigid sphere and a circular freestanding elastic membrane with initial radial tension. For the membranes following linear stretching elasticity, both the JKR- and DMT-type adhesion as well as the transition regime in-between are considered. The dependences of external force with respect to the contact radius and displacement are derived analytically. In essence, the general solution is governed by three dimensionless parameters, reflecting the effects of membrane stretching elasticity, the range of adhesion force and the membrane size, respectively. It is interestingly found that the membrane size does not affect the contact radius and displacement at zero-external force at all and has minor influence on the value of pull-off force. The presented closed form solutions might be useful for the understanding of adhesion behaviors of sphere-membrane systems.

Investigation of pull-out and mechanical performance of fibre reinforced concrete with recycled carbon fibres

This paper presents the pull-out bonding behaviour and mechanical performance of recycled carbon fibre (rCF) reinforced concrete based on the recent investigation of fibre reinforced concrete (FRC) with rCF recovered from pyrolysis. Single fibre pull-out tests have been carried out to identify the apparent interfacial shear strength of different types of rCF and virgin carbon fibre (vCF) to identify the fibre matrix connection. Furthermore, a series of tests have been carried out to identify the workability, compressive strength and tensile strength of FRC. Besides rCF, also vCF and steel fibre were used for fabrication of FRC test specimens. rCF have shown the same adhesion behaviour and strength like vCF. Furthermore, the use of unsized or acrylate-based sized rCF creates an adhesion between fibre and matrix material. During the pull-out tests, the failure does not occur as an adhesive crack between fibre and cement matrix, but as a cohesive crack in the cement matrix. The mechanical performance of FRC with rCF was compared with mortar and FRC with vCF and steel fibres. The results of compressive test conducted for FRC with vCF and rCF indicated that the influence of vCF and rCF on the compressive strength of FRC was insignificant. On the other hand, the results of tensile test conducted for FRC with vCF and rCF indicated that the tensile strength of FRC with rCF was at least 14.9% greater than that of FRC with vCF.

CYTOSKELETON DYNAMICS AND SPATIAL ORGANIZATION DURING EPITHELIAL-TO-MESENCHYMAL TRANSITION

Epithelial-to-mesenchymal transition (EMT) is a crucial process that occurs during normal development, such as embryogenesis and organ formation. If it is inappropriately activated, it can lead to pathological processes like metastasis. Although EMT is well studied at the morphological and transcriptome level, cytoskeleton changes during this process are less understood. In our work we aimed to describe the morphological changes that occurred in MCF-7, A-549 and HaCaT cells after EMT, analyze microtubule dynamics, spatial distribution and its contribution to cell motility, identify changes in actin filament organization and study focal adhesion turnover in the cells after EMT. We hypothesized that the dynamics of microtubules in cells undergoing EMT might change. Cells undergoing EMT were expected to have more dynamic microtubules. Also, cells undergoing EMT are expected to adhere more efficiently to diverse substrates, and therefore spread and move more easily. Focal contacts in cells undergoing EMT were expected to be more pronounced and dynamic than in cells that not undergoing EMT. The research methods used in the study included inducing EMT in modified MCF-7 cells through an inserted inducible Tet-on system and stimulation of EMT in A-549 and HaCaT cells using TGF-β. The cells were observed using bright field microscopy, and immunofluorescence analysis was conducted to visualize microtubules and actin filaments. Transfection with EB-3–RFP protein was done to describe and measure microtubule dynamics, while transduction with Talin-RFP and transient transfection with Ptag-RFP-vinculin was done to visualize focal adhesions. Time-lapse fluorescent microscopy was used to record films, and the Fiji Image J program was used to analyze the data. All statistical analysis was performed using GraphPad Prism (Dotmatics, USA), and a nonparametric Mann-Whitney U test or parametric t-test with Welch correction. The actin filament measurements were completed using Matlab scripts. The major research findings: In all three-cell models after EMT, cell morphology changed. Cells increased in size. MCF-7 and HaCaT became spread out, while A-549 became elongated. Some of the cells lost cell-cell contacts. All three cell models after EMT had alterations in microtubule organization and dynamics. MCF-7 and HaCaT cells showed more frequently individual MTs at cell edges, while A-549 had less covered nucleus by MTs after EMT. Microtubule dynamics (growth velocity) increased, and the length of microtubule growth tracks became longer. The average angle of MT growth trajectories to cell radius decreased. Actin fibers rearranged into more pronounced stress fibers after EMT. Alterations in the focal adhesion behaviors were different in three models used. These results indicate that cytoskeletal changes during EMT mainly include increased microtubule dynamics.