Significant Adhesion Enhancement Research Articles

Low temperature-curable superhydrophobic surface with ultra-mechanical durable and anti-corrosion properties through structural engineering of coniferous ZnO

Superhydrophobic surfaces (SHS) receive considerable attention because of their wide applications, such as building materials, biomedical materials, and different metallic coatings. This study reports a simple and cost-effective approach for fabricating a robust superhydrophobic surface consisting of 1H,1H,2H,2H-perfluorooctyltriethoxysilane-modified SiO2 and coniferous ZnO nanoparticles dispersed in fluoroethylene vinyl ether (FEVE/FS@ZnO) on a stainless steel substrate. The prepared SHS coatings were curable at room temperature and easy to handle. They exhibited unique hierarchical and re-entrant structures, reducing surface energy and resulting in a long lifetime, significant adhesion enhancement, and superhydrophobic and self-cleaning properties. The highest water contact angle (CA) and roll-off angle were 156° and 3°, respectively, achieved at an optimized ZnO:fluoroalkylsilane mass ratio of 10:0.6. The SHS coatings also showed a significant anti-corrosion effect in a corrosion solution (3.5 wt% NaCl solution) and high stability against various acidic (H2SO4, pH = 1) and basic (NaOH, pH = 13) solutions. In addition, the SHS coating layer exhibited improved durability and stability in sandpaper abrasion and tape peel tests, with a CA of 153° after 130 sandpaper abrasion cycles. These results provide a pathway for the future development of multifunctional coating materials. The robust FEVE/FS@ZnO SHS coating with superhydrophobic and self-cleaning properties could be applied to various functionalized solid surfaces.

Efficacy of organic and antioxidant agents to regain bond strength to bleached enamel in different dental adhesive solvents.

Materials like carbamide peroxide or hydrogen peroxide are commonly used for vital teeth bleaching. However, there have been concerns regarding their effect on composite-to-bleached enamel bonding strength. The study investigated the impact of organic and antioxidant agents on composite bond strength in bleached enamel with different dental adhesive solvents. Human third molar teeth were sectioned into buccal and lingual halves. The two main adhesive solvent groups evaluated were acetone and alcohol. Each main group was divided into six groups. The positive control group received no bleaching, the negative control group consisted of bleaching with no surface deoxidization; and other experimental categories involved post-bleach treatments with 95% ethanol, sodium ascorbate (10%), acetone solution, or sodium fluoride solution (1.1%). Following the surface treatment and enamel bonding procedure, nano-hybrid composite cylinders measuring 3 × 2 mm were directly cured over the bleached enamel substrate. The shear bond test was performed after 24-h storage and 12,000 thermocycles on a universal testing machine. In this study, one-way ANOVA was used along with Tukey's HSD tests at a significance level of 0.05. The negative control groups showed significantly lower bond strength than the positive control group. Ethanol surface treatment had superior mean bonding strength in acetone and alcohol-based adhesive solvent groups. The utilization of sodium ascorbate for surface treatment resulted in a significant enhancement of adhesion between the composite material and bleached enamel surface. Sodium fluoride application showed no significant recovery in shear bond strength in both dental adhesive groups. It was concluded that hydrogen peroxide severely compromised the immediate bond strength of composite resin. Surface treatment of bleached enamel with ethanol, sodium ascorbate, and acetone solutions is an effective option for restoring bond strength.

Effect of long carbon bombardment step on the adhesion of thick amorphous carbon coating deposited by cathodic arc evaporation

The main restriction in the application of thick hydrogen-free amorphous carbon (a-C) coatings is the adhesion to the substrate, since high compressive stresses tend to delaminate the coating when a certain thickness is reached. In the present work, amorphous carbon films were deposited by unfiltered cathodic arc over a gas nitrided stainless steel substrate with metallic chromium as bond layer. An additional step was included, where carbon ions were accelerated by high bias potential before the deposition of functional a-C, to produce a carbon transition layer to act as a buffer layer. Different thicknesses of this transition layer were produced, including a sample without this step, for reference purposes. The coating adhesion was evaluated by scratch test. In addition, the microstructure of the interface was analyzed by scanning transmission electron microscopy (STEM) and the sp-type bonds were quantified by electron energy loss spectroscopy (EELS). The analysis of the microstructure close to the interface with the chromium bond layer revealed a mixing layer of Cr and C. Furthermore, it was observed the formation of the transition layer characterized by a homogeneous carbon layer with high sp2 content, when compared to the functional amorphous carbon layer. Results indicate a significant enhancement of adhesion for the samples prepared with the carbon bombardment step, which can be correlated to the presence of the mixing layer and the carbon transition layer. Moreover, a decrease in adhesion was observed for an increase in the thickness of the transition layer, which can be attributed to the lower shear strength of this sp2 rich layer.

Exploiting the role of nanoparticle shape in enhancing hydrogel adhesive and mechanical properties

The ability to control nanostructure shape and dimensions presents opportunities to design materials in which their macroscopic properties are dependent upon the nature of the nanoparticle. Although particle morphology has been recognized as a crucial parameter, the exploitation of the potential shape-dependent properties has, to date, been limited. Herein, we demonstrate that nanoparticle shape is a critical consideration in the determination of nanocomposite hydrogel properties. Using translationally relevant calcium-alginate hydrogels, we show that the use of poly(L-lactide)-based nanoparticles with platelet morphology as an adhesive results in a significant enhancement of adhesion over nanoparticle glues comprised of spherical or cylindrical micelles. Furthermore, gel nanocomposites containing platelets showed an enhanced resistance to breaking under strain compared to their spherical and cylindrical counterparts. This study opens the doors to a change in direction in the field of gel nanocomposites, where nanoparticle shape plays an important role in tuning mechanical properties.

Enhanced interfacial strength of plasma treated polyethylene and glass

Low-temperature plasma treatment represents an important technology to influence surface properties of polymers. Less financially demanding and environmentally friendly way leads to a significant enhancement of adhesion to another type of surfaces. The article describes the influence of plasma treatment time of polyethylene (PE) powder leading to the increase of interfacial strength to glass substrate. This strength was quantified by the tensile test and compared with the industrially used chemical products, maleic anhydride or silane. The maximum value of the interfacial strength was achieved by plasma treatment with an exposure time of 60 s and is at least by 150 % higher than in the case of the interphase created by silane. The results of the research, also proven by ESCA measurement, represent the potential of using plasma treatment of powder semi-products for the preparation of fibre-reinforced composites with a thermoplastic matrix processed only at atmospheric pressures. Keywords: Plastics; Glass; Surface treatment; Interface/interphase

Significant Adhesion Enhancement of Bioinspired Dry Adhesives by Simple Thermal Treatment

Bioinspired dry adhesives with micropillar arrays can be harnessed for precise and environment-friendly manufacturing. This study presents a simple and robust approach for developing synthetic dry adhesives with significantly enhanced adhesion strength without sophisticated structural modification or chemical surface treatment. We show that when dry adhesives with micropillar arrays are annealed at slightly elevated temperatures of 150–200 °C, their adhesion strengths are remarkably enhanced (maximum normal adhesion: 50.0 N cm−2) compared to those that are not treated thermally (normal adhesion: 17.6 N cm−2). The enhanced adhesion levels obtained by simple annealing surpass those of previously reported dry adhesives having nanoscale hairs with high aspect ratios or mushroom-like pillars with large tips. Experimental investigations regarding the chemical structure, surface roughness, surface energy, and elastic modulus of the dry adhesive samples indicate that the enhanced adhesion originates from the annealing-induced enhancement of the adhesive’s elastic modulus

Adipogeneis in the Bone Marrow Microenvironment Confers a Proliferative Advantage in Residual Leukaemic Cell Populations in Acute Myeloid Leukaemia after Allogeneic Stem Cell Transplantation

Up to 40% of poor risk Acute Myeloid Leukaemia (AML) patients receiving an allogeneic bone marrow transplant (BMT) from a donor will suffer disease recurrence/relapse within a year, significantly shortening their overall survival. Drug development to date has focused on clearing the bulk of leukaemic cells and how to target residual ‘Leukaemic stem cells,‘ which may give rise to relapse, however little work has been undertaken to discover the mechanisms by which the bone marrow niche may be unable to support normal haematopoietic stem cell growth and this may have a significant impact on the re-emergence of the patient's leukaemia. With the rise in the use of reduced intensity conditioning (RIC) regimes prior to transplant, the role of the patient microenvironment into which donor HSCs are engrafted warrants closer investigation.Stromal layers (AML-MSC) were derived from a cohort of 45 serial diagnostic, early (1-3 month), mid (6-9 month) and late (12 month+) post-transplant AML patients. Uniformity of stromal immunophenotyping markers (CD29, CD73, CD90, CD105, CD166, CD44, CD146) was present from passage 2 with concomitant loss of CD45 and other myeloid lineage markers (CD14, CD13, CD33, CD34). Diagnostic AML-MSCs showed a significant increase in stromal multipotency (CFU-F colony assays and CD146 expression, p<0.001) compared to both NBM and post-transplant MSCs. In comparison, early post-transplant colony formation was significantly reduced compared to other timepoints.AML-MSC supportive capacity for matched allogeneic donor (normal HSC) or autologous (malignant) blast populations was investigated using 14 day co-culture assays. Flow cytometric analysis of suspension and adherent co-culture fractions revealed AML blast cell numbers were consistently higher than comparative donor cell cultures at all post-transplant stages (p<0.001), suggesting patient AML-MSCs retain a preference for supporting their own blasts throughout different treatment stages. This observation was also confirmed in long-term LTC-IC assays in the stroma-adherent cobblestone fraction. Throughout serial samples, supportive capacity increased in later transplant AML-MSCs samples, confirming previous multipotency observations that stromal fitness to support stem cell growth may be compromised early post-transplant.Cytokine induced differentiation of AML-MSCs to osteoblast and adipocyte lineages resulted in a significant enhancement of adhesion and supportive capacity in the adipocyte lineage for AML blasts at all timepoints (p<0.002), which was absent in donor cell cultures. Osteoblast cultures gave results similar to that of the undifferentiated stromal layers for both AML and donor blast support. Parallel experiments using donor NBM-MSC layers revealed reduced support for AML blasts compared to that of matched AML-MSC stroma, however the same predisposition for adipogenic support of AML blasts was also observed.Luminex secretome profiling of serial AML-MSC supernatants using a panel of 105 pro-survival, inflammatory, migratory and immunomodulation cytokines revealed significant alterations in a number of targets associated with the diagnostic and post-transplant setting. Of the 80/105 targets detectable (>100pg/ml), high expression levels were seen in adhesion and ECM remodelling targets highlighting the ability of stromal secretory molecules to modify the surrounding environment. Hierarchical clustering analysis revealed post-transplant AML profiles correlated more closely with that of NBM-MSC at later time points, however significant increases in inflammatory/metabolic stress signalling molecules including IGFBP-3, Protein S, DKK1, VEGF, MMP1,MMP3, TPO (p,0.001), which have all been implicated HSC quiescence were associated with diagnostic and early post-transplant secretory profiles.In conclusion we identified several changes in the molecular and functional behaviour of the patient bone marrow microenvironment that may promote pro-leukaemic cell survival in post-transplant AML. Alterations in stromal fitness, adipogenic preference and metabolic stress signalling may contribute to a failing ability to support normal donor blood cells. Further exploration of therapies that target these alterations and prime the niche in favour of donor cells may provide a critical window for early clinical intervention and improved patient outcome. DisclosuresOttmann:Novartis: Consultancy; Celgene: Consultancy, Research Funding; Pfizer: Consultancy; Amgen: Consultancy; Takeda: Consultancy; Fusion Pharma: Consultancy, Research Funding; Incyte: Consultancy, Research Funding.

Significant Enhancement of the Adhesion between Metal Films and Polymer Substrates by UV-Ozone Surface Modification in Nanoscale.

Polymer metallization is extensively used in a variety of micro- and nanosystem technologies. However, the deposited metal film exhibits poor adhesion to polymer substrates, which may cause difficulties in many applications. In this work, ultraviolet (UV)-ozone surface modification is for the first time put forward to enhance the adhesion between metal films and polymer substrates. The adhesion of sputtered Cu films on UV-ozone modified poly(methyl methacrylate) (PMMA) substrates is enhanced by a factor of 6, and that of Au films is improved by a factor of 10. Moreover, metal films on the modified PMMA substrates can withstand a long-time liquid immersion. To understand the mechanism for the adhesion enhancement, the surface modification is studied with contact angle measurements, attenuated total reflection Fourier-transform infrared spectrometry (ATR-FTIR) and atomic force microscopy (AFM). Detailed characterization results indicate that the significant adhesion enhancement is attributed to the increases of both the surface wettability by generating some polar functional groups and the roughness of the surface in nanoscale. To demonstrate this novel polymer metallization method, a 6-in. PMMA chip with arrays of three-electrode electrochemical microsensors is designed and fabricated, and the microsensor exhibits excellent reproducibility, uniformity, and long-term stability.

The significant adhesion enhancement of Ag–polytetrafluoroethylene antibacterial coatings by using of molecular bridge

Weak adhesion between the metal-based antibacterial coatings and polymer substrates limits their clinical applications; surface modification is an effective way to solve this intrinsic problem. In this study, UV irradiation was employed to activate the inert silicon rubber substrates, and the grafting of coupling agent (3-mercaptopropyl) trimethoxy silane into the UV-irradiated substrates generated reactive surface containing SH groups. During electroless plating S which has lone pair electrons anchored Ag+ and produced antibacterial coatings with improved adhesion. The grafting of (3-mercaptopropyl) trimethoxy silane into silicon rubber was verified by X-ray photoelectron spectroscopy (XPS). The adhesion was tested by American Society of Testing Materials (ASTM D 3359-02). Surface elements content and distribution were observed and analyzed by X-ray energy disperse spectroscopy (EDS). The antibacterial performance was characterized by inhibition halo test and shake flash method. The results showed that the as-prepared composite Ag–polytetrafluoroethylene coatings possessed remarkably enhanced adhesion and superior antibacterial activity.

Cross talk with hematopoietic cells regulates the endothelial progenitor cell differentiation of CD34 positive cells.

IntroductionDespite the crucial role of endothelial progenitor cells (EPCs) in vascular regeneration, the specific interactions between EPCs and hematopoietic cells remain unclear.MethodsIn EPC colony forming assays, we first demonstrated that the formation of EPC colonies was drastically increased in the coculture of CD34+ and CD34− cells, and determined the optimal concentrations of CD34+ cells and CD34− cells for spindle-shaped EPC differentiation.ResultsFunctionally, the coculture of CD34+ and CD34− cells resulted in a significant enhancement of adhesion, tube formation, and migration capacity compared with culture of CD34+ cells alone. Furthermore, blood flow recovery and capillary formation were remarkably increased by the coculture of CD34+ and CD34− cells in a murine hind-limb ischemia model. To elucidate further the role of hematopoietic cells in EPC differentiation, we isolated different populations of hematopoietic cells. T lymphocytes (CD3+) markedly accelerated the early EPC status of CD34+ cells, while macrophages (CD11b+) or megakaryocytes (CD41+) specifically promoted large EPC colonies.ConclusionOur results suggest that specific populations of hematopoietic cells play a role in the EPC differentiation of CD34+ cells, a finding that may aid in the development of a novel cell therapy strategy to overcome the quantitative and qualitative limitations of EPC therapy.

Adhesion selectivity by electrostatic complementarity. I. One-dimensional stripes of charge

Highly enhanced and selective adhesion can be achieved between surfaces patterned with charges even when each one has no net charge. In this and a companion paper [C. Jin, Y. Bai, A. Jagota, and C.-Y. Hui, J. Appl. Phys. 110, 054903 (2011)] we analyze the possibility of adhesion selectivity between two flat surfaces patterned with stripes of surface charge chosen such that each surface initially carries no net charge. A few combinations, with appropriately matching strip widths, are predicted to adhere to each other. We also find that the deformability of the materials plays a critical role in defining the range of patterns that recognize each other, i.e., their selectivity. With increasing compliance, a significant enhancement of adhesion can be achieved by deformation that allows better matching between charge patterns.

Effect of head shape on the adhesion capability of mushroom-like biological adhesive structures

Theoretical studies have been extensively performed to reveal the mechanism of the biological adhesive structure with a flat head. However, most biological adhesive structures have a big head. Here we investigate the effect of the head shape on the adhesion capability of a mushroomlike adhesion structure based on a finite element model. We show that a mushroom-like head produces significant adhesion enhancement. We investigate also the effect of the elastic modulus of the adhesive structure on the adhesion. Our results are consistent with existing experimental results.

Effect of Rate on Adhesion and Static Friction of a Film-Terminated Fibrillar Interface

A film-terminated fibrillar interface has been shown to result in significant enhancement of adhesion and static friction compared to a flat control. This enhancement increases with interfibril spacing. In this, the first of a two-part study, by studying the effect of rate on adhesion and static friction, we show that both adhesion and static friction enhancement are due to a crack-trapping mechanism. For adhesion, as measured by an indentation experiment, an analytical model is used to relate the applied indenter displacement rate and measured forces to contact line velocity and energy release rate, respectively. The two mechanisms for adhesion enhancement--varying rate and crack-trapping--are found to be coupled multiplicatively.

Electroporation chip for adherent cells on photochemically modified polymer surfaces

We present a polytetrafluoroethylene electroporation microchip with integrated electrodes for transfection of adherent biological cells. For fabrication, UV-surface modification was employed in combination with metal deposition. UV irradiation in reactive atmosphere resulted in introduction of polar chemical groups into the polytetrafluoroethylene surface for significant adhesion enhancement of both biological cells as well as metal electrodes thereon. Electroporation was demonstrated by transfection of human embryonic kidney cells with the enhanced green fluorescent protein. Transparent, working at low voltages, and easy to handle, this chip yields the potential to reduce the amount of sequential working steps necessary for transfection.

Enhanced friction of elastomer microfiber adhesives with spatulate tips

Previous studies have demonstrated that gecko foot-hair inspired elastomer microfibers with spatulate tips have significant adhesion enhancement compared to the flat elastomer surface. In this study, we report the friction enhancement of these highly adhesive fibers and analyze the relation between adhesion and friction of elastomer microfiber arrays with spatulate tips. Fabricated polyurethane fiber arrays with spatulate tips demonstrate macroscale static friction pressures up to 41N∕cm2 for a preload pressure of 1.5N∕cm2 on a 6mm diameter smooth glass hemisphere.

Ion beam pretreatment of polymeric substrates for ITO thin film deposition

Polycarbonate (PC) surfaces were pretreated by an 1 keV Ar + ion irradiation in oxygen environment to improve surface properties before depositing indium tin oxide (ITO) films. The hydrophobic PC surfaces were converted into more hydrophilic ones after a surface modification. Improved wettability of the treated PC surfaces was due to the formation of new polar groups on the surfaces, responsible for the increase of polar component in the surface energy. Chemical interaction between unstable chains induced by energetic ion bombardment and oxygen gas resulted in the formation of the polar groups, which were identified as oxygen containing carbon bonds such as carbonyl by the XPS study. In the initial growth stage of the ITO films on the PC substrates, the newly formed polar groups prevented hill-locks from growing on the surfaces, which contributed to the improvement of thermal stability in the ITO thin films on the modified PC substrates. The Ar + ion irradiation in oxygen environment also led to a significant adhesion enhancement of PC substrates to ITO films which was explained in terms of the physical and chemical changes on the PC surfaces.

Adhesion of multi-level hierarchical attachment systems in gecko feet

Several creatures including insects, spiders and lizards have developed a unique clinging ability that utilizes dry adhesion. Geckos, in particular, have developed the most complex adhesive structures capable of smart adhesion — the ability to cling to different smooth and rough surfaces as well as detach at will. These animals make use of about three million microscale hairs (setae) (about 14 000/mm2) that branch off into hundreds of nanoscale spatulae (about a billion spatulae). Van der Waals forces are the primary mechanism utilized to adhere to surfaces, and capillary forces are a secondary effect that can further increase adhesion force. The hierarchical surface construction gives the gecko the adaptability to create a large real area of contact with surfaces. Modeling of the gecko attachment system as a hierarchical spring model has provided insight into adhesion enhancement generated by this system. It is shown that a multi-level hierarchical structure produces adhesion enhancement, and this enhancement increases with an increase in applied load and a decrease in the stiffness of springs. A significant adhesion enhancement occurs when the maximum spring deformation is greater than two to three times the root mean square amplitude of surface roughness. Although a gecko is capable of producing on the order of 20 N of adhesion force, it retains the ability to remove its feet from an attachment surface at will. Adhesion design databases for biomimetic attachment systems are presented. These adhesion design databases are useful for understanding biological systems and for guiding the fabrication of biomimetic attachment systems. A man-made fibrillar structure capable of replicating gecko adhesion has the potential for use in dry, superadhesive tapes that would be of use in a wide range of applications. These adhesives could be created using micro/nanofabrication techniques or self-assembly.

Adhesion analysis of multi-level hierarchical attachment system contacting with a rough surface

Several creatures, including insects, spiders and lizards, have a unique ability to cling to ceilings and walls utilizing dry adhesion. Geckos in particular have developed the most complex adhesion structures capable of smart adhesion, i.e., the ability to cling to and detach from different smooth and rough surfaces and detach at will. Their foot pads are covered by a large number of small hairs (setae) that contain many branches per seta with a lower level of spatulae. This hierarchical structure gives the gecko the adaptability to create a large real area of contact with rough surfaces. van der Waals attraction between the large numbers of spatulae in contact with the rough surface is responsible for high adhesion. In order to investigate the effect of the gecko's hierarchical structure, a three-level hierarchical model for a gecko lamella consisting of setae, branches and spatulae has been developed. We consider one-, two- and three-level hierarchically structured spring models for simulation of a seta contacting with random rough surfaces and demonstrate the effect of the multi-level hierarchical structure on the efficiency of seta attachment. Rough surfaces with various roughness parameters which cover a common range of most natural and artificial rough surfaces at the scale of a gecko's pad were generated. It is shown that a multi-level hierarchical structure produces adhesion enhancement, and this enhancement increases with an increase in the applied load and a decrease in the stiffness of springs. A significant adhesion enhancement occurs when the maximum spring deformation is greater than 2–3-times the root mean square amplitude of surface roughness.

Adhesion of PDMS Elastomers to Functional Substrates

ABSTRACT The JKR technique was applied to study the influence of interfacial reactions on the adhesion between functional elastomer gels and functional solid substrates. The gelation chemistry of poly(dimethyl siloxane) (PDMS) gels cured by hydrosilylation reactions was purposely adjusted to produce an excess of either silane or vinyl functionality. Hemispherical lenses of these materials were then contacted under load with a variety of functionalized solid substrates: poly(styrene-b-butadiene) copolymers with vinyl functionality, vinyl-terminated trimethoxysilane self-assembled monolayers, and α,ω-functional PDMS brushes terminated with either monomethoxy or hydroxyl groups. To rule out chain interpenetration effects, the molecular weights were kept below the entanglement molecular weight or immiscible polymers were employed on opposite sides of the interface. Significant adhesion enhancement was observed for most systems, indicating that a variety of different interfacial reactions can occur across the interface between PDMS elastomers and solid polymeric substrates. The overall nature of the adhesion enhancement found is consistent with the predictions of the Lake–Thomas theory for failure of elastomers, increasing linearly with the length and areal density of covalent linker chains that span the interface.

The influence of structure of the interface and interphase on paint adhesion

It has been demonstrated earlier that significant adhesion enhancement to chemically inert polyolefins can be attained through surface grafted connector molecules reactive with oxidized substrate surface. The effectiveness of adhesion improvement through such tethered interfaces was shown to depend on the mode of interaction with the adjacent medium: interpenetration or chemical reaction, as well as surface density and length of grafted molecules. We have frequently observed that some systems, such as in painted products, fail through the delamination of the coating from the substrate surface at the stress levels well below the anticipated load-bearing capacity of the tethered interface. Two interim hypotheses have been formulated to explain the observed phenomenon: (i) The chain scission in surface oxidized polyolefins takes place not only in the uppermost polymer surface, but may propagate into the sub-surface region, thus creating a weak boundary layer which fails cohesively through its bulk, (ii) In order to increase the load-bearing capacity of the interphase, the sub-surface region of the substrate needs to be reinforced by short-chain molecules penetrating into and subsequently providing effective crosslinks between individual fragments of excessively oxidized and hence, weaker sub-surface part of the interphase. In this paper we verify the above hypotheses. The oxidized sub-surface layer reinforced by polyethyleneimine becomes an integral part of the effective interphase in addition to the tethered interface and the interpenetrated network of connector molecules and the paint.