Long-term Adhesion Research Articles

The effect of substrate pre-treatment on durability of rubber-stainless steel adhesion

In many applications, rubber linings protect metal surfaces from the environment and prolong the service life of the metal components significantly. The loss of adhesion and resulting premature failure at the rubber-metal interface may generate an un-planned shutdown and production losses. This work focuses on the effect of various sand blasting methods on the long-term adhesion between bromobutyl rubber and stainless steel in a hot and humid environment. Softer austenitic stainless steel and harder, chemically more resistant super duplex stainless steel grades were used as substrates. It was found, that the developed interfacial area ratio Sdr, which is the additional surface area contributed by the texture as compared to the planar definition area, had the best correlation with the sand blasting media characteristics, namely to the hardness. The proportionality between other sand blasting medium characteristics and the Sdr value was poor. The initial adhesion between the rubber and the substrates was defined by the cohesive strength of the rubber and unaffected by the substrate characteristics and the sand blasting medium contaminants on the substrates. After a 4–12-week exposure in hot and humid environment, the use of corrosive sand blasting medium (steel grit) resulted in significant adhesion loss whereas the use of inert sand blasting media (feldspar or corundum) maintained the adhesion better. However, the adhesion system at the interface degraded causing performance loss. Neither the better corrosion resistance of super duplex stainless steel nor increased surface roughness improved the reliability of rubber lining in extreme conditions.

Molecular insights into the powerful mucus-based adhesion of limpets (Patella vulgata L.).

Limpets (Patella vulgata L.) are renowned for their powerful attachments to rocks on wave-swept seashores. Unlike adult barnacles and mussels, limpets do not adhere permanently; instead, they repeatedly transition between long-term adhesion and locomotive adhesion depending on the tide. Recent studies on the adhesive secretions (bio-adhesives) of marine invertebrates have expanded our knowledge on the composition and function of temporary and permanent bio-adhesives. In comparison, our understanding of the limpets' transitory adhesion remains limited. In this study, we demonstrate that suction is not the primary attachment mechanism in P. vulgata; rather, they secrete specialized pedal mucus for glue-like adhesion. Through combined transcriptomics and proteomics, we identified 171 protein sequences from the pedal mucus. Several of these proteins contain conserved domains found in temporary bio-adhesives from sea stars, sea urchins, marine flatworms and sea anemones. Many of these proteins share homology with fibrous gel-forming glycoproteins, including fibrillin, hemolectin and SCO-spondin. Moreover, proteins with potential protein- and glycan-degrading domains could have an immune defence role or assist degrading adhesive mucus to facilitate the transition from stationary to locomotive states. We also discovered glycosylation patterns unique to the pedal mucus, indicating that specific sugars may be involved in transitory adhesion. Our findings elucidate the mechanisms underlying P. vulgata adhesion and provide opportunities for future studies on bio-adhesives that form strong attachments and resist degradation until necessary for locomotion.

Combination of nanolamellae and PDA coating on promoting the long-term adhesion, proliferation, and differentiation of osteoblasts

Nanotopographical and chemical cues were collectively introduced onto the poly(L-lactic acid) (PLLA) surface via alkali etching and polydopamine (PDA) coating. The surface pattern was made of dense-packed PLLA lamellae, and the PDA coating did not change the feature of surface topography. Both nanotopographical pattern and PDA coating showed long-term stability in cell culture medium for two weeks. In vitro evaluations displayed that there was a synergy between nanotopography and PDA coating on cell adhesion, proliferation, and differentiation of osteoblasts, even for a culture period of two weeks. This sustained effect was attributed to the activation of the wnt/β-catenin pathway. These results hold a promising prospect for the application of bone repair grafts.

Tough, Long-Term, Water-Resistant, and Underwater Adhesion of Low-Molecular-Weight Supramolecular Adhesives

Modern functional adhesives have attracted considerable attention due to their reversible adhesion capacities and stimuli-responsive adhesion behavior. However, for modern functional adhesives, polymeric structures were highly necessary to realize adhesion behaviors. Supramolecular adhesives from low-molecular-weight monomers were rarely recognized. Compared with polymeric adhesive materials, it remains challenging for supramolecualr adhesive materials to realize tough adhesion on wet surfaces or even under water. In this study, a new supramolecular adhesive consisting of low-molecular-weight monomers was successfully designed and prepared. Strong and long-term adhesion performance was realized on various surfaces, with a maximum adhesion strength of 4.174 MPa. This supramolecular adhesive exhibits tough and stable adhesion properties in high-moisture and underwater environments (including seawater). Long-term underwater adhesion tests display the potential application of low-molecular-weight adhesive as a marine adhesive.

Cell adhesion and proliferation on common 3D printing materials used in stereolithography of microfluidic devices.

Three-dimensional (3D) printing has recently emerged as a cost-effective alternative for rapid prototyping of microfluidic devices. The feature resolution of stereolithography-based 3D printing is particularly well suited for manufacturing of continuous flow cell culture platforms. Poor cell adhesion or material-induced cell death may, however, limit the introduction of new materials to microfluidic cell culture. In this work, we characterized four commercially available materials commonly used in stereolithography-based 3D printing with respect to long-term (2 month) cell survival on native 3D printed surfaces. Cell proliferation rates, along with material-induced effects on apoptosis and cell survival, were examined in mouse embryonic fibroblasts. Additionally, the feasibility of Dental SG (material with the most favored properties) for culturing of human hepatocytes and human-induced pluripotent stem cells was evaluated. The strength of cell adhesion to Dental SG was further examined over a shear force gradient of 1-89 dyne per cm2 by using a custom-designed microfluidic shear force assay incorporating a 3D printed, tilted and tapered microchannel sealed with a polydimethylsiloxane lid. According to our results, autoclavation of the devices prior to cell seeding played the most important role in facilitating long-term cell survival on the native 3D printed surfaces with the shear force threshold in the range of 3-8 dyne per cm2.

Slippery Liquid-Attached Surface for Robust Biofouling Resistance.

Materials for biodevices and bioimplants commonly suffer from unwanted but unavoidable biofouling problems due to the nonspecific adhesion of proteins, cells, or bacteria. Chemical coating or physical strategies for reducing biofouling have been pursued, yet highly robust antibiofouling surfaces that can persistently resist contamination in biological environments are still lacking. In this study, we developed a facile method to fabricate a highly robust slippery and antibiofouling surface by conjugating a liquid-like polymer layer to a substrate. This slippery liquid-attached (SLA) surface was created via a one-step equilibration reaction by tethering methoxy-terminated polydimethylsiloxane (PDMS-OCH3) polymer brushes onto a substrate to form a transparent "liquid-like" layer. The SLA surface exhibited excellent sliding behaviors toward a wide range of liquids and small particles and antibiofouling properties against the long-term adhesion of small biomolecules, proteins, cells, and bacteria. Moreover, in contrast to superomniphobic surfaces and liquid-infused porous surfaces (SLIPS) requiring micro/nanostructures, the SLA layer could be obtained on smooth surfaces and maintain its biofouling resistance under abrasion with persistent stability. Our study offers a simple method to functionalize surfaces with robust slippery and antibiofouling properties, which is promising for potential applications including medical implants and biodevices.

Syringe-Injectable, Self-Expandable, and Ultraconformable Magnetic Ultrathin Films.

Syringe-injectable biomaterials and medical devices are important as minimally invasive implants for diagnosis, therapy, and regenerative medicine. Free-standing polymeric nanosheets with a thickness less than 1 μm and a flexural rigidity less than 10-2 nN m are a promising platform of syringe-injectable, implantable devices that provide conformable and long-term stable adhesion to the target biological tissues for in situ delivery of therapeutic materials. Here, we developed free-standing ultrathin films (<1 μm thick) based on polyurethane-based shape-memory polymer (SMP) and magnetic nanoparticles (MNP), termed MNP-SMP nanosheets. With the temperature-mediated shape-memory effect of SMP, we overcome the limitation in the manipulation of the conventional polymer nanosheets. In particular, we demonstrated the following four capabilities using the 710 nm thick MNP-SMP nanosheet with the glass transition temperature (Tg) of 25 °C: (1) syringe-injectability through the medical needles, (2) self-expandability after ejection, (3) conformability and removability on the biological surfaces, and (4) guidability in an external magnetic field. The MNP-SMP nanosheets were readily interfaced with an additional layer of poly(lactic-co-glycolic acid) (PLGA) to extend their functionality as a carrier of molecular and cellular drugs. The MNP-SMP nanosheets will contribute to the development of advanced syringe-injectable medical devices as a platform to deliver drugs, sensors, cells, and engineered tissues to the specific site or lesion in the body for minimally invasive diagnosis and therapy.

Long-term anticoagulation and selective cells adhesion surface via combination of covalent grafting and layer by layer assembly

Surface modification by long-term active component is essential for biocompatible polymers-based vascular grafts to prevent thrombus formation and reduce intimal hyperplasia. In this study, a simple approach was developed to immobilize bioactive heparin to the surface of ε-polycaprolactone (PCL) grafts through a two-step strategy combining covalent grafting and layer by layer assembly of polyelectrolytes. The performance of heparinized PCL was evaluated in vitro, including the release behavior of heparin, anticoagulation and different types of cells adhesion characteristic. A sustained-release of heparin was achieved by this immobilization strategy. Surface remaining heparin was up to 1.10 μg cm−2 on the modified PCL after release in vitro for 30 d. Specifically, the heparinized PCL has the long-term ability to prevent adhesion of blood cells and thrombus formation, and significantly inhibit the adhesion of smooth muscle cells. The two-step strategy provides a simple and general route to incorporate heparin on PCL graft surface. The surface heparinized PCL demonstrated in this work can be a useful material platform for biodegradable vascular stent graft.

Well-defined monolith morphology regulates cell adhesion and its functions

Hydrophilic epoxy resin-based monoliths were employed as cell culture substrates. The monoliths were made of a porous material with a bicontinuous structure that consisted of a porous channel and a resin skeleton. Monolith disks were prepared with a skinless surface through polymerization-induced spinodal decomposition-type phase separation. The pore sizes, which were well controlled by the polymerization temperature, ranged from 70 to 380 nm. The quantity of protein adsorbed per unit area and the early-stage adhesion of HepG2 cells on the monolith substrates were independent of pore size, meaning they were not affected by surface topology. Long-term cell adhesion, as indicated by adherent cell number and shape, as well as liver-specific gene expression were significantly affected by pore size. In terms of cell shape, number, and gene expression, pores of approximately 200 nm were most suitable for HepG2 cell growth. These results highlight the importance of monolith morphology for use as a cell culture substrate. The well-controlled morphology demonstrated in this work indicates monoliths are capable of supporting growth for various types of cells in a range of applications.

Epithelial cell adhesion on films mimicking surface of polymeric scaffolds of artificial urethra compared to molecular modeling of integrin binding

In this study, a combined experimental and computational study of long-term human bladder epithelial cell line HBLAK adhesion and proliferation on five different polymeric surfaces, namely hyaluronic acid, amylose, collagen, polyhydroxybutyrate, and polylactic acid, was performed with the goal to understand the nature of the attraction between various surface materials and a simplified model of the cell surface (transmembrane protein integrin). These biodegradable polymers are frequently used as scaffolds for tissue engineering. During formation of the new tissue, the scaffold polymers are gradually replaced by the natural extracellular matrix of the proliferating cells. Cell adhesion and proliferation experiments were carried out employing thin polymer films prepared by solvent casting while for the computational approach three-dimensional molecular models of layers of ordered polymeric fibers were used as quasi-planar nano-sized models of polymeric surface patches. Experimental results indicated a good capability of amylose, polyhydroxybutyrate, and hyaluronic acid polymer films to foster cell adhesion. Proliferation experiment, carried out by incubating cells with the investigated polymer films for 72 h, showed that all the investigated polymers are able to sustain a good proliferation of HBLAK cells almost comparable to plain glass. Computational estimate of molecular mechanic interaction energies between three-dimensional models of polymeric films and the collagen-binding α2 I domain of the cell adhesion receptor integrin α2β1 confirmed elevated affinity to amylose and polyhydroxybutyrate that is related to higher polarity of function groups on the film surface as documented by the maps of molecular electrostatic potential. This combined experimental and modeling approach can contribute to rational design and surface modifications of polymeric material suitable for forming the scaffolds of human urethra that can be effectively colonized by stem cells.

Influence of physicochemical surface properties on the adhesion of bacteria onto four types of plastics

Bacterial adhesion onto plastics is common in natural environments and can also affect the fate and transport of plastics in aquatic environments. To date, the adhesion of bacteria to different types of plastics has not yet been systematically studied. In this study, we systematically investigated both the short-term and long-term adhesion of three types of bacteria (both model and wild-type bacteria) onto four types of plastics, including polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), and polyvinyl chloride (PVC), which are the most frequently encountered plastics in aquatic environments. The results showed that the amount of bacteria that adhered to PE and PVC surfaces was much greater than that attached to PP and PET, regardless of the bacteria type in both short-term and long-term adhesion experiments, following the trend as: PE ≈ PVC > PP ≈ PET. The similar adhesion behavior of bacteria onto plastics that was found in both short-term and long-term experiments showed that the intrinsic surface properties of the different types of plastics influenced the bacterial adhesion. Therefore, physicochemical factors, including surface charge, hydrophobicity/hydrophilicity, roughness, and hardness of the plastics, were further characterized. Compared with the minimal differences in surface charge, hydrophobicity/hydrophilicity, and roughness among the different types of plastics, the surface hardness of the plastics was found to be the key factor dominating the adhesion of bacteria onto plastic surfaces. The results give insights to assess the fate and transport of different types of plastics in real environments.

Fine-tuning of chemical and physical polymer surface modifications by atmospheric pressure post-discharge plasma and its correlation with adhesion improvement

Our study focuses on the use of a remote atmospheric pressure plasma process for the improvement of polymer surface reactivity. Indeed, surface activation of carbon-fiber-reinforced polymers that use a polyetheretherketone matrix is required to achieve strong and long-term adhesion of paint on the composite. Emphasis will be placed on the contribution of gas plasma used on surface modification. We use two techniques to characterize adherence improvement: a qualitative and industrial approach with a cross-cut test and a quantitative approach with a three-point bending test. However, to provide a better understanding of the plasma-induced modifications using air or nitrogen gas, diagnostics of the surface are also necessary. The wettability improvement, chemical surface modifications, and topography are analyzed by using contact angle measurement, X-ray photoelectron spectroscopy, and atomic force microscopy, respectively. The combination of these diagnostics highlights the capability of plasma treatment to tune the plasma/surface interactions depending on gas plasma, which results in improved adhesion.

Immunoadhesive regulation using multiphytoadaptogene for spontaneous hepatocarcinomas prevention

The purposeof this investigation was to evaluate the efficacy of correcting the LFA-1 and Mac-1 leukocyte integrins expression on peripheral blood cells as well as IL-6 and IL-10 serum levels using liquid form multiphytoadaptogene preventive application for hepatocarcinomas incidence suppression and life-span increase of CBA inbreed mice.Materials and methods.The study was carried out on 439 males of inbred CBA mouse strain (subline CBA/LacY). The experimental mice received 10 % liquid form multiphytoadaptogene complex (MPAC) solution in drinking water during the first month of life including the final time period of liver differentiation (preventive administration). MPAC is the standardized herbal formula composed of 40 plant extracts components including adaptogenes Panax ginseng, Eleutherococcus senticosus, Rhodiola rosea, as well as compounds with phenolic structure (flavonoids, triterpene glycosides, etc). Anti-mutagenic, anti-oxidant, immunomodifying activities of MPAC were demonstrated. The CD11a and CD11b antigens expressions on peripheral blood cells were analyzed by indirect immunofluorescence reaction, serum cytokines IL-6 and IL-10 concentrations were determined by enzyme-linked immunosorbent assay as well as the liver tissue morphology were analyzed at the age of 4, 8, 22 months. Tumor incidence and volumes were evaluated at the age of 8 and 22 months. Motor activity and physical status (body weight, coat state) were estimated in the ontogenesis. The average life-span and survival median was analyzed by the Kaplan–Meier method. Statistical analysis was performed with the program STATISTICA 6.0.Results.Inhibited expression of LFA-1 and Mac-1 leukocyte integrins on peripheral blood cells as well as elevated IL-6 and IL-10 serum levels, high incidence of liver tumors (100 % of mice-males), their high number and big sizes in the late period of postnatal ontogenesis in CBA high-cancer inbrede mice, also as life-span not reaching two years was demonstrated. At the same time plural tumor-infiltrating limphocytes were not found. Short-term MPAC preventive administration (during the first month of mouse life occupying the final differentiation period of liver tissue genetically predisposal to hepatoms incidence) revealed the long-term heterotypic adhesion molecules leukocyte integrins LFA-1 (CD11a/CD18) and Mac-1 (CD11b/CD18) up-regulated expression, providing the contact interactions of immune effectors and cancer cells. The events shown is able to enhance the anti-tumor activity of immune reactions including spontaneous hepatocarcinomas lymphocytes infiltration and destruction of tumor tissue. As a result, the hereditary tumors incidence, their number and sizes were reduced as well as life-span and life quality of animals were improved.Conclusion.Up-regulated leukocyte integrins expression on peripheral blood cells, reduced IL-6 and IL-10 serum levels accompanied by tumors lymphocyte infiltration and destruction using MPAC preventive administration is essential for tumor incidence down-regulation. The herbal formula with multiple components is capable to controle anti-tumor immune reactions, as well as the life-span and life quality of high-cancer animals. Hence, the regulation of adhesion violations involved in tumor incidence can be cancer preventive.

Immobilization of heparin on decellularized kidney scaffold to construct microenvironment for antithrombosis and inducing reendothelialization.

In recent years, rapid development of tissue engineering technology provides possibilities for the construction of artificial tissues or organs. In construction of engineered kidneys, researchers used native decellularized extracellular matrix (ECM) as the scaffolds to recellularization. However, thrombosis has been a great issue that hinders the progress of transplantation in vivo. In this study, heparin was immobilized to the collagen part of decellularized scaffold with collagen-binding peptide (CBP). Through the anticoagulant and endothelial cell reperfusion experiments, it can be demonstrated that the heparinized scaffolds absorbed less platelets and red blood cells which can effectively reduce the formation of thrombosis. Moreover, it is conducive to long-term adhesion of endothelial cells which is important for the formation of subsequent vascularization. Taken together, our results reveal that the whole kidney can be modified by CBP-heparin composite to reduce the thrombosis and provide the better conditions for neovascularization.

Single-Step Reactive Electrospinning of Cell-Loaded Nanofibrous Scaffolds as Ready-to-Use Tissue Patches.

A reactive electrospinning strategy is used to fabricate viable and proliferative cell-loaded nanofibrous hydrogel scaffolds in a single step using an all-aqueous approach. In situ gelling and degradable hydrazone-cross-linked poly(oligo ethylene glycol methacrylate)-based hydrogel nanofibrous networks can be produced directly in the presence of cells to support long-term cell viability, adhesion, and proliferation, in contrast to bulk hydrogels of the same composition. Furthermore, the capacity of the gel nanofibers to retain bound water maintains this high cell viability and proliferative capacity following a freeze/thaw cycle without requiring any cryoprotectant additives, ideal properties for ready-to-use functional tissue patches.

One-Step Fabrication of Bioinspired Lubricant-Regenerable Icephobic Slippery Liquid-Infused Porous Surfaces.

Icephobic coating and surfaces are essential for protecting infrastructures such as transmission lines, transportation vehicles, and many others from severe damages of excessive icing. The slippery liquid-infused porous surfaces (SLIPS) are attracting escalating attention because of their low-ice adhesion strength. Despite all of the encouraging laboratory scale results, the SLIPS are still far from being applicable in real environments owing to the key unsolved problem, namely anti-icing durability. Inspired by the functionality of the amphibians’ skin, lubricant regenerability was introduced to conventional SLIPS and realized by a facile and scalable fabrication route. A series of polydimethylsiloxane (PDMS)-based skinlike SLIPS were designed and fabricated by using a one-step method, the solvent evaporation-induced phase separation technique. The obtained skinlike SLIPS were able to regenerate surface lubricant constantly by internal residual stress because of phase separation and survive more than 15 cycles of wiping/regenerating tests. Thanks to the regenerability of the surface lubricant, the new SLIPS demonstrated durable icephobicity, showing a long-term low-ice adhesion strength below 70 kPa, which was only 43% of 160 kPa that for the pristine PDMS (Sylgard 184), even after 15 icing/deicing cycles. This work paves a new and facile way for achieving icephobic durability of SLIPS.

A novel polyurethane modified with biomacromolecules for small-diameter vascular graft applications

There is a growing demand for small-caliber tissue-engineered vascular grafts to replace damaged vessels. Fabricated scaffolds are unable to precisely mimic the mechanical properties of native vessels, provide long-term patency and support cell adhesion and growth, in particular support endothelialization. In this study, a new biodegradable poly(ether ester urethane) urea (PEEUU) was synthesized. The synthesized polyurethane was then functionalized by introducing free amino groups through aminolysis for further surface modification by immobilization of biomacromolecules on the surface of vascular grafts. The modified surfaces were then characterized using attenuated total reflectance-Fourier transform infrared spectroscopy, water contact angle measurement and atomic force microscopy. The mechanical properties of the fabricated scaffolds were analyzed, revealing mechanical properties close to that of the natural vessels. Surface modifications led to improved cell–scaffold interactions, showing appropriate cell attachment and function on the scaffolds. A confluent layer of endothelial cells was formed on biomacromolecule-immobilized PEEUU vascular grafts. The preliminary results of this study demonstrated that the new polyurethane modified with biomacromolecules can be considered as a candidate material for vascular tissue engineering application with capability to support endothelialization of fabricated vascular grafts.

Enhancing the Mechanical Durability of Icephobic Surfaces by Introducing Autonomous Self-Healing Function

Ice accretion presents a severe risk for human safety. Although great efforts have been made for developing icephobic surfaces (the surface with an ice adhesion strength below 100 kPa), expanding the lifetime of state-of-the-art icephobic surfaces still remains a critical unsolved issue. Herein, a novel icephobic material is designed by integrating an interpenetrating polymer network (IPN) into an autonomous self-healing elastomer, which is applied in anti-icing for enhancing the mechanical durability. The molecular structure, surface morphology, mechanical properties, and durable icephobicity of the material were studied. The creep behaviors of the new icephobic material, which were absent in most relevant studies on self-healing materials, were also investigated in this work. Significantly, the material showed great potentials for anti-icing applications with an ultralow ice adhesion strength of 6.0 ± 0.9 kPa, outperforming many other icephobic surfaces. The material also exhibited an extraordinary durability, showing a very low long-term ice adhesion strength of ∼12.2 kPa after 50 icing/deicing cycles. Most importantly, the material was able to exhibit a self-healing property from mechanical damages in a sufficiently short time, which shed light on the longevity of icephobic surfaces in practical applications.

Effect of moisture on the adhesion of CFRP-to-steel bonded joints using peel tests

In this work, an experimental study has been carried out to evaluate the effect of salt water condition on the long-term adhesion of composite-to-metal bonded joints using peel tests. A new test configuration is tested via fully and partially immersed specimens with 500 mm length. Fracture surfaces of non-aged samples exhibited a cohesive failure within the adhesive layer, which indicates a good adhesion of the joint. Results revealed a significant difference in the interface adhesion between aged and non-aged condition after 150 days of immersion. Partially immersed specimens allow to evaluate the adhesion performance of the joint under dry and wet condition in single specimen using a simple peel test.

High-Antifouling Polymer Brush Coatings on Nonpolar Surfaces via Adsorption-Cross-Linking Strategy.

A new "adsorption-cross-linking" technology is presented to generate a highly dense polymer brush coating on various nonpolar substrates, including the most inert and low-energy surfaces of poly(dimethylsiloxane) and poly(tetrafluoroethylene). This prospective surface modification strategy is based on a tailored bifunctional amphiphilic block copolymer with benzophenone units as the hydrophobic anchor/chemical cross-linker and terminal azide groups for in situ postmodification. The resulting polymer brushes exhibited long-term and ultralow protein adsorption and cell adhesion benefiting from the high density and high hydration ability of polyglycerol blocks. The presented antifouling brushes provided a highly stable and robust bioinert background for biospecific adsorption of desired proteins and bacteria after secondary modification with bioactive ligands, e.g., mannose for selective ConA and Escherichia coli binding.