Adhesion promoters concepts

The mechanism of chemical adhesion is probably best studied and demonstrated by the use of silanes as adhesion promoters. However, it must be emphasized that the formation of chemical bonds may not be the sole mechanism leading to adhesion. Details of the chemical bonding theory along with other more complex theories that particularly apply to silanes have been reviewed [48,63]. These are the Deformable Layer Hypothesis where the interfacial region allows stress relaxation to occur, the Restrained Layer Hypothesis in which an interphase of intermediate modulus is required for stress transfer, the Reversible Hydrolytic Bonding mechanism which combines the chemical bonding concept with stress relaxation through reversible hydrolysis and condensation reactions. 

E. Jaehne, S. Oberoi, and H-J. P. Adler, Ultra thin layers as new concepts for corrosion inhibition and adhesion promotion. Prog. Org. Coatings 61, 211-223 (2008). 

Such migration requires only partial miscibility in the polymer matrix, silicone in the particular case studied by Stein et al. Owen and co-workers [9] have suggested that solubility parameter calculations can be useful in designing suitable compositions with partial miscibility. These ideas appear superficially to be at odds with compatibility/penetration and interpenetrating network concepts. However, these contrary solubility requirements are a consequence of the initial placement of the adhesion promoter. When used as a primer, it is already placed at the interface so needs no partial solubility characteristic to drive it there, as is needed when it is initially dispersed throughout the polymer matrix. In both cases it is the development of a strengthening interfacial phase that accounts for the enhancement in adhesion that is sought by the user. 

A specific demand for a biomaterial surface is its compatibility with organ specific ceUs, which leads to the approach to cell seeding before implantation. Therefore, implants for blood contact may be durably covered with a monolayer of endothelial cells. Thus, a suitable interface between the synthetic carrier material and the individual cells is required [132]. For this reason, a concept based on covalent coupling of ceU adhesion promoters, like fibronectin or the pen-tapeptide GRGDS belonging to the endothelial cell binding domain of fibronectin, at the biomaterial surface is pursued. To achieve this the base polymer has... 

Another route towards biomolecular functionalisation of switchable cell culture carriers was proposed by Gramm et al. (2011). The thermo-responsive polymer poly (vinyl methyl ether) was blended with a small amount of the alternating copolymer of vinyl methyl ether and maleic anhydride. After electron beam cross-linking, stable films with a dry thickness of up to 70 nm were obtained. The introduced anhydride moieties allow for subsequent protein or peptide immobilization without toxic coupling agents. This concept was applied and further developed by Teich-mann et al. (2013). The impact of different adhesion-promoting molecules immobilised in different concentrations to the thermo-responsive coating was evaluated and compared. 

It is therefore desirable to improve the chemical interaction between the first monolayer of the coating and the substrate such that electrochemical reactions such as the reduction of oxygen are inhibited and the bonds may withstand the attack of water and other aggressive species such as OH-. Modem concepts are aimed at the development of molecular adhesion promoters (Fig. 1) [17-19], which will provide a link between the substrate and the organic coating. This model requires, however. 

Adhesion promoter chemistries, other than those of silanes, have been extensively evaluated for many years. These materials use the same concepts as silane-coupling agents, but they are based on other metallic elements. They have inorganic reactivity on the metallic atom and contain organofunctional groups, such as methacrylate, carboxylate, and others, with dual- or multi-functionality built into the... 

It has also been shown that a self-assembled monolayer (SAM) with proper functional groups can significantly improve the adhesion of CP thin film on a substrate. Based on this concept, Jung and Lee have demonstrated the fabrication of CP nanostmctures via a lift-off process. In their study, 16-mercaptohexadecanolc acid and 3-aminopropyltriethoxy silane SAM were used on Au and Si02/Si surfaces to promote the adhesion of PPY and PEDOT PSS, respectively. This allowed nanostmctures of these CP materials to be fabricated using standard e-beam lithography followed by a lift-off process [14]. 

The simultaneous spinning of two polymer solutions by using a triple orifice spinneret presents several benefits such as the possibility of forming each membrane layer by different concepts. Pereira et al. [55] studied the simultaneous spinning of two polymer solutions and the conditions that promote the adhesion of the two layers were... 

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