Concentrated brushes

Evidence for a similar membrane carrier for zinc in humans has been suggested from studies of zinc uptake in acrodermatitis enteropathica. In 1979, using mucosal samples obtained from acrodermatitis patients, Atherton e reported that, at lower lumenal zinc concentrations, brush border zinc uptake was inhibited in these patients, an effect overcome at higher zinc concentrations (48). As a result of these studies, they suggested the possibility of a membrane associated carrier for zinc in the brush border membrane. In the acrodermatitis enteropathica patients, this carrier could be altered or absent. Their hypothesis is supported by findings in rats by both Davies (38) and by this laboratory (43). 

In this work, we wiU discuss the characteristic size-exclusion effect and excellent protein repeUency of concentrated brushes on the basis of our experimental data previously reported with poly(2-hydroxyethyl methacrylate) (PHEMA) brushes. PHEMA is a hydrophilic, biocompatible polymer, but the biocompatibility of PHEMA cast film is reported to be not as good as e.g., poly(2-methacryloxyethyl-phosphorylcholine) and poly(2-metho-xyethylacrylate) cast films. Hence any favorable results on the PHEMA brushes could be ascribed more to the structural,... 

Schematic illustration of a size-exciusion effect for (a) concentrated brush and (b) semi-diiute brush, to is the swoiien brush thickness and d is the average distance between the nearest-neighbor graft points. The veiticai and horizontai axes show the distance from the substrate and the protein size, respectiveiy.

In order to investigate the interaction of the concentrated brush with proteins, we attempted a chromatographic test using a silica monolithic column modified with a well-defined, concentrated PHEMA brush. The chromatographic technique generally provides useful information on the interactions between the analytes and the stationary phase (the brush layer) with a high sensitivity if the stationary phase has a... 

We also examined the protein adsorption on the high-density brush with different graft thicknesses L — 2 and 10 nm. The high-density brushes with different graft thickness were aU free from protein adsorption. This means that a thick brush has a size-exclusion effect from its bottom to the outer surfaces through out. This is the very feature expected for a concentrated brush, as shown in Scheme 2a. 

It should be noted that depends on N in a linear way, while the dimension of an isolated chain in a good solvent is scaled as meaning that the graft chains adopt stretched conformations. This theoretical prediction has been extensively verified with the semidilute brushes prepared by the grafting-to methods [27-33]. However, in a concentrated brush, these approximations are no longer valid and higher-order interactions must be considered [34]. Therefore, concentrated brushes are expected to exhibit different properties from semidilute ones. However, they had previously been little studied because of the difficulty to obtain the concentrated brushes by conventional methods. 

Notable observations for dry concentrated brushes include that PMMA brushes in the melt had a glass transition temperature significantly higher [40], and a plate compressibility markedly smaller [41], than those of the equivalent cast films. More interestingly, they were immiscible even with free PMMA of an oligomeric chain length [42]. This last observation means that concentrated brushes in the melt have a size-exclusion effect of (conformational) entropic origin. A similar size-exclusion effect of concentrated brushes was also confirmed for molecules in solution. This will be detailed in Section 11.3. 

More details of the concentrated brush are described in an excellent review by Tsujii et al. [7]. 

Here, N and a are the degree of polymerization and the graft density (chains/nm ), respectively. The 1/3 power dependence of on characteristic feature of the semidilute brush. In a concentrated brush, the mentioned approximations are no longer valid and higher-order interactions should be taken into account. Therefore,... 

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