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The morphology of top-down and bottom-up nanostructured neutral brushes is studied as a function of the production process and the quality of solvent to which the brushes have been exposed. Neutral brushes of poly(tert-butyl methacrylate) (PtBuMA) were grafted from the substrate by surface-initiated radical-chain polymerization (SI-RCP). Brush patterning was conducted using deep ultraviolet (DUV) photolithography following either top-down (TD) or bottom-up (BU) approaches with patterned lines as small as 200 nm. The resulting brushes were immersed in toluene or methanol, and the change of morphology of the dried brushes was monitored using tapping mode atomic force microscopy (AFM). TD nanopatterned brushes (NPBs) exhibit a box-like and BU generated brushes a lens-like shape directly after the production process. We show that the pattern width for the BU brushed depends not only on the wetting properties of the areas adjacent to the pattern but also on the process history to which the sample has been exposed, especially the solvent quality. Furthermore, we show that TD NPBs are cross-linked on the edges of the pattern because of the high-energy process conditions during brush patterning and study the behavior of the thus-obtained structures. [ABSTRACT FROM AUTHOR]

The stability of strong polyelectrolyte brushes (PEBs) was studied in bulk and in patterned structures. Thick PEBs of poly([(2-methacryloyloxy)ethyl]trimethylammonium chloride) with thicknesses >100 nm were synthesized using single electron transfer living radical polymerization. Brush patterning was identified using deep-ultraviolet photolithography by means of either a top-down (TD) or bottom-up (BU) method, with features as small as 200 nm. The brushes were soaked in water under a range of pH or temperature conditions, and the hydrolysis was monitored through dry-state ellipsometry and atomic force microscopy measurements. BU patterns showed reduced degrafting for smaller patterns, which was attributed to increased stress relaxation at such dimensions. In contrast to the already relaxed BU-patterned brush, a TD-patterned brush possesses perpendicular structures that result from the use of orthogonal lithography. It was found that the TD process induces cross-linking on the sidewall, which subsequently fortifies the sidewall materials. This modification of the polymer brushes hindered the stress relaxation of the patterns, and the degrafting trends became irrelevant to the pattern sizes. With proper tuning, the cross-linking on the sidewall was minimized and the degrafting trends were again relaxation-dependent. [ABSTRACT FROM AUTHOR]

Advanced technologies for controlled cell adhesion and detachment in novel biointerface designs profit from stimuli-responsive systems that are able to react to their environment. Here, a multilayer system made of thiolated chitosan and thiolated chondroitin sulfate was constructed, with the potential of switchable inter- and intramolecular thiol/disulfide interactions representing a redox-sensitive nanoplatform. Owing to the formation and cleavage of inherent disulfide bonds by oxidation and reduction, surface properties of the multilayer can be controlled toward protein adsorption/desorption and cell adhesion in a reversible manner. Oxidation of thiols by chloramine-T promotes fibronectin (FN) adsorption and fibroblast cell adhesion, whereas the reduction by tris(2-carboxyethyl)phosphine reverses these effects, leading to low FN adsorption and little cell adhesion and spreading. These effects on the biological systems are related to significant changes of wetting properties, zeta potential, and mechanical properties of these multilayer films. The system presented may be useful for biomedical applications as responsive and obedient surfaces in medical implants and support tissue regeneration.

Control of the biomaterial properties through stimuli-responsive polymeric platforms has become an essential technique in recent biomedical applications. A multilayer system of thiolated chitosan (t-Chi) and thiolated chondroitin sulfate (t-CS), consisting of five double layers ([t-Chi/t-CS] 5 ), was fabricated here by applying a layer-by-layer coating strategy. To represent a novel class of chemically tunable nanostructures, the ability to cross-link pendant thiol groups was tested by a rise from pH 4 during layer formation to pH 9.3 and a more powerful chemical stimulus by using chloramine-T (ChT). Following both treatments, the resulting multilayers showed stimuli-dependent behavior, as demonstrated by their content of free thiols, wettability, surface charge, elastic modulus, roughness, topography, thickness, and binding of fibronectin. Studies with human dermal fibroblasts further demonstrated the favorable potential of the ChT-responsive multilayers as a cell-adhesive surface compared to pH-induced cross-linking. Because the [t-Chi/t-CS] 5 multilayer system is responsive to stimuli such as the pH and redox environment, multilayer systems with disulfide bond formation may help to tailor their interaction with cells, film degradation, and controlled release of bioactive substances like growth factors in a stimuli-responsive manner useful in future wound healing and tissue engineering applications.

The stability of strong polyelectrolyte brushes (PEBs) was studied in bulk and in patterned structures. Thick PEBs of poly([(2-methacryloyloxy)ethyl]trimethylammonium chloride) with thicknesses >100 nm were synthesized using single electron transfer living radical polymerization. Brush patterning was identified using deep-ultraviolet photolithography by means of either a top-down (TD) or bottom-up (BU) method, with features as small as 200 nm. The brushes were soaked in water under a range of pH or temperature conditions, and the hydrolysis was monitored through dry-state ellipsometry and atomic force microscopy measurements. BU patterns showed reduced degrafting for smaller patterns, which was attributed to increased stress relaxation at such dimensions. In contrast to the already relaxed BU-patterned brush, a TD-patterned brush possesses perpendicular structures that result from the use of orthogonal lithography. It was found that the TD process induces cross-linking on the sidewall, which subsequently fortifies the sidewall materials. This modification of the polymer brushes hindered the stress relaxation of the patterns, and the degrafting trends became irrelevant to the pattern sizes. With proper tuning, the cross-linking on the sidewall was minimized and the degrafting trends were again relaxation-dependent.

Spin-resolved scanning tunneling microscopy is used to reveal a commensurate hexagonal nanoskyrmion lattice in the hcp stacked Fe monolayer on Ir(111). The exact nature of the spin configuration is due to magnetic interactions between the Fe atoms and the Ir substrate, either originating from polarization effects, or due to a three-site hopping mechanism of the Dzyaloshinsky-Moriya interaction leading to a canting of the Dzyaloshinsky-Moriya vector with respect to the interface.

Forisomes are protein polymers found in leguminous plants that have the remarkable ability to undergo reversible "muscle-like" contractions in the presence of divalent cations and in extreme pH environments. To gain insight into the molecular basis of forisome structure and assembly, we used confocal laser scanning microscopy to monitor the assembly of fluorescence-labeled artificial forisomes in real time, revealing two distinct assembly processes involving either fiber elongation or fiber alignment. We also used scanning and transmission electron microscopy and X-ray diffraction to investigate the ultrastructure of forisomes, finding that individual fibers are arranged into compact fibril bundles that disentangle with minimal residual order in the presence of calcium ions. To demonstrate the potential applications of artificial forisomes, we created hybrid protein bodies from forisome subunits fused to the B-domain of staphylococcal protein A. This allowed the functionalization of the artificial forisomes with antibodies that were then used to target forisomes to specific regions on a substrate, providing a straightforward approach to develop forisome-based technical devices with precise configurations. The functional contractile properties of forisomes are also better preserved when they are immobilized via affinity reagents rather than by direct contact to the substrate. Artificial forisomes produced in plants and yeast therefore provide an ideal model for the investigation of forisome structure and assembly and for the design and testing of tailored artificial forisomes for technical applications.