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Abstract: One key for the successful integration of implants into the human body is the control of protein adsorption by adjusting the surface properties at different length scales. This is particularly important for titanium oxide, one of the most common biomedical interfaces. As for titania (TiO2) the interface is largely defined by its crystal surface structure, it is crucial to understand how the surface crystallinity affects the structure, properties and function of protein layers mediating subsequent biological reactions. For rutile TiO2 we demonstrate that the conformation and relative amount of human plasma fibrinogen (HPF) and the structure of adsorbed HPF layers depend on the crystal surface nanostructure by employing thermally etched multi-faceted TiO2 surfaces. Thermal etching of polycrystalline TiO2 facilitates a nanoscale crystal faceting and, thus, the creation of different surface nanostructures on a single specimen surface. Atomic force microscopy shows that HPF arranges into networks and thin globular layers on flat and irregular crystal grain surfaces, respectively. On a third, faceted category we observed an alternating conformation of HPF on neighboring facets. The bulk grain orientation obtained from electron backscatter diffraction and thermodynamic mechanisms of surface reconstruction during thermal etching suggest that the grain and facet surface-specific arrangement and relative amount of adsorbed proteins depend on the associated free crystal surface energy. The implications for potentially favorable TiO2 crystal facets regarding the inflammatory response and hemostasis are discussed with a view to the advanced surface design of future implants. [Copyright &y& Elsevier]

Abstract: The aim of this work was to demonstrate that conventional poly(N-isopropylacrylamide) (PNIPAAm) hydrogels can improve their shrinkage and release properties solely due to the introduction of a heterogeneous density fluctuation-based microstructure. To this end, a novel structurally engineered PNIPAAm hydrogel was designed and compared with a chemically similar, but homogeneous, PNIPAAm hydrogel reference. For the two-step preparation PNIPAAm microgels were firstly synthesized with surface amine groups and further functionalized with polymerizable acrylate groups. In the second step the microgels, themselves acting as crosslinkers, were crosslinked to form a bulk network by inter-connecting the microgels with linear PNIPAAm chains. Although the chemical composition of the newly prepared hydrogel was generally the same as conventional PNIPAAm hydrogels (a relative control), significantly improved shrinkage properties and a more efficient “on–off” switching induced by temperature modulations were observed for the novel gel as compared with the homogeneous reference. These improved shrinkage properties were ascribed to the novel structure, which is believed to enable rapid shrinking of the small microgel crosslinkers and, thereupon, the generation of a sufficient number of diffusion channels for quick water release. Rhodamine B and ibuprofen (IBU) as model compounds were completely released from this novel gel at 20°C, whereas at temperatures above the lower critical solution temperature release stopped after initial 40% and 70% “bursts” for rhodamine B and IBU, respectively, due to shrinkage of the gel network. This approach may provide an avenue to design temperature-sensitive drug delivery systems with state of the art switching properties and fast release kinetics by combining the here presented innovative strategy with complementary enhancements, such as the introduction of porosity. [ABSTRACT FROM AUTHOR]

Abstract: Aligned multi-wall carbon nanotube (MWCNT)/polymer composite films were created in a one-step process. 5wt% MWCNT/semi-crystalline polymer composite films of approximately thickness were obtained by melt-drawing. The matrix polymers were isotactic polypropylene (iPP), poly(1-butene) (PB-1) and high density polyethylene (HDPE). Transmission electron microscopy (TEM) investigations revealed an exceptionally high degree of local MWCNT alignment with an angular deviation of (HDPE) and (iPP and PB-1) parallel to the films’ drawing direction for a broad range of drawing velocities. For HDPE, the lamellar polymer-crystals at the interface between the MWCNT and the polymer film were identified as the nano-hybrid shish-kebab morphology by selected area electron diffraction. Based on the direct visualization of the MWCNT disentanglement process in the TEM, a polymer physics-based model for the unraveling of MWCNT entanglements, a source of aligned MWCNTs, is proposed that explains differences in MWCNT alignment encountered for different matrix polymers. The melt-drawing mediated MWCNT alignment provides both an innovative approach for the fabrication of applicable MWCNT containing films and a versatile tool for studying the interface in MWCNT/polymer composites. [Copyright &y& Elsevier]