Application of Small‐Angle X‐Ray Scattering as a Tool for the Structural Analysis of Industrial Polymer Dispersions

Small‐angle X‐ray scattering (SAXS) was applied for the structural analysis of an industrial polymer dispersion in water (synthetic latex). For the preparation of the spherical latex particles under investigation, butadiene, styrene, and acrylic acid were used as monomers in a seeded emulsion polymerization process. The product is widely being used as a film‐forming agent for coatings in the paper‐making industry. It is demonstrated that by measuring the SAXS curves at different contrasts the overall particle size, mass density, polydispersity, and degree of heterogeneity can be estimated with a good accuracy, even without the necessity of a detailed fitting procedure. In particular, one obtains information about the spatial distribution of the various monomer units within the particles. Five isoscattering points could be observed in the contrast variation measurements and the scattering curves at all contrasts could be modeled with a fully consistent set of fit parameters. It is thus safe to conclude that the contrast agent sucrose does not affect the particle structure. A quantitative fitting of the experimental data set revealed that a significant amount of the poly(acrylic acid) is preferentially located in a thin shell of ca. 2 nm thickness around the core of the particles, that is mainly formed by poly(styrene‐co‐butadiene). The obtained results are fully consistent with additional measurements of the particle mass density, of the hydrodynamic particle radius by dynamic light scattering, and of the particle surface charge by potentiometric titration. It is concluded that SAXS is a highly useful tool for characterizing the structure of industrial latexes.

SAXS data of a BAYSTAL® latex measured at various contrasts, the weight fraction of sucrose in the dispersion medium is given in the legend.     

3D Jet Writing: Functional Microtissues Based on Tessellated Scaffold Architectures

The advent of adaptive manufacturing techniques supports the vision of cell‐instructive materials that mimic biological tissues. 3D jet writing, a modified electrospinning process reported herein, yields 3D structures with unprecedented precision and resolution offering customizable pore geometries and scalability to over tens of centimeters. These scaffolds support the 3D expansion and differentiation of human mesenchymal stem cells in vitro. Implantation of these constructs leads to the healing of critical bone defects in vivo without exogenous growth factors. When applied as a metastatic target site in mice, circulating cancer cells home in to the osteogenic environment simulated on 3D jet writing scaffolds, despite implantation in an anatomically abnormal site. Through 3D jet writing, the formation of tessellated microtissues is demonstrated, which serve as a versatile 3D cell culture platform in a range of biomedical applications including regenerative medicine, cancer biology, and stem cell biotechnology.     

High‐Throughput Scaffold System for Studying the Effect of Local Geometry and Topology on the Development and Orientation of Sprouting Blood Vessels

Live tissues require vascular networks for cell nourishing. Mimicking the complex structure of native vascular networks in vitro requires understanding the governing factors of early tubulogenesis. Current vascularization protocols allow for spontaneous formation of vascular networks; however, there is still a need to provide control over the defined network structure. Moreover, there is little understanding on sprouting decision and migration, especially within 3D environments. Here, tessellated polymer scaffolds with various compartment geometries and a novel two‐step seeding protocol are used to study vessel sprouting decisions. Endothelial cells first organize into hollow vessels tracing the shape contour with high fidelity. Subsequent sprouts emerge in specific directions, responding to compartment geometry. Time‐lapse imaging is used to track vessel migration, evidencing that sprouts frequently emerge from the side centers, mainly migrating toward opposing corners, where the density of support cells (SCs) is the highest, providing the highest levels of angiogenic factors. SCs distribution is quantified by smooth muscle actin expression, confirming the cells preference for curved compartment surfaces and corners. Displacements within the hydrogel correlate with SCs distribution during the initial tubulogenesis phase. This work provides new insight regarding vessel sprouting decisions that should be considered when designing scaffolds for vascularized engineered tissues.     

Sensitization and radiation hardening of the photostimulable X-ray storage phosphor CsBr:Eu2+

The X-ray storage phosphor CsBr:Eu²⁺ in form of needle image plates is believed to be a promising alternative to the granular BaFBr:Eu²⁺ with regard to PSL yield and spatial resolution. Unfortunately, CsBr:Eu²⁺ exhibits poor radiation hardness, which is caused by a migration of europium ions initiated by naturally existing defect centers like (Eu²⁺-V_Cs)-centers and X-ray generated M_Eu-centers. It will be shown that the formation of (Eu²⁺-O²⁻)-dipoles at the expense of (Eu²⁺-V_Cs)-dipoles, incorporated by thermal annealing in O₂-containing and humid atmosphere, does not improve the radiation stability. There is, however, a strong improvement in the radiation hardness by codoping of CsBr:Eu²⁺ with lithium ions, which is accompanied by a complete suppression of the previously observed M_Eu-center formation.     

Modes of dynamic shear failure in solids

The technique of loading edge cracks by edge impact (LECEI) for generating high rates of crack tip shear (mode-II) loading is presented. The LECEI-technique in combination with a gas gun for accelerating the impactor is used to study the high rate shear failure behaviour of three types of materials. Epoxy resin (Araldite B) shows failure by tensile cracks up to the highest experimentally achievable loading rate; steel (high strength maraging steel X2 NiCoMo 18 9 5) shows a failure mode transition: at low rates failure occurs by tensile cracks, at higher rates, above a certain limit velocity, failure by adiabatic shear bands is observed; aluminum alloy (Al 7075) shows failure due to shear band processes in the high rate regime, but this failure mode is observed over the entire range of lower loading rates, even down to quasi-static conditions. Characteristics of the failure modes are presented. When transitions are observed in the failure process from tensile cracks to shear bands the limit velocity for failure mode transition depends on the bluntness of the starter crack the failure is initiated from: The larger the bluntness of the starter crack the higher the critical limit velocity for failure mode transition. The data indicate that adiabatic shear bands require and absorb more energy for propagation than tensile cracks. Aspects of the energy balance controlling mode-II instability processes in general are considered. Effects very different than for the mode-I instability process are observed: When failure by a tensile crack occurs under mode-II initiation conditions, a notch is formed between the initiated kinked crack and the original starter crack, and, at this notch a compressive stress concentration builds up. The energy for building up this stress concentration field is not available for propagation of the initiated kinked crack. The energy density of a mode-II crack tip stress field, however, when compared to an equivalent mode-I crack tip field, is considerably larger, and, consequently, the remaining driving energy for any mode-II initiated failure process, nevertheless, is higher than for the case of equivalent mode-I initiation conditions. Furthermore, mode-II crack tip plastic zones are considerably larger than equivalent mode-I crack tip plastic zones. Consequently, validity conditions for linear-elastic or small scale yielding failure behaviour are harder to fulfill and possibilities for the activation of nonlinear high energy ductile type failure processes are enhanced. Speculations on how these effects might favour failure by high energy processes in general and by shear bands processes in particular for conditions of high rate shear mode-II loading are presented. This revised version was published online in July 2006 with corrections to the Cover Date.     

Prejudice matters: Understanding the reactions of Whites to affirmative action programs targeted to benefit Blacks.

The authors examined, in 2 studies, the effects of equal employment opportunity/affirmative action (EEO/AA) policies on Whites' job-related attitudes. First, in an experiment, White prospective job recruits, as expected, rated a potential employer whose EEO/AA policies were framed as targeted to benefit Blacks as less attractive than a potential employer whose EEO/AA policies were framed more generally. Second, the results of a field study showed that prejudice against Blacks moderated the relationship between Whites' perceptions that their organization's EEO/AA policies were targeted to benefit Blacks and their satisfaction with promotion opportunities. Specifically, among prejudiced Whites, this relationship was negative and considerable in size (r = -.39, p r = -.04, ns). The implications of our findings for the study of prejudice in organizations are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of macro segregation on hydrogen environment embrittlement of SUS 316L stainless steel

The objective of this work is to identify microstructural variables that lead to the large scatter of the relative resistance of 316 grade stainless steels to hydrogen environment embrittlement. In slow displacement rate tensile testing, two almost identical (by nominal chemical composition) heats of SUS 316L austenitic stainless steel showed significantly different susceptibilities to HEE cracking. Upon straining, drawn bar showed a string-like duplex microstructure consisting of α′-martensite and γ-austenite, whereas rolled plate exhibited a highly regular layered α′-γ structure caused by measured gradients in local Ni content (9.5–13 wt%). Both martensite and austenite are intrinsically susceptible to HEE. However, due to Ni macro segregation and microstructural heterogeneity, fast H-diffusion in martensite layers supported a 10 times faster H-enhanced crack growth rate and thus reduced tensile reduction in area. Nickel segregation is thus a primary cause of the high degree of variability in H₂ cracking resistance for different product forms of 316 stainless steel.     

Evaluation of the tablet core factors influencing the release kinetics and the loadability of push-pull osmotic systems

Push-pull osmotic systems have been developed to deliver poorly soluble drugs in a modified-release fashion. The aim of this study was to investigate the influence of the tablet core factors on the drug release kinetics and loadability. The release kinetics was efficiently modulated by varying either the proportion of osmotic agent or the drug layer polymer grade as an alternative to change the membrane characteristics. High osmotic agent proportions and viscous-grade polymers were recommended to formulate high drug loads up to 20% without losing both the release completeness and the zero-order drug release kinetics.