Evaluation of direct light processing for the fabrication of bioactive ceramic scaffolds: Effect of pore/strut size on manufacturability and mechanical performance

Bioactive ceramic scaffolds for bone regeneration consisting of a three-dimensional mesh of interpenetrating struts with square section were fabricated via Digital Light Processing (DLP). The ability of the technique to manufacture 3D porous structures from β-tricalcium phosphate (β-TCP) powders with different dimensions of struts and pores was evaluated, identifying the possibilities and limitations of the manufacturing process. Small pore sizes were found to seriously complicate the elimination of excess slurry from the scaffold’s innermost pores. The effect of the strut/pore size on the mechanical performance of the scaffolds under compressive stresses was also evaluated, but no significant influence was found. Under compressive stresses, the structures resulted weaker when tested perpendicularly to the printing plane due to interlayer shear failure. Interlayer superficial grooves are proposed as potential failure-controlling defects, which could also explain the lack of a Weibull size effect on the mechanical strength of the fabricated DLP scaffolds.     

Value of information in remanufacturing complex products

Remanufacturing facilities usually face a trade-off between limited information about remanufacturing yields and potentially long supplier lead times. To improve production performance, these firms may attempt to acquire more timely and accurate information about remanufacturing yields or alternatively, to reduce the lead times of purchased parts. We develop four decision-making models to evaluate the impact of yield information and supplier lead time on manufacturing costs. We identify the operating conditions under which these capabilities are valuable, along with their relative impact on facility performance. Each model is formulated as an infinite horizon, stochastic dynamic program (Markov decision process). Our results indicate that the yield information is generally quite valuable, while investments in supplier responsiveness provide trivial returns to products with few parts. However, as product complexity increases with large number of target parts, the value of short lead times increases.     

Context-Processing Deficits in Schizotypal Personality Disorder.

Research suggests that schizotypal personality disorder (SPD) is a part of the spectrum of schizophrenia-related illnesses. This article hypothesizes that a deficit in the representation and maintenance of context is a core cognitive disturbance in schizophrenia and that SPD individuals should demonstrate context-processing deficits. To test this hypothesis, the authors administered 3 versions of their AX-CPT task, designed to assess context processing, to 35 healthy controls and 26 individuals with DSM-IV SPD. They also administered working memory and selective attention tasks. SPD individuals displayed context representation deficits similar to those found in schizophrenia but did not show the same additional deficits in context maintenance. Context processing was strongly associated with working memory and selective attention performance in the SPD individuals. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Synthesis and Properties of Photoisomerizable Derivatives of Isosorbide and Their Use in Cholesteric Filters

This paper describes the synthesis of photoisomerizable derivatives of isosorbide. These derivatives contain a stilbene or cinnamate moiety and can therefore be used as photoisomerizable chiral compounds in cholesteric liquid‐crystalline mixtures. The reflection wavelength of cholesteric layers made from these mixtures is increased by UV irradiation due to the fact that the Z‐isomers of these derivatives exhibit a lower helical twisting power than the corresponding E‐isomers. The cinnamate derivatives are very suitable for use in cholesteric color filters that find application in liquid‐crystal displays.     

Immunoglobulin A levels in southern elephant seal (Mirounga leonina) milk during the suckling period

Immunoglobulin A (IgA) levels in milk samples from southern elephant seals at King George Island, Antarctica are reported. IgA levels were determined throughout the suckling period (approximately 23 days). The IgA concentration in southern elephant seal milk was lower than in other mammals and, unlike most mammalian milk, was not high during early lactation. There was not a definite pattern in IgA levels, which fluctuated within narrow limits throughout the suckling period (mean +/- SD, 30.81 +/- 6.38 mg IgA/100 g milk). If IgG was present, its level was too low to be detected by the method used. This is the first evidence in Southern elephant seal of the possibility of transmission of passive immunity after birth involving secretion of IgA in the milk.     

Tau Exon 10 Inclusion by PrPC through Downregulating GSK3β Activity

Tau protein is largely responsible for tauopathies, including Alzheimer’s disease (AD), where it accumulates in the brain as insoluble aggregates. Tau mRNA is regulated by alternative splicing, and inclusion or exclusion of exon 10 gives rise to the 3R and 4R isoforms respectively, whose balance is physiologically regulated. In this sense, one of the several factors that regulate alternative splicing of tau is GSK3β, whose activity is inhibited by the cellular prion protein (PrP^C), which has different physiological functions in neuroprotection and neuronal differentiation. Moreover, a relationship between PrP^C and tau expression levels has been reported during AD evolution. For this reason, in this study we aimed to analyze the role of PrP^C and the implication of GSK3β in the regulation of tau exon 10 alternative splicing. We used AD human samples and mouse models of PrP^C ablation and tau overexpression. In addition, we used primary neuronal cultures to develop functional studies. Our results revealed a paralleled association between PrP^C expression and tau 4R isoforms in all models analyzed. In this sense, reduction or ablation of PrP^C levels induces an increase in tau 3R/4R balance. More relevantly, our data points to GSK3β activity downstream from PrP^C in this phenomenon. Our results indicate that PrP^C plays a role in tau exon 10 inclusion through the inhibitory capacity of GSK3β.     

Stress Analysis of Elastic-Plastic Contact Damage in Ceramic Coatings on Metal Substrates

An elastic-plastic analysis of damage in ceramic coatings on metal substrates from contacts with spherical indenters is made using finite element modeling. Computations are carried out specifically for plasma-sprayed alumina:titania on a soft steel. The algorithm assumes an elastic sphere with frictionless contact on a flat elastic-plastic layered specimen, and incrementally evaluates the expanding contact field as a function of applied load. Two key aspects of the contact field are examined: (i) the indentation stress-strain curve; (ii) the damage zone geometry. Composite coating/substrate indentation stress-strain curves are computed for two coating thicknesses, using input material parameters from iterative fits to data from control tests on free-standing coating and substrate materials. Contours of principal shear stresses, most notably those contours corresponding to yield zone boundaries in both the softer substrate and the harder coating, are mapped out in the fully plastic region. Corresponding distributions of tensile stresses are also mapped out, and are shown to correlate with the locations of transverse fractures in the coating. General implications concerning material and geometrical design of ceramic-based layer structures are discussed.     

Porous poly(2-hydroxyethyl acrylate) hydrogels prepared by radical polymerisation with methanol as diluent

Dynamic-mechanical and water sorption properties of porous and non-porous hydrogels have been studied as a function of their porosity and crosslinking density. Porous hydrogels with different crosslinking densities were prepared by co-polymerisation of 2-hydroxyethyl acrylate and ethyleneglycol dimethacrylate in solution in methanol. Pores were formed due to the segregation of the solvent from the polymer network during the polymerisation process. The porosity of the samples was observed by scanning electron microscopy. The pores collapse during the drying process after polymerisation but they reopen when the xerogel is immersed in liquid water. Bulk polymer networks with varying crosslinking densities were also synthesised and used as a reference in the analysis of the porous hydrogels. Water sorption from the gas phase and from the liquid phase was studied by means of equilibrium sorption isotherms and immersion experiments, respectively. Dynamic-mechanical spectroscopy conducted on the xerogels shows that the elastic modulus in the rubber-like state highly depends on the amount of solvent used in the polymerisation what is attributed to the presence of discontinuity surfaces in the xerogel although the pores are closed.