Bioinspired buckling of scaled skins.

Natural flexural armors combine hard, discrete scales attached to soft tissues, providing unique combinations of surface hardness (for protection) and flexibility (for unimpeded motion). Scaled skins are now inspiring synthetic protective materials which offer attractive properties, but which still suffer from limited trade-offs between flexibility and protection. In particular, bending a scaled skin with the scales on the intrados side jams the scales and stiffen the system significantly, which is not desirable in systems like gloves where scales must cover the palm side. Nature appears to have solved this problem by creating scaled skins that can form wrinkles and folds, a very effective mechanism to accommodate large bending deformations and to maintain flexural compliance. This study is inspired from these observations: we explored how rigid scales on a soft membrane can buckle and fold in a controlled way. We examined the energetics of buckling and stability of different buckling modes using a combination of discrete element modeling and experiments. In particular, we demonstrate how scales can induce a stable mode II buckling, which is required for the formation of wrinkles and which could increase the overall flexural compliance and agility of bioinspired protective elements.

Discrete element models of tooth enamel, a complex three-dimensional biological composite.

Enamel, the hard surface layer of teeth, is a three-dimensional biological composite made of crisscrossing mineral rods bonded by softer proteins. Structure-property relationships in this complex material have been difficult to capture and usually require computationally expensive models. Here we present more efficient discrete element models (DEM) of tooth enamel that can capture the effects of rod decussation and rod-to-interface stiffness contrast on modulus, hardness, and fracture resistance. Enamel-like microstructures were generated using an idealized biological growth model that captures rod decussation. The orthotropic elastic moduli were modeled with a unit cell, and surface hardness was captured with virtual indentation test. Macroscopic crack growth was also modeled directly through rupture of interfaces and rods in a virtual fracture specimen with an initial notch. We show that the resistance curves increase indefinitely when rod fracture is avoided, with the inelastic region, crack branching, and 3D tortuosity being the main sources of toughness. Increasing the decussation angle simultaneously increases the size of the inelastic region and the crack resistance while decreasing the enamel axial modulus, hardness, and rod stress. In addition, larger contrasts of stiffness between the rods and their interfaces promote high overall stiffness, hardness, and crack resistance. These insights provide better guidelines for reconstructive dental materials, and for development of bioinspired hard materials with unique combinations of mechanical properties. STATEMENT OF SIGNIFICANCE: Enamel is the hardest, most mineralized material in the human body with a complex 3D micro-architecture consisting of crisscrossing mineral rods bonded by softer proteins. Like many hard biological composites, enamel displays an attractive combination of toughness, hardness, and stiffness, owing to its unique microstructure. However few numerical models explore the enamel structure-property relations, as modeling large volumes of this complex microstructure presents computational bottlenecks. In this study, we present a computationally efficient Discrete-element method (DEM) based approach that captures the effect of rod crisscrossing and stiffness mismatch on the enamel hardness, stiffness, and toughness. The models offer new insight into the micromechanics of enamel that could improve design guidelines for reconstructive dental materials and bioinspired composites.

Occurrence of pharmaceutically active compounds in surface waters of the Henares-Jarama-Tajo River system (Madrid, Spain) and a potential risk characterization.

The Henares-Jarama-Tajo river system is the largest drainage basin in the Province of Madrid, Spain. This area is characterized by the presence of intensive urban and industrial activities influenced by a continental Mediterranean climate with rainfalls presenting substantial fluctuations along the different seasons. This research aimed to monitor seasonal variations in concentrations of 22 pharmaceutically active compounds (PhACs) in this river system and to establish the potential risk of sublethal effects on aquatic organisms. A total of 10 sampling sites were selected along the river system with samples collected in each of the four seasons during a year-round schedule. Most of the PhACs detected were present in sampling sites downstream in the vicinity of the most populated cities (i.e. Madrid, Guadalajara and Alcalá de Henares). Only two PhACs, fluoxetine and paraxantine, were detected in all sites regardless of the season, and showed median (+/- interquartile range) concentrations of 21.4 (+/-31.2) ng L(-1) and 8.5 (+/-5.3) ng L(-1), respectively. Other PhACs were detected with a frequency >80% and included, caffeine, diphenylhydantoin, hydrochlorotiazide, ibuprofen, ketoprofen, diclofenac, sulfamethoxazole, atenolol, naproxen, carbamazepine and propanolol. Seasonal variations were observed with the highest concentrations in December and the lowest in September. By combining measured environmental concentrations with toxicity data (either publicly available or obtained experimentally in our laboratory), and by calculating an Maximum Risk Index (MaxRI) that each combination of PhACs should have for non exceeding the risk threshold, a high potential for long-term risk (MaxRI<10) was estimated for most of the sampling sites and sampling dates. This research allowed the characterization of the potential risk for each of the PhACs to exert sublethal effects on aquatic organisms using acute screening methods, justifying the need for chronic data in order to refine the risk of these compounds to aquatic organisms.

Sewage sludge applied to agricultural soil: Ecotoxicological effects on representative soil organisms.

Application of sewage sludge to agricultural lands is a current practice in EU. European legislation permits its use when concentrations of metals in soil do not increase above the maximum permissible limits. In order to assess the fate and the effects on representative soil organisms of sewage sludge amendments on agricultural lands, a soil microcosm (multi-species soil system-MS3) experiment was performed. The MS3 columns were filled with spiked soil at three different doses: 30, 60 and 120tha(-1) fresh wt. Seed plants (Triticum aestivum, Vicia sativa and Brassica rapa) and earthworms (Eisenia fetida) were introduced into the systems. After a 21-d exposure period, a statistically significant increase for Cd, Cu, Zn and Hg concentrations was found for the soils treated with the highest application rate. Dose-related increase was observed for nickel concentrations in leachates. Plants and earthworm metal body burden offer much more information than metal concentrations and help to understand the potential for metal accumulation. Bioaccumulation factor (BAF(plant-soil)) presented a different behavior among species and large differences for BAF(earthworm-soil), from control or sewage-amended soil, for Cd and Hg were found. B. rapa seed germination was reduced. Statistically significant decrease in fresh biomass was observed for T. aestivum and V. sativa at the highest application rate, whereas B. rapa biomass decreased at any application rate. Enzymatic activities (dehydrogenase and phosphatase) as well as respiration rate on soil microorganisms were enlarged.

Ecotoxicological assessment of doxycycline in aged pig manure using multispecies soil systems.

This paper assesses the ecotoxicity of the antibiotic doxycycline in aged spiked pig manure using a multispecies soil system (MS 3) covering plants, earthworms and soil microorganisms. The study reproduced realistic exposure conditions, as well as higher exposure doses covering the uncertainty factors typically employed for covering interspecies variability. MS 3, consisting of columns of natural sieved soil assembled with earthworms and seeds from three plant species, were employed. Pig manure was spiked with doxycycline (75 or 7500 microg/ml), aged for 15 days under aerobic/anaerobic conditions and added on top of the soil columns (120 ml/column, equivalent to 220 kgN/ha). Water and doxycycline free manure were used as negative controls. Doxycycline (7500 microg/ml) solution was used as a positive control. No effects on plants or earthworms were observed. Significant effects on soil phosphatase activity, indicating effects on soil microorganisms, were observed at the highest exposure dose, affecting all soil layers in the doxycycline-solution-treated MS 3 (positive control) but only the top layer in the spiked pig manure system. Chemical analysis confirmed the different behavior of doxycycline in both systems (with and without manure) and those effects were observed in soil with measured concentrations over 1 mg/kg soil. The detection of doxycycline in leachates revealed a potential mobility. Leachate concentrations were similar for doxycycline solution and spiked manure treatments.

Presenile Alzheimer disease: amyloid plaques in the cerebellum.

Seven of 24 patients with pathologically proved Alzheimer disease had amyloid plaques resembling kuru plaques in the cerebellum. In all seven patients, the dementia was presenile in onset, there was a positive family history of the disease in five patients, and other neurologic symptoms were present in five. Similar plaques have been described in one of two patients with familial Alzheimer disease from whom spongiform encephalopathy was induced in subhuman primates after intracerebral inoculation of brain tissue. These observations suggest that some cases of familial Alzheimer disease may be clinically distinct from senile dementia and may not be genetic in origin.

Uveal melanoma occurring as a fourth primary malignancy: case report.

A patient developed 4 separate malignancies over a 26 year period, the last of which was a primary choroidal melanoma. She demonstrated that despite previous malignancies, suspicious lesions should never be dismissed as being metastatic in origin, but should be thoroughly evaluated and treated accordingly.