The Effects of Crosslinking on the Rheology and Cellular Behavior of Polymer-Based 3D-Multilayered Scaffolds for Restoring Articular Cartilage.

Polymer-based tri-layered (bone, intermediate and top layers) scaffolds used for the restoration of articular cartilage were prepared and characterized in this study to emulate the concentration gradient of cartilage. The scaffolds were physically or chemically crosslinked. In order to obtain adequate scaffolds for the intended application, the impact of the type of calcium phosphate used in the bone layer, the polymer used in the intermediate layer and the interlayer crosslinking process were analyzed. The correlation among SEM micrographs, physical-chemical characterization, swelling behavior, rheological measurements and cell studies were examined. Storage moduli at 1 Hz were 0.3-1.7 kPa for physically crosslinked scaffolds, and 4-5 kPa (EDC/NHS system) and 15-20 kPa (glutaraldehyde) for chemically crosslinked scaffolds. Intrinsic viscoelasticity and poroelasticity were considered in discussing the physical mechanism dominating in different time/frequency scales. Cell evaluation showed that all samples are available as alternatives to repair and/or substitute cartilage in articular osteoarthritis.

Design, construction, and biological testing of an implantable porous trilayer scaffold for repairing osteoarthritic cartilage.

Various tissue engineering systems for cartilage repair have been designed and tested over the past two decades, leading to the development of many promising cartilage grafts. However, no one has yet succeeded in devising an optimal system to restore damaged articular cartilage. Here, the design, assembly, and biological testing of a porous, chitosan/collagen-based scaffold as an implant to repair damaged articular cartilage is reported. Its gradient composition and trilayer structure mimic variations in natural cartilage tissue. One of its layers includes hydroxyapatite, a bioactive component that facilitates the integration of growing tissue on local bone in the target area after scaffold implantation. The scaffold was evaluated for surface morphology; rheological performance (storage, loss, complex, and time-relaxation moduli at 1 kHz); physiological stability; in vitro activity and cytotoxicity (on a human chondrocyte C28 cell line); and in vivo performance (tissue growth and biodegradability), in a murine model of osteoarthritis. The scaffold was shown to be mechanically resistant and noncytotoxic, favored tissue growth in vivo, and remained stable for 35 days postimplantation in mice. These encouraging results highlight the potential of this porous chitosan/collagen scaffold for clinical applications in cartilage tissue engineering.

Land sharing in South Patagonia: Conservation of above-ground beetle diversity in forests and non-forest ecosystems.

Land-sharing strategies, as variable retention silvicultural proposals, are useful to mitigate harmful effects of economic activities on forest biodiversity; benefits have been reported worldwide for several organisms. However, we suggest that this approach could be useful to improve beetle conservation not only in forests but also in other ecosystem types, based on the results from Southern Patagonia (Argentina). We studied above-ground beetle communities using pitfall traps in Nothofagus pumilio forests, Mulguraea tridens shrublands, and magellanic steppes. The forests were located in Tierra del Fuego Province, while the shrublands and the steppes were in Santa Cruz Province. In forests and shrublands, we compared retention approaches (aggregated/dispersed retention harvesting in forests, and managed cut and retention strips in shrublands) vs. control situations (without harvesting/cuttings). In dry and humid steppes, both impacted by livestock, we evaluated grazed and exclusion paddocks, comparable to structural retentions (reference areas without grazing do not exist). Richness, abundance, frequency, Shannon-Wiener diversity and Pielou evenness indices, and similarity among assemblages were evaluated using univariate and multivariate statistical tests. In forests and shrublands, retention approaches (aggregated/dispersed and strips) allowed the partial or total maintenance of beetle community richness, preserving them similar to natural and non-impacted ecosystems. In dry and humid steppes, exclusion areas presented significantly different richness, abundance and diversity of arthropod assemblages, but with inverse trends: lower values in grazed areas than in exclusions in dry steppe, and higher values in grazed areas than in exclusions in humid steppe. We concluded that land-sharing could be implemented in forests and non-forest ecosystems to preserve beetle communities, being the variable retention approaches and the grazing exclusion areas good alternatives for private or public lands. Likewise, we consider that legislation to promote conservation (like National Law 26331) should not be only applicable for and implemented in forests, but also in non-forest ecosystems.

Impact of cardiosynchronous brain pulsations on Monte Carlo calculated doses for synchrotron micro- and minibeam radiation therapy.

PURPOSE: The purpose of this study was to assess the effects of brain movements induced by heartbeat on dose distributions in synchrotron micro- and minibeam radiation therapy and to develop a model to help guide decisions and planning for future clinical trials. METHODS: The Monte Carlo code PENELOPE was used to simulate the irradiation of a human head phantom with a variety of micro- and minibeam arrays, with beams narrower than 100 µm and above 500 µm, respectively, and with radiation fields of 1 × 2 cm and 2 × 2 cm. The dose in the phantom due to these beams was calculated by superposing the dose profiles obtained for a single beam of 1 µm × 2 cm. A parameter δ, accounting for the total displacement of the brain during the irradiation and due to the cardiosynchronous pulsation, was used to quantify the impact on peak-to-valley dose ratios and the full width at half maximum. RESULTS: The difference between the maximum (at the phantom entrance) and the minimum (at the phantom exit) values of the peak-to-valley dose ratio reduces when the parameter δ increases. The full width at half maximum remains almost constant with depth for any δ value. Sudden changes in the two quantities are observed at the interfaces between the various tissues (brain, skull, and skin) present in the head phantom. The peak-to-valley dose ratio at the center of the head phantom reduces when δ increases, remaining above 70% of the static value only for minibeams and δ smaller than ∼200 µm. CONCLUSIONS: Optimal setups for brain treatments with synchrotron radiation micro- and minibeam combs depend on the brain displacement due to cardiosynchronous pulsation. Peak-to-valley dose ratios larger than 90% of the maximum values obtained in the static case occur only for minibeams and relatively large dose rates.

Enfisema subcutáneo y neumomediastino secundario a fracturas costales / Pneumomediastinum and subcutaneous emphysema due to ribs fractures

No disponible

Knowing the enemy: ant behavior and control in a pediatric hospital of Buenos Aires.

Ant control is difficult in systems even where a variety of control strategies and compounds are allowed; in sensitive places such as hospitals, where there are often restrictions on the methods and toxicants to be applied, the challenge is even greater. Here we report the methods and results of how we faced this challenge of controlling ants in a pediatric hospital using baits. Our strategy was based on identifying the species present and analyzing their behavior. On the one hand, we evaluated outdoors in the green areas of the hospital, the relative abundance of ant genera, their food preferences and the behavioral dominances. On the other hand, control treatments were performed using separately two boron compounds added to sucrose solution which was not highly concentrated to avoid constrains due to the viscosity. Most of the species in the food preference test accepted sugary food; only one species was recorded to visit it less than the protein foods. This result was consistent with the efficacy of control treatments by sugary baits within the rooms. For species that showed good acceptance of sugar solutions in the preference test outdoors, sugar bait control indoors was 100& effective. Conversely, for the only species that foraged significantly less on sugar food, the bait treatment was ineffective. This work reveals the importance of considering the behavior and feeding preferences of the species to be controlled by toxic baits.

Increased tensile strength of carbon nanotube yarns and sheets through chemical modification and electron beam irradiation.

The inherent strength of individual carbon nanotubes (CNTs) offers considerable opportunity for the development of advanced, lightweight composite structures. Recent work in the fabrication and application of CNT forms such as yarns and sheets has addressed early nanocomposite limitations with respect to nanotube dispersion and loading and has pushed the technology toward structural composite applications. However, the high tensile strength of an individual CNT has not directly translated into that of sheets and yarns, where the bulk material strength is limited by intertube electrostatic attractions and slippage. The focus of this work was to assess postprocessing of CNT sheets and yarns to improve the macro-scale strength of these material forms. Both small-molecule functionalization and electron-beam irradiation were evaluated as means to enhance the tensile strength and Young's modulus of the bulk CNT materials. Mechanical testing revealed a 57% increase in tensile strength of CNT sheets upon functionalization compared with unfunctionalized sheets, while an additional 48% increase in tensile strength was observed when functionalized sheets were irradiated. Similarly, small-molecule functionalization increased tensile strength of yarn by up to 25%, whereas irradiation of the functionalized yarns pushed the tensile strength to 88% beyond that of the baseline yarn.

Asymmetrical behavioral response towards two boron toxicants depends on the ant species (Hymenoptera: Formicidae).

Urban ants are a worldwide critical household pests, and efforts to control them usually involve the use of alimentary baits containing slow-acting insecticides. A common toxicant used is boron, either as borax or boric acid. However, the presence of these compounds can affect the consumption of baits by reducing their acceptance and ingestion. Moreover, as feeding motivation varies widely, according not only to food properties but also to colony conditions, bait consumption might be diminished further in certain situations. In this study, we compared the feeding response of ants toward two boron toxic baits (boric acid and borax) in low motivation situations that enhance any possible phago-deterrence the baits may produce. Most studies investigating bait ingestion evaluate whole nests or groups of ants; here, we analyzed the individual ingestion behavior and mortality of the Argentine ant, Linepithema humile (Mayr), and the carpenter ant, Camponotus mus (Roger), for two boron baits, to detect which compound generates a higher rejection in each of these species. Although these two species have similar feeding habits, our results showed that ants under low motivation conditions reduced the acceptance and consumption of the toxic baits asymmetrically. While L. humile mostly rejected the borax, C. mus rejected the boric acid. These results denote the importance of considering the preference of each species when developing a pest management strategy.

Reinforced thermoplastic polyimide with dispersed functionalized single wall carbon nanotubes.

Molecular pi-complexes were formed from pristine HiPCO single- wall carbon nanotubes (SWCNTs) and 1-pyrene- N-(4-N'-(5-norbornene-2,3-dicarboxyimido)phenyl butanamide, 1. Polyimide films were prepared with these complexes as well as uncomplexed SWCNTs and the effects of nanoadditive addition on mechanical, thermal, and electrical properties of these films were evaluated. Although these properties were enhanced by both nanoadditives, larger increases in tensile strength and thermal and electrical conductivities were obtained when the SWCNT/1 complexes were used. At a loading level of 5.5 wt %, the T(g) of the polyimide increased from 169 to 197 degrees C and the storage modulus increased 20-fold (from 142 to 3045 MPa). The addition of 3.5 wt % SWCNT/1 complexes increased the tensile strength of the polyimide from 61.4 to 129 MPa; higher loading levels led to embrittlement and lower tensile strengths. The electrical conductivities (DC surface) of the polyimides increased to 1 x 10(-4) Scm(-1) (SWCNT/1 complexes loading level of 9 wt %). Details of the preparation of these complexes and their effects on polyimide film properties are discussed.

Growth and characterization of branched carbon nanostructures arrays in nano-patterned surfaces from porous silicon substrates.

A method to grow branched carbon nanostructures arrays is presented. We employ the electron-beam-induced deposition method using a transmission electron microscope in poor vacuum conditions where hydrocarbons are present in the chamber. The hydrocarbons are attracted to the substrates by the local electric fields. Saw-tooth nano-patterns were made with a focused ion beam in porous silicon substrates with high porosity in order to create sites with high-local electric fields. We found that the adequate ion dose to create well-defined saw-tooth nano-patterns was between 8 and 10 nC/microm(2). Raman and electron energy-loss spectroscopy on the branched carbon nanostructures show a high concentration of sp(2) sites suggesting that they are made of graphite-like hydrogenated amorphous carbon. Selected area electron diffraction, high-resolution images and energy dispersive X-ray analysis (EDS) are also presented.