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Currently, the study and applications of morphing structures with cellular configurations and negative effective Poisson's ratio are of interest for the automotive and aerospace field, as also applications in optical, biological, microelectronic, structural and thermo-mechanical components. These structures have light weight, large shear stiffness and they resist large deformations in the elastic range of the constitutive material, if compared to a solid structure with the same material. This paper presents a numerical study of in-plane static behavior of hexachiral structure with negative effective Poisson's ratio, using the finite element method. The results obtained suggest a better control of the parameters of the structures because the geometrical restrictions of real applications are taken into account, making the design more flexible and reliable by the type of desired [ABSTRACT FROM AUTHOR]

The knowledge about manufacturing and the resulting mechanical properties using fibro-reinforced material is currently limited in Colombia. This preliminary study using beams made of fiber reinforced material was undertaken to evaluate the elastic modulus of the composite material, which will be subsequently used to design an external fixation system for bone transportation. Specimens were made of carbon fiber fabric using epoxy resin as the matrix. A hand lay-up manufacturing process varying number of carbon fiber layers was implemented to evaluate different fiber volumetric ratios. The elastic modulus was experimentally obtained by performing bending tests based on the ASTM D7264 standard. Also, the elastic modulus was theoretically calculated using the rule of mixtures. The experimental and theoretical elastic modulus was lineally increased for increasing the volumetric fiber ratio. However, the experimental results were considerably smaller than the theoretically obtained results, which might be produced by a possible presence of wrinkles or misalignment of the fabric produced during the handling inside the mold. It could be also produced by incomplete adhesion between the fiber and the resin. [ABSTRACT FROM AUTHOR]

Introduction: Convection enhanced delivery (CED) is a method to bypass the blood-brain barrier and deliver amounts controlled of drugs over localized zones of the brain for the treatment of disorders and tumors. Several experimental studies have been tested in animals and agarose gels to understand the effect of different parameters on the outcome this procedure. In infusion experiments with brain of animals at higher flow rates showed backflow. Objective: The objective of this study was to evaluate whether a needle with sharp tip can reduce the backflow. Methods: Infusions tests were performed on in 0.6 % agarose hydrogel. The infusions were performed with Evans blue albumin. Two different tips were used: blunt and sharp tip with 0.36 mm outside diameter. Results: For low flow rate (0.3 and 0.5 µl/min) the backflow lengths were similar for both needle tip geometries. In contrast, for high flow rates (1 and 2 µl/min), blunt tip needles presented smaller backflow distances. The flow distributions with blunt tip were symmetric, while with sharp tip, backflow started on the side of hole in the infusions with sharp tip. Conclusions: The greater backflow distances obtained with sharp tip needle could be due to the lack of symmetry of the needle. In the process of insertion of the catheter with sharp tip, the phantom gel is compressed only on one side and produce tearing in the tissue. Different response of phantom material for each tip could explain the differences on flow distributions. [ABSTRACT FROM AUTHOR]