The main objective of this study is to create a rigorous computer model of carbon nanotube composites to predict their mechanical properties before they are manufactured and to reduce the number of physical tests. A detailed comparison between experimental and computational results of a cement-based composite is made to match data and find the most significant parameters. It is also shown how the properties of the nanotubes (Young’s modulus, aspect ratio, quantity, directionality, clustering) and the cement (Young’s modulus) affect the composite properties. This paper tries to focus on the problem of modeling carbon nanotube composites computationally, and further study proposals are given.

A study involving the removal of blood clots in cerebral vessels by aspiration thrombectomy is presented. A robust design for the distal end geometry of a catheter is obtained that, together with adequate suction conditions, could avoid potential damage in the artery or fragmentation the thrombus. The optimization process of the parameters is undertaken by a Design of Experiments (DOE) that has been prepared based on Robust Design theories. In particular, 27 experiments are run for one factor at 9 levels (catheter geometry) and up to 9 factors at 3 levels. The experiments are formulated with virtual models that are solved with computing tools. Co-simulation between Computer Fluid Dynamics (CFD) and Finite Elements Method (FEM) structural analysis was used to obtain the suction conditions and the behavior of the blood clot during the intervention process. By comparing the results of the 27 experiments, the highest values of the suctioning force are obtained for a hole pattern based catheter design, that also gives the lowest risk for clot damage (based on the stress value obtained). Direct aspiration and designs based on conical catheter distal ends, give less robust solutions (results are not stable when the conditions of the environment change). Our study investigated the distance between the catheter and the clot, and it was noted that if the catheter was far from the clot, the suction generated a vessel narrowing and consequent potential damage. Up to 90 kPa could be applied when suctioning at a maximum distance equal to the diameter of the vessel between the distal end of the catheter and the proximal end of the clot. A maximum suctioning force of 0,514N was achieved without damage to the artery or the clot. This research enables us to determine and use the most representative parameters and geometries to be tested in in-vitro and in-vivo experiments. In this virtual study, hypothesizes are assumed with regard to the material properties, but the robustness of the design process allows to expect similar results in future in-vitro and in-vivo tests.

Concrete is well known for its compression resistance, making it suitable for any kind of construction. Several research studies show that the addition of carbon nanostructures to concrete allows for construction materials with both a higher resistance and durability, while having less porosity. Among the mentioned nanostructures are carbon nanotubes (CNTs), which consist of long cylindrical molecules with a nanoscale diameter. In this work, molecular dynamics (MD) simulations have been carried out, to study the effect of pristine or carboxyl functionalized CNTs inserted into a tobermorite crystal on the mechanical properties (elastic modulus and interfacial shear strength) of the resulting composites. The results show that the addition of the nanostructure to the tobermorite crystal increases the elastic modulus and the interfacial shear strength, observing a positive relation between the mechanical properties and the atomic interactions established between the tobermorite crystal and the CNT surface. In addition, functionalized CNTs present enhanced mechanical properties.

Thrombectomy by aspiration is a highly effective method of accomplishing vessel recanalization. This study aims to obtain a mathematical model that allows the prediction of the dynamic response of a thrombus in response to different suction conditions, in order to avoid potential damage or the breakage of the clot during the interventional procedure. Virtual computing models have been created using Bond-Graph data and mass-spring Multi-Degree of Freedom equations. The model allows the use of tensile and torsion loads that could potentially be generated by the suction pressure together with different catheter geometries. The stress generated in the clot depends on its length and on its stiffness. The results obtained with the mathematical model are validated with a Finite Element Method (FEM) model, shows good agreement in terms of stress and elongation values. The results are consistent with previous Bond Graph models which indicated that the forces needed to extract a blood clot from an artery in in-vitro experiments are within the range used experimentally (~40-90 kPa). Qualitative experiments are undertaken with 3D printed scale prototypes and gelatin. The results are consistent with Computer Fluid Dynamic (CFD) simulations.

Carbon nanotubes (CNTs) are nanometer-sized structures that can be used to reinforce cement matrices. The extent to which the mechanical properties are improved depends on the interfacial characteristics of the resulting materials, that is, on the interactions established between the CNTs and the cement. The experimental characterization of these interfaces is still impeded by technical limitations. The use of simulation methods has a great potential to give information about systems lacking experimental information. In this work, molecular dynamics (MD) and molecular mechanics (MM) were used in conjunction with finite element simulations to study the interfacial shear strength (ISS) of a structure formed by a pristine single-walled CNT (SWCNT) inserted in a tobermorite crystal. The results show that, for a constant SWCNT length, ISS values increase when the SWCNT radius increases, while for a constant SWCNT radius, shorter lengths enhance ISS values.