Ti-6Al-4V alloy has been widely used in restorative surgery due to its high corrosion resistance and biocompatibility. Nevertheless, some studies showed that V and Al release in the organism might induce cytotoxic effects and neurological disorders, which led to the development of V-free alloys and both V-and Al-free alloys containing Nb, Zr, Ta, or Mo. Among these alloys, Ti-13Nb-13Zr alloy is promising due to its better biomechanical compatibility than Ti-6Al-4V. In this work, the corrosion behavior of Ti, Ti-6Al-4V, and Ti-xNb-13Zr alloys (x ¼ 5, 13, and 20) was evaluated in Ringer's solution (pH 7.5) at 37 8C through open-circuit potential measurements, potentiodynamic polarization, and electrochemical impedance spectroscopy. Spontaneous passivity was observed for all materials in this medium. Low corrosion current densities (in the order of 10 À7 A/cm 2 ) and high impedance values (in the order of 10 5 Vcm 2 at low frequencies) indicated their high corrosion resistance. EIS results showed that the passivating films were constituted of an outer porous layer (very low resistance) and an inner compact layer (high resistance), the latter providing the corrosion resistance of the materials. There was evidence that the Ti-xNb-13Zr alloys were more corrosion resistant than both Ti and Ti-6Al-4V in Ringer's solution.
New perspectives have been developed to understand the processes of modeling heterogeneous membranes. These are crucial steps prior to applying advanced techniques like molecular dynamic simulations of whole membrane systems. Lipid, protein, and membrane packing problems are addressed based on biochemical properties in combination with computational optimization techniques. The CELLmicrocosmos 2.2 MembraneEditor (CmME) is introduced as an appropriate framework to handle such problems by offering diverse algorithmic approaches. Its algorithm plug-in-interface enables modelers to generate problem-specific algorithms. Good solutions concerning runtime and lipid density are realized by focusing on the outer shapes of the PDB-based molecules. Application cases are presented like the publication-based modeling of inner and outer mitochondrial membrane-fragments, semiautomatic incorporation of proteins, and the assembly of rafts. Concerning geometrical aspects of the lipids, the achieved results are consistent with experimental observations related to lipid densities and distributions. Finally, two membranes simulated with GROMACS are analyzed and compared: the first is generated with conventional scripting techniques, the second with the CmME Distributor algorithm. The examples prove that CmME is a valuable and versatile tool for a broad set of applications in analysis and visualization of biomembranes.
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