The chirality of the mitotic spindle provides a mechanical response to forces and depends on microtubule motors and augmin

Forces produced by motor proteins and microtubule dynamics within the mitotic spindle are crucial for proper chromosome segregation. In addition to linear forces, rotational forces or torques are present in the spindle, which are reflected in the left-handed twisted shapes of microtubule bundles that make the spindle chiral. However, the biological role and molecular origins of spindle chirality are unknown. By developing methods for measuring the spindle twist, we show that spindles are most chiral near the metaphase-to-anaphase transition. To assess the role of chirality in spindle mechanics, we compressed the spindles along their axis. This resulted in a stronger left-handed twist, suggesting that the twisted shape allows for a mechanical response to forces. Inhibition or depletion of motor proteins that perform chiral stepping, Eg5/kinesin-5, Kif18A/kinesin-8, MKLP1/kinesin-6, and dynein, decreased the left-handed twist or led to right- handed twist, implying that these motors regulate the twist by rotating microtubules within their antiparallel overlaps or at the spindle pole. A right-handed twist was also observed after the depletion of the microtubule nucleator augmin, indicating its contribution to the twist through the nucleation of antiparallel bridging microtubules. The uncovered switch from left- handed to right-handed twist reveals the existence of competing mechanisms that promote twisting in opposite directions. As round spindles are more twisted than the elongated ones are, we infer that bending and twisting moments are generated by similar molecular mechanisms and propose a physiological role for spindle chirality in allowing the spindle to absorb mechanical load

Numerical analysis of metallographic preparation effect on the hardness of titanium alloy

Titanium alloys due to their good properties are increasingly used in biomedicine. However, in order to improve certain properties, titanium- based alloys with new chemical compositions are designed. In order to be characterized in a satisfactory manner, they must first be adequately prepared. In this paper the two most influential parameters were varied: grinding time and force, while the speed of rotation of the grinding wheel was constant. After grinding with the highest gradation of grind paper, the samples were observed under a light microscope to determine the condition of the surface. Then their hardness was determined by the Vickers method with different indenter loads. After that, the samples were polished under the same conditions, and their hardness was determined again. The obtained hardness values were numerically analyzed and the corresponding functional dependences of the measured hardness on the grinding parameters (time and force) and on the indentation force were determined

Numerical analysis of metallographic preparation effect on the hardness of titanium alloy

Titanium alloys due to their good properties are increasingly used in biomedicine. However, in order to improve certain properties, titanium-based alloys with new chemical compositions are designed. In order to be characterized in a satisfactory manner, they must first be adequately prepared. In this paper the two most influential parameters were varied: grinding time and force, while the speed of rotation of the grinding wheel was constant. After grinding with the highest gradation of grind paper, the samples were observed under a light microscope to determine the condition of the surface. Then their hardness was determined by the Vickers method with different indenter loads. After that, the samples were polished under the same conditions, and their hardness was determined again. The obtained hardness values were numerically analyzed and the corresponding functional dependences of the measured hardness on the grinding parameters (time and force) and on the indentation force were determined