Effects of Helix Geometry on Magnetic Guiding of Helical Polymer Composites on a Gastric Cancer Model: A Feasibility Study

This study investigates the effects of soft-robot geometry on magnetic guiding to develop an efficient helical mediator on a three-dimensional (3D) gastric cancer model. Four different magnetically active helical soft robots are synthesized by the inclusion of 5-μm iron particles in polydimethylsiloxane matrices. The soft robots are named based on the diameter and length (D2-L15, D5-L20, D5-L25, and D5-L35) with samples having varied helical pitch and weight values. Then, the four samples are tested on a flat surface as well as a stomach model with various 3D wrinkles. We analyze the underlying physics of intermittent magnetomotility for the helix on a flat surface. In addition, we extract representative failure cases of magnetomotility on the stomach model. The D5-L25 sample was the most suitable among the four samples for a helical soft robot that can be moved to a target lesion by the magnetic-flux density of the stomach model. The effects of diameter, length, pitch, and weight of a helical soft robot on magnetomotility are discussed in order for the robot to reach the target lesion successfully via magnetomotility.

A thermophilic phage uses a small terminase protein with a fixed helix-turn-helix geometry

SUMMARYTailed bacteriophage use a DNA packaging motor to encapsulate their genome during viral particle assembly. The small terminase (TerS) component acts as a molecular matchmaker by recognizing the viral genome as well as the main motor component, the large terminase (TerL). How TerS binds DNA and the TerL protein remains unclear. Here, we identify the TerS protein of the thermophilic bacteriophage P74-26. TerSP76-26 oligomerizes into a nonamer that binds DNA, stimulates TerL ATPase activity, and inhibits TerL nuclease activity. Our cryo-EM structure shows that TerSP76-26 forms a ring with a wide central pore and radially arrayed helix-turn-helix (HTH) domains. These HTH domains, which are thought to bind DNA by wrapping the helix around the ring, are rigidly held in an orientation distinct from that seen in other TerS proteins. This rigid arrangement of the putative DNA binding domain imposes strong constraints on how TerSP76-26 can bind DNA. Finally, the TerSP76-26 structure lacks the conserved C-terminal β-barrel domain used by other TerS proteins for binding TerL, suggesting that a well-ordered C-terminal β-barrel domain is not necessary for TerS to carry out its function as a matchmaker.

Chirality-dependent forces in simple shear flow for helix aligned with streamlines

We consider the chiral properties for a helix in uniform shear flow. We decompose the helical structure into arrays of [Formula: see text] closely packed beads with radius [Formula: see text]. In low Reynolds number regime, the chirality-specific lift forces in the vorticity direction experienced by helices are given by a set of helix geometry parameters: helix radius [Formula: see text], pitch length [Formula: see text], number of turns [Formula: see text] and helix phase angle [Formula: see text]. The analytical formula of the force is firstly given. The chirality-specific forces are the physical reasons for the chiral separation of helices in shear flow. Our results provide new insights into the separations of all kinds of chiral objects.

Chirality-specific lift forces of helix under shear flows

Chiral objects in a shear flow experience a chirality-specific lift force. Shear flows past helices in low Reynolds number regime are studied by a highly efficient iterative method, based on the analytical solution of a sphere in uniform flow. The chirality-specific lift forces in the vorticity direction experienced by helices are dominated by a set of helix geometry parameters: helix radius ([Formula: see text]), pitch length (b), number of turns and helix phase angle. Its analytical formula is firstly given. The chirality-specific forces are the physical reasons for the chiral separation of helices in shear flow. Our results are qualitatively in agreement with the simulation results and well supported by the latest experimental observations.

Prediction for Strength of 3D Braided Composites Based on Helix Geometry Model

A numerical model capable of calculating the strength of 3D braided composites is developed, based on the micro-structure of 3D four-directional braided composites and the assumption of the braiding yarn with a helix configuration and ellipse cross-section. The strength of 3D braided composites have been predicted through a finite multiphase element method (FMEM). Comparison was conducted for those from the present model and experiment. The results are in good agreements with the experimental results in the previous literature. The influences of braiding angle on the strength are also studied.