Design of a Novel Sensing Method for a Pneumatic Artificial Muscle Actuator-Driven 2-Degrees of Freedom Parallel Joint.

The development of soft actuators and robots has spurred interest in human-friendly robots and devices that can operate in proximity with living things. Researchers have used soft actuators to drive hybrid soft/rigid mechanical platforms with multiple degrees of freedom (DOFs) that are both compliant and produce precise motions. However, the addition of sensors on these systems for feedback control remains a critical issue as they require multiple sensors operating simultaneously while the system undergoes complex motions. This article introduces the use of two spring-tensioned tendons passing through angular encoders for yaw and pitch orientation measurement into a pneumatic artificial muscle-driven two DOFs platform. This system possesses several advantages such as having a large range of motion and enables feedback control of the joint for position control. The joint is shown to be able to follow diverse motion patterns and capable of operating through external disturbances and was implemented as the base joint of an inflatable member.

Design of a dexterous robotic surgical instrument with a novel bending mechanism.

BACKGROUND: The robot-assisted minimally invasive surgery (RMIS) has developed rapidly in recent years, requiring highly articulated instruments to enable surgeons to perform complicated and precise procedures. METHODS: A novel wrist-type surgical instrument was proposed for RMIS. The wrist consists of superelastic-wire-driven snake-like joints and universal joints, which could perform two deflections and one distal rotation. The bending mechanism and the kinematics of universal joints were analysed. The forward and inverse kinematics of the wrist were derived. RESULTS: The performances of the instrument were evaluated using a prototype by experiments. The average motion deviation of the wrist's deflection was 0.15 ± 0.08 mm, and the maximum deviation was 0.52 mm. The maximum payload capability was 10 N. The suture task and ex vivo procedure verified the effectiveness of the instrument. CONCLUSIONS: The proposed instrument has high dexterity and payload capability, which contributes to improving the quality of the RMIS procedures.

Redox-Triggered Chirality Switching and Guest-Capture/Release with a Pillar[6]arene-Based Molecular Universal Joint.

A chiral electrochemically responsive molecular universal joint (EMUJ) was synthesized by fusing a macrocyclic pillar[6]arene (P[6]) to a ferrocene-based side ring. A single crystal of an enantiopure EMUJ was successfully obtained, which allowed, for the first time, the definitive correlation between the absolute configuration and the circular dichroism spectrum of a P[6] derivative to be determined. The self-inclusion and self-exclusion conformational change of the EMUJ led to a chiroptical inversion of the P[6] moiety, which could be manipulated by both solvents and changes in temperature. The EMUJ also displayed a unique redox-triggered reversible in/out conformational switching, corresponding to an occupation/voidance switching of the P[6] cavity, respectively. This phenomenon is an unprecedented electrochemical manipulation of the capture and release of guest molecules by supramolecular hosts.

Structure of Salmonella Flagellar Hook Reveals Intermolecular Domain Interactions for the Universal Joint Function.

The bacterial flagellum is a motility organelle consisting of a rotary motor and a long helical filament as a propeller. The flagellar hook is a flexible universal joint that transmits motor torque to the filament in its various orientations that change dynamically between swimming and tumbling of the cell upon switching the motor rotation for chemotaxis. Although the structures of the hook and hook protein FlgE from different bacterial species have been studied, the structure of Salmonella hook, which has been studied most over the years, has not been solved at a high enough resolution to allow building an atomic model of entire FlgE for understanding the mechanisms of self-assembly, stability and the universal joint function. Here we report the structure of Salmonella polyhook at 4.1 Å resolution by electron cryomicroscopy and helical image analysis. The density map clearly revealed folding of the entire FlgE chain forming the three domains D0, D1 and D2 and allowed us to build an atomic model. The model includes domain Dc with a long ß-hairpin structure that connects domains D0 and D1 and contributes to the structural stability of the hook while allowing the flexible bending of the hook as a molecular universal joint.

Evidence for the hook supercoiling mechanism of the bacterial flagellum.

The bacterial flagellar hook is a short, highly curved tubular structure connecting the basal body as a rotary motor and the filament as a helical propeller to function as a universal joint to transmit motor torque to the filament regardless of its orientation. This highly curved form is known to be part of a supercoil as observed in the polyhook structure. The subunit packing interactions in the Salmonella hook structure solved in the straight form gave clear insights into the mechanisms of its bending flexibility and twisting rigidity. Salmonella FlgE consists of four domains, D0, Dc, D1 and D2, arranged from inside to outside of the tube, and an atomic model of the supercoiled hook built to simulate the hook shape observed in the native flagellum suggested that the supercoiled form is stabilized by near-axial interactions of the D2 domains on the inner surface of the supercoil. Here we show that the deletion of domain D2 from FlgE makes the hook straight, providing evidence to support the proposed hook supercoiling mechanism that it is the near-axial interactions between the D2 domains that stabilize the highly curved hook structure.

Molecular dynamics simulation of bacterial flagella.

The bacterial flagellum is a biological nanomachine for the locomotion of bacteria, and is seen in organisms like Salmonella and Escherichia coli. The flagellum consists of tens of thousands of protein molecules and more than 30 different kinds of proteins. The basal body of the flagellum contains a protein export apparatus and a rotary motor that is powered by ion motive force across the cytoplasmic membrane. The filament functions as a propeller whose helicity is controlled by the direction of the torque. The hook that connects the motor and filament acts as a universal joint, transmitting torque generated by the motor to different directions. This report describes the use of molecular dynamics to study the bacterial flagellum. Molecular dynamics simulation is a powerful method that permits the investigation, at atomic resolution, of the molecular mechanisms of biomolecular systems containing many proteins and solvent. When applied to the flagellum, these studies successfully unveiled the polymorphic supercoiling and transportation mechanism of the filament, the universal joint mechanism of the hook, the ion transfer mechanism of the motor stator, the flexible nature of the transport apparatus proteins, and activation of proteins involved in chemotaxis.

An intrinsically disordered linker controlling the formation and the stability of the bacterial flagellar hook.

BACKGROUND: In a macro-molecular complex, any minor change may prove detrimental. For a supra-molecular nano-machine like the bacterial flagellum, which consists of several distinct parts with specific characteristics, stability is important. During the rotation of the bacterial flagellar motor, which is located in the membrane, the flagella rotate at speeds between 200 and 2000 rpm, depending on the bacterial species. The hook substructure of the bacterial flagellum acts as a universal joint connecting the motor to the flagellar filament. We investigated the formation of the bacterial flagellar hook and its overall stability between the FlgE subunits that make up the hook and attempted to understand how this stability differs between bacteria. RESULTS: An intrinsically disordered segment plays an important role for overall hook stability and for its structural cohesion during motor rotation. The length of this linker segment depends on the species of bacteria; for Salmonella enterica and Campylobacter jejuni it is approximately 37 and 54 residues, respectively. Few residues of the linker are conserved and mutating the conserved residues of the linker yields non-flagellated cells. In the case of Campylobacter, which rotates its flagella at a speed much higher than that of Salmonella, shortening the linker leads to a rupture of the hook at its base, decreasing cell motility. Our experiments show that this segment is required for polymerization and stability of the hook, demonstrating a surprising role for a disordered region in one of the most finely tuned and closely studied macromolecular machines. CONCLUSIONS: This study reveals a detailed functional characteristic of an intrinsically disordered segment in the hook protein. This segment evolved to fulfill a specific role in the formation of the hook, and it is at the core of the stability and flexibility of the hook. Its length is important in the case of bacteria with high-speed rotating flagella. Finding a way of disrupting this linker in Campylobacter might help in preventing infections.

Temperature-Driven Planar Chirality Switching of a Pillar[5]arene-Based Molecular Universal Joint.

The study of an enantiopure bicyclic pillar[5]arene-based molecular universal joint (MUJ) by single-crystal X-ray diffraction allowed for the first time the unequivocal assignment of the absolute configuration of a planar chiral pillar[5]arene by circular dichroism spectroscopy. Crucially, the absolute configuration of the MUJ was switched reversibly by temperature, with an accompanying sign inversion of the anisotropy factor that varied by as much as 0.03, which is the largest value ever reported. Mechanistically, the reversible chirality switching of the MUJ is driven by the threading/dethreading motion of the fused ring and hence is dependent on both the size and nature of the ring and the solvent employed, reflecting the critical balance between the self-complexation of the ring by pillar[5]arene, the solvation to the excluded ring, and the inclusion of solvent molecules in the cavity.