Conditions for optimal mechanical power generation by a bundle of growing actin filaments

Bundles of actin filaments are central to a large variety of cellular structures, such as filopodia, stress fibers, cytokinetic rings or focal adhesions. The mechanical properties of these bundles are critical for proper force transmission and force bearing. Previous mathematical modeling efforts have focused on bundles’ rigidity and shape. However, it remains unknown how bundle length and thickness are controlled by external physical factors, and how the attachment of the bundle to a load affects its ability to transmit forces. In this paper, we present a biophysical model for dynamic bundles of actin filaments that takes into account individual filaments, their interaction with each other and with an external load. In combination with in vitro motility assays of beads coated with formins, our model allowed us to characterize conditions for bead movement and bundle buckling. From the deformation profiles, we determined key biophysical properties of tethered actin bundles, such as their rigidity and filament density. Our model also demonstrated that filaments undulate under lateral constraints applied by external forces or by neighboring filaments of the bundle. Last, our model allowed us to identify optimum conditions in filament density and barbed end tethering to the load for a maximal yield of mechanical power by a dynamic actin bundle.

Maximal proper force, black hole horizons and matter as curvature in momentum space

Starting with the study of the geometry on the cotangent bundle (phase space), it is shown that the maximal proper force condition, in the case of a uniformly accelerated observer of mass [Formula: see text] along the [Formula: see text] axis, leads to a minimum value of [Formula: see text] lying [Formula: see text] the Rindler wedge and given by the black hole horizon radius [Formula: see text]. Whereas in the uniform circular motion case, we find that the maximal proper force condition implies that the radius of the circle cannot exceed the value of the horizon radius [Formula: see text]. A correspondence is found between the black hole horizon radius and a singularity in the curvature of momentum space. The fact that the geometry (metric) in phase spaces is observer-dependent (on the momentum of the massive particle/observer) indicates further that the matter stress energy tensor and vacuum energy in the underlying space-time may admit an interpretation in terms of the curvature in momentum spaces. Some final comments are made pertaining to the Asymptotic Safety program in gravity and why phase space geometry seems to be a proper arena for a space–time–matter unification.

Two spatially distinct Kinesin-14 Pkl1 and Klp2 generate collaborative inward forces against Kinesin-5 Cut7 inS. pombe

ABSTRACTKinesin motors play central roles in bipolar spindle assembly. In many eukaryotes, spindle pole separation is driven by Kinesin-5 that generates outward force. This outward force is balanced by antagonistic inward force elicited by Kinesin-14 and/or Dynein. In fission yeast, two Kinesin-14s, Pkl1 and Klp2, play an opposing role against Kinesin-5/Cut7. However, how these two Kinesin-14s coordinate individual activities remains elusive. Here we show that while deletion of eitherpkl1orklp2rescues temperature sensitivecut7mutants, onlypkl1deletion can bypass the lethality caused bycut7deletion. Pkl1 is tethered to the spindle pole body, while Klp2 is localized along the spindle microtubule. Forced targeting of Klp2 to the spindle pole body, however, compensates for Pkl1 functions, indicating that cellular localizations, rather than individual motor specificities, differentiate between the two Kinesin-14s. Interestingly, human Kinesin-14/HSET can replace either Pkl1 or Klp2. Moreover, overproducing HSET induces monopolar spindles, reminiscent of the phenotype of Cut7 inactivation. Taken together, this study has uncovered the biological mechanism of how two different Kinesin-14s exert their antagonistic roles against Kinesin-5 in a spatially distinct manner.SUMMARY STATEMENTProper force-balance generated by Kinesin-5 and Kinesin-14 is crucial for spindle bipolarity. Two fission yeast Kinesin-14s localize to different structures, thereby collaboratively producing inward forces against Kinesin-5-mediated outward force.Abbreviations usedGBPGFP-binding proteinMWP complexMsd1-Wdr8-Pkl1 complexSPBspindle pole bodytstemperature sensitiveγ-TuCthe γ-tubulin complex

Orthodontic Management in Aggressive Periodontitis

Aggressive periodontitis is a type of periodontitis with early onset and rapid progression and mostly affecting young adults who occupy a large percentage of orthodontic patients. The role of the orthodontist is important in screening the disease, making a provisional diagnosis, and referring it to a periodontist for immediate treatment. The orthodontist should be aware of the disease not only before starting the appliance therapy, but also during and after the active mechanotherapy. The orthodontic treatment plan, biomechanics, and appliance system may need to be modified to deal with the teeth having reduced periodontal support. With proper force application and oral hygiene maintenance, orthodontic tooth movement is possible without any deleterious effect in the tooth with reduced bone support. With proper motivation and interdisciplinary approach, orthodontic treatment is possible in patients with controlled aggressive periodontitis.

Optimal Design of Safe Planar Manipulators Using Passive Torque Limiters

This paper presents a synthesis approach to build safe planar serial robotic mechanisms for applications in human–robot cooperation. The basic concept consists in using torque limiting devices that slip when a prescribed torque is exceeded so that the maximum force and the maximum power that the robot can apply to its environment are limited. In order to alleviate the effect of the change of pose of the robot on the joint to Cartesian force mapping, it is proposed to include more torque limiters than actuated joints. The design of isotropic force modules is addressed in order to produce proper force capabilities while ensuring safety. The proposed isotropic module of torque limiting devices leads to such characteristics. In addition to modeling the contact forces at the end-effector, the forces that can be applied by the robot to its environment when contact is taking place elsewhere along its links are also analyzed as well as the power of potential collisions. Examples of manipulator architectures and their static analysis are given. Finally, the design of a spatial serial manipulator using the isotropic planar force modules developed in the paper is illustrated.

MMP inhibition as a potential method to augment the healing of skeletal muscle and tendon extracellular matrix

The extracellular matrix (ECM) of skeletal muscle and tendon is composed of different types of collagen molecules that play important roles in the transmission of forces throughout the body, and in the repair and regeneration of injured tissues. Fibroblasts are the primary cells in muscle and tendon that maintain, repair, and modify the ECM in response to mechanical loading, injury, and inactivity. Matrix metalloproteinases (MMPs) are enzymes that digest collagen and other structural molecules, which are synthesized and excreted by fibroblasts. MMPs are required for baseline ECM homeostasis, but disruption of MMP regulation due to injury or disease can alter the normal ECM architecture and prevent proper force transmission. Chronic injuries and diseases of muscles and tendons can be severely debilitating, and current therapeutic modalities to enhance healing are quite limited. This review will discuss the mechanobiology of MMPs, and the potential use of MMP inhibitors to improve the treatment of injured and diseased skeletal muscle and tendon tissue.

Robot Grasp Pattern Recognition Based on Wavlet and BP Neural Network

Tactile sensation is one of essential perceptions for a functional robot hand to monitor slip states, grasp objects with proper force, and distinguish different properties of objects etc. A practical tactile sensor based on acoustic-electric converting principle is introduced. The grasp signals of objects of three sort materials are collected by the tactile sensor. The power spectrum feature vectors of them are taken as learning sample book set. Transfer function of neurons in hidden layer is tangent function and that in output layer is logarithmic function. L-M algorithm is selected and convergence precision set is as 0.0001. The hidden layer nodes are taken by experiments as 13. When neural network structure is 8-13-4, BP neural network has the fastest convergence rate and short running time of milliseconds.

Can Pelvis Angle be Monitored From Seat Support Forces in Healthy Subjects?

Individuals who cannot functionally reposition themselves often need dynamic seating interventions that change body posture from automatic chair adjustments. Pelvis alignment directly affects sitting posture, and systems that adjust and monitor pelvis angle simultaneously might be applicable to control body posture in sitting. The present study explores whether it is feasible to monitor pelvis angle from seat support forces. Pelvis angle estimation was based on equivalent “two-force member” loading for which pelvis orientation equals the orientation of the equivalent contact force. Theoretical evaluation was done to derive important conditions for practical application. An instrumented wheelchair was developed for experimental validation in healthy subjects. Seat support forces were measured, and mechanical analysis was done to derive the equivalent contact force from which we estimated the pelvis angle. Model analysis showed a significant influence of pelvis mass, hip force, and lumbar torque on the relation between the actual pelvis angle and the predicted pelvis angle. Proper force compensation and minimal lumbar torque seemed important for accurate pelvis angle estimations. Experimental evaluation showed no body postures that involved a clear relation between the pelvis angle and the orientation of the equivalent contact force. Findings suggest that pelvis angle could not be estimated in healthy individuals under the described experimental seating conditions. Validation experiments with impaired individuals must be performed under different seating conditions to provide a better understanding whether the principle is of interest for clinical application.

BORN'S RECIPROCAL GENERAL RELATIVITY THEORY AND COMPLEX NON-ABELIAN GRAVITY AS GAUGE THEORY OF THE QUAPLECTIC GROUP: A NOVEL PATH TO QUANTUM GRAVITY

Born's reciprocal relativity in flat space–times is based on the principle of a maximal speed limit (speed of light) and a maximal proper force (which is also compatible with a maximal and minimal length duality) and where coordinates and momenta are unified on a single footing. We extend Born's theory to the case of curved space–times and construct a reciprocal general relativity theory (in curved space–times) as a local gauge theory of the quaplectic group and given by the semidirect product [Formula: see text], where the non-Abelian Weyl–Heisenberg group is H(1, 3). The gauge theory has the same structure as that of complex non-Abelian gravity. Actions are presented and it is argued why such actions based on Born's reciprocal relativity principle, involving a maximal speed limit and a maximal proper force, is a very promising avenue to quantize gravity that does not rely in breaking the Lorentz symmetry at the Planck scale, in contrast to other approaches based on deformations of the Poincaré algebra, quantum groups. It is discussed how one could embed the quaplectic gauge theory into one based on the U(1, 4), U(2, 3) groups where the observed cosmological constant emerges in a natural way. We conclude with a brief discussion of complex coordinates and Finsler spaces with symmetric and nonsymmetric metrics studied by Eisenhart as relevant closed-string target space backgrounds where Born's principle may be operating.

Design of Sub-Centimetre Underactuated Compliant Grippers

This paper proposes a methodology for the design of a sub-centimetre underactuated compliant gripper. The gripper is optimized in order to maintain a proper force distribution on the phalanges and to avoid the deformation of soft objects. In order to keep the design simple and to limit the complexity of the control, each finger is based on a planar five-bar linkage. The five-bar mechanism is a well known and efficient underactuated mechanism. In this work, the revolute joints are replaced by flexible hinges in order to allow the miniaturization of the mechanism and make it easy to clean and sterilize. The behaviour of the prototypes built shows the effectiveness of the proposed method.