Dual sensing-actuation artificial muscle based on polypyrrole-carbon nanotube composite

Dual sensing artificial muscles based on conducting polymer are faradaic motors driven by electrochemical reactions, which announce the development of proprioceptive devices. The applicability of different composites has been investigated with the aim to improve the performance. Addition of carbon nanotubes may reduce irreversible reactions. We present the testing of a dual sensing artificial muscle based on a conducting polymer and carbon nanotubes composite. Large bending motions (up to 127 degrees) in aqueous solution and simultaneously sensing abilities of the operation conditions are recorded. The sensing and actuation equations are derived for incorporation into a control system.The research was supported by European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No 641822

Instabilities in the transient response of muscle

We investigate the isometric transient response of muscle using a quantitative stochastic model of the actomyosin cycle based on the swinging lever-arm hypothesis. We first consider a single pair of filaments, and show that when values of parameters such as the lever-arm displacement and the crossbridge elasticity are chosen to provide effective energy transduction, the T2 curve (the tension recovered immediately after a step displacement) displays a region of negative slope. If filament compliance and the discrete nature of the binding sites are taken into account, the negative slope is diminished, but not eliminated. This implies that there is an instability in the dynamics of individual half-sarcomeres. However, when the symmetric nature of whole sarcomeres is taken into account, filament rearrangement becomes important during the transient: as tension is recovered, some half-sarcomeres lengthen while others shorten. This leads to a flat T2 curve, as observed experimentally. In addition, we investigate the isotonic transient response and show that for a range of parameter values the model displays damped oscillations, as recently observed in experiments on single muscle fibers. We conclude that it is essential to consider the collective dynamics of many sarcomeres, rather than the dynamics of a single pair of filaments, when interpreting the transient response of muscle.Comment: 11 pages, 11 figures, Submitted to Biophysical Journa

Factors Affecting the Calcium Sensitivity of the Contractile Proteins of the Heart

Force production by cardiac muscle can be altered by changing either the calcium available to the contractile proteins or their sensitivity to calcium. The work of this thesis principally concerns an investigation of factors affecting the calcium sensitivity of the contractile proteins of cardiac muscle . The calcium sensitivity of the contractile proteins was examined using chemically-skinned muscle mainly from rat heart. Completely and partially skinned preparations were used. The completely chemically-skinned preparations had their cellular membranes disrupted by exposure to the non-ionic detergent Triton-X100. This should leave the isolated contractile proteins in their physiological configuration. The second type of preparation uses saponin-treatment. Saponin is an agent which precipitates cholesterol molecules from membranes. As the sarcolemma is richer in cholesterol than the subcellular membranes, brief exposure of preparations to saponin punctures the sarcolemma while leaving the subcellular membranes intact and functional. In both types of preparation the 'intracellular' conditions are under experimental control since the bathing solution is effectively an extension of the sarcoplasm. These preparations can be used to establish the relationship between 'intracellular' calcium and tension by measuring the tension produced at a range of free calcium concentrations. Four general aspects of the calcium sensitivity of the contractile proteins were investigated, (1) hysteresis in the calcium sensitivity of cardiac muscle, (2) the changes in calcium sensitivity with sarcomere length, (3) the effect of altering myofilamental lattice spacing by hypertonic shrinkage and (4) the effect of imidazole-containing compounds on calcium sensitivity Chapter 1 and 2 report on an investigation of the hysteresis in, and the length dependence of, the pCa-tension relationship. Hysteresis means that a muscle can maintain a higher tension level than it can create de novo at any free calcium level. This phenomenon has only been reported in skeletal muscle to dates this thesis provides the first evidence for hysteresis in heart muscle. It is proposed that hysteresis is a special manifestation Of the length-dependence of calcium sensitivity. The calcium sensitivity of the contractile protein's increases as the sarcomere length is increased. I propose that both phenomenon are the result of reduced myofilament separation (i) brought about in the case of hysteresis by force production and (ii) by the change in length in the case of length-dependence of Ca-sensitivity. Experiments designed to test this proposal are described in chapter 2. Lattice spacing was altered independently of force production or sarcomere length change by the use of hypertonic shrinkage techniques. This technique involves addition of long chain polymers (Dextran M. Wt. >40,000) to the bathing solutions

Active elastic dimers: Cells moving on rigid tracks

Experiments suggest that the migration of some cells in the three-dimensional extra cellular matrix bears strong resemblance to one-dimensional cell migration. Motivated by this observation, we construct and study a minimal one-dimensional model cell made of two beads and an active spring moving along a rigid track. The active spring models the stress fibers with their myosin-driven contractility and alpha-actinin-driven extendability, while the friction coefficients of the two beads describe the catch/slip bond behavior of the integrins in focal adhesions. In the absence of active noise, net motion arises from an interplay between active contractility (and passive extendability) of the stress fibers and an asymmetry between the front and back of the cell due to catch bond behavior of integrins at the front of the cell and slip bond behavior of integrins at the back. We obtain reasonable cell speeds with independently estimated parameters. We also study the effects of hysteresis in the active spring, due to catch bond behavior and the dynamics of cross-linking, and the addition of active noise on the motion of the cell. Our model highlights the role of alpha-actinin in three-dimensional cell motility and does not require Arp2/3 actin filament nucleation for net motion.Comment: 13 pages, 9 figure

Acute effects of inspiratory pressure threshold loading upon airway resistance in people with asthma

This is the post-print version of the final paper published in Respiratory Physiology & Neurobiology. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2009 Elsevier B.V.Large inspiratory pressures may impart stretch to airway smooth muscle and modify the response to deep inspiration (DI) in asthmatics. Respiratory system resistance (Rrs) was assessed in response to 5 inspiratory manoeuvres using the forced oscillation technique: (a) single unloaded DI; (b) single DI at 25 cmH2O; (c) single DI at 50% maximum inspiratory mouth pressure [MIP]; (d) 30 DIs at 50% MIP; and (e) 30 DIs at 50% MIP with maintenance of normocapnia. Rrs increased after the unloaded DI and the DI at 25 cmH2O but not after a DI at 50% MIP (3.6 ± 1.6 hPa L s−1 vs. 3.6 ± 1.5 hPa L s−1; p = 0.95), 30 DIs at 50% MIP (3.9 ± 1.5 hPa L s−1 vs. 4.2 ± 2.0 hPa L s−1; p = 0.16) or 30 DIs at 50% MIP under normocapnic conditions (3.9 ± 1.5 hPa L s−1 vs. 3.9 ± 1.5 hPa L s−1; p = 0.55). Increases in Rrs in response to DI were attenuated after single and multiple loaded breaths at 50% MIP

Force-Velocity Relations of a Two-State Crossbridge Model for Molecular Motors

We discuss the force-velocity relations obtained in a two-state crossbridge model for molecular motors. They can be calculated analytically in two limiting cases: for a large number and for one pair of motors. The effect of the strain-dependent detachment rate on the motor characteristics is studied. It can lead to linear, myosin-like, kinesin-like and anomalous curves. In particular, we specify the conditions under which oscillatory behavior may be found.Comment: 5 pages, 4 figures, REVTeX; thoroughly revised version; also available at http://www.physik.tu-muenchen.de/~frey

Hysteresis in muscle

This paper presents examples of hysteresis from a broad range of scientific disciplines and demonstrates a variety of forms including clockwise, counterclockwise, butterfly, pinched and kiss-and-go, respectively. These examples include mechanical systems made up of springs and dampers which have been the main components of muscle models for nearly one hundred years. For the first time, as far as the authors are aware, hysteresis is demonstrated in single fibre muscle when subjected to both lengthening and shortening periodic contractions. The hysteresis observed in the experiments is of two forms. Without any relaxation at the end of lengthening or shortening, the hysteresis loop is a convex clockwise loop, whereas a concave clockwise hysteresis loop (labeled as "kiss-and-go") is formed when the muscle is relaxed at the end of lengthening and shortening. This paper also presents a mathematical model which reproduces the hysteresis curves in the same form as the experimental data