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1.
We describe a new method that uses straightforward physics to apply force to substrate-attached cells. In this method, collagen-coated
magnetic ferric oxide beads attach to the dorsal surface of cells via receptors of the integrin family, and a magnetic field
gradient is applied to produce a force. In this paper we present a complete characterization of the method in a configuration
that is easy to use, in which a permanent magnet provides a fairly uniform gradient over a relatively large area. This allows
a fairly uniform average force that can be controlled in magnitude, direction, and duration to be applied to a large number
of cells. We show how to determine the applied force per cell by measuring the force per unit volume of magnetic bead, the
distribution of bead diameters, and the distribution of beads per cell. We also show how to calculate the force per unit volume
of bead in a three-dimensional region near the permanent magnet on the basis of field measurements, and present results for
three of the magnets. An upward force applied to fibroblasts by this method produces a measurable time-dependent increase
in attachment of cytoskeletal actin filaments to the force application points, and an increase in actin cross-linking. This
is accompanied by an actin-dependent retraction of the force-induced upward movement of the dorsal surface of the cells.
Received: 27 February 1997 / Received after revision: 10 August 1997 / Accepted: 1 September 1997 相似文献
2.
Abstract: This paper describes a device used to measure the isometric forces generated during electrical stimulation of the canine latissimus dorsi muscle in vivo with a preserved neurovascular supply. This device uses 2 strain gauge force sensors linked to a movable alignment frame to which the muscle is attached. The muscle length is controlled by the application of known weights to the system. The device has a frequency of response of 17.5 Hz and compliance of -0.1 mm N-1 , and its experimental performance was tested in the anesthetized mongrel dog. 相似文献
3.
S.D. Heintze A. Cavalleri G. Zellweger A. Büchler G. Zappini 《Dental materials》2008,24(10):1352-1361
OBJECTIVE: The purpose of this laboratory study was to compare the frequency of failures (complete fractures or partial cracks) of molar crowns made of two different all-ceramic materials during dynamic loading in a chewing simulator, as well as the fracture load when subjected to static loading, in relation to different dynamic loading and luting protocols. METHODS: One hundred and forty-four molar crowns fabricated with IPS Empress or an experimental e.max Press material with high translucency (e.max Press Exp) were luted on CAD/CAM milled PMMA abutments (first lower molar, circular chamfer) either with Variolink or glass-ionomer cement (GIC). All crowns were loaded according to three different loading protocols (n=12 per group) and two force profiles (sinusoidal, rectangular) in a pneumatically driven chewing simulator with a steel stylus (? 8mm) and they underwent simultaneous thermocycling (5 degrees C/55 degrees C). After each phase the crowns were evaluated with regard to fractures or cracks. After dynamic testing, the crowns that did not fail were subjected to compression loading until complete fracture in a universal testing machine (UTM). As control groups, unloaded crowns were also subjected to a UTM. Survival statistics with log-rank tests were applied for the results of the dynamic loading, while ANOVA with post hoc Tukey B was used for the fracture load results and two-way ANOVA was carried out for logarithmically transformed data. Weibull statistics were calculated for pooled fracture load data of the dynamically loaded and control groups. RESULTS: In the 144 IPS Empress crowns, complete fractures were observed in 9 crowns and partial cracks in another 3 crowns. When the data was pooled, a statistically significant increase in fractures occurred when the sinusoidal force profile was applied compared to a rectangular force profile (log-rank, p<0.05). No fractures occurred in the e.max Press Exp crowns. The two-way ANOVA showed that the type of luting protocol used had the most significant effect on the fracture load of both materials. In conjunction with Empress, however, the luting material influenced the variability twice as much as in e.max Press Exp. There was no statistically significant difference in the fracture load of GIC-luted e.max Press Exp crowns and that of the Variolink luted Empress crowns. The force profile had a significant effect on the fracture load only of the Empress crowns but not of the e.max Press Exp crowns. Weibull statistics revealed a higher scattering of the data of dynamically loaded crowns compared to that of the control groups. CONCLUSIONS: For testing all-ceramic materials, dynamic loading is indispensable to draw valid conclusions on clinical performance of all-ceramic molar crowns. A sinusoidal profile is advisable, while a gradual increase of the force amplitude does not significantly affect the results. 相似文献
4.
5.
Single fibres of three different types, which had been characterized histochemically with regard to differences in myofibrillar adenosine triphosphatase (ATPase) activity and its pH stability, were microdissected from freeze dried preparations of the closer muscle in walking legs of the crab Eriphia spinifrons. Shortening velocities were determined in slack tests and under constant load conditions in maximally Ca2+-activated skinned muscle fibres. Force/pCa relationships were also measured for the different types of fibres. Compared with data on vertebrate muscles, all crab muscle fibres required large length changes to reach zero force and showed low Ca2+ sensitivity for isometric force generation. The length/time relationship obtained from slack tests had a biphasic course. Maximal velocity of filament sliding differed in the three types of fibres investigated. The filament sliding of type IV fibres was about 3 times faster than that of type I fibres. The values obtained for type II fibres ranged in between. These data are positively correlated with myofibrillar ATPase activity determined histochemically. Ca2+ sensitivity of force generation was lowest in the fast type IV fibres. It was high in the slow type I and the faster contracting type II fibres. Ca2+ sensitivity in crab muscle seems not to be correlated with speed of shortening. 相似文献
6.
The forces produced during stretches of passive and activated muscles, and isometric force deficits after stretching of activated
muscles were examined in rat plantor flexor muscle-tendon complexes with reduced collagen cross-links (pyridinoline). Female
Sprague-Dawley rats (n=6, age 87 days) were injected twice daily for 43 days with β-aminopropionitrile (BAPN, 333 mg/kg/day i.p.), an inhibitor
of lysyl oxidase, which is responsible for the production of collagen cross-links. The relative weights of the plantar flexor
muscles were similar for BAPN and saline-injected (control, C) rats (n=6). Pyridinoline was lower in the tendon (22.9%), and in the plantaris (17.1%), and soleus (7.4%) muscles (P<0.05), with no changes observed in collagen content (hydroxyproline), as determined by high-pressure liquid chromatography.
At an ankle position of 90°, groups had similar forces at 5, 10, 20, 40, 60 and 80 Hz before stretching. Forces at 40° with
stretches of the passive muscles (five times from 90° to 40°) were lower for all stretches in BAPN-injected rats (P<0.05). Isometric force deficits resulting from stretches of activated muscles (80 Hz, 20 times from 90° to 40°, rest intervals
3 min) followed similar courses for BAPN-injected and C rats, and were 51.1 (2.4)% (C) and 54.7 (4.6)% (BAPN) before the last
stretch. After 1 h of rest, isometric force deficits were 26% and 29% larger at 10 Hz and 5 Hz, respectively, in BAPN-treated
rats (P<0.05). The reduction in BAPN-injected collagen cross-linking of the skeletal muscle-tendon complex reduced the forces produced
during stretches without muscle stimulation (i.e. passive stretch), and stretching of activated muscles produced larger isometric
force deficits only at low stimulation frequencies.
Electronic Publication 相似文献
7.
H. P. J. Buschman M. Linari G. Elzinga R. C. Woledge 《Pflügers Archiv : European journal of physiology》1997,435(1):145-150
The mechanical and energy characteristics of isolated fast-twitch muscle fibres (type 1) of Xenopus laevis in isometric- and isovelocity contractions were measured at 20°C. The fibres were stimulated at either 60 Hz or 20 Hz to
produce contractions at different levels of activation. The high stimulation frequency gave fused contractions, while at the
low stimulation frequency tension fluctuated. When maximum isometric force had been reached, the fibres were shortened by
10% of the fibre length at different velocities. At 60 Hz stimulation during shortening the rate of heat production increased
above the isometric rate of heat production. At 20 Hz stimulation during shortening, however, the rate of heat production
was not different from the isometric rate of heat production. Mechanical efficiency was the same at the high and low level
of activation. The actomyosin efficiency (i.e. the mechanical efficiency corrected for ”activation heat”) was highest at the
low level of activation. We conclude that in fast-twitch muscle fibres from X. laevis, actomyosin efficiency is highest for partially activated muscle. From a comparison of the present results with those obtained
from a study of slow-twitch muscle fibres presented earlier, it is concluded that fast-twitch muscle fibres are less efficient
than slow-twitch muscle fibres.
Received after revision: 13 May 1997 / Accepted: 1 July 1997 相似文献
8.
Ca2+ is the primary regulator of force generation by cross-bridges in striated muscle activation and relaxation. Relaxation is as necessary as contraction and, while the kinetics of Ca2+-induced force development have been investigated extensively, those of force relaxation have been both studied and understood less well. Knowledge of the molecular mechanisms underlying relaxation kinetics is of special importance for understanding diastolic function and dysfunction of the heart. A number of experimental models, from whole muscle organs and intact muscle fibres down to single myofibrils, have been used to explore the cascade of kinetic events leading to mechanical relaxation. By using isolated myofibrils and fast solution switching techniques we can distinguish the sarcomeric mechanisms of relaxation from those of myoplasmic Ca2+ removal. There is strong evidence that cross-bridge mechanics and kinetics are major determinants of the time course of striated muscle relaxation whilst thin filament inactivation kinetics and cooperative activation of thin filament by cycling, force-generating cross-bridges do not significantly limit the relaxation rate. Results in myofibrils can be explained well by a simple two-state model of the cross-bridge cycle in which the apparent rate of the force generating transition is modulated by fast, Ca2+-dependent equilibration between off- and on-states of actin. Inter-sarcomere dynamics during the final rapid phase of full force relaxation are responsible for deviations from this simple model. 相似文献
9.
R. G. Cutlip Dr. W. T. Stauber R. H. Willison T. A. McIntosh K. H. Means 《Medical & biological engineering & computing》1997,35(5):540-543
A dynamometer is designed and fabricated to measure the force output during static and dynamic muscle actions of the plantar
flexor muscles of anaesthetised rats in vivo. The design is based on a computer-controlled DC servomotor capable of angular
velocities in excess of 17.5 rad s−1. The system controls the range of motion, angular velocity and electrical stimulation of the muscles, while monitoring the
force output at the plantar surface of the foot. The force output is measured by a piezo-electric load cell that is rated
at 5 kg capacity. Angular velocity and position are measured by a DC tachometer and potentiometer, respectively. All measurement
devices are linear (r2=0.9998). The design minimises inertial loading during high-speed angular motions, with a variation in force output of less
than 0.2%. The dynamometer proves to be an accurate and reliable system for quantifying static and dynamic forces of rat plantar
flexor muscles in vivo. 相似文献
10.
Recent advances in the development of transducers for the measurement of vertical and shear forces acting on the plantar surface
of the foot are reviewed. Barefoot and in-shoe discrete and matrix transducers are reviewed in terms of structure, operation,
performance and limitations. Examples of capacitive, piezoelectric, optical, conductive and resistive types of transducer
are presented. Where available, the current clinical status is specified. 相似文献