Closed-Loop Feedback Control of Magnetically-Activated Gels

Mitwalli, A.H.; Denison, Timothy A.; Jackson, D.K.; Leeb, Steven B.; Tanaka, Toyoichi

doi:10.1177/1045389x9700800704

Cited by 12 publications

(6 citation statements)

References 10 publications

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“…The stated objective of this research is the development of a muscle-and tendon-like actuator. While some investigators have proposed the use of commercially available actuators (e.g., Yoda and Shiota 1994;Cocatre-Zilgien, Delcomyn and Hart 1996;Wu, Hwang and Chang 1997), others have suggested novel actuators such as shape-memory alloys (Mills 1993), electro-reactive gels (Mitwalli et al 1997), ionic polymer-metal composites (Mojarrad and Shahinpoor 1997), and stepper motors with ball screw drives connected to elastic Strain − percent Stress − MPa Bobbert & Ingen Schenau 1990Zajac 1989Voigt et al 1995EST Model Bobbert et al 1986Hof 1998 Fig. 4.…”

Section: Artificial Muscle and Tendonmentioning

confidence: 99%

Artificial Muscles: Actuators for Biorobotic Systems

Klute

Czerniecki

Hannaford

2002

The International Journal of Robotics Research

177

102

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Biorobotic research seeks to develop new robotic technologies modeled after the performance of human and animal neuromuscular systems. The development of one component of a biorobotic system, an artificial muscle and tendon, is reported here. The device is based on known static and dynamic properties of biological muscle and tendon that were extracted from the literature and used to mathematically describe their force, length, and velocity relationships. A flexible pneumatic actuator is proposed as the contractile element of the artificial muscle and experimental results are presented that show the force-length properties of the actuator are muscle-like, but the force-velocity properties are not. The addition of a hydraulic damper is put forward to improve the actuator's velocity-dependent properties. Further, an artificial tendon is set forth whose function is to serve as connective tissue between the artificial muscle and a skeletal structure. A complete model of the artificial muscle-tendon system is then presented which predicts the expected force-lengthvelocity performance of the artificial system. Experimental results of the constructed device indicate muscle-like performance in general: higher activation pressures yielded higher output forces, faster concentric contractions resulted in lower force outputs, faster eccentric contractions produced higher force outputs, and output forces were higher at longer muscle lengths than shorter lengths.

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Section: Artificial Muscle and Tendonmentioning

confidence: 99%

Artificial Muscles: Actuators for Biorobotic Systems

Klute

Czerniecki

Hannaford

2002

The International Journal of Robotics Research

177

102

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“…By inductive heating in an alternating magnetic field, the shapememory effect of the composites can be triggered. Prior studies reported inductive heating of smart hydrogels (19), ferrogels (20,21), and ferrofluids (22,23) in alternating magnetic fields by using embedded magnetic particles (21)(22)(23)(24)(25)(26)(27). The mechanisms of heat generation are hysteresis loss and͞or related processes that are direct result of superparamagnetism (23).…”

mentioning

confidence: 99%

Initiation of shape-memory effect by inductive heating of magnetic nanoparticles in thermoplastic polymers

Mohr

Kratz

Weigel

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

756

586

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In shape-memory polymers, changes in shape are mostly induced by heating, and exceeding a specific switching temperature, T switch. If polymers cannot be warmed up by heat transfer using a hot liquid or gaseous medium, noncontact triggering will be required. In this article, the magnetically induced shape-memory effect of composites from magnetic nanoparticles and thermoplastic shapememory polymers is introduced. A polyetherurethane (TFX) and a biodegradable multiblock copolymer (PDC) with poly(p-dioxanone) as hard segment and poly( -caprolactone) as soft segment were investigated as matrix component. Nanoparticles consisting of an iron(III)oxide core in a silica matrix could be processed into both polymers. A homogeneous particle distribution in TFX could be shown. Compounds have suitable elastic and thermal properties for the shape-memory functionalization. Temporary shapes of TFX compounds were obtained by elongating at increased temperature and subsequent cooling under constant stress. Cold-drawing of PDC compounds at 25°C resulted in temporary fixation of the mechanical deformation by 50 -60%. The shape-memory effect of both composite systems could be induced by inductive heating in an alternating magnetic field (f ‫؍‬ 258 kHz; H ‫؍‬ 30 kA⅐m ؊1 ). The maximum temperatures achievable by inductive heating in a specific magnetic field depend on sample geometry and nanoparticle content. Shape recovery rates of composites resulting from magnetic triggering are comparable to those obtained by increasing the environmental temperature.nanocomposite ͉ shape-memory polymer ͉ stimuli-sensitive polymer S hape-memory polymers are able to recover their predefined original shape when exposed to an external stimulus. A prerequisite for the shape-memory effect is a preceding functionalization of the material to temporarily fix a mechanical deformation. Most shape-memory polymers are thermosensitive materials. The shape is actuated by exceeding a specific switching temperature, T switch (1). Thermoplastic shape-memory polymers have at least two separated phases, where the domains with the highest thermal transition (T perm ) stabilize the permanent shape by acting as physical netpoints. A second phase having another thermal transition T trans serves as switch. At temperatures above T trans the chain segments forming this phase are flexible and the material is highly elastic, whereas the flexibility of the chains below T trans is limited and enables the fixation of the temporary shape. T trans can either be a glass transition (T g ) or a melting temperature (T m ). Whereas T trans is the thermal transition of the switching segment phase, typically determined by differential scanning calorimetry (DSC), T switch is result of a thermomechanical test used to quantify the shape-memory effect.An important class of thermoplastic shape-memory polymers are polyurethanes. They often contain a hard segment from methylene bis(4-phenylisocyanate) (MDI) and 1,4-butanediol. Depending on the switching segment, T trans can be either a melting...

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“…Triggers other than solvent composition, such as temperature, light (14), and magnetic field (15), can, in principle, be used by properly designing the gel composition.…”

Section: Discussionmentioning

confidence: 99%

Gel catalysts that switch on and off

Wang

Kuroda

Enoki

et al. 2000

Proc. Natl. Acad. Sci. U.S.A.

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We report development of a polymer gel with a catalytic activity that can be switched on and off when the solvent composition is changed. The gel consists of two species of monomers. The major component, N-isopropylacrylamide, makes the gel swell and shrink in response to a change in composition of ethanol͞water mixtures. The minor component, vinylimidazole, which is capable of catalysis, is copolymerized into the gel network. The reaction rate for catalytic hydrolysis of p-nitrophenyl caprylate was small when the gel was swollen. In contrast, when the gel was shrunken, the reaction rate increased 5 times. The activity changes discontinuously as a function of solvent composition, thus the catalysis can be switched on and off by an infinitesimal change in solvent composition. The kinetics of catalysis by the gel in the shrunken state is well described by the Michaelis-Menten formula, indicating that the absorption of the substrate by the hydrophobic environment created by the N-isopropylacrylamide polymer in the shrunken gel is responsible for enhancement of catalytic activity. In the swollen state, the rate vs. active site concentration is linear, indicating that the substrate absorption is not a primary factor determining the kinetics. Catalytic activity of the gel is studied for substrates with various alkyl chain lengths; of those studied the switching effect is most pronounced for p-nitrophenyl caprylate.N atural enzymes catalyze chemical reactions, and equally importantly, regulate them by reversibly and repeatedly switching on and off the catalytic activities. To mimic this special feature of enzymes, we designed a polymer gel consisting of two species of monomers, each having a specific role. The major component allows the gel to reversibly swell and shrink in response to changes in environmental parameters such as temperature and solvent (1-9). On swelling and shrinking, the local density of the hydrophobic moiety changes and the affinity to substrate molecules is altered accordingly. The minor component capable of catalysis of substrate decomposition is copolymerized with the responsive monomers into the gel network. The catalytic activity of the gel is expected to be switched on and off as the substrate is reversibly bound and released during the cycle of gel swelling and shrinking. Materials and MethodsTo demonstrate the feasibility of the idea, we chose hydrolysis of p-nitrophenyl esters with different alkyl chain lengths as the chemical reaction to examine (Fig. 1a). This reaction is known to be catalyzed by 4(5)-vinylimidazole (10). We, therefore, used it as the minor catalytic monomer component of the gel (Fig. 1b). As the major component, we chose the widely used hydrophobic monomer N-isopropylacrylamide (NIPA). The substrate and gel monomer components were selected because (i) the substrate and one of the hydrolysis products, p-nitrophenol, were easily detected by using UV spectroscopy; (ii) the NIPA gel underwent a discontinuous swelling͞shrinking transition in response to changes in environmen...

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Closed-Loop Feedback Control of Magnetically-Activated Gels

Cited by 12 publications

References 10 publications

Artificial Muscles: Actuators for Biorobotic Systems

Artificial Muscles: Actuators for Biorobotic Systems

Initiation of shape-memory effect by inductive heating of magnetic nanoparticles in thermoplastic polymers

Gel catalysts that switch on and off

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