Intelligent Gels An Approach to Artificial Muscles

Transcription

1 Intelligent Gels An Approach to Artificial Muscles Yoshihito Osada, Gong Jiang Ping Division of Biological Sciences, Graduate School of Hokkaido University There are two basic differences between the motion in a man-made machine and in a biological motor. One is in their principles. The motion of a man-made machine, which is constructed from hard and dry materials such as metals, ceramics, or plastic, is realized by the relative displacement of the macroscopic constituent parts of the machine. In contrast to this, the motion of a living organism, which consists of soft and wet materials (protein and tissues), is caused by a molecular deformation that is integrated to a macroscopic level through its hierarchical structure. The other difference is in their energy sources. The man-made machine is fueled by electrical or thermal energy with an efficiency of around 30%, but a biological motor is driven by direct conversion from chemical energy with an efficiency as high as 80-90%. We have been employing polymer gels to create biomimetic motility systems, focusing to their reversible size and shape change, thereby realizing motion by integrating the deformation on a molecular level. Over the past number of years, we have proposed several kinds of artificial soft machines constructed by synthetic polymer gels. Examples include Gelooper(gel-looper),gelf(gel golf), shape memory gel actuators, chemical motors, etc. Gelooper,Gelf[1-2]: Since the polyelectrolyte gel has deep electrostatic potential valleys and wells along the polymer chains and at the crosslinked points[3], it attracts the oppositely charged surfactants and form complexes[4-5]. The complexation brings about macroscopic contraction of the gel. Using this phenomenon an electrically driven artificial [worm-like muscle] and a swinging pendulum made of water-swollen synthetic polymer gel have been constructed[6]. The principle of this eel-like swinging of the gel is associated with a reversible and cooperative complexation of the surfactant molecules on the surface of the polymer gel under the electric field. Shape memory gel: The water-swollen polymer hydrogels with molecularly ordered structure were obtained by copolymerizing hydrophilic monomers such as acrylic acid(aa) with hydrophobic monomers that form crystals, for example, steayl acrylate(sa), acryloylhexadecanoic acid(aha)[7-8]. These poly(sa-co-aa) gels exhibit shape mempry behaviors with a change in temperature[9]. The principleof this phenomenon is based on a reversible order-disorder transition associated with the hydrophobic interactions between stearyl groups in water. Below the transition temperature(50 ), stearyl side chains from crystalline aggregates and behave as a hard plastic, while above this temperature they transform to amorphous and the material abruptly becomes soft and flexible and is readily modified to a desired new shape. If the gel is cooled keeping its deformed shape, it becomes rigid and retains its new shape even after removing the load. When the modified gel is once again heated above the transition temperature, it is able to recover the original shape after a few seconds[10]. Chemical motor: Crosslinked amphiphilic copolymer gels such as poly(sa-co-aa) swelled in organic solvent undergo spontaneous motion when put on water surface[11-12]. The mode of motion largely depends on the shape and size of the gel. For example, the ethanol or THF-swollen square-shaped gel, 10 mm in size, rotates with a maximum velocity of 400 rpm for which decreases with time after an hour. Gel particles in several hundreds µm diameter rotate more than 3,000r.p.m. If the gel is placed on water, it rapidly forms a partially organized structure from its outer surface and gradually shrinks, simultaneously producing high osmotic pressure and hydrostatic pressure. By virtue of these two pressures, the organic solvent is pumped out of the gel for a prolong time. Thus, the driving force of the gel motion is originated from the surface spreading of the organic solvent[13-14]. The prolonged gel motion obtained by the surface spreading of the organic solvent has several advantages and unique characteristics. They produce no noise and no unnecessary exhaust products like combustion or

2 Akira Kakugo, Shin Sugimoto, Nozomi Takekawa, Jian Ping Gong, Yoshihito Osada Graduate School of Science, Hokkaido University Sapporo, Japan

3 9 13 NASA 3

4 Soft Machine Made of Gels Convert 0s deformation at molecular level 2s into macroscopic motion 4s 6s 8s 10s Shortage Electric energy Low efficiency Not biocompactable (NASA homepage ) NASA JPL DARPA Sandia Lab Osada et al. Nature, 1992

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6 Biological motor myofibril actin filament myosin filament Chemical energy (ATP) Hydrolysis(ATPase) Mechanical energy ATP Self-assembly Microscopic deformation Hierarchical structure Macroscopic contraction Actin Myosin Is muscle contraction cooperative at meso-scopic level?

7 G-actin Self-organization F-actin Chemical crosslinking Soft machine built from muscle proteins by self-organization and chemical crosslinking Myosin molecule Chemical crosslinking Self-organization Myosin fiber

8 How to obtain myosin gel with oriented filament array? Cross-linker Myosin fiber Myosin filament Myosin Self-assembly 10cm 50 5 SEM image AFM image 50 µm 1.54 m 15nm

9 Can actin filaments move on myosin gels? 0.8 Actin filament, Actin gel Myosin gel Ave.velocity (µm/s) Spacer Control EDC TG 0 GA 0sec. 3sec. 6sec. 10 m Actin filament shows a mobility on TG-myosin gel as high as on control.

10 Relationship between V max and ATPase activity. 0.9 Control V max (µm/sec.) EDC TG 0.6 GA V max = 2.69 Activity + C Mg-ATPase activity (µmol pi/mg/min) The velocity of actin filaments is proportional to the ATPase activity of myosin gels.

11 Giant actin by polyion complex formation G-actin Tropomyosin G-Actin F-actin Polyionene CH 3 CH 3 Polycation [(CH 2 ) 6 N + (CH 2 ) 6 N + ] n Fiber Crosslinking CH 3 Poly-L-Lysine CH 3 Giant actin [CO CH NH] n (CH 2 ) 4 NH + 3

12 Effect of cationic polymer Average Length (µ m) 25 ionene x, y=6, poly-lys 6, ,10 3, Time (min) Poly (L-lysine) NH CH CO x, y-ionene bromide CH 3 Br - CH 3 Br - CH 2 N + CH 2 N + x y n CH 3 CH 2 NH CH 3 n

13 What is a giant actin gel? G-actin F-actin Polycation Actin gel Cross-linking Native Poly (L-lysine) 25µ 25 [ CO CH NH ] n (CH 2 ) 4 NH µ 10µ x, y-ionene bromide CH Br - 3 CH Br - 3 [(CH 2 ) x N + (CH 2 ) y N + ] n CH 3 CH 3

14 µ Giant actin grows with time

15 Morphology of x, y-ionene-actin complex Native F-actin P-Lys 3,3 600nm 6,4 6,6 6,10

16 Do myosin gels still maintain the ATPase activity? Native myosin Native actin Mg-ATPase activity (µmol pi/mg/min) TG Myosin-gel EDC Myosin-gel GA Myosin-gel Native Actin TG Myosin-gel EDC Myosin-gel GA Myosin-gel Giant Actin Fiber Relative activity (%) Cross-linkers Glutaraldehyde : GA 1-ethyl-3-(dimethylaminopropyl)carbodiimide : EDC Transglutaminase : TG

17 400nm Native actin Actin gel 400nm Nature science update : Artificial muscle made from natural building blocks. 16. Aug

18 Can the Actin Gel Move? Actin filament, Actin gel Myosin Spacer Events V=0.82µm/s t = 0.4s Velocity (µm/s) Myosin gel Events V=7.06µm/s t=0.33s 200 Native myosin Velocity (µm/s)

19 Time resolution of acitn gel motion L t =1.0 (Translational motion 10 Slope=0.9 =0.5 (Random motion Displacement (µm) 1 Actin gel 0.6 F-actin L Time (sec.) Actin gel shows a less random motion with a higher velocity

20 HMM Actin Actin Heavy Mero Myosin (HMM) Myosin Arrowhead-structure 200nm

21 コンプレクス形成における自己集合 HMM Actin 運動発現 運動不可能 Illustration from <Stryer Biolochemistry> 認識能を持つ自己集合 創発 のための必要条件か

22 Conclusion Myosin gel with highly oriented filament array could be obtained. Giant actin gel could be obtained by forming complex with cationic polymer. Giant actin gel showed a increased motility along the axis of oriented myosin gel

23 Why does the actin gel move straight forward? Why does actin gel move fast? Synchronize Why do actin gel fibers synchronize? Emergency

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26 other chemical reactions. The motion is only obtained by the dilution of the organic fluid, which can be recovered by using separation technologies such as distillation or membranes. Protein Gel Nanomachine[15] Here we report an adenosine triphosphate(atp) fueled new-type gel machine reconstructed from the muscle proteins: actin and myosin. Chemically cross-linked actin gel filaments, several tens of times the length of native actin filaments(f-actin) move along a chemically cross-linked myosin fibrous gel(1cm long and 50mm in width) exceeding the velocity of native F-actin, by coupling to ATP hydrolysis. F-actins showed a preferential motion along the axis of oriented myosin gel fibers as elucidated by the degree of anisotropy(d.a.), which is defined as the ratio of the square-root average velocity in the fiber direction to that perpendicular to the fiber direction. The D.A. measured on the non-oriented myosin gel was 1.1(average over 66 samples), and that on the oriented myosin gel was 1.7(average over 91 samples). The mean velocity on the non-oriented myosin gel was 0.69 µms -1 with a standard deviation of 0.24µms -1, while that on the oriented myosin gel was 0.83µms -1 with a standard deviation of 0.30µms -1. Thus,F-actins prefer to move along the axis of the oriented myosin gel with enhanced velocity. The chemically cross-linked actin gel also showed a high motility on the oriented myosin gel in spite of its large dimension. Thus, despite of its increased mass (several tens to hundreds of time the volume of the native F-actin) and decreased effective surface for ATP hydrolysis, the actin gels move on the covalently cross-linked myosin gel, with an increased velocity. This means that the self-assembled and covalently bound actins and myosins can behave cooperatively, and exert a high motility coupling to ATP hydrolysis. This is rather surprising since the interaction between the myosin gel and the actin gel can occur only at the two-dimentional interface and due to cross-linking a considerable number of actin and myosin molecules are not involved in the sliding motion Although efficiency of the movement and the force generated during the sliding motion are not measured here, the described muscle protein-gels suggest that one might construct man-made machines fueled by chemical energy by using actin and myosin molecules as elementary elements. This kind of protein gel machine of the desired shape, size, and function might run in a human body without causing any immunoreactions if it is reconstructed with protein molecules from the same body. References [1] Y. Osada, H. Okuzaki, H. Hori, Nature 1992, 355, 242. [2] Y. Osada, S.B. Ross-Murphy, Sci, Am. 1993, 268, 82. [3] Gong J.P., Osada Y. Chem.Lett.,1995, p 449. [4] Okuzaki H., Osada Y., Macromolecules, 1994, 27, p502; 1995, 28, p380; 1995, 28, p [5] Khokhlov A.R., Kramarenko E.Y., Makhaeva E.E., Starodubtzev S.G., Macromol, Chem., Theory Simul., 1992,1,p.105. [6] Okuzaki H., Osada Y., J.Intelligent Materials Systems and Structure, 1993, 4, p.50. [7] Uchida M., Kurozawa M., Osada Y., Macromolecles,1995,28,p [8] Matsuda A., Sato J., Yasunaga H., Osada Y., Macromolecules, 1994, 27, p [9] Y. Osada, A.Matsuda, Nature 1995, 376, 219. [10] Kagami Y., Gong J.P., Osada Y., Macromol.Rapid Commun.,1996,17,p [11] Osada Y., Gong J.P., Uchida M., Isogai N., Jpn.J.Appl.Phys., 1995,34,p L511. [12] Gong J.P., Matsumoto S., Uchida M., Isogai N., Osada Y., J.Phys. Chem., 1996,100, p [13] Mitsumata T., Ikeda K., Gong J.P., Osada Y., Appl.Phys.Lett.,1998, 73, p [14] Mitsumata T., Ikeda K., Gong J.P., Osada Y., Langmuir, 2000, 16, p.307. [15] Kakugo A., Sugimoto S., Gong J.P., Osada Y., Gel Machines Constructed from Chemically Cross-linked Actins and Myosins., Advansed Materials, 2002,14,