WO2012105857A1

WO2012105857A1 - Gel actuator

Info

Publication number: WO2012105857A1
Application number: PCT/NZ2012/000010
Authority: WO
Inventors: Stephen Carl Moratti; Lyall Robert Hanton; Shailesh GOSWAMI; Christopher John MCADAM
Original assignee: University Of Otago
Priority date: 2011-02-04
Filing date: 2012-02-03
Publication date: 2012-08-09

Abstract

The invention relates to a polymeric gel actuator. The polymeric gel actuator comprises a polymeric gel in contact with solvent. The polymer contains redox components. Reduction or oxidation of the redox components change the affinity of the polymer for the solvent, changing the volume of the polymeric gel. The volume change of the polymeric gel can be used to perform work, such as moving objects or levers.

Description

GEL ACTUATOR

1. FIELD OF THE INVENTION

The present invention relates to a polymeric gel and its use in an actuator. The invention also relates to an actuator that utilizes the changes in volume of the gel upon oxidation or reduction of the polymer, to perform work.

2. BACKGROUND OF THE INVENTION

Electroactive polymeric gels change size or shape when stimulated by an electric current. The expansion and contraction of the polymeric gel can be converted into mechanical actuation. Therefore, such materials have application as actuators and sensors.

Application of a current through a polymeric gel may cause expansion or contraction by a variety of mechanisms, depending on the type of polymer and the nature of the solvent in which the polymer is dispersed. In some cases polymeric gel actuators employ ionisable polymeric gels that expand and contract when subjected to changes in pH, temperature or solvent. Where a redox polymer is used, electrochemical changes in the polymer cause uptake or expulsion of solvent from the gel, causing it to expand or contract.

However, these materials generally demonstrate small degrees of gel displacement and hence, low actuation forces. Generally, polymeric gel actuators are based on thin film devices that work in bending mode. Although bending modes are not always useful, the ionic diffusion necessary to facilitate the electrochemical changes is slow and limits the application of thick gels that would be capable of linear actuation. In addition, polymeric gels are normally non-electrically conducting, so it is difficult to place a charge across a thick sample.

Consequently, there is a need for polymeric gel actuators capable of relatively fast and large volume changes. Therefore, it is an object of the invention to go at least part-way in meeting this need, or to provide the public with a useful choice.

3. SUMMARY OF THE INVENTION

In a first aspect the invention provides a polymeric gel actuator comprising

(a) a polymeric gel in contact with a solvent, wherein the polymer comprises redox components and is mixed with a conductive filler, and wherein reduction or oxidation of the redox components changes the affinity of the polymer to the solvent, thereby changing the volume of the polymeric gel, and

(b) a current applicator for applying current to the gel for reducing or oxidizing the redox components of the polymer, wherein the actuator is configured such that the volume change of the polymeric gel causes movement of another object.

Optionally, the polymeric gel also comprises one or more biasing mechanisms embedded in the gel. In a second aspect the invention provides a polymeric gel actuator comprising

(a) a polymeric gel in contact with a solvent, wherein the polymer comprises redox components and is mixed with a conductive filler, and wherein reduction or oxidation of the redox components changes the affinity of the polymer for the solvent, thereby changing the volume of the polymeric gel,

(b) a container arrangement maintaining contact between the polymeric gel and the solvent, and

(c) a current applicator for applying current to the gel for reducing or oxidizing the redox components of the polymer, wherein the actuator is configured such that the volume change of the polymeric gel causes movement of another object.

Optionally, the polymeric gel actuator also comprises one or more biasing mechanisms, embedded in the gel.

In a third aspect the invention provides a polymeric gel actuator comprising (a) a polymeric gel in contact with a solvent, wherein the polymer comprises redox components and is optionally mixed with a conductive filler, and wherein reduction or oxidation of the redox components changes the affinity of the polymer to the solvent, thereby changing the volume of the polymeric gel, and (c) a current applicator for applying current to the gel for reducing or oxidizing the redox components of the polymer, wherein the actuator is configured such that the volume change of the polymeric gel causes movement of another object, and wherein one or more biasing mechanisms are embedded in the polymeric gel. In a fouth aspect the invention provides a polymeric gel actuator comprising

(a) a polymeric gel in contact with a solvent, wherein the polymer comprises redox components and is optionally mixed with a conductive filler, and wherein reduction or oxidation of the redox components changes the affinity of the polymer for the solvent, thereby changing the volume of the polymeric gel, (b) a container arrangement maintaining contact between the polymeric gel and the solvent, and

(c) a current applicator for applying current to the gel for reducing or oxidizing the redox components of the polymer, wherein the actuator is configured such that the volume change of the polymeric gel causes movement of another object and wherein one or more biasing mechanisms are embedded in the polymeric gel.

In a fifth aspect the invention provides a polymeric gel in contact with a solvent, wherein the polymer comprises redox components and is optionally mixed with a conductive filler, and wherein reduction or oxidation of the redox components changes the affinity of the polymer for the solvent, thereby changing the volume of the polymeric gel.

In a sixth aspect, the invention provides a use of a polymeric gel in contact with a solvent, as an actuator wherein the polymer comprises redox components and is optionally mixed with a conductive filler, and wherein reduction or oxidation of the redox components changes the affinity of the polymer for the solvent, thereby changing the volume of the polymeric gel.

Optionally, the polymeric gel also comprises one or more biasing mechanisms embedded in the polymeric gel. In a seventh aspect the invention provides a polymeric gel in which one or more biasing mechanisms is embedded, wherein the polymer, which is in contact with a solvent, comprises redox components and is optionally mixed with a conductive filler, and wherein reduction or oxidation of the redox components changes the affinity of the polymer for the solvent, thereby changing the volume of the polymeric gel. In an eighth aspect, the invention provides a use of a polymeric gel in which one or more biasing mechanisms is embedded, as an actuator, wherein the polymer is in contact with a solvent, and wherein the polymer comprises redox components and is optionally mixed with a conductive filler, and wherein reduction or oxidation of the redox components changes the affinity of the polymer for the solvent, thereby changing the volume of the polymeric gel.

In a ninth aspect the invention provides a method of preparing a polymeric gel of the invention, the method comprising

(a) dispersing a quantity of conductive filler in a monomer solution,

(b) immersing a metal spring in the monomer dispersion formed in step (a), and

(c) polymerizing the monomer dispersion of step (b) for a time and under conditions sufficient to form a polymeric gel.

The following embodiments may relate to any of the above aspects:

In one embodiment the polymer is derived from one or more monomers selected from the group comprising styrenes, acrylates, methacrylates, vinyl ethers, acrylamides, and methacrylamides.

In one embodiment the redox component is selected from the group comprising hydroquinones, napthoquinones, quinones, ferrocenes, phenazines, triarylamine derivatives, thionines, flavines, alkylviologens, N-oxides including 2,2,6,6- tetramethylpiperidin-l-oxyl (TEMPO), tetrathiafulvalenes, phenazines, phenothiazines and metal complexes, for example, ruthenium bipyridines and terpyridines. In another embodiment the redox component is a quinone, ferrocene or TEMPO group.

In one embodiment the polymer is derived from acrylate monomers comprising quinone, ferrocene or TEMPO redox components. In one embodiment the polymer comprises poly (hydroxyethyl acrylate). Preferably, the polymer is cross-linked with poly (oligoethylene glycol) diacrylate. In one embodiment, the polymer comprises poly(trimethylquinone-2-hydroxyethyl methacrylate-co-hydroxyethyl acrylate-co- (oligo ethylene glycol) diacrylate). In another embodiment the polymer comprises poly (2,2,5, 5-tetramethylpiperinyloxy-4- acrylamide (TEMPO). Preferably, the polymer is cross-linked with methylene diacrylamide, acrylamide or a mixture of both. In one embodiment the polymer is poly 4-(5-amino-2-ethyl-4-methyl-5-oxopentanamido)-2,2,6,6-tetramethylpiperidin-l-olate.

In one embodiment the solvent is selected from the group comprising water, alcohols, acetonitrile, acetone, DMSO, DMF, glycols and derivatives, and ionic liquids and mixtures thereof, for example, lithium nitrate and NaBF₄. In one embodiment the solvent is a DMF/water mixture containing lithium acetate as electrolyte. In another embodiment, the solvent is lithium nitrate. In another embodiment the solvent isNaBF₄.

In another embodiment, the solvent is a bodily fluid, for example, blood, urine or saliva. In one embodiment, the conductive filler is selected from the group comprising conductive nanotubes, metal nanowires, and fibres of conducting polymers such as polyaniline, polythiophene or polypyrrole. In one embodiment the conductive filler is conductive nanotubes, preferably carbon nanotubes, more preferably, MWCNTs.

In one embodiment, the conductive filler has an aspect ratio of greater than about 2, 10, 25, 50, 75, 100, 125, 150, 175 or 200 and useful ranges may be selected between any of these values (for example, from about 2 to about 200, about 10 to about 200, about 25 to about 200, about 50 to about 200, about 75 to about 200, about 100 to about 200, about 125 to about 200, about 150 to about 200, about 175 to about 200, about 10 to about 150, about 20 to about 150, about 25 to about 150, about 50 to about 150, about 75 to about 150, about 100 to about 150, about 125 to about 150).

In one embodiment the polymeric gel comprises about 0.1, 0.2, 0.5, 0.75, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0 or 10wt% of conductive filler, and useful ranges may be selected between any of these values (for example, about 0.1 to about 10wt%, 0.1 to about 9.0wt%, 0.1 to about 8.0wt%, 0.1 to about 7.0wt%, 0.1 to about 6.0wt%, 0.1 to about 5.0wt%, 0.1 to about 4.0wt%, 0.1 to about 3.0wt%, 0.1 to about 2.0wt%, 0.1 to about 0.75wt%, 0.1 to about 0.5wt%, or 0.1 to about 0.2wt%). In one embodiment the polymeric gel comprises 0.2 to 2wt% conductive filler, preferably 0.5 to 1.5wt%, more preferably 1%.

In one embodiment, the volume of the gel in its contracted state is at least about 0.001, 0.005, 0.01, 0.025, 0.05, 0.075, 0.1, 0.25, 0.5, 0.75, 1.0, 1.5, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0 or 10cm³ and useful ranges may be selected between any of these values (for example, about 0.001 to about 10cm³, 0.005 to about 10cm³, 0.01 to about 10cm³, 0.025 to about 10cm³, 0.05 to about 10cm³, 0.075 to about 10cm³, 0.1 to about 10cm³, 0.25 to about 10cm³, 0.5 to about 10cm³, 0.75 to about 10cm³, 1.0 to about 10cm³, 1.5 to about 10cm³, 2.0 to about 10cm³, 3.0 to about 10cm³, 4.0 to about 10cm³, 5.0 to about 10cm³, 6.0 to about 10cm³, 7.0 to about 10cm³, 8.0 to about 10cm³, 9.0 to about 10cm³).

In one embodiment, upon oxidation or reduction the volume of the gel changes by at least about 1, 5, 10, 25, 50, 75, 100, 150, 200, 250, 300, 350, 400, 450 or 500%, and useful ranges may be selected between any of these values (for example, about 25% to about 500%, about 50% to about 500%, about 75% to about 500%, about 100% to about 500%, about 150% to about 500%, about 200% to about 500%, about 250% to about 500%, about 300% to about 500%, about 350% to about 500%, about 400% to about 500%, about 450% to about 500%, about 25% to about 200%, about 50% to about

200%, about 100% to about 200% or about 150% to about 200%). In one embodiment, the volume of the gel changes at least about 20 to 200%, preferably at least about 40 to 100%.

In one embodiment, the volume of the gel increases upon application of the current. In another embodiment the volume of the gel decreases upon application of the current. In one embodiment, upon oxidation or reduction, the polymeric gel expands or contracts substantially in one direction only.

In one embodiment, the current applicator comprises a first electrode and a counter electrode, both coupled to the polymeric gel so that an electrical current can pass through the polymeric gel.

In one embodiment, the first electrode is a platinum wire. In another embodiment the counter electrode is selected from an inert conductive material, and a second polymeric redox gel.

In one embodiment, the object moved by the volume change of the polymeric gel is selected from the group comprising a plunger, a piston, a plate and a shaft.

In one embodiment the polymeric gel is in direct contact with the other object. In another embodiment, the polymeric gel is in indirect contact with the other object, via a further object. In one embodiment, the further object is selected from the group comprising a plunger, a piston, a plate and a shaft. In one embodiment, the polymeric gel incorporates one or more biasing mechanisms. The biasing mechanism is embedded in the gel. In one embodiment, the biasing mechanism can act as an electrode. In a preferred embodiment, the biasing mechanism is the first electrode.

In one embodiment, the biasing mechanism is a platinum spring. The biasing mechanism, such as a spring, helps the polymeric gel to expand linearly. The presence of the spring hinders expansion in the direction sideways to the spring.

In one embodiment, the polymeric gel actuator is a linear actuator.

It is intended that reference to a range of numbers disclosed herein (for example, 1 to 10) also incorporates reference to all rational numbers within that range (for example, 1, 1.1, 2, 3, 3.9, 4, 5, 6, 6.5, 7, 8, 9 and 10) and also any range of rational numbers within that range (for example, 2 to 8, 1.5 to 5.5 and 3.1 to 4.7) and, therefore, all sub-ranges of all ranges expressly disclosed herein are hereby expressly disclosed. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner.

In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents is not to be construed as an admission that such documents, or such sources of information, in any jurisdiction, are prior art, or form part of the common general knowledge in the art. This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

4. BRIEF DESCRIPTION OF THE DRAWINGS

Further aspects of the present invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawings in which: Figure 1 is a picture of a polymeric gel actuator of the invention configured to demonstrate the lifting capability of a polymeric gel of the invention (in black in the syringe). The actuator was prepared in accordance with Example 8.

Figure 2 is a picture of the polymeric gel actuator shown in Figure 1, focusing on the polymer gel (black) in its contracted state, before the application of current. Figure 3 is a picture of the polymeric gel actuator shown in Figure 1 , with the polymeric gel in its expanded state (black). Figure 4 is a picture of the polymeric gel actuator system described in Example 9. The working electrode is on the left (quinone form of the gel) and the counter electrode on the right (hydroquinone form).

Figure 5 is a picture of the polymeric gel actuator system of Example 9 after the electrochemical reduction/oxidation. The working electrode has expanded, while the counter electrode has contracted.

Figure 6 is a graph showing the change in length of poly(trimefhylquinone-2- hydroxyethyl methacrylate-co-hydroxyethyl acrylate-co-(oligoethylene glycol) diacrylate) gel with 1% nano tubes as working electrode during 20 redox cycles, according to Example 9.

Figure 7 is a series of pictures of the polymeric gel actuator according to Example l ie. Figure 7 shows the TEMPO gel containing a spring biasing mechanism before electrooxidation (Figure 7a), after electrooxidation (Figure 7b) and after

electroreduction (Figure C). Figure 8 is a series of pictures showing the polymeric gel actuator described in Example 12c. Figure 8a shows the gel before electrochemical reduction. After electrochemical reduction, the gel has extended (Figure 8b). When the polarity is reversed, the gel returns to its original length, as shown in Figure 8c.

5. DETAILED DESCRIPTION OF THE INVENTION The foregoing description of the invention includes preferred forms thereof.

Modifications may be made thereto without departing from the scope of the invention.

5.1 Definitions

The term "comprising" as used in this specification and claims means "consisting at least in part of. When interpreting each statement in this specification and claims that includes the term "comprising", features other than that or those prefaced by the term may also be present. Related terms such as "comprise" and "comprises" are to be interpreted in the same manner. As used herein the term "and/or" means "and" or "or", or both.

As used herein "(s)" following a noun means the plural and/or singular forms of the noun.

5.2 The polymer The polymer for use in the invention is a redox polymer. Hence, it comprises redox components that are capable of being reversibly oxidized and/or reduced. The redox components may be the links of the polymer chain or side groups of the chains.

Without being bound by theory, it is believed that the change in polymer charge density upon oxidation/reduction of the redox groups, attracts or repels the solvent into or from the gel, causing the gel to expand or contract, thereby changing its volume. Also contributing to the change in volume is the inflow or outflow of counterions needed for charge balance, which drag associated solvent along with them.

Suitable redox components include hydroquinones, napthoquinones, quinones, ferrocenes, phenazines, triarylamine derivatives, thionines, flavines, alkylviologens, N- oxides, for example, 2,2,6,6-tetramethylpiperidin-l-oxyl (TEMPO), tetrathiafulvalenes, phenazines, phenothiazines and metal complexes, for example, ruthenium bipyridines and terpyridines. In one embodiment the redox component is a quinone, ferrocene or TEMPO group. Quinone groups include haloquinones such as mono and

dichloroquinone. As would be recognized by a person of skill in the art, some redox groups can be oxidized and some reduced. Others such as metal dithiolenes can be both stably oxidized and reduced.

The redox polymer may be an addition polymer synthesized by polymerizing redox monomers that contain vinyl groups, or condensation polymers prepared by

polycondensation of suitable compounds.

Typical monomers that can be used to prepare polymers with redox components as side groups include styrenes, acrylates, methacrylates, vinyl ethers, acrylamides, and methacrylamides. In one embodiment, the polymer is derived from acrylate monomers comprising quinone or ferrocene redox components, for example, poly(trimethylquinone-2- hydroxyethyl methacrylate-co-hydroxyethyl acrylate-co-(oligoethylene glycol) diacrylate). Generally, the monomer is constructed with the redox component in the side chain, then the monomers polymerized. However, in some cases the polymer may be synthesized first, with reactive groups available to later bind the redox components to the polymer. The method of making the redox component-containing polymer depends on the nature of the polymer. (See "Conjugated metallopolymers. Redox polymers with interacting metal based redox sites" Peter G. Pickup, J. Mater. Chem. 1999, 9, 1641-1653; and "Electrochemically Active Polymers for Rechargeable Batteries", Petr Novak, Klaus Muller, K. S. V. Santhanam, Otto Haas, Chem. Rev. 1997, 97, 207-28).

Co-monomers can be used to modify the properties of the gel and to dilute expensive monomers. Examples of co-monomers that could be used include but are not limited to styrenes, acrylates, methacrylates, vinyl ethers, acrylamides and methacrylamides.

Co-monomers can also be used to increase the solubility of the polymeric gel, should the combination of the selected monopolymer and redox component prove not suitable in the chosen solvent.

For example, the water compatibility of the gel could be improved by including co- monomers including maleic anhydride, acrylic acid, hydroxyethyl (meth)acrylates, alkyl derivatives of (meth)acrylamide, methyl vinyl ether, and styrenesulfonic acid.

In one embodiment, the co-monomer is hydroxyethyl acrylate.

The cross-linker maybe any di or higher functional vinyl compound such as divinyl styrene, ethylene glycol dimethacrylate, or oligo(ethylene glycol) diacrylate. The selection of cross-linker may be influenced by the solvent, as the cross-linker should be hydro lytically stable and electrochemically inert. If water is used as the solvent, a water soluble cross-linker such as oligo(ethylene glycol) diacrylate may be used. The polymer may also be a condensation polymer, for example, via synthesis of difunctional monomers or grafting into existing polymers such as chitosan or cellulose.

In one embodiment the polymer for use in the invention is a ferrocene-containing polymer. For example, ferrocene can be incorporated into a cross-linked gel comprising acrylamide monomers, or attached to a polyacrylamide backbone.

In another embodiment the polymer contains quinone redox groups, for example, poly(trimethylquinone-ethan-2-yl methacrylate).

Examples 1-5 describe the synthesis of a quinone/hydroxyethyl acylate polymer suitable for use in the invention. The quinone monomers were constructed via the commercially available

trimethylhydroquinone 1. Alkylation of the hydroquinone 1 with acrylic acid 2 gave the desired coumarin 3 in 70 % yield (see Example 1). Reduction of the coumarin with lithium aluminium hydride gave the hydroxyl-hydroquinone 4 in high yield (see Example 2). The hydroquinone was then oxidized to the quinone with eerie ammonium nitrate, to give 5, which was then reacted with methacryloyl chloride to furnish the desired monomer 6 (see Examples 3 and 4). The monomers were polymerized using 1 , 1 '- azobis(cyclohexane carbonitrile) as initiator (see Example 5).

5.3 The polymeric gel A polymeric gel is a polymer-solvent system which forms a solid. The gel comprises a three-dimensional polymer network dispersed in a continuous liquid phase, which is the solvent. As would be recognized by a person skilled in the art, the term solvent, in the context of polymeric gel chemistry, means the liquid in which the polymer network is dispersed. In the present invention the polymeric gel is in contact with a solvent which can be absorbed into, or expelled from the gel matrix, depending on the polymer's affinity for the solvent. In one embodiment the polymeric gel of the invention can be prepared by placing the monomers together with the conductive filler (if required), solvent and initiator and polymerizing in a mould, for example, by free radical polymerization. The conductive fillers may need to be dispersed, for example, using ultrasonication or stirring, where large attractive forces between them cause aggregation (see Example 6).

The polymeric gel is then placed in contact with a suitable solvent. Generally, the solvent in contact with the gel, is the same or similar to the solvent that forms the continuous phase of the gel. Examples of suitable solvents include water, alcohols, acetonitrile, acetone, DMSO, DMF, glycols and derivatives, esters, carbonates, and ionic liquids and mixtures thereof. The solvent must contain an electrolyte, or be an electrolytic solution. The electrolyte must also be inert under the redox conditions. In one embodiment the solvent comprises an electrolyte selected from the group comprising lithium acetate, tetraalkylammonium and lithium salts of stable anions, for example PF₆\ BF₄ ^", CIO4^". The polymeric gels and actuators of the invention may have application as medical devices for implantation in living systems. Therefore, in some embodiments the solvent in contact with the gel is a bodily fluid, for example, blood, urine or saliva.

5.4 The conductive filler

The conductive filler speeds up the electrochemical processes taking place within the gel, allowing expansion or contraction of the gel to occur relatively quickly.

Any conductive filler that provides electrical conductivity when mixed with the polymer can be used, as long as the filler does not unduly affect the ability of the polymeric gel to expand.

Conductive fillers with long aspect ratios (greater than 10) provide good conductivity at low concentration. Preferred are aspect ratios of over 100

Examples of suitable conductive fillers are conductive nanotubes, metal nanowires, and fibres of conducting polymers such as polyaniline, polythiophene or polypyrrole. In one embodiment, the conductive filler comprises conductive nanotubes, preferably carbon nanotubes, more preferably multiwalled carbon nanotubes (MWCNTs).

Addition of lwt% MWCNT into a polymeric gel increases the conductivity of the gel, with the resistance of a 1cm block of gel dropping from about 3x10 ohm to about 10 ohms. In some cases, the polymer may contain sufficient redox groups to be conductive without addition of a conductive filler.

5.5 Reduction or oxidation of the polymeric gel

Upon oxidation of reduction of the redox component of the polymeric gel, the gel will expand or contract, causing a change in volume. Whether the gel responds by expanding or contracting depends on whether the redox component is initially present in the oxidized or reduced form, the polarity of this form relative to its redox partner and whether the solvent is polar or non-polar.

For example, if the polymeric gel is a ferrocene polymer gel, ferrocene will be poorly solvated in a polar solvent, creating a contracted polymer gel. If an oxidizing current is directed through the polymeric gel, the ferrocene components are oxidized to the ferrocinium ion. Such ions are more attractive to the polar solvent so the affinity of the polymer to the solvent increases. This causes the gel to take up solvent and expand.

In a non-polar solvent such as dichloromethane, the polymeric gel would initially exist in a swollen state. When oxidized, the increase in charge would reduce the affinity of the polymer to the solvent, repelling solvent from the polymer gel causing the gel would contract.

If a polymer gel were made with oxidized ferrocinium ions the opposite would occur upon reduction.

In a quinone polymeric gel, the quinone components can be electro chemically reduced to hydroquinone units. In alkaline pH, the final product will be a hydroquinone anion. In polar solvents the hydroquinone anion facilitates more expansion of the gel (due to greater hydrophilicity and the presence of the counterion). Upon reduction or oxidation of a polymeric gel of the invention generally, the volume of the gel changes by about 1 to about 500%.

In one embodiment the polymeric gel expands or contracts substantially in one direction only (linear actuation). For linear actuation, the expansion cannot be too great, otherwise internal stresses will cause the gel to tear away from the biasing mechanism.

The amount of expansion of contraction can be calculated for example, by

(a) measuring the length of a polymeric gel that has expanded linearly, for example, when placed in a tube to constrain lateral expansion, or

(b) by calculating the amount of solvent taken up by the gel, as the density of the gel is usually similar to that of the solvent.

5.6 The actuator

Actuation generally refers to a mechanism by which an object can be moved by converting energy (such as electrical or chemical energy) into mechanical energy.

The polymeric gel actuator of the invention allows the chemical energy that causes a change in the volume of the polymeric gel to be converted into useful work.

In the polymeric gel actuator of the invention, the polymeric gel is in contact with the solvent, so that the solvent may enter and leave the gel.

In one embodiment the actuator includes a container arrangement allowing contact between the polymeric gel and the solvent. In one embodiment, the container arrangement may comprise a container that holds both the polymeric gel and the solvent, maintaining contact between them.

In other embodiments, for example, when the actuator is present in a living system, the living system acts to contain the solvent, so as to keep it in contact with the polymeric gel. The actuator must also comprise a current applicator for applying current to the polymeric gel for reducing or oxidizing the redox components. In one embodiment the current applicator comprises a first electrode and a counter electrode. The electrodes may be of any inert conductive material, for example, platinum, or gold.

In one embodiment the first electrode is a platinum wire. In another embodiment the counter electrode is selected from an inert conductive material, and a second different polymeric gel. In this way it is possible, if the gels are carefully chosen, to oxidize one gel while reducing the second gel, both providing actuation in the same direction. The advantage of this arrangement is that the energy expended on the redox reactions at the counter electrode is not wasted. The polymeric gel actuator may also include a reference electrode, so that the voltages across each electrode can be assessed. Electrochemical reduction or oxidization can be performed, for example, using a three-electrode undivided electrochemical cell.

The actuator is configured such that the volume change of the polymeric gel causes movement of another object. The other object may be any object whose movement provides a useful effect. For example, the object may be selected from the group comprising a plunger, a piston, a plate and a shaft.

In one embodiment the polymeric gel is in direct contact with the other object. In another embodiment, the polymeric gel is in indirect contact with the other object, via a further object. The further object may also comprise a plunger, piston, plate or shaft, or could be a door to be opened, or lever to be pushed.

As described in example 8, the polymeric gel is oxidized or reduced in a syringe and the other object is a plunger of the syringe. The further object, which the polymeric gel is in indirect contact with, is a weight placed on top of the plunger. 5.7 Biasing mechanisms

The rate, direction and force of a polymeric gel actuator can be augmented using a biasing mechanism such as a spring, resilient material or flexible band. For example, a helical spring incorporated within the polymeric gel can enhance or oppose the expansion or contraction of the polymeric gel. As the spring can expand only in one direction, any stress in the gel is directed as movement in the direction of the spring. The presence of the spring hinders expansion of the gel sideways to the spring.

Accordingly, a biasing mechanism such as a spring can be used to achieve linear actuation.

The use of a curved, bent or kinked spring will direct movement of the gel in a sideways direction. Where the polymeric gel must expand against the biasing mechanism, it will expand more slowly and with less force.

Biasing mechanisms can be incorporated in various ways, depending on the size, shape and intended application of the polymeric gel actuator.

In one embodiment, the biasing mechanism can act as an electrode. In a preferred embodiment, the biasing mechanism is the first electrode.

Preferably, the biasing mechanism is a platinum spring.

An example of a linear polymeric gel actuator of the invention is provided in Example 8. As described in Example 8, a syringe containing the quinone polymer

gel/MWCNT/spring assembly was placed in an electrolysis cell in a DMF/water solution (70/30) with 2% lithium acetate.

Upon reduction of the polymeric gel at -0.8V, the gel slowly expands. The Pt spring channels the expansion of the gel lengthwise along the tube formed by the syringe, providing linear expansion of 40%. The plunger, which is inserted into the opening of the syringe, is pushed upwards as the polymeric gel expands, thereby converting the volume change in the gel into linear mechanical actuation. The expansion is reversible. Upon oxidation at 0.5V, the gel returned to its former volume. 6. EXAMPLES

Example 1: Synthesis of 4-hydroxy-3,5,6-tetrahydrocoumarin (3)

Methanesulfonic acid (10 mL) was heated to 70 °C in an oil bath, and 5.0 g (3.2 mmol) of 2,3,5 trimethylhydroquinone 1 dissolved in 5 mL of dichloroethane and 4.73 g (6.5 mmol) of acrylic acid 2 added together all at once with stirring. Stirring was continued at 100 °C for 120 min, and the reaction mixture was diluted to 125 mL with water and extracted with 3 x 50 mL portions of ethyl acetate. The extracts were washed with water, saturated NaHC0₃, and brine solutions and dried over MgS0₄. Solvent removal on a rotary evaporator under reduced pressure gave 5.0 g (73%) of the crude lactone as an off-white solid. Recrystallization from 30% CHC1₃, in hexane gave the pure lactone 3 in 70 % yield as a white powder, mp 172-3 °C.

IR (KBr) (cm^"1) 3475 (OH), 1744 cm^'1 (0=0) NMR: *H NMR (CDCI₃) 2.053 (s, 3H, Ar-CH₃), 2.063 (s, 3H, Ar-CH₃), 2.071 (s, 3H, Ar-CH₃), 2.63 ( 2H, t, CH₂), 2.81(t, 2H, CH₂).

¹³C NMR (CDCI₃): 12.2, 12.6, 13.1 (3 ^χ Ar-CH₃), 21.1 (Ar-CH₃₎, 28.95 (CH₂), 119.8, 120.3, 121.6, 123.4, 143.8, 149.2, 169.3. m/z 207.10 (calculated for Ci₂Hi₅0₃Na) Example 2: Reduction of 4-hydroxy-3,5,6-tetrahydrocoumarin (3)

To a stirred suspension of LiAlH₄ (1.47 gm, 28.7 mmol) in 200 mL of dry THF at 0 C was added drop wise 100 mL of THF containing 4-hydroxy-3,5,6-tetrahydrocoumarin 3 (5 g, 24.24 mmol). After the vigorous reaction has been subsided, the mixture was refluxed for 2 hr. Excess hydride was decomposed by careful addition of water, and the mixture was neutralised with acetic acid. To this was added 650 mL of saturated aq. NH C1 solution. The upper organic layer was decanted and the lower aqueous layer extracted with four 150 mL portions of THF. The combined THF layers were dried over MgS0₄. After removal of solvent by rotary evaporator, the residue was recrystallized from diethyl ether to give 4.1 gm (91 %) of 4 as a white solid. Mp: 135-136 °C (Lit ³ 135-135 °C).

NMR: Ή NMR (DMSO d⁶) 1.53 (m, 2H, CH₂), 2.02 (s, 6H, 2 Ar-CH₃), 2.05 (s, 3H, Ar-CH₃), 2.55 ( 2H, dd, J= 6.4 Hz, 7.6 CH₂), 3.38(q, J= 6.4 Hz, 2H, CH₂), 4.62 (t, J= 5.2, 1H, CH₂-OH), 7.27 (s,lH, OH), 7.37 (s,lH, OH).

¹³C NMR (DMSO d⁶): 12.80, 12.33, 13.34 (3 Ar-CH₃), 23.43 (CH₂), 32.59 (Ar-CH₃), 60.68 (CH₂-OH), 121.59, 122.08, 126.02, 146.17, 146.21 m/z 317.0311 (calculated for C₁₂H₁₈0₃Ag) Example 3: Oxidation of hydroquinone (4)

To a solution of hydroquinone 4 (4 gm, 19.03 mmol) in CH₃CN (100 mL) at 0 °C was added a solution of eerie ammonium nitrate (CAN) (26.09 gm, 47.58 mmol) in H₂0 (25 mL) in one portion with stirring. After 5 min, the reaction mixture was diluted four times with CH₂C1₂/H₂0 (50:50). The organic layer was separated and washed with water. The solution was dried over anhydrous MgSCv The solvent was removed under reduced pressure. The crude oily product was purified using column chromatography using petroleum ether/ethyl acetate (90:10) as eluant. After evaporation of the solvent using a rotary evaporator quinone 5 was yielded as yellow oil. Yield: 3.5 gm (88%)

NMR: 1H NMR (CDC1₃) 1.62 (m, 2H, CH₂), 1.95 (s, 6H, 2 x Ar-CH₃), 1.98 (s, 3H, Ar- CH₃), 2.52 ( 2H, t, J= 7.5 Hz, 7.6 CH₂), 3.52(t, J= 7.5 Hz, 2H, CH₂), 6.50 (s, 1H, CH₂- OH).

¹³C NMR (CDC1₃): 12.10, 12.33, 13.37 (3 x Ar-CH₃), 22.43 (CH₂), 31.38 (Ar-CH₃), 61.59 (CH₂-OH), 140.39, 140.72, 141.02, 143.58, 187.54, 187.79 m/z 231.0992 (calculated for d₂Hi₆0₃Na)

Example 4: Synthesis of quinone methacrylate (6)

The alcohol 5 (3.00 g, 14.54 mmol) was dissolved in DCM (25 ml). Tnethylamine (3.67 mL, 36.36 mmol) was injected into the solution via a syringe and the solution was stirred for 30 min at 0 °C. Methacryloyl chloride (3.80 g, 36.36 mmol) was added drop wise with continuous stirring. The reaction mixture was stirred for 2 h under nitrogen atmosphere at 0 °C and then at room temperature for 4 h. The progress of the reaction was monitored by thin layer chromatography (TLC). The reaction mixture was diluted four times with CH₂C1₂/H₂0 (3:1). The organic layer was separated and washed with water. The solution was dried over anhydrous MgS0₄. The solvent was removed under reduced pressure. The crude oily product was chromato graphed on silica using petroleum ether/ethyl acetate (90: 10) as eluant. The solvent was removed using a rotary evaporator and the product was dried under vacuum. The colourless solid product 6 was stored in the fridge until further use. Yield: 3.5 gm (88 %)

NMR: Ή NMR (CdCl₃) 2.03 (m, 2H, CH₂), 2.16 (3H, q, J= 2 Hz, CH₃), 2.22 (s, 6H, 2 x Ar-CH₃), 2.24 (s, 3H, Ar-CH₃), 2.81 ( 2H, t, J= 8 Hz, CH₂), 4.38 (t, J= 8 Hz, 2H, CH₂), 5.77(m, 1H, C=CH₂), 6.31 (m, 1H, C=CH₂).

¹³C NMR (CDC1₃): 12.06, 12.26, 13.36 (3 Ar-CH₃), 17.92, 18.26, 23.33, 27.66, 64.09, 125.40, 128.94, 136.27, 140.43, 140.52, 143.10, 167.27, 186.90, 187.49 m/z 299.1254 (calculated for Ci₆H₂o0₄Na)

Example 5: General synthesis of polymeric gel using quinone methacrylatc monomer and 2-hydroxyethyl acrylate

The polymerization reactions were performed in a 1 mL plastic tube. Initiator 1,1 '- azobis(cyclohexane carbonitrile) (ABCC) (10 mg), polyethylene glycol diacrylate (10 mg, MW ca. 250), hydroxyethyl acetate (HEA) (45 mg) and quinone methacrylate monomer 6 (45 mg) were added to the 0.45 mL of dry and degassed DMF at room temperature. The mixture was shaken thoroughly until formation of homogeneous solution. The feed mixture was purged with argon for 15 min to remove dissolved oxygen followed by 3 cycles of freeze drying, and then the reaction tube was sealed and placed in oil bath at 70 °C for 24hr. To stop the polymerization the tube was cooled down using cold water for 5 min, which resulted in the termination of the initiation reaction. Then the gel were transferred from the tube to a vial and soaked in DMF for 24 hours to remove unreacted monomer if any.

Example 6: Synthesis of quinone/HE A gel with 1% nanocyl 3100 acutator including spring biasing mechanism

Nanocyl 3100 (50 mg) was dispersed in DMF (5 mL) with polyvinylpyridine (150 mg) for 2 hr in an ultrasonic bath at 5 to 10 °C.

The polymerization reactions described in Example 5 were performed in a 1 ml plastic tube (inner diameter 4.7 mm), inside of which was a spring of Pt wire (about 12 turns of a Pt wire of thickness 0.0127 mm, coil length 1 cm, coil diameter 3.5 mm). Initiator 1,1 '-azobis(cyclohexane carbonitrile) (10 mg), PEG diacrylate (10 mg, MW ca. 250), hydroxyethyl acrylate (45 mg) and quinone methacrylate monomer 6 (45 mg) were added to the predispersed solution of nanocyl 3100 in DMF (0.4 mL of a 1%

dispersion). The mixture was shaken thoroughly until formation of homogeneous solution. The feed mixture was purged with argon for 15 min to remove dissolved oxygen followed by 3 cycles of freeze drying, and then the reaction tube was sealed and placed in an oil bath at 70 °C for 24hr. To stop the polymerization the tube was cooled using cold water for 5 min. The gel was transferred from the tube to a vial and soaked in 50 mL DMF for 24 hours to remove any unreacted monomer if any. The DMF was changed several times during this process.

Example 7: Electrochemical reduction of quinone/HEA gel with 1% nanocyl 3100 with Pt wire in 25% water DMF mixture

Lithium acetate (2g) was dissolved in a mixture of DMF (70 ml ) and water (30 ml ) and the quinone/HEA gel /Pt wire assembly of Example 6 was allowed to soak in it for 24 hours to equilibrate. Electrochemical reduction was performed in a three-electrode undivided

electrochemical cell (platinum foil counter electrode, platinum wire as quasi-reference electrode, ferrocene standard measured at 0.55 V) in 70 % DMF, 30 % water containing 2% w/w lithium acetate at -0.80 V potential. During the electrochemical reduction the gel showed linear expansion from 1 cm length to 1.4 cm (a 40% increase in length). After 2 hours there was no further change in the length of the gel.

The polarity was then reversed and oxidation proceeded at 0.5 V. The gel returned to its original length of 1 cm within 1 hr. The gel could be cycled at least twenty times before serious deterioration occurred. Example 8: Construction of piston using the polymeric gel actuator

The quinone/HEA gel with 1 % nanocyl 3100 was prepared as in Example 7. The polymerization reactions were performed in a 0.5 ml syringe (3.5 mm diameter) having a spring of Pt wire (length of the coiled spring: 1.4 cm, diameter 2.2 mm and diameter of the Pt wire: 0.0127 mm, 12 turns). The same mixture and procedure as in Example 7 was used, except that 0.2 ml was used. After polymerisation the gel was washed several times with DMF (weight of the gel-spring assembly was 150 mg) and transferred in a 1 mL plastic syringe (inner diameter: 4.7 mm) and soaked in a DMF water LiOAc (70:30:2) for 24 hours. Weights were was placed on top of the syringe, and the extension measured upon reduction at -0.8 V in : 70 % DMF + 30 % Water + 2% LiOAc as before. Figure 1 shows the polymeric gel actuator system whereby the plunger of the syringe is forced upwards by expansion of the polymeric gel, lifting the weight on top. The device was able to lift up to 50 g before no extension could be measured.

Example 9: Use of quinone/HEA gel with 1% nanocyl 3100 as a working and counter electrode: Simultaneous oxidation/reduction of gels

Electrochemical reduction/oxidation of the gel prepared in accordance with Example 6 was performed in a three-electrode divided electrochemical cell with two gels as counter and working electrodes at 0.8 volts. A reduced gel (the hydroquinone form of the gel) was used as a counter electrode while a second non-reduced gel (the quinone form of the gel) was used as a working electrode. The reduced hydroquinone form was prepared using the reduction process set out in Example 7. Platinum wire was used as a reference electrode. The solvent system used was DMF/water (75/25 v/v) containing 2% ammonium acetate. Figure 4 shows the system set up with the working electrode on the left and the counter electrode on the right.

During the electrochemical reduction/oxidation the working electrode gel showed an expansion while the counter electrode contracted (Figure 5). During the electrochemical reduction the gels showed a 20 % linear expansion and contraction in 6 hours. The polarity was then reversed and reduction proceeded at -0.7 volts. The gels returned to their original length in another 5 hours.

To evaluate reproducibility of the actuation and vitality of the actuator during electrochemical process, the gels were cycled through the electrochemical

reduction/oxidation process 20 times and the change in length during each cycle was recorded. After twenty cycles the performance of the gel was essentially the same as that of the first cycle (see Figure 6).

Example 10: Synthesis of Monochloroquinone

Mono chloro quinone was prepared in accordance with the scheme below:

10 11

COOMe

MgOMe/ MeOH eOOC

Synthesis of 2,3,6- trimethylbenzoquinone (10)

A suspension of 15.2 g. of trimethylhydroquinone in 100ml of acetic acid was stirred mechanically in a round bottom flask, heated until the solid had dissolved, and chilled in an ice-bath until the temperature had dropped to 40 °C. A cooled solution of 10.8 g. of sodium dichromate dihydrate in 25 ml. of acetic acid was then run in the course of about 25 min. with constant ice cooling to control the temperature to 35-40 °C. After stirring for 5 min. more the solution was diluted with water and cooled. After suitable further dilution the mixture was extracted with ether three times and the bright yellow extract was washed free of acid with salt solution, filtered through sodium sulfate and the solvent evaporated. The residual pure yellow oil solidified readily and melted at 29- 30 °C.

Yield 12.83 gm (86 %) m.p. 29-30 °C; FT— IR cm^"1 1675 (C=0); ^LH-NMR (400 MHz, CDC13): δ 2.20 (s, 3H), 2.21 (s, 3H), 3.78 (s, 3H), 5.56 (s, 1H). 13C-NMR (100 MHz, CDC13): δ 12.6, 12.8, 13.8, 140.21, 140.61, 141.10, 141.91

(Fieser, Louis F.; Ardao, Maria Isabel. Journal of the American Chemical Society (1956), 78 774-81).

Synthesis of 2-Chloro-2,3,6- trimethylbenzoquinone (11)

Vigorous swirling of a suspension of trimethyl-p-benzoquinone (10 gm) in concentrated hydrochloric acid (100 ml.) gave a black precipitate. The yellow color was removed completely by maintaining the mixture at reflux for 3 hr. after dilution with water (100 ml.)-concentrated hydrochloric acid (50 ml.). The crude solid was dissolved in glacial acetic acid-water solution and aqueous sodium dichromate (100 gm. in 100 ml.) was added in portions. After the mixture had stood for 15 min., a yellow solid was precipitated by dilution with water. The precipitate was filtered, wadhed several times with water and recrystallised from petroleum ether gave yellow flakes.

Yield 9.83 gm (80 %) m.p. 71-73 °C (lit. 72 - 73 °C); Ή-NMR (400 MHz, CDC13): δ 2.05 (s, 3H), 2.08 (s, 3H), 2.18 (s, 3H). 13C-NMR (100 MHz, CDC13): δ 12.6, 12.8, 13.8, 140.21, 140.61, 141.10, 141.9, 179.58, 184.96. ( Bishop, R. F. Porter, L. K. J. Tong J. Am. Chem. Soc, 1963, 85 (24), pp 3991-3998) Synthesis of 5-Chloro-6-hydroxy-7,8-dimethylchroman-2-one (13)

A solution of methyl malonate (12.88 g, 97 mmol) in dry MeOH (25 ml) was refluxed for one hour with finely powdered MgOMe (16.84 g, 195 mmol). A solution of chlorotrimethyl-p-quinone (9 g, 48.7 mmol) in dry MeOH (50 ml) was added dropwise to the refluxing solution and reflux continued for 13 hr. The solid was removed from the cooled mixture, washed with ether and carefully mixed with HC1 (10%, 50 ml) and stirred to remove impurities. The yellow solid product (3 g) was filtered out and dissolved in acetone and stirred with dil. hydrochloric acid (100 ml). The resulting white suspension was then refluxed for 5 hr. The solution was cooled and extracted with ether (3 x 30 mL) and the combined organic extracts washed with brine, dried (MgS04) and evaporated. To the crude residue of 12 in toluene (60 ml), 4-methylbenzenesulfonic acid (0.47 g, 27 mmol) was added with stirring, and the mixture then refluxed. After 12 hr, the nearly colourless solution was cooled to room temp, and extracted with EtOAc (3 x 30 ml). The organic extract was washed with sat. aqueous NaHC03 and the aqueous layer back-extracted once with EtOAc (30 ml). The combined organic extracts were washed with brine and dried over MgS04. X-ray quality crystals of the title compound, 5-chloro-6-hydroxy-7,8-dimethylchroman-2-one were obtained from EtOAc/hexane (7.1 g, 80%): m.p. 139- 1°C; FT— IR cm-1 1777 (O— C=0); 1H-NMR (400 MHz, CDC13): δ 2.20 (s, 3H), 2.33 (s, 3H), 2.74 (t, J = 8 Hz, 2H), 3.02 (t, J = 8 Hz, 2H), 5.5 (s, 1H); 13C-NMR (100 MHz, CDC13): δ 12.0, 12.6, 22.0, 28.6,115.1, 117.8, 123.8, 125.0, 143.8, 145.9, 165.3.

Synthesis of 2-chloro-3-(3-hydroxypropyl)-5,6-dimethylbenzene-l,4-diol (14) To a stirred suspension of LAH in 200 mL of dry THF, cooled with ice was added drop wise 100 mL of THF containing 13. After the vigorous reaction has been subsided, the mixture was refluxed for 2 hr. Excess hydride was decomposed by careful addition of water, and the mixture was extracted with ethyl acetate (3 X 50 mL). The combined organic layer was washed with water, brine and dried over MgS0₄. After the solvent was removed by evoparation, the residue was recrystallised from diethyl ether to give 14 as a white solid.

Yield 85 %, 4.2 gm

m.p. 122-23 °C; 1H-NMR (400 MHz, CDC13): 5 1.90 (q, J= 7 & 12 Hz, 2H), 2.16 (s, 3H), 2.19 (s, 3H), 2.92 (t, J = 6 Hz, 2H), 3.60 (t, J = 6 Hz, 2H). 13C-NMR (100 MHz, CDC13): δ 12.5, 12.7, 23.0, 29.4, 60.5, 117.1 1, 121.6, 122.53, 124.28, 143.42, 146.66. Synthesis of 2-chloro-3-(3-hydroxypropyl)-5,6-dimethylcyclohexa-2,5-diene-l,4- dione (14)

To a solution of 14 ( 4 gm, 0.0017 mol) in CH₃CN (50 mL) at 0 tO 10 °C was added a solution of ceric ammonium nitrate (19 gm, 0.0037 mol) in H₂0 (50 mL) in one portion with stirring. After 30 min, H₂0 (120 mL) and cH2ci2 (120 mL) were added, and the layers were separated. The aqueous phase was extracted with CH₂C1₂ (3 ^χ 50 mL). The combined organic phases were washed with brine, dried (MgS0₄), and concentrated in vacuo. The residue was purified by column chromatography (DCM/MeOH) (95:5) to give product as red oil.

Yield: 3.57 gm (90 %) ; FT— IR cm^"1 1670 ; 1H-NMR (400 MHz, CDC13): δ 1.75 (q, J = 7 & 12 Hz 2H), 2.03 (s, 3H), 2.06 (s, 3H), 2.72 (t, J = 6 Hz, 2H), 3.60 (t, J = 6 Hz, 2H). 13C-NMR (100 MHz, CDC13): δ 12.5, 12.8, 24.2, 30.5, 61.83, 140.4, 140.8, 141.2, 145.1, 179.7, 185.2 Synthesis of 3-(2-chloro-4,5-dimethyl-3,6-dioxocyclohexa-l,4-dien-l-yl)propyl methacrylate (16)

The alcohol 15 (3.5 g, 0.0015 mole) was dissolved in DCM (100ml). Triethylamine (1.5 ml, 0.0015 mole) was injected into the solution via a syringe and the solution was stirred for 30 min at 0 °C. Methacryloyl chloride (1.92 g, 0.0018 mole) was added dropwise with continuous stirring. The reaction mixture was stirred for 2 h under nitrogen at 0 °C and then at room temperature for 4 h. The progress of the reaction was monitored by thin layer chromatography (TLC). The reaction mixture was diluted four times with CH₂C1₂/H₂0 (3:1). The organic layer was separated and washed with water. The solution was dried over anhydrous MgS0₄. The solvent was removed under reduced pressure. The crude oily product was chromatographed on silica using petroleum ether/ethyl acetate (90:10) as eluant. The solvent was removed using a rotary evaporator and the product was dried under vacuum.

Yield: 3.86 gm (86 %) ; FT— IR cm-11675, 1765; ^!H-NMR (400 MHz, CDC13): δ 1.78 (m, 2H), 1.93 (s, 3H), 2.03 (s, 3H), 2.07 (s, 3H), 2.76 (t, J = 6 Hz, 2H), 4.17 (t, J = 6

Hz, 2H) 5.54 (m, IH), 6.09 (m, IH). 13C-NMR (100 MHz, CDC13): δ 12.6, 12.8, 18.25, 24.84, 26.82, 63.93, 125.43, 136.26, 140.47, 140.76, 141.20, 144.48, 167.22, 179.54, 184.51.

Example 11: Monochloroquinone/HEA gel with 1% nanocyl 3100 as actuator

Monochloroquinone methacrylate was used as the monomer in the synthesis of a redox gel in accordance with the process outlined in Example 5. Replacing a methyl group with a chlorine atom decreases the redox potential of the quinone from -0.8 to -0.49 volts. Actuation performance and percentage swelling remains substantially the same as seen with the quinine/HEA gels.

Example 11: TEMPO based electroactive gels TEMPO or 2,2,6,6-tetramethylpiperidin- 1 -yl)oxyl, or (2,2,6,6-tetramethylpiperidin- 1 - yl)oxidanyl is a chemical compound with the formula (CH₂)3(CMe₂)₂NO. As a stable radical, it has applications throughout chemistry and biochemistry. TEMPO is widely used as a radical trap. Its stability is partially attributed to the steric protection provided by the four methyl groups adjacent to the nitroxyl group. TEMPO is capable of reversibly being oxidized to an oxoammonium ion, and has been proposed as a new rechargeable polymer for battery technology.

A general synthetic scheme of a TEMPO polymer is shown below.

To prepare a TEMPO gel, a piperidine (17) is first converted to the corresponding acrylamide (18) which is then copolymerised with acrylamide in presence of N,N-bis acrylamide as a crosslinker. Oxidation of the copolymer (acrylamide gel) (19) in the presence of peroxide generates the nitroxide polymer (20). The nitroxide can be oxidised to oxoammonium ion (21) using eerie ammonium nitrate as a chemical oxidant, or electro chemically.

Example 11a: Preparation of N-( 2,2,6,6-tetramethylpiperidine-4-yl)acrylamide (18)

Acryloyl chloride (1.3 ml) was added dropwise to an ice-cold solution of 4-amino- 2,2,6,6-tetramethylpiperidine (2.8 ml) in anhydrous toluene (60 ml) and triethylamine (0.9 ml) under an argon atmosphere with magnetic stirring. The mixture was vigorously stirred for 1 h at 5°C and then for 1 h at room temperature. At the end of the reaction, the precipitate was collected by filtration, extracted with dichloromethane and washed with aqueous K₂C0₃. The solvent was removed in vacuo, and the residue was purified using a silica gel column with ethyl acetate. An appropriate fraction was collected and crystallized from an ethanol/hexane mixed solution. The acrylamide monomer was isolated as white crystals.

Yield: 1.90 gm, 50 %. δΗ (500 MHz; CDC13; Me4Si) 6.27 (1H, d, J= 1.5 Hz, vinyl CH2), 6.10 (1H, q, J= 10.4 Hz, vinyl CH), 5.63 (1H, s, amide ΝΗ), 5.50 (1H, dd, J= 1.5 Hz, vinyl CH2), 4.34 (1H, d, J= 12.2 Hz, piperidine CH), 1.95 (2H, dd, J= 4.0 Hz, piperidine CH2), 1.28 (6 H, s, 2 x CH3), 1.20 (6 H, s, 2 x CH3), 1.1 1 (2H, t, J= 12.2 Hz, piperidine CH2); 5C(500 MHz; CDC13 ; Me4Si) 28.23, 34.63, 42.43, 44.82, 51.27, 126.2, 131.0, 164.89. HRMS (EI⁺): cald. For ([M]^ 234.1464, found: 234.1476 (calculated for C12H21NaN02).

Example lib: Synthesis of Poly 4-(5-amino-2-ethyl-4-methyl-5-oxopentanamido)- 2,2,6,6-tetramethylpiperidin-l-olate gel (acrylamide gel) using radical

polymerization of the N-(2,2,6,6-tetramethylpiperidin-4-yl)acrylamide monomer (1) with acrylamide and N, iV-methylenebisacrylamide including spring biasing mechanism.

The polymerization was performed in a 1 ml plastic tube (inner diameter 4.7 mm), inside of which was a spring of Pt wire (about 12 turns of a Pt wire of thickness 0.0127 mm, coil length 1 cm, coil diameter 3.5 mm). Initiator 1,1 '-azobis(cyclohexane carbonitrile) (ABCN) (5 mg), N-(2,2,6,6-tetramethylpiperidine-4-yl)acrylamide (50 mg), N, N-methylene diacrylamide (20 mg) and acrylamide (50mg) were added to acetic acid (0.5 mL). The mixture was shaken thoroughly until formation of a homogeneous solution. The feed mixture was purged with argon for 15 min to remove dissolved oxygen followed by 3 cycles of freeze drying, and then the reaction tube was sealed and placed in an oil bath at 70°C for 24 hr. To stop the polymerization the tube was cooled using cold water for 5 min. The gel was transferred from the tube to a vial and soaked in 50 mL acetic acid for 24 hours to remove any unreacted monomer. The acetic acid was changed several times during this process. Example 11c: Oxidation of acrylamide gel to corresponding N-Oxide (TEMPO) gel using 3-chlorobenzoperoxoic acid

Poly 4-(5-amino-2-ethyl-4-methyl-5-oxopentanamido)-2,2,6,6-tetramethylpiperidin- 1 - olate gel (acrylamide gel) was added to ice-cold solution of 3-chlorobenzoperoxoic acid (620 mg) in dioxane (5 ml), and keep at room temperature for 24 hours. The color of the gel changed from colorless to yellow on oxidation. After completion of the oxidation the gel were transferred from the tube to a vial and soaked in dioxane for 24 hours to remove MCPBA.

Example lid: Oxidation of TEMPO gel to oxoammonium salt using eerie ammonium nitrate

Ceric ammonium nitrate (5 gm) and the TEMPO gel i.e poly 4-(5-arnino-2-ethyl-4- methyl-5-oxopentanan ido)-2,2,6,6-tetramethylpiperidin-l-olate were mixed in water in a round flask equipped with condenser and magnetic bar. The mixture was heated at 100 °C with an oil bath under continuous stream of oxygen. The color of the gel changed from yellow to orange on oxidation. After completion of the oxidation the gel was transferred to a vial and soaked in water for 24 hours to remove ceric ammonium nitrate. The N-oxide gel (TEMPO gel) and oxoammonium salt form of the gel were put in a 0.5 M solution of NaBF₄ (pH 4.3) to study their swelling and shrinking properties. The oxoammonium form of gel swelled in 0.5 M solution of NaBF₄ in water while the TEMPO form of the gel remained the same. An 0.5 M solution of lithium nitrate also gave the same results. Thus the oxoammonium form of the gel swells in 0.5 M aqueous solution of NaBF₄ and LiN0₃.

Example lie: Electromechanical study

To determine the appropriate potentials for operation of the actuator, the

electrochemical behavior of the TEMPO gel was studied in 0.5 M NaBF₄ aqueous solution. The cyclic voltammogram of polymer film repeatedly displayed a redox wave at 0.72 V (vs Ag/AgCl) in 0.5 M NaBF₄ aqueous solution, which was assigned to the one electron oxidation of the TEMPO nitroxide to the corresponding oxoammonium cation salt.

To investigate the actuation performance, electrochemical oxidation of TEMPO gel was performed in a three-electrode undivided electrochemical cell (platinum foil counter electrode, platinum wire as quasi-reference electrode, in 0.5 M NaBF₄ in water at 0.75 V potential.

During the electrochemical reduction the gel showed 20% linear expansion in 30 minutes (Figure 7). The polarity was then reversed and reduction proceeded at -0.7 volts. The gel returned to its original length within 1 hr.

Example 12a: Synthesis of acrylamide gel with 1% nanocyl 3100 acutator including spring biasing mechanism

Nanocyl 3100 (50 mg) was dispersed in acetic acid (5 mL) with polyvinylpyridine (150 mg) for 2 hr in an ultrasonic bath at 5 to 10 °C. The polymerization was performed in a 1 ml plastic tube (inner diameter 4.7 mm), inside of which was a spring of Pt wire (about 12 turns of a Pt wire of thickness 0.0127 mm, coil length 1 cm, coil diameter 3.5 mm). Initiator l,l '-azobis(cyclohexane carbonitrile) (ABCN) (5 mg), 2,2,6,6-Tetramethylpiperidine-4-yl acrylamide (50 mg), NN-methylene diacrylamide (20 mg) and acrylamide (50mg) were added to the predispersed solution of nanocyl 3100 in acetic acid (0.5 mL of a 1 % dispersion). The mixture was shaken thoroughly until formation of homogeneous solution. The feed mixture was purged with argon for 15 min to remove dissolved oxygen followed by 3 cycles of freeze drying, and then the reaction tube was sealed and placed in an oil bath at 70°C for 24 hr. To stop the polymerization the tube was cooled using cold water for 5 min. The gel was transferred from the tube to a vial and soaked in 50 mL acetic acid for 24 hours to remove any unreacted monomer. The acetic acid was changed several times during this process.

Example 12b: Oxidation of acrylamide gel to corresponding N-oxide (TEMPO) gel using 3-chIorobenzoperoxoic acid

Poly 4-(5-ammo-2-ethyl-4-methyl-5-oxopentanamido)-2,2,6,6-tetramethylpiperidin- 1 - olate Gel (acrylamide Gel) was added to an ice-cold solution of 3-chlorobenzoperoxoic acid (620 mg) in dioxane (5 ml), and keep at room temperature for 24 hours. After completion of the oxidation the gel were transferred from the tube to a vial and soaked in dioxane for 24 hours to remove MCPBA.

Example 12c: Actuation performance

To investigate the actuation performance (Figure 8), electrochemical oxidation of the TEMPO gel was performed in a three-electrode undivided electrochemical cell (platinum foil counter electrode, platinum wire as quasi-reference electrode, in 0.5 M NaBF₄ in water at 0.75 V potential. During the electrochemical reduction the gel showed 30% linear expansion in 30 minutes. The polarity was then reversed and reduction proceeded at -0.7 volts. The gel returned to its original length within 1 hr.

7. INDUSTRIAL APPLICABILITY

The polymeric gel of the invention can be used as an actuator. The expansion of the gel can be used as a force to do work, such as opening or closing a valve, or pushing a piston.

The polymeric gel actuator of the invention can be used in wet environments such as in a "lab on a chip" situation, or in the human body, where bodily fluids provide the solvent needed for expansion.

The polymeric gel actuators of the invention can be used for drug delivery by incorporating the gel into the gel, which is released when the gel expands. Alternatively, the polymeric gel actuator of the invention could be used to open a valve to release the drug. In a "lab on a chip" device, the polymeric gel actuator of the invention could be used to open and close valves to direct fluid flow, or to act like a pump. The polymeric gel actuator can also be used as the driving force in a piston, for example, to move a robotic arm.

Claims

1. A polymeric gel actuator comprising

2. A polymeric gel actuator comprising

(b) a container arrangement allowing contact between the polymeric gel and the solvent, and

3. A polymeric gel actuator comprising

(a) a polymeric gel in contact with a solvent, wherein the polymer comprises redox components and is optionally mixed with a conductive filler, and wherein reduction or oxidation of the redox components changes the affinity of the polymer to the solvent, thereby changing the volume of the polymeric gel, and

(b) a current applicator for applying current to the gel for reducing or oxidizing the redox components of the polymer, wherein the actuator is configured such that the volume change of the polymeric gel causes movement of another object, and wherein one or more biasing mechanisms are embedded in the polymeric gel.

4. A polymeric gel actuator comprising

(a) a polymeric gel in contact with a solvent, wherein the polymer comprises redox components and is optionally mixed with a conductive filler, and wherein reduction or oxidation of the redox components changes the affinity of the polymer for the solvent, thereby changing the volume of the polymeric gel,

(c) a current applicator for applying current to the gel for reducing or oxidizing the redox components of the polymer, wherein the actuator is configured such that the volume change of the polymeric gel causes movement of another object, and wherein one or more biasing mechanisms are embedded in the polymeric gel.

5. A polymeric gel actuator of claim 3 or claim 4 wherein the biasing mechanism is a spring.

6. A polymeric gel actuator as claimed in any preceeding claim wherein the polymer is derived from one or more monomers selected from the group comprising styrenes, acrylates, methacrylates, vinyl ethers, acrylamides, and methacrylamides.

7. A polymeric gel actuator of claim 6 wherein the redox component of the polymer is a quinone, ferrocene or TEMPO group.

8. A polymeric gel actuator of claim 7 wherein the polymer is derived from acrylate monomers comprising quinone, ferrocene or TEMPO redox components.

9. A polymeric gel actuator of any preceding claim wherein the solvent is selected from the group comprising water, alcohols, acetone, acetonitrile, DMSO, DMF, glycols and derivatives, and ionic liquids and mixtures thereof.

10. A polymeric gel actuator of claim 9 wherein the solvent is a DMF/water mixture containing one or more of lithium acetate lithium nitrate or NaBF₄ as electrolyte.

11. A polymeric gel actuator of any preceding claim wherein the conductive filler is selected from the group comprising conductive nanotubes, metal nanowires, and fibres of conducting polymers such as polyaniline, polythiophene or polypyrrole.

12. A polymeric gel actuator of claim 13 wherein the conductive filler is conductive nanotubes, preferably carbon nanotubes, more preferably, MWCNTs.

13. A polymeric gel actuator of claim 11 or claim 12 wherein the conductive filler has an aspect ratio of about 2 to about 200, preferably about 10 to about 200, more preferably about 50 to about 200.

14. A polymeric gel actuator of any preceding claim wherein the polymeric gel comprises about 0.1 to 10wt% conductive filler, preferably about 0.1 to about 2.0wt% conductive filler.

15. A polymeric gel actuator wherein the volume of the polymeric gel in its contracted state is about 0.001 to about 10cm³, preferably about 0.05 to about 10cm³, more preferably about 1 to about 10cm³.

16. A polymeric gel actuator wherein upon oxidation or reduction the volume of the polymeric gel changes by about 25% to about 200%.

17. A polymeric gel actuator wherein upon oxidation of reduction, the volume of the polymeric gel changes by about 35% to about 200%.

18. A polymeric gel actuator wherein upon oxidation of reduction, the volume of the polymeric gel changes by about 45% to about 200%.

19. A polymeric gel actuator of any preceeding claim wherein the polymer is selected from poly(trimethylquinone-2-hydroxyethyl methacrylate-co-hydroxyethyl acrylate-co-(oligoethylene glycol) diacrylate) and poly 4-(5-amino-2-ethyl-4-methyl-5- oxopentanamido)-2,2,6,6-tetramethylpiperidin- 1 -olate.