Electroactive polymers and systems using the same

Abstract

In one aspect, novel robust electroactive polymers (EAPs) is described, which contract and expand at low voltages to provide for a shape-morphing system, e.g., a prosthetic liner, and potentially entire prosthetic socket, to contract and expand in strategic areas as needed to maintain a comfortable and good fit throughout the day. In some embodiments, as the residual limb changes, these novel robust EAPs can change dynamically as needed to maintain a comfortable, snug fit of the prosthetic liner or socket with the hard shell of the prosthetic socket device. In some embodiments, the EAPs used in prosthetic liners or sockets can also be used to detect pressure as the device is being used, and automatically adjust to maintain fit through a control unit, so that the patient does not even have to stop and adjust his or her device as he or she goes about an active day.

We claim: 
     
         1 . An electroactive polymer shape-morphing system comprising:
 a first electrode;   a second electrode counter to the first electrode and spaced apart from the first electrode;   an ionically conductive fluid; and   a first actuator electrically connected to the first electrode and comprising a first electroactive ionic polymer, said electroactive polymer selected to expand or contract on application of an electrical potential, and said first actuator spaced apart from and in fluidic communication with the second electrode;   wherein the first electroactive ionic polymer is selected from the group consisting of polymethacrylic acid, poly2-hydroxyethyl methacrylate, poly(vinyl alcohol), ionized poly(acrylamide), poly(acrylic acid), poly(acrylic acid)-co-(poly(acrylamide), poly(2-acrylamide-2-methyl-1-propane sulfonic acid), poly(methacrylic acid), poly(styrene sulfonic acid), quarternized poly(4-vinyl pyridinium chloride), poly(vinylbenzyltrimethyl ammonium chloride), sulfonated poly(styrene-b-ethylene-co-butylene-b-styrene), sulfonated poly(styrene), a cross-linked polymer thereof, and a combination thereof.   
     
     
         2 . The shape-morphing system of  claim 1 , further comprising an electrically conducting backing disposed along and in electrical contact with a surface of the first actuator, wherein one or both of the first actuator or the backing is electrically connected to the first electrode. 
     
     
         3 . The shape-morphing system of  claim 2 , wherein the surface of the first actuator is bonded to the conducting backing to restrict the contraction or expansion of the first actuator in a direction parallel to the surface. 
     
     
         4 . The shape-morphing system of  claim 3 , wherein the first actuator is configured to contract or expand in a direction perpendicular to the surface. 
     
     
         5 . The shape-morphing system of  claim 1 , wherein the first electroactive ionic polymer is selected to expand or contract in a predetermined direction. 
     
     
         6 . The shape-morphing system of  claim 5 , wherein the actuator has an area and a transverse thickness and the first electroactive ionic polymer is selected to expand or contract the thickness of the actuator. 
     
     
         7 . The shape-morphing system of  claim 1 , wherein the shape-morphing system further comprises a fluid reservoir in fluidic communication with the first electroactive ionic polymer and connected to the second electrode; 
     
     
         8 . The shape-morphing system of  claim 7 , wherein the fluid reservoir comprises a fluid absorption pad or an open cell foam for containing the fluid. 
     
     
         9 . The shape-morphing system of  claim 1 , wherein the ionically conductive fluid is an aqueous solution of a salt. 
     
     
         10 . The shape-morphing system of  claim 1 , further comprising a second actuator comprising a second electroactive ionic polymer, said second actuator electrically connected to the second electrode and spaced apart from and in fluidic communication with the first electroactive ionic polymer, wherein the first and second electroactive ionic polymers are the same or different. 
     
     
         11 . The shape-morphing system of  claim 10 , wherein the first electroactive ionic polymer is selected to expand and the second electroactive ionic polymer is selected to contract along predetermined directions on application of an electrical potential to the first and second electrodes. 
     
     
         12 . The shape-morphing system of  claim 10 , wherein the first electroactive ionic polymer is selected to contract and the second electroactive ionic polymer is selected to expand along predetermined directions on application of an electrical potential to the first and second electrodes. 
     
     
         13 . The shape-morphing system of  claim 1 , wherein the first actuator is in a shape selected from the group consisting of sheet, pad, sphere, cylinder, cone, pyramid, prism, spheroid ellipse, ellipsoid, rectangular prism, toroid, parallelepiped, rhombic prism and a combination thereof. 
     
     
         14 . The shape-morphing system of  claim 1 , wherein the first actuator comprises one or more electroactive ionic polymer sheets. 
     
     
         15 . The shape-morphing system of  claim 14 , wherein each electroactive ionic polymer sheet is in electrical contact with a conductive layer electrically connected to the first electrode. 
     
     
         16 . The shape-morphing system of  claim 14 , wherein the conductive layer is made from a material selected from the group consisting of metal, carbon, and a combination thereof. 
     
     
         17 . The shape-morphing system of  claim 10 , wherein the second electroactive ionic polymer is selected from the group consisting of polymethacrylic acid, poly2-hydroxyethyl methacrylate, poly(vinyl alcohol), ionized poly(acrylamide), poly(acrylic acid), poly(acrylic acid)-co-(poly(acrylamide), poly(2-acrylamide-2-methyl-1-propane sulfonic acid), poly(methacrylic acid), poly(styrene sulfonic acid), quarternized poly(4-vinyl pyridinium chloride), poly(vinylbenzyltrimethyl ammonium chloride), sulfonated poly(styrene-b-ethylene-co-butylene-b-styrene), sulfonated poly(styrene), a cross-linked polymer thereof, and a combination thereof. 
     
     
         18 . The shape-morphing system of  claim 1 , wherein the first electroactive ionic polymer is cross-linked with one or more cross-linking polymer agents each selected from the group consisting of a dimethacrylate based cross-linking agent with a polymeric chain comprising poly(dimethylsiloxane) (PDMS), a dimethacrylate based cross-linking agent with a polymeric chain comprising poly(ethylene glycol), an ethylene glycol dimethacrylate, 1,1,1-trimethylolpropane trimethacrylate, and a combination thereof. 
     
     
         19 . The shape-morphing system of  claim 1 , wherein the first electroactive ionic polymer is cross-linked with one or more elastomeric cross-linking polymer agents. 
     
     
         20 . The shape-morphing system of  claim 1 , wherein the first electroactive ionic polymer is cross-linked with a first dimethacrylate based cross-linking agent with a polymeric chain comprising a poly(dimethylsiloxane) (PDMS). 
     
     
         21 . The shape-morphing system of  claim 20 , wherein the first dimethacrylate based cross-linking agent with a polymeric chain comprising the poly(dimethylsiloxane) (PDMS) is a dimethacrylate terminated PDMS selected from the group consisting of methacryloxypropyl-terminated PDMS, methacryloxybutyl-terminated PDMS, and a combination thereof. 
     
     
         22 . The shape-morphing system of  claim 1 , wherein the first electroactive ionic polymer is cross-linked with a first dimethacrylate based cross-linking agent with a polymeric chain comprising a poly(dimethylsiloxane) (PDMS) and a second crossing linking polymeric agent different from the first cross-linking polymeric agent. 
     
     
         23 . The shape-morphing system of  claim 22 , wherein the second cross-linking agent is selected from the group consisting of a dimethacrylate based cross-linking agent with a poly(ethylene glycol) chain, an ethylene glycol dimethacrylate, 1,1,1-trimethylolpropane trimethacrylate, and a combination thereof. 
     
     
         24 . The shape-morphing system of  claim 1 , wherein the first and/or second electrodes are flexible, bendable or stretchable electrodes. 
     
     
         25 . The shape-morphing system of  claim 1 , wherein the first and/or second electrodes are spiral-shaped or spring-shaped. 
     
     
         26 . The shape-morphing system of  claim 1 , wherein the first and/or second electrodes are made from a material selected from the group consisting of metal, carbon, other conductive materials, and a combination thereof. 
     
     
         27 . The shape-morphing system of  claim 1 , further comprising an electroconductivity-enhancing material in ionic communication with the first electroactive ionic polymer. 
     
     
         28 . The shape-morphing system of  claim 27 , wherein the electroconductivity-enhancing material is selected from the group consisting of solvent, electrolyte solution, electrolyte gel formulation, carbon particles, conductive fibers, preceding weaves, preceding felts, preceding nano-particles, preceding nanotubes, metal ions, salt, and a combination thereof. 
     
     
         29 . The shape-morphing system of  claim 1 , further comprising a power source. 
     
     
         30 . The shape-morphing system of  claim 29 , wherein the power source is a rechargeable or non-rechargeable battery pack. 
     
     
         31 . The shape-morphing system of  claim 1 , wherein the shape-morphing system is in a form selected from the group consisting of fibers, bulk, slabs, bundles, and combinations thereof. 
     
     
         32 . The shape-morphing system of  claim 1 , configured for filling a void between the first actuator and a target element. 
     
     
         33 . The shape-morphing system of  claim 1 , configured for securing or engaging a target element. 
     
     
         34 . A liner for securing a limb in a prosthetic device or a prosthetic socket comprising:
 a flexible layer configured to surround a limb of a patient or conform to the inside circumference of a prosthesis; and   at least one shape-morphing system of  claim 1  embedded in the flexible layer and configured to secure or engage a limb of a patient.   
     
     
         35 . The liner or prosthetic socket of  claim 34 , wherein the flexible layer is made of silicone. 
     
     
         36 . The liner or prosthetic socket of  claim 34 , wherein the liner or prosthetic socket comprises a plurality of the shape-morphing systems of  claim 1  embedded in the flexible layer; wherein the shape-morphing systems are fluidically isolated from each other and arranged around the limb of a patient to secure the limb. 
     
     
         37 . The liner or prosthetic socket of  claim 34 , wherein the prosthesis has a hard body and upon the application of an electrical potential to the first electrode, the first actuator is configured to expand against the hard body towards the limb of the patient. 
     
     
         38 . The liner or prosthetic socket of  claim 34 , further comprises a control unit configured to receive or measure the impedance and/or the pressure of the first electroactive ionic polymer. 
     
     
         39 . The liner or prosthetic socket of  claim 38 , wherein the control unit automatically adjusts the voltage of the first electrode to adjust the pressure of the first electroactive ionic polymer. 
     
     
         40 . The liner or prosthetic socket of  claim 39 , wherein the control unit is configured to adjust the pressure to a pre-determined value or a pre-set value. 
     
     
         41 . The liner or prosthetic socket of  claim 34 , wherein the shape-morphing system is configured to be a sensor. 
     
     
         42 . The liner or prosthetic socket of  claim 41 , wherein the sensor is a pressure sensor. 
     
     
         43 . The liner or prosthetic socket of  claim 42 , wherein the pressure sensor is configured to provide feedback for adjusting the expansion or contraction of the first electroactive ionic polymer. 
     
     
         44 . An actuation device comprising one or more of the shape-morphing systems of  claim 1 , wherein upon the application of an electrical potential to the first electrode, the first electroactive ionic polymer is configured to expand or contract to generate an actuation force to result in a movement of the first actuator to move from a first position to a second position. 
     
     
         45 . A method of operating a prosthesis, comprising:
 providing a prosthesis having a hard body;   providing the liner or prosthetic socket of  claim 34 ,   providing an electrical potential to the first electrode to contract the first electroactive ionic polymer to adjust the fit of the prosthesis to a patient's limb; or   expand the first electroactive ionic polymer material against the hard body towards the limb of the patient and secure the limb.   
     
     
         46 . The method of  claim 45 , wherein the first electroactive ionic polymer is subjected to a voltage of less than about 1.23 V. 
     
     
         47 . The method of  claim 46 , wherein the first electroactive ionic polymer is configured to contract when subjected to the voltage and is configured to expand when the electric polarity of voltage is reversed. 
     
     
         48 . The method of  claim 46 , further comprising measuring or receiving the pressure of the first electroactive ionic polymer through a control unit. 
     
     
         49 . The method of  claim 48 , further comprising automatically adjusting the voltage to maintain the pressure to a pre-determined or pre-set value. 
     
     
         50 . The method of  claim 45 , wherein the first electroactive ionic polymer is subjected to a voltage of from about 1.23 V to about 12 V, from about 1.5 V to about 6 V, from about 1.5 V to about 3 V, from about 3 V to about 5 V, or from about 5 V to about 6 V. 
     
     
         51 . The method of  claim 50 , wherein the first electroactive ionic polymer is configured to contract when subjected to the voltage and is configured to expand when the electric polarity of voltage is reversed. 
     
     
         52 . The method of  claim 50 , further comprising measuring or receiving the pressure of the first electroactive ionic polymer through a control unit. 
     
     
         53 . The method of  claim 52 , further comprising automatically adjusting the voltage to maintain the pressure to a pre-determined or pre-set value. 
     
     
         54 . A sensor comprising the shape-morphing system of  claim 1 . 
     
     
         55 . The sensor of  claim 54 , wherein the sensor is configured to be a pressure sensor. 
     
     
         56 . The sensor of  claim 55 , wherein the pressure sensor is configured to provide feedback for adjusting the expansion or contraction of the first electroactive ionic polymer.