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1. EP3007742 - ELECTROACTIVE ACTUATORS

Note: Text based on automatic Optical Character Recognition processes. Please use the PDF version for legal matters

Claims

1. An actuator (10) comprising:

an inner tubular structure (12);

an outer tubular structure (13, 14) surrounding the inner tubular structure (12) and comprising a plurality of layers of a dielectric elastomeric material (13) and a tubular elastic support structure (14), the elastic support structure (14) configured to maintain a pre-stress in the layers of the dielectric elastomeric material (13),

wherein the outer tubular structure (14) is configured to contract in a radial direction around the inner tubular structure (12) upon application of an actuation voltage signal across the dielectric elastomeric material layers (13).


  2. The actuator (10) of claim 1 wherein the tubular elastic support structure (14) comprises a plurality of layers alternating with one or more of the plurality of layers of the dielectric elastomeric material (13).
  3. The actuator (10) of claim 1 or claim 2 wherein the tubular elastic support structure (14) comprises an auxetic structure configured such that a ratio between expansion in the circumferential direction and contraction in the axial direction of the tubular elastic support structure when unconstrained is zero or negative.
  4. The actuator (10) of any preceding claim wherein the inner tubular structure (12) is a braided tubular structure.
  5. An implantable device (60) comprising the actuator (10) according to any preceding claim and an electronic controller (61) configured to apply the actuation voltage signal to the dielectric elastomeric material layers (13).
  6. The implantable device (60) of claim 5 wherein the device (60) is a cardiac assist device, the actuator (10) being configured to be implanted as an intra-aortic pump.
  7. The implantable device (60) of claim 5 or claim 6 wherein the actuator (10) comprises electromagnetic shielding layers on inner and outer sides of the plurality of layers of the dielectric elastomeric material (13).
  8. A method of fabricating an actuator (10) according to any of claims 1 to 4, the method comprising the steps of:

i) applying (73) a layer of a dielectric elastomeric material (33) to a substrate (31);

ii) stretching (74) the layer of dielectric elastomeric material (33) to apply a pre-stress;

iii) applying (76) an electrode layer (38) to a surface of the layer of dielectric elastomeric material (33);

iv) applying (79) a layer of an elastic support structure (40) over the layer of dielectric elastomeric material (33) while the layer is stretched; and

v) relaxing (81) the layer of dielectric elastomeric material (33) and elastic support structure (40).


  9. The method of claim 8 wherein steps i) to iii) are repeated to build up a plurality of layers of the dielectric elastomeric material (33) prior to applying the elastic support structure (40), the method further comprising relaxing a current layer of dielectric elastomeric material (33) before applying a subsequent layer.
  10. The method of claim 8 or claim 9 wherein steps i) to v) are repeated to build up an actuator structure comprising layers of the elastic support structure (40) alternating with one or more layers of the dielectric elastomeric material (33) and associated electrodes (38).
  11. The method of any one of claims 8 to 10 wherein the layers (33, 38, 40) are applied over an expandable substrate (31), expansion of the substrate (31) providing the pre-stress to each layer of dielectric elastomeric material (33).
  12. The method of any of claims 8 to 11 wherein the layer of dielectric elastomeric material (33) is applied by a spray deposition process.
  13. The method of any of claims 8 to 12 wherein the elastic support structure (40) is applied by a three dimensional printing process.
  14. The method of claim 11 wherein the layers (33, 38, 40) form a tubular structure around the expandable substrate (31).
  15. The method of claim 14 wherein the expandable substrate comprises an inflatable balloon (31).