Actuated thrombectomy device

Abstract

To provide a new mechanical thrombectomy device which improves both the effectiveness of an operation and the good outcome of a patient.SOLUTION: The tip 101 at the distal end of the catheter 100 is designed to vibrate vigorously to break up the thrombus. The broken thrombus is aspirated directly into the catheter to avoid "coking". Unlike minimally invasive surgical devices in which access to organs to be resected is achieved through small incisions formed at convenient locations, access to locations within the vascular space is often achieved via long catheters having a flexibility equal to or greater than the length 100cm. An electroactive polymer (EAP) tip at the distal end actuates vibrations from the proximal end of the catheter that break up the thrombus without transmitting mechanical work along substantially the entire length of the catheter.SELECTED DRAWING: Figure 2A

Description

[Technical Field]

[0001] The present invention relates to medical devices enabled by electroactive polymers ("EAPs", e.g., piezoelectric polymers). In particular, the present invention relates to EAP-based surgical instruments for thrombectomy. [Background technology]

[0002] Heart attacks, pulmonary embolism, and strokes are examples of diseases caused by intravascular clots that form or travel to a specific location and clog blood vessels. These acute conditions are treated with both pharmaceutical and mechanical procedures known as "mechanical thrombectomy." For example, Figure 1A shows a stent retriever (e.g., Medtronic Neurovascular's Solitaire X) being used to mechanically retrieve a clot. As another example, Figure 1B shows the removal of a clot by direct aspiration using a catheter (e.g., the Penumbra® system available from Penumbra, Inc., Alameda, California). Each of these techniques can be used alone or in combination with each other. Unfortunately, the success rate of these procedures is low, especially in the case of stroke, with clots typically being removed in only 40–50% of attempts. Therefore, there is a need to improve both the effectiveness of surgery and positive patient outcomes.

[0003] In mechanical thrombectomy procedures, access to the thrombus is typically achieved using a catheter approximately 100 cm long that is threaded through a tortuous path through the vasculature. At the end of the procedure, the catheter is withdrawn in the reverse direction along the same path. During aspiration, the thrombus frequently becomes lodged at the tip of the catheter, preventing aspiration into the catheter. As a result, the thrombus often breaks apart during withdrawal, leading to either (i) a return to its original location, a condition known as "Embolism Distal Territory (EDT)," or (ii) migration to a new location, a condition known as "Embolism New Territory (ENT)."

[0004] Current trends call for clot removal devices to access more distal locations within the vasculature. However, typical mechanical clot removal devices are too bulky to track through vessels smaller than 2 mm in diameter. Similarly, aspiration catheters are limited by their size. As the diameter of aspiration catheters decreases to fit into narrower vessels, the force the aspirator exerts on a clot rapidly decreases at a given aspiration pressure.

[0005] Therefore, there is a long-felt need for new mechanical thrombectomy devices that overcome the limitations of the prior art devices mentioned above. Summary of the Invention [Means for solving the problem]

[0006] According to one embodiment of the present invention, a catheter includes: (a) a proximal end configured to connect to drive electronics to receive one or more electrical signals; (b) a distal end having a tip with an electroactive polymer actuator configured to undergo oscillatory motion in response to the electrical signals; and (c) a shaft connected to the proximal end, the shaft including wiring for transmitting electrical signals between the proximal and distal ends. The electroactive polymer actuator comprises a material including one or more of vinylidene fluoride (VDF), trifluoroethylene (TrFE), 1,1-chlorofluoroethylene (CFE), and chlorotrifluoroethylene (CTFE). For example, the electroactive polymer actuator comprises a material including one or more of P(VDF-TrFE-CTFE) and P(VDF-TrFE-CFE). When the electrical signal provides an electric field of 20 to 200 volts / μmm, the electroactive polymer actuator exhibits an electrical distortion of greater than 3%. The oscillatory motion has a frequency substantially tuned to the resonant frequency of the tip.

[0007] In one embodiment, the shaft has a non-conductive braid or coil on which wiring is provided, the non-conductive braid or coil being made of polytetrafluoroethylene (PTFE) or polyetheretherketone (PEEK), and the distal end further has an opening for aspirating thrombus that has been broken up by the vibrational motion.

[0008] According to one embodiment of the present invention, an electroactive polymer actuator includes a plurality of capacitors, each of which includes an electroactive polymer layer disposed between a first electrode and a second electrode. The electroactive polymer layer has a thickness of 2.0 to 20.0 μm and is formed by dip-coating in a solution of an electroactive polymer dissolved in a polar solvent (e.g., diethylformamide (DMF) or methyl ethyl ketone (MEK)). The electrodes are formed by sputtering, dip-coating, pad printing, or spray-coating using a conductive electroink.

[0009] According to another embodiment of the invention, the first and second electrodes are braided to form coaxially spaced coils, each formed from fine wire having a diameter of 0.0127 to 0.0254 mm (0.5 to 1.0 mils (i.e., thousandths of an inch)). Alternatively, the first and second electrodes may be formed from conductive wire in a triaxial braid pattern.

[0010] According to yet another embodiment of the present invention, the electroactive polymer actuator is one of many integrated actuators arranged in a three-dimensional array.

[0011] The present invention is better understood from the following detailed description considered in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0012] [Figure 1A] FIG. 1 shows a stent retriever being used to mechanically retrieve a thrombus. [Figure 1B] Illustrates removal of a thrombus by direct aspiration through a catheter. [Figure 2A] FIG. 1 is a top view showing a vibratable tip 101 ("actuator") and catheter shaft 104 at the distal end of a catheter 100, according to one embodiment of the present invention. [Figure 2B] 2B is a cross-sectional view across the cross section of FIG. 2A showing the electrode layer 108 and electroactive polymer layer (EAP layer 109) of the actuator (tip section 101) at the distal end of the catheter 100. FIG. [Figure 3] 1 illustrates (conceptually) an inner coil 201 at the distal end of a catheter 100 connected to a return electrode 106b in the catheter shaft 104, according to one embodiment of the present invention. [Figure 4A] 4 shows a tri-axe wire 401 in a tri-axe wire braid pattern 400. FIG. [Figure 4B] FIG. 1 illustrates first and second sets of electrodes formed from Tri-Axe wires in an actuator (tip section 101) at the distal end of a catheter 100, according to one embodiment of the present invention. [Figure 5A] A diagram showing a commercially available EAP actuator. [Figure 5B] FIG. 1 is a cross-sectional view of a vibratable tip 101 according to an embodiment of the present invention. [Figure 5C] FIG. 1 is an axial view of a vibratable tip 101 according to an embodiment of the present invention. [Figure 6A] 6A-6C illustrate one method for forming an actuator 600 according to one embodiment of the present invention. [Figure 6B] 6A-6C illustrate one method for forming an actuator 600, according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention provides an aspiration catheter with a distal tip that vibrates violently to disrupt thrombi. The disrupted thrombi are aspirated directly into the catheter to avoid "corking." Unlike minimally invasive surgical devices, where access to the organ to be resected is achieved through a small, conveniently located incision, access to a location within the vascular space is often achieved through a long, flexible catheter, often 100 cm or longer. An electroactive polymer (EAP) at the distal tip activates thrombus-disrupting vibrations from the proximal end of the catheter without transmitting mechanical action along substantially the entire length of the catheter. Suitable electroactive polymers include various combinations of vinylidene fluoride (VDF), trifluoroethylene (TrFE), 1,1-chlorofluoroethylene (CFE), and chlorotrifluoroethylene (CTFE). For example, the terpolymers P(VDF-TrFE-CTFE) and P(VDF-TrFE-CFE) are commercially available from Piezotech (a subsidiary of Arkema SA, Paris, France). These terpolymers, which have various electroactive properties, exhibit large electrical distortions (>3%) under electric fields of 20-200 V / μm (e.g., about 50 V / μm).

[0014] FIG. 2A is a top view of the vibratable tip 101 and catheter shaft 104 at the distal end of a catheter 100, according to one embodiment of the present invention. The vibratable tip 101 may itself be an actuator or may include one or more actuators, each capable of electrically controlled movement. The catheter 100 has a proximal end (not shown) watertightly connected to an electronic driver circuit for receiving an electrical signal (e.g., 20-200 Hz) optimized for the resonant frequency of the vibratable tip 101 at the distal end of the catheter 100, making it suitable for both disrupting thrombus and aspirating thrombus debris by suction. For intended operation, the electrical signal has an amplitude of, for example, 50.0-250.0 volts, with or without a DC offset.

[0015] The catheter shaft 104 may be of conventional mechanical design, for example, having an inner layer of polytetrafluoroethylene (PTFE) in the form of a braid or coil, which provides mechanical integrity and kink resistance for the catheter shaft 104. The PTFE inner layer may be surrounded by an outer layer of a reflowable material (e.g., Pebax®, which has a durometer that varies over the length of the catheter shaft 104). Additionally, the catheter shaft 104 houses both an active electrode 106a and a return electrode 106b, which are electrically isolated from each other and extend along the entire length of the catheter shaft 104. These electrodes are formed from any suitable conductive wire. Such wire may be embedded in a non-conductive braid or coil (e.g., constructed from polyetheretherketone (PEEK)) that extends along the entire length of the catheter 100. These braids or coils are commercially available in various patterns from, for example, Steeger USA, Inc., US Biodesign, Inc., and Admedes, Inc. Alternatively, it may be an all-metal braid with electrically insulated wires for the active electrode 106a and return electrode 106b. However, embedding the electrodes in a non-conductive braid or coil is preferred to avoid short circuits. Purely for purposes of illustration, only the active electrode 106a and return electrode 106b are shown in FIG. 1, although any suitable number of active and return electrodes may be used.

[0016] The vibratory tip 101 at the distal end of the catheter 100 is configured to engage the thrombus. The vibratory tip 101 may have a flat or angled tip shape to maximize the opening for suction of the thrombus. EAP layers are embedded within the vibratory tip 101. As an electric field crosses each EAP layer, it is strained (note that a larger electric field achieves a larger strain, but the relationship between strain and electric field is generally nonlinear). As shown in FIG. 2A, each EAP layer is disposed between a thin, flexible layer of electrodes (e.g., between electrode 102 and electrode 103 below electrode 102). Electrodes 102 and 103 are electrically connected to either active electrode 106a or return electrode 106b, respectively. In this manner, movement occurs only at the vibratory tip 101 at the distal end of the catheter 100; no energy is lost when moving the active electrode 106a and return electrode 106b within the catheter shaft 104. In one embodiment, each EAP layer is 2 to 20 μm thick.

[0017] According to one embodiment of the present invention, each EAP layer is formed by dip coating. For example, the vibrable tip 101 at the distal end of the catheter 100 is immersed in a solution of EAP in a polar solvent such as diethylformamide (DMF) or methyl ethyl ketone (MEK). In this manner, a coaxial 20-200 μm thick EAP layer is formed within the vibrable tip 101 by successive immersions. After forming each EAP layer, an electrode layer is formed on the exposed surface of the EAP layer by, for example, sputtering (e.g., gold or aluminum), dip coating (e.g., silver-embedded urethane), pad printing, or spray coating using a conductive electrical ink or a particle-free metal complex conductive ink (e.g., conductive inks available from Electroninks or LiquidX). The process of forming a combination of an EAP layer and an electrode layer may be repeated multiple times. The electrode layer thus formed is connected to either the active electrode 106a or the return electrode 106b, with electrodes of opposite polarity formed on both sides of the EAP layer, effectively forming a capacitor. Figure 2B is a cross-sectional view across the cross-section of Figure 2A showing the electrode layer 108 and EAP layer 109 of the vibrable tip 101. Depending on the desired mechanical properties, each EAP layer may have any thickness. Additional non-EAP layers (not shown) may also be included.

[0018] According to another embodiment of the present invention, the electrode layer in the vibrable tip 101 at the distal end of the catheter 100 may be braided to form two coaxially spaced coils to avoid electrical shorting. Figure 3 is a diagram (conceptually) illustrating an inner coil 201 in the vibrable tip 101 at the distal end of the catheter 100 connected to a return electrode 106b in the catheter shaft 104, according to one embodiment of the present invention. The inner coil 201 is coaxially positioned with and surrounded by an outer coil 202 connected to the active electrode 106a. Figure 3 is a conceptual diagram, purely for illustrative purposes, showing six turns of a single wire in the inner coil 201. In a practical implementation, a braided coil with more turns and more wire is envisioned. For example, braided coils of up to 288 wires, sized up to (0.0005" x 0.002") for flat wire and 0.0005" for round wire (available, for example, from Steeger USA, see https: / / steegerusa.corn / product / medical-braiders). The EAP can cover and fill the space between the inner coil 201 and outer coil 202, and when a voltage difference is established between the coils, an electric field is generated in that space. Each coil is formed from thin wire having a diameter of 0.0127 to 0.0254 mm (0.5 to 1.0 mils (i.e., 1 / 1000 of an inch)). This embodiment has the advantages of requiring only a single application or dip of the EAP, reducing manufacturing time and simplifying electrode connections by using wires already installed throughout the catheter 100.

[0019] According to a third embodiment of the present invention, electrodes of the vibrable tip 101 are provided at the distal end of the catheter 100 by "tri-axe" wires in a tri-axe braid pattern. FIG. 4A shows tri-axe wire 401 in tri-axe wire braid pattern 400. A tri-axe wire braid pattern consists of a single wire (e.g., wire 401) routed straight and enclosed within a tri-axe braid pattern (e.g., tri-axe wire braid pattern 400). As shown in FIG. 4A, in tri-axe wire braid pattern 400, the tri-axe wire itself (e.g., tri-axe wire 401) is not braided. Such tri-axe wires can be used up to half their maximum load capacity, providing many "tri-axe" wires that can be integrated and used as electrodes. Generally, the greater the number and smaller the size of the wires, the better the electromechanical response. Figure 4B shows a first and second set of electrodes formed from Tri-Axe wire within the vibrable tip 101 at the distal end of the catheter 100, according to one embodiment of the present invention. The remainder of the Tri-Axe braid pattern is omitted from Figure 4B. The first and second sets of electrodes are each provided by round or flat wires as thin as 0.0127 mm (0.5 mils), allowing for up to 288 electrodes.

[0020] In the above embodiments, the electrodes and one or more EAP layers are provided separately. However, according to one embodiment of the present invention, commercially available EMP actuators ("integrated actuators") exist. These integrated actuators have distinctive electromechanical properties and are wound into any desired shape for deployment within the vibratable tip 101 at the distal end of the catheter 100. Thus, one or more integrated actuators are incorporated into the vibratable tip 101 at the distal end of the catheter 100 (e.g., as a three-dimensional array of integrated actuators). Figure 5A illustrates a commercially available EAP actuator. Each such actuator may function at the same or different frequencies or patterns.

[0021] Each of the above embodiments is driven by drive electronics. If the vibrable tip 101 is designed with multiple independently controlled actuators, two or more waveforms are provided to each of the active electrodes. In most of the above embodiments, the drive circuitry may provide a drive waveform of, for example, 50.0 to 250.0 volts (peak-to-peak). The drive waveform may be a sine wave, a triangular wave, a square wave, or any desired waveform (preferably a square wave) to provide maximum acceleration or vibration. For example, a Microchip HV 56020 or Microchip HV 56022 may be used to provide a suitable drive circuit.

[0022] According to another embodiment of the present invention, the vibratory tip 101 of the catheter 100 has an actuator formed from two or more layers of EAP film wrapped around a recess in a cylindrical shaft. Figures 5B and 5C show cross-sectional and axial views, respectively, of the vibratory tip 101 according to this embodiment of the present invention. As shown in Figure 5B, the catheter 100 has a lumen 601 extending along the axis of the catheter 100 for substantially its entire length. Figure 5B is a cross-sectional view through the longitudinal axis of the catheter 100, showing a portion of the catheter shaft 104 and the vibratory tip 101. The catheter material 602 within the catheter shaft 104 extends into the vibratory tip 101. The diameter of the catheter material 602 is reduced over a 2.0-5.0 mm portion along the longitudinal axis of the vibratory tip 101, creating a recess in the vibratory tip 101. A tubular actuator 600 having a circular cross-section (i.e., cylindrical with a hollow core) is attached to, wrapped around, or otherwise integrated into the recess. FIG. 5C is an axial view in an orthogonal plane cross section through the vibratable tip 101 showing that the actuator surrounds the catheter material 602, which in turn surrounds the lumen 601.

[0023] 6A and 6B illustrate one method for forming an actuator 600 according to one embodiment of the present invention. As shown in FIG. 6A, EAP film 604 is layered on top of EAP film 605, offset by a small distance (d), to form a composite sheet 603. One side of each film is coated with a conductive material (e.g., a metal coating such as a copper film). In composite sheet 603, EAP film 604 includes EAP material 604a and conductive coating 604b. Similarly, EAP film 605 includes EAP material 605a and conductive coating 605b. EAP material 604a and EAP material 605a may each be, for example, a terpolymer. As shown in FIG. 6A, conductive coating 604b and conductive coating 605b are disposed on each other's surfaces in composite sheet 603, thereby providing an EAP layer consisting of EAP material 604a and EAP material 605a between conductive coating 604b and conductive coating 605b in a parallel-plate capacitor configuration. In this configuration, conductive coating 604b and conductive coating 605b are disposed on the exterior of composite sheet 603, thereby functioning as electrodes for composite sheet 603 and enabling composite sheet 603 to receive signals via electrical leads that may be provided within lumen 601. The electrical leads electrically connect composite sheet 603 to electronic or electrical circuitry provided at distal end 105 of catheter 100.

[0024] To form actuator 600, composite sheet 603 is wrapped multiple times around cylindrical mandrel 607, as shown in FIG. 6B. In these FIGS. 6A and 6B, the thickness of composite sheet 603 is exaggerated to clearly show EAP material 604a and EAP material 605a and conductive coating 604b and conductive coating 605b. In actual implementation, composite sheet 603 is made very thin (e.g., a few tenths of a micron (μmm) or a few millimeters) so that composite sheet 603 can be wrapped multiple times around mandrel 607, providing a large surface area (i.e., a tightly wrapped configuration) for improved control of the electromechanical response of composite sheet 603. Mandrel 607 is then withdrawn, leaving actuator 600 in a cylindrical shape with a hollow core. Actuator 600 is then attached to a recess in vibrable tip 101 of catheter 100. Electrical leads can then be attached to the exposed electrical coating (conductive coating 604b) and electrical coating (conductive coating 605b) to electrically connect the composite film (composite sheet 603) to control circuitry at the distal end of catheter 100. The offset (distance d) of composite sheet 603 facilitates attachment.

[0025] When a voltage is applied to the conductive layer (conductive coating 604b) and conductive layer (conductive coating 605b) of composite sheet 603 in actuator 600, the EAP material in EAP material 604a and EAP material 605a volumetrically expands or contracts (i.e., strain response), providing a circumferential strain response for actuator 600. As a result, a series of electrical pulses (e.g., square waves) at an appropriate frequency (e.g., 20.0-500.0 Hz) generates the desired circumferential vibration in vibrable tip 101. Note that in actuator 600, a waveform alternating between -50.0 volts and 50.0 volts provides substantially the same electromechanical response for any given frequency as a waveform alternating between 0.0 volts and 50.0 volts, so the polarity orientation has little effect on device performance. Any high-slew-rate waveform that provides a rapidly changing electric field across conductive coating 504b and conductive coating 504d may also be used.

[0026] The above detailed description is provided to illustrate particular embodiments of the present invention and is not intended to limit the invention. Numerous variations and modifications are possible within the scope of the present invention, which is set forth in the appended claims.

Claims

1. A catheter comprising: a proximal end configured to connect to drive electronics to receive one or more electrical signals; a distal end having a tip portion comprising an electroactive polymer actuator configured to undergo oscillatory motion in response to the electrical signals, the electroactive polymer actuator formed as a hollow cylindrical structure, the electroactive polymer actuator having a plurality of overlapping capacitors, each of the capacitors having an electroactive polymer layer disposed between a first electrode and a second electrode and configured to receive one of the electrical signals, the electroactive polymer layer of each of the capacitors undergoing a volumetric deformation in response to the received electrical signal, thereby contributing to the oscillatory motion; a tubular shaft coupled between the proximal end and the distal end, the shaft including wiring for transmitting the electrical signal between the proximal end and the distal end, the shaft comprising a catheter material having an extension that extends further to form the distal end, the extension having a recess formed in its outer periphery, the electroactive polymer actuator disposed within the recess.

2. 10. The catheter of claim 1, wherein the electroactive polymer layers each comprise a material including one or more of vinylidene fluoride (VDF), trifluoroethylene (TrFE), 1,1-chlorofluoroethylene (CFE), and chlorotrifluoroethylene (CTFE).

3. 10. The catheter of claim 1, wherein the electroactive polymer layers each comprise a material including one or more of vinylidene fluoride (VDF), trifluoroethylene (TrFE), 1,1-chlorofluoroethylene (CFE), and chlorotrifluoroethylene (CTFE).

4. 10. The catheter of claim 1, wherein the electroactive polymer layers each exhibit an electrostrain of greater than 3% when the electrical signal provides an electric field of 20 to 200 volts / μm.

5. The catheter of claim 1 , wherein the oscillatory motion has a frequency that is substantially tuned to a resonant frequency of the tip.

6. The catheter of claim 1 , wherein one of the electrical signals has an amplitude between 50 volts and 250 volts.

7. The catheter of claim 6 , wherein one of the electrical signals has a DC offset.

8. The catheter of claim 1 , wherein the shaft has a non-conductive braid or coil on which the wiring is provided.

9. 9. The catheter of claim 8, wherein the non-conductive braid or coil is formed from polytetrafluoroethylene (PTFE) or polyetheretherketone (PEEK).

10. The catheter of claim 1 , wherein the tip of the distal end further has an opening for sucking in thrombus that is broken up by the vibrational motion.

11. The catheter of claim 10 , configured to be connected to a suction device for providing pressure to aspirate the thrombus.

12. The catheter of claim 1 , wherein each of the electroactive polymer layers has a thickness of 2.0 to 20.0 μm.

13. 12. The catheter of claim 11, wherein the electroactive polymer layer comprises the first electrode and the second electrode, each formed by a dip-coating process in a solution of the electroactive polymer dissolved in a polar solvent.

14. 14. The catheter of claim 13, wherein the polar solvent comprises one or more of diethylformamide (DMF) and methyl ethyl ketone (MEK).

15. 10. The catheter of claim 1, wherein each of the first electrode and the second electrode comprises a material formed by one of the following processes: sputtering, dip coating, pad printing, or spray coating with a conductive electrical ink.

16. The catheter of claim 1 , wherein the first electrode and the second electrode are braided to form a spaced apart, coaxially arranged coil.

17. 17. The catheter of claim 16, wherein each of the coils is formed from a thin wire having a diameter of 0.0127 to 0.0254 mm (0.5 to 1.0 mil).

18. The catheter of claim 1 , wherein the first electrode and the second electrode each have conductive wires in a triaxial braid pattern.

19. The catheter of claim 1 , wherein the electroactive polymer actuator is one of a plurality of electromagnetic pulse (EMP) actuators arranged in a three-dimensional array.

20. The catheter of claim 1 , wherein one of the electrical signals is a sine wave.

21. The catheter of claim 1 , wherein one of the electrical signals comprises a square wave.

22. The catheter of claim 1 , wherein each of the electroactive polymer layers comprises two or more layers of electroactive polymer (EAP) material in a tightly wound roll.

23. 23. The catheter of claim 22, wherein each layer of electroactive polymer (EAP) material is coated on one side with an electrically conductive material.

24. 24. The catheter of claim 23, wherein the conductive material comprises a metal.

25. 24. The catheter of claim 23, wherein each capacitor has a wound parallel plate capacitor structure and includes electrodes formed by a coating process of the conductive material.

26. 26. The catheter of claim 25, wherein the electroactive polymer actuator provides a vibrational response when driven by the electrical signal at a frequency between 20.0 and 500.0 Hz.

27. 26. The catheter of claim 25, wherein the electrical signal has a high slew rate waveform.

28. 26. The catheter of claim 25, wherein the waveform has a peak-to-peak amplitude of 50.0 to 250.0 volts.

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