USE OF A THERMOSET SHAPE MEMORY MATERIAL IN A THREAD-LIKE VARIABLE STIFFNESS DEVICE AND THREAD-LIKE VARIABLE STIFFNESS DEVICE

Abstract

A thread-like variable stiffness device including an elongate shaft, the shaft includes a polymeric material, and a heat conducting device configured to exchange heat with the polymeric material to cause a phase transition of the polymeric material conferring a variable stiffness to the thread-like device, wherein the polymeric material is a thermoset shape memory material.

Claims

1. A thread-like variable stiffness device comprising an elongate shaft, the shaft comprising a polymeric material, and a heat conducting device configured to exchange heat with the polymeric material to cause a phase transition of the polymeric material conferring a variable stiffness to the thread-like device, the polymeric material being a thermoset shape memory material, wherein the thermoset shape memory material is a mercaptoester polyurethane.

2. The device according to claim 1, wherein the mercaptoester polyurethane is prepared at least by a component A comprising a compound having at least two alkene groups and a component B comprising a compound having at least two thiol groups.

3. The device according to claim 2, wherein component A comprises a compound selected from the group consisting of triallyl cyanurate, triallyl thiocyanurate, trimethallyl thiocyanurate, 2-hydroxyethyl cyanurate tris(acrylate), 2-hydroxyethyl cyanurate tris(methacrylate), 2-hydroxyethyl cyanurate tris(allyl carbonate), 2-hydroxyethyl cyanurate tris(methallyl carbonate), triallyl isocyanurate, triallyl isothiocyanurate, trimethallyl isothiocyanurate, 2-hydroxyethyl isocyanurate tris(acrylate), 2-hydroxyethyl isocyanurate tris(methacrylate), 2-hydroxyethyl isocyanurate tris(allyl carbonate) and 2-hydroxyethyl isocyanurate tris(methallyl carbonate).

4. The device according to claim 2, wherein component B comprises a compound selected from the group consisting of pentaerythritol tetrakis (3-mercaptopropionate), ethoxylated pentaerythritol tetrakis(3-mercaptopropionate), thiol-functionalized polydimethyl siloxanes, thiol-terminated polysulfides, dipentaerythritol hexakis thioglycolate, trimethylolpropane tris(2-mercaptoacetate), pentaerythritol tetrakis(2-mercaptoacetate), tripentaerythritol octakis thioglycollate, mercaptan-terminated propoxylated glycerol, ethyleneglycol bis(3-mercaptopropionate) and trimethylolpropane tris(thioglycolate).

5. The device according to claim 1, wherein the thermoset shape memory material additionally comprises an electrically conductive filler.

6. The device according to claim 1, wherein the shaft comprises a thermoset material body made of the thermoset shape memory material and extending along a longitudinal axis of the shaft, and a heat conducting member of the heat conducting device, said heat conducting member extending along at least a portion of the thermoset material body and being designed to exchange heat with the thermoset material body.

7. The device according to claim 6, wherein the heat conducting member is at least partially embedded in the thermoset material body.

8. The device according to claim 6, wherein the shaft includes a conduit extending therethrough from a proximal end to a distal end of the shaft for the passage of a tool.

9. The device according to claim 8, wherein an information transfer device is arranged in the conduit to transmit information between the proximal end and the distal end of the shaft.

10. The device according to claim 6, wherein the device comprises a magnet arranged at its distal end to provide means to control the distal end of the device, when it is submitted to a magnetic field.

11. The device according to claim 6, wherein the thermoset material body is designed as a solid tube extending along a longitudinal axis of the shaft.

12. The device according to claim 5, wherein the shaft comprises a thermoset material body made of the thermoset shape memory material and extending along a longitudinal axis of the shaft, and a heat conducting member of the heat conducting device, said heat conducting member extending along at least a portion of the thermoset material body and being designed to exchange heat with the thermoset material body, and wherein the heat conducting member comprises a first electrode and a second electrode arranged across the thermoset material body and is configured to allow the passage of an electric current between them in the thermoset material body.

13. The device according to claim 12, wherein, viewed in the longitudinal direction, the first electrode is arranged in a proximal end region and the second electrode is arranged in a distal end region of the thermoset material body.

14. (canceled)

Description

DESCRIPTION OF THE FIGURES

[0072] FIG. 1 shows a schematic perspective of a thread-like variable stiffness device according to the invention;

[0073] FIG. 2 shows a schematic cross-section along the line II-II of the thread-like variable stiffness device according to FIG. 1;

[0074] FIG. 3 shows a schematic cross-section of a further thread-like variable stiffness device according to an embodiment of the invention;

[0075] FIG. 4 shows a schematic partial cross-section side view of a distal end region of a further thread-like variable stiffness device according to the invention; and

[0076] FIG. 5 shows a schematic cross-section side view of a distal end region of a further thread-like variable stiffness device according to the invention.

[0077] FIG. 6 shows a schematic diagram of stiffness against temperature of an example of NOA.

[0078] A thread-like variable stiffness device according to the invention is configured as a catheter 10 as illustrated in FIG. 1.

[0079] The catheter 10 has an at least approximately rotationally symmetrical structure in relation to its longitudinal axis with a narrow circular section in proportion to its length. It comprises an elongate shaft 20, whose longitudinal axis corresponds to the longitudinal axis of the catheter 10, having a circular section and extending over the whole length of the catheter 10. The catheter 10 has a proximal end 30 on the side of an operator, a distal end 40 on the side of the operation site and a distal end region 50 arranged at its distal end 40.

[0080] A magnet 60 is provided in the end region 50 to provide a means to control the distal end 40, when it is submitted to a magnetic field.

[0081] In the present embodiment, the catheter 10 comprises two variable stiffness shaft segments 70 and 80 extending directly one after the other in the longitudinal direction, i.e. without rigid shaft segments between them, and their stiffness can be controlled independently from each other, as illustrated by the different radius of curvature R1 and R2 of the variable stiffness shaft segments 70 and 80. For this purpose, as illustrated in FIG. 2, the variable stiffness shaft segments 70 and 80 comprise a thermoset material body 90 extending along the longitudinal direction of the variable stiffness shaft segments 70 and 80. The thermoset material body 90 has essentially a tubular form centered on the longitudinal axis of the variable stiffness shaft segment 70.

[0082] Further, the shaft 20 comprises a protective layer 92 surrounding the thermoset material body 90 and a conduit 94 extending inside the shaft 20 from the proximal end 30 to the distal end 40 for the passage of a tool, said conduit 94 being centered on the longitudinal axis of the shaft. However, it is also conceivable to provide for an outermost biocompatible layer of the catheter by choosing an adequate thermoset shape memory material. In this case, the protective layer 92, especially a biocompatible protective layer, is not necessary so that the outer diameter can be further reduced.

[0083] Further, the catheter 10 comprises a heat conducting device designed to exchange heat with the thermoset shape memory material in a controlled manner. In the embodiment of FIG. 2, the heat conducting device comprises each time a conducting member 100 in the respective variable stiffness shaft segments 70 and 80, said conducting member 100 extending along the longitudinal direction. Presently, the conducting member 100 is designed as a conductive coil 100 which allows heating by Joule effect of the thermoset shape memory material, when electric current passes through the coil 100. As result of the heat exchange, the thermoset shape memory material undergoes a phase transition when its temperature passes through the glass transition temperature and the stiffness of the device varies from stiff to flexible or from flexible to stiff depending on the direction of the temperature change.

[0084] In a further catheter embodiment illustrated in FIG. 3, the thermoset material body 90 is designed as a solid tube 90 having a circular section and extending parallel to the longitudinal direction. The catheter further comprises a heat conducting device having a conducting member in the form of a conductive wire 100 allowing heating by Joule effect of the thermoset shape memory material, when electric current passes through the conductive wire 100.

[0085] Further, the shaft 20 comprises a protective layer 92 surrounding the thermoset material body 90 and a conduit 94 extending inside the shaft 20. The conduit 94 extends parallel to the longitudinal direction therethrough from the proximal end to the distal end of the shaft for the passage of a tool. In the embodiment of FIG. 3 a tool 115 in the form of an optic fiber 115 is embedded in the protective layer 92 and schematically illustrated. It can be used to transfer information between the proximal end and the distal end, for example from a camera or a sensor located at the distal end and used for medical application like diagnostic or mapping.

[0086] In a similar embodiment not represented, a lumen extending inside the shaft 20 from a proximal end 30 to a distal end 40 of the shaft can be provided in the thermoset material body instead of the conductive wire 100. The lumen is part of a cooling loop designed to cool the thermoset shape memory material. In this case, a cooling fluid is delivered from the proximal end in the lumen to a variable stiffness shaft segment and returned to the proximal end.

[0087] A further catheter according to the invention whose distal end region 50 only is illustrated in FIG. 4 has a particularly simple structure, allowing a simple and economical manufacturing. The catheter comprises a shaft 20 made essentially of biocompatible thermoset shape memory material so that no outermost layer made of a different material is required. In addition, the shaft includes a conduit 94 extending therethrough from the proximal end (no represented) to the distal end 40 of the shaft 20 for the passage of a tool, wherein the conduit 94 has a circular cross section and is centered on the longitudinal axis of the shaft. A permanent magnet 60 is arranged at the distal end 40 to provide means to control the distal end 40, when it is submitted to a magnetic field. The catheter further comprises a heat conducting device having a conducting member in the form of a conductive coil 100 in a variable stiffness shaft segment 80 located in the end region 50. The conductive coil 100 allows heating by Joule effect of the thermoset shape memory material, when electric current passes through the conductive coil 100.

[0088] The distal end region 50 of a further catheter 10 according to the invention is illustrated in FIG. 5. The catheter 10 is made of thermoset shape memory material comprising an electrically conductive filler comprising graphene and neodymium. Consequently, the flow of an electric current through the thermoset shape memory material is possible.

[0089] In the exemplary embodiment, the catheter 10 comprises at least a variable stiffness shaft segment 70 and a further variable stiffness shaft segment 80 extending one after the other in the longitudinal direction, viewed from the distal to the proximal end of the catheter, with a rigid shaft segment 82 arranged between the variable stiffness shaft segments 70 and the further variable stiffness shaft segment 80. A further rigid shaft segment 72 extends from the proximal end of the variable stiffness shaft segment 70 to the proximal end of the catheter.

[0090] The stiffness of the variable stiffness shaft segments 70 and 80 can be controlled independently from each other. In this embodiment, the rigid shaft segment 82 and the further rigid shaft segment 72 are also made of thermoset shape memory material comprising the electrically conductive filler. However, their stiffness is not varied during the use of the device.

[0091] The variable stiffness shaft segments 70 and the further variable stiffness shaft segment 80 comprise each time a thermoset material body 90a, 90 extending along the longitudinal direction and having substantially a tubular form centered on the longitudinal axis.

[0092] Further, the catheter comprises a heat conducting device designed to exchange heat with the thermoset shape memory material in a controlled manner. In the embodiment of FIG. 5, the heat conducting device comprises a heat conducting member arranged each time in the thermoset material body 90a, 90 of the variable stiffness shaft segments 70 and the further variable stiffness shaft segment 80, respectively.

[0093] Presently, each heat conducting member comprises a first electrode 120, 120a and a second electrode 122, 122a arranged across the thermoset material body 90, 90a respectively. The first electrode 120 is arranged in a proximal end region and the second electrode 122 is arranged in a distal end region of the further variable stiffness shaft segment 80, viewed in the longitudinal direction. The first electrode 120a and the second electrode 122a are arranged similarly in the variable stiffness shaft segment 70.

[0094] The first electrode and second electrode are configured to allow the passage of an electric current between them in the thermoset material body. For the sake of clarity, the connecting electrical wires extending each time from the first electrode and the second electrode to the proximal end of catheter are not represented in FIG. 5. As a result of the current flow between the first electrode and the second electrode in each thermoset material body 90, 90a, the thermoset shape memory material can be heated by Joule effect in the variable stiffness shaft segments 70 and the further variable stiffness shaft segment 80.

[0095] A permanent magnet 60 is arranged at the distal end 40 to provide a means to control the distal end 40, when it is submitted to a magnetic field.

[0096] The catheter further comprises a temperature sensor in the form of a control coil 130, 130a in each shaft segment to measure the temperature in each variable stiffness shaft segments 70, 80. The temperature measurement can rely on the resistivity change upon temperature change of the control coil.

[0097] Experimental Results

[0098] All samples are prepared according to the following recipe. The mixture of NOA86H and filler is prepared by mixing the two components with a stirrer and a sonicator tip. The mixture is injected into a mold and cured with UV-A light (10 min) and heat (oven at 100° C. for 30 min). UV-A light is used to cure the surface and avoid chemical interactions with the mold surface while heat is used to cure the bulk material.

[0099] Table 1 shows the effect of graphene and NdFeB fillers on the Youngs modulus (above and below the Tg), the Tg, the thermal conductivity, and the electrical conductivity.

[0100] The effect of fillers on the glass transition temperature and the mechanical properties were characterized with DMA (Dynamic mechanical analysis) measurements on cylindrical shaft segments. The addition of graphene and NdFeB particles increases the mechanical strength both in the rigid (−10° C.) and flexible state (100° C.). NdFeB, compared to Graphene, leads to a higher increase in mechanical properties which leads to a decreased stiffness variation.

[0101] The glass transition temperature is decreasing with increasing filler concentration. The effect on the glass transition temperature is comparable for both fillers.

[0102] The thermal and electrical conductivity were measured on a cubic sample. The thermal conductivity is increasing with filler concentration (NdFeB and graphene), however the increase is approx. doubled with graphene compared to neodymium.

[0103] An effect on the electrical conductivity is visible only in graphene/NOA samples. A concentration of higher or equal to 3 w % of graphene allows for direct joule heating. No increase in electrical conductivity in the NdFeB/NOA samples could be observed due to oxidation on the NdFeB surface.

[0104] The magnetic properties (e.g. remanence) are increasing linearly with NdFeB concentration. Hysteresis curves were measured in a VSM (Vibrating-sample magnetometry) on cylindrical shaft segments.

TABLE-US-00001 TABLE 1 NOA NOA w9% C NOA w40% NdFeB E solid [MPa] 2864 4200 4452 E soft [MPa] 29 45 59 Tg [° C.] 75 51 53 Lambda [W/mK] 0.176 0.399 0.261 Sigma [Sm] 0 1.05 0 Remanence [Oe] 0 0 27

[0105] FIG. 6 shows a diagram of stiffness against temperature of an example of NOA with or without filler. The curve can be characterized as follows. The first flat section relates to a temperature increase in the rigid state. The adjacent quick decrease in stiffness is related to the stiffness transition from a glassy to a rubbery state. The glass transition temperature is characterized as the point with maximum gradient. The curve flattens with increasing temperature in the rubbery state.

LIST REFERENCE SIGNS

[0106] thread-like variable stiffness device, catheter 10 [0107] elongate shaft 20 [0108] proximal end 30 [0109] distal end 40 [0110] distal end region 50 [0111] magnet 60 [0112] variable stiffness shaft segments 70, 80 [0113] thermoset material body 90, 90a [0114] radius of curvature R1, R2 (of the shaft segments 70, 80) [0115] protective layer 92 [0116] conduit 94 [0117] conductive coil 100 [0118] optic fiber 115 [0119] first electrode 120, 120a [0120] second electrode 122, 122a [0121] control coil 130, 130a