Abstract
A device comprising a bendable fibre comprising a fibre axis, a thermally expandable material and a resistance wire extending longitudinally through the fibre spaced apart from the fibre axis; wherein, in use, electrical power applied to the resistance wire causes the temperature of the resistance wire to increase.
Claims
1. A device comprising a bendable fibre comprising a fibre axis, a thermally expandable material and a resistance wire extending longitudinally through the fibre spaced apart from the fibre axis; wherein, in use, electrical power applied to the resistance wire causes the temperature of the resistance wire to increase.
2. A device according to claim 1, wherein the thermally expandable material has a coefficient of linear thermal expansion between 0.2?10.sup.?4 and 10?10.sup.?4 K.sup.?1.
3. A device according to claim 1, wherein the resistance wire comprises a material having a resistivity between 1?10.sup.?7 and 5?10.sup.?6 ?.Math.m at 20? C.
4. A device according to claim 1, wherein the fibre further comprises one or more voids extending longitudinally at least partially through the fibre.
5. A device according to claim 4, wherein one of the voids forms a central lumen.
6. A device according to claim 4, wherein one of the voids forms an air gap between the resistance wire and an outer surface of the fibre.
7. A device according to claim 4, wherein one of the voids forms a fluid channel diametrically opposite the resistance wire.
8. A device according to claim 1, further comprising an electrical conductor operatively connected to the resistance wire for applying electrical power to the resistance wire.
9. A device according to claim 8, wherein the electrical conductor comprises a conducting wire extending longitudinally through the fibre spaced apart from the resistance wire, which conducting wire is electrically connectable to the resistance wire.
10. A device according to claim 8, wherein the electrical conductor comprises a first conducting wire and a second conducting wire, each extending longitudinally through the fibre spaced apart from the resistance wire and one another, and the first and second conducting wires are each electrically connectable to the resistance wire.
11. A device according to claim 1, wherein a portion of the resistance wire comprises an etched surface.
12. A device according to claim 1, wherein a portion of the fibre comprises a plurality of circumferential grooves positioned incrementally along the portion.
13. A device according to claim 1, wherein a portion of the fibre has a smaller diameter than the rest of the fibre.
14. A device according to claim 1, wherein the fibre comprises a first portion comprising a first thermally expandable material and a second portion comprising a second thermally expandable material, the first portion being more bendable than the second portion and/or the first thermally expandable material having a higher coefficient of linear thermal expansion than the second thermally expandable material.
15. A device according to claim 1, further comprising a restrictive sheath adapted to receive the at least part of the fibre and restrict deflection of any part of the fibre received within the restrictive sheath.
16. A device according to claim 1, wherein the fibre further comprises a plurality of resistance wires, each extending longitudinally through the fibre and spaced apart from the fibre axis.
17. A method of manufacturing a bendable fibre comprising a fibre axis, thermally expandable material and a resistance wire spaced apart from the fibre axis using a draw apparatus, the method comprising the steps of: providing a preform comprising a preform axis, a thermally expandable material and a resistance wire channel extending longitudinally through the preform spaced apart from the preform axis, to the draw apparatus; heating a portion of the preform; drawing the heated portion of the preform in order to form a fibre; and feeding a resistance wire into the resistance wire channel during or after the draw such that the resistance wire is positioned within the resistance wire channel of the fibre spaced apart from the fibre axis.
18. A method according to claim 17, wherein the preform further comprises a first conducting wire channel, the method further comprising the further step of: feeding a first conducting wire into the first conducting wire channel during or after the draw.
19. A method according to claim 18, wherein the preform further comprises a second conducting wire channel, the method further comprising the further step of: feeding a second conducting wire into the second conducting wire channel during or after the draw.
20. A method according to claim 17 comprising the further step of etching the surface of the resistance wire prior to feeding it into the resistance wire channel.
21. A method according to claim 17 comprising the further step of laser profiling a plurality of circumferential grooves positioned incrementally along a portion of the fibre.
22. A method according to claim 17, wherein the step of drawing the heated portion of the preform comprises varying the speed at which the heated portion of the preform is drawn in order to vary the diameter of the resulting fibre along its length.
23. A method according to claim 17, wherein the preform comprises a plurality of resistance wire channels, and the step of feeding the resistance wire into the resistance wire channel comprises feeding each of the plurality of resistance wires into a respective one of the plurality of resistance wire channels.
Description
[0071] The invention will now be described by way of example only with reference to the accompanying drawings in which:
[0072] FIG. 1a is a cross-sectional schematic representation of a fibre according to an embodiment of the first aspect of the invention.
[0073] FIG. 1b is a schematic representation showing deflection of the fibre shown in FIG. 1a.
[0074] FIG. 2a is a cross-sectional schematic representation of a fibre according to a further embodiment of the first aspect of the invention.
[0075] FIG. 2b is a schematic representation showing deflection possible of the fibre shown in FIG. 2a.
[0076] FIG. 3a is a cross-sectional schematic representation of a fibre according to a further embodiment of the first aspect of the invention.
[0077] FIG. 3b is a schematic representation showing deflection of the fibre shown in FIG. 3a.
[0078] FIG. 4a is a cross-sectional schematic representation of a fibre according to a further embodiment of the first aspect of the invention.
[0079] FIG. 4b is a schematic representation showing deflection of the fibre shown in FIG. 4a.
[0080] FIG. 5a is a cross-sectional schematic representation of a fibre according to a further embodiment of the first aspect of the invention.
[0081] FIG. 5b is a schematic representation showing deflection of the fibre shown in FIG. 5a.
[0082] FIG. 6a is a cross-sectional schematic representation of a fibre according to a further embodiment of the first aspect of the invention.
[0083] FIG. 6b is a schematic representation of actuation possible of the fibre shown in FIG. 6a.
[0084] FIGS. 7, 8 and 9 are cross-sectional schematic representations of different fibres according to further embodiments of the first aspect of the invention.
[0085] FIGS. 10a and 10b are schematic representation of a fibre according to a further embodiment of the first aspect of the invention.
[0086] FIG. 11 is schematic representation of a fibre, according to a further embodiment of the first aspect of the invention, that has been laser profiled to provide circumferential grooves.
[0087] FIG. 12 is a schematic representation of a fibre, according to a further embodiment of the first aspect of the invention, comprising a plurality of resistance wires connected to a circuit board.
[0088] FIGS. 13 and 14 are graphical representations of deflections that may be performed by a fibre according to an embodiment of the first aspect of the invention.
[0089] FIG. 15 is a schematic representation of a method drawing a fibre according to an embodiment of the second aspect of the invention.
[0090] FIG. 16 is a schematic representation of a draw apparatus for carrying out the method shown in FIG. 15.
[0091] FIG. 17 is a close-up view of a feed apparatus similar to that forming part of the draw apparatus shown in FIG. 16.
[0092] FIG. 18 is a cross-sectional schematic representation of a preform to be drawn into a fibre comprising a plurality of resistance wires in accordance with an embodiment of the invention.
[0093] FIG. 19 is a schematic representation of the preform shown in FIG. 18, being drawn to form a fibre.
[0094] FIG. 20 is a cross-sectional view of the preform of FIG. 19.
[0095] FIG. 21 is a cross-sectional schematic representation of a fibre according to a further embodiment of the first aspect of the invention.
[0096] FIGS. 22 is a graphical representation of deflections that may be performed by a fibre according to an embodiment of the first aspect of the invention.
[0097] FIG. 23 is a cross-sectional schematic representation of a fibre according to a further embodiment of the first aspect of the invention.
[0098] FIG. 24 is a cross-sectional schematic representation of a fibre according to a further embodiment of the first aspect of the invention.
[0099] FIG. 25 shows graphical representations of deflections and temperature gradients that may be exhibited by a fibre according to an embodiment of the first aspect of the invention.
[0100] Referring initially to FIGS. 1a and 1b, a bendable fibre according to an embodiment of the first aspect of the invention is defined generally by the reference numeral 102. The fibre 102 comprises a resistance wire 8, thermally expandable material 9, a void 40 and a conducting wire 44 spaced slightly apart from the resistance wire 8. In this embodiment of the invention the fibre 102 has a deactivated configuration 150, which is straight and an activated configuration 151, which is curved in the opposite direction of the resistance wire 8.
[0101] The resistance wire 8 may have a high electrical resistance meaning that an electrical power applied to the resistance wire 8 may cause it to increase in temperature. When the resistance wire 8 is heated it may cause the thermally expandable material 9 proximal to the resistance wire 8 to also heat such that a temperature gradient forms across the cross-section of the fibre. Due to the material forming the fibre 102 being thermally expandable, the thermally expandable material 9 proximal to the resistance wire 8 may expand while thermally expandable material 9 further away from the resistance wire 8 will expand less or not at all.
[0102] In FIG. 1b, the fibre 102 holds the deactivated configuration 150 when power is not supplied to the resistance wire 8. However, when electrical power is supplied to the resistance wire 8, the resistance wire 8 increases in temperature, thereby heating the surrounding thermally expandable material 9 and causing that material to expand. The asymmetric expansion of the fibre 102 causes a deflection of the fibre 102 towards the activated configuration 151. When the power is turned off again, the fibre 102 will return to its deactivated configuration 150. This deflection process is repeatable and is also adjustable based on the amount of electrical power applied to the resistance wire. The greater the electrical power applied, the hotter the resistance wire will get and the greater the degree of deflection that will be caused. This allows precise control of a tip of the fibre without disadvantages associated with known tendon driven devices such as friction and backlash.
[0103] The conducting wire 44 may close the electrical circuit required such that electrical current may flow through the resistance wire 8. For example, an electrical power source at a proximal end of the fibre may be connectable to both the resistance wire 8 and the conducting wire 44 while, at a distal end of the fibre, the resistance wire 8 may be connected to the conducting wire 44. Accordingly, electrical current may flow from the electrical power source, along the resistance wire 8 in a first direction through the fibre 102 and then along the conducting wire 44 in a second direction through the fibre 102 opposite to the first direction. In some embodiments of the invention the conducting wire 44 may have a lower resistance than the resistance wire 8 so that only the resistance wire increases substantially in temperature. In other embodiments of the invention the conducting wire 44 may have a resistance similar or equal to the resistance wire 8 so that an electrical current passing through the conducting wire 44 causes it to increase in temperature similarly to the resistance wire 8. This may be beneficial if the resistance wire 8 and the conducting wire 44 are positioned close to one another within the cross-section of the fibre 102, as is the case in FIGS. 1a and 1b, because the deflection of the fibre caused by heat expansion of material close to the wires may be amplified.
[0104] The void 40 may extend through part or all of the fibre and may be any suitable shape. In this embodiment of the invention the void 40 is a central lumen with a substantially circular cross-section extending the length of the fibre 102. The void 40 may increase the distance that heat must radiate through the thermally expandable material 9 in order to travel from the resistance wire 8 to an opposite side of fibre 102. The time required for heat to radiate through the fibre 102 is therefore increased such that a greater temperature gradient may be maintained across the cross-section of the fibre. In other words, the void 40 acts to thermally insulate one side of the fibre 102 from the opposite side so that a greater difference in temperature across the cross-section of the fibre 102 may be achieved. The greater the difference in temperature of the thermally expandable material 9 in two opposite parts of the fibre, the greater the resulting deflection of the fibre 102 may be.
[0105] In use, the void/central lumen 40 may act as a working channel through which a surgeon may deploy surgical instruments such as probes or catheters. For example, the fibre 102 could form part of an endoscope in which an optical fibre extends through the central lumen 40. In this example, the fibre 102 may be electrothermally actuated to scan an area of in-vivo or ex-vivo tissue sample. The images acquired by the distal lens of the optical fibre may then be mosaiced to build up a larger image of the tissue sample covering the entire scan area. Another example application is rapid evaporative ionisation mass spectrometry (REIMS) in which a surgical laser fibre extends through the central lumen 40 and a suction tube is attached to the fibre 102. In this example, the fibre 102 may be electrothermally actuated to scan the laser over an area of in-vivo or ex-vivo tissue sample. As the laser evaporates the tissue sample, the suction tube would aspirate the aerosol which would then be thermally ionised for analysis by a mass spectrometer to create a data map for the entre scan area.
[0106] Referring now to FIGS. 2a and 2b, a fibre 202 according to a further embodiment of the first aspect of the invention is similar to the fibre 102 shown in FIGS. 1a and 1b. However, fibre 202 comprises two resistance wires 8a, 8b positioned in opposite sides of the fibre 202 and two conducting wires 44a, 44b each positioned close to a respective resistance wire 8a, 8b. In this embodiment of the invention each resistance wire 8a, 8b may be caused to increase in temperature, by applying an electrical current, in order to heat and expand the surrounding thermally expandable material 9 of the fibre 202.
[0107] In FIG. 2b, the fibre 202 holds a deactivated configuration 250 when power is not supplied to either resistance wire 8a, 8b. However, when power is supplied to one of the resistance wires 8a, the resistance wire 8a increases in temperature, heats the surrounding thermally expandable material 9 and thereby causes expansion of that material surrounding the resistance wire 8a. The partial expansion of the fibre 202 causes a deflection of the fibre 202 towards a first activated configuration 251 (away from the resistance wire 8a). When the power is turned off again, the fibre 202 will return to its neutral configuration 250. Further, when power is supplied to the other of the resistance wires 8b, the resistance wire 8b causes expansion of material on the other side of the fibre 202 and therefore deflection of the fibre 202 towards a first configuration 252 (away from the resistance wire 8b). The deflection processes are each repeatable in any desired sequence, and the degree of deflection in either direction is adjustable based on the amount of electrical power applied to either resistance wire 8a, 8b. The fibre 202 further comprises a first conducting wire 44a and a first conducting wire 44b that may function similarly to the conducting wire 44 shown in FIGS. 8a and 8b with respect to the resistance wires 8a and 8b respectively.
[0108] Referring now to FIGS. 3a and 3b, a fibre 302 according to a further embodiment of the first aspect of the invention is similar to the fibre 202 shown in FIGS. 2a and 2b. However, fibre 302 comprises only a single conducting wire 44 which is positioned evenly between the resistance wires 8a, 8b. In this embodiment of the invention the deflection that may be achieved by providing electrical power to each resistance wire is similar to that achieved by the fibre 202 shown in FIG. 2b. However, here each resistance wire 8a, 8b may be connected to the single conducting wire 44 to form parallel circuits that may be activated independently of one another. In such embodiments of the invention it may be beneficial that the conducting wire 44 has a lower resistance than the resistance wires 8a, 8b so that it does not substantially increase in temperature (relative to the resistance wires 8a, 8b) and cause heat expansion that may affect the deflections achieved in either of the activated configurations 351, 352.
[0109] Referring now to FIGS. 4a and 4b a fibre 402 according to a further embodiment of the first aspect of the invention is similar to the fibre 202 shown in FIGS. 2a and 2b. However, fibre 402 comprises four resistance wires 8a, 8b, 8c, 8d spaced apart from one another and four conducting wires 44a, 44b, 44c, 44d each positioned close to a respective resistance wire 8a, 8b, 8c, 8d. In this embodiment of the invention each resistance wire 8a, 8b, 8c, 8d may be heated by applying an electrical current similarly to the resistance wires shown in FIGS. 1a to 3b.
[0110] In FIG. 4b, the fibre 402 holds a deactivated configuration 450 when power is not supplied to any of the resistance wires 8a, 8b, 8c, 8d. When power is supplied to one of the four resistance wires 8a, 8b, 8c, 8d the selected resistance wire is heated and causes expansion of the material of the fibre 402 which surrounds the selected resistance wire. The fibre 402 is thereby deflected in the direction away from the side of the fibre in which the selected resistance wire is positioned. For example, when power is supplied to only resistance wire 8a, the fibre 402 deflects to a first activated configuration 451. Powering only resistance wire 8b provides a second activated configuration 452, resistance wire 8c a third activated configuration 453 and resistance wire 8d a fourth activated configuration 454.
[0111] It is also possible to supply power to two resistance wires at the same time to provide further possible deflections of the fibre 402. For example, when power is supplied to the resistance wires 8a and 8b the fibre 402 deflects to a fifth activated configuration 455. Powering resistance wires 8b and 8c provides a sixth activated configuration 456, resistance wires 8c and 8d a seventh activated configuration 457 and resistance wires 8d and 8a an eighth activated configuration 458.
[0112] The deflection processes are each repeatable in any desired sequence and the degree of deflection towards each configuration is adjustable based on the amount of electrical power applied to one or two of the resistance wires 8a, 8b, 8c, 8d. The fibre 402 is therefore capable of a large range of precise deflections.
[0113] In use, the fibre 402 may form part of a device according to an embodiment of the first aspect of the invention with a surgical instrument attached to, or extending from, the tip of the fibre 402. The fibre 402 may act as an actuation mechanism to actuate the surgical instrument through a sequence of precise movements, as demonstrated in FIGS. 13 and 14. The fibre 402 has been demonstrated to provide sub-micron precision. The thermal expansion driven actuation may obviate flaws of tendon drive actuation mechanisms such as imprecision caused by friction and/or backlash. Further, the fibre 402 may have smaller cross-sectional dimensions than known tendon driven actuation mechanisms as there is no requirement for tendons, or other moving parts, to extend through the fibre 402. Use of the fibre 402 may therefore be less invasive than use of known actuation mechanisms for surgical instruments. Also, the fibre 402 is bendable and hence more compliant to its surroundings and less likely to cause harm to surrounding soft tissues than known actuation mechanisms with hard surfaces and edges.
[0114] The conducting wires 44a, 44b, 44c, 44d may each provide a closed loop for the current to return to an electrical power source having flowed along the associated resistance wire 8a, 8b, 8c, 8d. In some embodiments of the invention the conducting wires 44a, 44b, 44c, 44d may have a lower resistance than the resistance wires 8a, 8b, 8c, 8d so that only the resistance wire increases substantially in temperature. In other embodiments of the invention the conducting wires 44a, 44b, 44c, 44d may have a resistance similar or equal to the resistance wires 8a, 8b, 8c, 8d so that an electrical current passing through one of the conducting wires 44a, 44b, 44c, 44d causes it to increase in temperature similarly to the respective resistance wire 8a, 8b, 8c, 8d.
[0115] Referring now to FIGS. 5a and 5b, a fibre 502 according to a further embodiment of the first aspect of the invention is similar to the fibre 402 shown in FIGS. 4a and 4b. However, fibre 502 comprises only a single conducting wire 44. In this embodiment of the invention the deflection that may be achieved by applying a current to each resistance wire is similar to that achieved by the fibre 402 shown in FIG. 4b. However, here each resistance wire 8a, 8b, 8c, 8d may be connected to the single conducting wire 44 similarly to the embodiment of the invention shown in 3a and 3b. An advantage of this embodiment of the invention over that shown in FIGS. 4a and 4b is that fewer wires are required which may reduce manufacturing complexity and cost. However, control of such an embodiment may be more complicated compared to control of embodiments of the invention where each resistance wire has its own associated conducting wire.
[0116] Referring now to FIGS. 6a and 6b, a fibre 602 according to a further embodiment of the first aspect of the invention is similar to the fibres 402, 502 shown in FIGS. 4a to 5b. However, fibre 602 does not comprise a conducting wire. Instead, the plurality of resistance wires 8a, 8b, 8c, 8d may be electrically connected to one another at a distal end of the fibre. Therefore, rather than closed circuit loops being formed by a combination of a resistance wire and a conducting wire, they may be formed by a combination of two resistance wires. For example, electrical power may be selectively applied to flow along resistance wires 8a and 8b (the electrical current flowing out along resistance wire 8a and back along resistance wire 8b or vice versa) to cause the fibre 602 to deflect towards a first activated configuration 651 similarly to how the fibres 402 and 502 may be caused to deflect towards their respective fifth activated configurations 455, 555. Accordingly, powering resistance wires 8b and 8c provides a second activated configuration 652, resistance wires 8c and 8d a third activated configuration 653 and resistance wires 8d and 8a a fourth activated configuration 654.
[0117] An advantage of this embodiment of the invention is obviating the requirement for one or more conducting wires separate to the resistance wires. Instead, each resistance wire may act both as a resistance wire and a conducting wire. Fewer wires being required may reduce manufacturing complexity and cost. However, the range of control achievable with such an embodiment may be reduced in comparison to the embodiments shown in FIGS. 4a to 5b which have an equivalent number of resistance wires.
[0118] Referring now to FIG. 7, a fibre 702 according to a further embodiment of the first aspect of the invention is similar to the fibre 602 except that it comprises and additional four resistance wires 8e, 8f, 8g, 8h. The resistance wires are positioned in pairs: 8a and 8b, 8c and 8d, 8e and 8f, 8g and 8h. In use, power may be provided to a pair of resistance wires simultaneously (with the electrical current flowing out along one wire and back along the other wire) in order to generate a more acute deflection than may be possible if power was provided to only one resistance wire or to two resistance wires spaced further apart. In a sense, one wire in each pair of resistance wires acts as a conducting wire for the other wire in the pair similarly to the embodiment of the invention shown in FIGS. 4a and 4b.
[0119] Referring now to FIG. 8, a fibre 802 according to a further embodiment of the first aspect of the invention is similar to the fibre 602 except that it comprises a void 46 between each resistance wire 8a, 8b, 8c, 8d and the outer surface of the fibre 802 in addition to the void 40 extending centrally through the fibre 802. The voids 46 may be considered as air gaps between the resistance wires 8a, 8b, 8c, 8d and the outer surface of the fibre 802 rather than as the central lumen provided by the void 40.
[0120] Each void 40, 46 may act as a barrier to heat transmission through the fibre 802. In particular, each void 40, 46 may act to insulate regions of the fibre 802 proximal to the resistance wires 8a, 8b, 8c, 8d, reducing dissipation of heat and causing a greater increase of temperature in the thermally expandable material proximal to the resistance wires 8a, 8b, 8c and 8d. Facilitating a greater temperature increase may also facilitate greater expansion of material and therefore a more acute deflection of the fibre 802. Additionally, the voids/air gaps 46 may act to reduce the amount that the outer surface of the fibre 802 increases when it is deflected, which may be particularly advantageous if the fibre is used in minimally invasive surgery, for example, as the patient may be protected from high temperature material.
[0121] Referring now to FIG. 9, a fibre 902 according to a further embodiment of the first aspect of the invention combines the features of the fibre 802 shown in FIG. 8 and the fibre 802 shown in FIG. 8. That is, the fibre 902 comprises eight resistance wires positioned in pairs and voids/air gaps 46 between each pair of resistance wires and the outer surface of the fibre 902. The fibre 902 may therefore benefit from the advantages of both features.
[0122] For each of the fibres 602, 702, 802 and 902 a deflection caused by providing power to two resistance wires was simulated. Table 1, below, shows the minimum and maximum temperatures recorded in each fibre, the resulting maximum temperature difference across the cross-section of each fibre and the maximum fibre tip deflection recorded when simulating an actuation of each fibre. The results demonstrate that the incorporation of paired resistance wires in fibre 702 and the incorporation of voids/air gaps 46 in fibre 802 both increase the temperature difference that may be achieved within the fibres, which is representative of a greater temperature gradient across the fibre's cross-section. The greater variation in temperature causes a greater variation in expansion of the thermally expandable material in each fibre and hence a greater maximum fibre tip deflection. The effect is amplified in fibre 902 in which both paired resistance wires and voids/air gaps 46 are incorporated.
TABLE-US-00001 TABLE 1 Results from simulating an actuation in the fibres for a 3 cm long fibre 602, 702, 802 and 902. Minimum Maximum Temperature Maximum fibre Fibre temperature temperature difference tip deflection 602 57.17? C. 109.19? C. 52.02? C. 1.3484 mm 702 52.51? C. 131.23? C. 78.72? C. 1.4523 mm 802 57.93? C. 132.99? C. 75.06? C. 1.4521 mm 902 45.39? C. 153.53? C. 108.14? C. 1.5382 mm
[0123] Experimentally, for a longer fibre, a temperature difference of 10? C. across the cross-section of the fibre was sufficient to deflect the fibre tip 4 mm while maintaining the maximum fibre temperature below 70? C.
[0124] Referring now to FIGS. 10a and 10b, a fibre 1002, according to a further embodiment of the first aspect of the invention, comprises a resistance wire 8 (e.g. stainless steel wire) similarly to the embodiment shown in FIGS. 1a and 1b. However, rather than comprising a single conducting wire, the fibre 1002 comprises a first conducting wire 1044a (e.g. copper wire), a second conducting wire 1044b (e.g. copper wire) and two electrical connections 1045one that electrically connects the first conducting wire 1044a to the resistance wire 8 and another that electrically connects the resistance wire 8 to the second conducting wire 1044b. The electrical connections 1045 may be any suitable connector capable of conducting electricity, such as a solder or conductive epoxy/ink paste. Alternatively, the electrical connections 1045 may be formed by exposing the conducting wire 1044a or 1044b and resistance wire 8, twisting the relevant wires together, applying a conductive paint (e.g. silver paint) to the twisted wires and covering the painted wires with a conductive tape (e.g. copper tape). The conductive tape may then optionally be covered with an insulating tape (e.g. Kapton tape) to insulate the electrical connections 1045.
[0125] Accordingly an electrical circuit loop may be formed wherein an electrical current may flow along the first conducting wire 1044a in a first direction through the fibre 1002 and then along the resistance wire 1008 and the second conducting wire 1044b in a second direction through the fibre opposite to the first direction, as demonstrated by the electrical current line 1080 in FIG. 10b.
[0126] In use, when electrical power is applied to the circuit formed by the resistance wire 1008 and first and second conducting wires 1044a, 1044b, electrical current may flow through a portion of the resistance wire 1008 between the two electrical connections 1045 only. Hence only that portion of the resistance wire will increase in temperature due to its high resistance. Meanwhile, the rest of the resistance wire 1008 will exhibit minimal change in temperature as no electrical current will flow through it and the conducting wires 1044a, 1044b may also show relatively low change in temperature due to having lower electrical resistance. Accordingly, the temperature increase in the fibre 1002 will be localised to the thermally expandable material 9 around the heated portion of the resistance wire 1008 and resulting deflection of the fibre 1002 will be similarly localised.
[0127] Referring now to FIG. 11, a fibre 1102, according to a further embodiment of the first aspect of the invention, comprises a plurality of circumferential grooves 1160 positioned incrementally along a portion of the fibre 1102. The circumferential grooves 1160 may be provided by laser profiling the fibre 1102. The circumferential grooves 1160 reduce the stiffness of the fibre 1102 and therefore allow the fibre 1102 to bend further in response to expansion of part of the material forming the fibre 1102. FIG. 11 shows a comparison of the deflection possible with a laser profiled fibre, such as fibre 1102, against the deflection that may be provided by a fibre without laser profiling (such as fibre 402 shown in FIGS. 4a and 4b), despite the same amount of power being supplied.
[0128] In other embodiments of the invention, varying the degree of deflection achievable along the length of a fibre may be facilitated in a variety of different ways. For example, in embodiments of the invention, a portion of a resistance wire may comprise an etched surface that increases the electrical resistance through that portion of the fibre. Increasing the electrical resistance increases how hot that portion of the wire will become when electrical power is applied, increases the heating of the surrounding thermally expandable material and causes a greater degree of deflection. In embodiments of the invention, the diameter of the fibre may be varied along its length wherein thinner sections are more flexible and may therefore deflect more than thicker portions. In embodiments of the invention, the fibre may comprise two or more thermally expandable materials with varied material characteristics. For example, a portion of the fibre comprising a softer thermally expandable material will deflect more than a portion comprising a stiffer thermally expandable material. Also, portion of the fibre comprising a thermally expandable material with a greater coefficient of linear thermal expansion will deflect more than a portion comprising a thermally expandable material with a lower coefficient of linear thermal expansion.
[0129] Referring now to FIG. 12, a device 1200, according to an embodiment of the first aspect of the invention, comprises the fibre 602 (shown in FIGS. 6a and 6b) wherein the plurality of resistance wires 8a, 8b, 8c, 8d extends from a proximal end of the fibre 602. The device 1200 further comprises a circuit board 48 and an electrical connection 1245 positioned at the distal end of the fibre 602.
[0130] Each of the resistance wire 8a, 8b, 8c, 8d extending from the fibre 602 is connected to the circuit board 48 and is also connected to the other resistance wires via the electrical connection 1245, thereby creating a plurality of parallel electrical circuits.
[0131] The circuit board 48 may provide digital control of the resistance wires 8, providing electrical power to them in a variety of different combinations to generate desired deflections of the fibre 1202 similar to those shown in FIG. 6b, for example.
[0132] The electrical connect 1245 may be any suitable electrically conductive means for connecting the resistance wires 8a, 8b, 8c, 8d, such as solder of conductive ink paste for example.
[0133] Referring now to FIGS. 13 and 14, a fibre according to an embodiment of the invention comprising four or more resistance wires, such as any of those shown in FIGS. 4a to 12, may be capable of complex deflections. FIGS. 13 and 14 show simulated movements of a fibre tip caused by sequentially providing power to different combinations of resistance wires. In each Figure, the X and Y axes represent the amount of deflection of the fibre tip from a straight configuration, i.e. coordinates 0,0 would be recorded when the fibre is straight.
[0134] In particular FIG. 13 shows a circle 1300 drawn by the fibre tip that is approximately 5 mm in diameter. Meanwhile, FIG. 14 shows a line 1400 drawn by the fibre tip. In this case the fibre tip was actuated and caused to follow a guideline 1401 comprising seven horizontal lines 1.8 mm in length, spaced 0.3 mm apart and joined by vertical lines. FIG. 14 shows that the fibre tip was controlled accurately to within less than 0.1 mm of the guideline 1401.
[0135] A fibre capable of such complex and precise actuations may be particularly advantageous in the field of minimally invasive surgery wherein an end effector could be attached to the tip of a fibre and actuated in intricate patterns such as those demonstrated in FIGS. 13 and 14.
[0136] Referring now to FIG. 15, a method for drawing a fibre according to the second aspect of the invention is shown wherein the fibre is defined generally by the reference numeral 2. The fibre 2 is drawn from a preform 4 with a preform cross-section 5 wherein the preform is provided to a temperature-controlled apparatus 24 that comprises a pre-heating apparatus 12, a heating apparatus 14 and a quenching apparatus 16. The preform 4 is fed sequentially through the pre-heating apparatus 12 and the heating apparatus 14 in order to raise the temperature of a leading part of the preform 4 and provide a heated portion 15 of the preform 4 that is then suitable to be drawn. The speed of drawing of the fibre 2 may be controlled primarily by gravity or the control of the draw rate may be controlled by a draw apparatus.
[0137] In some embodiments of the invention, the preform is initially allowed to neck-down under gravity, after which the tip of the necked-down portion is cut off. Once the necked-down portion has been removed, the remaining drawn fibre may be connected to a capstan which may be used to draw the fibre. Control of the draw speed may be provided by the capstan or may be controlled by any other suitable apparatus. The heated portion 15 of the preform 4 which has been drawn into a fibre 2 is quenched in order to set the fibre shape. Quenching the fibre 2 may be achieved by removing the fibre 2 from the influence of the heating apparatus or, as shown in the example of FIG. 1, the fibre 2 may be cooled slowly to a temperature below the draw temperature by using the quenching apparatus 16. The quenching apparatus 16 may be a heater set to provide a temperature lower than the draw temperature but higher than room temperature, for example.
[0138] During the drawing process, the preform cross-section 5 is substantially maintained as the preform 4 transitions to the fibre 2 with a fibre cross-section 3. However the dimensions that traverse the fibre cross-section 3 are significantly smaller than those of the preform cross-section 5. It is therefore possible to provide a preform 4 with a complex cross-sectional design that is relatively straight forward to produce at a large scale and then draw the preform 4 to form the fibre 2 with the same cross-sectional design at a scale that might otherwise be difficult to produce due to its intricacy.
[0139] Referring now to FIG. 16, a draw apparatus 10 for drawing a fibre using the method represented in FIG. 1 is shown, wherein the draw apparatus 10 may be known as a draw tower. The draw apparatus 10 comprises a preform mount 20 and a temperature-controlled apparatus 24 that may be equivalent to the temperature-controlled apparatus 24 shown in FIG. 1. The draw apparatus further comprises a wire feed apparatus 30, in this embodiment of the invention the feed apparatus 30 comprises eight resistance wire feeders 32.
[0140] In this embodiment of the invention, a preform 4 is mounted in the draw apparatus 10 by way of the preform mount 20, which may be configured to receive preforms of differing sizes. During drawing of the preform 4 into a fibre, the preform 4 is lowered, by the draw apparatus 10, into the temperature-controlled apparatus 24 in order to provide heating and subsequent cooling of the preform 4 and resultant fibre.
[0141] Referring now to FIG. 17, a feed apparatus 1730 is similar to, and interchangeable with, the feed apparatus 30 shown in FIG. 16. In this embodiment of the invention the feed apparatus 1730 comprises four resistance wire feeders 32, although it is to be appreciated that a feed apparatus may comprise any suitable number of feeders and the feeders are not limited to being resistance wire feeders only (for example, one or more of the feeders may be conducting wire feeders). Each resistance wire feeder 32 comprises a resistance wire spool 34 that is rotatably attached to the resistance wire feeder 32 and may rotate to dispense a resistance wire 8. Each resistance wire 8 is dispensed and fed into a respective channel 6 of a preform 4. Each resistance wire spool 34 may be driven by a motor to dispense the corresponding resistance wire 8 at the required speed.
[0142] FIG. 18 shows a cross-section of the preform 4 which further illustrates each channel 6 and the resistance wire 8 fed into each channel 6. Before the preform 4 is drawn to form a fibre, the diameter of the channels 6 is much larger than the diameter of the resistance wires 8. For example, the channels 6 may have a diameter of 2.5 mm while the resistance wires may have an outer diameter of 50 ?m. Hence each resistance wire 8 is loose within its respective channel 6. The preform 4 also comprises a void 40 that extends centrally through the preform 4.
[0143] Referring now to FIGS. 19 and 20, a heated portion 15 of a preform 4 is shown being drawn to form a fibre 2. The preform 4, and the channels 6 within it, gradually become narrower in size. The drawing process is continued until a fibre with a desired diameter is formed wherein the diameter of each channel 6 is approximately equal to the outer diameter of each resistance wire, as shown in FIG. 20. For example, the preform may have a diameter of 40 mm and the resultant fibre may have a diameter of 1 mm, meanwhile the diameter of each channel may reduce from 2.5 mm to 50 ?m.
[0144] Once the fibre 2 is formed, one of the resistance wires 8 may be electrically connected to a voltage power source, causing the resistance wire 8 to be heated. The heated wire may increase the temperature of the surrounding material of the fibre, causing that material to expand. Due to the eccentricity of the resistance wires 8 in the cross-section of the fibre 2, a side of the fibre 2 comprising the heated resistance wire 8 expands while an opposite side of the fibre 2 (not comprising the heated resistance wire 8) maintains its normal length. As a result, the fibre 2 exhibits a deflection in the direction opposite to the expanded part of the fibre 2. The deflection can be varied by activating different combinations of the resistance wires 8, as is shown in the FIGS. 2a to 6b.
[0145] It has been found from experiments that when the resistance wires 8 (and conducting wires 44) are fed into the respective channels 6 during the draw, they can sometimes be attached to the expandable material in the formed fibre 2. This has the effect of restricting motion, and therefore displacement of the fibre 2, in subsequent use because the metal typically does not expand as much as the polymer. To address this issue, the diameter of the channels 6 in the preform 4 can be increased so that they have a larger diameter than the wires 8, 44 in the formed fibre 2 and the wires 8, 44 are held more loosely. It is also possible to feed the wires 8, 44 into the respective channels 6 after the preform 4 has been drawn.
[0146] FIG. 21 shows a fibre 2102 according to a further embodiment of the first aspect of the invention. This fibre 2102 is similar to those shown in FIGS. 4a and 7 except that it comprises three pairs of wires 8a-f instead of four. Each pair may include two resistance wires 8 as shown, or one resistance wire 8 and one conducting wire 44. By actuating each pair individually or in combination, the use of three pairs of wires 8a-f has been shown to enable displacement of the fibre 2102 in any radial direction. By removing the need for a fourth pair of wires 8g-h, therefore, this fibre 2102 may provide a more cost-effective option from a manufacturing perspective than those shown in FIGS. 4a and 7.
[0147] FIG. 22 shows the improved tip displacement that can be achieved when the wires 8, 44 are fed into the respective channels 6 after the preform 4 has been drawn into a fibre 2. This experiment was conducted using a fibre 2102 with the configuration shown in FIG. 21 and demonstrates that displacement of around 7.5 mm in each radial direction is possible.
[0148] FIG. 23 shows a fibre 2302 according to another embodiment of the first aspect of the invention. This fibre 2302 is similar to that shown in FIG. 21 except that each pair of wires has been replaced with a set of three wires. As shown, each set of wires comprises first 44a,c,e and second 44b,d,f conducting wires separated by a resistance wire 8a-c as per the embodiment of FIGS. 10a and 10b. This fibre 2302 therefore provides the additional technical advantage of localised heating and deflection.
[0149] FIG. 24 shows a fibre 2402 according to another embodiment of the first aspect of the invention. This fibre 2402 is similar to that shown in FIG. 21 except that it further comprises a plurality of voids 70 extending longitudinally at least partially through the fibre 2402. Each void 70 is positioned substantially diametrically opposite a corresponding pair of wires 8a-f and forms a fluid channel along a portion of the fibre 2402. The voids 70 enable a cooling fluid (e.g. a gas such as air, nitrogen or oxygen; or a liquid such as water) to be passed through the thermally expandable material 9 on the opposite side of the central lumen 40 from the corresponding pair of wires 8a-f. This has been found to increase the temperature gradient across the cross-section of the fibre 2402 and thus increase the range of deflection. Furthermore, because each pair of wires 8a-f has a corresponding void 70, the cooling fluid can be applied selectively to increase the range of deflection in any radial direction.
[0150] The cooling fluid may additionally or alternatively be passed through the central lumen 40 of the fibre 2402. This has the effect of cooling the thermally expandable material 9 surrounding the central lumen which reduces the surface temperature of the fibre 2402. This may be beneficial for preventing overheating of the thermally expandable material 9 by the resistance wires and also for preventing a patient from being burned by the fibre 2402 during an in-vivo procedure. Cooling the thermally expandable material via the central lumen, however, also reduces the temperature gradient across the cross-section of the fibre 2402 and the associated displacement as described further below.
[0151] FIG. 25 shows the results of an experiment in which an air hose was connected to the proximal end of the fibre 2402 by a needle and used to pass cooling air through the central lumen 40 during use of the fibre 2402. In this experiment, the fibre 2402 had a length of 11 cm and a diameter of 1.65 mm, the air was provided from a compressed air supply and a laser displacement sensor was used to measure deflection of the fibre 2402. Furthermore, the experiment was performed within an incubator configured to maintain the temperature of the surrounding environment to 38? C.?1? C., and the pressure inside the fibre 2402 was gradually increased from 0-5 bar using the compressed air.
[0152] As illustrated in FIG. 25, the surface temperature on the actuated side of the fibre 2402 (i.e. adjacent the wires 8a-b when viewed in cross-section) decreased from around 90? C. to around 43? C. as the pressure increased, while the surface temperature of the passive side of the fibre 2402 (i.e. adjacent the void 70 when viewed in cross-section) decreased from around 65? C. to around 35? C. as the pressure increased. This represents a decrease in temperature gradient across the cross-section of the fibre 2402 from around 25? C. to around 8? C. as the cooling air was passed through the central lumen. As such, the measured displacement showed a corresponding decrease from around 3.7 mm to around 1.7 mm.
[0153] Preferences and options for a given aspect, feature or parameter of the invention should, unless the context indicates otherwise, be regarded as having been disclosed in combination with any and all preferences and options for all other aspects, features and parameters of the invention. For example, it should be regarded that the conducting wire 44 feature shown in FIGS. 1a to 5b has been disclosed in combination with the air gap 46 feature shown in FIGS. 8 and 9. Similarly, the cooling fluid channels 70 shown in FIG. 24 may be applied to the other embodiments of the first aspect of the invention.
