Bidirectional thermally actuated components for use in medical devices

Abstract

To provide an actuator component that is activated by application or generation of heat in order to expand or contract in a predictable manner to provide adjustment of medical equipment.SOLUTION: A bidirectional thermally actuated component 10 includes a heating element 16 and wax material 14 provided in an enclosed housing, where the heating element is activated to melt the wax which expands to cause movement of the housing or an element mounted therein. When the heating element is deactivated, the wax hardens and contracts to allow movement in the opposite direction based on application of a force in the opposite direction, which may be provided by a biasing spring or a second actuator. An adjustable medical device may include the thermally actuated component to control adjustment of the device.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This application claims the benefit of and priority to U.S. Provisional Patent Application No. 62 / 976,841, entitled "BIDIRECTIONAL THERMALLY ACTUATED COMPONENT FOR USE IN MEDICAL DEVICES," filed February 14, 2020, the entire contents of which are incorporated herein by reference. Field of Disclosure

[0002] The present invention relates to a bidirectional thermally actuated component for use in a medical device. More particularly, the present invention relates to an actuator component that is driven by the application or generation of heat to expand or contract in a predictable manner to provide adjustment of the medical device. The component is preferably used in a medical device, but may be used in other applications. [Background technology]

[0003] A variety of medical devices and equipment exist for driving, correcting, or maintaining alignment in a certain direction and / or providing compression and / or traction to a patient. Many conventional devices are limited to manually actuated adjustment elements, such as rotating turnbuckles. Some devices use battery-powered electric motors and gears to maintain alignment or provide compression and traction. These powered devices are typically complex and expensive. Additionally, these devices are susceptible to errors, including uncontrollable, catastrophic errors. Sometimes a user may provide incorrect or incomplete input, resulting in inaccurate operation. In some cases, a motor or gear may fail or malfunction. Even if a user provides a correct input, the device may not accept it or may be unable to provide the correct output. In some cases, a device may not operate at all or may over-operate. A motor may continue to operate (or fail to operate) over a relatively unlimited range of motion, which may have an adverse effect on the user. In fact, errors may not be identified until the user's next visit, either by direct visualization or a series of x-rays by a physician to assess whether everything is progressing as planned.

[0004] When human-operated controls are used, users may forget to provide required inputs or may provide incorrect inputs. These types of errors are also often only discovered at the next visit.

[0005] It would therefore be desirable to provide actuator components for use with medical devices, medical devices using such actuators, or other applications that address these and other challenges. Summary of the Invention

[0006] The present invention aims to provide a bidirectional thermally actuated component that is safe and has a limited output relative to the input. In embodiments, the output of the component is finite, thus eliminating the possibility of serious or even catastrophic errors.

[0007] In embodiments, the two-way thermally actuated component may use a material that transitions between solid and fluid based on temperature, and may be as non-toxic as crayon material or paraffin wax, to name a few.

[0008] In embodiments, the bidirectional thermal actuation components may communicate data to ensure they are safe and that a given input resulted in the correct output. In embodiments, data may be shared with physicians or other medical personnel via the internet or other communication systems or networks to facilitate remote patient monitoring, which may reduce the need and cost of multiple visits and x-rays and allow for coordination.

[0009] A thermally actuated component according to one embodiment of the present disclosure includes a flexible container element expandable in a first direction to an expanded position and biased to return to a contracted position, a thermally responsive material contained in the flexible container, and a heating element arranged such that when the heating element is activated, heat from the heating element melts the thermally responsive material, causing the flexible container to expand to the expanded position, and when the heating element is deactivated, the thermally responsive material contracts as it cools, causing the flexible container to return to the contracted position.

[0010] In embodiments, the thermally responsive material is a eutectic wax.

[0011] In an embodiment, the flexible container includes at least a first opening formed therein.

[0012] In an embodiment, the first opening is configured to receive at least a portion of the first heating element.

[0013] In an embodiment, the thermally actuated component comprises a plug disposed in the first opening to retain the thermally responsive material within the flexible container.

[0014] In an embodiment, the plug further includes a passage formed therein and configured to receive the heating element.

[0015] In an embodiment, the thermal actuation component comprises at least one power source operatively connected to the heating element for selectively energizing the heating element to expand and contract the flexible container.

[0016] In an embodiment, the power supply is an inductive power supply.

[0017] According to one embodiment of the present disclosure, an intermedullary extension nail includes a hollow body, a shaft extending through the hollow body and slidable within the hollow body, a tension rod engaged with the shaft, a bidirectional pump mounted within the hollow body between a first void having a first volume and a second void having a second volume, the first void being between the bidirectional pump and the shaft, the second void being located between the bidirectional pump and a piston, the first void and the second void containing a liquid, and a control circuit operably connected to the bidirectional pump and configured to control operation of the pump, the control circuit controlling the pump to move fluid from the first void to the second void to retract the piston, and the control circuit controlling the pump to move fluid from the second void to the first void to extend the tension rod and the shaft.

[0018] In an embodiment, the bidirectional pump includes a first thermally actuated component arranged to move fluid from a first void to a second void, a second thermally actuated component arranged to move fluid from the second void to the first void, and an intermediate portion arranged between the first thermally actuated component and the second thermally actuated component.

[0019] In an embodiment, the intermedullary extension nail comprises a first coil disposed about the intermediate portion and electrically connected to the control circuit and the bidirectional pump for providing power to at least the control circuit and the bidirectional pump.

[0020] In an embodiment, the control circuitry is provided in the intermediate portion.

[0021] In an embodiment, the control circuitry is mounted within a potting material to provide water resistance.

[0022] In an embodiment, the first thermally actuated component comprises a first flexible container element expandable in a first direction to an expanded position and biased to return to a contracted position; a first thermally responsive material contained in the flexible container; and a first heating element arranged such that when the first heating element is activated, heat from the first heating element melts the thermally responsive material, causing the first flexible container to expand to the expanded position, and when the first heating element is deactivated, the thermally responsive material contracts as it cools, causing the first flexible container to return to the contracted position, wherein the expansion and contraction of the first flexible container is used to pump fluid from the first void to the second void.

[0023] In an embodiment, the first heating element is operably connected to the control circuit and is selectively activated by the control circuit to expand and contract the first flexible container.

[0024] In an embodiment, the first heating element is electrically connected to the coil and is selectively activated when a current is induced in the coil.

[0025] In an embodiment, the second thermally actuated component comprises a second flexible container element expandable in a first direction to an expanded position and biased to return to a contracted position; a second thermally responsive material contained in the flexible container; and a second heating element arranged such that when the second heating element is activated, heat from the second heating element melts the thermally responsive material, causing the second flexible container to expand to the expanded position, and when the second heating element is deactivated, the thermally responsive material contracts as it cools, causing the second flexible container to return to the contracted position, wherein the expansion and contraction of the second flexible container is used to pump fluid from the second void to the first void.

[0026] In an embodiment, the second heating element is operably connected to the control circuit and is selectively activated by the control circuit to expand and contract the second flexible container.

[0027] In an embodiment, a second heating element is electrically connected to the coil and selectively activated to expand and contract the second flexible container when an electrical current is induced in the coil.

[0028] In an embodiment, the intermedullary extension nail includes a third void provided in the intermediate portion and fluidically connected to the bidirectional pump and the first void and the second void so that fluid moving between the first void and the second void and fluid moving from the second void to the first void can be temporarily contained therein.

[0029] an intermedullary extension nail according to one embodiment of the present disclosure, comprising: a body; a power source mounted within the body; a control circuit mounted within the body and electrically connected to the power source; a first partition disposed between the control circuit and a first open space within the body; a second partition spaced from the first partition in a direction opposite to the control circuit; eutectic wax disposed between the first and second partitions; a piston mounted within the eutectic wax, extending through the second partition, and movable to extend and contract through the second partition; a heating element electrically connected to the control circuit so that the heating element is selectively activated by the control circuit, the heating element positioned so that heat from the heating element melts the wax and extends the piston; and an extension rod operably connected to the piston such that the piston is biased to a retracted position such that it returns to the retracted position when activation of the heating element is stopped and the eutectic wax hardens, and an extension rod operably connected to the piston such that expansion of the piston extends the extension rod.

[0030] In an embodiment, the extension rod is operatively connected to the piston such that contraction of the piston causes the extension rod to contract.

[0031] In an embodiment, the power source is an induction coil wrapped around the body. [Brief explanation of the drawings]

[0032] The above and related objects, features, and advantages of the present disclosure will be more fully understood by reference to the following detailed description of illustrative but preferred embodiments of the invention, taken in conjunction with the accompanying drawings.

[0033] [Figure 1] 1 illustrates an exemplary cross-sectional view of a two-way thermally actuated component according to an embodiment of the present application.

[0034] [Figure 2] 2 illustrates a hydraulic system using the bidirectional thermal actuation component of FIG. 1 according to one embodiment of the present application.

[0035] [Figure 3]1 illustrates an exemplary intermedullary extension nail suitable for use with a bidirectional thermally actuated component according to another embodiment of the present application.

[0036] [Figure 4] 4 shows a cross-sectional view of the intermedullary extension nail of FIG. 3 according to one embodiment of the present application.

[0037] [Figure 4A] 4 illustrates an exemplary embodiment of the intermedullary extension nail of FIG. 3 in an expanded position.

[0038] [Figure 5] 5 shows a more detailed view of the drive portion of the intermedullary extension nail of FIG. 4.

[0039] [Figure 6] 6 shows a cross-sectional view of the driver of the intermedullary extension nail of FIG. 5.

[0040] [Figure 7] 5 shows a more detailed view of another drive part of the intermedullary extension nail of FIG. 4.

[0041] [Figure 7A] 8 shows an expanded view of the detail provided in FIG. 7.

[0042] [Figure 8] 5 shows a more detailed view of the jack screw portion of the intermedullary extension nail of FIG. 4.

[0043] [Figure 9] 7 shows an exploded view of the drive unit of FIG. 6.

[0044] [Figure 10] 2 illustrates a hydraulic system using the components of FIG. 1 according to another embodiment of the present application.

[0045] [Figure 11] 1 illustrates a two-way thermal actuation component according to another embodiment of the present application.

[0046] [Figure 12] 12 shows a partial perspective view of the intermedullary extension nail of FIG. 11, illustrating the bidirectional pump included therein.

[0047] [Figure 13] FIG. 13 is a further detailed view of the bidirectional pump of FIG. 12.

[0048] [Figure 14] 13 shows a partial perspective view of the intermedullary extension nail of FIG. 12.

[0049] [Figure 15] 13 shows a detailed view of the interstage portion of the intermedullary extension nail of FIG. 12.

[0050] [Figure 16] 13 shows an exploded view of the interstage portion of the intermedullary extension nail of FIG. 12.

[0051] [Figure 17] 13 shows a detailed view of the pump mechanism used in the intermedullary extension nail of FIG. 12.

[0052] [Figure 18] 18 shows an exploded view of the pump mechanism of FIG. 17.

[0053] [Figure 19] 19 shows a detailed view of the wax capsule of the pump mechanism of FIGS. 17-18. FIG.

[0054] [Figure 20] 12 shows a partial perspective view of the bidirectional thermal actuation component of FIG. 11.

[0055] [Figure 21A] 1 illustrates an exemplary embodiment of a bellows structure in an extended state.

[0056] [Figure 21B] 1 illustrates an exemplary embodiment of a bellows structure in a contracted state.

[0057] [Figure 22] 1 illustrates an exemplary implant device that may include a thermally actuated element according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0058] In embodiments, medical devices using bidirectional thermally actuated actuator components may be implemented in at least two embodiments. In a first embodiment, the medical device may include a thermally actuated bidirectional actuator component that utilizes a hydraulic approach where movement and structural support may be provided using a working fluid selectively transferred between two sides of a piston assembly via the expansion and resulting pressure changes of the thermal actuator. In another embodiment, the device may use a thermally actuated actuator component with a mechanical approach where a mechanism converts linear movement and forces generated by the expansion and contraction of the thermal actuator component into rotary movement for actuating a screw. In embodiments, the rotary movement may be used to rotate a jackscrew. In both embodiments, the collected eutectic wax may be used in combination with the piston in either a bellows structure, a bladder, or any enclosed volume.

[0059] FIG. 1 illustrates a cross-sectional view of an exemplary bidirectional thermally actuated actuator component 10. In an embodiment, the bidirectional thermally actuated actuator component 10 may include a metal bellows structure 12 that receives and accommodates a wax material 14. In an embodiment, an electric heating element 16 may be disposed within the metal bellows structure 12 so as to contact the wax material 14. In an embodiment, the electric heating element 16 may be disposed adjacent to the wax material but not in contact therewith, so that heating by the heating element does not melt the wax material 14. Although the term metal bellows is used, in an embodiment, the bellows structure 16 need not be metal. In an embodiment, the bellows structure 12 may be a flexible, expandable bladder. In an embodiment, the bellows structure 12 may be any suitable container that is expandable and has the resilience to return to its previous state after expansion.

[0060] In embodiments, the heating element 16 may be a resistive heating element. In embodiments, a plug 18 may be provided at the base of the metal bellows structure 12 to retain the wax material 14 inside the bellows structure. In embodiments, the plug 18 may include an opening providing access to the bellows structure 12 to allow the heating element 16 to pass into the interior of the bellows structure 12. In embodiments, a seal 18a may be provided around the opening of the plug 18 to allow the heating element 16 to pass through while preventing wax leakage. In embodiments, the plug 18 may not be used, and the heating element 16 may enter the metal bellows structure 12 through the opening. In embodiments, the opening in the metal bellows structure 12 may be configured to securely receive the heating element 16 to avoid leakage. In embodiments, the heating element 16 may be a ceramic or other type of heating element. In embodiments, the heating element 16 may be energized using a near-field charger or other inductive power source. In embodiments, the near-field charger operates on the principles of inductive coupling or electrical conversion. In an embodiment, an alternating current may be applied to a primary coil (not shown) placed in close proximity to a secondary coil.

[0061] In embodiments, the primary coil may be located outside the user's body, and the secondary coil may be located within an implant including the actuator component 10 within the user's body. In embodiments, the secondary coil may be integrated with the actuator component 10. In embodiments, the secondary coil may be the heating element 16 or may be electrically connected to the heating element 16 to provide power to drive the heating element. In embodiments, the bidirectional thermally actuated actuator component 10 may be included in an implant located within the user's body to provide regulation thereof. In embodiments, the placement of the primary coil may be based on the location of the implant within the user's body to ensure that a current is induced in the secondary coil that can be used to drive the implant and the thermally actuated actuator component 10. In embodiments, the orientation of the primary and secondary coils may be optimized to maximize inductive coupling based on the location of the implant within the user's body. In embodiments, both the primary and secondary coils may be stacked coaxially, like a cell phone charging pad. In embodiments, the primary and secondary coils may be oriented parallel. In either case, magnetic materials may be used to focus the magnetic flux depending on the location within the body where the implant is located. In embodiments, the heating element 16 may be electrically connected to one or more other power supplies, such as a battery or a capacitor, to name a few. In embodiments, a wired electrical connection may be provided, for example, to an AC line voltage. In embodiments, the power source may include a transformer to provide an appropriate voltage suitable for use with the heating element 16. In embodiments, the heating element 16 may be connected to a processor, microprocessor, or other control device or control circuitry that may be used to activate and deactivate the heating element. In embodiments, the heating element 16 is preferably selectively activated and deactivated to activate the actuator component 10.

[0062] In embodiments, metal bellows structure 12 may be configured to allow linear expansion, for example, as shown by the arrow in FIG. 1 . During operation, when electrical current is induced or otherwise provided to heating element 16, heat from heating element 16 melts wax material 14, expanding to move metal bellows structure 12 in the direction of the arrow in FIG. 1 . FIG. 21A provides an illustration of metal bellows structure 12 in a contracted position, and FIG. 21B shows the metal bellows structure in an extended position. When power is turned off, heating element 16 and wax material cool, contracting as the wax material hardens, causing bellows structure 12 to contract in the direction opposite the arrow to its original state. In embodiments, metal bellows structure 12 may be biased toward a contracted state such that the bellows structure returns to or substantially returns to the contracted state once the wax material hardens. In embodiments, metal bellows 12 is resilient and has a spring constant sufficient to allow the bellows to return to its original contracted state after the wax hardens. In embodiments, a higher spring constant may allow the bellows structure 12 to return to a contracted state more quickly, but a higher spring constant may also require more pressure to allow the bellows to expand. In embodiments, it is preferable to minimize the amount of pressure required for expansion. In embodiments, the spring constant of the bellows 12 may vary depending on the application in which it is used. In embodiments, if both expansion and contraction are used in a reciprocating manner, the spring constant may be set so that the net force output is equal in both stages. In one example where a wax actuator is used to provide 100 lbF based on volumetric expansion, in embodiments, the spring force of the bellows 12 may have a 50 lbF initial spring load at constant zero, so that even at full extension there is a 50 lbF initial spring load and 50 lbF available actuator output. In embodiments, there is a 50 lbF spring load at contraction, which can be used all the way back to full contraction. In embodiments, the initial spring load and initial spring rate may be adjusted to maximize the available work relative to maintaining the required work, and the balance of force, distance, and direction may depend largely on both clinical application and design choice.

[0063] In an embodiment, cyclical heating (expansion) and cooling (contraction) of wax 14 within bellows 12 of component 10 may be used to provide a fluid pump for use in hydraulic system 50 shown in FIG. 2 . In an embodiment, component 10 may be used with a hydraulic cylinder 20, for example, as can be seen in FIG. 2 . In an embodiment, hydraulic cylinder 20 may include a piston 22 held within closed cylinder 20. In an embodiment, piston 22 may extend through one end of closed cylinder 20 and be connected to a rod 24 that extends and contracts as the piston moves within the cylinder. In an embodiment, dynamic seals 26 may be provided around the periphery of piston 22 and around a cylindrical opening 20 a at the end of cylinder 20 through which rod 24 exits to divide cylinder 20 into two isolated volumes V1, V2. In an embodiment, piston 22 moves along the axis of cylinder 20 toward the volume of lower pressure by transferring fluid to one volume while removing it from the other. The first volume is designated V1, and the second volume is designated V2. The amount of working fluid in each of the first volume V1 and second volume V2 increases or decreases in response to the translational movement of the piston, but at different rates because volume V1 is located in the swept area of ​​piston 22 and second volume V2 is located in the swept area of ​​piston 22 minus the area of ​​rod 24. The total volume V1 + V2 increases as rod 24 extends and decreases as it retracts.

[0064] In some embodiments, a third connected variable volume V3 may be used. In some embodiments, this third volume V3 may be referred to as a “rod accumulator” and may be formed using a spring-loaded piston in a cylinder. In some embodiments, the “rod accumulator” may be a flexible, sealed bellows containing a gas. In some embodiments, the rod accumulator may be a bladder or a piston in a cylinder. In some embodiments, the “rod accumulator” may be a passive device whose sole function is to accommodate the differential volume change between V1 and V2 as rod 24 extends and retracts. This differential volume is a result of rod 24 having a cylindrical volume that must be accounted for when extending and retracting from V2, but not V1. In some embodiments, to fix rod 24 in a given position, volumes V1, V2, and V3 may be isolated from one another to form three closed volumes. In some embodiments, the isolation of volumes V1, V2, and V3 may be achieved using a simple shut-off valve S1. In an embodiment, opening valve S1 allows fluid to flow to allow free positioning of rod 24 as needed.

[0065] In an embodiment, two pumps may be configured using actuators that use a wax material (such as paraffin wax or eutectic wax), which may be embodied by or include component 10 of FIG. 1, to cause movement by extending or retracting rod 24. In an embodiment, a thermally actuated component 10 may be housed in each of respective sealed volumes V4 and V5. Check valves CV2 and CV5 are provided for volume V5. Check valves CV4 and CV1 and a pressure-activated release valve PARV2 are provided for volume V4. In an embodiment, these pumps are referred to as the "extension pump" and the "retraction pump."

[0066] In embodiments, extension of piston 24 may be affected by application of a voltage to electrical input V1in. In embodiments, the voltage may be used, for example, to power electric heater 16, described above, which melts wax and causes actuator 10 to expand within volume V4, increasing pressure within volume V4. In embodiments, voltage V1in may be used to power a controller or control circuit, which may be used to control heater 16 to control the application of heat. Alternatively, the controller or control circuit may be used to selectively provide voltage V1 to the heater. In embodiments, voltage V1in may be applied from a power source, such as an inductively coupled power source described above, or any other suitable power source, such as a DC source. In embodiments, check valve CV1 allows fluid to flow from V4 to V1 within cylinder 20 when pressure at V4 exceeds a predetermined value. In embodiments, the predetermined value depends on the externally applied load and the cross-sectional area of ​​the actuator component 10 for a given apparatus or device, such as that used in an implantable medical device. In embodiments, a eutectic wax actuator, such as actuator component 10, may generate pressures up to approximately 3000 psi during expansion due to the melting process. In embodiments, expansion occurs at a lower pressure when no significant load is applied. In embodiments, simultaneously, the increased pressure at V4 is applied to pressure relief valve PARV2, thereby allowing fluid to flow from volume V2 to volume V3. In embodiments, the increase in pressure at volume V1 as fluid flows from volume V4 to volume V1, combined with the decrease in pressure at volume V2 as fluid flows from volume V2 to volume V3, allows piston 22 to move upward and extend rod 24. In embodiments, when voltage V1in is removed, the heating element is released and the wax within actuator 10 in volume V4 begins to contract, reducing the pressure at volume V4, which in turn closes check valve CV1 and opens valve CV4, allowing fluid to flow from volume V3 to volume V4.When the actuator 10 in volume V4 fully contracts to its original state, the pressure in volume V4 may return to its value prior to the actuation cycle by taking up fluid from volume V3. In embodiments, the relative volumes of volumes V1, V2, V3, and V4 may vary depending on the size of the component 10 and the implant in which it is mounted, and the amount of stretch required for a single expansion cycle.

[0067] In embodiments, contraction of rod 24 may be affected by application of a voltage to electrical input V2in. This voltage may be provided via a power source, such as the induction coil described above, or in other ways. In embodiments, voltage V2in may drive heating element 16 of second actuator component 10 in volume V5. In embodiments, the actuator component may be powered by direct current, as described above. In embodiments, application of voltage V2in causes heating element 16 in second actuator component 10 housed in volume V5 to heat wax, expanding the actuator and increasing the pressure in volume V5. In embodiments, check valve CV2 allows fluid to flow from volume V5 to volume V2 of cylinder 20 when the pressure in volume V5 exceeds a certain value. In embodiments, the relief pressure varies depending on the desired application, and is dependent on the applied external load. In embodiments, the check valve may operate at a very low differential pressure sufficient to eliminate the possibility of backflow. In an embodiment, simultaneously, the increased pressure at V5 is applied to pressure-activated relief valve PARV1, thereby allowing fluid to flow from volume V1 to volume V3. In an embodiment, this increased pressure at volume V2 and decreased pressure at volume V1 causes piston 22 to move downward, retracting rod 24. In an embodiment, when voltage V2in is removed, actuator component 10 in volume V5 begins to contract back to its original state, reducing the pressure at V5, thereby closing check valve CV2 and opening valve CV5, allowing fluid to flow from volume V3 to volume V5. In an embodiment, once actuator component 10 in volume V5 has fully contracted to its original state, the pressure at volume V5 returns to its value prior to the actuation cycle by drawing in fluid from volume V3. The pressure at the various volumes may vary depending on the applied external load. Preferably, eutectic wax is capable of generating pressures in excess of 3000 psi that can be applied to a given desired cross-sectional area to support an externally applied load.

[0068] In embodiments, any of the expansion or contraction cycles described above may be repeated as many times as necessary to move the rod 24 to any incremental position. The advantage of this is that when such an actuator is used in an implant or orthotic medical device, each adjustment made is limited to the extension length of the rod 24, making it less susceptible to uncontrolled or catastrophic failure. In embodiments, the size of each increment of movement may be set based on limiting how much the component 10 expands. As noted above, in embodiments, the amount of expansion may vary. In embodiments, different sizes or volumes of actuator component 10 may be used for different applications. In embodiments, the volume may depend on the size of the component 10 and / or the implant or device in which it is used and the amount of extension required for a single expansion cycle.

[0069] In embodiments, feedback regarding rod position may be provided using a position or pressure sensor used to measure the state of a rod accumulator within a volume (volume V3 in FIG. 2 ). This is because this feedback follows a predictable relationship with rod extension. In embodiments, a simple position sensor may be used, which may operate on the same principle as a potentiometer, where a linear strip of resistive material may be coupled to a sliding contact. In embodiments, the resistance is a known function of the contact position along the linear strip. In embodiments, for pressure embodiments, the rod accumulator (e.g., volume V3 in FIG. 2 ) may contain a closed volume of compressible gas, whose pressure varies with the volume of the closed volume. As the volume decreases, the pressure increases, and vice versa. This relationship may be characterized with respect to rod extension so that the position of the rod can be determined based on the pressure in the rod accumulator. In embodiments, a pressure sensor may be placed within the closed volume of the rod accumulator. Such pressure sensors come in many different forms, ranging from strain gauge-based designs to piezoelectric elements. Different sensor types may be selected based on the particular application. In embodiments, a position or location sensor may be provided between the rod 24 and the cylinder 20 to determine their relative positions, using, for example, the resistance sensor described above. In embodiments, if a load cell is used, the sensor may be disposed in series between the cylinder wall, the spring, and the rod. Movement of the rod 24 changes the length of the spring, resulting in a change in spring force detected by the load cell. A correlation between load and displacement may be established to determine the relative position. In embodiments, the position information collected as described above may be communicated to a physician or other medical professional and used, for example, to verify that a device using the hydraulic system 50 is properly adjusted and providing the desired corrective force to the patient's body. That is, in embodiments, the hydraulic system 50 may be integrated with an implant 1000 (see, for example, FIG. 22 ) or other medical device and implanted within the patient's body to provide corrective treatment.

[0070] In embodiments, the position information may be used to provide feedback that can be used to ensure that adjustments are being made properly. In embodiments, a control circuit or controller may be provided with or operatively connected to the implant 1000. FIG. 22 shows an exemplary block diagram of the implant 1000, which may incorporate the hydraulic pump system 50 shown in FIG. 2, which may include two thermally actuated components 10 such as those described above. In embodiments, as described above, a control circuit 1010 or any other suitable control element may be provided with or operatively connected to the implant 1000 to control the extension and contraction of the rod 24. In embodiments, the rod 24 may be, or operatively connected to, a brace or other corrective structure and may be used to make adjustments thereto in a controlled and measurable manner that avoids the risks described above.

[0071] In embodiments, the implant 1000 may include one or more transceivers (transmitters / receivers) or other communication devices 1020 configured to receive control signals or other information related to the operation of the implant 1000 and / or transmit information related to the operation of the implant, such as the feedback position information described above regarding the position of the rod 24. As described above, for example, the hydraulic system 50 may include one or more sensors for providing feedback related to the position of the rod 24. In embodiments, this feedback information may be provided to a physician or other medical professional so that appropriate positioning and adjustments can be provided by the implant 1000. In embodiments, a power source 1030 may be provided in the implant 1000 and operably connected to the hydraulic system 50 and the control circuitry 1010 and / or individual actuator components 10 included in the hydraulic system. In embodiments, the power source 1030 may be a secondary coil as described above or any other inductive power source. In embodiments, the power source 1030 may be any suitable power supply element, including, for example, a battery or a DC source. As described above, the actuator components 10 may be controlled, for example, by the control circuitry 1010. In embodiments, feedback information regarding the operation of implant 1000, including the position of rod 24 in hydraulic system 50, may be sent periodically or aperiodically to a physician or medical professional, or to one or more computer systems or associated communication devices. In embodiments, a physician or medical professional may provide instructions related to the operation of implant 1000 to control circuitry 1010 via transceiver 1030 via a computer system or associated communication device to adjust the position of rod 24.

[0072] FIG. 10 illustrates an alternative embodiment of a hydraulic system 150 similar to the system 50 described above that may be used in an implant 1000. In an embodiment, similar to FIG. 2, a hydraulic cylinder 20 includes a piston 22 held within a closed cylinder 20. In an embodiment, the piston 22 may be connected to a rod 24 that extends through both ends of the closed cylinder 20 and expands and contracts as the piston moves within the cylinder. In an embodiment, a dynamic seal 26 may be provided around the periphery of the piston 22. In an embodiment, an additional dynamic seal may be provided around a cylindrical opening 20a at the end of the cylinder 20 from which the rod 24 exits. As shown, the cylinder 20 may be divided into two isolated volumes V1, V2 by the piston and dynamic seal 26. In an embodiment, the piston 22 moves in one direction along the axis of the cylinder 20 toward the volume of lower pressure by transferring fluid into one volume while removing it from the other, similar to that described above with respect to FIG. 2. The first volume is designated V1 and the second volume is designated V2. The first volume V1 and the second volume V2 increase and decrease in response to the translational movement of the piston. Because the rod extends into both volume V1 and volume V2, the total volume V1 + V2 remains approximately constant as the rod 24 extends and retracts.

[0073] In embodiments, extension of piston 24 may be affected by application of a voltage to electrical input V1in. In embodiments, the voltage may be used, for example, to power electric heater 16, described above, which melts wax and causes actuator 10 to expand within volume V1a, increasing pressure within volume V1a. In embodiments, voltage V1in may be used to power a controller or control circuit that may be used to control heater 16. In embodiments, voltage V1in may be applied using inductive coupling or may be a DC source. In embodiments, check valve CV1 allows fluid to flow from V1s to V1 within cylinder 20 when pressure at V1s exceeds a predetermined value. In embodiments, the predetermined value depends on the externally applied load and the cross-sectional area of ​​the actuator for a given device. In embodiments, the increased pressure at V1s is simultaneously applied to pressure relief valve PARV2, which allows fluid to flow from volume V2 to volume V3, referred to as the accumulator. In embodiments, the increase in pressure in volume V1 as fluid flows from volume V1s into volume V1, combined with the decrease in pressure in volume V2 as fluid flows from volume V2 to volume V3, causes piston 22 to move upward, extending rod 24 upward. In embodiments, when voltage V1in is removed, the wax in actuator 10 at volume V4 begins to contract, reducing the pressure in volume V1s, which closes check valve CV1 and opens valve CV1a, allowing fluid to flow from volume V3 into volume V1s. Once actuator 10 at volume V1s has fully contracted to its contracted state, the pressure in volume V1s returns to its value prior to the actuation cycle by drawing fluid from volume V3 as needed. In embodiments, the relative volumes depend on the size of the implant and the amount of extension required for a single expansion cycle.

[0074] In an embodiment, contraction of the rod 24 may be affected by application of a voltage to the electrical input V2in. This voltage may be provided to induce a current in the actuator component 10 in volume V2s, or may be used to provide a direct current. In an embodiment, application of the voltage causes a heating element 16 in the actuator component 10 housed in volume V2s to heat wax, expanding the actuator and increasing the pressure in volume V2s. In an embodiment, check valve CV2 allows fluid to flow from volume V2s to volume V2 of the cylinder 20 when the pressure in volume V2s exceeds a predetermined value. In an embodiment, the relief pressure depends on the applied external load, with specific values ​​varying depending on the desired application. In an embodiment, the check valve operates at a very low differential pressure sufficient to eliminate the possibility of backflow. In an embodiment, the increased pressure in V2s is simultaneously applied to pressure-activated relief valve PARV1, thereby allowing fluid to flow from volume V1 to volume V3. In an embodiment, this increase in pressure in volume V2 and decrease in pressure in volume V1 causes piston 22 to move downward, causing rod 24 to retract from the top and extend through the bottom. In an embodiment, when voltage V2in is removed, actuator component 10 in volume V2s begins to retract back to its original state, causing the pressure in V2s to decrease, which closes check valve CV2 and opens valve CV2a, allowing fluid to flow from volume V3 into volume V2s. In an embodiment, once actuator component 10 in volume V2s has fully retracted to its original state, the pressure in volume V2s returns to its value prior to the actuation cycle by drawing in fluid from volume V3. The pressures in the various volumes vary only in response to applied external loads.

[0075] In embodiments, any of the expansion or contraction cycles described above may be repeated as many times as necessary to move the rod 24 to any incremental position. In embodiments, the size of each increment of movement may be set based on limiting how much the component 10 expands. In embodiments, different sizes or volumes of actuator component 10 may be used for different applications. In embodiments, the volume depends on the size of the implant and the amount of extension required for a single expansion cycle. In the embodiment of FIG. 10, the rod 24 extends from both the bottom and top of the cylinder 20, so the rod accumulator volume Acc may be smaller than that described above with respect to FIG. 2. In the embodiment of FIG. 10, the extension or contraction of the rod 24 causes substantially identical volume changes in both volumes V1 and V2, and the accumulator Acc only needs to accommodate the volume change for a single cycle. In embodiments, a hydraulic system 150 may be implemented in the implant 1000 described above in place of the hydraulic system 50. Alternatively, the implant 1000 operates in substantially the same manner as described above.

[0076] FIGS. 3-8 illustrate an embodiment of an intermedullary extension nail 110 that may utilize a bidirectional thermally actuated component 110 that operates in concert with the actuator component 10 described above. In an embodiment, the implant 1000 may be the intermedullary extension nail 110. FIG. 3 illustrates an embodiment of the intermedullary extension nail 110 that utilizes the mechanical extension of a thermally actuated actuator component. FIG. 4 illustrates a cross-sectional view of the intermedullary extension nail 110 along section AA. In an embodiment, the intermedullary extension nail 110 extends by driving either the threaded portion or the nut portion of a typical jack screw device based on the operation of one or more thermally actuated actuator elements using a heating element in a manner similar to that used in the actuator component 10 described above. In an embodiment, a drive mechanism may be provided at both ends of the device 110, as shown in circles B and D in FIG. 4. Embodiments of these portions are shown in more detail in FIGS. 5 and 7. An exemplary jack screw device is shown in circle C in FIG. 2 and in more detail in FIG. 8.

[0077] In embodiments, the drive section, highlighted in circles B and D in FIG. 3 and shown in more detail in FIGS. 5 and 7, may include a body 101 that includes an inductive pickup coil 119 beneath a cover article 118. In embodiments, this inductive pickup coil 119 may be the power source 1030 described above. In embodiments, when an external, varying electromagnetic field approaches the pickup coil 119, a current may be induced in the pickup coil. In embodiments, the external, varying electromagnetic field may be provided by a primary coil, as described above, and may be provided outside the user's body where the IM nail 110 may be implanted. In embodiments, the current may be applied to internal control electronics 121, which may be or include the control circuit 1010 described above. In embodiments, the control electronics 121 may be used to turn power to the heating element 120 on and off. In embodiments, the heating element 120 surrounds a eutectic wax material 130 stored between the bulkheads 114 and 115. Heating element 120 may be a resistive heating element similar to heating element 116 described above, or any other suitable heating device. In embodiments, piston 116 may be encased in wax material 130 and may exit through septum 114. In embodiments, seal 117 may prevent wax material 130 from leaking out of the enclosed volume between septums 114, 115 while allowing piston 116 to move in and out of the enclosed volume. In embodiments, when heating element 120 heats wax material 130, the wax melts and expands, creating an internal pressure on the order of 3000 psi. In embodiments, the expansion of the wax pushes piston 116 out of septum 114 and compresses male helical spline 103. In embodiments, spline 103 slides within female helical spline 102 fixed to body 101. In embodiments, the helical shape of spline 103 results in the spline rotating as it is pushed linearly by piston 116. In an embodiment, this rotation operates the roller clutch shown in Figure 6. In an embodiment, the roller clutch may include a bore in the spline 103 with the shaft 104 positioned therein.In an embodiment, shaft 104 may include rollers 105 aligned within angled slots machined into the shaft. In an embodiment, rollers 105 are biased toward the narrow side of the angled slot using wire springs 104a. In an embodiment, a clutch engages drive spline 103 to drive rotation of shaft 104 when rotating counterclockwise. In an embodiment, this rotation occurs while piston 116 is extending; that is, linear extension of the piston is converted into rotation.

[0078] In an embodiment, when the piston 116 retracts, the spline 103 rotates in a clockwise direction. In an embodiment, when this occurs, the shaft 104 disengages from the spline 103. In an embodiment, the shaft 104 drives an integral nut 111 (see FIG. 8). In an embodiment, counterclockwise rotation of the nut 111 extends the rod 113. In an embodiment, a return spring 107 is utilized to return the piston 116 and male helical spline 103 to their original state. In an embodiment, the return spring 107 acts between a partition wall 112 (see FIG. 8) and the piston 116. In an embodiment, the partition wall 112 is fixed to the body 101. In an embodiment, the return spring 107 applies force through thrust bearings 109, 110 such that the male spline 103 is free to rotate as it moves linearly back and forth.

[0079] In an embodiment, the jack screw mechanism, which can be seen in more detail in FIG. 8, includes a shaft 104, a nut 111, and a jack screw 113. In an embodiment, the shaft 104 may be supported between a pair of thrust bearings 110a fixed to the body 101. In an embodiment, the jack screw 113 is fixed in a linear direction but is free to rotate relative to the nail rod 108. In an embodiment, an additional bearing 110a may be incorporated between the items 108 and 113 to allow rotation. In an embodiment, a bearing race 123 may be fixed to the nail rod 108. The bullet tip 126 of the nail 110 is visible in FIG. 7a. In an embodiment, the bullet tip 126 may be a stationary component and may be attached to the shaft 108. As can be seen with reference to FIG. 7, for example, the drive mechanism highlighted in circle D and shown in detail in FIG. 7 has a similar structure and operation to that shown in FIG. 5, except that the piston 116 moves in the opposite direction.

[0080] In operation, the intermedullary extension nail 110 may either extend or retract. For extension, in an embodiment, the mechanism shown in circle B and FIG. 5 provides for counterclockwise rotation of the shaft 104 relative to the jack screw 113, causing the jack screw to extend from the shaft according to the thread pitch of the nut 111. For retraction, in an embodiment, the mechanism shown in circle D and FIG. 7 provides for clockwise rotation of the jack screw 113 relative to the shaft 104, causing the jack screw to retract within the shaft 104 according to the thread pitch of the nut 111. FIG. 4A shows the intermedullary extension nail 110 in the extended position.

[0081] In embodiments, power and data communication may be provided to / from the implant 1000, which may be embodied by the intermedullary extension nail 110. In embodiments, direct communication may be provided via a direct connection to a mobile phone, for example, via the transceiver 1020. In embodiments, the direct connection may be provided using a charging cable, USB cable, or other wired connection. In embodiments, the charging cable may be used, for example, to both provide power and capture or communicate positional data regarding the movement of the piston 124. In embodiments, power may be provided based on induction using near-field inductive coupling, as outlined above with respect to the power source 1030. In embodiments, command transmission and exchange of positional data may also occur via inductive coupling. In embodiments, this information may be transmitted wirelessly via the transceiver 1020.

[0082] In embodiments, internal control electronics 121, which may correspond to the control circuitry 1010 described above, may be used to communicate location information either directly or via inductive coupling. In embodiments, the control electronics 121 may include one or more processors or microprocessors or other control circuitry. In embodiments, the control electronics 121 may include or be connected to a port or plug to allow direct connection to a mobile phone or other mobile device. In embodiments, the control electronics 1020 may include a transceiver, such as the transceiver 1020 described above, for wirelessly transmitting and receiving information. In embodiments, communication may be achieved via inductive coupling, as described above. In embodiments, wireless communication may occur using any suitable wireless protocol or network, which may be implemented via the transceiver 1020, for example.

[0083] FIG. 11 illustrates another embodiment of an intermedullary (IM) extension nail 210 that uses a bidirectional thermal actuation component similar to the actuator component 10 described above. In an embodiment, the nail body 201 may be the primary structural element of the IM nail 210 and may be hollow to accommodate the nail shaft 202, which is slidably engaged with the body and sealed by a pair of O-rings 205. In an embodiment, other sealing structures may be used in place of the O-rings. In an embodiment, the body 201 and shaft 202 may share a common curvature and may be configured to prevent rotation using a bushing 206. In an embodiment, the body 201 and shaft 202 may have a substantially cylindrical shape. In an embodiment, a bidirectional pump element 207 may be provided on the nail body 201 and may be fixed to prevent movement of the pump relative to the body 201. In an embodiment, a seal 209 may be provided to prevent fluid from passing between the first volume V1 and the second volume V2. In an embodiment, a seal 209 (see FIG. 14), which may be a static seal, may be used to prevent this fluid transfer. In an embodiment, a tension rod 211 may be engaged with the nail shaft 202 and may connect to a piston 211 which may continue through the pump 207 and be sealed by an O-ring 205.

[0084] 12 shows the pump 207 and cylinder volumes V1 and V2 included in the nail body 201. In an embodiment, the pump 207 may be disposed in the body 201 with the tension rod 211 extending through it as described above. Volume V1 may be provided in the space between the pump 207 and the nail shaft 202. Volume V2 may be provided between the pump 207 and the piston 212. In an embodiment, the pump 207 may move fluid from volume V1 to volume V2 to retract the piston 212. The pump 207 may also move fluid from volume V2 to volume V1 to extend the rod 211. In an embodiment, a cannula 203 within the rod extends through the tension rod 211, which is slidably engaged with the shaft 202. In an embodiment, the cannula 203 may be used to facilitate insertion over a guidewire, a common technique used to implant IM nails into a patient's body. In an embodiment, the IM nail 210 may be an example of the implant 1000 described above.

[0085] 13-14 illustrate components of bi-directional pump 207. In embodiments, pump 207 may include three main sections. Inter-stage section 221 may include a power source, electronics, and an accumulator volume. In embodiments, a pair of thermal pump mechanisms 207a, 207b may be provided at opposite ends of inter-stage section 221. In embodiments, pump mechanisms 207a, 207b may be used to push fluid from pump 207 into volumes V1, V2 to effect expansion and contraction. In embodiments, the hydraulic fluid may be sterile water, among other substances, isolated from the sealed thermal wax actuators in pump mechanisms 207a, 207b and contained within cylinder volumes V1, V2. In embodiments, application of voltage V1in or voltage V2in energizes a heating element, such as heating element 16 described above in the wax actuators used in pump mechanisms 207a, 207b, resulting in a solid-to-liquid phase change and accompanying expansion of the wax actuators. This expansion of the thermally actuated actuator, which in embodiments is similar to the actuator component 10 described above, displaces and pressurizes the actuating fluid, resulting in an increase in actuating fluid pressure within the pump 207 .

[0086] 15-16 show a cross-sectional view and an exploded view of the interstage portion 221, respectively. The interstage body 221a may function as a housing for the other components. In an embodiment, a pair of fluid passages 221b may be provided in the housing 221a. In an embodiment, the electronic circuit 221c may be potted within the cavity and isolated from the working fluid. In an embodiment, the electronic circuit 221c may include, for example, the control circuit 1010 and the transceiver 1030 described above. In an embodiment, a bladder 221e may be provided in the second cavity and may function as an accumulator to accommodate displacement of fluid from the volumes V1 and V2, which shrink as fluid is transferred between the volumes V1 and V2. In an embodiment, as the volume of one volume V1 decreases, the other volume V2 correspondingly increases, thereby causing movement of the nail shaft 202. In an embodiment, a coil 221f may be provided around the body 221a. In embodiments, the coil 221f may be a coil of wire and may act as an inductive pickup to provide power to the electronic circuitry 221c. In embodiments, the coil 221f may be the power source 1030 described above. In embodiments, the coil 221f may be the secondary coil described above. In embodiments, the electronic circuitry 221c may control the operation of the pump 207 and send signals to an external controller or computing device associated with a physician, medical professional, or administrator (not shown). In embodiments, a near-field wireless charging and communication protocol such as Bluetooth may be used to provide power and for communication using, for example, the power source 1030 and transceiver 1020 described above, which may be incorporated into the electronic circuitry 221c. In embodiments, the ability to communicate with an external controller allows for the transmission and monitoring of information such as position feedback, load sensing, pressure and temperature sensing, etc.

[0087] 17-18 show cross-sectional and exploded views of pump mechanisms 207a and 207b, respectively. In embodiments, body 208a houses other components and allows for fluid path isolation between the telescopic pump mechanisms. In embodiments, static O-rings 208b may isolate the interior volumes of pumps 207a and 207b from cylinder volumes V1 and V2. In embodiments, dynamic O-rings 208c may provide a dynamic seal between pump mechanisms 207a and 207b and tension rod 212. In embodiments, tension rod 212 may completely traverse pump assembly 207 between cylinder volumes V1 and V2, eliminating the need for a rod accumulator. In embodiments, each pump mechanism 207a and 207b may include a wax capsule or bellows W enclosed within the actuation fluid volume. In embodiments, capsule W may be bellows 12, as described above, with its shape tailored to match the curvature of body 201. In an embodiment, a pair of check valves CV1, CV2 may include a poppet 301, a seat 302, a spring 303, and a stop 304 and may be used to control flow into and out of pump mechanisms 207a, 207b during expansion and contraction of the wax capsule or bellows W. In an embodiment, spring 303 may bias poppet 301 against seat 302 to provide a fluid seal. In an embodiment, one of the check valves CV1 allows fluid from pump 207 to flow into the corresponding cylinder volumes V1, V2 when the pump is undergoing positive expansion of the wax capsule W, and the second check valve CV12 allows flow into the pump from a bladder 221f located in interstage portion 221 during contraction of the wax capsule W. In an embodiment, pressure-actuated relief valve PARV1 may be formed similarly to that of the valves described above and includes a pressure-actuated bellows PAB. In an embodiment, bellows PAB allows internal pressure to be transmitted across interstage portion 221 from the opposing pump volume.In embodiments, valve PARV1 allows fluid from cylinder volume V1 or V2, which is decreasing in volume, to flow into bladder 221e so that the respective cylinder volume V1 or V2, which is increasing in volume, has room to extend into the accommodation provided by the bladder. In embodiments, various bushings 305 and 306 function to connect each of pump mechanisms 207a, 207b to interstage portion 221. In embodiments, plug 308 may be provided to temporarily seal the flow path to allow for manufacturing and assembly of the pump components. In embodiments, check valves CV1, CV1a and pressure relief valve PARV1 may be configured differently as needed. In embodiments, check valves CV1, CV1a and pressure relief valve PARV1 may be magnetically actuated valves, flapper valves, or any other mechanical device that provides flow control.

[0088] FIG. 19 shows a detailed view of bellows B, which is provided with paraffin wax formulated to melt at an appropriate temperature and can be used as the wax capsule W described above. As noted above, capsule W can be bellows 12 described above. In embodiments, heating element 316 can provide the energy input to melt the wax and can be controlled by electronic circuitry 221c. In embodiments, the wax undergoes up to a 20% volumetric expansion during melting. In embodiments, the pressure generated during this expansion approaches 3000 psi when properly constrained. As shown in FIG. 18, bellows B is shown as a typical edge-welded bellows assembly, although other structures for wax containment can be used, such as a silicone bladder or a piston within a cylinder, to name a few. In embodiments, the wax containment isolates the wax from the working fluid and maintains its proximity to heating element 316. Heating element 316 can be similar to heating element 16 described above. In embodiments, when power is removed from heating element 316, the wax dissipates heat to the working fluid and solidifies, causing the bellows to contract. In embodiments, bellows B may include two opposing end caps B1, B2 with a flexible segmented diaphragm D disposed therebetween to expand and contract as the wax melts and solidifies. In embodiments, other flexible structures may be used as bellows B.

[0089] FIG. 20 shows a cutaway hydraulic pump section 207. In an embodiment, a piston 212 may be held within a closed cylinder 201 (see FIG. 12). In an embodiment, the piston may be connected to a rod extending through the end of each of the closed cylinder volumes V1, V2 to cause movement outside the cylinder. In an embodiment, dynamic seals are provided around the periphery of the piston and around cylindrical openings at the ends of the cylinder volumes V1, V2 from which the rod R exits, dividing the cylinder C into two isolated cylinder volumes V1 and V2. In an embodiment, the piston P moves in one direction along the axis of the cylinder C by transferring hydraulic fluid into one volume V1, V2 while removing it from the other volume. In an embodiment, a first volume, designated V1, and a second volume, designated V2, increase and decrease in response to the translational movement of the piston. In embodiments, using such an actuator in a closed fluid cycle includes a third connected variable volume V3 for accommodating fluid flowing from the decreasing volume while fluid is being pumped to the increasing volume. This third volume, Acc, is referred to as an accumulator and may be formed using a spring-loaded piston in a cylinder, flexible bellows, or a gas-filled bladder, to name a few, in a closed volume as shown. In embodiments, a second function of this accumulator Acc may be to resupply the pump 207 during the period when the wax capsule is cooling and decreasing in volume, thereby allowing fluid to be drawn from Acc to prepare the pump for the next operating cycle.

[0090] While embodiments of the present invention have been shown and described in detail, various modifications and improvements may become readily apparent to those skilled in the art. Accordingly, the exemplary embodiments of the present invention set forth above are intended to be illustrative rather than limiting. The spirit and scope of the present invention should be broadly interpreted.

Claims

1. A hollow body; a shaft extending through the hollow body and slidable within the hollow body; a tension rod engaged with the shaft; a bidirectional pump mounted within the hollow body between a first gap having a first volume and a second gap having a second volume, the first gap being between the bidirectional pump and the shaft and the second gap being between the bidirectional pump and a piston, the first gap and the second gap containing a liquid; a control circuit operatively connected to the bidirectional pump and configured to control operation of the pump; Equipped with the control circuit controls the pump to move fluid from the first cavity to the second cavity to move the piston in a first longitudinal direction; the control circuit controls the pump to move the fluid from the second gap to the first gap to move the tension rod and the shaft in a second longitudinal direction opposite to the first longitudinal direction. Intermedullary extension nail.

2. The bidirectional pump is a first thermally actuated component positioned to move fluid from the first void to the second void; a second thermally actuated component positioned to move fluid from the second void to the first void; an intermediate portion disposed between the first thermally actuated component and the second thermally actuated component; The intermedullary extension nail of claim 1 further comprising:

3. 3. The intermedullary extension nail of claim 2, further comprising a first coil disposed around the intermediate portion and electrically connected to the control circuit and the bidirectional pump to provide power to at least the control circuit and the bidirectional pump.

4. The intermedullary extension nail of claim 2 , wherein the control circuit is provided in the intermediate portion.

5. The intermedullary extension nail of claim 4 , wherein the control circuit is mounted within a potting material to provide water resistance.

6. The first thermally actuated component comprises: a first flexible container element expandable in a first direction to an expanded position and biased to return to a contracted position; a first thermally responsive material contained in the flexible container; a first heating element arranged such that when the first heating element is activated, heat from the first heating element melts the thermally responsive material, causing the first flexible container to expand to the expanded position, and when the first heating element is deactivated, the thermally responsive material contracts as it cools, causing the first flexible container to return to the contracted position, the expansion and contraction of the first flexible container being used to pump the fluid from the first gap to the second gap; The intermedullary extension nail of claim 3 , comprising:

7. 7. The method of claim 6, wherein the first heating element is operably connected to the control circuit and selectively activated by the control circuit to expand and contract the first flexible container. Inter-extension nail.

8. The intermedullary extension nail of claim 6 , wherein the first heating element is electrically connected to the coil and is selectively activated when an electric current is induced in the coil.

9. The second thermally actuated component comprises: a second flexible container element expandable in a first direction to an expanded position and biased to return to a contracted position; a second thermally responsive material contained in the flexible container; a second heating element arranged such that when the second heating element is activated, heat from the second heating element melts the thermally responsive material, causing the second flexible container to expand to the expanded position, and when the second heating element is deactivated, the thermally responsive material contracts as it cools, causing the second flexible container to return to the contracted position, the expansion and contraction of the second flexible container being used to pump the fluid from the second gap to the first gap; The intermedullary extension nail of claim 3 , comprising:

10. 10. The intermedullary extension nail of claim 9, wherein the second heating element is operably connected to the control circuit and selectively activated by the control circuit to expand and contract the second flexible container.

11. An intermedullary extension nail as described in claim 10, wherein a first heating element is electrically connected to the coil and selectively actuated to expand and contract the second flexible container when an electric current is induced in the coil.

12. 4. The intermedullary extension nail according to claim 3, further comprising a third void provided in the intermediate portion and fluidically communicating with the bidirectional pump and the first void and the second void so that fluid moving between the first void and the second void and fluid moving from the second void to the first void can be temporarily contained therein.

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