Method for force, displacement, and rate control of shaped memory material implants

Abstract

A method for force, displacement, and rate control of shape memory material implant. The rate of implant shape change as well as the force exerted on the surrounding tissue of the implant can be controlled by the surgeon and the extent of movement is controlled in circumstances where the bone element is free to move. The invention allows for the first time the fine control of force when fixating osteoporotic bone and rate of bone transport when working near the spinal cord. This heating profile of the implant provides the surgeon to control the extent of microstructure phase transformation so that the rate, force or extent of tissue movement can be controlled individually or together.

Claims

1. A method comprising: (a) selecting an implant comprising a memory material having a shape changing transition temperature range that has a shape that is designed to be controlled with an energy delivery device, wherein (i) the memory material comprises martensitic phase memory material, (ii) the martensitic phase memory material is operable to transition to austenitic phase memory material in the shape changing transition temperature range, and (iii) the step of selecting the implant is based, at least in part, on a maximum level of force the implant can apply when changed in shape; (b) implanting the implant during a surgical procedure; (c) utilizing the energy delivery device to deliver an amount of energy to change the shape of the implant by transitioning at least some of the martensitic phase memory material to the austenitic phase memory material, wherein (i) the amount of energy delivered by the energy deliver device is selected to change the shape of the implant to a selected shape having a selected amount of force from a plurality of pre-selected increments of energy that correspond to a plurality of incremental shape changing forces that change the shape of the implant to a corresponding plurality of incremental shape change positions, (ii) the corresponding plurality of incremental shape change positions are positions of the implant that successively further change the shape of the implant, and (iii) the energy delivery device is used to control (A) the rate of change in the shape of the implant and (B) the amount of energy delivered by the energy delivery device to the implant.

2. The method of claim 1, wherein the implant is selected from the group consisting of catheters, intrauterine contraceptive devices, gastrointestinal compression clip, blood vessel filter, coronary artery stent, skin staple, bone staple, and bone plate.

3. The method of claim 1, wherein the implant comprises a plurality of members, wherein the plurality of members are operable to be controlled together by the energy delivery device.

4. The method of claim 1, wherein the implant comprises a plurality of members, wherein the plurality of members are operable to be controlled independently by the energy delivery device.

5. The method of claim 1, wherein the memory material has martensitic to austenitic finish transition temperatures sufficiently different so that the plurality of incremental shape change positions can be implemented so as to achieve high resolution control of a characteristic selected from the group consisting of an implant force, rate of shape change, extent of shape change.

6. The method of claim 1, wherein the change in the shape of the implant is opening or closing of the implant.

7. The method of claim 1, wherein the plurality of the pre-selected increments are pre-selected to control a pre-selected characteristic selected from the group consisting of (a) a corresponding plurality of incremental shape change forces, (b) a corresponding plurality of periods of time of incremental rate of shape change of the implant, (c) a corresponding plurality of extents of shape change of the implant, and (d) combinations thereof.

8. The method of claim 7, wherein the pre-selected characteristic comprises a combination of (a) the corresponding plurality of the incremental shape change forces, (b) the corresponding plurality of the periods of time of the incremental rate of shape change of the implant, and (c) the corresponding plurality of the extents of shape change of the implant.

9. The method of claim 7, wherein the pre-selected characteristic comprises the corresponding plurality of the incremental shape change forces.

10. The method of claim 9, wherein the corresponding plurality of the incremental shape change forces are incrementally between 10% and 20% increments of the maximum level of force.

11. The method of claim 9, wherein the corresponding plurality of the incremental shape change forces are 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100% of the maximum level of force.

12. The method of claim 9, wherein the pre-selected characteristic further comprises the corresponding plurality of the periods of time of the incremental rate of shape change of the implant.

13. The method of claim 9, wherein the pre-selected characteristic further comprises the corresponding plurality of the extents of shape change of the implant.

14. The method of claim 7, wherein the pre-selected characteristic comprises the corresponding plurality of the periods of time of the incremental rate of shape change of the implant.

15. The method of claim 14, wherein the corresponding plurality of the periods of time of the incremental rate of shape change of the implant are incrementally one second increments.

16. The method of claim 14, wherein the pre-selected characteristic further comprises the corresponding plurality of the extents of shape change of the implant.

17. The method of claim 7, wherein the pre-selected characteristic comprises the corresponding plurality of the extents of shape change of the implant.

18. The method of claim 17, wherein the corresponding plurality of the extents of shape change of the implants are incrementally between 10% and 20% increments.

19. The method of claim 17, wherein the corresponding plurality of the extents of shape change of the implant are 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100%.

20. The method of claim 1, wherein the implant is operable to be being controlled with the energy delivery device using a feedback control loop.

21. The method of claim 20, wherein the feedback control loop measures temperature of the implant.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further objects and advantages of this invention will become apparent from consideration of the drawings and ensuing description of the preferred embodiment.

(2) FIG. 1 Memory metal implant temperature versus heating duration curve

(3) FIG. 2 Implant tissue force versus implant temperature curve

(4) FIG. 3 Implant tissue force versus shape change period curve

(5) FIG. 4 System diagram based on lookup table

(6) FIG. 5 Lookup table example

(7) FIG. 6 System diagram based on models, algorithms and lookup tables

(8) FIG. 7 Multi-element implant example

(9) FIG. 8 Multi-element implant electrode example

(10) FIG. 9 Electrode handle and system circuit diagram for simple feedback and control system example

LIST OF REFERENCE NUMERALS

(11) 100 Two second heating curve for martensitic to austinetic phase transformation

(12) 110 Ten second heating curve for martensitic to austinetic phase transformation

(13) 200 Austinetic transformation start temperature and inflection in force curve

(14) 210 Austinetic transformation end temperature

(15) 220 Minimum tissue force seen at body temperature

(16) 230 Maximum tissue force seen at body temperature

(17) 300 Force versus time curve while heating

(18) 400 Power supply with isolation transformer

(19) 410 AC to DC power converter

(20) 420 User set timer circuit

(21) 430 User set power circuit

(22) 440 Current delivery electrode

(23) 450 Circuit board

(24) 460 Electrode conductor to implant

(25) 470 Heating control button

(26) 475 Implant-system continuity light

(27) 480 Implant-system heat energy light

(28) 485 Lookup table

(29) 490 Front control panel with time, power, on-off switch, and indicator lights

(30) 495 Audible operational indicator

(31) 500 Implant force and rate control lookup table

(32) 510 Heating duration data

(33) 520 Force level data

(34) 530 Power level within cells of the lookup table

(35) 600 Power supply with isolation transformer

(36) 610 AC to DC power converter

(37) 620 Timer circuit

(38) 630 Front panel control with keyboard and monitor

(39) 640 Current delivery electrode

(40) 650 Microprocessor running model, algorithm or sorting the lookup table

(41) 655 Circuit board

(42) 660 Audible operational indicator

(43) 670 Power circuit

(44) 680 Electrode handle

(45) 685 Electrode start button

(46) 690 Implant-system continuity light and heat energy light combined

(47) 695 Electrode conductor to implant

(48) 700 Spinal plate

(49) 705 First length or angle shape-changing member

(50) 710 Second length or angle shape-changing member

(51) 720 First bone anchoring shape-changing member

(52) 730 Second bone anchoring shape-changing member

(53) 740 Third bone anchoring shape-changing member

(54) 750 Fourth bone anchoring shape-changing member

(55) 760 First electrode contact point for member 720

(56) 765 Second electrode contact point for member 720

(57) 770 First electrode contact point for member 710

(58) 775 Second electrode contact point for member 710

(59) 780 First electrode contact point for member 750

(60) 785 Second electrode contact point for member 750

(61) 800 First electrode element for FIG. 7 member 720

(62) 810 First electrode element for FIG. 7 member 730

(63) 820 First electrode element for FIG. 7 member 740

(64) 830 First electrode element for FIG. 7 member 750

(65) 840 Second electrode element for FIG. 7 member 740

(66) 850 Second electrode element for FIG. 7 member 730

(67) 860 Second electrode element for FIG. 7 member 720

(68) 870 Second electrode element for FIG. 7 member 750

(69) 880 Multi-electrode handle

(70) 890 Electrode conductor bundle

(71) 895 Individual electrode conductors

(72) 900 Power supply

(73) 910 User operated switch

(74) 920 Temperature cutout switch

(75) 930 Thermocouple temperature sensing transducer

(76) 940 Implant heating electrode with thermocouple

(77) 950 Implant heating electrode

(78) 960 Thermocouple leads to temperature cutout switch

DESCRIPTION OF THE PREFERRED EMBODIMENT

(79) The preferred embodiment of the invention consists of an electronic control console that operates using a lookup table, algorithm or mathematical model to control the temperature of a memory ahoy implant in such a manner so as to control the extent of its transformation from a martensitic to austenitic microstructure. The rate of heat application controls the rate of implant shape change (FIG. 1). Rapid heating curves (100) and slow controlled heating curves (110) both can provide sufficient heat energy to fully convert the material's phase and shape. The magnitude of heat transferred controls the state-of-the-metal's phase change thus the force exerted on surrounding tissue (FIG. 2). Force and temperature relationships exist for each shape-changing element of an implant. In an implant restrained in bone the force exerted by the implant increases with temperature. The tissue force begins at or near the austinetic start temperature [A.sub.s] (200) and increases until the austinetic finish temperature [A.sub.f] (210) as shown in the implant temperature versus force curve (FIG. 2). The force can be controlled from a minimum value of the force at body temperature [F.sub.min] (220) before heating and at body temperature after heating [F.sub.max] (230). With these relationships for a given implant shape-changing member and power setting, a force versus time curve will exist (FIG. 3). Consequently, a force versus power curve will exist for any shape-changing member at a constant heating period.

(80) The control of the heat energy to the implant is implemented using a device: having a power supply with electrical patient isolation transformer (400), rectifying circuit to convert alternating to direct current (410), user controllable timing circuit (420), user controllable power circuit (430), a user operated current delivery electrode (440), circuit board (450), bipolar current delivery electrode (460), heating control button (470), implant-system continuity light (475), implant-system heat energy light (480), lookup table (485), front control panel with time, power, on-off switch, and indicator lights (490), and an audible operational indicator (495) (FIG. 4). The lookup table (485) could be in the form of an alphanumeric table, mathematical model, or algorithm.

(81) The primary data from the surgeon consists of the 1) the implant selected, 2) the period of which the implant should change shape, and 3) the percentage of the total force available in this style of implant to be applied to the surrounding tissue. Each implant has a separate lookup table (500) (FIG. 5). This table can be within an operator's manual or embedded in the instrument.

(82) The rate data, time for the implant to close, is used as row (510) or column (520) headings and the force is the alternate column heading. The voltage setting to achieve the desired implant result is read from within the cells (530) of the table.

Operation of the Invention

(83) In the operation of the preferred embodiment, the surgeon will select the implant to be used; maximum level of force for the implant to apply to the surrounding tissue, and the amount of time that the implant should take to change shape. Other variables such as ambient temperature of the implant, amount of bone movement expected, and extent of shape change when correcting bone angulation can also be inputted or listed in the lookup table (485).

(84) Once the instrument is connected to a source of electricity so as to energize the power supply (400), the surgeon after review of the lookup table (485) sets the controls on the front panel of the instrument (490). After placing the implant into bone the surgeon will bring the electrodes (460) into contact with the implant. The electrodes (460) when touching the implant cause the continuity light (475) to illuminate to show the surgeon that the force and rate control system is in optimal contact with the implant to deliver a user selected amount of heat energy over a user specified period of time. The surgeon then applies heat energy to the implant by actuating the heating control button (470). As the heating current flows the continuity light (475) turns off and the heat energy light (480) illuminates during the user-selected period for heat energy delivery. The front panel (490) time control knob sets the timing circuit (420) so as to control the rate of heat energy delivery and shape change period. Audible current flow indicator (495) assists the surgeon in the use of the system. The continuity light (475) and heat energy light (480) are located on the electrode handle (440) so as to be in clear view of the surgeon when working in the operative site. The circuit board (450) holds the electrical conductors, user controlled power circuit (430) and the other components required to complete the system.

(85) If, as in most cases in bone fixation, the bony elements do not move in response to the force applied by the implant the force magnitude applied to tissue is as listed in the lookup table. If bone transport occurs then the force will be less than predicted. Under this condition the surgeon can measure the amount of bone transport, input these data into the lookup table and correct to obtain the actual applied force. This allows the surgeon to adjust the amount of displacement of bone as well as force exerted on bone during the implantation procedure. This provides fine control for the physician when stabilizing bone elements or fragments.

(86) Once the heating energy is delivered the energy light (480) turns off and the cycle is complete. The heating energy can be applied multiple times to the implant. In the condition of osteoporosis the surgeon may sequentially increase the closing force of the implant through stepping the closing force up at 10% to 20% increments until the surgeon receives operative clues that the maximum implant fixation force has been applied without causing fracture of the osteoporotic bone. The subject invention for the first time gives full control to the physician to provide a plurality of implant force and closing rate characteristics to each of plurality of implant designs.

Description of the First Alternate Embodiment

(87) The first alternate embodiment of the invention is based on the same principals of the preferred embodiment which controls the conversion of the martensitic to austenitic phase transition of the implant material. This first alternate embodiment integrates elements such as but not limited to a lookup table, algorithms, heat transfer models of the implants (640) and predictive graphics model of the shape change of the implant and force applied to the tissue. These image and numeric data are displayed on the front panel (630) monitor and controlled using the front panel (630) keyboard to allow the surgeon to observe the theoretical effects of heating to the implant and adjust the heat energy to the implant to get the desired clinical effect.

(88) In this embodiment the power supply (600), AC to DC converter (610), and circuit board (655) are configured to support a microprocessor (650) and computer memory which contains model data, model algorithms, and lookup tables (640) to allow the modeling of the effects of heat energy application to the implant. This intelligent system front panel (630) displays implant images, shape change data, and allows the model predictions of the rate and force of implant shape change to be compared to the operative observations. The timer relay (620) and power circuit (670) in this embodiment are microprocessor (650) controlled. An audible current flow indicator (660) and combined continuity and heat energy light (690), in addition to the front panel (630) enhance surgeon feedback to the operation of the subject invention in this embodiment. In this configuration the surgeon will program the force and rate profile and then using the electrode handle (680) place the electrodes (695) on the point of the implant shown on the front panel (630) monitor to apply heat. Once the electrode (695) is in contact with the element of the implant the electrode start button (685) is pushed, the front panel (630) monitor then displays the theoretical effect on the implant and directs the surgeon to the next element of the implant for heat energy application.

Operation of the First Alternate Embodiment of the Invention

(89) This first alternate embodiment allows the surgeon to predict the changes to the implant and then observe the in vivo effects of the implant on bony elements. These features increase the feedback to the surgeon, compensate for and controls heating of multiple elements of an implant and enhances the degree of force and rate control of the implant for the surgeon.

(90) In use the surgeon will select and display the implant on the front panel (630) monitor. Then the desired rate and tissue force will be input by the surgeon, using the front panel (630) for each shape-changing element incorporated into the implant. Once set the front panel (630) monitor will guide the surgeon in using the electrode handle (680). The monitor will display the point of contact for the electrode (695) and instruct the surgeon to actuate the electrode start button (685). The monitor will then display the theoretical shape change and tissue force and guide the surgeon to place the electrode handle (680) on the next shape-changing member of the implant.

(91) As shown in the spinal plate of FIG. 7 multiple shape changing members may need to be controlled. Members that lock into bone (720, 730, 740, and 750) or shrink to shorten the plant (705 and 710) can be selectively controlled. In FIG. 7 member 720 can be affected by applying current to circular points 760 and 765. Member 750 can be affected by applying heat energy to points 780 and 785. And length shortening or angle changing member 710 can be affected by applying heating energy across x marked points 770 and 775. A single bipolar electrode can be used at multiple locations to close each shape-changing member one at a time. Alternatively a multi-electrode handle FIG. 8 can be placed on the implant and the subject invention can then heat each implant shape changing element (FIG. 7) in the selected sequence. In this manner electrode handle 880 can heat the shape-changing member 720 by having the electrode handle apply current to electrode points 830 and 870. Or member 705 of FIG. 7 can be shortened or lengthened by applying heat energy with the handle (880) and electrodes 840 and 850.

(92) During the process the surgeon can adjust the force applied to the tissue, correct for bone transport that may make the force estimate inaccurate and then instruct the surgeon when the implant is in its final configuration.

Description of the Second Alternate Embodiment

(93) In the second alternate embodiment the implant-heating model and lookup table are replaced with a measurement of the implant temperature. This temperature measurement is taken from the surface of the implant. Temperature measurement devices include but are not limited to thermocouples and thermal imaging. Other feedback mechanisms such as strain gauges that measure the shape change of the implant can be used for feedback control. These measured data are input to the model or a switch that stops current flow to the implant.

(94) The system diagram of FIG. 6 now takes data from the heat sensing transducers to input into the algorithm and implant models (640) so that the microprocessor (650) can correlate force and rate data with temperature and accurately control the implant's shape change. This method accounts for the environmental temperature issues associated with a cold operating room and a warm patient.

(95) The FIG. 9 system diagram illustrates the temperature feedback embodiment of the invention. Here the power supply (900) is connected to the user-actuated electrode start button (910) which provides power to a current cutout switch (920) that receives input from the thermocouple (930), located on the electrode (940), through the thermocouple wires (960). The electrode (950) could hold an additional thermocouple for product redundancy and additional points of temperature measurement.

Operation of the Second Alternate Embodiment of the Invention

(96) In this embodiment the amount of power set on the power supply (900) will control the rate of heating and the setting for the cutout switch (920) is related to the force. In the simple configuration of FIG. 9 a lookup table is used to set the power level and the cutout parameters.

(97) In use the surgeon selects these two parameters and the system automatically cuts out at the implant temperature corresponding to a specific tissue force.

Conclusions, Ramifications and Scope of the Invention

(98) The reader will see that the system and method described in the specifications to control the rate, displacement and force of a shape changing implant provides an important modality for the surgeon in the treatment of skeletal injury and disease.

(99) While the above description is specific this should not be construed as limitations of the scope of the invention, but rather as an example of a plurality of possible embodiments which exhibit the characteristics of controlling implants formed from shape memory material. Thus any system that individually or in concert controls the rate, displacement and force exerted on tissue by a shape memory material implant is within the scope and spirit of this invention.

(100) Accordingly, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their legal equivalents.