MINIATURE MAGNETIC ROBOT SWIMMER GEOMETRIES

Abstract

A miniature magnetic rotating swimmer includes a cylindrical body having a central axis and extending from an aft end to a forward end, a magnet positioned inside of the body, first helical fins extending aft from the forward end, and second helical fins extending forward from the aft end, where the first helical fins and the second helical fins have the same pitch.

Claims

1. A miniature magnetic rotating swimmer (MMRS), comprising: a cylindrical body having a central axis and extending from an aft end to a forward end; a magnet positioned inside of the body; first helical fins extending aft from the forward end; and second helical fins extending forward from the aft end, where the first helical fins and the second helical fins have the same pitch.

2. The MMRS of claim 1, wherein the MMRS terminates at the forward end.

3. The MMRS of claim 1, wherein the MMRS comprises a nose extending from the forward end coaxial with the central axis.

4. The MMRS of claim 1, wherein the first helical fins terminate forward of the second helical fins.

5. The MMRS of claim 1, wherein the body has a cone-shaped head portion proximate the forward end.

6. The MMRS of claim 1, wherein the MMRS has an outside diameter of about 3 mm or less and a total length of about 9 mm or less.

7. The MMRS of claim 1, wherein the number of the first helical fins and the second helical fins is equal.

8. The MMRS of claim 1, wherein the first helical fins is less than or equal to six fins.

9. The MMRS of claim 1, wherein the first helical fins comprise four or fewer fins and the number of the first helical fins and the second helical fins are equal.

10. The MMRS of claim 1, wherein the pitch of the first helical fins and the second helical fins is in the range of about 16 mm to 29 mm.

11. The MMRS of claim 1, wherein: the first helical fins comprises three helical fins; the second helical fins comprise three helical fins; the pitch of the first helical fins and the second helical fins is less than about 29 mm; the MMRS terminates at the forward end; and the MMRS has an outside diameter of about 3 mm or less and a total length of about 7 mm or less.

12. The MMRS of claim 11, wherein the body has a cone-shaped head portion proximate the forward end.

13. The MMRS of claim 11, wherein: the body has a cone-shaped head portion proximate the forward end; the first helical fins terminate forward of second helical fins; and the pitch of the first helical fins and the second helical fins is about 20 mm or less.

14. A miniature magnetic rotating swimmer (MMRS), comprising: a cylindrical body having a central axis and extending from an aft end to a forward end; a magnet positioned inside of the body; first helical fins extending aft from the forward end; a corkscrew-shaped extension extending from the forward end coaxial with the central axis; and second helical fins extending forward from the aft end, where the first helical fins and the second helical fins have the same pitch, and the pitch is less than about 29 mm: wherein the MMRS has a total length of less than about 9 mm and an outside diameter of about 3 mm or less.

15. The MMRS of claim 14, wherein the first helical fins comprise four or fewer fins and the number of the first helical fins and the second helical fins are equal.

16. The MMRS of claim 14, wherein the body has a cone-shaped head portion proximate the forward end.

17. The MMRS of claim 14, wherein the first helical fins terminate forward of the second helical fins.

18. The MMRS of claim 14, wherein: the body has a cone-shaped head portion proximate the forward end; and the first helical fins terminate forward of the second helical fins.

19. The MMRS of claim 14, wherein: the first helical fins is two fins; and the second helical fins is two fins.

20. The MMRS of claim 14, wherein: the body has a cone-shaped head portion proximate the forward end; the first helical fins terminate forward of the second helical fins; the first helical fins is two fins; and the second helical fins is two fins.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The disclosure is best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of various features may be arbitrarily increased or reduced for clarity of discussion. As will be understood by those skilled in the art with the benefit of this disclosure, elements and arrangements of the various figures can be used together and in configurations not specifically illustrated without departing from the scope of this disclosure.

[0009] FIG. 1 illustrates an example a miniature magnetic rotating swimmer according to one or more aspects of the disclosure.

[0010] FIG. 2 is a schematic illustration of the pitch of a helical fin according to one or more aspects of the disclosure.

[0011] FIG. 3 illustrates an example of a magnet arrangement of a miniature magnetic rotating swimmer according to one or more aspects of the disclosure.

[0012] FIG. 4 illustrates an example a miniature magnetic rotating swimmer with a different number of head helical fins and body helical fins.

[0013] FIG. 5 illustrates an example a miniature magnetic rotating swimmer with a cone-shaped head and without a nose extension according to one or more aspects of the disclosure.

[0014] FIG. 6 illustrates another example a miniature magnetic rotating swimmer with a cone-shaped head and without a nose extension according to one or more aspects of the disclosure.

[0015] FIG. 7 illustrates an example a miniature magnetic rotating swimmer with a cork-screw extension according to one or more aspects of the disclosure.

[0016] FIG. 8 illustrates another example a miniature magnetic rotating swimmer with a cork-screw extension according to one or more aspects of the disclosure.

[0017] FIG. 9 illustrates an example a miniature magnetic rotating swimmer with a cylinder shaft nose according to one or more aspects of the disclosure.

[0018] FIG. 10 illustrates another example a miniature magnetic rotating swimmer with a hook typic extension according to one or more aspects of the disclosure.

DETAILED DESCRIPTION

[0019] It is to be understood that the following disclosure provides many different embodiments, or examples, for implementing different features of various illustrative embodiments. Specific examples of components and arrangements are described below to simplify the disclosure. These are, of course, merely examples and are not intended to be limiting. For example, a figure may illustrate an exemplary embodiment with multiple features or combinations of features that are not required in one or more other embodiments and thus a figure may disclose one or more embodiments that have fewer features or a different combination of features than the illustrated embodiment. Embodiments may include some but not all the features illustrated in a figure and some embodiments may combine features illustrated in one figure with features illustrated in another figure. Therefore, combinations of features disclosed in the following detailed description may not be necessary to practice the teachings in the broadest sense and are instead merely to describe particularly representative examples. In addition, the disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not itself dictate a relationship between the various embodiments and/or configurations discussed.

[0020] Miniature, or milliscale, magnetic rotating swimmers (MMRS) are an attractive technology that provides an alternative approach for treating biological disorders inside the body, especially inside the vascular system. An external rotating magnetic field creates a torque on the MMRS and makes it rotate. The rotational motion can be used to disrupt a thrombus mechanically. The head design of the MMRS is an important factor affecting drilling performance. Many researchers have used cone-shaped heads or helical designs to test thrombus disruption performance in in vitro models.

[0021] This disclosure presents new MMRS designs with an increased permanent magnet volume to increase the available torque and prevent the MMRS from becoming stuck inside a thrombus; new helix designs that produce an increased force to compensate for the weight added by the larger permanent magnet volume; different head drill shape designs that have different interactions with thrombi. Two MMRS designs were tested experimentally by removing a partially dried 1-hour-old thrombus with flow in a bifurcating artery model. The first MMRS disrupted a large portion of the thrombus. The second MMRS retrieved a small remaining piece of the thrombus. The optimized geometries also demonstrated they can perform accurate 3D path-following.

[0022] The experimental tests, in a model that mimics a complicated vascular system, show that removing a partially dried, bigger thrombus (500 L, 1-hour-old) with flow is difficult. For instance, the flow may push the MMRS so that it gets stuck in the thrombus. Also, the flow may push the remaining thrombus to a deep, narrow channel, preventing the MMRS from maintaining sufficient contact with the thrombus for disruption. As a result, drilling performance may be reduced to zero. It is challenging to navigate the MMRS in a complicated bifurcating artery model because the MMRS needs to swim backward against the flow and steer itself to swim between bifurcations. Therefore, we must optimize both the swimming and thrombus disruption performance.

[0023] FIG. 1 illustrates an example miniature magnetic rotating swimmer generally denoted by the number 10. Swimmer 10 has a cylindrical body 12, coaxial with a central axis 14, extending from an aft end 16 to a forward end 18. First, or head, helical fins 20 are located on the outer surface 22 of body 12 and extend aft from forward end 18. First helical fins 20 have a lead end 20a and tail end 20b. Second helical fins 24 are located on outer surface 22 and extend forward from aft end 16. Second helical fins 24 have a lead end 24a and a tail end 24b.

[0024] In this example, the first helical fins and the second helical fins have the same pitch. In this example, MMRS terminates at forward end 18. In some embodiments, a nose or other extension extends outward from the forward end coaxial with central axis 14.

[0025] MMRS 10 has a total length 10L and an outside diameter 10D encompassing first helical fins 20 and second helical fins 24. In some embodiments, such as shown in FIG. 1, first helical fins 20 terminate at tail end 20b forward of lead end 24a of second helical fins 24 creating a longitudinal gap 26 between the first helical fins and the second helical fins.

[0026] FIG. 2 schematically illustrates a pitch 28 of a helix, such as the helical fins. Pitch 28 of a helix is the distance covered parallel to the axis of the helix after one complete turn.

[0027] FIG. 3 is a sectional view of a non-limiting example of a MMRS 10. Prior swimmers incorporate a single permanent magnet, while maintaining the miniature size necessary for vascular systems. Prior swimmers however have lacked sufficient power to disrupt a soft thrombus without flow. Embodiments tested and disclosed herein utilize three magnets 30. Magnets 30 are cube shaped NdFeB permanent magnets with a side length of 1 mm. The cube magnets have the same radial magnetization orientation when inside the swimmer. The volume of permanent magnet embedded inside these new designs are 6.8 times larger than the magnet volume used in previous studies.

[0028] FIGS. 4-10 illustrate example miniature magnetic rotating swimmers 10 representative of the experimentally tested swimmers, which are described with reference to FIGS. 1-3. Each of the tested embodiments had an outside diameter 10D of 2.8 mm to accommodate the larger magnet volume from prior swimmers with a 2.5 mm diameter and a length 10L ranging from 5 mm to 8.5 mm. The inventive embodiment are not limited to the larger outside diameter.

[0029] Several helix designs were experimentally tested to enhance the propulsive force of swimmers 10 at a constant length of 6 mm and diameter of 2.8 mm by measuring their hovering frequencies. The hovering frequency is the rotational speed that makes the swimmer hover in place when oriented vertically, when the propulsive force exactly compensates for the vectorial sum of the weight and buoyancy. We chose the hovering frequency as a property to minimize in our designs for multiple reasons. First, this parameter is not only affected by the propulsion efficiency but also by the mass and buoyancy of the designs, which are important properties. The permanent magnets embedded in the swimmers make them denser than water. It is important to minimize mass and maximize buoyancy while having efficient propulsion. Secondly, propellers that rotate slowly to produce a given amount of force are generally more efficient than propellers that rotate fast. The velocity of the liquid surrounding the MMRS can be separated into axial and tangential components. Only the axial component of the fluid velocity produces a propulsive force. The tangential component creates losses and increases with the rotational speed of the MMRS. Finally, the magnetic field induces currents in parts of our system that are made with conductive materials, such as the aluminum extrusions holding the electromagnet supports. These induced currents produce losses that increase with the rotational speed of the magnetic field. Different capacitors were used in these experiments. Capacitors were mounted in series with electromagnets to compensate for the reactive power consumed by electromagnets and increase the available torque for different swimmer designs. The value of the capacitor for each test was chosen based on the swimmer's take-off frequency. We selected the capacitor that allows generating the largest current at this frequency. A PID controller was implemented to regulate the rotational speed of the MMRS and make it hover in the middle of the workspace at a constant z position.

[0030] FIG. 4 is an example MMRS 10 with three first, or head, fins 20 and four second fins 24. When the number of head helices 20 and body helices 24 are not the same, the swimmer becomes unstable and cannot hover in the center of the workspace.

[0031] FIGS. 5 and 6 are representative of swimmers 10 with cone-shaped head portions 32 extending aft from forward end 18. Swimmers 10 were tested with fin (helical) pitches 28 ranging from 16 mm to 29 mm. The addition of second fins 24 increases the propulsive force and lower the hovering frequency. The number of first fins 20 and number of second fins 24 are equal. Swimmers cannot takeoff when first helical fins 20 are greater than 6. FIG. 5 illustrates an embodiment with three first helical fins 20 and three second helical fins 24 and FIG. 6 illustrates an embodiment the four first helical fins 20 and four second helical fins 24. With the same number of first and second helical fins, the hovering frequency slightly increases when the pitches are increased. The lowest hovering frequency occurred with a pitch of 16 mm. For example, testing of the FIG. 5 embodiment with three first helical fins 20 and three second helical fins 24 with 16 mm pitches produced a hovering frequency of 59.9 Hz. The FIG. 6, embodiment with a larger number of fins produced a similar hovering frequency at 60.0 Hz.

[0032] FIGS. 7 to 10 illustrate swimmer 10 designs that include a nose 34 that extends from forward end 18 coaxial with the central axis.

[0033] FIGS. 7 and 8 illustrate MMRS 10 with a nose 34 in the form of a corkscrew-shaped extension 36. Forward end 18 corresponds substantially with a location of lead end 20a of first helical fins 20. Swimmer 10 in FIG. 7 has an equal number, two, of first and second helical fins 20, 24 and swimmer 10 in FIG. 8 includes first helical fins 20, for example two fins, and does not have any second helical fins. The difference in hovering frequency is significant. The FIG. 7 swimmer produced a hovering frequency of 82.9 Hz, and the FIG. 8 swimmer produced a hovering frequency of 118.9 Hz. Each of the illustrated designs with corkscrew-shaped extensions 36 also have a cone-shaped head 32.

[0034] FIG. 9 illustrates an MMRS 10 with a nose 34 extending from forward end 18 in the form of a cylinder-shaped shaft 38 without any external fins or threads. This example has three first helical fins 20 and three second helical fins 24. This design produced a hovering frequency of 77.2 Hz.

[0035] FIG. 10 illustrate an MMRS 10 with a nose 34 in the form of a hook-shaped nose 40. Hook-shaped nose 40 includes a cylindrical shaft 42 with external ridges or threads 44. It has an equal number, three, of first helical fins 20 and second helical fins 24. This design does not have a cone-shaped head portion. The design produced a hovering frequency of 90.3 Hz.

[0036] The FIG. 5 (conehead), 7 (corkscrew), and 9 (cylinder shaft) designs were chosen for additional tested for disrupting a thrombus. Each of the designs was experimentally tested to remove a 1-hour-old thrombus in a single PDMS channel without flow. Each channel contained 100 L blood and was placed into the magnetic manipulator (pre-heated to 37 C.) for 1 hour to form the thrombus. A temperature sensor and a heater were present inside the magnetic manipulator to regulate the temperature. Each electromagnet was connected in series with a 30 F capacitor. These capacitors generate a resonating frequency of 63 Hz. We used the same rotational frequency (63 Hz) for testing each MMRS' thrombus disruption performance.

[0037] The FIG. 5 swimmer design with a cone-shaped head 32 and without a nose portion can completely disrupt the thrombus in 436 seconds. The removal rate is 13.74 mm3 min1. This design can effectively reduce the size of thrombi.

[0038] The FIG. 7 swimmer 10 with a corkscrew extension 36 disrupted the thrombus and reopened the channel in 78 seconds. The removal rate is 76.92 mm3 min1. During this test, a small piece of the thrombus stayed attached to the tip of corkscrew extension 36 indicating that the design can collect a small thrombus and retrieve it. This piece of the thrombus could be used for analysis during real procedures.

[0039] The FIG. 9 swimmer design with cylinder-shaped nose 38 can reduce the size of the thrombus, however, the swimmer became stuck in the thrombus. As a result, the drilling performance is reduced significantly, and the swimmer cannot completely disrupt the thrombus.

[0040] The magnetic manipulator used in the experimental testing has six electromagnets arranged in a cube shape. The system can generate a magnetic field with any 3D orientation inside the workspace. A set of two Kepco BOP 20-50 MG power supplies connected in series is used to power each electromagnet. The power supplies are controlled via an external analog signal generated by an IC3173 industrial controller manufactured by National Instrument. Two Basler acA800 cameras viewing from the top and right sides of the manipulator were used to measure the swimmer's position.

[0041] The swimmers 10 ere 3D-printed using a Formlabs SLA 3D printer with 50 m resolution. After printing, the MMRSs were cleaned using ethanol to remove the resin left on the surface and inside the hole that receives the magnets. They were then placed under a UV light for approximately 45 minutes to finish curing the resin. After inserting the magnets, a small amount of epoxy was placed at the bottom of the swimmer to hold the magnets in place.

[0042] Example protocols and experimental results to estimate the efficiency of MMRS designs for a thrombus disruption procedure. Two aspects of the designs were studied, the swimming performance and the thrombus disruption performance. The path-following performance was also measured. Swimmers need to perform well on all these aspects to achieve a successful thrombus disruption procedure.

[0043] As discussed above, the MMRS 10 designs of FIGS. 5, 7 and 9 were experimentally tested to remove a 1-hour-old thrombus in a single PDMS channel without flow. The swimmer designs in FIGS. 5 and 7 were also tested to remove a partially dried thrombus in a bifurcating artery model with flow.

[0044] A pipette was used to measure 500 L of blood and insert it inside a 6 mm diameter tube held vertically. This tube was then placed into the magnetic manipulator, which was preheated to human body temperature (37 C.) and left inside for 1 hour. The thrombus was then removed from the manipulator and the tube, placed on a paper towel, and immediately rolled to remove adherent serum by hand for approximately 1 minute. Then, the partially dried 1-hour-old thrombus was ready to deliver to the artificial vessel made with PDMS for the experiment. The vessel model starts with a channel that has a diameter of 3.5 mm and then separates into two channels that are each 3 mm in diameter. Each channel then further separates into two channels that are each 1.5 mm in diameter. The total length of the vessel is 78 mm. We use this model to represent an arterial tree.

[0045] An input tank containing phosphate-buffered saline (PBS) solution was used to apply pressure and flow to the artificial artery model. PBS is a water-based salt solution with the same pH as human blood. The tank was raised 80 mm above the channel. The tank's fluid was manually refilled during the test to keep a positive pressure difference between the input of the channel and the output. This method produces changes in flow rate when the tank is refilled and when the tank level decreases. To generate a blockage, the thrombus is inserted into the tube inside the PBS tank. The thrombus moves with the flow to the channel, simulating how thrombi form in the vascular system. This tube is also used to insert the swimmer using the insertion/retrieval tool presented below. A Canon EOS RebelSL2 camera was placed on top of the magnetic manipulator to monitor the experiment process in real-time through a display screen. An output tank placed on the right side of the manipulator was used to collect the liquid. A tube connected from the bottom of this tank to a pressure sensor measures the flow through the artificial artery model during experiments. The pressure sensor was designed with an Omron 2SMPP-02 sensor and an instrumentation amplifier. The output of the amplifier was connected to an Arduino analog input. The sensors were calibrated from 0 to 20 000 Pa using a column of water with variable height.

[0046] In this experiment, the magnetic field rotational speed and axis were controlled manually via the LabVIEW user inter-face. The thrombus disruption process started with the FIG. 5 swimmer 7 with a cone-shaped head and no nose extension. When the thrombus became too small to interact efficiently with this MMRS, the cone-shaped head MMRS was retrieved and was replaced by the FIG. 7 corkscrew design.

[0047] Initially, the thrombus was delivered to the channel and stayed at the first bifurcation. The FIG. 5 cone-shaped head was inserted in the channel and the swimmer pushed the thrombus to the upper channel, disrupted it, and reduced its size. Next, the fluid flow pushed the remaining thrombus to a deeper, narrow channel at the second bifurcation. As a result, the FIG. 5 swimmer's drilling performance was reduced and no longer reduced the size of the thrombus.

[0048] The FIG. 7 corkscrew swimmer design was able to reduce the size of the thrombus further and collect the remaining piece. Finally, the swimmer was moved to the retrieval location with the remaining piece of thrombus, and both were retrieved.

[0049] To show that the selected MMRS designs can swim and follow a predefined path in liquid, we made the MMRSs follow a racetrack path that has 40 mm straightaways and 40 mm diameter curves using closed-loop control. The 3D path controller was implemented in LabVIEW. The MMRSs swam inside a cube-shaped acrylic tank with 160 mm side lengths filled with tap water. The magnetic field started at low frequencies and increased until the swimmer took off and followed the path centerline. 30 F capacitors were used in these tests. We recorded 3000 data points (experiment duration is 1 minute) for each swimmer tested. The swimmer's position was detected from camera views at the top and right sides of the manipulator, and the closest point on the path centerline was recorded for calculating the average path tracking error. The tracking error is the Euclidean distance between the swimmer's position and the closest point on the path centerline. The FIG. 5 swimmer design followed the path when rotating at 71 Hz with an average path tracking error of 2.8 mm. The FIG. 7 swimmer design followed the path when rotating at 84 Hz with an average path tracking error of 3.5 mm. Both swimmers followed the path reliably.

[0050] Although relative terms such as outer, inner, upper, lower, and similar terms have been used herein to describe a spatial relationship of one element to another, it is understood that these terms are intended to encompass different orientations of the various elements and components in addition to the orientation depicted in the figures. Furthermore, as used herein, the terms connect, connection, connected, in connection with, and connecting may be used to mean in direct connection with or in connection with via one or more elements. Similarly, the terms couple, coupling, and coupled may be used to mean directly coupled or coupled via one or more elements. The terms substantially, approximately, generally, and about are defined as largely but not necessarily wholly what is specified (and includes what is specified; e.g., substantially 90 degrees includes 90 degrees and substantially parallel includes parallel), as understood by a person of ordinary skill in the art. The extent to which the description may vary will depend on how great a change can be instituted and still have a person of ordinary skill in the art recognized the modified feature as still having the required characteristics and capabilities of the unmodified feature.

[0051] The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the disclosure. Those skilled in the art should appreciate that they may readily use the disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the disclosure and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the disclosure. The scope of the invention should be determined only by the language of the claims that follow. The term comprising within the claims is intended to mean including at least such that the recited listing of elements in a claim are an open group. The terms a, an and other singular terms are intended to include the plural forms thereof unless specifically excluded.