Magnetic Microrobot

Abstract

1. A microrobot comprising: a) an attachment module (300) for connecting the microrobot to a delivery device (100); and b) a tip module (200), the tip module (200) comprising: (i) a bullet-shaped portion (230) having an outer shell (231) and one or more first magnets (232), the outer shell (231) having a design capable of being propelled by an external magnetic field when the one or more first magnets (232) interact with the external magnetic field; and (ii) a holder (220) for holding the bullet-shaped portion (230), the holder (220) comprising a release mechanism for releasing the bullet-shaped portion (230) from the holder (220).

Description

[Technical field]

[0001] The present invention relates to a magnetic microrobot for accessing hard-to-reach areas in tubular environments such as blood vessels. [Background technology]

[0002] Endovascular intervention is a common approach to treat vascular diseases. In the procedure, a flexible guidewire / catheter is inserted through a small incision (e.g., femoral artery in the groin, radial artery in the wrist) and then guided to the target lesion in the vasculature. However, traditional interventions have technical challenges. Standard instruments do not have active maneuverability and are manipulated at the remote end by push-pull and rotation. Therefore, the success of the procedure is entirely dependent on the surgeon's high expertise and extensive experience.

[0003] To date, various steerable interventional devices have been designed for improved maneuverability, among which magnetic actuation is one of the popular methods, and such designs are characterized by small size, good adaptability, and low cost. Nevertheless, the success rate through tortuous arteries and veins (e.g., curved, kinked, annular, spirally twisted) has hardly been evaluated, and it has been reported that these structures are difficult to manipulate and even cause instrument breakage due to the contact forces between the wires and the complex vessel walls. On the other hand, wireless miniature robots have been widely studied for their ability to access complex and hard-to-reach areas and can further perform various tasks. However, control under rapid blood flow remains difficult, specifically, the small robots may be lost during migration to the lesion or during withdrawal after treatment.

[0004] Therefore, there is a need to develop a device that integrates the advantages of both wired and wireless miniature robots, which will be convenient for clinical needs and useful to clinicians for the treatment of vascular diseases. Related inventions are still in the research gap. The present invention has a compact design, consisting of a commercially available guidewire and an assembled tip module. The rotating rocker and magnetic ejector structure allow flexible bending and controllable tip ejection, realizing two different operating modalities in a single design. Summary of the Invention

[0005] The present invention provides a microrobot. In one embodiment, the microrobot comprises: a) an attachment module (300) for connecting the microrobot to a delivery device (100); and b) a tip module (200) comprising: (i) a bullet-shaped portion (230) having an outer shell (231) and one or more first magnets, the outer shell (231) having a design capable of being propelled by an external magnetic field when the one or more first magnets interact with the external magnetic field; and (ii) a holder (220) for holding the bullet-shaped portion, the holder (220) comprising a release mechanism for releasing the bullet-shaped portion from the holder.

[0006] The present invention further provides a method of using the microrobot of the present invention for intravascular intervention in a subject. In one embodiment, the method of using the microrobot comprises the steps of: a) connecting the microrobot to a delivery device (100) via the attachment module (300), b) inserting the microrobot into a blood vessel of a subject via the insertion point, and c) positioning the microrobot at a suitable site, where the forward and backward movement of the microrobot is adjusted by a motorized feeder or manually, and steering the movement of the microrobot is adjusted by an external magnetic field.

[0007] The present invention also provides a system for intravascular intervention in a subject, in one embodiment, the system comprising: a) a microrobot of the present invention for positioning at a site in the subject, b) an electromagnetic array (720) for generating the external magnetic field, c) an ultrasound probe (730) for medical imaging-based feedback on the position of the microrobot, and d) a parallel manipulator (710) for driving the ultrasound probe and the electromagnetic array into the vicinity of the site. [Brief description of the drawings]

[0008] [Figure 1] Figure 1 shows the operation of a guidewire-attached magnetic microrobot in the vasculature. Tethered (upper branch) and untethered (lower branch) modes are implemented under different scenarios to enhance the accessibility. [Diagram 2] FIG. 2 is an overall structure and exploded perspective view of a guidewire-mounted magnetic microrobot. [Diagram 3] FIG. 3 shows the internal state of the rotating rocker and the magnetic ejector during the flexible bending stage and the tip eject stage. [Figure 4] Figure 4 shows a schematic diagram of the magnet array, the calculated magnetic torque and force at different stages, and the distribution of magnetic field flux density at maximum attractive and repulsive forces. [Diagram 5] FIG. 5 is a kinematic analysis for a tethered mode actuated by directional external magnetic fields and an untethered mode actuated by rotating external magnetic fields. [Figure 6] Two functionalized helical bullets are shown (perforator-type design for clot removal, carrier-type design for targeted drug delivery). [Figure 7] FIG. 1 is a conceptual diagram of an actuation system employed in a remote control system. [Figure 8]FIG. 2 is a block diagram showing a system configuration and a control process. [Figure 9] Figure 9 contains the fabricated guidewire-mounted magnetic microrobot prototype and characterization results. [Figure 10] FIG. 10 includes photographs illustrating the experimental setup for tethered modes in a model with multiple 3D branches, untethered modes in a model with a loop structure, and a full-scale leg artery model. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] In this invention, a guidewire-mounted magnetic microrobot with two motion modalities is proposed to access hard-to-reach areas in tubular environments. The microrobot is composed of a commercially available guidewire and an assembled tip module. The rotating rocker and magnetic ejector structure allows flexible bending and controllable tip ejection. The tethered mode is for navigation through tubular networks with large diameters and high flow rates, where forward and backward motion is controlled by a feeder device and steering motion is actuated by a directional external magnetic field. The untethered mode is for accessing lesions with narrow and tortuous configurations, where the ejected helical bullet is wirelessly propelled by a rotating external magnetic field.

[0010] In this invention, a guidewire-attached magnetic microrobot with two operating modalities, characterized by good maneuverability and adaptability, is developed. It consists of a commercially available guidewire and an assembled tip module. The latter further has three functional components called base frame, rotating holder, and helical bullet, on which an array of three permanent magnets is attached. The actuation of the microrobot relies on both a well-designed mechanical structure and magnetic effects. In particular, the rotating rocker enables omnidirectional flexible bending in tethered mode, the combination of the rotating rocker and magnetic ejector realizes controllable tip ejection for mode switching, and the spiral configuration realizes wireless helical propulsion in untethered mode.

[0011] The tethered mode is similar to conventional interventional procedures for long-distance navigation through vascular networks, but with improved maneuverability due to guided magnetic navigation. This mode of operation has high efficiency and reliability, with forward and backward motion controlled by adjusting the position of the guidewire using a feeder device, and steering motion actuated by a directional external magnetic field. The untethered mode is freed from the constraints of the wire, where the released helical bullet acts as a free swimmer powered by a rotating external magnetic field, converting rotation to linear motion and entering tortuous lesions. This mode of operation has enhanced adaptability.

[0012] The control mode is selected according to the applied environment for better performance. For example, at the beginning of the intervention, the tethered mode is adopted for navigation in vasculature with large diameter and high blood flow for fast operation speed and loss avoidance. When the narrow and tortuous configuration of the vessel is reached, the untethered mode is utilized and the helical bullet is released for access to the target and retrieved after treatment.

[0013] Besides the overall structural design of the guidewire-mounted magnetic microrobot, the following related researches are also included: the principle of tip ejection is discussed for the general design across dimensions; a kinematic model including two modes is established for the purpose of control; various functionalized helical bullets are proposed for different procedures; a moving coil electromagnetic actuation system is adopted for human-scale validation and demonstration. The following figures and detailed description provide a better understanding of the claimed invention.

[0014] Definitions and Abbreviations

[0015] The following terms shall be used to describe the present invention. In the absence of specific definitions set forth herein, the terms used to describe the present invention shall be given their ordinary meanings as understood by those of ordinary skill in the art.

[0016] As used herein, the phrase directional external magnetic field refers to an applied magnetic field that has any direction in any dimension. The direction can vary either continuously or discretely.

[0017] As used herein, the expression rotating external magnetic field refers to an applied magnetic field having a direction that varies continuously along the axis of rotation. The generated magnetic field vectors of one period form a disk perpendicular to the axis of rotation.

[0018] Referring to Fig. 1, the guidewire-mounted magnetic microrobot (1) has two motion modalities that can be selected according to the applied environment (2), such as a tethered mode with fast movement speed and high reliability shown in a branch vessel (upper branch), and a non-tethered mode for improved compliance shown in a circular vessel (lower branch). The two-in-one design of the present invention can integrate the advantages of both wired and wireless microrobots and overcome the challenge of reaching hard-to-reach areas in clinical treatment.

[0019] Referring to FIG. 2, the guidewire-mounted magnetic microrobot (1) is composed of a commercially available guidewire (100) and an assembled tip module (200), with the two parts connected by a segment of silicone cannula (300). The assembled tip module (200) has three functional components: a base frame (210), a rotating holder (220), and a helical bullet (230). The base frame (210) consists of a lower stick for connecting to the guidewire (100) and an upper cavity for holding the rotating holder (220). The rotating holder (220) has a lower shaft for plugging into the base frame (210), two central holes for placing axially magnetized cylindrical magnets (221, 222) with opposite magnetization directions, and an upper bucket for housing the helical bullet (230). The helical bullet (230) includes a spiral outer shell (231) and a radially magnetized inner cylindrical magnet (232). For assembly purposes, the base frame (210) is divided into a left section (211) and a right section (212), and the rotating holder (220) is divided into an upper section (223) and a lower section (224), which are glued together using a medical grade adhesive.

[0020] Referring to FIG. 3, the cavity of the base frame (210) has a stopper (213) and the shaft of the rotating holder has a slider (223). Such a fit allows the rotating holder (220) to rotate along the axis within limits while restricting its radial deflection and axial movement. This structure is called a rotating locker. The buckets of the rotating holder (220) have an inner diameter slightly larger than the outer diameter of the helical bullet (230), thereby maintaining the relative position between them and allowing axial rotation and movement. This structure is called a magnetic ejector. The combination of these two structures allows both flexible bending for tethered mode and tip ejection to switch to untethered mode.

[0021] For flexible bending, an external magnetic field is applied to ensure that there is no blocking effect between the slider (223) and the stopper (213). As a result, the attractive force between the cylindrical magnets (221, 222, 231) keeps the helical bullet (230) stable in the rotating holder (220), and for active steering, the combination of the rotating holder (220) and the helical bullet (230) is aligned with the external magnetic field. For tip ejection, the external magnetic field is first applied to stop the slider (223) against the stopper (213) (either from the left or right side), and then the direction of the external magnetic field is kept changed to rotate only the helical bullet (230). When the crossing angle (<5) reaches a critical value, the repulsive force between the cylindrical magnets (221, 222, 231) ejects the helical bullet (230) from the rotating holder (220). Furthermore, the remaining part attached to the guidewire has a near-zero magnetic moment. Therefore, it is not influenced by the external magnetic field during the subsequent untethered mode and waits in place until the helical bullet (230) returns.

[0022] Referring to FIG. 4, tip ejection is a transitional step between two modalities of operation that can be magnetically triggered. In principle, the magnetic force (F m ) and torque (T m )teeth,

[0023]

number

[0024] In this disclosure, finite element analysis (FEA) simulations are performed (COMSOL Multiphysics 5.3a, COMSOL Inc.). Examples of magnetic torque and force calculated for magnet (231) at various δ are shown in (420, 430). The results show that the interaction force changes between attractive and repulsive forces during rotation. Also, the interaction moment reaches a maximum at δ=90° and δ=270°. Furthermore, the magnetic field distribution maps for δ=0° for attractive force and δ=180° for repulsive force are shown as (440, 450). Furthermore, an external magnetic field can be applied to rotate the helical bullet (230) and eject the tip due to the repulsive forces between the cylindrical magnets (221, 222, 231).

[0025] For a prototype guidewire-mounted magnetic microrobot, the dimensions of the cylindrical magnet are first selected according to an existing product model. Then, other parameters are determined by parametric sweep to balance the maximum attractive force and the effective external magnetic field rotation effect for stable angular steering and at the same time for magnetically triggered ejection. Using this procedure, a series of customized guidewires can be designed across dimensions.

[0026] Referring to FIG. 5, the proposed guidewire-mounted magnetic microrobot has two motion modalities. In the tethered mode, the rotating holder (220) and the helical bullet (230) can be considered as one entity. As shown in (510), a directional external magnetic field (B d )

[0027]

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[0028]

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[0029]

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[0030]

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[0031] In untethered mode,

[0032]

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[0033]

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[0034] Referring to FIG. 6, the aforementioned helical bullet can be modified to integrate various functions for different treatments. One example is a perforator type design (610) used to treat thrombi and restore blood flow. It has an outer shell with a tapered head. Once the occluded area is reached, a high frequency rotating external magnetic field can be applied to cause high speed perforation, and the clot can be removed by mechanical rubbing. Another example is a porter type design (620) that can be used for targeted drug delivery. It has an outer shell with a loading cavity to carry the drug. Drug delivery can be achieved at the desired lesion under environmental stimuli in combination with material technology.

[0035] With reference to Figures 7 and 8, the present invention also proposes a remote control method. Currently, we use the so-called DeltaMag system for actuation, which has an array of three moving electromagnetic coils, and other systems are also applicable. A conceptual diagram is given, including the patient, the surgeon, and the actuation system. A homemade system with a parallel manipulator (710) and an electromagnet array (720) is adopted for magnetic field generation in a large working space. Furthermore, a 2D ultrasound (US) probe (730) is mounted on a movable end plate for medical imaging-based feedback, and a motorized feeder (740) is designed for back and forth movement of the guidewire. During actuation, the parallel manipulator (710) has 3 degrees of freedom (DOF) to drive the US probe (730) and the electromagnet array into the vicinity of the device, the US probe (730) has 1 DOF to adjust the imaging viewing angle, and the electromagnet array (720) has 3 DOF to generate an arbitrary magnetic field. All modules are coordinately controlled through a user interface (750) with commands entered by a joystick (760).

[0036] The present invention provides a guidewire-mounted magnetic microrobot, which in one embodiment comprises a commercially available guidewire with no active steering capability and an assembled tip module with a magnetic response that changes under different external magnetic fields.

[0037] In one embodiment, the assembled tip module comprises a body that includes various functional components, such as a base frame, a rotating holder, and a helical bullet.

[0038] In one embodiment, the assembled tip module comprises a base frame with a lower stick for connecting to a guidewire and an upper cavity for holding a rotating holder.

[0039] In one embodiment, the assembly tip module includes a rotating holder having a lower shaft for inserting into the base frame, two middle holes for mounting magnets, and an upper bucket for accommodating a helical bullet.

[0040] In one embodiment, the assembled tip module comprises a helical bullet comprising a spiral outer shell and an inner magnet.

[0041] In one embodiment, the assembled tip module comprises a helical bullet that can be modified to integrate different functionalities such as thrombus removal, targeted drug delivery, biopsy, and embolization.

[0042] In one embodiment, the assembled tip module utilizes a helical bullet propulsion strategy and can be modified into other mechanisms such as flexible-ora type, oscillating type, and climbing type.

[0043] In one embodiment, a commercially available guidewire and assembled tip module can be connected through a variety of methods, such as a silicone cannula and a small spring.

[0044] In one embodiment, the assembled tip module includes a rotating rocker that allows flexible bending in all directions, and a magnetic ejector provides controllable tip ejection for mode switching.

[0045] In one embodiment, the rotating rocker comprises a mechanism that utilizes a stopper on the base frame and a slider on the shaft of the rotating holder, allowing the rotating holder to rotate along its axis within limits while limiting its radial deflection and axial movement.

[0046] In one embodiment, the magnetic ejector includes a mechanism that requires the rotating holder bucket to have an inner diameter slightly larger than the outer diameter of the helical bullet, maintaining the relative position between the helical bullet and the rotating holder and allowing axial rotation and movement.

[0047] In one embodiment, the magnetic ejector uses the attractive and repulsive forces between magnets relative to a crossing angle to hold and release the helical bullet, the crossing angle being controlled by an external magnetic field.

[0048] In one embodiment, the magnetic ejector comprises a magnet array whose dimensions and relative position can be redesigned to suit the overall dimensional requirements and the operating field.

[0049] In one embodiment, the magnetic ejector comprises a magnet array, which is not limited to cylindrical magnets, but also includes other ferromagnetic materials of various shapes and manufacturing methods.

[0050] In one embodiment, the guidewire-mounted magnetic microrobot has two operational modalities and magnetically triggered switching: tethered mode, tip eject phase, and untethered mode.

[0051] In one embodiment, the tethered mode controls the back and forth motion by the insertion and withdrawal of a guidewire, and the steering motion is actuated by a directional external magnetic field.

[0052] In one embodiment, the tethered mode provides manual or robotic back and forth motion.

[0053] In one embodiment, the tip eject step involves first locking the rotation rocker, and then the intersection angle is changed.

[0054] In one embodiment, the untethered mode involves wirelessly propelling an ejected helical bullet by a rotating external magnetic field.

[0055] In one embodiment, in the untethered mode, the remaining portion attached to the guidewire after ejection has approximately zero magnetic moment.

[0056] In one embodiment, in the untethered mode, the helical bullet can swim back and be retrieved by a guidewire.

[0057] In one embodiment, the guidewire-mounted magnetic microrobot is for accessing hard-to-reach areas within tubular environments such as the vascular, gastrointestinal, and urinary systems.

[0058] In one embodiment, the guidewire-attached magnetic microrobot is remotely controlled using an operating system that includes a magnetic field generation module, where an instrument with an electromagnetic coil or permanent magnet generates a directional and rotating external magnetic field; a guidewire insertion module, where the instrument robotically inserts and retrieves the guidewire with both speed and distance control; an imaging feedback module, where the imaging methods include standard medical imaging methods such as X-ray fluoroscopy, computed tomography (CT), and ultrasound; and a user control module, where the user control module includes a controller for user command input, such as a joystick or 5D mouse, and a programmed user interface for monitoring.

[0059] The present invention provides a microrobot. In one embodiment, the microrobot comprises: a) an attachment module (300) for connecting the microrobot to a delivery device (100); and b) a tip module (200), comprising: (i) a bullet (230) having an outer shell (231) and one or more first magnets, the outer shell (231) having a design capable of being propelled by an external magnetic field when the one or more first magnets interact with the external magnetic field; and (ii) a holder (220) for holding the bullet, the holder (220) comprising a release mechanism for releasing the bullet from the holder.

[0060] In one embodiment, the delivery device (100) is a guidewire or a catheter.

[0061] In one embodiment, the bullet (230) has a functionalized design selected from the group consisting of a perforator type design and a porter type design.

[0062] In one embodiment, the bullet (230) is propelled by the external magnetic field using a propulsion strategy selected from the group consisting of a spiral type, a flexible-ora type, an oscillatory type, and a climbing type.

[0063] In one embodiment, the outer shell (231) is a spiral or helical shell capable of converting rotation into linear motion.

[0064] In one embodiment, the attachment module (300) is a cannula or a spring.

[0065] In one embodiment, the one or more first magnets (232) include radially magnetized cylindrical magnets.

[0066] In one embodiment, the release mechanism comprises: a) one or more second magnets (221, 222) in the holder (220); and b) a configuration for controlling relative motion between the one or more first magnets (232) and the one or more second magnets (221, 222) so as to generate a magnetic repulsive force to release the bullet-shaped portion (230) from the holder (220).

[0067] In one embodiment, the arrangement comprises: a) a cylindrical bucket in the holder (220) for receiving the bullet (230); b) a cylindrical portion of the bullet (230) for insertion into the cylindrical bucket, which allows the bullet (230) to rotate within the holder (220) upon application of a suitable external magnetic field; and c) a blocking mechanism operable to arrest rotation of the one or more second magnets (221, 222) under the suitable external magnetic field. In another embodiment, the blocking mechanism comprises a first component comprising a slider (223) and a second component comprising a stopper (213), and the one or more second magnets (221, 222) are attached to the first component or the second component, the first component and the second component are configured to rotate about the same axis, and when the slider (223) abuts the stopper (213), no relative motion can occur between the first component and the second component. In a further embodiment, the one or more second magnets (221, 222) comprise two axially magnetized cylindrical magnets with opposite magnetization directions.

[0068] The present invention further provides a method for intravascular intervention in a subject using the microrobot of the present invention, in one embodiment, the method comprises the steps of a) connecting the microrobot to a delivery device (100) via the attachment module (300), b) inserting the microrobot into a blood vessel of the subject via an insertion point, and c) positioning the microrobot at a suitable site, where the back and forth motion of the microrobot is adjusted by a motorized feeder or manually, and the steering motion of the microrobot is adjusted by an external magnetic field.

[0069] In one embodiment, the method further includes actuating the release mechanism to release the bullet (230) from the holder (220). In another embodiment, the method further includes controlling the movement of the bullet (230) using an external magnetic field. In a further embodiment, the method further includes controlling the bullet (230) to reattach to the holder (220).

[0070] The present invention also provides a system for intravascular intervention in a subject, in one embodiment, the system comprising: a) a microrobot of the present invention for positioning at a site in the subject, b) an electromagnetic array (720) for generating the external magnetic field, c) an ultrasound probe (730) for medical imaging-based feedback on the position of the microrobot, and d) a parallel manipulator (710) for driving the ultrasound probe and the electromagnetic array into the vicinity of the site.

[0071] In one embodiment, the system further comprises a delivery device (100) attached to the microrobot. In another embodiment, the system further comprises a motorized feeder (740) for coordinating the back and forth motion of the delivery device (100). In a further embodiment, the bullet (230) is propelled by the external magnetic field using a propulsion strategy selected from the group consisting of a flexible-ora type, a vibration type, and a climbing type.

[0072] In one embodiment, the release mechanism comprises: a) one or more second magnets (221, 222) in the holder (220); and b) a configuration for controlling relative motion between the one or more first magnets (232) and the one or more second magnets (221, 222) so as to generate a magnetic repulsive force to release the bullet-shaped portion (230) from the holder (220).

[0073] The present invention will be better understood by reference to the following experimental details, but those of skill in the art will readily recognize that the specific experiments described are for illustrative purposes only and are not intended to limit the invention to the precise form described herein, as defined by the claims which follow.

[0074] Throughout this application, various references or publications are cited. The disclosures of these references or publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art to which this invention pertains. The transitional term "comprising," which is synonymous with "including" or "containing" or "characterized by," is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. EXAMPLES

[0075] Example 1

[0076] Referring to Figure 9, a guidewire-attached magnetic microrobot prototype (910) has been fabricated and correspondingly characterized. The components of the current prototype were fabricated by 3D printing, but other fabrication methods may be utilized in the future. The assembled tip (911) had an outer diameter of 2.8 mm and a length of 12.5 mm, and the attached commercially available guidewire (912) had an outer diameter of 0.025 inches and a length of 1500 mm.

[0077] Plot (920) shows a comparison between the calculated and measured bending angles of the guidewire-mounted magnetic microrobot under various directional external magnetic fields with a strength of 9 mT. Deformation segments of different lengths were included, including 30 mm, 40 mm, and 50 mm. The maximum bending error was 4.5° and the average error was 1.9°. These demonstrated the validity of the proposed kinematic model.

[0078] Plot (930) shows the performance of tip ejection. For convenient operation, tip ejection was triggered by a rotating external magnetic field with the rotation axis along the centerline, and then a command was given to stop the magnetic field. The results showed that a rotating external magnetic field with low frequency and medium intensity was preferred. When the intensity of the external magnetic field was small, for example, from 1 mT to 5 mT, the external magnetic torque was not strong enough to change the existing state of internal traction, and the tip ejection failed. When the frequency of the rotating external magnetic field was high, for example, above 6 Hz, the helical bullet-shaped part (230) could be caught by the rotating holder (220) during the ejection process due to the rapidly alternating cross angle, which reduced the success rate. These verified the mechanism of tip ejection.

[0079] Plot (940) displays the motion velocity of the ejected helical bullet (230) under a rotating external magnetic field. The frequency was varied from 1 Hz to 20 Hz in 1 Hz increments, and the test was repeated three times. The forward velocity increased with the rotation frequency. These verified wireless propulsion.

[0080] Example 2

[0081] In vitro test results are provided with reference to Figure 10. Two tubular models were designed by modeling software and fabricated by 3D printing to validate different operating modalities.

[0082] The first tubular model (110) had five branches uniformly distributed in 3D space. The guidewire-mounted magnetic microrobot can be easily inserted into any channel under the guidance of a directional external magnetic field. The results showed good maneuverability in tethered mode.

[0083] The second tubular model (120) had a loop structure. When the guidewire-attached magnetic microrobot reached the target location, the tip eject was triggered. After this, a rotating external magnetic field was applied so that the helical bullet (230) was wirelessly propelled through the serpentine structure. If the entire procedure was performed in tethered mode while continuing to insert the guidewire-attached magnetic microrobot with a directional external magnetic field steering the orientation, the guidewire-attached magnetic microrobot could get caught in the annular region. The results demonstrated the improved compliance in untethered mode.

[0084] Example 3

[0085] A full-sized leg artery phantom 130 was applied, fabricated based on real CT data for physiological fidelity. This phantom was used clinically to train surgeons on interventional procedures. The overall dimensions of the model were 715 mm × 239 mm × 100 mm (length × width × height), with inner diameters ranging from 3 mm to 20 mm. Different pathways were designed, including the renal artery (131), iliac artery (132), and femoral artery (133). A guidewire-mounted magnetic microrobot prototype (910) was inserted through the insertion point (135).

[0086] First, the tethered mode was utilized, with the back and forth motion controlled by the motorized feeder (730) and the bending operation induced by a directional external magnetic field. The guidewire-mounted magnetic microrobot first passed through the left and right renal arteries successively. It then returned to the bifurcation region and pointed towards the iliac artery (132). The tip eject was prepared to be triggered when it reached a relatively narrow vessel. Next, a rotating external magnetic field was applied to eject the helical bullet (230). Finally, the untethered mode was adopted to reach the deep lesion (133). The demonstration on the phantom verified the effectiveness of the present invention over long distance operation.

[0087] Example 4

[0088] The performance of the present invention in an environment with flow velocity is tested. Flow-induced disturbances should not significantly affect the tethered mode. The effect of flow can be mitigated by combining with a functional catheter such as a balloon catheter to stabilize the guidewire and temporarily block blood flow during tip ejection and untethered modes.

[0089] Various guidewire-mounted magnetic microrobot prototypes are designed and fabricated across dimensions to suit different working scenarios. Ex vivo and in vivo experiments using medical imaging methods for monitoring are performed to validate the invention.

Claims

1. A microrobot, a. a mounting module (300) for connecting said microrobot to a delivery device (100); b. A tip module (200), i. a bullet (230) comprising an outer shell (231) and one or more first magnets, the outer shell (231) having a design capable of being propelled by an external magnetic field when the one or more first magnets interact with the external magnetic field; ii. a holder (220) for holding the bullet, the holder (220) comprising a release mechanism for releasing the bullet from the holder. A tip module (200) comprising: A microrobot comprising:

2. The microrobot of claim 1 , wherein the delivery device (100) is a guidewire or a catheter.

3. 10. The microrobot of claim 1, wherein the bullet-shaped portion (230) has a functionalized design selected from the group consisting of a perforator-type design and a porter-type design.

4. 10. The microrobot of claim 1, wherein the bullet-shaped portion (230) is propelled by the external magnetic field using a propulsion strategy selected from the group consisting of a spiral type, a flexible-ora type, an oscillation type, and a climbing type.

5. The microrobot of claim 1, wherein the outer shell (231) is a spiral or helical shell capable of converting rotation into linear motion.

6. The microrobot of claim 1 , wherein the attachment module (300) is a cannula or a spring.

7. The microrobot of claim 1 , wherein the one or more first magnets (232) comprise radially magnetized cylindrical magnets.

8. The release mechanism comprises: a. one or more second magnets (221, 222) in said holder (220); and b. A configuration for controlling relative motion between the one or more first magnets (232) and the one or more second magnets (221, 222) to generate a magnetic repulsion force to release the bullet (230) from the holder (220). The microrobot of claim 1 .

9. The above-mentioned configuration is a. a cylindrical bucket within said holder (220) for receiving said bullet (230); b. a cylindrical portion of the bullet (230) for insertion into the cylindrical bucket, whereby the bullet (230) can rotate within the holder (220) upon application of a suitable external magnetic field; and c. a blocking mechanism operable to arrest rotation of said one or more second magnets (221, 222) under said appropriate external magnetic field. The microrobot of claim 8 .

10. The blocking mechanism is a. a first component comprising a slider (223); and b. A second component comprising a stopper (213) 10. The microrobot of claim 9, further comprising: one or more second magnets (221, 222) attached to the first component or the second component, the first component and the second component rotating about the same axis such that when the slider (223) abuts against the stopper (213), no relative motion can occur between the first component and the second component.

11. The microrobot of claim 8, wherein the one or more second magnets (221, 222) comprise two axially magnetized cylindrical magnets having opposite magnetization directions.

12. 13. A method of using the microrobot of claim 1 for intravascular intervention in a subject, comprising: a. connecting the microrobot to a delivery device (100) via the attachment module (300); b. inserting the microrobot into a blood vessel of the subject via an insertion point; and c) positioning the microrobot at a suitable location, adjusting the back and forth motion of the microrobot by an electric feeder or manually, and adjusting the steering motion of the microrobot by an external magnetic field; A method comprising:

13. The method of claim 12, further comprising actuating the release mechanism to release the bullet (230) from the holder (220).

14. The method of claim 13, further comprising controlling the movement of the bullet (230) using an external magnetic field.

15. The method of claim 13, further comprising controlling the bullet (230) to be reattached to the holder (220).

16. 1. A system for intravascular intervention in a subject, comprising: a. the microrobot of claim 1 for placement at a site in the subject; b. an electromagnet array (720) for generating the external magnetic field; c. an ultrasound probe (730) for medical imaging based feedback regarding the position of said microrobot; and d. A parallel manipulator (710) for driving the ultrasound probe and the electromagnetic array into the vicinity of the site. A system comprising:

17. The system of claim 16, further comprising a delivery device (100) attached to the microrobot.

18. 20. The system of claim 17, further comprising a motorized feeder (740) for coordinating back and forth movement of the delivery device (100).

19. The system of claim 16, wherein the bullet (230) is propelled by the external magnetic field using a propulsion strategy selected from the group consisting of a flexible-ora type, a vibration type, and a climbing type.

20. The release mechanism comprises: a. one or more second magnets (221, 222) in said holder (220); and b. A configuration for controlling relative motion between the one or more first magnets (232) and the one or more second magnets (221, 222) to generate a magnetic repulsive force to release the bullet (230) from the holder (220). The system of claim 16, comprising:

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