Bioinspired claw-engaged and biolubricated swimming microrobots creating active retention in blood vessels

Abstract

Swimming microrobots guided in the circulation system offer considerable promise in precision medicine but currently suffer from problems such as limited adhesion to blood vessels, intensive blood flow, and immune system clearance-all reducing the targeted interaction. A swimming microrobot design with clawed geometry, a red blood cell (RBC) membrane-camouflaged surface, and magnetically actuated retention is discussed, allowing better navigation and inspired by the tardigrade's mechanical claw engagement, coupled to an RBC membrane coating, to minimize blood flow impact. Using clinical intravascular optical coherence tomography in vivo, the microrobots' activity and dynamics in a rabbit jugular vein was monitored, illustrating very effective magnetic propulsion, even against a flow of ~2.1 cm/s, comparable with rabbit blood flow characteristics. The equivalent friction coefficient with magnetically actuated retention is elevated ~24-fold, compared to magnetic microspheres, achieving active retention at 3.2 cm/s, for >36 hours, showing considerable promise across biomedical applications.

Fig. 1.. Schematic overview of active navigated retention using swimming microrobots in vivo.

(A) Conceptional development of claw-engaged and biolubricated swimming microrobots (CBSMRs). The tardigrades inspired the clawed geometry design and magnetically actuated claw engagement of the swimming microrobot, and the red blood cell (RBC) membrane–camouflaged coating was functionalized on the swimming microrobots to reduce the impact of the blood flow. (B) Schematic of imaging and navigation of the swimming microrobots in blood vessels of a rabbit in vivo. IVOCT, intravascular optical coherence tomography. (C) Navigated locomotion and active retention of the swimming microrobots in blood vessels through the manipulation of external magnetic field.

Fig. 2.. Fabrication and characterization of swimming microrobots.

(A) Schematic of the fabrication steps of the swimming microrobots. (B) Scanning electron microscopy (SEM) image of the swimming microrobot. Scale bar, 10 μm. CHI, chitosan; ALG, alginate. (C) Fluorescence microscopic images of the swimming microrobots of different sizes through manipulation of the thermal treatment (where the RBC membrane was stained with rhodamine B). Scale bars, 5 μm. (D) Magnetization loop from the superconducting quantum interference device analysis of the swimming microrobots. Br, remanence; Hc, coercivity; emu, electromagnetic unit. (E) Adhesion force analysis of the swimming microrobots using atomic force microscopy (AFM). Magnetic clawed particles and magnetic spheres (MSs) were also measured as controls. (F) The maximum flow resistance that the swimming microrobots can offer, using a glass slide and blood vessel as substrates and PBS and blood as flow media, respectively (the inset shows the optical image of the swimming microrobots and the MSs of the same size on the blood vessel surface). Scale bar, 20 μm. PBS, phosphate-buffered saline. (G) Computational simulated flow profile of the swimming microrobot and the MSs (same size as the microrobot) under flow conditions [the yellow arrows indicate the angular positions (value of ϕ) of the flow separations]. (H) The angular positions of the swimming microrobot and MS in the flow stream.

Fig. 3.. Magnetically actuated locomotion and retention of swimming microrobots in blood vessels.

(A) Schematic movement of the swimming microrobot in the blood vessels under a rotating magnetic field (RMF) in the xz plane. (B) Time-lapse images showing the magnetic motion of the magnetic clawed particles and the swimming microrobot in the blood vessel with a flow rate (FR) of 2.1 cm/s. The blue dashed line indicates the path of the microrobot’s upstream motion. Scale bars, 30 μm. (C) Velocity of the swimming microrobots and the MSs (sizes of 20 and 5 μm, respectively) as control upon the flow at different rates. (D) Flow resistance of the swimming microrobot and the magnetic particles, with maximum FR. Schematic illustrating the force analysis of the swimming microrobot with the RMF on (left) and RMF off (right) (in inset). (E) Dependence of the magnetic actuation force and the flow resistance on the size of the swimming microrobots (with an FR of 2.1 cm/s). (F) Schematic of the magnetically actuated retention of the swimming microrobots in the blood vessels through the manipulation of the RMF. (G) Time-lapse images showing the dynamics of the swimming microrobots and the microrobots with the RMF applied in the xy plane in the presence of blood flow. Scale bars, 30 μm. The red dotted line indicates the motion path of the microrobot floating away with the blood flow. (H) The phase diagram showing the FR that swimming microrobots can overcome, in the presence of the RMF, with different rotation angles. (I) Retention of the swimming microrobots in the presence of the flow, under different periods of rotation, with a rotation angle of 0°. (J) Equivalent friction coefficient (EFC) of the swimming microrobots with different magnetic actuation conditions (MSs were used as controls).

Fig. 4.. Active navigated retention of swimming microrobots on the intraperitoneal vein of mice in vivo.

(A) Schematic autonomous control of swimming microrobots on blood vessel of mice. (B) Time-lapse images showing the self-correcting of path deviation of swimming microrobots on blood vessel. The blue and green lines represent the trajectories of the microrobot’s normal magnetic-driven motion and path self-correcting motion, respectively. Scale bars, 50 μm. (C) Comparison between the estimated route and actual path of autonomous navigation for the swimming microrobot in the process of path self-correcting. (D) Time-lapse images showing the multiple launch and retention of swimming microrobots on blood vessel. The blue line and the green lines represent the motion trajectories of microrobot in consecutive two movement-retention, respectively. Scale bars, 50 μm. (E) Input voltage signal of the coil group in the x, y, and z directions of the Helmholtz coil corresponding to twice motion-retention. (F) Time-lapse images illustrating the controllable locomotion and extended retention of swimming microrobots on model thrombus which was connected with mice. I-II-III-IV, crossing-upstream-downstream-crossing. Scale bar, 150 μm.

Fig. 5.. IVOCT evaluation of active navigated retention of swimming microrobots on jugular vein of rabbit in vivo.

(A) Schematic illustrating the investigation of localization and active retention of swimming microrobot on blood vessels. (B) Schematic and IVOCT images of initial position, locomotion, and retention of swimming microrobots in vivo. (C) Time-lapse IVOCT images of swimming microrobots (robot + RMF group) in different positions as function of time. RMF of 30 mT and 30 Hz was carried in yz plane during 0 to 10 min and changed to xy plane at 10 min. The green spots were indicated as signal from swimming microrobots. (D) Corresponding normalized number of swimming microrobots counted from green spots in (C), displaying the distribution of swimming microrobots on blood vessels upon magnetically actuated locomotion and retention. Experimental statistics were summarized from parallel experiments performed on five rabbits. Error bars represent the SDs from five independent measurements. All data are normalized to their maxima. Scale bar, 1 mm. (E) Microscopic images displaying active retention of the swimming microrobots and control MSs on blood vessels in vivo. Scale bar, 1 mm. (F) Fluorescence analysis of the distribution of swimming microrobots after active navigated retention in vivo.

Fig. 6.. Biosafety analysis of swimming microrobots.

(A) Cell viability of human umbilical vein endothelial cell after 24 hours of incubation with swimming microrobots. Comprehensive blood cell counts (B) and blood chemistry panel (C) taken from nontreated mice and mice with treatment. The green dashed lines indicate the mouse reference ranges of each analyte. WBC, white blood cell; PLT, platelet; ALP, alkaline phosphatase; GLOB, globulin; TP, total protein. (D) The major organs were harvested from the swimming microrobot–administrated mice for hematoxylin and eosin (H&E) staining analysis. Scale bars, 200 μm.