Light-controlled soft bio-microrobot

Abstract

Micro/nanorobots hold exciting prospects for biomedical and even clinical applications due to their small size and high controllability. However, it is still a big challenge to maneuver micro/nanorobots into narrow spaces with high deformability and adaptability to perform complicated biomedical tasks. Here, we report a light-controlled soft bio-microrobots (called "Ebot") based on Euglena gracilis that are capable of performing multiple tasks in narrow microenvironments including intestinal mucosa with high controllability, deformability and adaptability. The motion of the Ebot can be precisely navigated via light-controlled polygonal flagellum beating. Moreover, the Ebot shows highly controlled deformability with different light illumination duration, which allows it to pass through narrow and curved microchannels with high adaptability. With these features, Ebots are able to execute multiple tasks, such as targeted drug delivery, selective removal of diseased cells in intestinal mucosa, as well as photodynamic therapy. This light-controlled Ebot provides a new bio-microrobotic tool, with many new possibilities for biomedical task execution in narrow and complicated spaces where conventional tools are difficult to access due to the lack of deformability and bio-adaptability.

Fig. 1. Characterization of EG cells and Ebots.

a Schematic illustration of EG structure and multifunctional applications of Ebots. (I) Eyespot structure and phototaxis behavior of EG. (II) Phototaxis and deformation of EG cell. (III-V) Schematic illustration of Ebot for (III) targeted drug delivery, (IV) selective removal of diseased cells in intestinal mucosa and (V) PDT. b (I) Phase contrast microscopy and (II) fluorescent microscopy images of EG. c Swimming speeds of Ebot in the natural state and under periodic light irradiation, respectively. d The viability of Ebot as a function of time during light irradiation of different light intensities. Scale bar: 5 μm. Data for (d) are presented as mean values ± s.d. (n = 18)

Fig. 2. Motion control of the Ebot.

a–c Three different motion modes of (a) helical swimming under low intensity light, (b) polygonal swimming under medium intensity light, and (c) spinning swimming under high intensity light. Panels I: schematic illustration of these three motion modes, blue curves show the motion strategy. Panels II: microscopic images showing the flagellum beating patterns for each motion mode, red curve indicates the flagellum. Panels III-V: microscopic images showing the movement of the Ebot. Red dot indicates the eyespot position. Panels IV: microscopic images showing final swimming trajectories with several images superimposed (blue curves indicated). d Different polygonal trajectories of Ebot at medium light intensity. e Microscopic images showing different directions of polygonal trajectories. f Microscopic images showing the effect of illumination duration on the turning angle of the Ebot under high intensity light. g Probability of different motion modes as a function of light intensity. h Measured turning angle under different illumination duration. i Microscopic image showing Ebot passing through a microfluidic maze, dashed curve indicates the Ebot trajectory. Scale bars: 50 μm. Data for (g) and (h) are presented as mean values ± s.d. (n = 20)

Fig. 3. Deformation control of Ebot.

a Microscopic images showing overall observation of deformation by light irradiation. Panel I: without light irradiation, no deformation is observed. Panel II: under light illumination (3000 lx), Ebot deformation is observed with various shapes. b Deformation progress of Ebot, upper panels: schematic illustrations, lower panels: microscopic images. Insets are microscopic images showing beating patterns of malfunctional flagellum. c Microscopic images showing Ebot moving forward during light-induced deformation. Red dashed lines indicate the initial position of Ebot, and white dashed arrows indicate the moving distance of Ebot. d Deformation rate of Ebot as a function of time under light irradiation with different intensities. e Deformation cycle under light irradiation with different intensities. f Schematic illustration of Ebot passing through different microfluidic channels. The red arrows indicate the movement direction. g–i Microscopic images showing Ebot navigating in (g) a 2D straight channel, width: 10 μm, (h) a 3D straight channel, width: 10 μm, and depth: 5 μm, (i) a curved channel, width: 5 μm. Red dashed arrows indicate the motion direction of the Ebot. The yellow arrows in (h) indicate obstacles. Scale bar: 20 μm. Data for (d) and (e) are presented as mean values ± s.d. (n = 20)

Fig. 4. Ebots for multifunctional biomedical task execution.

a Motion speeds of naked and drug-loaded Ebots in different biological fluids. b Speed comparison of naked and drug-loaded Ebots in different temperature. c–f Ebot for multifunctional biomedical task execution. Panels I are schematic illustrations, panels II-VI are microscopic images at different time. c Targeted drug delivery in cell clusters. Panel VI is fluorescent image, live HeLa cells are green fluorescent. The yellow and white dashed circle indicates the DLSP and cultured HeLa cells, respectively. Red dashed curve shows the trajectory of the Ebot. d Selective removal of diseased cells in cell clusters. The yellow dashed circle indicates the target cell. e Intestinal-targeted drug delivery in vitro. The yellow dashed circle indicates the DLSP. f Removal of porous silica particle in the gut gap in vitro. The yellow and blue dashed circle indicates the particle and the adipocytes in the intestine, respectively. Scale bar: 30 μm. Data for (a) and (b) are presented as mean values ± s.d. (n = 16)

Fig. 5. Ebot for photodynamic therapy (PDT).

a Schematic illustration of PDT using Ebot. b Light absorption of EG. c, d Experimental results showing Ebot navigation and ROS generation. (I, II) Microscopic images showing navigation of Ebot to designated locations with blue light irradiation, (III) Fluorescent images showing the generation of ROS (green fluorescence) with different light irradiation. e Histogram showing the efficiency of PDT under different treatments of Ebot. f Fluorescent images showing the results of PDT with different treatments of Ebot. HeLa cells stained with Calcein-AM (green, live cells) and PI (red, dead cells), the white dashed circle represents Ebots. Scale bar: 50 μm. Data for (e) are presented as mean values ± s.d. (n = 16)