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A magnetically actuated microrobot for targeted neural cell delivery and selective connection of neural networks

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Science Advances  25 Sep 2020:
Vol. 6, no. 39, eabb5696
DOI: 10.1126/sciadv.abb5696
  • Fig. 1 Schematic illustration and fabrication process of a magnetically actuated microrobot for neural networks.

    (A) Schematic of the active construction between two neural clusters using the microrobot on an HD-MEA chip that can measure axonal signal transmission. (B) Computer-aided design images and dimensions of the microrobot. (C) Overall fabrication process of the microrobots; two-photon laser lithography and nickel (Ni, for magnetic properties)/titanium oxide (TiO2, for biocompatibility) deposition. (D) Scanning electron microscopy images of the fabricated microrobot with the microgrooves.

  • Fig. 2 Effects of the microgrooves on the microrobot for hippocampal cell alignment.

    (A to C) Height coding fluorescence confocal micrographs of β-III tubulin (TUBB3)– and 4′,6-diamidino-2-phenylindole (DAPI)–stained hippocampal neurons and orientation histogram of neurites on glass substrates as a control after (A) 4 days in vitro (DIV), (B) 8 DIV, and (C) 17 DIV from plating (0 DIV). (D to F) Height coding fluorescence confocal micrographs of neurons on the microrobots with microgrooves after (D) 4 DIV, (E) 8 DIV, and (F) 17 DIV from plating (0 DIV). Subimages indicate (i) micrographs color-mapped by height relative to z-axis scale, (ii) color-mapped micrographs by orientation angles of the neurites of the white dotted area in each (i) image, and (iii) polar frequency histograms of orientation angles of the neurites in each (ii) image. (G) Plot of OI calculated from orientation angles of neurites on a plain surface and the microgrooved surface (microrobot) at 4, 8, and 17 DIV.

  • Fig. 3 Magnetic manipulation of the microrobot on a glass substrate with an array of neural clusters.

    (A) Experimental setup for microrobot manipulation using the magnetic field control system (left) and a glass substrate (right) with an array of neural clusters (ANC) cultured for 1 DIV. White dashed boxes indicate neural networks. The red dashed box indicates the target point of the microrobot. (B) Snapshots of positional control of the microrobot between two neural clusters during magnetic manipulation in the area presented in (A) (white solid-line box, right). Green dotted boxes indicate the position of the microrobot in the previous snapshot.

  • Fig. 4 Hippocampal neural connections between neural clusters with and without the microrobot at 17 DIV.

    (A and B) Morphology [bright-field images in (A) and height coding fluorescence confocal micrographs in (B)] of hippocampal neurons of two neural clusters without the microrobot as a control. (C and D) Morphology [bright-field images in (C) and height coding fluorescence confocal micrographs in (D)] of hippocampal neurons of two neural clusters with the microrobot where cells were seeded. White dotted boxes presented in the left panels indicate the areas of a′, b′, c′, and d′, respectively. Red solid-line boxes presented in the left panels indicate the areas of a′′, b′′, c′′, and d′′, respectively. (E) Color-mapped micrograph (top) and polar frequency histogram (bottom) by orientation angles of the neurites of the white dotted area in a′ and b′ as a control. (F) Color-mapped micrograph (top) and polar frequency histogram (bottom) by orientation angles of the neurites of the white dotted area in c′′ and d′′ on the microrobot. (G) Plot of OI calculated from orientation angles of neurites on the control and on the microrobot. Cultures were immunostained for neurites in green (TUBB3) and stained for nuclei in blue (DAPI).

  • Fig. 5 Magnetic manipulation of the microrobot and the spontaneous activity map on an HD-MEA chip with an ANC.

    (A) Photograph of the moving microrobot (left) during magnetic manipulation. Red arrows represent the trajectory of the moving microrobot. The red asterisk indicates the starting point. The microrobot with cells was placed (middle) between separate neural networks after magnetic manipulation at 1 DIV. A photograph of the HD-MEA chip (right) taken at 2 DIV (1 day after the microrobot placement) is shown. Dotted lines indicate an ANC. (B) Spontaneous activity map of the hippocampal neural culture with the microrobot on an HD-MEA chip with an ANC at 17 DIV. Amplitudes recorded by each electrode were averaged and color-coded. (C) Overlap image of the spontaneous activity map at 17 DIV of the white boxed area in (B) and a photograph of the HD-MEA chip of the right panel in (A). Yellow dashed boxes indicate the position of the microrobot in (B) and (C).

  • Fig. 6 Electrical stimulation and AP propagation of hippocampal neurons cultured without the microrobot and with the microrobot on an ANC at 17 DIV.

    (A and B) Evoked neural activity by stimulation of (A) an ANC without the microrobot and (B) AP propagation in 1 to 3 (left) and AP waveforms (right) from electrodes corresponding to the left panel. (C and D) Evoked neural activity by stimulation of (C) an ANC with the microrobot and (D) AP propagation in 1 to 6 (left) and AP waveforms (right) from electrodes corresponding to the left panel. (E and F) Evoked neural activity by stimulation between neural clusters with the microrobot in (E) and both directions of AP propagation of 1 to 3 and i to iii (left) and AP waveforms (right) from electrodes corresponding to the left panel in (F). Yellow stars indicate stimulation electrodes in all figures. Red dashed boxes indicate the microrobot location in (C) and (E). Gray lines and black lines represent single trials and the median overall trials, respectively, in the right panels of (B), (D), and (F).

Supplementary Materials

  • Supplementary Materials

    A magnetically actuated microrobot for targeted neural cell delivery and selective connection of neural networks

    Eunhee Kim, Sungwoong Jeon, Hyun-Kyu An, Mehrnoosh Kianpour, Seong-Woon Yu, Jin-young Kim, Jong-Cheol Rah, Hongsoo Choi

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