Research ArticleBIOENGINEERING

Flexible and stretchable nanowire-coated fibers for optoelectronic probing of spinal cord circuits

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Science Advances  29 Mar 2017:
Vol. 3, no. 3, e1600955
DOI: 10.1126/sciadv.1600955
  • Fig. 1 Fabrication of flexible neural probes.

    (A) Illustration of the fiber probe fabrication. (B) Spool of a fiber with PC core and COC cladding. (C) Transmission electron microscopy (TEM) image of the AgNWs. (D) Cross-sectional image of the fiber probe. (E) Scanning electron microscopy image shows a portion of the ring AgNW electrode cross section. (F) Scanning electron microscopy image of the AgNW mesh on top of the fiber surface.

  • Fig. 2 Optical characterization of flexible neural probes.

    (A) Normalized transmission at a wavelength λ = 473 nm as a function of length for fiber probes with and without COC cladding to separate AgNW mesh from the PC optical core with a diameter of 120 μm. (B) Transmission at λ = 473 nm for PC/COC/AgNW/PDMS fiber probes (core diameter, 120 μm) bent at 90° or 180° as radii of curvature (0.5 to 10 mm) displayed relative to straight probes. All scale bars and shaded areas represent SEM. n = 5 samples for each data point. (C) Image of a PC/COC/AgNW/PDMS fiber probe connected to a laser source, threaded through a needle, and used to create several stitches on fabric.

  • Fig. 3 Electrical characterization of flexible neural probes.

    (A) Resistivity of the mesh as a function of AgNW solution concentration. Inset: TEM images of the AgNW meshes deposited from solutions with 2, 6, and 10 mg/ml concentrations. AgNW mesh deposited from the 10 mg/ml solution was used for further characterization and in vivo evaluation. (B) Impedance spectra of the AgNW mesh electrodes deposited on 1-, 5-, and 10-cm-long fibers with 120-μm PC/COC cores. All scale bars and shaded regions represent SEM. n = 5 samples for each data point.

  • Fig. 4 Mechanical and electrical characterization of stretchable neural probes.

    (A) Tensile tests performed for a thermally drawn COCE fiber and a COCE fiber probe coated with three layers of AgNW mesh and a protective PDMS cladding (COCE/AgNW/PDMS) (n = 5 devices). (B) Impedance spectra of the AgNW mesh electrodes deposited onto 200 × 200 μm2 COCE core fiber with lengths of 1, 5, and 10 cm. (C) Impedance of a three-layer AgNW mesh within COCE/AgNW/PDMS probes with core dimensions of 200 × 200 μm2 as a function of tensile strain. (D) Scanning electron microscopy images of the three-layer AgNW mesh deposited onto COCE fiber at 0, 10, and 20% strain. (E) Impedance of fiber probes characterized in (C) measured over five extension and release cycles. All scale bars represent SEM. n = 5 samples for each data point.

  • Fig. 5 Probing spinal cord electrophysiology with flexible and stretchable neural probes.

    (A) Schematic depicting optical stimulation and electrophysiological recording with a fiber probe in a mouse spinal cord. (B) Image of mouse implanted with a flexible neural probe between L1 and L2 exploring its environment. (C) Spontaneous activity recorded in acute conditions with AgNW concentric mesh electrodes deposited onto PC/COC core fibers in spinal cord of wild-type (WT) mice. (D) Action potentials isolated from the recording in (C). (E) Spontaneous activity recorded in acute conditions with AgNW concentric mesh electrodes deposited onto COCE core fibers. (F) Action potentials isolated from the recording in (E). (G) Sensory-evoked potentials recorded acutely from the dorsal column with AgNW mesh electrodes within PC/COC-based probes at different input currents (1 to 8 mA; 125 μs per phase biphasic). Sensory potentials are preceded by the electrical stimulus artifact. (H) Sensory-evoked potential (SEP) recruitment curve relating the area under the first positive peak to the stimulus amplitude. (I) Neural activity in a spinal cord of a Thy1-ChR2-YFP mouse evoked by optical stimulation (wavelength λ = 473 nm, 168 mW/mm2, 5-ms pulse width, 10 Hz) delivered through the PC/COC fiber and recorded with the concentric AgNW mesh electrodes. (J) Neural activity in spinal cord of a Thy1-ChR2-YFP mouse evoked by optical stimulation (wavelength λ = 473 nm, 125 mW/mm2, 5-ms pulse width, 10 Hz) delivered through the COCE fiber and recorded with the concentric AgNW mesh electrodes. (K) EMG evoked by the optical stimulation in (J). (L) Optically evoked local field potentials recorded with AgNW mesh electrodes within COCE fiber. (M) An expanded view of the averaged EMG signal from (K).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/3/e1600955/DC1

    fig. S1. Controlled parameters during the drawing of the PC/COC fiber.

    fig. S2. Optical transmission spectra of PC/COC fibers at visible wavelengths.

    fig. S3. Transmission at a wavelength λ = 473 nm for COCE fiber.

    fig. S4. Impedance of COCE fibers coated with a single layer of AgNW mesh and measured at 0, 10, and 20% extension strain.

    fig. S5. Spontaneous single units isolated during acute anesthetized recordings (see Fig. 5, C to F).

    fig. S6. Electrophysiological recording collected from the freely moving mice implanted with fiber probes.

    fig. S7. Additional in vivo sensory and electromyographic recordings.

    fig. S8. Electrophysiological recordings of optically stimulated activity.

    fig. S9. In vivo EMG recordings.

    fig. S10. Immunohistochemical analysis of the dorsal horn 2 weeks after device implantation surgeries.

    video S1. Optical spinal control of muscle activity.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Controlled parameters during the drawing of the PC/COC fiber.
    • fig. S2. Optical transmission spectra of PC/COC fibers at visible wavelengths.
    • fig. S3. Transmission at a wavelength λ = 473 nm for COCE fiber.
    • fig. S4. Impedance of COCE fibers coated with a single layer of AgNW mesh and measured at 0, 10, and 20% extension strain.
    • fig. S5. Spontaneous single units isolated during acute anesthetized recordings (see Fig. 5, C to F).
    • fig. S6. Electrophysiological recording collected from the freely moving mice implanted with fiber probes.
    • fig. S7. Additional in vivo sensory and electromyographic recordings.
    • fig. S8. Electrophysiological recordings of optically stimulated activity.
    • fig. S9. In vivo EMG recordings.
    • fig. S10. Immunohistochemical analysis of the dorsal horn 2 weeks after device implantation surgeries.
    • Legend for video S1

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    Other Supplementary Material for this manuscript includes the following:

    • video S1 (.mp4 format). Optical spinal control of muscle activity.

    Files in this Data Supplement:

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