Name: silicon nanowires and optical stimulation for investigations of intra- and intercellular electrical coupling
Uploaded: 2021-01-28T14:00:00
Description: Watch this Scientific Journal Video about Silicon Nanowires and Optical Stimulation for Investigations of Intra- and Intercellular Electrical Coupling at JoVE.com

This work is supported by the Air Force Office of Scientific Research (AFOSR FA9550-18-1-0503).

To ensure compliance with ethical standards, all animal procedures related to isolating cardiomyocytes from rodent hearts were first approved by the University of Chicago Institutional Animal Care and Use Committee (IACUC). Additionally, all animal experiments were conducted in complete accordance with guidance from the University of Chicago IACUC.
1. Preparation of cell-SiNWs hybrids
<ol>
	<li>Isolate primary cardiomyocytes (CMs) using a commercial kit following manufacturer&#8217;s guidelines....

<ol>
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We have demonstrated here a simple way to perform intracellular electrical stimulation of cells. In this demonstration, we used MFs that were prehybridized with SiNWs, then co-cultured with CMs. In general, most proliferating cells have the tendency to internalize SiNWs, which allows the use of this methodology with many other cell types. Moreover, while we demonstrated the intracellular stimulation of cells, the same principles can be used to perform extracellular stimulation of cells. This can be done by blocking endos...

All biological organisms use electricity, in the form of ions, to regulate the cellular behavior. Cell membranes contain various types of specific ion channels allowing the passive and active transport of ions. These ions govern the functions of excitable cells, such as neuronal activity and skeletal and cardiac muscle contractility. However, bioelectricity also plays an important role in non-excitable cells, governing many cellular functions such as cell proliferation1, neuroimmunity2,3,4, and stem cell differentiation5.
In recent decades, the field of bioelectricity has drawn an increasing level of interest, which has contributed to the development of numerous technologies for bioelectronic interfaces. Microelectrode patch pipettes are the gold standard of intracellular recording and stimulation6. In this methodology, a glass pipette is pulled under specific conditions to form a sharp edge with a pore size of few microns. This pipette is filled with a buffer and the pipette allows direct contact of the buffer with the intracellular volume. This results in a bioelectric interface that yields extremely high signal to noise ratios, precise control over cellular electrical activity, and extremely high temporal resolution. Although this methodology is an extremely powerful tool, which was recently downscaled to a nano-pipette configuration7, it is associated with several important technical limitations. The cytosol dilution effect8, as well as mechanical vibrations, limits its utility to short term interrogations, and it requires expensive specialized equipment and a high level of technical skill. Moreover, its bulkiness limits the number of cells that can be recorded or stimulated simultaneously, and due to its invasiveness, it cannot be reconfigured throughout an experiment. To overcome these limitations, microelectrode arrays were developed, but the size of the electrodes limits the spatial resolution as well as intracellular access. Nanoelectrode arrays allow intracellular recording and stimulation but require abrasive electroporation to access the cytosol9,10. In addition, all these methodologies are substrate bound and are thus limited to in vitro cell cultures, or to external superficial cells, with no access to cells that are inside a 3-dimensional (3D) tissue.
Optogenetics11 is widely used to address these 3D and in vivo limitations. However, optogenetic methods are based on the perturbations of light-activated plasma membrane ion channels that are distributed at the plasma membrane, limiting the 3D spatial resolution12 and intracellular capabilities.
We have recently shown that silicon nanowires (SiNWs) can be used to perform intracellular bioelectric interrogation with submicron spatial resolution with different non-excitable cells, namely cardiac myofibroblasts and oligodendrocytes13. Moreover, we used these SiNWs to perform ex-vivo cell specific interrogation within a 3D cardiac tissue, to investigate how cardiac cells electrically couple in vivo14. A major advantage of this methodology is its simplicity; it does not require any genetic modification or bulky instrumentation. Many cells will spontaneously internalize photo-responsive SiNWs with no need for sonication or electroporation15. In addition, they will spontaneously escape the endosomal encapsulation and form a seamless integration with the cytosol and intracellular organelles13,15. These cell-SiNWs composites, termed cell-silicon hybrids, possess the dynamic, soft and versatile nature of the original cell, as well as the optoelectric capabilities of the SiNWs. After hybridization, the cell-SiNW hybrid can be harvested using standard tissue culture techniques and used for various applications such as intracellular bioelectric stimulation; studying intercellular bioelectric coupling in vitro; and for in vivo cell specific interrogation. As an effective stimulation requires co-localization of high optical power densities and SiNWs, one can achieve high spatial resolution both in 2D and 3D. In this protocol we describe in detail the methodology, as well as how the results can be analyzed. The focus is placed on the intra- and intercellular investigation in vitro, but the in vivo implementation of this methodology can be directly utilized for many other biological scenarios.

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			<td height="21" style="height:21px;width:216px;">35 mm Glass bottom dishes</td>
			<td style="width:121px;">Cellvis</td>
			<td style="width:161px;">D35-10-0-N</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">3i Marianas Spinning Disk Confocal</td>
			<td style="width:121px;">3i</td>
			<td style="width:161px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Calcein-AM</td>
			<td style="width:121px;">Invitrogen</td>
			<td style="width:161px;">C1430</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">CellMask Orange Plasma membrane Stain</td>
			<td style="width:121px;">Invitrogen</td>
			<td style="width:161px;">C10045</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Collagen I, rat tail</td>
			<td style="width:121px;">Gibco</td>
			<td style="width:161px;">A1048301</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Deluxe Diamond Scribing Pen</td>
			<td style="width:121px;">Ted Pella</td>
			<td style="width:161px;">54468</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">DMEM, high glucose, pyruvate, no glutamine</td>
			<td style="width:121px;">Gibco</td>
			<td style="width:161px;">10313039</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">DMSO, Anhydrous</td>
			<td style="width:121px;">Invitrogen</td>
			<td style="width:161px;">D12345</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Falcon Standard Tissue Culture Dishes</td>
			<td style="width:121px;">Falcon</td>
			<td style="width:161px;">08-772E</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Fetal Bovine Serum, certified, heat inactivated,</td>
			<td style="width:121px;">Gibco</td>
			<td style="width:161px;">10082147</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Fibronectin Human Protein, Plasma</td>
			<td style="width:121px;">Gibco</td>
			<td style="width:161px;">33016015</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Fisherbrand 112xx Series Advanced Ultrasonic Cleaner</td>
			<td style="width:121px;">Fisher Scientific</td>
			<td style="width:161px;">FB11201</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Fluo-4, AM, cell permeant</td>
			<td style="width:121px;">Invitrogen</td>
			<td style="width:161px;">F14201</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">FluoroBrite DMEM Media</td>
			<td style="width:121px;">Gibco</td>
			<td style="width:161px;">A1896701</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">L-Glutamine (200 mM)</td>
			<td style="width:121px;">Gibco</td>
			<td style="width:161px;">25030081</td>
			<td></td>
		</tr>
		<tr height="84">
			<td height="84" style="height:84px;width:216px;">OKO full environmental control chamber (constant temperature, humidity and CO2)</td>
			<td style="width:121px;">OKO</td>
			<td style="width:161px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">PBS, pH 7.4</td>
			<td style="width:121px;">Gibco</td>
			<td style="width:161px;">10010023</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Penicillin-Streptomycin (10,000 U/mL)</td>
			<td style="width:121px;">Gibco</td>
			<td style="width:161px;">15140122</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Pierce Primary Cardiomyocyte Isolation Kit</td>
			<td style="width:121px;">Thermo Scientific</td>
			<td style="width:161px;">88281</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Trypsin-EDTA (0.25%), phenol red</td>
			<td style="width:121px;">Gibco</td>
			<td style="width:161px;">25200056</td>
			<td></td>
		</tr>
	</tbody>
</table>

silicon nanowires and optical stimulation for investigations of intra- and intercellular electrical coupling

Myofibroblasts can spontaneously internalize silicon nanowires (SiNWs), making them an attractive target for bioelectronic applications. These cell-silicon hybrids offer leadless optical modulation capabilities with minimal perturbation to normal cell behavior. The optical capabilities are obtained by the photothermal and photoelectric properties of SiNWs. These hybrids can be harvested using standard tissue culture techniques and then applied to different biological scenarios. We demonstrate here how these hybrids can be used to study the electrical coupling of cardiac cells and compare how myofibroblasts couple to one another or to cardiomyocytes. This process can be accomplished without special equipment beyond a fluorescent microscope with coupled laser line. Also shown is the use of a custom-built MATLAB routine that allows the quantification of calcium propagation within and between the different cells in the culture. Myofibroblasts are shown to have a slower electrical response than that of cardiomyocytes. Moreover, the myofibroblast intercellular propagation shows slightly slower, though comparable velocities to their intracellular velocities, suggesting passive propagation through gap junctions or nanotubes. This technique is highly adaptable and can be easily applied to other cellular arenas, for in vitro as well as in vivo or ex vivo investigations.

The ability of this methodology to allow direct access to the intracellular cytosol depends on the spontaneous internalization of the SiNW into the cells. Although SiNWs will undergo spontaneous internalization into many cell types15, some cells, such as cardiomyocytes and neurons, will need the SiNWs to be treated to allow their internalization19. In this protocol we describe the internalization process of p-i-n SiNWs with 200-300 nm diameter and ~1-3 &#181;m long into car...

Watch this Scientific Journal Video about Silicon Nanowires and Optical Stimulation for Investigations of Intra- and Intercellular Electrical Coupling at JoVE.com

Silicon Nanowires and Optical Stimulation for Investigations of Intra- and Intercellular Electrical Coupling

This protocol describes the use of silicon nanowires for intracellular optical bio-modulation of cell in a simple and easy to perform method. The technique is highly adaptable to diverse cell types and can be used for in vitro as well as in vivo applications.

Myofibroblasts can spontaneously internalize silicon nanowires (SiNWs), making them an attractive target for bioelectronic applications. These ...

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