This work was supported in part by an AO Foundation Start-Up Grant (S-14-03H) and the Friedrichsheim Foundation (Stiftung Friedrichsheim) based in Frankfurt/Main, Germany.

1. Construction of electrical stimulation cell culture chamber
<ol>
	<li>To build the EStim chamber, collect two lids of standard 6-well cell culture plates; 99.99% platinum wire, 60 cm in length with a diameter of 0.5&#8211;1 mm; silver-coated copper wire, 70 cm in length with a diameter of 0.6 mm; cutting pliers; soldering iron kit; one tube of superconductive glue; one wire terminal block connector, six small 2.2 V LEDs (optional); one tube of noncorrosive silicone adhesive coating (optional); one roll of black electrical insulation tape; standard, flexible, insulated copper electric wire (0.14 mm2), 2 m in length (Table of materials).</li>
	<li>In a 6-well plate lid, mark and then drill two holes (with a diameter of ~1 mm), 25 mm apart, near the outer edge of each of the six wells (12 holes in total), as shown in Figure 1A,B.</li>
	<li>Cut twelve 5 cm lengths of platinum wire with cutting pliers. Bend each of the wires manually into an L-shape, leaving one end 3 cm long and the other 2 cm. Cut the silver-coated wire into two 35 cm lengths.</li>
	<li>Insert the longer (3 cm) bent end of one platinum wire (from inside to out) into each drilled hole, leaving 1&#8211;2 mm protruding from the outside of the lid,&#160;bend it using forceps. Secure the platinum wires in the lid holes with superconductive glue and leave it to dry for around 6 h.</li>
	<li>Solder the tips of all six platinum wires (that will later serve as cathodes, see Figure 1A) protruding from the lids to one of the silver-coated wires. Repeat the same procedure, soldering the remaining six platinum wires (that will later serve as anodes) to the other silver-coated wire.
	<ol>
		<li>Add LEDs in the circuit between each of the six anode-cathode platinum electrode pairs, to confirm functionality during the experiments (optional). Place a piece of black insulation tape under each LED to prevent exposing the cells in the culture plates to the LED light (Figure 1C).</li>
	</ol>
	</li>
	<li>Glue the wire terminal block connector to the top left corner of the 6-well plate lid and connect both silver-coated wires to the input terminals, as shown in Figure 1C.</li>
	<li>Cut out a 20 mm x 20 mm section from the top left corner of a second 6-well plate lid (Figure 1B, Lid Nr. 2) to accommodate the terminal block connector on the first lid. Cover the first lid, equipped with the electrodes, with the second lid and tape them together with adhesive tape.
	<ol>
		<li>To improve the bonding of the two lids, use silicone adhesive coating (optional). To do so, cover the lid with the silver electrodes with a 3&#8211;5 mm layer of silicone adhesive and cover it with the other lid, allowing 12 h for the adhesive to dry.</li>
	</ol>
	</li>
	<li>Connect one end of the two standard insulated copper wires to the output terminals of the wire connector and the other ends to banana male connectors (4 mm). 
	NOTE: The length of these wires depends on the distance from the shelf in the incubator, where the cells will be kept, to the power supply, outside the incubator (Figure 1D).</li>
	<li>Adjust the dosage (voltage) and regimen of EStim delivered to the cells by regulating the DC power supply.
	<ol>
		<li>Turn on the power supply by pressing the ON/OFF button on the front panel. Activate channel 1 by pressing button 1.</li>
		<li>Press button Nr. 4 (V-set) to set the voltage. Press buttons 2, . and 5 to set the load output at 2.5 V. Press Enter.</li>
		<li>Ensure that the load output of 2.5 V (2,500 mV) corresponds to an EStim of 100 mV/mm, according to the following, simplified equation. 
		VEStim = <img alt="Equation" src="/files/ftp_upload/59127/59127eq1.jpg" />; or 
		V&#160;=&#160;VEStim &#215; d 
		Here, V&#160;= the power supply voltage output in millivolts; d = the distance between electrodes in millimeters; VEStim = the stimulation voltage in millivolts per millimeter. 
		NOTE: This simplification applies only in case of constant DC voltage. The resistance between the medium and the cells is negligible as electrodes are not in direct contact with the cells; instead, EStim is delivered to the cells through the medium.</li>
	</ol>
	</li>
</ol>
2. Mesenchymal stem cell culture in osteogenic medium
<ol>
	<li>Purchase and store commercially available rat MSCs (see Table of Materials) in liquid nitrogen until the day of the experiment. Alternatively, isolate MSCs from other animals according to protocols published elsewhere7,8 in accordance with local institutional regulations for the use of experimental animals.</li>
	<li>On the day of the experiment, remove one vial (1 x 106 cells) of MSCs from the liquid nitrogen storage, and quickly (within 1 min) thaw the cells in a water bath preheated to 37 &#176;C.
	<ol>
		<li>Under sterile conditions in a laminar flow hood, pipette the vial content into a 50 mL falcon tube and add 9 mL of normal medium (NM) prewarmed to 37 &#176;C, consisting of Dulbecco&#8217;s modified Eagle&#8217;s medium (DMEM; 1x) with 10% heat-inactivated fetal bovine serum (FBS) and 1% penicillin/streptomycin solution. Pellet the cells for 5 min by centrifugation at 300 x g.</li>
		<li>In a laminar flow hood, remove the supernatant and carefully resuspend the cell pellet in 12 mL of NM prewarmed to 37 &#176;C. Transfer the resuspended cells to a T-75 cell culture flask.</li>
	</ol>
	</li>
	<li>Culture the cells at 37 &#176;C, 5% CO2, 5% O2 until they reach an 80%&#8211;90% confluence (after approximately 3&#8211;5 days).</li>
	<li>Passage the cells. 
	NOTE: Perform all operations except centrifugation and incubation under sterile conditions in a laminar flow hood.
	<ol>
		<li>After reaching an 80%&#8211;90% confluence, retrieve the cells with cell detachment solution. Aspirate the cell culture medium, wash 2x with 1x phosphate-buffered saline (PBS), add 5 mL of 1x cell detachment solution, and return the cells to the incubator for 5 min.</li>
		<li>Once the cells are detached, add an equal amount of culture medium to inactivate the detachment solution. Collect the cells in a 50 mL falcon tube and spin them at 300 x g for 5 min.</li>
		<li>Discard the medium and resuspend cells in 1 mL of fresh normal medium. Assess the number of viable cells with trypan blue stain.</li>
		<li>Seed 1 x 106 cells in a new T-75 flask with 12 mL of prewarmed NM. Culture the cells at 37 &#176;C, 5 % CO2, 5 % O2 until they reach an 80%&#8211;90% confluence. 
		NOTE: Cell passaging (steps 2.4.1&#8211;2.4.4) can be repeated a few times until the needed number of cells is obtained. Do not use cells older than passage 8.</li>
	</ol>
	</li>
	<li>Seed 9 x 104 cells in 3 mL of NM (10% heat-inactivated fetal bovine serum, 1% penicillin/streptomycin, DMEM) in each well of a 6-well culture plate. Incubate the cells for 1 day at 37 &#176;C, 5 % CO2, 5 % O2.</li>
	<li>The next day, aspirate culture medium and apply 3 mL of osteogenic differentiation medium (OM; normal medium supplemented with 10-7 M dexamethasone, 10 mM &#946;-glycerophosphate, and 0.05 mM ascorbic acid-2-phosphate).</li>
	<li>Place the 6-well plate with cells in the incubator and incubate at 37 &#176;C, 5% CO2, 5% O2 overnight.</li>
</ol>
3. Treating MSCs with EStim
<ol>
	<li>On the day the cells are treated with EStim, sterilize the electrodes in 70% ethanol solution for 30 min; then, dry them under UV light in a safety cabinet for an additional 30 min.</li>
	<li>In a laminar flow hood, cover the 6-well plate containing the cultured MSCs with the lid equipped with the electrodes, making sure that the electrodes are completely submerged in medium (if necessary, add medium). Transfer the covered 6-well plate (EStim chamber) with the cells to the incubator and connect its wires to the power supply.</li>
	<li>Set the power supply to 2.5 V load output and treat the cells with EStim for 1 h3,9.</li>
	<li>After stimulation, disconnect the power supply and remove the EStim chamber from the incubator. Under sterile conditions, exchange the lid equipped with electrodes with a standard 6-well plate lid.</li>
	<li>Return the cells to the incubator and leave them overnight. Clean the electrodes, first with PBS and then with 70% ethanol solution. Clean the accumulated corrosion products from the electrode surface with fine sandpaper.</li>
	<li>Repeat steps 3.1&#8211;3.5 for 6 consecutive days. On day 4, prior to applying EStim and under sterile conditions, change the culture medium by aspirating 1.5 mL of medium and replacing it with 1.5 mL of prewarmed fresh OM.</li>
	<li>After applying EStim for 7 consecutive days, maintain the cells in culture for an additional 7 days, exchanging the medium every 3&#8211;4 days.</li>
</ol>
4. Osteogenic differentiation measurements
<ol>
	<li>Analyze cell morphology changes under a microscope.</li>
	<li>To assess the effect of EStim on MSC osteogenic differentiation, measure calcium deposition, alkaline phosphatase activity, and osteogenic marker gene expression, as described elsewhere3,9.</li>
</ol>

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H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vitro+effect+of+direct+current+electrical+stimulation+on+rat+mesenchymal+stem+cells.">In vitro effect of direct current electrical stimulation on rat mesenchymal stem cells.</a> PeerJ. 5, e2821 (2017).</li><li>Leppik, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Combining+electrical+stimulation+and+tissue+engineering+to+treat+large+bone+defects+in+a+rat+model.">Combining electrical stimulation and tissue engineering to treat large bone defects in a rat model.</a> Scientific Reports. 8 (1), S1 (2018).</li><li>Song, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Application+of+direct+current+electric+fields+to+cells+and+tissues+in+vitro+and+modulation+of+wound+electric+field+in+vivo.">Application of direct current electric fields to cells and tissues in vitro and modulation of wound electric field in vivo.</a> Nature Protocols. 2 (6), 1479-1489 (2007).</li><li>Hronik-Tupaj, M., Kaplan, D. 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B., Barker, J. H., Leppik, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pretreating+mesenchymal+stem+cells+with+electrical+stimulation+causes+sustained+long-lasting+pro-osteogenic+effects.">Pretreating mesenchymal stem cells with electrical stimulation causes sustained long-lasting pro-osteogenic effects.</a> PeerJ. 6, 4959 (2018).</li><li>Livak, K. J., Schmittgen, T. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+relative+gene+expression+data+using+real-time+quantitative+PCR+and+the+2(-Delta+Delta+C(T))+Method.">Analysis of relative gene expression data using real-time quantitative PCR and the 2(-Delta Delta C(T)) Method.</a> Methods. 25 (4), 402-408 (2001).</li><li>Curtis, K. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=EF1alpha+and+RPL13a+represent+normalization+genes+suitable+for+RT-qPCR+analysis+of+bone+marrow+derived+mesenchymal+stem+cells.">EF1alpha and RPL13a represent normalization genes suitable for RT-qPCR analysis of bone marrow derived mesenchymal stem cells.</a> BMC Molecular Biology. 11, 61 (2010).</li><li>Wang, L., Li, Z. -. y., Wang, Y. -. p., Wu, Z. -. h., Yu, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dynamic+Expression+Profiles+of+Marker+Genes+in+Osteogenic+Differentiation+of+Human+Bone+Marrow-derived+Mesenchymal+Stem+Cells.">Dynamic Expression Profiles of Marker Genes in Osteogenic Differentiation of Human Bone Marrow-derived Mesenchymal Stem Cells.</a> Chinese Medical Sciences Journal (Chung-kuo i hsueh k'o hsueh tsa chih). 30 (2), 108-113 (2015).</li><li>Kim, H. B., Ahn, S., Jang, H. J., Sim, S. B., Kim, K. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaluation+of+corrosion+behaviors+and+surface+profiles+of+platinum-coated+electrodes+by+electrochemistry+and+complementary+microscopy:+biomedical+implications+for+anticancer+therapy.">Evaluation of corrosion behaviors and surface profiles of platinum-coated electrodes by electrochemistry and complementary microscopy: biomedical implications for anticancer therapy.</a> Micron. 38 (7), 747-753 (2007).</li><li>Cho, Y., Son, M., Jeong, H., Shin, J. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electric+field-induced+migration+and+intercellular+stress+alignment+in+a+collective+epithelial+monolayer.">Electric field-induced migration and intercellular stress alignment in a collective epithelial monolayer.</a> Molecular Biology of the Cell. , mbcE18010077 (2018).</li><li>Tai, G., Tai, M., Zhao, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrically+stimulated+cell+migration+and+its+contribution+to+wound+healing.">Electrically stimulated cell migration and its contribution to wound healing.</a> Burns &amp; Trauma. 6, 20 (2018).</li><li>Love, M. R., Palee, S., Chattipakorn, S. C., Chattipakorn, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+electrical+stimulation+on+cell+proliferation+and+apoptosis.">Effects of electrical stimulation on cell proliferation and apoptosis.</a> Journal of Cellular Physiology. 233 (3), 1860-1876 (2018).</li><li>Adams, D. S., Levin, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=General+principles+for+measuring+resting+membrane+potential+and+ion+concentration+using+fluorescent+bioelectricity+reporters.">General principles for measuring resting membrane potential and ion concentration using fluorescent bioelectricity reporters.</a> Cold Spring Harbor Protocols. 2012 (4), 385-397 (2012).</li><li>Jin, G., Li, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+electrically+conductive+scaffold+as+the+skeleton+of+stem+cell+niche+in+regenerative+medicine.">The electrically conductive scaffold as the skeleton of stem cell niche in regenerative medicine.</a> Materials Science &amp; Engineering. C, Materials for Biological Applications. 45, 671-681 (2014).</li><li>Hronik-Tupaj, M., Rice, W. L., Cronin-Golomb, M., Kaplan, D. 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The authors have nothing to disclose.

Here we describe the construction of a chamber and a method for treating mesenchymal stem cells with EStim that results in enhanced osteogenic differentiation.
The EStim setup presented does not require special equipment/knowledge and can be performed in a standard stem cell biology/biochemistry laboratory by junior researchers. However, when building and using the EStim chamber, special care must be taken in a few critical steps. When handling the platinum electrodes, extra care must be taken...

An increase in trauma and/or disease-induced bone defects are being treated using different combinations of cell therapy and regenerative medicine technologies. MSCs are the cell of choice in such treatments, due to their relatively high osteogenic activity, isolation and expansion efficiency, and safety1. To maximize their osteogenic activity and, thus, optimize their therapeutic effectiveness, several methods have been introduced to manipulate MSCs prior to their use in these treatments (as reviewed by Mauney et al.2). One such method is EStim, which has been shown to enhance MSC osteogenic differentiation in vitro3 and promote bone healing in vivo4. Despite the growing number of studies focusing on treating MSCs with EStim, an optimal regimen for maximizing EStim&#8217;s pro-osteogenic effect has yet to be defined.
Other in vitro methods using EStim utilize salt bridges submerged in the culture medium, which separates cells from metallic electrodes5. The advantage of this is that delivering EStim through salt bridges eliminates the introduction of chemical byproducts (e.g., corrosion of metallic electrodes) that may be cytotoxic. Despite this advantage, salt bridges are cumbersome to work with, and the EStim they deliver differs from that delivered in in vivo models, making it difficult to correlate results obtained when using the two systems. Setups that deliver EStim via metallic or carbon electrodes fixed inside the cell culture wells (as reviewed by Hronik-Tupaj and Kaplan6) better simulate devices used in vivo; however, these devices are difficult to clean/sterilize between uses and the number of cells that can be studied per experiment is limited. We designed the EStim chamber presented here specifically to address the limitations of these other setups. While most of our experience using this EStim chamber has been with 2D and 3D cultures containing bone-marrow- and adipose-tissue-derived MSCs3,4, a major benefit of this chamber is that it is versatile and, with relatively minor changes, can be adapted to study other cell types under a variety of different conditions.
Here we describe the construction of an EStim cell culture chamber; then, we demonstrate its use by treating MSCs with different regimens of EStim and measuring the resulting effect on osteogenic differentiation. MSC osteogenic differentiation is assessed via calcium deposition, alkaline phosphatase activity, and osteogenic marker gene expression. Importantly, in past experiments that used this setup, we observed that these pro-osteogenic effects persist long after the EStim treatment was discontinued.

<table>
	<tbody>
		<tr>
			<td>Estim fabrication</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Banana connector/Jack adaptor</td>
			<td>Poppstars</td>
			<td>1008554</td>
			<td>2 pieces</td>
		</tr>
		<tr>
			<td>Cutting pliers</td>
			<td>Knipex</td>
			<td>78 03 125</td>
			<td></td>
		</tr>
		<tr>
			<td>DC power supply (0-30V/0-3A)</td>
			<td>B&#38;K Precision</td>
			<td>Model 9130B</td>
			<td>Any simular model could be used</td>
		</tr>
		<tr>
			<td>Insulated flexible wires (0.14 mm2)</td>
			<td>Conrad Electronic International</td>
			<td>604794, 604093</td>
			<td>2 pieces</td>
		</tr>
		<tr>
			<td>Non-corrosive silicone rubber</td>
			<td>Dow Corning</td>
			<td>3140 RTV</td>
			<td>*could be purchased by many stores</td>
		</tr>
		<tr>
			<td>Platinum Wire (999,5/1000; 1mm &#248;)</td>
			<td>Junker Edelmetalle</td>
			<td>00D-3010</td>
			<td>0.6 m needed for 1 Estim chamber</td>
		</tr>
		<tr>
			<td>70% Ethanol solution</td>
			<td>any</td>
			<td></td>
			<td>Sterilisation of Estim chamber</td>
		</tr>
		<tr>
			<td>Silver coated copper wire (0.6 mm &#248;)</td>
			<td>Conrad Electronic International</td>
			<td>409334 - 62</td>
			<td>&#8776;70 cm needed for 1 Estim device</td>
		</tr>
		<tr>
			<td>Soldering iron Set</td>
			<td>Conrad Electronic International</td>
			<td>1611410 - 62</td>
			<td>Any simular model could be used</td>
		</tr>
		<tr>
			<td>TPP 6-well plate lid</td>
			<td>Sigma-Aldrich</td>
			<td>Z707759-126EA</td>
			<td>2 lids for Estim chamber</td>
		</tr>
		<tr>
			<td>2.2V wired circular LEDs</td>
			<td>Conrad Electronic International</td>
			<td>599525 - 62</td>
			<td>6 pieces</td>
		</tr>
		<tr>
			<td>UHU Super glue</td>
			<td>UHU GmbH &#38; Co. KG</td>
			<td>n/a</td>
			<td>*could be purchased by many stores</td>
		</tr>
		<tr>
			<td>MSC culture</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>&#946;-Glycerophosphate disodium salt hydrate</td>
			<td>Sigma-Aldrich</td>
			<td>G9422</td>
			<td>osteogenic cell culture</td>
		</tr>
		<tr>
			<td>DMEM, low glucose, GlutaMAX Supplement, pyruvate</td>
			<td>Thermo-Fischer Scientific</td>
			<td>21885025</td>
			<td>cell culture</td>
		</tr>
		<tr>
			<td>DPBS, no calcium, no magnesium</td>
			<td>Thermo-Fischer Scientific</td>
			<td>14190144</td>
			<td>cell culture</td>
		</tr>
		<tr>
			<td>Dexamethasone</td>
			<td>Sigma-Aldrich</td>
			<td>D4902</td>
			<td>osteogenic cell culture</td>
		</tr>
		<tr>
			<td>Fetal Bovine Serum</td>
			<td>Thermo-Fischer Scientific</td>
			<td>10500064</td>
			<td>cell culture</td>
		</tr>
		<tr>
			<td>50 ml Falcon tube</td>
			<td>Sarstedt</td>
			<td>62,547,004</td>
			<td>cell culture</td>
		</tr>
		<tr>
			<td>L-Ascorbic acid</td>
			<td>Sigma-Aldrich</td>
			<td>A4544</td>
			<td>osteogenic cell culture</td>
		</tr>
		<tr>
			<td>Penicillin/Streptomycin</td>
			<td>Thermo-Fischer Scientific</td>
			<td>15140122</td>
			<td>cell culture</td>
		</tr>
		<tr>
			<td>Sprague-Dawley (SD) rat mesenchymal stem cells, bone marrow origin</td>
			<td>Cyagen</td>
			<td>RASMX-01001</td>
			<td>cell culture</td>
		</tr>
		<tr>
			<td>Cell detachment solution</td>
			<td>Thermo-Fischer Scientific</td>
			<td>A1110501</td>
			<td>cell culture, cell detachment</td>
		</tr>
		<tr>
			<td>TC Flask, T75</td>
			<td>Sarstedt</td>
			<td>833911302</td>
			<td>cell culture</td>
		</tr>
		<tr>
			<td>TPP 6-well plates</td>
			<td>Sigma-Aldrich</td>
			<td>Z707759-126EA</td>
			<td>cell culture</td>
		</tr>
		<tr>
			<td>Trypan Blue Dye, 0.4% solution</td>
			<td>Bio-Rad</td>
			<td>1450021</td>
			<td>cell count</td>
		</tr>
	</tbody>
</table>

construction and use of an electrical stimulation chamber for enhancing osteogenic differentiation in mesenchymal stem/stromal cells in vitro

Mesenchymal stem/stromal cells (MSCs) have been used extensively to promote bone healing in tissue engineering approaches. Electrical stimulation (EStim) has been demonstrated to increase MSC osteogenic differentiation in vitro and promote bone healing in clinical settings. Here we describe the construction of an EStim cell culture chamber and its use in treating rat bone-marrow-derived MSC to enhance osteogenic differentiation. We found that treating MSCs with EStim for 7 days results in a significant increase in the osteogenic differentiation, and importantly, this pro-osteogenic effect persists long after (7 days) EStim is discontinued. This approach of pretreating MSCs with EStim to enhance osteogenic differentiation could be used to optimize bone tissue engineering treatment outcomes and, thus, help them to achieve their full therapeutic potential. In addition to this application, this EStim cell culture chamber and protocol can also be used to investigate other EStim-sensitive cell behaviors, such as migration, proliferation, apoptosis, and scaffold attachment.

To evaluate the effect of 100 mV/mm of EStim on the osteogenic differentiation of MSCs, cells treated with EStim for 3, 7, and 14 days or nontreated (control) were analyzed at day 14 of culturing by assessing morphological changes and calcium deposition (Figure 2). This was done by imaging cells using bright-field microscopy (morphology changes) or by fixing cells in 4% paraformaldehyde solution, staining them with 0.02% alizarin red solution and then imaging...

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Construction and Use of an Electrical Stimulation Chamber for Enhancing Osteogenic Differentiation in Mesenchymal Stem/Stromal Cells In Vitro

Here we present a protocol for the construction of a cell culture chamber designed to expose cells to various types of electrical stimulation, and its use in treating mesenchymal stem cells to enhance osteogenic differentiation.

Mesenchymal stem/stromal cells (MSCs) have been used extensively to promote bone healing in tissue engineering approaches. Electrical stimulation (EStim) ...

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Research

JoVE Journal

Bioengineering

11.1K Views.  Johann Wolfgang Goethe-University. Here we present a protocol for the construction of a cell culture chamber designed to expose cells to various types of electrical stimulation, and its use in treating mesenchymal stem cells to enhance osteogenic differentiation.

Video: Construction and Use of an Electrical Stimulation Chamber for Enhancing Osteogenic Differentiation in Mesenchymal Stem/Stromal Cells In Vitro

Engineering Skeletal Muscle Tissues from Murine Myoblast Progenitor Cells and Application of Electrical Stimulation

Engineered muscle tissues can be used for several different purposes, which include the production of tissues for use as a disease model in vitro, e.g. to study pressure ulcers, for regenerative medicine and as a meat alternative 1. The first reported 3D muscle constructs have been made many years ago and pioneers in the field are Vandenburgh and colleagues 2,3. Advances made in muscle tissue engineering are not only the result from the vast gain in knowledge of biochemical factors, stem cells and progenitor cells, but are in particular based on insights gained by researchers that physical factors play essential roles in the control of cell behavior and tissue development. State-of-the-art engineered muscle constructs currently consist of cell-populated hydrogel constructs. In our lab these generally consist of murine myoblast progenitor cells, isolated from murine hind limb muscles or a murine myoblast cell line C2C12, mixed with a mixture of collagen/Matrigel and plated between two anchoring points, mimicking the muscle ligaments. Other cells may be considered as well, e.g. alternative cell lines such as L6 rat myoblasts 4, neonatal muscle derived progenitor cells 5, cells derived from adult muscle tissues from other species such as human 6 or even induced pluripotent stem cells (iPS cells) 7. Cell contractility causes alignment of the cells along the long axis of the construct 8,9 and differentiation of the muscle progenitor cells after approximately one week of culture. Moreover, the application of electrical stimulation can enhance the process of differentiation to some extent 8. Because of its limited size (8 x 2 x 0.5 mm) the complete tissue can be analyzed using confocal microscopy to monitor e.g. viability, differentiation and cell alignment. Depending on the specific application the requirements for the engineered muscle tissue will vary; e.g. use for regenerative medicine requires the up scaling of tissue size and vascularization, while to serve as a meat alternative translation to other species is necessary.

Engineered muscle tissue has great potential in regenerative medicine, as disease model and also as an alternative source for meat. Here we describe the engineering of a muscle construct, in this case from mouse myoblast progenitor cells, and the stimulation by electrical pulses.

Engineered muscle tissues can be used for several different purposes, which include the production of tissues for use as a disease model in vitro, e.g. to ...

Eye Irritation Test (EIT) for Hazard Identification of Eye Irritating Chemicals using Reconstructed Human Cornea-like Epithelial (RhCE) Tissue Model

To comply with the Seventh Amendment to the EU Cosmetics Directive and EU REACH legislation, validated non-animal alternative methods for reliable and accurate assessment of ocular toxicity in man are needed. To address this need, we have developed an eye irritation test (EIT) which utilizes a three dimensional reconstructed human cornea-like epithelial (RhCE) tissue model that is based on normal human cells. The EIT is able to separate ocular&#160;irritants and corrosives (GHS Categories 1 and 2 combined) and those that do not require labeling (GHS No Category). The test utilizes two separate protocols, one designed for liquid chemicals and a second, similar protocol for solid test articles. The EIT prediction model uses a single exposure period (30 min for liquids, 6 hr for solids) and a single tissue viability cut-off (60.0% as determined by the MTT assay). Based on the results for 83 chemicals (44 liquids and 39 solids) EIT achieved 95.5/68.2/ and 81.8% sensitivity/specificity and accuracy (SS&#38;A) for liquids, 100.0/68.4/ and 84.6% SS&#38;A for solids, and 97.6/68.3/ and 83.1% for overall SS&#38;A. The EIT will contribute significantly to classifying the ocular irritation potential of a wide range of liquid and solid chemicals without the use of animals to meet regulatory testing requirements. The EpiOcular EIT method was implemented in 2015 into the OECD Test Guidelines as TG 492.

Eye Irritation Test EIT for Hazard Identification of Eye Irritating Chemicals using Reconstructed Human Cornea-like Epithelial RhCE Tissue Model

We have developed an eye irritation test which utilizes a three dimensional reconstructed human cornea-like epithelial (RhCE) tissue model. The test is able to discriminate between ocular irritant and corrosive materials (GHS Categories 1 and 2 combined) and those that do not require labeling (GHS No Category).

To comply with the Seventh Amendment to the EU Cosmetics Directive and EU REACH legislation, validated non-animal alternative methods for reliable and ...

Polyelectrolyte Complex for Heparin Binding Domain Osteogenic Growth Factor Delivery

During reconstructive bone surgeries, supraphysiological amounts of growth factors are empirically loaded onto scaffolds to promote successful bone fusion. Large doses of highly potent biological agents are required due to growth factor instability as a result of rapid enzymatic degradation as well as carrier inefficiencies in localizing sufficient amounts of growth factor at implant sites. Hence, strategies that prolong the stability of growth factors such as BMP-2/NELL-1, and control their release could actually lower their efficacious dose and thus reduce the need for larger doses during future bone regeneration surgeries. This in turn will reduce side effects and growth factor costs. Self-assembled PECs have been fabricated to provide better control of BMP-2/NELL-1 delivery via heparin binding and further potentiate growth factor bioactivity by enhancing in vivo stability. Here we illustrate the simplicity of PEC fabrication which aids in the delivery of a variety of growth factors during reconstructive bone surgeries.

Self-assembled polyelectrolyte complexes (PEC) fabricated from heparin and protamine were deposited on alginate beads to entrap and regulate the release of osteogenic growth factors. This delivery strategy enables a 20-fold reduction of BMP-2 dose in spinal fusion applications. This article illustrates the benefits and fabrication of PECs.

During reconstructive bone surgeries, supraphysiological amounts of growth factors are empirically loaded onto scaffolds to promote successful bone ...

An In Vitro Organ Culture Model of the Murine Intervertebral Disc

Intervertebral disc (IVD) degeneration is a significant contributor to low back pain. The IVD is a fibrocartilaginous joint that serves to transmit and dampen loads in the spine. The IVD consists of a proteoglycan-rich nucleus pulposus (NP) and a collagen-rich annulus fibrosis (AF) sandwiched by cartilaginous end-plates. Together with the adjacent vertebrae, the vertebrae-IVD structure forms a functional spine unit (FSU). These microstructures contain unique cell types as well as unique extracellular matrices. Whole organ culture of the FSU preserves the native extracellular matrix, cell differentiation phenotypes, and cellular-matrix interactions. Thus, organ culture techniques are particularly useful for investigating the complex biological mechanisms of the IVD. Here, we describe a high-throughput approach for culturing whole lumbar mouse FSUs that provides an ideal platform for studying disease mechanisms and therapies for the IVD. Furthermore, we describe several applications that utilize this organ culture method to conduct further studies including contrast-enhanced microCT imaging and three-dimensional high-resolution finite element modeling of the IVD.

An In Vitro Organ Culture Model of the Murine Intervertebral Disc

Whole organ culture of the intervertebral disc (IVD) preserves the native extracellular matrix, cell phenotypes, and cellular-matrix interactions. Here we describe an IVD culture system using mouse lumbar and caudal IVDs in their functional spinal units and several applications utilizing this system.

Intervertebral disc (IVD) degeneration is a significant contributor to low back pain. The IVD is a fibrocartilaginous joint that serves to transmit and ...

Improved 3D Hydrogel Cultures of Primary Glial Cells for In Vitro Modelling of Neuroinflammation

In the central nervous system, numerous acute injuries and neurodegenerative disorders, as well as implanted devices or biomaterials engineered to enhance function result in the same outcome: excess inflammation leads to gliosis, cytotoxicity, and/or formation of a glial scar that collectively exacerbate injury or prevent healthy recovery. With the intent of creating a system to model glial scar formation and study inflammatory processes, we have generated a 3D cell scaffold capable of housing primary cultured glial cells: microglia that regulate the foreign body response and initiate the inflammatory event, astrocytes that respond to form a fibrous scar, and oligodendrocytes that are typically vulnerable to inflammatory injury. The present work provides a detailed step-by-step method for the fabrication, culture, and microscopic characterization of a hyaluronic acid-based 3D hydrogel scaffold with encapsulated rat brain-derived glial cells. Further, protocols for characterization of cell encapsulation and the hydrogel scaffold by confocal immunofluorescence and scanning electron microscopy are demonstrated, as well as the capacity to modify the scaffold with bioactive substrates, with incorporation of a commercial basal lamina mixture to improved cell integration.

Improved 3D Hydrogel Cultures of Primary Glial Cells for In Vitro Modelling of Neuroinflammation

Herein, we present a protocol for the 3D culture of rat brain-derived glia cells, including astrocytes, microglia, and oligodendrocytes. We demonstrate primary cell culture, methacrylated hyaluronic acid (HAMA) hydrogel synthesis, HAMAphoto-polymerization and cell encapsulation, and sample processing for confocal and scanning electron microscopic imaging.

In the central nervous system, numerous acute injuries and neurodegenerative disorders, as well as implanted devices or biomaterials engineered to enhance ...

Isolation of Mesenchymal Stem Cells from Human Alveolar Periosteum and Effects of Vitamin D on Osteogenic Activity of Periosteum-derived Cells

Mesenchymal stem cells (MSCs) are present in a variety of tissues and can be differentiated into numerous cell types, including osteoblasts. Among the dental sources of MSCs, the periosteum is an easily accessible tissue, which has been identified to contain MSCs in the cambium layer. However, this source has not yet been widely studied.
Vitamin D3 and 1,25-(OH)2D3 have been demonstrated to stimulate in vitro differentiation of MSCs into osteoblasts. In addition, vitamin C facilitates collagen formation and bone cell growth. However, no study has yet investigated the effects of Vitamin D3 and Vitamin C on MSCs.
Here, we present a method of isolating MSCs from human alveolar periosteum and examine the hypothesis that 1,25-(OH)2D3 may exert an osteoinductive effect on these cells. We also investigate the presence of MSCs in the human alveolar periosteum and assess stem cell adhesion and proliferation. To assess the ability of vitamin C (as a control) and various concentrations of 1,25-(OH)2D3 (10&#8722;10, 10&#8722;9, 10&#8722;8, and 10&#8722;7 M) to alter key mRNA biomarkers in isolated MSCs mRNA expression of alkaline phosphatase (ALP), bone sialoprotein (BSP), core binding factor alpha-1 (CBFA1), collagen-1, and osteocalcin (OCN) are measured using real-time polymerase chain reaction (RT-PCR).

We present a protocol to investigate the mRNA expression biomarkers of periosteum-derived cells (PDCs) induced by vitamin C (vitamin C) and 1,25-dihydroxy vitamin D [1,25-(OH)2D3]. In addition, we evaluate the ability of PDCs to differentiate into osteocytes, chondrocytes, and adipocytes.

Mesenchymal stem cells (MSCs) are present in a variety of tissues and can be differentiated into numerous cell types, including osteoblasts. Among the ...

Simultaneous Electrical and Mechanical Stimulation to Enhance Cells' Cardiomyogenic Potential

Cardiovascular diseases are the leading cause of death in developed countries. Consequently, the demand for effective cardiac cell therapies has motivated researchers in the stem cell and bioengineering fields to develop in vitro high-fidelity human myocardium for both basic research and clinical applications. However, the immature phenotype of cardiac cells is a limitation on obtaining tissues that functionally mimic the adult myocardium, which is mainly characterized by mechanical and electrical signals. Thus, the purpose of this protocol is to prepare and mature the target cell population through electromechanical stimulation, recapitulating physiological parameters. Cardiac tissue engineering is evolving toward more biological approaches, and strategies based on biophysical stimuli, thus, are gaining momentum. The device developed for this purpose is unique and allows individual or simultaneous electrical and mechanical stimulation, carefully characterized and validated. In addition, although the methodology has been optimized for this stimulator and a specific cell population, it can easily be adapted to other devices and cell lines. The results here offer evidence of the increased cardiac commitment of the cell population after electromechanical stimulation. Electromechanically stimulated cells show an increased expression of main cardiac markers, including early, structural, and calcium-regulating genes. This cell conditioning could be useful for further regenerative cell therapy, disease modeling, and high-throughput drug screening.

Here we present a protocol for training a cell population using electrical and mechanical stimuli emulating cardiac physiology. This electromechanical stimulation enhances the cardiomyogenic potential of the treated cells and is a promising strategy for further cell therapy, disease modeling, and drug screening.

Cardiovascular diseases are the leading cause of death in developed countries. Consequently, the demand for effective cardiac cell therapies has motivated ...

Advanced 3D Liver Models for In vitro Genotoxicity Testing Following Long-Term Nanomaterial Exposure

Due to the rapid development and implementation of a diverse array of engineered nanomaterials (ENM), exposure to ENM is inevitable and the development of robust, predictive in vitro test systems is essential. Hepatic toxicology is key when considering ENM exposure, as the liver serves a vital role in metabolic homeostasis and detoxification as well as being a major site of ENM accumulation post exposure. Based upon this and the accepted understanding that 2D hepatocyte models do not accurately mimic the complexities of intricate multi-cellular interactions and metabolic activity observed in vivo, there is a greater focus on the development of physiologically relevant 3D liver models tailored for ENM hazard assessment purposes in vitro. In line with the principles of the 3Rs to replace, reduce and refine animal experimentation, a 3D HepG2 cell-line based liver model has been developed, which is a user friendly, cost effective system that can support both extended and repeated ENM exposure regimes (&#8804;14 days). These spheroid models (&#8805;500 &#181;m in diameter) retain their proliferative capacity (i.e., dividing cell models) allowing them to be coupled with the &#8216;gold standard&#8217; micronucleus assay to effectively assess genotoxicity in vitro. Their ability to report on a range of toxicological endpoints (e.g., liver function, (pro-)inflammatory response, cytotoxicity and genotoxicity) has been characterized using several ENMs across both acute (24 h) and long-term (120 h) exposure regimes. This 3D in vitro hepatic model has the capacity to be utilized for evaluating more realistic ENM exposures, thereby providing a future in vitro approach to better support ENM hazard assessment in a routine and easily accessible manner.

This procedure was established to be used for developing advanced 3D hepatic cultures in vitro, which can provide a more physiologically relevant assessment of the genotoxic hazards associated with nanomaterial exposures over both an acute or long-term, repeated dose regimes.

Due to the rapid development and implementation of a diverse array of engineered nanomaterials (ENM), exposure to ENM is inevitable and the development of ...

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.

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 ...

An In vitro System to Gauge the Thrombolytic Efficacy of Histotripsy and a Lytic Drug

Deep vein thrombosis (DVT) is a global health concern. The primary approach to achieve vessel recanalization for critical obstructions is catheter-directed thrombolytics (CDT). To mitigate caustic side effects and the long treatment time associated with CDT, adjuvant and alternative approaches are under development. One such approach is histotripsy, a focused ultrasound therapy to ablate tissue via bubble cloud nucleation. Pre-clinical studies have demonstrated strong synergy between histotripsy and thrombolytics for clot degradation. This report outlines a benchtop method to assess the efficacy of histotripsy-aided thrombolytic therapy, or lysotripsy.
Clots manufactured from fresh human venous blood were introduced into a flow channel whose dimensions and acousto-mechanical properties mimic an iliofemoral vein. The channel was perfused with plasma and the lytic&#160;recombinant tissue-type plasminogen activator. Bubble clouds were generated in the clot with a focused ultrasound source designed for the treatment of femoral venous clots. Motorized positioners were used to translate the source focus along the clot length. At each insonation location, acoustic emissions from the bubble cloud were passively recorded, and beamformed to generate passive cavitation images. Metrics to gauge treatment efficacy included clot mass loss (overall treatment efficacy), and the concentrations of D-dimer (fibrinolysis) and hemoglobin (hemolysis) in the perfusate. There are limitations to this in vitro design, including lack of means to assess in vivo side effects or dynamic changes in flow rate as the clot lyses. Overall, the setup provides an effective method to assess the efficacy of histotripsy-based strategies to treat DVT.

Histotripsy-aided lytic delivery or lysotripsy is under development for the treatment of deep vein thrombosis. An in vitro procedure is presented here to assess the efficacy of this combination therapy. Key protocols for the clot model, image guidance, and assessment of treatment efficacy are discussed.