This work is supported by the Rowland Junior Fellow program. The authors would like to express gratitude to the scientists and staff at the Rowland Institute at Harvard: Chris Stokes for his help in the development of the custom-built, computer-assisted pressure control setup, Diane Schaak, Ph.D. for her input for biological sample handling, Winfield Hill for developing the electrical setup, Alavaro Sanchez, Ph.D. for granting access to the flow cytometer, Scott Bevis, Kenny Spencer and Don Rogers for machining mechanical plumbing components required for the pressure setup. Microfluidic masters were fabricated at the Center for Nanoscale Systems (CNS) at Harvard University.

1. Cell Preparation
<ol>
	<li>Plate 1&#215;105 cells/ml of metastatic breast cancer cell line MDA-MB-231 in a volume of 10 ml per tissue culture T75 flask in Leibovitz&#8217;s L-15 Medium supplemented with 10% (v/v) fetal bovine serum and 1% penicillin-streptomycin.</li>
	<li>Incubate MDA-MB-231 cells in a humidified incubator at 37 &#176;C with 0% CO2 environment.</li>
	<li>Harvest cells for experiments 2 days after seeding by treating cells with 0.25% trypsin-EDTA for 2 min and inactivate trypsin&#8217;s enzymatic activity by adding 8 ml of the growth media.</li>
	<li>Pellet cells by centrifuging for 5 min at 200 &#215; g and resuspend in Dulbecco&#8217;s phosphate buffered saline (DPBS, 1x, without Ca2+ and Mg2+) to a final concentration of 5 &#215; 105 cells/ml.</li>
</ol>
2. Device Design and Fabrication
NOTE: The mask, master mold fabrications and the microchannel enclosing process are to be conducted inside a clean room while the polydimethylsiloxane (PDMS) microchannel casting process can be performed on a regular laboratory benchtop.
<ol>
	<li>Design a microfluidic device as illustrated in Figure 1 with AutoCAD. The device should consist of an inlet with multiple injection ports, coarse filters and two parallel straight rectangular inertial focusing channels (L = 7 mm, W = 40 &#956;m, and H = 70 &#956;m). Individual straight channel consists of 5 electroporation chambers, which are placed 800 &#956;m apart (WC = 400 &#956;m) with two via holes for aluminum electrodes. Two transversally adjacent electroporation chambers share the hole for the negative electrode. Two straight channels merge into an outlet at the downstream of the electroporation region.</li>
	<li>Convert the CAD file with micro-patterns to a GDSII file using LinkCAD. Write the micro-patterns on a 5&#8221; x 5&#8221; photomask blank using a laser mask writer. Develop the mask by following the manufacturer&#8217;s protocol. NOTE: The mask development process includes photoresist developing, chrome etching and resist removal. Alternatively, micro-patterns printed on a high resolution transparency (&#62;20,000 dpi) can be purchased from a third party manufacturer and used as a photomask. Final microscale features on a photomask should be transparent to match the polarity of a negative photoresist.</li>
	<li>Fabricate the casting mold of the device design using standard soft lithography techniques23 with a negative photoresist spun coat on a 4 inch silicon wafer at 2,000 rpm to have the final thickness of 70 &#956;m.</li>
	<li>Prebake the wafer with negative photoresist for 20 min at 95 &#176;C.</li>
	<li>Contact the mask with the wafer and expose to a UV source (17.4 mJ/cm2) for 80 sec using a mask aligner.</li>
	<li>Develop the exposed wafer for 4 min in a SU-8 developer.</li>
	<li>Measure the developed photoresist thickness using a surface profilometer.</li>
	<li>Rigorously mix a 10:1 ratio of elastomer to curing agent (silicone elastomer kit) and pour the mixture on the casting mold to generate PDMS replicas. Degas the casting elastomer for 30 min and cure the casting mold with degassed elastomer in an oven at 70 &#176;C for 2 hr.</li>
	<li>Delaminate cured PDMS replica with microchannel patterns from the mold and punch holes for inlets, outlet and electrode insertions using a pin vise. NOTE: The normal cutting edge diameter of the pin vise should be 0.76 mm, adequate for tightly holding PEEK tubing (O.D. of 1/32&#8221;) and aluminum electrodes (O.D. of 0.029&#8221;) in place.</li>
	<li>Create enclosed microfluidic channels by bonding PDMS replicas to a glass slide treated in an oxygen-plasma cleaner for 7 sec at a radio frequency power and oxygen partial pressure of 75 W and 500 mTorr, respectively.</li>
</ol>
3. Flow Experiments
<ol>
	<li>Insert aluminum electrodes (0.029&#8221; OD) and an outlet PEEK tubing (1/32&#8221; OD) into designated places via holes in the microchannel (see Figure 3B).</li>
	<li>Connect the electrical equipment18 responsible for generating high-voltage short square-wave pulses to the aluminum electrodes (see Figure 3C) that are in contact with flowing solutions in the PDMS mold. NOTE: The equipment should consist of a pulse generator and an in-house built high voltage amplifier.18</li>
	<li>Prepare four 50 ml centrifuge tubes individually containing DPBS, solutions with cells and biomolecules, and attach each tube to its respective vial holder connected to the pneumatic flow control system (see Figure 3A).18</li>
	<li>Connect inlet PEEK tubing from the vial holders into the respective inlet holes in the microfluidic device.</li>
	<li>Set the magnitude of square-wave pulses, V, to 100 V in order to have the electric field strength, E =V/Le, across the electroporation chamber be equivalent to 0.7 kV/cm. NOTE: Here, Le is the distance between two points where the positive and negative electrodes are in contact with the flowing solution (see Figure 1).</li>
	<li>Set the pressure regulator to 40 psi. NOTE: A single manually adjustable nitrogen source is used to uniformly pressurize all sample vials and a high-speed manifold is utilized to timely activate individual solution ports using the custom-built LabVIEW software.18</li>
	<li>For valve control, open the custom-built LabVIEW software labeled Valve Runner, and click run from the dropdown menu entitled operate.</li>
	<li>Turn on valves by clicking on each corresponding valve icon. NOTE: The valve icon should turn green when it is activated. Clicking the active icon will deactivate and close the valve. The closed valve icon should turn grey.</li>
	<li>Open the valve for the DPBS reservoir (i.e., washing solution) to prime the flow speed required for stable cell-trapping vortex generation for 1.5 min.</li>
	<li>Switch the active solution port from the washing solution to the cell solution to trap cells in the electroporation chamber for 30 sec (i.e., the cell-trapping step).</li>
	<li>Flow both washing and cell solutions through the device simultaneously for 10 sec prior to the cell-trapping step to ensure undisrupted flow during the solution-switching step. NOTE: This brief co-flow step should be repeated at each solution-switching step.</li>
	<li>Turn on the washing port and flush the device for 20 sec in order to remove non-trapped contaminating cells.</li>
	<li>Inject the solution containing the first molecule of interest (0.2 mg/ml of 3,000 Da neutral and anionic dextran molecules or 1.5 mg/ml of 70,000 Da neutral dextran molecule) into the device.</li>
	<li>Apply five short pulses (&#916;t= 30 msec with 2 sec intervals) promptly after injection of the molecular solution and monitor the magnitude and duration of the applied electrical pulses in real-time using an oscilloscope.</li>
	<li>Repeat step 3.10 as many times as the number of additional molecules to be delivered. For each molecular delivery, incubate cells for 100 s in the molecular solution then flush the device with the washing solution for 100 s to remove excess molecules.</li>
	<li>Release the cells in a 96-well plate for downstream analysis by lowering the operating pressure below 5 psi. NOTE: Approximately 100 &#956;l of solution with 100 cells is collected from each release.</li>
	<li>Run the experimental steps 3.9 through 3.16 three times to collect enough cells for flow cytometry.</li>
	<li>Centrifuge the 96-well plate containing processed cells for 5 min at 228 &#215; g.</li>
	<li>Remove the supernatant that contains excess fluorescent molecules.</li>
	<li>Resuspend cells in DPBS for flow cytometry analysis.</li>
	<li>Load cells in the flow cytometer for molecular uptake efficiency analysis.</li>
</ol>

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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=High-efficiency+gene+transfer+into+skeletal+muscle+mediated+by+electric+pulses.">High-efficiency gene transfer into skeletal muscle mediated by electric pulses.</a> Proc Natl Acad Sci USA. 96, 4262-4267 (1999).</li><li>Heller, R., 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=Intradermal+delivery+of+interleukin-12+plasmid+DNA+by+in+vivo+electroporation.">Intradermal delivery of interleukin-12 plasmid DNA by in vivo electroporation.</a> DNA Cell Biol. 20, 381-381 (2001).</li><li>Boukany, P. 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The authors have nothing to disclose.

With the new parallelized electroporation platform, 10-fold enhancement in throughput and efficiency of multi-molecule delivery was achieved in addition to all the merits that the previously developed single-chamber system provides.18 Previously available merits include (i) pre-purification of target cells with uniform size distribution for viability enhancement, (ii) precise and individual molecular dosage control, and (iii) low operational electrical current. Fluorescently labeled dextrans were chosen as molecules of interest because they are readily available in a wide range of molecular weights, conjugated fluorophore types, and electrical charges. These macro-molecules are good candidates for such a study since they are inherently membrane impermeable for living cells and do not exhibit cytotoxicity.24 Optimum concentration of fluorescent dextran, incubation time, and electrical parameters were identified for the current system prior to the electroporation experiments. The optimization process was rather simple and efficient due to the platform&#8217;s ability to monitor the molecular uptake process in real-time. Visualization of this process is very beneficial if a molecule or cell type with little-to-no knowledge of electroporation parameters is being tested. The incubation time for all molecules tested was set to be 100 s by which cells trapped in all 10 chambers exhibit detectable fluorescent intensity signals in real time, indicating the completion of successful molecular delivery. Note that this is not the minimum incubation duration required for molecular delivery.
There has been a long-standing debate regarding the molecular delivery process using electroporation, whether it is solely mediated by diffusion4,19,25 or by electrophoresis.26 Identification of the dominant mechanism of molecular delivery involves a series of laborious individual tests, comparing the outcomes depending on molecular sizes, electrical charges and electroporation parameters. To the best of the authors&#8217; knowledge, these laborious optimization processes were not reported with conventional electroporation systems.4,26-28 The developed system&#8217;s simple parameter optimization capability allowed for identification of the dominant molecular delivery mechanism, by examining variations in the electroporation efficiency depending on molecular and electric parameters. Results showed that the efficiency of anionic 3,000 Da dextran was not significantly different than that of its neutral counterpart (83 and 75%, respectively), suggesting that the molecular uptake observed was possibly mediated by diffusion. Unlike other electroporation systems, processed cells were continuously agitated throughout the electroporation process in this system. Gradual increase in fluorescent signals of orbiting cells was observed, suggesting that diffusion would be the dominant delivery mechanism. High efficiency molecular uptake (90%) of neutral 70,000 Da dextran molecules further implies that even at high molecular weights the delivery process occurs as a result of diffusion. Lastly, successful sequential delivery of 3,000 Da anionic and neutral dextran molecules solidifies the claim that molecular delivery occurs despite the molecules charge. This result also suggests that membrane resealing is not completed within 3 min of electroporation (100 sec per molecular delivery).
The presented molecular delivery platform can sequentially deliver wide ranges of molecular sizes regardless of their electrical charges. Timely fine-tuning and modification of individual parameters can be achieved with little effort aided by the real-time process monitoring capability. The system&#8217;s size-based cell purification process eliminates the need for laborious sample preparation and time-consuming centrifugation pre- and post-electroporation steps. Furthermore, the system&#8217;s low operational current substantially reduces cell mortality.

In recent years, the use of electric pulses to facilitate cytosolic delivery of extracellular molecules has become an attractive means of manipulating mammalian cells.1 This process, also known as electroporation, reversibly permeabilizes the cellular membrane, allowing for inherently membrane impermeable molecules to gain access to the cells&#8217; intracellular milieu. Because virtually any molecule can be introduced into the cytosol via temporary created pores in the membrane of any type of cells using electroporation, the technique has been reported as being more reproducible, universally applicable, and more efficient than other methods including virus-mediated, chemical and optical approaches.2-3 This technique has been utilized to introduce fluorescent molecules,4 drugs5 and nucleic acids6-7 while keeping cells viable and intact. Given these benefits, electroporation has been adopted as a common laboratory technique for DNA transfection, in vivo gene therapy8 and cell vaccination studies. It is, however, still difficult for conventional electroporation systems to simultaneously achieve practical efficiency and viability for samples with large heterogeneity in size because the electric field strength required for successful electroporation closely correlates with the cell&#8217;s diameter. Moreover, those systems do not allow precise control of the multiple molecular amounts being delivered due to reliance on bulk stochastic molecular delivery process.9 In order to address these issues, many groups have developed microfluidic electroporation platforms, offering the advantage of lower poration voltages, better transfection efficiency, a large reduction in cell mortality, and ability to deliver multiple molecules.10-13 These advantages were made possible owing to the small footprints of microscale electroporation systems whose electrode pitch lengths are sub-millimeters, dramatically decreasing voltages required for successful delivery. Moreover, these microscale electroporation systems can achieve uniform electric field distribution and rapidly dissipate generated heat, yielding reduced cell mortality while enhancing delivery efficiency. The utilization of transparent materials for these microchips further allows in situ observation of the electroporation process for prompt parameter modifications.2,12 However, precise dosage control and molecular- and cellular-dependent parameter control, required for emerging research and therapeutic applications,6,14-16 still remain unresolved.
This work presents a microfluidic vortex-assisted electroporation system, capable of delivering multiple molecules sequentially into a pre-selected identical population of target cells. Cells with uniform size distribution are isolated prior to electroporation using previously reported size-selective trapping mechanism.17-18 By having a uniform size distribution, less variation in electroporation efficiency and enhanced viability per given electric field strength were achieved.19 Furthermore, continuously agitating trapped cells using microscale vortices allowed for uniform delivery of molecules across the entire cytosol, in agreement with the results previously reported using another vortex-assisted electroporation platform.20 To demonstrate that this system would be applicable to a broad range of molecules commonly utilized in biological applications, macromolecules with a wide range of molecular weights were delivered to metastatic breast cancer cells. In addition, with the aid of real-time process monitoring, this work provides more evidence to put an end to the long standing debate regarding the mechanism of molecular delivery during electrporation, being predominantly electrophoresis-mediated versus diffusion-mediated.14 Unlike other electroporation systems, this platform uniquely provides the combined advantages of precise multi-molecule delivery, high molecular delivery efficiency, minimal cell mortality, a wide span of size and charges of delivered molecules, as well as real-time visualization of the electroporation process. Given these capabilities, the developed electroporation system has practical potential as a versatile tool for cellular reprogramming studies,6,14,21-22 drug delivery applications10,19 and applications requiring for in-depth understanding of electroporation molecular delivery mechanisms.

<table border="0" cellpadding="0" cellspacing="0" width="1056">
	<tbody>
		<tr height="20">
			<td height="20" style="height:21px;width:475px;">MDA-MB-231 cancer cell line</td>
			<td style="width:297px;">American Type Culture Collection (ATCC)</td>
			<td style="width:119px;">HTB-26</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">Leibovitz&#8217;s L-15 Medium</td>
			<td style="width:297px;">Cellgro, Mediatech, Inc.</td>
			<td style="width:119px;">10-045-CV</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">fetal bovine serum (FBS)</td>
			<td style="width:297px;">Gibco, Life Technologies</td>
			<td style="width:119px;">16000-044</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">penicillin-streptomycin</td>
			<td style="width:297px;">Sigma-Aldrich</td>
			<td style="width:119px;">P4333</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:475px;">Dulbecco&#39;s phosphate buffered saline (DPBS)</td>
			<td style="width:297px;">Cellgro, Mediatech, Inc.</td>
			<td style="width:119px;">21-030</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">Trypsin</td>
			<td style="width:297px;">Gibco, Life Technologies</td>
			<td style="width:119px;">25200-056</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">Flow Cytometer easyCyte HT</td>
			<td style="width:297px;">Millipore</td>
			<td style="width:119px;">0500-4008</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">Oxygen Plasma Cleaner</td>
			<td style="width:297px;">Technics Micro-RIE</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">Dektak 6M surface profiler</td>
			<td style="width:297px;">Veeco</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">KMPR 1050</td>
			<td style="width:297px;">Microchem</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">SYLGARD 184 SILICONE ELASTOMER KIT</td>
			<td style="width:297px;">Dow Corning</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">Compressed Nitrogen gas</td>
			<td style="width:297px;">Airgas</td>
			<td style="width:119px;">NI 300</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:475px;">High Pressure Regulator</td>
			<td style="width:297px;">McMaster-Carr</td>
			<td>6162K22</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">Downstream regulator</td>
			<td style="width:297px;">McMaster-Carr</td>
			<td style="width:119px;">4000K563</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">high-speed 3/2way-8 valve manifold</td>
			<td style="width:297px;">Festo</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">Inline Check Valve</td>
			<td style="width:297px;">Idex Health and Science</td>
			<td style="width:119px;">CV3320</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:475px;">5/32&#34; OD x 3/32&#34;ID Polyurethan tubes</td>
			<td style="width:297px;">Pneumadyne</td>
			<td>PU-156F-0</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">1/4&#34; OD X 0.17&#34; ID Polyurethan tubes</td>
			<td style="width:297px;">Pneumadyne</td>
			<td style="width:119px;">PU-250PB-4</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">1/16&#34; PEEK tubings</td>
			<td style="width:297px;">Festo</td>
			<td style="width:119px;">P1533</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">1/32&#34; PEEK tubings</td>
			<td style="width:297px;">Idex Health and Science</td>
			<td style="width:119px;">P1569</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">PEEK tubing unions</td>
			<td style="width:297px;">Idex Health and Science</td>
			<td style="width:119px;">P881</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">Pulse Generator</td>
			<td style="width:297px;">HP</td>
			<td style="width:119px;">8110A</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">Aluiminum Wire</td>
			<td style="width:297px;">Bob Martin Company</td>
			<td style="width:119px;">6061 ALUM</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">oscilloscope</td>
			<td style="width:297px;">Agilent</td>
			<td style="width:119px;">DSO3062A</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">50 mL centrifuge tubes</td>
			<td style="width:297px;">VWR</td>
			<td style="width:119px;">21008-178</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">15 mL centrifuge tube</td>
			<td style="width:297px;">VWR</td>
			<td style="width:119px;">21008-216</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">T75 culture flask</td>
			<td style="width:297px;">VWR</td>
			<td style="width:119px;">82050-862</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">Dextran, Tetramethylrhodamine, 3000 MW, Anionic</td>
			<td style="width:297px;">Gibco, Life Technologies</td>
			<td style="width:119px;">D3307</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">Dextran, Tetramethylrhodamine, 70,000 MW, Neutral&#160;</td>
			<td style="width:297px;">Gibco, Life Technologies</td>
			<td style="width:119px;">D1819</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">Dextran, Texas Red, 3000 MW, Neutral</td>
			<td style="width:297px;">Gibco, Life Technologies</td>
			<td style="width:119px;">D3329</td>
			<td></td>
		</tr>
	</tbody>
</table>

microscale vortex-assisted electroporator for sequential molecular delivery

Electroporation has received increasing attention in the past years, because it is a very powerful technique for physically introducing non-permeant exogenous molecular probes into cells. This work reports a microfluidic electroporation platform capable of performing multiple molecule delivery to mammalian cells with precise and molecular-dependent parameter control. The system&#8217;s ability to isolate cells with uniform size distribution allows for less variation in electroporation efficiency per given electric field strength; hence enhanced sample viability. Moreover, its process visualization feature allows for observation of the fluorescent molecular uptake process in real-time, which permits prompt molecular delivery parameter adjustments in situ for efficiency enhancement. To show the vast capabilities of the reported platform, macromolecules with different sizes and electrical charges (e.g., Dextran with MW of 3,000 and 70,000 Da) were delivered to metastatic breast cancer cells with high delivery efficiencies (&#62;70%) for all tested molecules. The developed platform has proven its potential for use in the expansion of research fields where on-chip electroporation techniques can be beneficial.

The developed parallel microfluidic electroporator delivered macromolecules with varied sizes and electrical charges into living metastatic breast cancer cells. Successful molecular delivery was qualitatively determined by monitoring changes in fluorescent intensity of electroporated orbiting cells in situ and confirmed by quantitative measurements via flow cytometry analysis. Figure 4A&#160;shows that 90% of treated cells uptake the 70,000 Da neutral dextran. For the statistical analysis, an intensity threshold for each fluorophore was established such that the majority (&#62;99%) of unprocessed living cells is counted below the threshold (see Figure 4 (c)). The efficiency is defined as the ratio of the number of cells successfully taking up the molecules of interest to the total number of processed cells. Figure 4B&#160;illustrates that the efficiency does not substantially vary depending on molecular weight or electrical charges (P &#62;0.1). All tested dextran molecules were delivered into the cytosol with efficiency greater than 70%. In addition, Figure 4D&#160;exhibits that sequential molecular delivery was successfully performed with a dual molecule delivery efficiency of 56% using the anionic and neutral dextrans with identical molecular weight (MW = 3,000 Da). The current system can process cells with 10-fold higher throughput and multi-molecule delivery efficiency than the previously reported system18 and this improvement does not affect single-molecule delivery (82% and 70% for anionic and neutral dextran, respectively).
<img alt="Figure 1" src="/files/ftp_upload/51702/51702fig1highres.jpg" /> 
Figure 1. (A) A schematic of the microfluidic electroporation system, consisting of inlets for cells (denoted as C), molecules (denoted as M1 and M2) and a flush solution (denoted as F), two straight channels where inertial focusing occurs, 10 electroporation chambers with electrodes and an outlet. (B) Solution exchange demonstration at the inlet using a 1&#956;M FITC solution and a flush solution (DPBS) indicates that the active solution can be uniformly injected to all arrays of chambers downstream. Image contrast is enhanced by adjusting look-up table (LUT). Scale bars are 250 &#956;m. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/51702/51702fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/51702/51702fig2highres.jpg" /> 
Figure 2. A photograph of the 15-pin electrode utilized for short-pulse high voltage application, consisting of 10 positive (+) and five negative electrodes (-). Each positive electrode is spaced 2 mm apart from a negative electrode, and each electrode of the same polarity is spaced 1.35 mm apart. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/51702/51702fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" src="/files/ftp_upload/51702/51702fig3highres.jpg" /> 
Figure 3. Schematic of the experimental apparatus, consisting of (A) the fluid control unit, (B) the microfluidic electroporator, and (C) the electrical equipment. (A) Vials containing solutions with molecules, cells and clean buffer are individually pressurized on demand using the LabView controlled pneumatic flow system. The solution from the pressurized vial is injected into the microfluidic electroporator through PEEK tubing with a check valve installed. (B)&#160;and&#160;(C) The electric signals are sent to 15-pin electrodes in contact with the flowing solution in the microfluidic system during the electroporation step. The electric pulses with the programmed duration are generated using the pulse generator and the magnitude of the electric pulse is amplified to 100 V by the high voltage amplifier. All applied electrical parameters are monitored in real time using an oscilloscope. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/51702/51702fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" src="/files/ftp_upload/51702/51702fig4highres.jpg" /> 
Figure 4. Representative flow cytometry data. (A) Fluorescent signals of MDA-MB-231 cells, which successfully took up the 70,000 Da anionic dextran molecule, compared to that of the control counterpart. (B) The efficiencies for each transferred dextran molecule do not exhibit significant molecular dependent variation (p &#62;0.1). (C) Representative flow cytometry profiles for cells, which were not treated with electroporation (control). The fluorescent threshold indicating successful molecular delivery is set from the data such that the signals from control samples are found below the threshold. (D) Representative flow cytometry data for sequentially electroporated cells. Green, red and yellow boxes in the flow cytometry plot and fluorescent streak images on the right-side represent fluorescent signals from cells uptaking 3,000 Da neutral dextran-only, anionic dextran-only and both dextran molecules, respectively. Scale bar is 100 m. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/51702/51702fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Microscale Vortex-assisted Electroporator for Sequential Molecular Delivery at JoVE.com

Microscale Vortex-assisted Electroporator for Sequential Molecular Delivery

A microfluidic vortex assisted electroporation platform was developed for sequential delivery of multiple molecules into identical cell populations with precise and independent dosage control. The system&#8217;s size based target cell purification step preceding electroporation aided to enhance molecular delivery efficiency and processed cell viability.

Electroporation has received increasing attention in the past years, because it is a very powerful technique for physically introducing non-permeant ...

microscale-vortex-assisted-electroporator-for-sequential-molecular

Nanyang Technological University

Research

JoVE Journal

Bioengineering

8.5K Views.  Harvard University. A microfluidic vortex assisted electroporation platform was developed for sequential delivery of multiple molecules into identical cell populations with precise and independent dosage control. The system’s size based target cell purification step preceding electroporation aided to enhance molecular delivery efficiency and processed cell viability.

Video: Microscale Vortex-assisted Electroporator for Sequential Molecular Delivery

Low Molecular Weight Protein Enrichment on Mesoporous Silica Thin Films for Biomarker Discovery

The identification of circulating biomarkers holds great potential for non invasive approaches in early diagnosis and prognosis, as well as for the monitoring of therapeutic efficiency.1-3 The circulating low molecular weight proteome (LMWP) composed of small proteins shed from tissues and cells or peptide fragments derived from the proteolytic degradation of larger proteins, has been associated with the pathological condition in patients and likely reflects the state of disease.4,5 Despite these potential clinical applications, the use of Mass Spectrometry (MS) to profile the LMWP from biological fluids has proven to be very challenging due to the large dynamic range of protein and peptide concentrations in serum.6 Without sample pre-treatment, some of the more highly abundant proteins obscure the detection of low-abundance species in serum/plasma. Current proteomic-based approaches, such as two-dimensional polyacrylamide gel-electrophoresis (2D-PAGE) and shotgun proteomics methods are labor-intensive, low throughput and offer limited suitability for clinical applications.7-9 Therefore, a more effective strategy is needed to isolate LMWP from blood and allow the high throughput screening of clinical samples. 
Here, we present a fast, efficient and reliable multi-fractionation system based on mesoporous silica chips to specifically target and enrich LMWP.10,11 Mesoporous silica (MPS) thin films with tunable features at the nanoscale were fabricated using the triblock copolymer template pathway. Using different polymer templates and polymer concentrations in the precursor solution, various pore size distributions, pore structures, connectivity and surface properties were determined and applied for selective recovery of low mass proteins. The selective parsing of the enriched peptides into different subclasses according to their physicochemical properties will enhance the efficiency of recovery and detection of low abundance species. In combination with mass spectrometry and statistic analysis, we demonstrated the correlation between the nanophase characteristics of the mesoporous silica thin films and the specificity and efficacy of low mass proteome harvesting. The results presented herein reveal the potential of the nanotechnology-based technology to provide a powerful alternative to conventional methods for LMWP harvesting from complex biological fluids. Because of the ability to tune the material properties, the capability for low-cost production, the simplicity and rapidity of sample collection, and the greatly reduced sample requirements for analysis, this novel nanotechnology will substantially impact the field of proteomic biomarker research and clinical proteomic assessment.

We developed a technology based on mesoporous silica thin film for the selective recovery of low molecular weight proteins and peptides from human serum. The physico-chemical properties of our mesoporous chips were finely tuned to provide substantial control in peptide enrichment and consequently profile the serum proteome for diagnostic purposes.

The identification of circulating biomarkers holds great potential for non invasive approaches in early diagnosis and prognosis, as well as for the ...

Skin Tattooing As A Novel Approach For DNA Vaccine Delivery

Nucleic acid-based vaccination is a topic of growing interest, especially plasmid DNA (pDNA) encoding immunologically important antigens. After the engineered pDNA is administered to the vaccines, it is transcribed and translated into immunogen proteins that can elicit responses from the immune system. Many ways of delivering DNA vaccines have been investigated; however each delivery route has its own advantages and pitfalls. Skin tattooing is a novel technique that is safe, cost-effective, and convenient. In addition, the punctures inflicted by the needle could also serve as a potent adjuvant. Here, we a) demonstrate the intradermal delivery of plasmid DNA encoding enhanced green fluorescent protein (pCX-EGFP) in a mouse model using a tattooing device and b) confirm the effective expression of EGFP in the skin cells using confocal microscopy.

Skin tattooing is a potent and safe way to delivery DNA vaccine intradermally. Here, a DNA plasmid encoding EGFP is delivered by tattooing to the skin of a laboratory mouse, and the expression of EGFP in the skin cells is then inspected by confocal microscopy.

Nucleic acid-based vaccination is a topic of growing interest, especially plasmid DNA (pDNA) encoding immunologically important antigens. After the ...

Self-reporting Scaffolds for 3-Dimensional Cell Culture

Culturing cells in 3D on appropriate scaffolds is thought to better mimic the in vivo microenvironment and increase cell-cell interactions. The resulting 3D cellular construct can often be more relevant to studying the molecular events and cell-cell interactions than similar experiments studied in 2D. To create effective 3D cultures with high cell viability throughout the scaffold the culture conditions such as oxygen and pH need to be carefully controlled as gradients in analyte concentration can exist throughout the 3D construct. Here we describe the methods of preparing biocompatible pH responsive sol-gel nanosensors and their incorporation into poly(lactic-co-glycolic acid) (PLGA) electrospun scaffolds along with their subsequent preparation for the culture of mammalian cells. The pH responsive scaffolds can be used as tools to determine microenvironmental pH within a 3D cellular construct. Furthermore, we detail the delivery of pH responsive nanosensors to the intracellular environment of mammalian cells whose growth was supported by electrospun PLGA scaffolds. The cytoplasmic location of the pH responsive nanosensors can be utilized to monitor intracellular pH (pHi) during ongoing experimentation.

Biocompatible pH responsive sol-gel nanosensors can be incorporated into poly(lactic-co-glycolic acid) (PLGA) electrospun scaffolds. The produced self-reporting scaffolds can be used for in&#160;situ monitoring of microenvironmental conditions whilst culturing cells upon the scaffold. This is beneficial as the 3D cellular construct can be monitored in real-time without disturbing the experiment.

Culturing cells in 3D on appropriate scaffolds is thought to better mimic the in vivo microenvironment and increase cell-cell interactions. The resulting ...

Aplysia Ganglia Preparation for Electrophysiological and Molecular Analyses of Single Neurons

A major challenge in neurobiology is to understand the molecular underpinnings of neural circuitry that govern a specific behavior. Once the specific molecular mechanisms are identified, new therapeutic strategies can be developed to treat abnormalities in specific behaviors caused by degenerative diseases or aging of the nervous system. The marine snail Aplysia californica is well suited for the investigations of cellular and molecular basis of behavior because neural circuitry underlying a specific behavior could be easily determined and the individual components of the circuitry could be easily manipulated. These advantages of Aplysia have led to several fundamental discoveries of neurobiology of learning and memory. Here we describe a preparation of the Aplysia nervous system for the electrophysiological and molecular analyses of individual neurons. Briefly, ganglion dissected from the nervous system is exposed to protease to remove the ganglion sheath such that neurons are exposed but retain neuronal activity as in the intact animal. This preparation is used to carry out electrophysiological measurements of single or multiple neurons. Importantly, following the recording using a simple methodology, the neurons could be isolated directly from the ganglia for gene expression analysis. These protocols were used to carry out simultaneous electrophysiological recordings from L7 and R15 neurons, study their response to acetylcholine and quantitating expression of CREB1 gene in isolated single L7, L11, R15, and R2 neurons of Aplysia.

Aplysia Ganglia Preparation for Electrophysiological and Molecular Analyses of Single Neurons

Marine snail Aplysia californica has been widely used as a neurobiology model for the studies on cellular and molecular basis of behavior. Here a methodology is described for exploring the nervous system of Aplysia for the electrophysiological and molecular analyses of single neurons of identified neural circuitry.

A major challenge in neurobiology is to understand the molecular underpinnings of neural circuitry that govern a specific behavior. Once the specific ...

Porous Silicon Microparticles for Delivery of siRNA Therapeutics

Small interfering RNA (siRNA) can be used to suppress gene expression, thereby providing a new avenue for the treatment of various diseases. However, the successful implementation of siRNA therapy requires the use of delivery platforms that can overcome the major challenges of siRNA delivery, such as enzymatic degradation, low intracellular uptake and lysosomal entrapment. Here, a protocol for the preparation and use of a biocompatible and effective siRNA delivery system is presented. This platform consists of polyethylenimine (PEI) and arginine (Arg)-grafted porous silicon microparticles, which can be loaded with siRNA by performing a simple mixing step. The silicon particles are gradually degraded over time, thereby triggering the formation of Arg-PEI/siRNA nanoparticles. This delivery vehicle provides a means for protecting and internalizing siRNA, without causing cytotoxicity. The major steps of polycation functionalization, particle characterization, and siRNA loading are outlined in detail. In addition, the procedures for determining particle uptake, cytotoxicity, and transfection efficacy are also described.

Delivery remains the main challenge for the therapeutic implementation of small interfering RNA (siRNA). This protocol involves the use of a multifunctional and biocompatible siRNA delivery platform, consisting of arginine and polyethylenimine grafted porous silicon microparticles.

Small interfering RNA (siRNA) can be used to suppress gene expression, thereby providing a new avenue for the treatment of various diseases. However, the ...

Biofunctionalized Prussian Blue Nanoparticles for Multimodal Molecular Imaging Applications

Multimodal, molecular imaging allows the visualization of biological processes at cellular, subcellular, and molecular-level resolutions using multiple, complementary imaging techniques. These imaging agents facilitate the real-time assessment of pathways and mechanisms in vivo, which enhance both diagnostic and therapeutic efficacy. This article presents the protocol for the synthesis of biofunctionalized Prussian blue nanoparticles (PB NPs) - a novel class of agents for use in multimodal, molecular imaging applications. The imaging modalities incorporated in the nanoparticles, fluorescence imaging and magnetic resonance imaging (MRI), have complementary features. The PB NPs possess a core-shell design where gadolinium and manganese ions incorporated within the interstitial spaces of the PB lattice generate MRI contrast, both in T1 and T2-weighted sequences. The PB NPs are coated with fluorescent avidin using electrostatic self-assembly, which enables fluorescence imaging. The avidin-coated nanoparticles are modified with biotinylated ligands that confer molecular targeting capabilities to the nanoparticles. The stability and toxicity of the nanoparticles are measured, as well as their MRI relaxivities. The multimodal, molecular imaging capabilities of these biofunctionalized PB NPs are then demonstrated by using them for fluorescence imaging and molecular MRI in vitro.

This protocol describes the synthesis of biofunctionalized Prussian blue nanoparticles and their use as multimodal, molecular imaging agents. The nanoparticles have a core-shell design where gadolinium or manganese ions within the nanoparticle core generate MRI contrast. The biofunctional shell contains fluorophores for fluorescence imaging and targeting ligands for molecular targeting.

Multimodal, molecular imaging allows the visualization of biological processes at cellular, subcellular, and molecular-level resolutions using multiple, ...

Analyzing Mixing Inhomogeneity in a Microfluidic Device by Microscale Schlieren Technique

In this paper, we introduce the use of microscale schlieren technique to measure mixing inhomogeneity in a microfluidic device. The microscale schlieren system is constructed from a Hoffman modulation contrast microscope, which provides easy access to the rear focal plane of the objective lens, by removing the slit plate and replacing the modulator with a knife-edge. The working principle of microscale schlieren technique relies on detecting light deflection caused by variation of refractive index1-3. The deflected light either escapes or is obstructed by the knife-edge to produce a bright or a dark band, respectively. If the refractive index of the mixture varies linearly with its composition, the local change in light intensity in the image plane is proportional to the concentration gradient normal to the optical axis. The micro-schlieren image gives a two-dimensional projection of the disturbed light produced by three-dimensional inhomogeneity.
To accomplish quantitative analysis, we describe a calibration procedure that mixes two fluids in a T-microchannel. We carry out a numerical simulation to obtain the concentration gradient in the T-microchannel that correlates closely with the corresponding micro-schlieren image. By comparison, a relationship between the grayscale readouts of the micro-schlieren image and the concentration gradients presented in a microfluidic device is established. Using this relationship, we are able to analyze the mixing inhomogeneity from associate micro-schlieren image and demonstrate the capability of microscale schlieren technique with measurements in a microfluidic oscillator4. For optically transparent fluids, microscale schlieren technique is an attractive diagnostic tool to provide instantaneous full-field information that retains the three-dimensional features of the mixing process.

Herein, we describe a procedure that employs microscale schlieren technique to measure mixing inhomogeneity in a microfluidic device. Through calibration, distribution of concentration gradient can be derived from the micro-schlieren image.

In this paper, we introduce the use of microscale schlieren technique to measure mixing inhomogeneity in a microfluidic device. The microscale schlieren ...

Adapting the Electrospinning Process to Provide Three Unique Environments for a Tri-layered In Vitro Model of the Airway Wall

Electrospinning is a highly adaptable method producing porous 3D fibrous scaffolds that can be exploited in in vitro cell culture. Alterations to intrinsic parameters within the process allow a high degree of control over scaffold characteristics including fiber diameter, alignment and porosity. By developing scaffolds with similar dimensions and topographies to organ- or tissue-specific extracellular matrices (ECM), micro-environments representative to those that cells are exposed to in situ can be created. 
The airway bronchiole wall, comprised of three main micro-environments, was selected as a model tissue. Using decellularized airway ECM as a guide, we electrospun the non-degradable polymer, polyethylene terephthalate (PET), by three different protocols to produce three individual electrospun scaffolds optimized for epithelial, fibroblast or smooth muscle cell-culture. Using a commercially available bioreactor system, we stably co-cultured the three cell-types to provide an in vitro model of the airway wall over an extended time period.
This model highlights the potential for such methods being employed in in vitro diagnostic studies investigating important inter-cellular cross-talk mechanisms or assessing novel pharmaceutical targets, by providing a relevant platform to allow the culture of fully differentiated adult cells within 3D, tissue-specific environments.

Adapting the Electrospinning Process to Provide Three Unique Environments for a Tri-layered In Vitro Model of the Airway Wall

Advancements in biomaterial technologies enable the development of three-dimensional multi-cell-type constructs. We have developed electrospinning protocols to produce three individual scaffolds to culture the main structural cells of the airway to provide a 3D in vitro model of the airway bronchiole wall.

Electrospinning is a highly adaptable method producing porous 3D fibrous scaffolds that can be exploited in in vitro cell culture. Alterations to ...

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 ...

Mesenchymal Stromal Cell Culture and Delivery in Autologous Conditions: A Smart Approach for Orthopedic Applications

Human Mesenchymal Stromal Cells (hMSCs) are cultured in vitro with different media. Limits on their use in clinical settings, however, mainly depend on potential biohazard and inflammation risks exerted by xenogeneic nutrients for their culture. Human derivatives or recombinant materials are the first choice candidates to reduce these reactions. Therefore, culture supplements and materials of autologous origin represent the best nutrients and the safest products.
Here, we describe a new protocol for the isolation and culture of bone marrow hMSCs in autologous conditions &#8212;&#160;namely,&#160;patient-derived serum as a supplement for the culture medium and fibrin as a scaffold for hMSC administration. Indeed, hMSC/fibrin clot constructs could be extremely useful for several clinical applications. In particular, we focus on their use in orthopedic surgery, where the fibrin clot derived from the donor&#39;s own blood allowed effective cell delivery and nutrient/waste exchanges. To ensure optimal safety conditions, it is of the utmost importance to avoid the risks of hMSC transformation and tissue overgrowth. For these reasons, the approach described in this paper also indicates a minimally ex vivo hMSC expansion, to reduce cell senescence and morphologic changes, and short-term osteo-differentiation before implantation, to induce osteogenic lineage specification, thus decreasing the risk of subsequent uncontrolled proliferation.

Culturing human Mesenchymal Stromal Cells (hMSCs) with autologous serum, reduces the risks of rejection by xenogeneic material and other negative effects. It also allows for the recovery of a subset of mesodermal progenitors, which can deliver fresh hMSCs. Embedding hMSCs in an autologous fibrin clot enables easy handling and effective surgical implantation.

Human Mesenchymal Stromal Cells (hMSCs) are cultured in vitro with different media. Limits on their use in clinical settings, however, mainly depend on ...