This work was funded in part by the National Institute of General Medical Sciences (NIGMS) T32 program (T32 GM133369) and the National Science Foundation (NSF 1454230). Additionally, WVU Shared Research Facilities and Applied Biophysics assistance and support are acknowledged.

1. ZIF-8 synthesis
<ol>
	<li>For the purpose of this example, use a 1:10:100 (metal:linker:solvent) mass ratio to synthesize the ZIF-8. For this, measure out zinc nitrate hexahydrate, and record the measurement. Utilize the example mass ratio to calculate the amount needed for the linker, 2-methylimidazole, and the solvent (i.e., methanol).</li>
	<li>Place the zinc nitrate hexahydrate and linker into two different glass vials. Add half of the calculated amount of methanol to the zinc nitrate hexahydrat...

Evaluating MOF-Induced Cell Behavior Changes by Electric Cell-Substrate Sensing

The authors report no conflicts of interest in this work.

Previous analysis showed that ECIS could be used to assess the behavior of cells exposed to analytes (i.e., carbon nanotubes35, drugs43, or nanoclays16). Furthermore, Stueckle et al. used ECIS to evaluate the toxicity of BEAS-2B cells exposed to nanoclays and their byproducts and found that the cellular behavior and attachment were dependent on the physicochemical characteristics of such materials42. Herein, we proposed to det...

Metal-organic frameworks (MOFs) are hybrids formed through the combination of metal ions and organic linkers1,2 in organic solvents. Due to the variety of such combinations, MOFs possess structural diversity3, tunable porosity, high thermal stability, and high surface areas4,5. Such characteristics make them attractive candidates in a variety of applications, from gas storage6,7 to catalysis8,9, and from contrast agents10,11 to drug delivery units12,13. However, the implementation of MOFs into such applications has raised concerns relative to their safety to both the users and the environment. Preliminary studies have shown, for instance, that cellular function and growth change upon the exposure of cells to metal ions or linkers used for MOF synthesis1,14,15. For instance, Tamames-Tabar et al. demonstrated that ZIF-8 MOF, a Zn-based MOF, was leading to more cellular changes in a human cervical cancer cell line (HeLa) and a mouse macrophage cell line (J774) relative to Zr-based and Fe-based MOFs. Such effects were&#160;presumably due to the metal component of ZIF-8 (i.e., Zn), which could potentially induce cell apoptosis upon framework disintegration and Zn ion release1. Similarly, Gandara-Loe et al. demonstrated that HKUST-1, a Cu-based MOF, caused the highest reduction in mouse retinoblastoma cell viability when used at concentrations of 10 &#181;g/mL or greater. This was presumably due to the Cu metal ion incorporated during the synthesis of this framework, which, once released, could induce oxidative stress in the exposed cells15.
Moreover, analysis showed that the exposure&#160;to MOFs with different physicochemical characteristics could lead to varying responses of exposed cells. For instance, Wagner et al. demonstrated that ZIF-8 and MIL-160 (an Al-based framework), used in the exposure of an immortalized human bronchial epithelial cell, led to cellular responses dependent on frameworks&#39; physicochemical properties, namely hydrophobicity, size, and structural characteristics16. Complementarily, Chen et al. demonstrated that a concentration of 160 &#181;g/mL MIL-100(Fe) exposed to human normal liver cells (HL-7702) caused the largest loss in cellular viability, presumably due to the metal component of this specific framework (i.e., Fe17).
While these studies categorize MOFs&#39; deleterious effects on cellular systems based on their physicochemical characteristics and exposure concentrations, thus raising potential concerns with framework implementation, especially in biomedical fields, most of these evaluations are based on single time point colorimetric assays. For instance, it was shown that when (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) tetrazolium (MTT) and water-soluble tetrazolium salt (WST-1) assays were used, these biochemical reagents could lead to false positives upon&#160;their&#160;interactions with the particles that the cells were also exposed to18. The tetrazolium salt and neutral red reagents were&#160;shown to possess a high adsorption or binding affinity onto the surfaces of the particles, resulting to agent signal interference19. Moreover, for other types of assays, such as flow cytometry, which was previously shown to be used for assessing changes in cells exposed to MOFs20,21, it was shown that major issues have to be circumvented if a viable analysis of particles&#39; deleterious effects is to be considered. In particular, detection ranges of the particles&#39; sizes, especially in mixed populations like the ones offered by MOFs or references of the particles used for calibration before cellular changes, have to be addressed22. It was also shown that the dye used during cell labeling for such cytometry assays could also interfere with the nanoparticles that the cells were exposed to23.
The goal of this study was to use a real-time, high-throughput evaluation assay to assess changes in cell behavior upon exposure to a select MOF. Real-time evaluations can help provide insights into time-dependent effects, as related to the windows of exposures16. Further, they provide information on changes in cell-substrate interactions, cell morphology, and cell-cell interactions, as well as how such changes depend on the physicochemical properties of the materials of interest and exposure times24,25 respectively.
To demonstrate the validity and applicability of the proposed approach, human bronchial epithelial (BEAS-2B) cells, ZIF-8 (a hydrophobic framework of zeolitic imidazolate16), and electric cell-substrate impedance sensing (ECIS) were used. BEAS-2B cells represent a model for lung exposure26 and have been previously used to evaluate changes upon the exposure of cells to nanoclays and their thermally degraded byproducts26,27,28,&#160;as well as assess the toxicity of nanomaterials, such as single-walled carbon nanotubes (SWCNTs)18. Furthermore, such cells have been used for more than 30 years as a model for pulmonary epithelial function29. ZIF-8 was chosen due to its wide implementation&#160;in catalysis30 and as contrast agents31 for bioimaging and drug delivery32, and thus for the extended potential for lung exposure during such applications. Lastly, ECIS, the noninvasive, real-time technique, was previously used to evaluate changes in cell adherence, proliferation, motility, and morphology16,26 as a result of a variety of interactions between analytes (both materials and drugs) and exposed cells in real-time16,18,28. ECIS uses an alternating current (AC) to measure the impedance of cells immobilized on gold electrodes, with the impedance changes giving insights into changes in resistance and capacitance at the&#160;cell-gold substrate interface, barrier function as induced by cell-cell interactions, and over-cell layer coverage of such gold electrodes33,34. Using ECIS allows quantitative measurements at a nanoscale resolution in a noninvasive, real-time manner26,34.
This study assesses and compares the simplicity and ease of evaluation of MOF-induced changes in cellular behavior in real-time with single-point assay evaluations. Such a study could be further extrapolated for evaluating cell profiles in response to exposure to other particles of interest, thus allowing for safe-by-design particle testing and subsequent helping with&#160;implementation. Moreover, this study could complement genetic and cellular assays that are single-point evaluations. This could lead to a more informed analysis of the deleterious effects of particles on the cellular population and could be used for screening such particles&#39; toxicity in a high-throughput manner16,35,36.

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			<td>&#160;4-[3-(4-idophenyl)-2-(4-nitrophenyl)-2H-5-tetrazolio]-1,3-benzene disulfonate (WST-1 assay)&#160;</td>
			<td>Roche</td>
			<td>5015944001</td>
			<td></td>
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			<td>0.25% Trypsin-EDTA (1x)</td>
			<td>Gibco</td>
			<td>25255-056</td>
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			<td>100 mm plates</td>
			<td>Corning</td>
			<td>430167</td>
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			<td>1300 Series A2 biofume hood</td>
			<td>Thermo Scientific</td>
			<td>323TS</td>
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			<td>2510 Branson bath sonicator</td>
			<td>Process Equipment &#38; Supply, Inc.&#160;</td>
			<td>251OR-DTH</td>
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			<td>2-methylimidazole, 97%</td>
			<td>Alfa Aesar</td>
			<td>693-98-1</td>
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			<td>5 mL sterile microtube</td>
			<td>Argos Technologies</td>
			<td>T2076S-CA</td>
			<td></td>
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			<td>50 mL&#160; tubes&#160;</td>
			<td>Falcon</td>
			<td>352098</td>
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			<td>96W10idf well plates</td>
			<td>Applied Biophysics&#160;</td>
			<td>96W10idf PET</td>
			<td></td>
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			<td>96-well plates</td>
			<td>Fisherbrand</td>
			<td>FB012931</td>
			<td></td>
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		<tr>
			<td>Biorender</td>
			<td>Biorender</td>
			<td>N/A</td>
			<td></td>
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		<tr>
			<td>Countess cell counting chamber slides</td>
			<td>Invitrogen</td>
			<td>C10283</td>
			<td></td>
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			<td>Countess II FL automated cell counter</td>
			<td>Life Technologies</td>
			<td>C0916-186A-0303</td>
			<td></td>
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			<td>Denton Desk V sputter and carbon coater</td>
			<td>Denton Vacuum</td>
			<td>N/A</td>
			<td></td>
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			<td>Dimethly sulfoxide&#160;</td>
			<td>Corning</td>
			<td>25-950-CQC</td>
			<td></td>
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		<tr>
			<td>DPBS/Modified</td>
			<td>Cytiva</td>
			<td>SH30028.02</td>
			<td></td>
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			<td>Dulbecco&#39;s modified Eagle medium</td>
			<td>Corning</td>
			<td>10-014-CV</td>
			<td></td>
		</tr>
		<tr>
			<td>ECIS-Z&#920;</td>
			<td>Applied Biophysics&#160;</td>
			<td>ABP 1129</td>
			<td></td>
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			<td>Excel</td>
			<td>Microsoft</td>
			<td>Version 2301</td>
			<td></td>
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			<td>Falcon tubes (15 mL)</td>
			<td>Corning</td>
			<td>352196</td>
			<td></td>
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			<td>Fetal bovine serum</td>
			<td>Gibco</td>
			<td>16140-071</td>
			<td></td>
		</tr>
		<tr>
			<td>FLUOstar OPTIMA plate reader</td>
			<td>BMG LABTECH</td>
			<td>413-2132</td>
			<td></td>
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			<td>GraphPad Prism Software (9.0.0)</td>
			<td>GraphPad Software, LLC</td>
			<td>Version 9.0.0</td>
			<td></td>
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			<td>HERAcell 150i CO2 Incubator</td>
			<td>Thermo Scientific</td>
			<td>50116047</td>
			<td></td>
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		<tr>
			<td>Hitachi S-4700 Field emission scanning electron microscope equipped with energy dispersive X-ray&#160;</td>
			<td>Hitachi High-Technologies Corporation</td>
			<td>S4700 and EDAX TEAM analysis software</td>
			<td></td>
		</tr>
		<tr>
			<td>ImageJ software</td>
			<td>National Institutes of Health</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Immortalized human bronchial epithelial cells</td>
			<td>American Type Culture Collection</td>
			<td>CRL-9609</td>
			<td></td>
		</tr>
		<tr>
			<td>Isotemp freezer</td>
			<td>Fisher Scientific&#160;</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Methanol, 99%</td>
			<td>Fisher Chemical</td>
			<td>67-56-1</td>
			<td></td>
		</tr>
		<tr>
			<td>Parafilm sealing film</td>
			<td>The Lab Depot</td>
			<td>HS234526A</td>
			<td></td>
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		<tr>
			<td>Penicillin/Steptomycin</td>
			<td>Gibco</td>
			<td>15140-122</td>
			<td></td>
		</tr>
		<tr>
			<td>Sorvall Legend X1R Centrifuge&#160;</td>
			<td>Thermo Scientific</td>
			<td>75004220</td>
			<td></td>
		</tr>
		<tr>
			<td>Sorvall T 6000B</td>
			<td>DU PONT</td>
			<td>&#160;T6000B</td>
			<td></td>
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		<tr>
			<td>Trypan blue, 0.4% solution in PBS</td>
			<td>MP Biomedicals, LLC</td>
			<td>1691049</td>
			<td></td>
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		<tr>
			<td>Vacuum Chamber</td>
			<td>Belart</td>
			<td>999320237</td>
			<td></td>
		</tr>
		<tr>
			<td>Zinc Nitrate Hexahydrate, 98% extra pure</td>
			<td>Acros Organic</td>
			<td>101-96-18-9</td>
			<td></td>
		</tr>
	</tbody>
</table>

electric cell-substrate sensing for real-time evaluation of metal-organic framework toxicological profiles

Metal-organic frameworks (MOFs) are hybrids formed through the coordination of metal ions and organic linkers in organic solvents. The implementation of MOFs in biomedical and industrial applications has led to concerns regarding their safety. Herein, the profile of a selected MOF, a zeolitic imidazole framework, was evaluated upon exposure to human lung epithelial cells. The platform for evaluation was a real-time technique (i.e., electric cell-substrate impedance sensing [ECIS]). This study identifies and discusses some of the deleterious effects of the selected MOF on the exposed cells. Furthermore, this study demonstrates the benefits of using the real-time method versus other biochemical assays for comprehensive cell evaluations. The study concludes that observed changes in cell behavior could hint at possible toxicity induced upon exposure&#160;to MOFs of different physicochemical characteristics and the dosage of those frameworks being used. By understanding changes in cell behavior, one foresees the ability to improve safe-by-design strategies of MOFs to be used for biomedical applications by specifically tailoring their physicochemical characteristics.

Author Spotlight: Advances in Evaluating Human Lung Epithelial Cells&#039; Response to Metal-Organic Frameworks 

Electric Cell-Substrate Sensing for Real-Time Evaluation of Metal-Organic Framework Toxicological Profiles

My research aims to evaluate changes in human lung epithelial cells'behavior upon exposure to metal organic framework, hybrids formed by combining metal ions in organic linkers in organic solvents. This research demonstrated that the physical and chemical composition of metal organic frameworks, as well as their cellular exposure ratios, affects the behavior of human lung epithelial cells in a time and dose-dependent manner. This can be recorded in a high throughput in real time fashion.Our research helps to evaluate, understand the mechanisms of toxicity of metal organic frameworks upon exposure to cellular systems. The current method allows continuous cell monitoring in a real time and in high throughput manner. Additionally, this method does not rely on any external reagents, and thus it reduces any possible interference they could have with the frameworks used for exposure.Our laboratory will continue to focus on understanding and evaluating the mechanisms of toxicity associated with nanomaterials exposures, as well as using such information to synthesize new and safe systems that could be implemented in biomedical applications at minimum risks to the user or the environment.

Using a common in vitro model cell line39 (BEAS-2B), this study aimed to demonstrate the feasibility and applicability of ECIS to assess changes in cell behavior upon exposure to a lab-synthesized MOF. These changes assessment was&#160;complemented by analysis through&#160;conventional colorimetric assays.
The physicochemical characteristics of the framework were first evaluated to ensure the reproducibility of the methods employed, the validity of the obtained...

Watch this Scientific Journal Video about Advances in Evaluating Human Lung Epithelial Cells' Response to Metal-Organic Frameworks at JoVE.com

The following study evaluates the toxicological profile of a selected metal-organic framework utilizing electric cell-substrate impedance sensing (ECIS), a real-time, high-throughput screening technique.

Metal-organic frameworks (MOFs) are hybrids formed through the coordination of metal ions and organic linkers in organic solvents. The implementation of ...

electric-cell-substrate-sensing-for-real-time-evaluation-metal

Research

JoVE Journal

Bioengineering

Electrical Cell-Substrate Impedance Sensing (ECIS)

To begin, take a 96 well plate containing interdigitated finger connection electrodes covering an area of about four square millimeters. Place the plate onto the well station and click the setup button. If the wells are connected properly, green readings will appear.Any unconnected wells will be identified as red. Add 200 microliters of media to each well being used and then place the plate into the electrical cell substrate impedance sensing, or ECIS station. To stabilize the wells and prepare them for experiments, click setup, followed by check, and then click on stabilize.After 40 minutes, remove the plate from the station and remove the media from each well. Seed the B2B cells at a density of 40, 000 cells per milliliter into the wells containing the cells, and place the plate onto the ECIS station in the incubator. Next, click on check to ensure all the electrodes are read by the sensors on the station.Select multiple frequency time to measure each electrode at seven different frequencies. Click on start and allow it to run for 24 hours so the cells can form a confluent monolayer. Every well's reading is displayed in a different color.After about 24 hours, the wells containing cells will show increased resistance on the monitor indicating the attachment of the cells to the electrodes. Press pause to interrupt the data collection. For example, for media changes, reagents edition, and so on.Expose the ZIF8 nanoparticles to the blank well and the cell wells with a volume of 100 microliters per well, Place the plate onto the station and click on check again to ensure that the sensors are reading all the electrodes. Click on resume to resume the experiments after the chosen pause. After the data collection, click finish to save the data as a spreadsheet file.To get the alpha parameters click on model, and on the popped up screen, click on media only well, then select the well that has only media. Click on set reference for data evaluation and select the reference related to the control experiment. Click on find to start the reference fitting.Select set then fit T range to process the data relative to the selected reference. To evaluate the cell attachment, select alpha. Finally, after the system finishes the analysis, click save RBA and save the parameters as a spreadsheet file.The analysis of the cell behavior upon exposure to ZIF8 MOFs was performed through electrical cell substrate impedance sensing. The images showed changes in the cell substrate interactions and the changes are dependent on the time of exposure and the dose being used.

579 Views.  West Virginia University.  The following study evaluates the toxicological profile of a selected metal-organic framework utilizing electric cell-substrate impedance sensing (ECIS), a real-time, high-throughput screening technique. 

Evaluating MOF-Induced Cell Behavior Changes by Electric Cell-Substrate Sensing

Summary