The authors wish to acknowledge funding sources, including AHA (13GRNT16990019 to W.T) and NHLBI (HL097246 and HL119371 to W.T.).

1. Silanization and Biomolecule Functionalization of Slide or Polycarbonate Membrane
Note: Many of the chemicals and solutions within this protocol have high evaporation rates (ethanol (EtOH), acetone, etc.). Other steps entail long incubation times for low evaporation rates. Paraffin film is recommended to seal containers. Caution: Many of the chemicals (including: sulfuric acid, acetone, (3-aminopropyl)triethoxysilane, glutaraldehyde, EtOH) are considered hazardous, or volatile. Consult material safety data sheet (MSDS) of each material for proper storage, handling, and disposal before use.
<ol>
	<li>Place new glass slide measuring 75 mm by 50 mm by 1 mm, in clean, glass slide staining dish without regard to orientation, ensuring full immersion. Use container for steps 1.1-1.12. 
	Note: For co-culture, include polycarbonate (PC) membrane with 0.4 micron pore size, cut to size of 75 mm by 50 mm, for all subsequent steps for PC functionalization and EC seeding.</li>
	<li>Immerse slide in sulfuric acid (20%), O/N. 
	Caution: Consult MSDS for sulfuric acid before use.</li>
	<li>Wash slide by immersing in deionized water (DI) for 5 min, three times, changing DI each time.</li>
	<li>Immerse slide in acetone for 30 min. 
	Caution: Consult MSDS for acetone before use.</li>
	<li>Immerse slide in 6% (3-aminopropyl)triethoxysilane / acetone solution O/N. 
	Caution: Consult MSDS for (3-aminopropyl)triethoxysilane and acetone before use.</li>
	<li>Immerse slide in acetone for 5 min, three times, changing acetone each time. 
	Caution: Consult MSDS for acetone before use.</li>
	<li>Wash slide by immersing in DI for 5 min, three times, changing DI each time.</li>
	<li>Immerse slide in 1.5% glutaraldehyde / DI solution for 60 min. 
	Caution: Consult MSDS for glutaraldehyde before use.</li>
	<li>Wash slide by immersing in DI for 5 min, two times, changing DI each time.</li>
	<li>Place slides into 70% ethanol (EtOH) for 30 min in sterile, laminar flow hood.</li>
	<li>Remove EtOH and allow remaining residue to evaporate. Immerse slides in sterile DI and drain in order to rehydrate the slides. 
	Note: Slides or PC membrane may be sealed in glass slide holder and stored at 4 &#176;C up to one week. Upon use for cell culture, repeat steps 1.10 and 1.11.</li>
	<li>Remove the slide from the slide holder and place it into a 100 mm by 100 mm square petri dish in the laminar flow hood. 
	Note: This container will be used for all remaining steps.
	<ol>
		<li>Prepare slide or PC for endothelial cell seeding for monoculture experiment.
		<ol>
			<li>Coat the functionalized slide or PC (step 1.11) with 1 ml fibronectin solution (25 &#956;g/ml), on one side, covering the approximate area exposed to cell culture chamber.</li>
			<li>Incubate slides or PC in sterile incubator set at 37 &#176;C for 1-2 hr.</li>
			<li>After incubation, aspirate the remaining solution using a glass aspirator pipette connected to a vacuum. 
			Note: Slides may now be stored O/N at 4 &#176;C for future use.</li>
		</ol>
		</li>
		<li>Follow 1.12.2 steps only for preparing EC/SMC co-culture. Prepare and seed smooth muscle cell (SMC) culture for co-culture experiment.
		<ol>
			<li>Place silicone gasket on top of the slide (step 1.11), with dimensions of 75 mm by 50 mm outer diameter, inner diameter of 50 mm by 30 mm, thickness of 0.5 mm, and perforations which align with flow chamber vacuum.</li>
			<li>Prepare 1 ml SMC in 10% FBS/DMEM suspension. Neutralize 1 ml solution of 2 mg/ml collagen type-I with 7% NaHCO3 and 0.1 M NaOH solution to pH of 7.4, and mix with SMC suspension with final cell density of 2 x 106 cells/ml.</li>
			<li>Spread SMC solution within gasket and incubate slides at 37 &#176;C and 5% CO2 for 30 min.</li>
			<li>After incubation, cover the slide with 25 ml 0.1% fetal bovine serum (FBS) mixed in Dulbecco&#8217;s Modified Eagle Medium (DMEM) for 72 hr.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Culture endothelial cells (ECs) on glass slide/polycarbonate membrane.
	<ol>
		<li>Seed 1 ml ECs in 10% FBS/DMEM, with initial concentration of 6.0 x 105 cells/ml, on fibronectin surfaces of glass slide or polycarbonate membrane.</li>
		<li>Incubate cells in an incubator at 37 &#176;C, 5% CO2, and 10% FBS for 120 min.</li>
		<li>Cover slides containing cells with additional 10% FBS/DMEM, and place in incubator in 37 &#176;C, 5% CO2 O/N, until 70%-80% confluent.</li>
	</ol>
	</li>
</ol>
2. Determination of Fluid Viscosity and Volumetric Flow Rate
Note: Rotating viscometers are sensitive equipment, and the viscometer user manual should be consulted before calibrating, zeroing, or performing measurements.
<ol>
	<li>Determine desired fluid shear (&#964;) from literature of the experiment&#8217;s targeted vasculature.</li>
	<li>Measure 1% FBS/DMEM viscosity (&#956;), using a rotational viscometer.</li>
	<li>Determine required volumetric flow rate (Q) from Poiseuille equation: 
	<img alt="Equation 1" src="/files/ftp_upload/53224/53224eq1.jpg" />, 
	where &#964; = fluid shear, &#956; = viscosity, Q = vol. flow rate, w = chamber width, and h = chamber height).</li>
	<li>Set pump to flow rate derived in step 2.3, and use for all subsequent steps.</li>
</ol>
3. Determination of Pulsatility Index
Note: All connection ports within the system should be connected with appropriately sized lock-ring-to-barb, or female luer-to-barb connections. Connecting PVC tubing may then be connected to barb fittings, and circuit completed.
<ol>
	<li>Connect flow circuit as in Figure 2, with damping chamber (Figure 3) and ultrasonic flow meter in correct flow direction. 
	Note: Ultrasonic flow meter is a sensitive piece of equipment, and the user manual should be consulted before use.</li>
	<li>Fill flow circuit and reservoir with DI water, by ensuring reservoir outlet tube (to pump) is submerged within reservoir volume. Visualize flow waveform using a flow meter.</li>
	<li>Open air release valve on the damping chamber to change fluid/air volume ratio. Close air release valve at different fluid level intervals and calculate pulsatility index (PI = (VMax - VMin) / VMean) by using flow waveform peak (VMax), trough (VMin), and mean (VMean). Record PI values in notebook.</li>
	<li>Mark resulting fluid level and PI on the damping chamber, using a felt tipped, permanent ink pen for future use. Determine desired PI levels from pathology literature11.</li>
	<li>Silicon Tube Formation- Optional, more advanced method of controlling pulsatility
	<ol>
		<li>Mix the silicone elastomer base and curing agent at different ratios (e.g., a base-to-crosslinker ratio from 10:1 to 36:1) for varied targeted elastic moduli, as illustrated previously.2</li>
		<li>Fabricate silicone tubes by repeated dip-cure process, briefly dipping steel cannula (14 G) into silicone prepolymer mixture with a predetermined base-to-crosslinker ratio.</li>
		<li>Place the prepolymer-coated cannula into an oven set at 60 &#176;C for 4 hr to cure the polymer coating on the cannula, switching the direction in the middle of curing process.</li>
		<li>Repeat the dipping process with the same silicone elastomer mixture and place back in the oven for additional 4 hr, which results in ~0.3 mm thick tubes.</li>
		<li>Remove the ultrathin silicone tube from the stainless steel cannula.</li>
		<li>Connect tubes to flow circuit instead of damping chamber, and test PI for each as in 3.3.</li>
	</ol>
	</li>
</ol>
4. Pump Sterilization
<ol>
	<li>Immerse the flow chamber (Figure 2), PVC tubing, and gaskets in 10% hydrogen peroxide (H2O2). Wash with sterile DI before step 4.</li>
	<li>Place the blood pump on a spare incubator shelf. 
	Note: Incubator shelves should be stainless steel, and be able to support the weight of the entire flow circuit.</li>
	<li>Fill the flow circuit and reservoir with 10% H2O2 by ensuring reservoir outlet tube (to pump) is submerged within reservoir volume. Circulate H2O2 by pumping through circuit for 20 min in the laminar flow hood with UV light on.</li>
	<li>Aspirate all H2O2 from tubing, and wash with sterile PBS by pumping through flow circuit.</li>
</ol>
5. Flow Chamber Assembly
Note: The flow chamber consists of an acrylic, custom made plate, with vacuum ports and inlet and outlet flow ports (see Figure 2). Chamber assembly consists of placing the flow chamber and gaskets on top of culture slides, properly aligned, and is described below.
<ol>
	<li>Warm up 1% FBS/DMEM in a 37 &#176;C water bath and prepare flow chamber.
	<ol>
		<li>Take EC slide out of media (from step 1.13) and place gasket on top with cell side up.</li>
		<li>(Optional) Take PC membrane out of media (from step 1.13) and place gasket on top with cell side up. Place co-culture slide with seeded SMC (step 1.12.2) underneath PC membrane.</li>
	</ol>
	</li>
	<li>Align vacuum channel of the flow chamber with the holes in the gasket (Figure 2).</li>
	<li>Attach vacuum tube to vacuum ports (Figure 2) ensuring no media leaks to vacuum.</li>
	<li>Place polycarbonate sheet underneath glass slide and clamp flow chamber assembly with spring clamps, one on each side of flow chamber (Figures 2 and 5).</li>
	<li>Place flow system in incubator at 37 &#176;C and 5% CO2, and fill circuit with media by pumping from filled reservoir at low pulsatility. Maintain this flow for 4 hr for preconditioning cells.</li>
	<li>Adjust fluid volume in damping chamber to marked PI level, and culture for desired time.</li>
</ol>

<ol>
	<li>Scott-Drechsel, D., Su, Z., Hunter, K., Li, M., Shandas, R., Tan, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+new+flow+co-culture+system+for+studying+mechanobiology+effects+of+pulse+flow+waves.">A new flow co-culture system for studying mechanobiology effects of pulse flow waves.</a> Cytotechnology. 64 (6), 649-666 (2012).</li><li>Tan, Y., 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=Stiffening-Induced+High+Pulsatility+Flow+Activates+Endothelial+Inflammation+via+a+TLR2/NF-&#954;B+Pathway.">Stiffening-Induced High Pulsatility Flow Activates Endothelial Inflammation via a TLR2/NF-&#954;B Pathway.</a> PLoS ONE. 9 (7), e102195 (2014).</li><li>Wexler, 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=Coronary+Artery+Calcification:+Pathophysiology,+Epidemiology,+Imaging+Methods,+and+Clinical+Implications+A+Statement+for+Health+Professionals+From+the+American+Heart+Association.">Coronary Artery Calcification: Pathophysiology, Epidemiology, Imaging Methods, and Clinical Implications A Statement for Health Professionals From the American Heart Association.</a> Circulation. 94 (5), 1175-1192 (1996).</li><li>Lan, T. -. H., Huang, X. -. Q., Tan, H. -. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vascular+fibrosis+in+atherosclerosis.">Vascular fibrosis in atherosclerosis.</a> Cardiovasc Pathol. 22 (5), 401-407 (2013).</li><li>Lee, C. H., 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=Promoting+endothelial+recovery+and+reducing+neointimal+hyperplasia+using+sequential-like+release+of+acetylsalicylic+acid+and+paclitaxel-loaded+biodegradable+stents.">Promoting endothelial recovery and reducing neointimal hyperplasia using sequential-like release of acetylsalicylic acid and paclitaxel-loaded biodegradable stents.</a> Int J Nanomedicine. 9, 4117-4133 (2014).</li><li>Intengan, H. D., Schiffrin, E. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vascular+Remodeling+in+Hypertension+Roles+of+Apoptosis+Inflammation,+and+Fibrosis.">Vascular Remodeling in Hypertension Roles of Apoptosis Inflammation, and Fibrosis.</a> Hypertension. 38 (3), 581-587 (2001).</li><li>Greil, O., 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=Changes+in+carotid+artery+flow+velocities+after+stent+implantation:+a+fluid+dynamics+study+with+laser+Doppler+anemometry.">Changes in carotid artery flow velocities after stent implantation: a fluid dynamics study with laser Doppler anemometry.</a> J Endovasc Ther. 10 (2), 275-284 (2003).</li><li>Egorova, A. D., van der Heiden, K., Poelmann, R. E., Hierck, B. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Primary+cilia+as+biomechanical+sensors+in+regulating+endothelial+function.">Primary cilia as biomechanical sensors in regulating endothelial function.</a> Differentiation. 83 (2), S56-S61 (2012).</li><li>Liu, S. Q., Goldman, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Role+of+blood+shear+stress+in+the+regulation+of+vascular+smooth+muscle+cell+migration.">Role of blood shear stress in the regulation of vascular smooth muscle cell migration.</a> IEEE T Bio-Med Eng. 48 (4), 474-483 (2001).</li><li>Scott, D., Tan, Y., Shandas, R., Stenmark, K. R., Tan, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High+pulsatility+flow+stimulates+smooth+muscle+cell+hypertrophy+and+contractile+protein+expression.">High pulsatility flow stimulates smooth muscle cell hypertrophy and contractile protein expression.</a> AJP: Lung C. 304 (1), L70-L81 (2013).</li><li>Panaritis, V., 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=Pulsatility+Index+of+Temporal+and+Renal+Arteries+as+an+Early+Finding+of+Arteriopathy+in+Diabetic+Patients..">Pulsatility Index of Temporal and Renal Arteries as an Early Finding of Arteriopathy in Diabetic Patients..</a> Ann Vasc Surg. 19 (1), 80-83 (2005).</li><li>Miao, H., 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=Effects+of+Flow+Patterns+on+the+Localization+and+Expression+of+VE-Cadherin+at+Vascular+Endothelial+Cell+Junctions:+In+vivo+and+in+vitro+Investigations.">Effects of Flow Patterns on the Localization and Expression of VE-Cadherin at Vascular Endothelial Cell Junctions: In vivo and in vitro Investigations.</a> J Vasc Res. 42 (1), 77-89 (2005).</li></ol>

The authors have nothing to disclose.

This protocol describes a method of reproducing pulsatile flow in vitro, and may be instrumental first step in determining contribution of flow conditions to disease pathologies. Previous studies using this protocol have found flow conditions contribute to vascular inflammatory response.1,10 Additionally, this protocol is intended for experienced laboratories. As such, neither in depth fluid mechanics, nor biochemical analysis is described herein. For more advanced fluid dynamics,1</su...

Morbidity rates for cardiovascular diseases are the largest in America, with many resulting from unhealthy vasculature. Healthy arteries consist of elastic tissue, with soft luminal surface coated with an endothelial cell (EC) monolayer. Arterial flow may be modeled as an oscillating wave function with positive mean flow rate. The pulsatility index (PI) is the quotient of oscillation magnitude and mean flow (PI = (Max. - Min.) / Mean),1 and has been modeled in vitro with variable vessel elasticity.2 Arterial elasticity is important in storage of flow energy from heart contractions, dilating under systolic pressure, and plays a significant role in modulating blood flow PI. Because the heart maintains a consistent, pulsatile, volumetric flow, arterial expansion increases cross-sectional area, enhancing flow stability by reducing flow velocity, shear stress, and PI. Frequently, unhealthy arteries present changes to elasticity or compliance, displaying stiffening from vascular remodeling, scar tissue or calcification3,4. Additionally, other vascular disorders, such as neointimal hyperplasia (NIH),5 aneurysm and hypertension6 and vascular fibrosis4, may constrict vessel diameter. However, current drug treatment and device treatment of vascular diseases often neglect the importance of vessel wall compliance or blood flow dynamics in vascular disease which is often complicated by changes in vessel morphology and properties. Neither balloon angioplasty nor stenting answer the complication of wall elasticity7. Therefore, in vitro modeling of blood flows resulting from arterial disease and treatments is important in investigating disease pathologies and future efficacy of treatment. Herein, we describe a method of replicating physiological and pathological blood flow designed to determine cell response in vascular disease pathologies. Fluid flow causes shear stress at the vessel wall, which is an important mechanical signal in vessel health, affecting all cells within the vasculature. Several mechanical sensors on the vascular endothelium for fluid shear have been identified, including primary cilium shown in recent studies for endothelial mechanosensing8. Endothelial cell activity and morphology are affected by flow velocity, direction, and pulsatility. Additionally, smooth muscle cell (SMC) migration can be affected by mechano-signals of low velocity flow through interstitial fluid9, and can also be through the paracrine signaling from endothelial cells through their response to flow and mechano-transduction of flow signals via cytokine release10. The &#8220;dose&#8221; dependence of mean shear, PI, and paracrine signaling may also be interdependent. To this end, the determination of vascular cell response to fluid shear with varied &#8220;dosing&#8221; in monolayer culture or co-culture in vitro could provide mechanistic insights into vascular remodeling and improve disease and treatment prediction. The flow system used in this experiment consists of a blood pump, an upstream flow damping air reservoir, a downstream flow meter only used during experimental setup, a downstream cell culture, parallel-plate flow chamber, and media reservoir. Control of vascular flow variables such as mean flow rate, beats per minute, and PI may be achieved through controlling flow rate, pulse frequency, and introduction of pressure damping. Pulsatile blood pumps are available with variable stroke displacement, at controlled stroke frequency, relating directly to mean volumetric flow rate, and pulse frequency. Introduction of an air reservoir within the flow circuit allows for pressure damping, reducing flow oscillation magnitude. Media is an incompressible fluid, while air within the damping chamber is compressible, allowing excess pressure from the flow wave to be absorbed by air compression. The air to media ratio allows for control over how much damping occurs. A custom cell culture flow chamber 75 mm in length by 50 mm in width was created from acrylic. Flow enters through the inlet port, and expands through the inlet manifold, providing consistent flow across the entirety of the flow chamber. Similar flow and structures are present at chamber outlet. Cells are seeded onto functionalized slides, and subsequently attached to the flow chamber. This allows for large populations, easily retrieved after the study. Co-culture experiments may use a porous polycarbonate membrane to eliminate cell-to-cell contact between cultures while allowing cytokine/flow transport. This system has previously been used to model high PI flow and its effect on endothelial monolayer culture and EC/SMC co-culture1,10, to investigate cell response to pathologically high PI disease. By describing the protocol used to model these flow conditions, we hope to aid others in determining flow signal contribution to cell response.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>Acetone</td>
			<td>Sigma-Aldrich</td>
			<td>34850</td>
			<td></td>
		</tr>
		<tr>
			<td>Sulfuric Acid</td>
			<td>Sigma-Aldrich</td>
			<td>320501</td>
			<td></td>
		</tr>
		<tr>
			<td>(3-Aminopropyl)trethoxysilane</td>
			<td>Sigma-Aldrich</td>
			<td>440140</td>
			<td></td>
		</tr>
		<tr>
			<td>Glutaraldehyde Solution</td>
			<td>Sigma-Aldrich</td>
			<td>G5882</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethanol</td>
			<td>Sigma-Aldrich</td>
			<td>459844</td>
			<td></td>
		</tr>
		<tr>
			<td>Glass Slide (70mm x 50mm)</td>
			<td>Sigma-Aldrich</td>
			<td>CLS294775X50</td>
			<td></td>
		</tr>
		<tr>
			<td>Polycarbonate Membrane</td>
			<td>Millipore Corp.</td>
			<td>HTTP09030</td>
			<td></td>
		</tr>
		<tr>
			<td>Silicone Gasket</td>
			<td>Grace Bio-Labs</td>
			<td>RD 475464</td>
			<td></td>
		</tr>
		<tr>
			<td>Fibronectin (25 &#956;g/mL)</td>
			<td>Sigma-Aldrich</td>
			<td>F1141</td>
			<td></td>
		</tr>
		<tr>
			<td>Collagen Type-I</td>
			<td>Sigma-Aldrich</td>
			<td>C3867</td>
			<td></td>
		</tr>
		<tr>
			<td>NaHCO3</td>
			<td>Fluka</td>
			<td>36486</td>
			<td></td>
		</tr>
		<tr>
			<td>NaOH</td>
			<td>Sigma-Aldrich</td>
			<td>S5881</td>
			<td></td>
		</tr>
		<tr>
			<td>Damping Chamber</td>
			<td></td>
			<td></td>
			<td>This chamber is custom made, and may be requested using the engineering drawing of Figure 3.</td>
		</tr>
		<tr>
			<td>Blood Pump</td>
			<td>Harvard Apparatus</td>
			<td>529552</td>
			<td></td>
		</tr>
		<tr>
			<td>Poly-Vinyl Carbonate Tubing</td>
			<td>US Plastic</td>
			<td>65066, 65063, 65062</td>
			<td>Various sizes may be required</td>
		</tr>
		<tr>
			<td>Luer Connections</td>
			<td>Nordson Medical</td>
			<td>Various</td>
			<td>Various sizes will be required, and a number of parts should be purchased for replacement use.</td>
		</tr>
		<tr>
			<td>Culture Chamber</td>
			<td>Machined in-house</td>
			<td>Custom</td>
			<td>Acrylic may be purchased in sheets and machined for intended use. The engineering drawing shown in Figure 2 may be used to recreate this chamber</td>
		</tr>
		<tr>
			<td>Square Petri Dish</td>
			<td>Cole-Parmer</td>
			<td>EW-14007-10</td>
			<td></td>
		</tr>
		<tr>
			<td>Glass Slide Holder</td>
			<td>Capitol Scientific</td>
			<td>WHE-900303</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal Bovine Serum</td>
			<td>Mediatech, Inc.</td>
			<td>35-010-CV</td>
			<td></td>
		</tr>
		<tr>
			<td>Dulbecco&#39;s Modified Eagle Medium</td>
			<td>Mediatech, Inc.</td>
			<td>10-013-CV</td>
			<td></td>
		</tr>
		<tr>
			<td>Flow Meter</td>
			<td>Sonotec, GmbH</td>
			<td>Sonoflow co.55/060</td>
			<td></td>
		</tr>
		<tr>
			<td>Sylgard Elastomer Kit</td>
			<td>Sigma-Aldrich</td>
			<td>761036-5EA</td>
			<td></td>
		</tr>
		<tr>
			<td>14 G Steel Cannula</td>
			<td>General Laboratory Supply</td>
			<td>S8365-1</td>
			<td></td>
		</tr>
	</tbody>
</table>

in vitro model of physiological and pathological blood flow with application to investigations of vascular cell remodeling

Vascular disease is a common cause of death within the United States. Herein, we present a method to examine the contribution of flow dynamics towards vascular disease pathologies. Unhealthy arteries often present with wall stiffening, scarring, or partial stenosis which may all affect fluid flow rates, and the magnitude of pulsatile flow, or pulsatility index. Replication of various flow conditions is the result of tuning a flow pressure damping chamber downstream of a blood pump. Introduction of air within a closed flow system allows for a compressible medium to absorb pulsatile pressure from the pump, and therefore vary the pulsatility index. The method described herein is simply reproduced, with highly controllable input, and easily measurable results. Some limitations are recreation of the complex physiological pulse waveform, which is only approximated by the system. Endothelial cells, smooth muscle cells, and fibroblasts are affected by the blood flow through the artery. The dynamic component of blood flow is determined by the cardiac output and arterial wall compliance. Vascular cell mechano-transduction of flow dynamics may trigger cytokine release and cross-talk between cell types within the artery. Co-culture of vascular cells is a more accurate picture reflecting cell-cell interaction on the blood vessel wall and vascular response to mechanical signaling. Contribution of flow dynamics, including the cell response to the dynamic and mean (or steady) components of flow, is therefore an important metric in determining disease pathology and treatment efficacy. Through introducing an in vitro co-culture model and pressure damping downstream of blood pump which produces simulated cardiac output, various arterial disease pathologies may be investigated.

Maintenance of flow conditions is reliant on correct assembly of the flow circuit (Figure 1). Tubing diameter is an important selection in assembly, with larger diameters reducing flow resistance and subsequent pressure drop before and after the culture chamber. To ensure intended pressure and flow velocity, assemble the system with flow meter before experiment with intended tubing. Alignment of culture chamber vacuum channel (Figure 2), with perforations on silicon gasket (not pictured)...

Watch this Scientific Journal Video about In Vitro Model of Physiological and Pathological Blood Flow with Application to Investigations of Vascular Cell Remodeling at JoVE.com

In Vitro Model of Physiological and Pathological Blood Flow with Application to Investigations of Vascular Cell Remodeling

This protocol replicates physiological or pathological blood flow in vitro to aid in determining cell response in disease pathologies. By introducing a pressure damping chamber downstream of a blood pump, blood flow across the vasculature can be recapitulated and imposed on a monolayer of vascular endothelium or a mimetic co-culture.

In Vitro Model of Physiological and Pathological Blood Flow with Application to Investigations of Vascular Cell Remodeling

Vascular disease is a common cause of death within the United States. Herein, we present a method to examine the contribution of flow dynamics towards ...

in-vitro-model-physiological-pathological-blood-flow-with-application

Research

JoVE Journal

Bioengineering

9.6K Views.  University of Colorado at Boulder. This protocol replicates physiological or pathological blood flow in vitro to aid in determining cell response in disease pathologies. By introducing a pressure damping chamber downstream of a blood pump, blood flow across the vasculature can be recapitulated and imposed on a monolayer of vascular endothelium or a mimetic co-culture.

Video: In Vitro Model of Physiological and Pathological Blood Flow with Application to Investigations of Vascular Cell Remodeling

Improved Method for the Preparation of a Human Cell-based, Contact Model of the Blood-Brain Barrier

The blood-brain barrier (BBB) comprises impermeable but adaptable brain capillaries which tightly control the brain environment. Failure of the BBB has been implied in the etiology of many brain pathologies, creating a need for development of human in vitro BBB models to assist in clinically-relevant research. Among the numerous BBB models thus far described, a static (without flow), contact BBB model, where astrocytes and brain endothelial cells (BECs) are cocultured on the opposite sides of a porous membrane, emerged as a simplified yet authentic system to simulate the BBB with high throughput screening capacity. Nevertheless the generation of such model presents few technical challenges. Here, we describe a protocol for preparation of a contact human BBB model utilizing a novel combination of primary human BECs and immortalized human astrocytes. Specifically, we detail an innovative method for cell-seeding on inverted inserts as well as specify insert staining techniques and exemplify how we use our model for BBB-related research.

Establishment of human models of the blood-brain barrier (BBB) can benefit research into brain conditions associated with BBB failure. We describe here an improved technique for preparation of a contact BBB model, which permits coculturing of human astrocytes and brain endothelial cells on the opposite sides of a porous membrane.

The blood-brain barrier (BBB) comprises impermeable but adaptable brain capillaries which tightly control the brain environment. Failure of the BBB has ...

A Novel Three-dimensional Flow Chamber Device to Study Chemokine-directed Extravasation of Cells Circulating under Physiological Flow Conditions

Extravasation of circulating cells from the bloodstream plays a central role in many physiological and pathophysiological processes, including stem cell homing and tumor metastasis. The three-dimensional flow chamber device (hereafter the 3D device) is a novel in vitro technology that recreates physiological shear stress and allows each step of the cell extravasation cascade to be quantified. The 3D device consists of an upper compartment in which the cells of interest circulate under shear stress, and a lower compartment of static wells that contain the chemoattractants of interest. The two compartments are separated by porous inserts coated with a monolayer of endothelial cells (EC). An optional second insert with microenvironmental cells of interest can be placed immediately beneath the EC layer. A gas exchange unit allows the optimal CO2 tension to be maintained and provides an access point to add or withdraw cells or compounds during the experiment. The test cells circulate in the upper compartment at the desired shear stress (flow rate) controlled by a peristaltic pump. At the end of the experiment, the circulating and migrated cells are collected for further analyses. The 3D device can be used to examine cell rolling on and adhesion to EC under shear stress, transmigration in response to chemokine gradients, resistance to shear stress, cluster formation, and cell survival. In addition, the optional second insert allows the effects of crosstalk between EC and microenvironmental cells to be examined. The translational applications of the 3D device include testing of drug candidates that target cell migration and predicting the in vivo behavior of cells after intravenous injection. Thus, the novel 3D device is a versatile and inexpensive tool to study the molecular mechanisms that mediate cellular extravasation.

The three-dimensional flow chamber device is a novel in vitro technology for the quantitative and step-wise evaluation of the extravasation cascade of cells circulating under conditions of physiological shear stress. The device therefore fills a critical need for basic, preclinical, and clinical studies of cell migration.

Extravasation of circulating cells from the bloodstream plays a central role in many physiological and pathophysiological processes, including stem cell ...

Shock Wave Application to Cell Cultures

Shock waves nowadays are well known for their regenerative effects. Basic research findings showed that shock waves do cause a biological stimulus to target cells or tissue without any subsequent damage. Therefore, in vitro experiments are of increasing interest. Various methods of applying shock waves onto cell cultures have been described. In general, all existing models focus on how to best apply shock waves onto cells.
However, this question remains: What happens to the waves after passing the cell culture? The difference of the acoustic impedance of the cell culture medium and the ambient air is that high, that more than 99% of shock waves get reflected! We therefore developed a model that mainly consists of a Plexiglas built container that allows the waves to propagate in water after passing the cell culture. This avoids cavitation effects as well as reflection of the waves that would otherwise disturb upcoming ones. With this model we are able to mimic in vivo conditions and thereby gain more and more knowledge about how the physical stimulus of shock waves gets translated into a biological cell signal (&#8220;mechanotransduction&#34;).

Shock waves nowadays are well known for their regenerative effects. Therefore in vitro experiments are of increasing interest. We therefore developed a model for in vitro shock wave trials (IVSWT) that enables us to mimic in vivo conditions thereby avoiding distracting physical effects.

Shock waves nowadays are well known for their regenerative effects. Basic research findings showed that shock waves do cause a biological stimulus to ...

Tissue Engineering of Tumor Stromal Microenvironment with Application to Cancer Cell Invasion

3D organotypic cultures of epithelial cells on a matrix embedded with mesenchymal cells are widely used to study epithelial cell differentiation and invasion. Rat tail type I collagen and/or matrix derived from Engelbreth-Holm-Swarm mouse sarcoma cells have been traditionally employed as the substrates to model the matrix or stromal microenvironment into which mesenchymal cells (usually fibroblasts) are populated. Although experiments using such matrices are very informative, it can be argued that due to an overriding presence of a single protein (such as in type I Collagen) or a high content of basement membrane components and growth factors (such as in matrix derived from mouse sarcoma cells), these substrates do not best reflect the contribution to matrix composition made by the stromal cells themselves. To study native matrices produced by primary dermal fibroblasts isolated from patients with a tumor prone, genetic blistering disorder (recessive dystrophic epidermolysis bullosa), we have adapted an existing native matrix protocol to study tumor cell invasion. Fibroblasts are induced to produce their own matrix over a prolonged period in culture. This native matrix is then detached from the culture dish and epithelial cells are seeded onto it before the entire coculture is raised to the air-liquid interface. Cellular differentiation and/or invasion can then be assessed over time. This technique provides the ability to assess epithelial-mesenchymal cell interactions in a 3D setting without the need for a synthetic or foreign matrix with the only disadvantage being the prolonged period of time required to produce the native matrix. Here we describe the application of this technique to assess the ability of a single molecule expressed by fibroblasts, type VII collagen, to inhibit tumor cell invasion.

Tissue engineered fibroblast-derived native matrix is an emerging tool to generate a stromal substrate which supports epithelial cell proliferation and differentiation. Here a protocol applying this methodology to assess the impact of different stromal cell types on tumor cell biology is presented.

3D organotypic cultures of epithelial cells on a matrix embedded with mesenchymal cells are widely used to study epithelial cell differentiation and ...

In vitro Cell Culture Model for Toxic Inhaled Chemical Testing

Cell cultures are indispensable to develop and study efficacy of therapeutic agents, prior to their use in animal models. We have the unique ability to model well differentiated human airway epithelium and heart muscle cells. This could be an invaluable tool to study the deleterious effects of toxic inhaled chemicals, such as chlorine, that can normally interact with the cell surfaces, and form various byproducts upon reacting with water, and limiting their effects in submerged cultures. Our model using well differentiated human airway epithelial cell cultures at air-liqiuid interface circumvents this limitation as well as provides an opportunity to evaluate critical mechanisms of toxicity of potential poisonous inhaled chemicals. We describe enhanced loss of membrane integrity, caspase release and death upon toxic inhaled chemical such as chlorine exposure. In this article, we propose methods to model chlorine exposure in mammalian heart and airway epithelial cells in culture and simple tests to evaluate its effect on these cell types.

In vitro Cell Culture Model for Toxic Inhaled Chemical Testing

This protocol is designed to demonstrate exposure method of cell cultures to inhaled toxic chemicals. Exposure of differentiated air-liquid&#160;interface (ALI) cultures of airway epithelial cells provides a unique model of airway exposure to toxic gases such as chlorine. In this manuscript we describe effect of chlorine exposure on air-liquid&#160;interface cultures of epithelial cells and submerged culture of cardiomyocytes. In vitro exposure systems allow important mechanistic studies to evaluate pathways that could then be utilized to develop novel therapeutic agents.

Cell cultures are indispensable to develop and study efficacy of therapeutic agents, prior to their use in animal models. We have the unique ability to ...

Using Cell-substrate Impedance and Live Cell Imaging to Measure Real-time Changes in Cellular Adhesion and De-adhesion Induced by Matrix Modification

Cell-matrix adhesion plays a key role in controlling cell morphology and signaling. Stimuli that disrupt cell-matrix adhesion (e.g., myeloperoxidase and other matrix-modifying oxidants/enzymes released during inflammation) are implicated in triggering pathological changes in cellular function, phenotype and viability in a number of diseases. Here, we describe how cell-substrate impedance and live cell imaging approaches can be readily employed to accurately quantify real-time changes in cell adhesion and de-adhesion induced by matrix modification (using endothelial cells and myeloperoxidase as a pathophysiological matrix-modifying stimulus) with high temporal resolution and in a non-invasive manner. The xCELLigence cell-substrate impedance system continuously quantifies the area of cell-matrix adhesion by measuring the electrical impedance at the cell-substrate interface in cells grown on gold microelectrode arrays. Image analysis of time-lapse differential interference contrast movies quantifies changes in the projected area of individual cells over time, representing changes in the area of cell-matrix contact. Both techniques accurately quantify rapid changes to cellular adhesion and de-adhesion processes. Cell-substrate impedance on microelectrode biosensor arrays provides a platform for robust, high-throughput measurements. Live cell imaging analyses provide additional detail regarding the nature and dynamics of the morphological changes quantified by cell-substrate impedance measurements. These complementary approaches provide valuable new insights into how myeloperoxidase-catalyzed oxidative modification of subcellular extracellular matrix components triggers rapid changes in cell adhesion, morphology and signaling in endothelial cells. These approaches are also applicable for studying cellular adhesion dynamics in response to other matrix-modifying stimuli and in related adherent cells (e.g., epithelial cells).

Here, we present a protocol to continuously quantify cell adhesion and de-adhesion processes with high temporal resolution in a non-invasive manner by cell-substrate impedance and live cell imaging analyses. These approaches reveal the dynamics of cell adhesion/de-adhesion processes triggered by matrix modification and their temporal relationship to adhesion-dependent signaling events.

Cell-matrix adhesion plays a key role in controlling cell morphology and signaling. Stimuli that disrupt cell-matrix adhesion (e.g., myeloperoxidase and ...

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 ...

Microfluidic Flow Chambers Using Reconstituted Blood to Model Hemostasis and Platelet Transfusion In Vitro

Blood platelets prepared for transfusion gradually lose hemostatic function during storage. Platelet function can be investigated using a variety of (indirect) in vitro experiments, but none of these is as comprehensive as microfluidic flow chambers. In this protocol, the reconstitution of thrombocytopenic fresh blood with stored blood bank platelets is used to simulate platelet transfusion. Next, the reconstituted sample is perfused in microfluidic flow chambers which mimic hemostasis on exposed subendothelial matrix proteins. Effects of blood donation, transport, component separation, storage and pathogen inactivation can be measured in paired experimental designs. This allows reliable comparison of the impact every manipulation in blood component preparation has on hemostasis. Our results demonstrate the impact of temperature cycling, shear rates, platelet concentration and storage duration on platelet function. In conclusion, this protocol analyzes the function of blood bank platelets and this ultimately aids in optimization of the processing chain including phlebotomy, transport, component preparation, storage and transfusion.

Microfluidic Flow Chambers Using Reconstituted Blood to Model Hemostasis and Platelet Transfusion In Vitro

Platelet transfusion and hemostasis was modeled using blood reconstitution and microfluidic flow chambers to investigate the function of blood banking platelets. The data demonstrate the consequences of platelet storage lesion on hemostasis, in vitro.

Blood platelets prepared for transfusion gradually lose hemostatic function during storage. Platelet function can be investigated using a variety of ...

A Microfluidic Flow Chamber Model for Platelet Transfusion and Hemostasis Measures Platelet Deposition and Fibrin Formation in Real-time

Microfluidic models of hemostasis assess platelet function under conditions of hydrodynamic shear, but in the presence of anticoagulants, this analysis is restricted to platelet deposition only. The intricate relationship between Ca2+-dependent coagulation and platelet function requires careful and controlled recalcification of blood prior to analysis. Our setup uses a Y-shaped mixing channel, which supplies concentrated Ca2+/Mg2+ buffer to flowing blood just prior to perfusion, enabling rapid recalcification without sample stasis. A ten-fold difference in flow velocity between both reservoirs minimizes dilution. The recalcified blood is then perfused in a collagen-coated analysis chamber, and differential labeling permits real-time imaging of both platelet and fibrin deposition using fluorescence video microscopy. The system uses only commercially available tools, increasing the chances of standardization. Reconstitution of thrombocytopenic blood with platelets from banked concentrates furthermore models platelet transfusion, proving its use in this research domain. Exemplary data demonstrated that coagulation onset and fibrin deposition were linearly dependent on the platelet concentration, confirming the relationship between primary and secondary hemostasis in our model. In a timeframe of 16 perfusion min, contact activation did not take place, despite recalcification to normal Ca2+ and Mg2+ levels. When coagulation factor XIIa was inhibited by corn trypsin inhibitor, this time frame was even longer, indicating a considerable dynamic range in which the changes in the procoagulant nature of the platelets can be assessed. Co-immobilization of tissue factor with collagen significantly reduced the time to onset of coagulation, but not its rate. The option to study the tissue factor and/or the contact pathway increases the versatility and utility of the assay.

This paper describes an experimental model of hemostasis that simultaneously measures platelet function and coagulation. Platelet and fibrin fluorescence is measured in real-time, and platelet adhesion rate, coagulation rate, and onset of coagulation are determined. The model is used to determine platelet procoagulant properties under flow in concentrates for transfusion.

Microfluidic models of hemostasis assess platelet function under conditions of hydrodynamic shear, but in the presence of anticoagulants, this analysis is ...

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 ...