1. Modifying Polymeric Surfaces with recCD47
NOTE: The protocol is summarized schematically in Figure 1. Figure 1A illustrates generation of thiol-reactive polymeric surfaces. Figure 1B illustrates generation of thiol-reactive recCD47.
<ol>
	<li>Day 1
	<ol>
		<li>Prepare a solution of PDT-BzPh (1 mg/ml) and potassium bicarbonate (KHCO3) (0.7 mg/ml) in sterile water. Stir overnight at 4 &#176;C (protect from light).</li>
	</ol>
	</li>
	<li>Day 2
	<ol>
		<li>Cut polymeric tubing into 40 cm long pieces (long enough to fit around rotating wheels).</li>
		<li>Soak tubes in a 0.1% aqueous solution of hexacylpyridinium for 90 min at room temperature on a shaker or on Chandler Loop Apparatus. Rinse the tubes with sterile water 3x after the 90 min soak.</li>
		<li>Acidify the solution of PDT-BzPh from Day 1 by adding 15% aqueous potassium phosphate monobasic (KH2PO4). Add 50 &#181;l KH2PO4 per ml of PDT-BzPh, forming a cloudy micellar solution.</li>
		<li>Soak the tubes in the acidified PDT-BzPh solution for 40 min at room temperature on a shaker or on apparatus.</li>
		<li>Rinse the tubes with dilute acetic acid (1:1,000) once.</li>
		<li>Expose the tubes to UV irradiation for a total duration of 60 min. Rotate tubes &#188; turn every 15 min to irradiate the entire surface area.</li>
		<li>Soak the tubes in a solution of 20 mg/ml potassium bicarbonate (KHCO3) for 20 min at room temperature on a shaker or on apparatus.</li>
		<li>Rinse the tubes with sterile water 3x and store at 4 &#176;C in sterile water.</li>
	</ol>
	</li>
	<li>Day 3
	<ol>
		<li>Dissolve 5 mg Sulfo-SMCC in 200 &#181;l Dimethylformamide (DMF) (Caution:&#160;Perform in fume hood).</li>
		<li>Add 50 &#181;l of the Sulfo-SMCC solution prepared in step 1 to 0.1 mg/ml of recCD47 poly-lysine solution, and stir for 60 min at room temperature.</li>
		<li>During 60 min stir, degas sterile Dulbecco&#8217;s Phosphate Buffered Saline (DPBS) and set aside.</li>
		<li>Purify Sulfo-SMCC reacted recCD47 using a 7K molecular weight cut-off spin desalting column per manufacturer&#8217;s instructions. Collect final flow-through (high-quality thiol-reactive recCD47) and dilute to a volume necessary to coat the interior of the tube with DPBS.</li>
		<li>Rinse the tubes from day 2 with sterile, degassed DPBS 3x.</li>
		<li>React the modified surface of the tubes with a solution of 20 mg/ml with tris(2-carboxyethyl) phosphine hydrochloride (TCEP) in degassed DPBS for less than 2 min. Rinse the tubes with sterile degassed DPBS 4x.</li>
		<li>Add the Sulfo-SMCC-reacted recCD47 to the tubes and incubate overnight at 4 &#176;C on a shaker or on apparatus.</li>
	</ol>
	</li>
</ol>
2. Immunoassay Quantification of recCD47 on Modified Surfaces
<ol>
	<li>Rinse modified tubes to be quantified from Day 3 with DPBS 3x. Store tubes not used for quantification in DPBS at 4 &#176;C.</li>
	<li>Use a 4 mm biopsy punch to make duplicate tube samples and place biopsy punches in wells of a 96-well plate.</li>
	<li>Prepare a negative control consisting of an unmodified tube sample not treated with the detection antibody. Prepare an antibody control consisting of an unmodified tube sample treated with the detection antibody. Prepare the modified tubing test samples treated with the detection antibody.</li>
	<li>Block samples with 0.4% bovine serum albumin (BSA) in DPBS for 60 min at room temperature on a shaker.</li>
	<li>After blocking, aspirate BSA and rinse with tris-buffered saline plus 1% Tween-20 (TBST) 3x, 10 min each on a shaker.</li>
	<li>Prepare a working dilution of antibody in 0.4% BSA according to manufacturer&#8217;s recommended dilution for immunoassays. Dilute human CD47 Antibody B6H12-FITC 1:100 in 0.4% BSA.</li>
	<li>Add 200 &#181;l of antibody dilution to appropriate wells. Incubate negative controls with 0.4% BSA only. Incubate at room temperature for 60 min on a shaker (protect from light).</li>
	<li>Rinse with TBST 3x, 10 min each on a shaker. Aspirate the last TBST rinse and add 200 &#181;l DPBS to tube sample wells.</li>
	<li>Collect the final flow-through, which is high-quality thiol-reactive recombinant CD47 and dilute to a volume necessary to coat the interior of the tubes with DPBS.</li>
	<li>Read FITC signal intensity using a microplate reader with FITC excitation (485 nm) and emission (538 nm) settings.</li>
	<li>Calculate recCD47 bound to polymeric surface based on standard values, accounting for auto-fluorescence and non-specific binding from the antibody control sample.</li>
</ol>
3. Chandler Loop Apparatus Protocol
Seek Institutional Review Board (IRB) approval of blood collection protocol and informed consent paperwork prior to initiation of collection of human blood samples. Obtain informed consent from a human blood donor. 
NOTE: A diagram depicting the apparatus is shown in Figure 2.
<ol>
	<li>Fill water bath with distilled water until approximately 1/2 of the diameter wheels are submerged. Add enough bleach to the water bath to make a 10% bleach solution. Set water bath to 37 &#176;C and allow temperature to equilibrate.</li>
	<li>Gather metal adapters (shown in Figure 1B), unmodified tubing and modified tubing, and assemble around apparatus wheels, as shown in Figure 1C. Ensure that tubing fits snuggly around the wheel with the metal adapter in place.</li>
	<li>Obtain 30 ml blood sample using an IRB-approved protocol, in a vial prefilled with 2 ml of citrate or other anticoagulant, and mix by inversion to prevent clotting once the specimen has been collected.</li>
	<li>Add approximately 10 ml of blood to each tube using the metal valve and syringe, leaving some air in the tube. Secure the valve cap and rotate for 3 hr.</li>
	<li>Drain the blood into a waste beaker treated with a 10% bleach solution (or as required by institutional policy).</li>
	<li>Gently rinse tubing interior with DPBS to remove all traces of blood. Collect flow-through in the waste beaker. Dispose of blood in accordance with institutional policy.</li>
	<li>Disinfect the apparatus and any blood contacting surfaces using a 10% bleach solution or according to institutional policy.</li>
	<li>Process samples for fluorescent microscopy or scanning electron microscopy as described below.</li>
</ol>
4. Fluorescent Microscopy and Cell Counting
<ol>
	<li>Prepare a 4% paraformaldehyde (PFA) solution (Caution:&#160;Perform in fume hood).</li>
	<li>Incubate tubing in a 4% PFA solution overnight at 4 &#176;C.</li>
	<li>After overnight incubation, remove 4% PFA and rinse films very gently with DPBS.</li>
	<li>Cut the tubing into sections to expose the lumen surface for staining.</li>
	<li>Stain a section of the tubing with a few drops of mounting media with 4&#39;,6-diamidino-2-phenylindole (DAPI) for 30 min at room temperature (protect from light). After staining, rinse the tubing very gently with DPBS to reduce background DAPI signal.</li>
	<li>Image using a fluorescent microscope equipped with a DAPI filter and digital camera to count the number of cells in 9 blindly selected fields of view under 200X magnification.</li>
	<li>Record cell counts per field of view and perform appropriate statistical analyses to determine statistical significance of results.</li>
</ol>
5. Scanning Electron Microscopy
<ol>
	<li>Prepare a 2% glutaraldehyde solution (Caution:&#160;Perform in fume hood).</li>
	<li>Incubate tubing in a 2% glutaraldehyde solution overnight at 4 &#176;C.</li>
	<li>After overnight incubation, gently rinse the tubing 3x with DPBS.</li>
	<li>Prepare a 1% solution of osmium tetroxide (Caution:&#160;Severe inhalation hazard! Use in fume hood).</li>
	<li>Incubate tubing in a 1% solution of osmium tetroxide for 15 min at room temperature.</li>
	<li>Gently rinse the tubing 3x with DPBS.</li>
	<li>Prepare a series of ethanol concentrations (25%, 50%, 75%, 95%, and 100% ethanol).</li>
	<li>Dehydrate the tubing by incubation in the series of ethanol concentrations. Incubate in 25%, 50%, 75%, and 95% ethanol for 20 min each. Incubate in 100% ethanol for 30 min.</li>
	<li>Supercritical point dry the tubing with CO2 for 45 min to remove all moisture.</li>
	<li>Mount tube sections on a specimen stub with silver paste or graphite.</li>
	<li>Coat tube sections with 12.5 nm of gold-palladium.</li>
	<li>Examine in a scanning electron microscope. &#160;&#160;</li>
</ol>

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F., Groth, T., Werner, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vitro+blood+reactivity+to+hydroxylated+and+non-hydroxylated+polymer+surfaces.">In vitro blood reactivity to hydroxylated and non-hydroxylated polymer surfaces.</a> Biomaterials. 28, 3617-3625 (2007).</li><li>Sperling, C., Schweiss, R. B., Streller, U., Werner, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vitro+hemocompatibility+of+self-assembled+monolayers+displaying+various+functional+groups.">In vitro hemocompatibility of self-assembled monolayers displaying various functional groups.</a> Biomaterials. 26, 6547-6457 (2005).</li><li>Vasita, R., Shanmugam, I. K., Katt, D. 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E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Inhibition+of+'self'+engulfment+through+deactivation+of+myosin-II+at+the+phagocytic+synapse+between+human+cells.">Inhibition of 'self' engulfment through deactivation of myosin-II at the phagocytic synapse between human cells.</a> J Cell Biol. 180 (5), 989-1003 (2008).</li><li>Berg, T. K., vander Schoot, C. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Innate+immune+'self'+recognition:+a+role+for+CD47-SIRPalpha+interactions+in+hematopoietic+stem+cell+transplantation.">Innate immune 'self' recognition: a role for CD47-SIRPalpha interactions in hematopoietic stem cell transplantation.</a> Trends Immunol. 29 (5), 203-206 (2008).</li><li>Oldenborg, P. A., Zheleznyak, A., Fang, Y. F., Lagenaur, C. F., Gresham, H. D., Lindberg, F. P. <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+CD47+as+a+marker+of+self+on+red+blood+cells.">Role of CD47 as a marker of self on red blood cells.</a> Science. 288 (5473), 2051-2054 (2000).</li><li>Stachelek, S. J., 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=The+effect+of+CD47+modified+polymer+surfaces+on+inflammatory+cell+attachment+and+activation.">The effect of CD47 modified polymer surfaces on inflammatory cell attachment and activation.</a> Biomaterials. 32 (19), 4317-4326 (2001).</li><li>Finley, M. J., Rauva, L., Alferiev, I. S., Weisel, J. W., Levy, R. J., Stachelek, S. 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Research reported in this publication was supported by National Institute of Biomedical Imaging and Bioengineering, under award number R21 EB015612 (SJS), and the National Heart, Lung, and Blood Institute, under award number T32 HL007915 (JBS and RJL), of the National Institute of Health.

The photoactivation chemistry (summarized in Figure 1) allows for the modification of virtually any polymer surface that has sufficient hydrocarbons to facilitate PDT-BzPh attachment and subsequent UV irradiation to photo-activate the PDT-BzPh. Functionalizing the polymeric surface with reactive thiol groups allows for the subsequent attachment of a range of testable molecules of interest. In our particular studies we chose recombinant CD4711-13. The particular conjugation chemistry that we us...

Many clinical procedures, such as cardiopulmonary bypass and renal dialysis, require the use of polymeric blood conduits and are often associated with post-procedural complications1. When perfused with blood, these polymers illicit the foreign body reaction (FBR), resulting in adsorption of blood proteins and platelets, monocyte/macrophage adhesion, and the release of pro-inflammatory cytokines, all of which contribute to post-procedural complications and/or device failure2,3. Thus, strategies to address this issue remain an important and ongoing area of biomaterials research. Investigators have attempted to address this issue by modifying blood contacting surfaces with bioactive or bioinert molecules4-6. Research in our laboratory has focused on appending recombinant CD47 (recCD47) to polymeric biomaterials as a strategy to mitigate the FBR and increase the efficacy of these materials. CD47 is a ubiquitously expressed transmembrane protein with a known role in immune evasion, conferring &#8220;self&#8221; status upon expressing cells7-10 and shows promise at conferring biocompatibility when appended to polymeric surfaces11-13. Signal-regulatory protein alpha (SIRP&#945;), the cognate receptor for CD47, and a member of the immunoreceptor tyrosine-based inhibitory motif (ITIM)-containing family of transmembrane proteins, is expressed on cells of myeloid origin14. We have previously demonstrated that CD47, via SIRP&#945;-mediated cell signaling, down-regulates the immune responses to polyurethane (PU) and polyvinylchloride (PVC) in in vitro, ex vivo, and in vivo models11-13.
Central to our investigations is a relatively novel photoactivation chemistry, described herein, in which chemically reactive thiol groups are covalently appended to polymeric tubing by reacting the tubing with a multifunctional polymer (PDT-BzPh), composed of 2-pyridyldithio (PDT), the photoreactive benzophenone (BzPh) and a carboxy-modified polyallylamine11-13. Reducing the covalently appended PDT groups with tris(2-carboxyethyl) phosphine hydrochloride (TCEP)11 yields a thiolated surface that can be subsequently reacted with therapeutic moieties. Detailed herein and previously12,13, recCD47, further modified with the addition of a C-terminal poly-lysine tail12,13, is reacted with Sulfosuccinimidyl-4-[N-maleimidomethyl]cyclohexane-1-carboxylate (sulfo-SMCC) for 1 hr to generate thiol-reactive groups, allowing for a monosulfide bond formation between the tubing and recCD4711. The anti-inflammatory capacity of the CD47 functionalized surfaces was tested, ex vivo, using the Chandler Loop Apparatus with whole human blood, which was originally described in 1958 as an in vitro model of thrombotic coagulation15. The apparatus relies on a closed tube system partially filled with air and a rotary motor to circulate the blood through the tubing15. This experimental model provides the opportunity to examine the effect of blood exposure upon modified and unmodified surfaces as well as the effect of those surface modifications upon the physiology of cells of the blood.
recCD47 can be appended to a variety of polymeric surfaces using this photoactivation chemistry, and its anti-inflammatory capacity can be assessed by utilizing a clinically relevant ex vivo model mimicking blood perfusion over polymeric surfaces11,12. Clinical grade blood conduits modified with recCD47 show significantly less platelet and inflammatory cell attachment as compared to unmodified polymers when exposed to human blood in the apparatus. A step-by-step description of this modification process is detailed below.

<table border="0" cellpadding="0" cellspacing="0" width="802">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:269px;">Name</td>
			<td style="width:175px;">Company</td>
			<td style="width:107px;">Catalog Number</td>
			<td style="width:251px;">Comments</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:269px;">16% Paraformaldehyde (PFA)</td>
			<td style="width:175px;">Thermo Scientific</td>
			<td style="width:107px;">58906</td>
			<td>Caution! Use in fume hood</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:269px;">25% Glutaraldehyde</td>
			<td style="width:175px;">VWR</td>
			<td style="width:107px;">AAA17876-AP&#160;</td>
			<td>Caution! Use in fume hood</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:269px;">2-pyridyldithio,benzophenone (PDT-BzPH)</td>
			<td style="width:175px;">Synthesized in lab</td>
			<td style="width:107px;">N/A</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:269px;">Bovine Serum Albumin (BSA)</td>
			<td style="width:175px;">Sigma</td>
			<td style="width:107px;">A3059-100G</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:269px;">Citrate</td>
			<td style="width:175px;">Sigma</td>
			<td style="width:107px;">S5770-50ML</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:269px;">Digital Camera</td>
			<td style="width:175px;">Leica</td>
			<td style="width:107px;">DC500</td>
			<td>Out of production</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:269px;">Dimethylformamide (DMF)</td>
			<td style="width:175px;">Sigma</td>
			<td style="width:107px;">270547-100ML</td>
			<td>Caution! Use in fume hood</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:269px;">Dulbecco&#8217;s Phosphate Buffered Saline (DPBS)</td>
			<td style="width:175px;">Gibco/Life Technologies</td>
			<td style="width:107px;">14190-136</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:269px;">Fluorescent Microscope</td>
			<td style="width:175px;">Nikon</td>
			<td style="width:107px;">TE300</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:269px;">Glacial Acetic Acid</td>
			<td style="width:175px;">Fisher Scientific</td>
			<td style="width:107px;">A38-212</td>
			<td>Caution! Use in fume hood</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:269px;">Human CD47 (B6H12) &#8211; FITC Antibody</td>
			<td style="width:175px;">Santa Cruz Biotechnology</td>
			<td style="width:107px;">SC-12730</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:269px;">Osmium Tetroxide</td>
			<td style="width:175px;">Acros Organics</td>
			<td style="width:107px;">197450050</td>
			<td>Caution! Use in fume hood</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:269px;">Potassium Bicarbonate (KHCO3)</td>
			<td style="width:175px;">Sigma</td>
			<td style="width:107px;">237205-100G</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:269px;">Potassium Phosphate Monobasic (KH2PO4)</td>
			<td style="width:175px;">Sigma</td>
			<td style="width:107px;">P5655-100G</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:269px;">PVC Tubing (Cardiovascular Procedure Kit)</td>
			<td style="width:175px;">Terumo Cardiovascular Systems</td>
			<td style="width:107px;">60050</td>
			<td>Most clinical-grade tubing will work</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:269px;">Scanning Electron Microscope</td>
			<td>JEOL</td>
			<td>JSM-T330A</td>
			<td></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;width:269px;">Sodium Chloride (NaCl)</td>
			<td style="width:175px;">Fisher Scientific</td>
			<td>BP358-212</td>
			<td></td>
		</tr>
		<tr height="36">
			<td height="36" style="height:36px;width:269px;">Microplate Reader</td>
			<td style="width:175px;">Molecular Devices</td>
			<td style="width:107px;">Spectramax Gemini EM&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:269px;">Sulfo-SMCC</td>
			<td style="width:175px;">Sigma</td>
			<td style="width:107px;">M6035-10MG</td>
			<td>Moisture Sensitive!</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:269px;">tris (2-carboxyethyl) phosphine (TCEP-HCl)</td>
			<td style="width:175px;">Thermo Scientific</td>
			<td style="width:107px;">20491</td>
			<td></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;width:269px;">Tris Base</td>
			<td style="width:175px;">Sigma</td>
			<td>T1503-100G</td>
			<td></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;width:269px;">Tween-20</td>
			<td>Bio-Rad</td>
			<td>170-6531</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:269px;">Vectashield with DAPI</td>
			<td style="width:175px;">Fisher Scientific</td>
			<td style="width:107px;">H-1200</td>
			<td>Light sensitive!</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:269px;">Zeba Spin Desalt Columns &#8211; 7K MWCO</td>
			<td style="width:175px;">Thermo Scientific</td>
			<td style="width:107px;">89891</td>
			<td></td>
		</tr>
	</tbody>
</table>

the use of the ex vivo chandler loop apparatus to assess the biocompatibility of modified polymeric blood conduits

The foreign body reaction occurs when a synthetic surface is introduced to the body. It is characterized by adsorption of blood proteins and the subsequent attachment and activation of platelets, monocyte/macrophage adhesion, and inflammatory cell signaling events, leading to post-procedural complications. The Chandler Loop Apparatus is an experimental system that allows researchers to study the molecular and cellular interactions that occur when large volumes of blood are perfused over polymeric conduits. To that end, this apparatus has been used as an ex vivo model allowing the assessment of the anti-inflammatory properties of various polymer surface modifications. Our laboratory has shown that blood conduits, covalently modified via photoactivation chemistry with recombinant CD47, can confer biocompatibility to polymeric surfaces. Appending CD47 to polymeric surfaces could be an effective means to promote the efficacy of polymeric blood conduits. Herein is the methodology detailing the photoactivation chemistry used to append recombinant CD47 to clinically relevant polymeric blood conduits and the use of the Chandler Loop as an ex vivo experimental model to examine blood interactions with the CD47 modified and control conduits.

Generating thiol-reactive polymeric surfaces through the use of PDT-BzPh and TCEP along with thiol-reactive recCD47 poly-lysine using SMCC allows for the attachment of recCD47 to polymeric surfaces. The modification process is summarized schematically in Figure 1. The convenience of this modification process is that it can be applied to many different proteins and many different polymeric surfaces, assuming the protein can be modified with sufficient chemically reactive groups such as amine-containing ly...

Watch this Scientific Journal Video about The Use of the Ex Vivo Chandler Loop Apparatus to Assess the Biocompatibility of Modified Polymeric Blood Conduits at JoVE.com

The Use of the Ex Vivo Chandler Loop Apparatus to Assess the Biocompatibility of Modified Polymeric Blood Conduits

Blood exposure to polymeric blood conduits initiates the foreign body reaction that has been implicated in clinical complications. Here, the Chandler Loop Apparatus, an experimental tool mimicking blood perfusion through these conduits, is described. Appendage of recombinant CD47 results in decreased evidence of the foreign body reaction on these conduits.

The Use of the Ex Vivo Chandler Loop Apparatus to Assess the Biocompatibility of Modified Polymeric Blood Conduits

The foreign body reaction occurs when a synthetic surface is introduced to the body. It is characterized by adsorption of blood proteins and the ...

the-use-ex-vivo-chandler-loop-apparatus-to-assess-biocompatibility

Research

JoVE Journal

Bioengineering

11.5K vistas.  The Children's Hospital of Philadelphia. Blood exposure to polymeric blood conduits initiates the foreign body reaction that has been implicated in clinical complications. Here, the Chandler Loop Apparatus, an experimental tool mimicking blood perfusion through these conduits, is described. Appendage of recombinant CD47 results in decreased evidence of the foreign body reaction on these conduits. 

Video: The Use of the Ex Vivo Chandler Loop Apparatus to Assess the Biocompatibility of Modified Polymeric Blood Conduits

Design of a Cyclic Pressure Bioreactor for the Ex Vivo Study of Aortic Heart Valves

The aortic valve, located between the left ventricle and the aorta, allows for unidirectional blood flow, preventing backflow into the ventricle. Aortic valve leaflets are composed of interstitial cells suspended within an extracellular matrix (ECM) and are lined with an endothelial cell monolayer. The valve withstands a harsh, dynamic environment and is constantly exposed to shear, flexion, tension, and compression. Research has shown calcific lesions in diseased valves occur in areas of high mechanical stress as a result of endothelial disruption or interstitial matrix damage1-3. Hence, it is not surprising that epidemiological studies have shown high blood pressure to be a leading risk factor in the onset of aortic valve disease4. 
The only treatment option currently available for valve disease is surgical replacement of the diseased valve with a bioprosthetic or mechanical valve5. Improved understanding of valve biology in response to physical stresses would help elucidate the mechanisms of valve pathogenesis. In turn, this could help in the development of non-invasive therapies such as pharmaceutical intervention or prevention. Several bioreactors have been previously developed to study the mechanobiology of native or engineered heart valves6-9. Pulsatile bioreactors have also been developed to study a range of tissues including cartilage10, bone11 and bladder12. The aim of this work was to develop a cyclic pressure system that could be used to elucidate the biological response of aortic valve leaflets to increased pressure loads. 
The system consisted of an acrylic chamber in which to place samples and produce cyclic pressure, viton diaphragm solenoid valves to control the timing of the pressure cycle, and a computer to control electrical devices. The pressure was monitored using a pressure transducer, and the signal was conditioned using a load cell conditioner. A LabVIEW program regulated the pressure using an analog device to pump compressed air into the system at the appropriate rate. The system mimicked the dynamic transvalvular pressure levels associated with the aortic valve; a saw tooth wave produced a gradual increase in pressure, typical of the transvalvular pressure gradient that is present across the valve during diastole, followed by a sharp pressure drop depicting valve opening in systole. The LabVIEW program allowed users to control the magnitude and frequency of cyclic pressure. The system was able to subject tissue samples to physiological and pathological pressure conditions. This device can be used to increase our understanding of how heart valves respond to changes in the local mechanical environment.

Design of a Cyclic Pressure Bioreactor for the Ex Vivo Study of Aortic Heart Valves

A cyclic pressure bioreactor capable of subjecting heart valve tissue to physiological and pathological pressure conditions has been designed. A LabVIEW program allows users to control pressure magnitude, amplitude and frequency. This device can be used to study the mechanobiology of heart valve tissue or isolated cells.

The aortic valve, located between the left ventricle and the aorta, allows for unidirectional blood flow, preventing backflow into the ventricle. Aortic ...

Determination of the Transport Rate of Xenobiotics and Nanomaterials Across the Placenta using the ex vivo Human Placental Perfusion Model

Decades ago the human placenta was thought to be an impenetrable barrier between mother and unborn child. However, the discovery of thalidomide-induced birth defects and many later studies afterwards proved the opposite. Today several harmful xenobiotics like nicotine, heroin, methadone or drugs as well as environmental pollutants were described to overcome this barrier. With the growing use of nanotechnology, the placenta is likely to come into contact with novel nanoparticles either accidentally through exposure or intentionally in the case of potential nanomedical applications. Data from animal experiments cannot be extrapolated to humans because the placenta is the most species-specific mammalian organ 1. Therefore, the ex vivo dual recirculating human placental perfusion, developed by Panigel et al. in 1967 2 and continuously modified by Schneider et al. in 1972 3, can serve as an excellent model to study the transfer of xenobiotics or particles.
Here, we focus on the ex vivo dual recirculating human placental perfusion protocol and its further development to acquire reproducible results.
The placentae were obtained after informed consent of the mothers from uncomplicated term pregnancies undergoing caesarean delivery. The fetal and maternal vessels of an intact cotyledon were cannulated and perfused at least for five hours. As a model particle fluorescently labelled polystyrene particles with sizes of 80 and 500 nm in diameter were added to the maternal circuit. The 80 nm particles were able to cross the placental barrier and provide a perfect example for a substance which is transferred across the placenta to the fetus while the 500 nm particles were retained in the placental tissue or maternal circuit. The ex vivo human placental perfusion model is one of few models providing reliable information about the transport behavior of xenobiotics at an important tissue barrier which delivers predictive and clinical relevant data.

Determination of the Transport Rate of Xenobiotics and Nanomaterials Across the Placenta using the ex vivo Human Placental Perfusion Model

The ex vivo dual recirculating human placental perfusion model can be used to investigate the transfer of xenobiotics and nanoparticles across the human placenta. In this video protocol we describe the equipment and techniques required for a successful execution of a placenta perfusion.

Decades ago the human placenta was thought to be an impenetrable barrier between mother and unborn child. However, the discovery of thalidomide-induced ...

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 ...

Gene Transfection toward Spheroid Cells on Micropatterned Culture Plates for Genetically-modified Cell Transplantation

To improve the therapeutic effectiveness of cell transplantation, a transplantation system of genetically modified, injectable spheroids was developed. The cell spheroids are prepared in a culture system on micropatterned plates coated with a thermosensitive polymer. A number of spheroids are formed on the plates, corresponding to the cell adhesion areas of 100 &#181;m diameter that are regularly arrayed in a two-dimensional manner, surrounded by non-adhesive areas that are coated by a polyethylene glycol (PEG) matrix. The spheroids can be easily recovered as a liquid suspension by lowering the temperature of the plates, and their structure is well maintained by passing them through injection needles with a sufficiently large caliber (over 27 G). Genetic modification is achieved by gene transfection using the original non-viral gene carrier, polyplex nanomicelle, which is capable of introducing genes into cells without disrupting the spheroid structure. For primary hepatocyte spheroids transfected with a luciferase-expressing gene, the luciferase is sustainably obtained in transplanted animals, along with preserved hepatocyte function, as indicated by albumin expression. This system can be applied to a variety of cell types including mesenchymal stem cells.

This protocol describes a cell transplantation system using genetically modified, injectable spheroids. Cell spheroids are cultured on micropatterned culture plates and recovered after gene introduction using polyplex nanomicelles. This system facilitates prolonged transgene expression from the transplanted cells in host animals while maintaining the innate function of the cells.

To improve the therapeutic effectiveness of cell transplantation, a transplantation system of genetically modified, injectable spheroids was developed. ...

Intra-cardiac Side-Firing Light Catheter for Monitoring Cellular Metabolism using Transmural Absorbance Spectroscopy of Perfused Mammalian Hearts

Absorbance spectroscopy of cardiac muscle provides non-destructive assessment of cytosolic and mitochondrial oxygenation via myoglobin and cytochrome absorbance respectively. In addition, numerous aspects of the mitochondrial metabolic status such as membrane potential and substrate entry can also be estimated. To perform cardiac wall transmission optical spectroscopy, a commercially available side-firing optical fiber catheter is placed in the left ventricle of the isolated perfused heart as a light source. Light passing through the heart wall is collected with an external optical fiber to perform optical spectroscopy of the heart in near real- time. The transmission approach avoids numerous surface scattering interference occurring in widely used reflection approaches. Changes in transmural absorbance spectra were deconvolved using a library of chromophore reference spectra, providing quantitative measures of all the known cardiac chromophores simultaneously. This spectral deconvolution approach eliminated intrinsic errors that may result from using common dual wavelength methods applied to overlapping absorbance spectra, as well as provided a quantitative evaluation of the goodness of fit. A custom program was designed for data acquisition and analysis, which permitted the investigator to monitor the metabolic state of the preparation during the experiment. These relatively simple additions to the standard heart perfusion system provide a unique insight into the metabolic state of the heart wall in addition to conventional measures of contraction, perfusion, and substrate/oxygen extraction.

Here we introduce a method for using an intra-ventricle optical catheter in perfused hearts to perform absorbance spectroscopy across the heart wall. The data obtained provides robust information on tissue oxygen tension as well as substrate utilization and membrane potential simultaneously with cardiac performance measures in this ubiquitous preparation.

Absorbance spectroscopy of cardiac muscle provides non-destructive assessment of cytosolic and mitochondrial oxygenation via myoglobin and cytochrome ...

Mitigation of Blood Borne Cell Attachment to Metal Implants through CD47-Derived Peptide Immobilization

The key complications associated with bare metal stents and drug eluting stents are in-stent restenosis and late stent thrombosis, respectively. Thus, improving the biocompatibility of metal stents remains a significant challenge. The goal of this protocol is to describe a robust technique of metal surface modification by biologically active peptides to increase biocompatibility of blood contacting medical implants, including endovascular stents. CD47 is an immunological species-specific marker of self and has anti-inflammatory properties. Studies have shown that a 22 amino acid peptide corresponding to the Ig domain of CD47 in the extracellular region (pepCD47), has anti-inflammatory properties like the full-length protein. In vivo studies in rats, and ex vivo studies in rabbit and human blood experimental systems from our lab have demonstrated that pepCD47 immobilization on metals improves their biocompatibility by preventing inflammatory cell attachment and activation. This paper describes the step-by step protocol for the functionalization of metal surfaces and peptide attachment. The metal surfaces are modified using polyallylamine bisphosphate with latent thiol groups (PABT) followed by deprotection of thiols and amplification of thiol-reactive sites via reaction with polyethyleneimine installed with pyridyldithio groups (PEI-PDT). Finally, pepCD47, incorporating terminal cysteine residues connected to the core peptide sequence through a dual 8-amino-3,6-dioxa-octanoyl spacer, are attached to the metal surface via disulfide bonds. This methodology of peptide attachment to metal surface is efficient and relatively inexpensive and thus can be applied to improve biocompatibility of several metallic biomaterials.

Presented here is a protocol for appending peptide CD47 (pepCD47) to metal stents using polybisphosphonate chemistry. Functionalization of metal stents using pepCD47 prevents the attachment and activation of inflammatory cells thus improving their biocompatibility.

The key complications associated with bare metal stents and drug eluting stents are in-stent restenosis and late stent thrombosis, respectively. Thus, ...

Blood Flow Imaging with Ultrafast Doppler

The pulsed-Doppler effect is the main technique used in clinical echography to assess blood flow. Applied with conventional focused ultrasound Doppler modes, it has several limits. Firstly, a finely tuned signal filtering operation is needed to distinguish blood flows from surrounding moving tissues. Secondly, the operator must choose between localizing the blood flows or quantifying them. In the last two decades, ultrasound imaging has undergone a paradigm shift with the emergence of ultrafast ultrasound using unfocused waves. In addition to a hundredfold increase in framerate (up to 10000 Hz), this new technique also breaks the conventional quantification/localization trade-off, offering a complete blood flow mapping of the field of view and a simultaneous access to fine velocities measurements at the single-pixel level (down to 50 &#181;m). This data continuity in both spatial and temporal dimensions strongly improves the tissue/blood filtering process, which results in an increase sensitivity to small blood flow velocities (down to 1 mm/s). In this method paper, we aim to introduce the concept of ultrafast Doppler as well as its main parameters. Firstly, we summarize the physical principles of unfocused wave imaging. Then, we present the Doppler signal processing main steps. Particularly, we explain the practical implementation of the critical tissue/blood flow separation algorithms and on the extraction of velocities from these filtered data. This theoretical description is supplemented by in vitro experiences. A tissue phantom embedding a canal with flowing blood-mimicking fluid is imaged with a research programmable ultrasound system. A blood flow image is obtained and the flow characteristics are displayed for several pixels in the canal. Finally, a review of in vivo applications is proposed, showing examples in several organs such as carotids, kidney, thyroid, brain and heart.

This protocol shows how to apply ultrafast ultrasound Doppler imaging to quantify blood flows. After a 1 s long acquisition, the experimenter has access to a movie of the full field of view with axial velocity values for each pixel every &#8776;0.3 ms (depending on the ultrasound time of flight).

The pulsed-Doppler effect is the main technique used in clinical echography to assess blood flow. Applied with conventional focused ultrasound Doppler ...

&quot;Avatar&quot;- Optimized Ex Vivo Work Loop Experiment to Emulate In Vivo Muscle Force

"Avatar", a Modified Ex vivo Work Loop Experiments Using In vivo Strain and Activation

Movement behaviors are emergent features of dynamic systems that result from muscle force production and work output. The interplay between neural and mechanical systems occurs at all levels of biological organization concurrently, from the tuning of leg muscle properties while running to the dynamics of the limbs interacting with the ground. Understanding the conditions under which animals shift their neural control strategies toward intrinsic muscle mechanics (&#39;preflexes&#39;) in the control hierarchy would allow muscle models to predict in vivo muscle force and work more accurately. To understand in vivo muscle mechanics, ex vivo investigation of muscle force and work under dynamically varying strain and loading conditions similar to in vivo locomotion is required. In vivo strain trajectories typically exhibit abrupt changes (i.e., strain and velocity transients) that arise from interactions among neural activation, musculoskeletal kinematics, and loads applied by the environment. The principal goal of our &#34;avatar&#34; technique is to investigate how muscles function during abrupt changes in strain rate and loading when the contribution of intrinsic mechanical properties to muscle force production may be highest. In the &#34;avatar&#34; technique, the traditional work-loop approach is modified using measured in vivo strain trajectories and electromyographic (EMG) signals from animals during dynamic movements to drive ex vivo muscles through multiple stretch-shortening cycles. This approach is similar to the work-loop technique, except that in vivo strain trajectories are scaled appropriately and imposed on ex vivo mouse muscles attached to a servo motor. This technique allows one to: (1) emulate in vivo strain, activation, stride frequency, and work-loop patterns; (2) vary these patterns to match in vivo force responses most accurately; and (3) vary specific features of strain and/or activation in controlled combinations to test mechanistic hypotheses.

Author Spotlight: Bridging the Gap Between In Vivo and Ex Vivo Studies with the &quot;Avatar&quot; Technique to Advance Muscle Mechanics Research 

This article details the methodology for emulating in vivo muscle force production during ex vivo work loop experiments using an "avatar" muscle from a laboratory rodent to assess the contributions of strain transients and activation to the muscle force response.

Movement behaviors are emergent features of dynamic systems that result from muscle force production and work output. The interplay between neural and ...

Preparation of Cardiomyocytes and Setting-Up the Apparatus for the Slow Injection Method

Prepare the 10%gelatin stock solution by weighing and dissolving the gelatin in the ADS buffer, and autoclaving the solution. Rewarm the 10%gelatin stock at 37 degrees Celsius, until it becomes liquid. Then dilute the gelatin stock, using a prewarmed ADS buffer, to obtain the final injectable 5%gelatin solution.Suspend 96 cardiomyocyte balls in 100 microliters of prewarmed injection solution. Load the cardiomyocyte ball suspension into the cell injection syringe without aspirating the excess air. Next, hold the syringe vertically, with the needle facing upward, and tap the syringe to collect the bubbles at the upper ridge of the syringe.Also, observe the cardiomyocyte balls gradually settling onto the rubber seal of the plunger. Maintain the vertical position of the syringe, and slowly push the plunger to discard the bubbles and excess cell suspension solution, until 20 microliters of the cell suspension remain in the syringe, and the cardiomyocyte ball remains resting on the rubber seal of the plunger. Once done, immerse the capped syringe in an ice bath for five minutes, and fix the injection syringe apparatus on the animal stage before activating the main syringe pump during percutaneous cell transplantation in an anesthetized rat.

Analysis of Blood-Brain Barrier Models via Immunofluorescence Staining

Use of the MicroSiM (&#181;SiM) Barrier Tissue Platform for Modeling the Blood-Brain Barrier

The microSiM (&#181;SiM) is a membrane-based culture platform for modeling the blood-brain barrier (BBB). Unlike conventional membrane-based platforms, the&#160;&#181;SiM provides experimentalists with new capabilities, including live cell imaging, unhindered paracrine signaling between &#39;blood&#39; and &#39;brain&#39; chambers, and the ability to directly image immunofluorescence without the need for the extraction/remounting of membranes. Here we demonstrate the basic use of the platform to establish monoculture (endothelial cells) and co-culture (endothelial cells and pericytes) models of the BBB using ultrathin nanoporous silicon-nitride membranes. We demonstrate compatibility with both primary cell cultures and human induced pluripotent stem cell (hiPSC) cultures. We provide methods for qualitative analysis of BBB models via immunofluorescence staining and demonstrate the use of the &#181;SiM for the quantitative assessment of barrier function in a small molecule permeability assay. The methods provided should enable users to establish their barrier models on the platform, advancing the use of tissue chip technology for studying human tissues.

Author Spotlight: Advancing the Use of Tissue Chip Technology for Studying Human Tissues 

This report provides protocols for assembly, cell culture, and assays on the &#181;SiM platform for the construction of blood-brain barrier models.

The microSiM (&#181;SiM) is a membrane-based culture platform for modeling the blood-brain barrier (BBB). Unlike conventional membrane-based platforms, ...