The authors thank Tyra Witt, Cheri Mueske, Brant Newman and Dr. Peter J. Psaltis, MBBS, PhD for their valuable contributions. This study was financially supported by European Regional Development Fund &#8211; FNUSA-ICRC (No. CZ.1.05/1.100/02.0123), American Heart Association Scientist Development Grant (AHA #06-35185N), National Institutes of Health (T32HL007111) and The Grainger Innovation Fund &#8211; Grainger Foundation.

All animal studies were approved by the Institutional Animal Care and Utilization Committee (IACUC) at Mayo Clinic.
1. Design and Analysis of a 2205 Stainless Steel Stent
<ol>
	<li>Designing a bare metal stent using CAD
	<ol>
		<li>Make an extruded hollow cylinder by selecting on &#8216;extruded boss/base&#8217; feature with the wall thickness equal to the stent strut thickness.</li>
		<li>Design a stent pattern on a different sketch plane tangential to the extruded cylinder. Make the width ...

<ol>
	<li>Garg, S., Serruys, P. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Coronary+stents:+current+status.">Coronary stents: current status.</a> J Am Coll Cardiol. 56, 1-42 (2010).</li><li>Austin, D., 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=Drug-eluting+stents+versus+bare-metal+stents+for+off-label+indications:+a+propensity+score-matched+outcome+study.">Drug-eluting stents versus bare-metal stents for off-label indications: a propensity score-matched outcome study.</a> Circ Cardiovasc Interv. 1 (1), 45-52 (2008).</li><li>Polyak, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High+field+gradient+targeting+of+magnetic+nanoparticle-loaded+endothelial+cells+to+the+surfaces+of+steel+stents.">High field gradient targeting of magnetic nanoparticle-loaded endothelial cells to the surfaces of steel stents.</a> P Natl Acad Sci USA. 105 (2), 698-703 (2008).</li><li>Tassiopoulos, A. 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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=Magnetic+forces+enable+rapid+endothelialization+of+synthetic+vascular+grafts.">Magnetic forces enable rapid endothelialization of synthetic vascular grafts.</a> Circulation. 114, I314-I318 (2006).</li><li>Uthamaraj, S., 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=Design+and+validation+of+a+novel+ferromagnetic+bare+metal+stent+capable+of+capturing+and+retaining+endothelial+cells).">Design and validation of a novel ferromagnetic bare metal stent capable of capturing and retaining endothelial cells).</a> Ann Biomed Eng. 42 (12), 2416-2424 (2014).</li><li>Gulati, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Diverse+origin+and+function+of+cells+with+endothelial+phenotype+obtained+from+adult+human+blood.">Diverse origin and function of cells with endothelial phenotype obtained from adult human blood.</a> Circ Res. 93 (11), 1023-1025 (2003).</li><li>Lee, 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=Nanoparticles+of+magnetic+ferric+oxides+encapsulated+with+poly(D,L+latide-co-glycolide)+and+their+applications+to+magnetic+resonance+imaging+contrast+agent.">Nanoparticles of magnetic ferric oxides encapsulated with poly(D,L latide-co-glycolide) and their applications to magnetic resonance imaging contrast agent.</a> J Magn Magn Mater. 272 (3 Special Issue), 2432-2433 (2004).</li><li>Lee, 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=Magnetic+enhancement+of+iron+oxide+nanoparticles+encapsulated+with+poly(D,L-latide-co-glycolide).">Magnetic enhancement of iron oxide nanoparticles encapsulated with poly(D,L-latide-co-glycolide).</a> Colloid Surface A. (1-3), 255-251 (1016).</li><li>Forbes, Z. 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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=Magnetic+stent+hyperthermia+for+esophageal+cancer:+an+in+vitro+investigation+in+the+ECA-109+cell+line.">Magnetic stent hyperthermia for esophageal cancer: an in vitro investigation in the ECA-109 cell line.</a> Oncol Rep. 27 (3), 791-797 (2012).</li><li>Gunn, J., Cumberland, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Does+stent+design+influence+restenosis.">Does stent design influence restenosis.</a> Eur Heart J. 20 (14), 1009-1013 (1999).</li><li>Aviles, M. 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=In+vitro+study+of+ferromagnetic+stents+for+implant+assisted-magnetic+drug+targeting.">In vitro study of ferromagnetic stents for implant assisted-magnetic drug targeting.</a> J Magn Magn Mater. 311 (1), 306-311 (2007).</li><li>Mardinoglu, A., 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=Theoretical+modelling+of+physiologically+stretched+vessel+in+magnetisable+stent+assisted+magnetic+drug+targeting+application.">Theoretical modelling of physiologically stretched vessel in magnetisable stent assisted magnetic drug targeting application.</a> J Magn Magn Mater. 323 (3-4), 324-329 (2011).</li><li>Liu, Z. 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=Stress+corrosion+cracking+of+2205+duplex+stainless+steel+in+H2S-CO2+environment.">Stress corrosion cracking of 2205 duplex stainless steel in H2S-CO2 environment.</a> J Mater Sci. 44 (16), 4228-4234 (2009).</li><li>Alverez-Armas, I., Degallaix-Moreuill, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Duplex stainless steels. , (2009).</li><li>Tefft, B. 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=Magnetizable+Duplex+Steel+Stents+Enable+Endothelial+Cell+Capture.">Magnetizable Duplex Steel Stents Enable Endothelial Cell Capture.</a> Ieee T Magn. 49 (1), 463-466 (2013).</li><li>Pelton, A. R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fatigue+and+durability+of+Nitinol+stents.">Fatigue and durability of Nitinol stents.</a> J Mech Behav Biomed Mater. 1 (2), 153-164 (2008).</li><li>Knowles, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Finite+element+analysis+of+a+balloon-expandable+stent+and+superior+mesenteric+arterial+wall+interaction.">Finite element analysis of a balloon-expandable stent and superior mesenteric arterial wall interaction.</a> J Vasc Surg. 60 (6), 1722-1723 (2014).</li><li>Veeram Reddy, S. 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We developed a magnetic stent which can function as a bare metal stent and can attract SPION-labeled endothelial cells. In previous studies involving magnetic stents, researchers have used nickel coated commercial stents and coils or meshes made of magnetic materials due to the unavailability of a ferromagnetic stent5,10-14. Other groups have also used the paramagnetic nature of commercially available 304-grade stainless steel stents for targeting nanoparticle loaded endothelial cells3. Nickel coati...

Patients implanted with vascular stents manufactured from thrombogenic materials like stainless steel, cobalt chromium, and platinum chromium &#8211; both bare metal stents (BMS) and drug eluting stents (DES) &#8211; need anti-platelet therapy to prevent thrombus formation. BMS heal rapidly, but are subject to late stage restenosis due to incomplete healing. DES require long term anti-platelet therapy due to delayed healing. Anti-platelet therapy administered to avoid thrombosis as a result of incomplete or delayed healing leads to increased bleeding risk and may not be suitable for certain patients1,2. An ideal stent will heal completely and quickly thus avoiding long-term anti-platelet therapy and late stage restenosis. This complete healing can only be achieved if the stent is rapidly coated with a monolayer of endothelial cells after implantation. Coating the stents with biocompatible materials such as gold or other biopolymers has been shown to improve thrombo-resistance, but none of these techniques achieved ideal blood compatibility as may be possible by coating with endothelial cells3,4.
A stent can be coated with endothelial cells post implantation by attracting circulating progenitor cells. This self-seeding technique can be achieved by utilizing ligands and antibodies. But this technique is limited by the low number of circulating endothelial progenitor cells. A promising strategy is to deliver cells directly to the stent immediately following implantation during a short period of blood flow occlusion3,5. This strategy requires a technique for rapidly capturing cells and retaining them on the stent even after restoring blood flow. We have developed a technique in which a magnetic stent is used to attract and retain magnetically-labeled endothelial cells delivered post implantation. To achieve this, a functional BMS with sufficient magnetic properties to capture and retain magnetically-labeled endothelial cells is required6.
In this paper, we discuss the methods for designing, manufacturing, and testing a 2205 stainless steel stent. The stents were designed using CAD and FEA. The manufactured stents were magnetized using a neodymium magnet and the retained magnetic field was measured using a magneto-resistance microsensor probe. We then tested the stents for magnetically-labeled cell capture in a culture dish during our in-vitro experiments. Finally, the stents were tested in-vivo by implanting magnetic and non-magnetic stents in 4 pigs and histologically analyzing the stented arteries.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>2205 Stainless steel</td>
			<td>Carpenter Technology Corporation</td>
			<td>N/A</td>
			<td>Round bar stock material</td>
		</tr>
		<tr>
			<td>Abaqus</td>
			<td>Dassault systems</td>
			<td>N/A</td>
			<td>Software</td>
		</tr>
		<tr>
			<td>Atropine</td>
			<td></td>
			<td></td>
			<td>Prescription drug.</td>
		</tr>
		<tr>
			<td>Clopidogrel</td>
			<td></td>
			<td></td>
			<td>Commercial name: Plavix. Prescription drug.</td>
		</tr>
		<tr>
			<td>CM-DiI</td>
			<td>Life Technologies</td>
			<td>V-22888</td>
			<td>Molecular Probes, Eugene, OR</td>
		</tr>
		<tr>
			<td>Endothelial growth medium-2</td>
			<td>Lonza</td>
			<td>CC-3162</td>
			<td></td>
		</tr>
		<tr>
			<td>Hand Held Crimping tool</td>
			<td>Blockwise engineering</td>
			<td>M1-RMC</td>
			<td></td>
		</tr>
		<tr>
			<td>Hydrochloric acid (HCl)</td>
			<td>Sigma Aldrich</td>
			<td>MFCD00011324</td>
			<td>CAUTION: wear proptective equipment and handle under fume hood</td>
		</tr>
		<tr>
			<td>Isoflurane anesthesia</td>
			<td>Piramal Critical Care, Inc.&#160;</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Isopropyl alcohol</td>
			<td>Sigma Aldrich</td>
			<td>MFCD00011674</td>
			<td></td>
		</tr>
		<tr>
			<td>NdFeB magnet 2&#34; Dia x 1&#34; thick</td>
			<td>Amazing magnets</td>
			<td>D1000P</td>
			<td>Axially magnetized disc magnet with poles on flat faces</td>
		</tr>
		<tr>
			<td>Over-The-Wire trifold balloon</td>
			<td>N/A</td>
			<td>N/A</td>
			<td>Any commercially available OTW trifold balloon can be used</td>
		</tr>
		<tr>
			<td>Phosphate buffered saline</td>
			<td>Life Technologies</td>
			<td>10010-023</td>
			<td>Commonly known as PBS</td>
		</tr>
		<tr>
			<td>Sodium Bicarbonate (NaHCO3)</td>
			<td>Sigma Aldrich</td>
			<td>MFCD00003528</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium pentobarbital</td>
			<td>Zoetis</td>
			<td></td>
			<td>Commercial Name: Sleepaway (26%), FatalPlus, Beuthanasi.&#160; Controlled substance to be ordered only by licensed veternarian</td>
		</tr>
		<tr>
			<td>SolidWorks</td>
			<td>Dassault systems</td>
			<td>N/A</td>
			<td>Software</td>
		</tr>
		<tr>
			<td>SpinTJ-020 micro sensor</td>
			<td>MicroMagneitcs Sensible Solutions</td>
			<td>N/A</td>
			<td>Long probe STJ-020 microsensor</td>
		</tr>
		<tr>
			<td>SPION</td>
			<td>Mayo Clinic</td>
			<td>N/A</td>
			<td>Nanoparticles synthesized internally (Ref: Lee, S. J. et al. Nanoparticles of magnetic ferric oxides encapsulated with poly(D,L latide-co-glycolide) and their applications to magnetic resonance imaging contrast agent. J Magn Magn Mater 272, 2432-2433, doi:DOI 10.1016/j.jmmm.2003.12.416 (2004))</td>
		</tr>
		<tr>
			<td>Telazol</td>
			<td>Zoetis</td>
			<td></td>
			<td>Controlled substance to be ordered only by licensed veternarian</td>
		</tr>
		<tr>
			<td>Trypsin EDTA</td>
			<td>Life Technologies</td>
			<td>25200-056</td>
			<td>Gibco, Grand Island, NY</td>
		</tr>
		<tr>
			<td>Xylazine</td>
			<td>Bayer Animal Health</td>
			<td></td>
			<td>Commercial name: Rompun. Controlled sunstance to be ordered only by a licensed veternarian</td>
		</tr>
	</tbody>
</table>

ferromagnetic bare metal stent for endothelial cell capture and retention

Rapid endothelialization of cardiovascular stents is needed to reduce stent thrombosis and to avoid anti-platelet therapy which can reduce bleeding risk. The feasibility of using magnetic forces to capture and retain endothelial outgrowth cells (EOC) labeled with super paramagnetic iron oxide nanoparticles (SPION) has been shown previously. But this technique requires the development of a mechanically functional stent from a magnetic and biocompatible material followed by in-vitro and in-vivo testing to prove rapid endothelialization. We developed a weakly ferromagnetic stent from 2205 duplex stainless steel using computer aided design (CAD) and its design was further refined using finite element analysis (FEA). The final design of the stent exhibited a principal strain below the fracture limit of the material during mechanical crimping and expansion. One hundred stents were manufactured and a subset of them was used for mechanical testing, retained magnetic field measurements, in-vitro cell capture studies, and in-vivo implantation studies. Ten stents were tested for deployment to verify if they sustained crimping and expansion cycle without failure. Another 10 stents were magnetized using a strong neodymium magnet and their retained magnetic field was measured. The stents showed that the retained magnetism was sufficient to capture SPION-labeled EOC in our in-vitro studies. SPION-labeled EOC capture and retention was verified in large animal models by implanting 1 magnetized stent and 1 non-magnetized control stent in each of 4 pigs. The stented arteries were explanted after 7 days and analyzed histologically. The weakly magnetic stents developed in this study were capable of attracting and retaining SPION-labeled endothelial cells which can promote rapid healing.

Iterative stent design based on FEA (Figure 1) showed a stent which can crimp and expand with a principal strain of 20% which is less than the 30% ultimate strain. Crimping and expansion test (Figure 2) showed no signs of fracture. Pictures of the deformed stent showed good agreement with FEA calculated deformations and also microscopy pictures showed no fractures (Figure 3). As expected from the retained magnetic field measurements (Figures 4 &#38; 5), ...

Watch this Scientific Journal Video about Ferromagnetic Bare Metal Stent for Endothelial Cell Capture and Retention at JoVE.com

Ferromagnetic Bare Metal Stent for Endothelial Cell Capture and Retention

Our goals were to design, manufacture and test ferromagnetic stents for endothelial cell capture. Ten stents were tested for fracture and 10 more stents were tested for retained magnetism. Finally, 10 stents were tested in-vitro and 8 more stents were implanted in 4 pigs to show cell capture and retention.

Rapid endothelialization of cardiovascular stents is needed to reduce stent thrombosis and to avoid anti-platelet therapy which can reduce bleeding risk. ...

ferromagnetic-bare-metal-stent-for-endothelial-cell-capture

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Bioengineering

11.4K vistas.  Mayo Clinic.  Nuestros objetivos eran para diseñar, fabricar y probar los stents ferromagnéticos para la captura de las células endoteliales. Diez stents fueron probados para la fractura y 10 más stents se ensayaron para determinar el magnetismo retenido. Finalmente, 10 stents se probaron in vitro y 8 más stents fueron implantados en 4 cerdos para mostrar la captura de células y la retención. 