Name: Fabrication of Small Caliber Stent-grafts Using Electrospinning and Balloon Expandable Bare Metal Stents (Video) | JoVE Journal
Uploaded: 2016-10-26T15:00:00.000+00:00
Duration: 6 min 55 s
Description: Learn to fabricate small caliber stent-grafts using electrospinning and balloon expandable bare metal stents. This method encapsulates stents in polyurethane nanofibers for improved healing and new medical applications.

ai_agent_IP

ai_agent

maintenance

instantTrialDurationMinutes

isBiopharma

enableNewMyJoveSectionDesign

educationFeatures

seoMetaApi

ai_copilot_institution_blacklist

ai_chat_institution_blacklist

freeAccessWindow

ssoRoleCapture

scheduledMaintenanceBanner

joveLabsFeatures

disable_autoplay_for_bots

extended_trial_duration

5 minutes

We would like to thank the Division of Engineering, Mayo Clinic for their technical support. This study was financially supported by European Regional Development Fund - FNUSA-ICRC (No. CZ.1.05/1.100/02.0123), National Institutes of Health (T32 HL007111), American Heart Association Scientist Development Grant (AHA #06-35185N), and The Grainger Innovation Fund - Grainger Foundation.

1. Electrospinning of Polyurethane on Mandrel Collector
<ol>
	<li>Prepare mandrel for electrospinning
	<ol>
		<li>Melt approximately 8 ml of biocompatible, food-grade, water soluble support material in a graduated cylinder (approximately 9 mm diameter and 110 mm deep) at 155 &#176;C using an oven.</li>
		<li>Dip a 3 mm diameter and 100 mm long stainless steel mandrel to obtain a coating of support material on the surface of the mandrel. Prior to dipping, place the mandrels in the oven at 155 &#176;C for approximately 15 min to raise the temperature of the mandrel surface which helps in wetting the surface with the molten support material.</li>
		<li>Let the dipped mandrel cool to approximately 140 &#176;C while the molten support material solidifies forming a uniform thin coating on the mandrel surface. During the cooling process, hang the mandrel vertically so that gravity causes excess support material to drip off. This coating enables easy removal of the finished stent-graft from the mandrel.</li>
	</ol>
	</li>
	<li>Setup of the mandrel collector of the electrospinning system (as shown in Figure 1)
	<ol>
		<li>Align the laboratory mixer horizontally and connect a plastic rod which will hold the stainless steel mandrel at the opposite end inside the fume hood.</li>
		<li>Dissolve the support material from the tip of the mandrel by submerging only the tip of the mandrel in water to accommodate the plastic support rod at the end of the mandrel. Support the plastic support rod at the free end of the mandrel to assist in uniform rotation of the mandrel collector.</li>
		<li>Use set screws in the plastic support rods to secure the stainless steel mandrel and avoid slipping during electrospinning.</li>
		<li>Ground the mandrel collector by attaching a U-shaped ground wire to the stainless steel mandrel. Use rubber O-rings to hold the ground wire to the sides of the mandrel.</li>
	</ol>
	</li>
	<li>Setting up liquid polyurethane extrusion system of the electrospinning system
	<ol>
		<li>Mix dimethylacetamide (DMA) with 25% (m/v) polyurethane (PU) stock solution to obtain 15% (m/v) PU in DMA solution (e.g., add 6 ml of DMA to 9 ml of 25% PU solution). 
		CAUTION! Work inside a fume hood with proper personal protective equipment.</li>
		<li>Fill a 5 ml glass syringe with blunt end stainless steel needle (spinneret) with 15% PU solution.</li>
		<li>Program the syringe pump to extrude at 0.01 ml/min based on the inner diameter of the syringe.</li>
		<li>Mount the syringe with spinneret on the syringe pump horizontally with the needle tip approximately 20 cm from the mandrel collector. Insulate the syringe from the conductive parts of the syringe pump using rubber sheets to avoid electrical arcing.</li>
		<li>Connect the high voltage generator to the spinneret of the syringe using an alligator clip.</li>
	</ol>
	</li>
	<li>Run the syringe pump at 0.01 ml/min and rotate the mandrel with the laboratory mixer running at slow speed (e.g., 50 rpm).</li>
	<li>Apply a voltage differential of 20 kV across the spinneret and the collector mandrel. PU nanofibers will start depositing on the rotating mandrel and a thin layer will be visible within several minutes. Ensure the fume hood is turned off and exhaust is closed to avoid loss of electrospun nanofibers.</li>
</ol>
2. Electrospinning a Stent-graft
<ol>
	<li>Electrospin PU nanofibers on a rotating mandrel for 2 hr to create a uniform tube (as explained in step 1).</li>
	<li>Remove the mandrel from the plastic rod connected to the laboratory mixer to install the bare metal stent. Turn on fume hood and open exhaust prior to removing the mandrel to ensure that remnant solvent fumes are removed.</li>
	<li>Slide the balloon expandable stainless steel stent26 onto the electrospun tube to a desired location. It may be necessary to slightly expand the stent so it slips on without damaging the electrospun tube.</li>
	<li>Crimp the stent to make sure that the stent is tightly set on the tube material on the mandrel and not loose enough to slide. This will also help to prevent delamination of the inner and outer layers.</li>
	<li>Load the mandrel with tube and stent again on the plastic rod of the laboratory mixer for electrospinning the outer layer of the stent-graft.</li>
	<li>Electrospin nanofibers for 3 hr as explained in step 1 to fabricate the outer layer of the stent-graft.</li>
	<li>After electrospinning the outer later, circumferentially cut the PU material approximately 1 mm from the ends of the stent using a scalpel.</li>
	<li>Soak the mandrel with stent-graft in deionized water to dissolve the support material from the mandrel which will release the stent-graft from mandrel. Replace with fresh water as needed to dissolve the support material completely.</li>
	<li>Once the support material is dissolved, gently remove the stent-graft from the mandrel and allow to dry. Consider soaking the removed stent-graft in deionized water to dissolve any remaining support material before allowing to air dry.</li>
</ol>
3. Testing of Manufactured Stent-grafts
<ol>
	<li>Slide the stent-graft on a 3 mm trifold balloon.</li>
	<li>Crimp the stent-graft onto the balloon using a hand held crimping tool.</li>
	<li>Inspect the crimped stent-graft using a microscope for uniform crimping and any other signs of failure like delamination or puncture of the cover material due to stent deformation.</li>
	<li>Expand the stent-graft to the designed diameter of 3 mm by pressurizing the trifold balloon with an inflation device and water. Again, examine the expanded stent-graft for uniform expansion and signs of failure.</li>
</ol>

<ol><li>Elsner, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Coronary+stent+grafts+covered+by+a+polytetrafluoroethylene+membrane%5BTitle%5D)+AND+%22Am.+J.+Cardiol%22%5BJournal%5D)">Coronary stent grafts covered by a polytetrafluoroethylene membrane.</a> Am. J. Cardiol. 84 (3), 335-338 (1999).</li>
<li>Störger, H., Haase, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Polytetrafluoroethylene-Covered+Stents%3A+Indications%2C+Advantages%2C+and+Limitations%5BTitle%5D)+AND+%22J.+Interv.+Cardiol%22%5BJournal%5D)">Polytetrafluoroethylene-Covered Stents: Indications, Advantages, and Limitations.</a> J. Interv. Cardiol. 12 (6), 451-456 (1999).</li>
<li>Moreno, P. R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Macrophage+infiltration+predicts+restenosis+after+coronary+intervention+in+patients+with+unstable+angina%5BTitle%5D)+AND+%22Circulation%22%5BJournal%5D)">Macrophage infiltration predicts restenosis after coronary intervention in patients with unstable angina.</a> Circulation. 94 (12), 3098-3102 (1996).</li>
<li>Briguori, C., Sarais, C., Colombo, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((The+polytetrafluoroethylene-covered+stent%3A+a+device+with+multiple+potential+advantages%5BTitle%5D)+AND+%22Int.+J.+Cardiovasc.+Interv%22%5BJournal%5D)">The polytetrafluoroethylene-covered stent: a device with multiple potential advantages.</a> Int. J. Cardiovasc. Interv. 4 (3), 145-149 (2001).</li>
<li>Qureshi, M. A., Martin, Z., Greenberg, R. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Endovascular+management+of+patients+with+Takayasu+arteritis%3A+stents+versus+stent+grafts%5BTitle%5D)+AND+%22Semin.+Vasc.+Surg%22%5BJournal%5D)">Endovascular management of patients with Takayasu arteritis: stents versus stent grafts.</a> Semin. Vasc. Surg. 24 (1), 44-52 (2011).</li>
<li>Ahmadi, R., Schillinger, M., Maca, T., Minar, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Femoropopliteal+arteries%3A+immediate+and+long-term+results+with+a+Dacron-covered+stent-graft%5BTitle%5D)+AND+%22Radiology%22%5BJournal%5D)">Femoropopliteal arteries: immediate and long-term results with a Dacron-covered stent-graft.</a> Radiology. 223 (2), 345-350 (2002).</li>
<li>Geremia, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Experimental+arteriovenous+fistulas%3A+treatment+with+silicone-covered+metallic+stents%5BTitle%5D)+AND+%22AJNR.+Am.+J.+Neuroradiol%22%5BJournal%5D)">Experimental arteriovenous fistulas: treatment with silicone-covered metallic stents.</a> AJNR. Am. J. Neuroradiol. 18 (2), 271-277 (1997).</li>
<li>Saatci, I., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Treatment+of+internal+carotid+artery+aneurysms+with+a+covered+stent%3A+experience+in+24+patients+with+mid-term+follow-up+results%5BTitle%5D)+AND+%22AJNR.+Am.+J.+Neuroradiol%22%5BJournal%5D)">Treatment of internal carotid artery aneurysms with a covered stent: experience in 24 patients with mid-term follow-up results.</a> AJNR. Am. J. Neuroradiol. 25 (10), 1742-1749 (2004).</li>
<li>Stefanadis, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Stents+Wrapped+in+Autologous+Vein%3A+An+Experimental+Study1%5BTitle%5D)+AND+%22J.+Am.+Coll.+Cardiol%22%5BJournal%5D)">Stents Wrapped in Autologous Vein: An Experimental Study1.</a> J. Am. Coll. Cardiol. 28 (4), 1039-1046 (1996).</li>
<li>Palmaz, J. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Review+of+polymeric+graft+materials+for+endovascular+applications%5BTitle%5D)+AND+%22J.+Vasc.+Interv.+Radiol%22%5BJournal%5D)">Review of polymeric graft materials for endovascular applications.</a> J. Vasc. Interv. Radiol. 9, 7-13 (1998).</li>
<li>Bruckheimer, E., Dagan, T., Amir, G., Birk, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Covered+Cheatham-Platinum+stents+for+serial+dilation+of+severe+native+aortic+coarctation%5BTitle%5D)+AND+%22Catheter+Cardiovasc.+Interv%22%5BJournal%5D)">Covered Cheatham-Platinum stents for serial dilation of severe native aortic coarctation.</a> Catheter Cardiovasc. Interv. 74 (1), 117-123 (2009).</li>
<li>Tzifa, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Covered+Cheatham-platinum+stents+for+aortic+coarctation%3A+early+and+intermediate-term+results%5BTitle%5D)+AND+%22J.+Am.+Coll.+Cardiol%22%5BJournal%5D)">Covered Cheatham-platinum stents for aortic coarctation: early and intermediate-term results.</a> J. Am. Coll. Cardiol. 47 (7), 1457-1463 (2006).</li>
<li>Kuraishi, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Development+of+nanofiber-covered+stents+using+electrospinning%3A+in+vitro+and+acute+phase+in+vivo+experiments%5BTitle%5D)+AND+%22J.+Biomed.+Mater.+Res.+Part+B+Appl.+Biomater%22%5BJournal%5D)">Development of nanofiber-covered stents using electrospinning: in vitro and acute phase in vivo experiments.</a> J. Biomed. Mater. Res. Part B Appl. Biomater. 88 (1), 230-239 (2009).</li>
<li>Pant, S., Bressloff, N. W., Limbert, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Geometry+parameterization+and+multidisciplinary+constrained+optimization+of+coronary+stents%5BTitle%5D)+AND+%22Biomech.+Model+Mechanobiol%22%5BJournal%5D)">Geometry parameterization and multidisciplinary constrained optimization of coronary stents.</a> Biomech. Model Mechanobiol. 11 (1-2), 61-82 (2012).</li>
<li>Muller-Hulsbeck, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Experience+on+endothelial+cell+adhesion+on+vascular+stents+and+stent-grafts%3A+first+in+vitro+results%5BTitle%5D)+AND+%22Invest.+Radiol%22%5BJournal%5D)">Experience on endothelial cell adhesion on vascular stents and stent-grafts: first in vitro results.</a> Invest. Radiol. 37 (6), 314-320 (2002).</li>
<li>Sarkar, S., Salacinski, H. J., Hamilton, G., Seifalian, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((The+mechanical+properties+of+infrainguinal+vascular+bypass+grafts%3A+their+role+in+influencing+patency%5BTitle%5D)+AND+%22Eur.+J.+Vasc.+Endovasc.+Surg%22%5BJournal%5D)">The mechanical properties of infrainguinal vascular bypass grafts: their role in influencing patency.</a> Eur. J. Vasc. Endovasc. Surg. 31 (6), 627-636 (2006).</li>
<li>Shirota, T., Yasui, H., Shimokawa, H., Matsuda, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Fabrication+of+endothelial+progenitor+cell+%28EPC%29-seeded+intravascular+stent+devices+and+in+vitro+endothelialization+on+hybrid+vascular+tissue%5BTitle%5D)+AND+%22Biomaterials%22%5BJournal%5D)">Fabrication of endothelial progenitor cell (EPC)-seeded intravascular stent devices and in vitro endothelialization on hybrid vascular tissue.</a> Biomaterials. 24 (13), 2295-2302 (2003).</li>
<li>Grasl, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Electrospun+polyurethane+vascular+grafts%3A+in+vitro+mechanical+behavior+and+endothelial+adhesion+molecule+expression%5BTitle%5D)+AND+%22J.+Biomed.+Mater.+Res.+A%22%5BJournal%5D)">Electrospun polyurethane vascular grafts: in vitro mechanical behavior and endothelial adhesion molecule expression.</a> J. Biomed. Mater. Res. A. 93 (2), 716-723 (2010).</li>
<li>Kidoaki, S., Kwon, I. K., Matsuda, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Structural+features+and+mechanical+properties+of+in+situ-bonded+meshes+of+segmented+polyurethane+electrospun+from+mixed+solvents%5BTitle%5D)+AND+%22J.+Biomed.+Mater.+Res.+Part+B+Appl.+Biomater%22%5BJournal%5D)">Structural features and mechanical properties of in situ-bonded meshes of segmented polyurethane electrospun from mixed solvents.</a> J. Biomed. Mater. Res. Part B Appl. Biomater. 76 (1), 219-229 (2006).</li>
<li>Stegemann, J. P., Kaszuba, S. N., Rowe, S. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Review%3A+advances+in+vascular+tissue+engineering+using+protein-based+biomaterials%5BTitle%5D)+AND+%22Tissue+Eng%22%5BJournal%5D)">Review: advances in vascular tissue engineering using protein-based biomaterials.</a> Tissue Eng. 13 (11), 2601-2613 (2007).</li>
<li>Sankaran, K. K., Subramanian, A., Krishnan, U. M., Sethuraman, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Nanoarchitecture+of+scaffolds+and+endothelial+cells+in+engineering+small+diameter+vascular+grafts%5BTitle%5D)+AND+%22Biotechnol.+J%22%5BJournal%5D)">Nanoarchitecture of scaffolds and endothelial cells in engineering small diameter vascular grafts.</a> Biotechnol. J. 10 (1), 96-108 (2015).</li>
<li>Gibson, P., Schreuder-Gibson, H., Rivin, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Transport+properties+of+porous+membranes+based+on+electrospun+nanofibers%5BTitle%5D)+AND+%22Colloid+Surf.%2C+A%22%5BJournal%5D)">Transport properties of porous membranes based on electrospun nanofibers.</a> Colloid Surf., A. 187, 469-481 (2001).</li>
<li>Zdrahala, R. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Small+caliber+vascular+grafts.+Part+II%3A+Polyurethanes+revisited%5BTitle%5D)+AND+%22J.+Biomater.+Appl%22%5BJournal%5D)">Small caliber vascular grafts. Part II: Polyurethanes revisited.</a> J. Biomater. Appl. 11 (1), 37-61 (1996).</li>
<li>Uthamaraj, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Design+and+validation+of+a+novel+ferromagnetic+bare+metal+stent+capable+of+capturing+and+retaining+endothelial+cells%5BTitle%5D)+AND+%22Ann.+Biomed.+Eng%22%5BJournal%5D)">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>Tefft, B. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Cell+Labeling+and+Targeting+with+Superparamagnetic+Iron+Oxide+Nanoparticles%5BTitle%5D)+AND+%22J.+Vis.+Exp%22%5BJournal%5D)">Cell Labeling and Targeting with Superparamagnetic Iron Oxide Nanoparticles.</a> J. Vis. Exp. (105), e53099(2015).</li>
<li>Uthamaraj, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Ferromagnetic+Bare+Metal+Stent+for+Endothelial+Cell+Capture+and+Retention%5BTitle%5D)+AND+%22J.+Vis.+Exp%22%5BJournal%5D)">Ferromagnetic Bare Metal Stent for Endothelial Cell Capture and Retention.</a> J. Vis. Exp. (103), e53100(2015).</li>
<li>de Giovanni, J. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Covered+stents+in+the+treatment+of+aortic+coarctation%5BTitle%5D)+AND+%22J.+Interv.+Cardiol%22%5BJournal%5D)">Covered stents in the treatment of aortic coarctation.</a> J. Interv. Cardiol. 14 (2), 187-190 (2001).</li>
<li>Hans, F. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Treatment+of+wide-necked+aneurysms+with+balloon-expandable+polyurethane-covered+stentgrafts%3A+experience+in+an+animal+model%5BTitle%5D)+AND+%22Acta.+Neurochir.+%28Wien%29%22%5BJournal%5D)">Treatment of wide-necked aneurysms with balloon-expandable polyurethane-covered stentgrafts: experience in an animal model.</a> Acta. Neurochir. (Wien). 147 (8), 871-876 (2005).</li>
<li>Hasan, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Electrospun+scaffolds+for+tissue+engineering+of+vascular+grafts%5BTitle%5D)+AND+%22Acta.+Biomater%22%5BJournal%5D)">Electrospun scaffolds for tissue engineering of vascular grafts.</a> Acta. Biomater. 10 (1), 11-25 (2014).</li>
</ol>

The authors declare that they have no competing financial interests.

We have developed a fabrication technique for a small caliber stent-graft which can be deployed using a standard percutaneous coronary intervention (PCI) procedure. Stent-grafts currently available are limited in their ability to maintain a low profile and flexibility for deployment. Bare metal stents developed by our group in our previous studies have proven to assist in rapid healing of the stented artery24,26. Various polymers have been electrospun by other groups and polyurethane has been proven biostable ...

Coronary intervention procedures cause significant vessel wall injury due to disruption of the plaque and vessel wall. This results in restenosis, peripheral embolism in vein grafts, and discontinuity of coronary lumen1-4. To avoid these complications, a promising strategy will be to cover the vascular surface in the angioplasty site, which will potentially inhibit restenosis, mitigate risks from discontinuity of vessel lumen, and prevent peripheral embolism. Previous studies have compared bare metal stents to stent-grafts with positive outcomes for stent-grafts5. Researchers have used several materials to manufacture membranes to cover the stents. This includes synthetic materials like polyethylene tetraphthalate (PET), polytetrafluoroethylene (PTFE), polyurethane (PU), and silicon or autologous vessel tissue to manufacture covered stents6-9. An ideal graft material used to cover the stent should be thromboresistant, non-biodegradable, and should integrate with native tissue without excessive proliferation and inflammation10. The graft material used to cover the stent should also promote healing of the stent-graft.
Stent-grafts are widely used for the treatment of aortic coarctation, pseudo-aneurysms of the carotid artery, arteriovenous fistulae, degenerated vein grafts, and large to giant cerebral aneurysms. But the development of small caliber stent-grafts is limited by the ability to maintain low profile and flexibility, which aids in deployment of the stent-grafts11-14. PU is an elastomeric polymer with good mechanical strength which is a desired trait for achieving a low profile and good flexibility15,16. In addition to having good deliverability, stent-grafts should also promote rapid healing and endothelialization. PU covered stent-grafts have demonstrated better biocompatibility and enhanced endothelialization17. Researchers have previously tried to endothelialize PU covered stent-grafts by seeding them with endothelial cells17. Electrospinning of PU to create nanofiber matrix has been shown to be a valuable technique for the production of vascular grafts18,19. The existence of nanofibers that mimic the architecture of native extracellular matrix is also known to promote endothelial cell proliferation20,21. Electrospinning also allows for control over the thickness of the material22. Small caliber vascular grafts made of PU have been studied to promote healing by using modifications such as surface coatings, anti-coagulants, and cell proliferation suppressants. All these modifications are designed to mediate host acceptance and promote graft healing23.
Our group has developed a balloon expandable bare metal stent which can be deployed in animal models24-26. The combination of an electrospun polyurethane mesh and a balloon expandable stent has enabled us to generate small caliber balloon expandable stent-grafts. Most of the currently available stent-grafts are introduced through the femoral artery during an interventional procedure, but only a few commercial covered stents can be introduced 1 French size larger than that required for an un-inflated balloon27. In this study we have developed a small caliber vascular stent-graft by encapsulating a balloon expandable stent between two layers of electrospun PU which can be delivered to a coronary artery using a standard 8-9 French guide catheter in a percutaneous interventional procedure.

<table><tbody><tr><td>Glass syringe</td><td>Air Tite</td><td>7.140-33</td><td>Syringe for spinneret</td></tr><tr><td>Graduated cylinder 5 ml</td><td>Fisher Scientific</td><td>08-552-4G</td><td>5 ml pyrex graduated cylinder about 9 mm diameter and 11 cm long</td></tr><tr><td>High voltage generator</td><td>Bertan Accociates, Inc.</td><td>205A-30P</td><td>Used to apply voltage difference across spinneret and collector</td></tr><tr><td>Laboratory mixer with rpm control</td><td>Scilogex</td><td>SCI-84010201</td><td>Available from various laboratory equipment suppliers</td></tr><tr><td>Polyurethane</td><td>DSM</td><td>BioSpan SPU</td><td>Biospan Segmented Polyurethane</td></tr><tr><td>Rubber sheet</td><td>McMaster Carr</td><td>1370N11</td><td>Used to insulate syringe during electrospinning</td></tr><tr><td>Stainless steel mandrel</td><td>N/A</td><td>N/A</td><td>Manufactured&amp;nbsp;</td></tr><tr><td>Stainless steel needle</td><td>Hamilton</td><td>91018</td><td>Used as spinneret in electrospinning</td></tr><tr><td>Support material</td><td>EnvisionTec</td><td>B04-HT-DEMOMAT</td><td>Biocompatible water soluble material</td></tr><tr><td>Syringe Pump</td><td>Harvard Apparatus</td><td>55-3333</td><td></td></tr></tbody></table>

fabrication of small caliber stent-grafts using electrospinning and balloon expandable bare metal stents

Fabrication of Small Caliber Stent-grafts Using Electrospinning and Balloon Expandable Bare Metal Stents

Stent-grafts are widely used for the treatment of various conditions such as aortic lesions, aneurysms, emboli due to coronary intervention procedures and perforations in vasculature. Such stent-grafts are manufactured by covering a stent with a polymer membrane. An ideal stent-graft should have a biocompatible stent covered by a porous, thromboresistant, and biocompatible polymer membrane which mimics the extracellular matrix thereby promoting injury site healing. The goal of this protocol is to manufacture a small caliber stent-graft by encapsulating a balloon expandable stent within two layers of electrospun polyurethane nanofibers. Electrospinning of polyurethane has been shown to assist in healing by mimicking native extracellular matrix, thereby promoting endothelialization. Electrospinning polyurethane nanofibers on a slowly rotating mandrel enabled us to precisely control the thickness of the nanofibrous membrane, which is essential to achieve a small caliber balloon expandable stent-graft. Mechanical validation by crimping and expansion of the stent-graft has shown that the nanofibrous polyurethane membrane is sufficiently flexible to crimp and expand while staying patent without showing any signs of tearing or delamination. Furthermore, stent-grafts fabricated using the methods described here are capable of being implanted using a coronary intervention procedure using standard size guide catheters.

Our electrospinner setup (Figure 1) has resulted in high quality polyurethane nanofibers (Figure 2). A stent-graft is manufactured by electrospinning an inner layer of polyurethane onto a mandrel, slipping a bare metal stent over this layer, and electrospinning a second outer layer of polyurethane (Figure 3). Polyurethane nanofibers are electrospun at the rate of 50 µm/hr, which results in an inner layer of 100 µm and an outer layer of 150 µm on the stent-grafts. Electro...

In the protocol, we present a method to manufacture a small caliber stent-graft by sandwiching a balloon expandable stent between two electrospun nanofibrous polyurethane layers.

Stent-grafts are widely used for the treatment of various conditions such as aortic lesions, aneurysms, emboli due to coronary intervention procedures and ...

The overall goal of this manufacturing process is to develop a small caliber stent-graft by encapsulating a balloon expandable stent within two layers of electrospun polyurethane nanofibers. This research is helping us develop small caliber stent-grafts that actually heal very quickly, and can potentially open up new medical applications that have not been done before. Advantages of this technique are the stent-grafts are made from polymer nanofibers that mimic extracellular matrix.The fabrication process is also straightforward, and provides favorable mechanical and cell adhesion properties. To begin first melt about 8 milliliters of bio-compatible food grade water soluble support material in a graduated cylinder at 155 degrees Celsius. Also, warm the 100 millimeter long, 3 millimeter wide, stainless steel mandrel to 155 degrees Celsius.Next turn off the oven and dip the mandrel into the support material. Then hang the mandrel vertically in the oven and let the material solidify, which should occur around 140 degrees Celsius. Excess material should drip off the end.Next set up the mandrel collector of the electrospinning system. This requires a laboratory mixer with an attached plastic rod that ends in a grip for the mandrel. Dissolve the support material off the tip of the mandrel so it can attach to the grip.Next use rubber O rings on both sides of the mandrel to protect the electrospun material from the ground-wire, and electrically ground the mandrel with the U-shaped ground-wire. Next attach the exposed mandrel to a short grip at the far end for support. At the other end, attach the mandrel to the rotating rod from the laboratory mixer.Secure both supports to the mandrel using screws, and electrically ground the mandrel. Now set up the liquid polyurethane extrusion system. First, load a five milliliter glass syringe that fits the syringe pump, with freshly made 15%polyurethane solution, and attach a blunt end stainless steel needle, which will function as a spinneret.Taking into account the inner diameter of the syringe, program the pump to extrude the solution at zero point zero one milliliters per minute. To prevent electrical arcing insulate the syringe from the conductive parts of the syringe pumps using rubber sheets. Then position the syringe in the pump so the tip of the spinneret is 20 centimeters from the mandrel collector.Next, connect the high voltage generator to the spinneret using an alligator clip. Before starting the electrospinning, turn off the fume hood exhaust. For operation, start the syringe pump and rotate the mandrel at about 50 RPM.Then apply a voltage differential of 20 kilovolts across the spinneret and the collector mandrel. Polyurethane nanofibers will start depositing on the rotating mandrel and a thin layer will be visible within several minutes. Let the polyurethane nanofibers build up for two hours to make a uniform tube.Once the nanofibers have been spun, turn the hood exhaust back on, and proceed to remove the mandrel from the plastic supports. Then carefully slide the balloon expandable stent onto the electrospun tube without damaging the tube. If necessary slightly expand the stent so that it slips on more easily.Next crimp the stent at the desired location so it is tight to the tube and will not slide around. This will help prevent delamination of the inner and outer layers. Return the mandrel to the set up, and continue the electrospinning as before for three hours to fabricate an outer layer onto the stent-graft.Next while still on the mandrel, circumferentially cut the excess polyurethane approximately one millimeter from each end of the stent using a scalpel. Next soak the mandrel and stent-graft in de-ionized water to dissolve the support material. Change the water as needed until the support material is completely dissolved.Then gently remove the stent-graft from the mandrel and allow it to air dry. To test the stent-graft slide it onto a three millimeter trifold balloon, and crimp it onto the balloon using a handheld crimping tool. Under a microscope, inspect the crimped stent-graft for uniform crimping and any other signs of failure such as delamination or a puncture of the cover material which could occur with a deformed stent.If it looks good, then expand the stent-graft to three millimeters by pressuring the trifold balloon with an inflation device and water. Once expanded use the microscope to inspect the stent-graft once again. Look for uniform expansion and any signs of failure.Using the electrospinner, high quality polyurethane nanofibers can be produced. Electrospinning polyurethane nanofibers using this setup generates a uniform layer of polyurethane at 50 microns of nanofibers per hour. Crimping and expansion of the resulting small caliber stent-graft show that these devices are capable of being deployed using a standard trifold balloon without uneven expansion or signs of material failure.Following this procedure other methods like animal model implantation can be performed to investigate the functionality, durability and performance characteristics of the device. While attempting this procedure, it's important to remember to work in a chemical fume-hood with the exhaust turned off during electrospinning and turned back on prior to removing the sample.

fabrication-small-caliber-stent-grafts-using-electrospinning-balloon

Research

JoVE Journal

Medicine

Electrospun scaffolds can be processed post production for tissue engineering applications. Here we describe methods for spinning complex scaffolds (by consecutive spinning), for making thicker scaffolds (by multi-layering using heat or vapour annealing), for achieving sterility (aseptic production or sterilisation post production) and for achieving appropriate biomechanical properties.

Postproduction Processing of Electrospun Fibres for Tissue Engineering

A model of stent implantation in mouse carotid artery is described. Compared to other similar methods, this procedure is very rapid, simple and accessible, offering the possibility to study in a convenient way the vascular wall reaction to different drug-eluting stents and the molecular mechanisms of restenosis.

A Murine Model of Stent Implantation in the Carotid Artery for the Study of Restenosis

We report a technique for the fabrication of micropockets within electrospun membranes in which to study cell behavior. Specifically, we describe a combination of microstereolithography and electrospinning for the production of PLGA (Poly(lactide-co-glycolide)) corneal biomaterial devices equipped with microfeatures.

Combination of Microstereolithography and Electrospinning to Produce Membranes Equipped with Niches for Corneal Regeneration

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.

Ferromagnetic Bare Metal Stent for Endothelial Cell Capture and Retention

Reproducable experimental animal models are needed for the testing of novel embolization materials, which have been designed to treat endovascular occlusion of intracranial aneurysms (IA). The present study aims to develop a safe and standardized surgical technique for stent assisted embolization of saccular aneurysms in a rat animal model.

Biodegradable Magnesium Stent Treatment of Saccular Aneurysms in a Rat Model - Introduction of the Surgical Technique

Here, we present a modified electrospinning method to fabricate PCL vascular grafts with thick fibers and large pores, and describe a protocol to evaluate the in vivo performance in a rat model of abdominal aorta replacement.

Implantation of Electrospun Vascular Grafts with Optimized Structure in a Rat Model

Using a 3D printer, a shape memory polymer filament is extruded to form a branched tubular structure. The structure is patterned and shaped such that it can contract into a compact form once folded and then return to its formed shape when heated.

4D Printed Bifurcated Stents with Kirigami-Inspired Structures

The presented method offers an innovative way for engineering biomimetic fiber structures in three-dimensional (3D) scaffolds (e.g., heart valve leaflets). 3D-printed, conductive geometries were used to determine shape and dimensions. Fiber orientation and characteristics were individually adjustable for each layer. Multiple samples could be manufactured in one setup.

Combining 3D-Printing and Electrospinning to Manufacture Biomimetic Heart Valve Leaflets

This work illustrates a low-cost fabrication technique for shape-setting nitinol wires/frames with a small form factor using sacrificial fixtures. The technique is demonstrated for the fabrication of self-expanding frames designed for minimally invasive implants with complex shapes.

Rapid Formation and Testing of Self-expanding NiTi Frames with a Small Form Factor Suitable for Minimally Invasive Implants

Contrast enhanced small animal vessel imaging by microCT is a rapid, cost-effective and high-throughput technique for serial in situ examination for tumor development, for analyzing the network of blood vessels that nourish them, and for following the response of tumors to preclinical therapeutic intervention(s).

Contrast Enhanced Vessel Imaging using MicroCT

Learn to fabricate small caliber stent-grafts using electrospinning and balloon expandable bare metal stents. This method encapsulates stents in polyurethane nanofibers for improved healing and new medical applications.

Fabrication of Small Caliber Stent-grafts Using Electrospinning and Balloon Expandable Bare Metal Stents

Explore More Videos