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Fabrication and in vitro deployment of a laser-activated shape memory polymer vascular stent.

Baer GM, Small W, Wilson TS, Benett WJ, Matthews DL, Hartman J, Maitland DJ - Biomed Eng Online (2007)

Bottom Line: A shape memory polymer (SMP) stent may enhance flexibility, compliance, and drug elution compared to its current metallic counterparts.At a physiological flow rate, the stent did not fully expand at the maximum laser power (8.6 W) due to convective cooling.Though further studies are required to optimize the device and assess thermal tissue damage, photothermal actuation of the SMP stent was demonstrated.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biomedical Engineering, University of California, Davis, California 95616 USA. gmbaer@ucdavis.edu

ABSTRACT

Background: Vascular stents are small tubular scaffolds used in the treatment of arterial stenosis (narrowing of the vessel). Most vascular stents are metallic and are deployed either by balloon expansion or by self-expansion. A shape memory polymer (SMP) stent may enhance flexibility, compliance, and drug elution compared to its current metallic counterparts. The purpose of this study was to describe the fabrication of a laser-activated SMP stent and demonstrate photothermal expansion of the stent in an in vitro artery model.

Methods: A novel SMP stent was fabricated from thermoplastic polyurethane. A solid SMP tube formed by dip coating a stainless steel pin was laser-etched to create the mesh pattern of the finished stent. The stent was crimped over a fiber-optic cylindrical light diffuser coupled to an infrared diode laser. Photothermal actuation of the stent was performed in a water-filled mock artery.

Results: At a physiological flow rate, the stent did not fully expand at the maximum laser power (8.6 W) due to convective cooling. However, under zero flow, simulating the technique of endovascular flow occlusion, complete laser actuation was achieved in the mock artery at a laser power of ~8 W.

Conclusion: We have shown the design and fabrication of an SMP stent and a means of light delivery for photothermal actuation. Though further studies are required to optimize the device and assess thermal tissue damage, photothermal actuation of the SMP stent was demonstrated.

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Related in: MedlinePlus

SMP stent. Close-up of the SMP stent mounted over the SMP foam cylinder (black arrow) and the coaxial SMP diffuser (white arrow) prior to crimping (a) and after crimping (b). The distal end of the stainless steel hypotube containing the optical fiber is indicated by the asterisk in (a). An image of the diffuser emission, which decreases with distance from the optical fiber tip, is shown in (c). A cross-sectional diagram of the expanded stent with the diffuser and foam cylinder in place is shown in (d).
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Figure 1: SMP stent. Close-up of the SMP stent mounted over the SMP foam cylinder (black arrow) and the coaxial SMP diffuser (white arrow) prior to crimping (a) and after crimping (b). The distal end of the stainless steel hypotube containing the optical fiber is indicated by the asterisk in (a). An image of the diffuser emission, which decreases with distance from the optical fiber tip, is shown in (c). A cross-sectional diagram of the expanded stent with the diffuser and foam cylinder in place is shown in (d).

Mentions: Fabrication of the stent began by dissolving pellets of MM5520 in tetrahydrofuran (THF) to prepare a solution with a composition of 17.5% by weight of polymer in solvent. A SMP tube was first made by dip coating a 4 mm diameter stainless steel pin in the solution multiple times at a constant rate of withdrawal. The coated pin was then dried for 24 hours at 50°C under vacuum. After cooling, the SMP tube was laser etched to impart a specific pattern based on an imported CAD file using a computer-controlled system. As shown in Fig. 1(a), solid rings are connected by S-shaped struts, enhancing its longitudinal flexibility. The stent was then removed from the pin using hot water, dried, doped with a laser-absorbing platinum dye (Epolight 4121, Epolin, Inc.), and dried again for 24 hours at 50°C under vacuum. The dye was incorporated by coating the stent with a solution of 4440 ppm dye in THF. The stent diameter decreased slightly after removal from the pin due to residual stress in the SMP. The final stent in its expanded state was 4.1 mm outer diameter by 16 mm long with a wall thickness of 250 μm.


Fabrication and in vitro deployment of a laser-activated shape memory polymer vascular stent.

Baer GM, Small W, Wilson TS, Benett WJ, Matthews DL, Hartman J, Maitland DJ - Biomed Eng Online (2007)

SMP stent. Close-up of the SMP stent mounted over the SMP foam cylinder (black arrow) and the coaxial SMP diffuser (white arrow) prior to crimping (a) and after crimping (b). The distal end of the stainless steel hypotube containing the optical fiber is indicated by the asterisk in (a). An image of the diffuser emission, which decreases with distance from the optical fiber tip, is shown in (c). A cross-sectional diagram of the expanded stent with the diffuser and foam cylinder in place is shown in (d).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2211751&req=5

Figure 1: SMP stent. Close-up of the SMP stent mounted over the SMP foam cylinder (black arrow) and the coaxial SMP diffuser (white arrow) prior to crimping (a) and after crimping (b). The distal end of the stainless steel hypotube containing the optical fiber is indicated by the asterisk in (a). An image of the diffuser emission, which decreases with distance from the optical fiber tip, is shown in (c). A cross-sectional diagram of the expanded stent with the diffuser and foam cylinder in place is shown in (d).
Mentions: Fabrication of the stent began by dissolving pellets of MM5520 in tetrahydrofuran (THF) to prepare a solution with a composition of 17.5% by weight of polymer in solvent. A SMP tube was first made by dip coating a 4 mm diameter stainless steel pin in the solution multiple times at a constant rate of withdrawal. The coated pin was then dried for 24 hours at 50°C under vacuum. After cooling, the SMP tube was laser etched to impart a specific pattern based on an imported CAD file using a computer-controlled system. As shown in Fig. 1(a), solid rings are connected by S-shaped struts, enhancing its longitudinal flexibility. The stent was then removed from the pin using hot water, dried, doped with a laser-absorbing platinum dye (Epolight 4121, Epolin, Inc.), and dried again for 24 hours at 50°C under vacuum. The dye was incorporated by coating the stent with a solution of 4440 ppm dye in THF. The stent diameter decreased slightly after removal from the pin due to residual stress in the SMP. The final stent in its expanded state was 4.1 mm outer diameter by 16 mm long with a wall thickness of 250 μm.

Bottom Line: A shape memory polymer (SMP) stent may enhance flexibility, compliance, and drug elution compared to its current metallic counterparts.At a physiological flow rate, the stent did not fully expand at the maximum laser power (8.6 W) due to convective cooling.Though further studies are required to optimize the device and assess thermal tissue damage, photothermal actuation of the SMP stent was demonstrated.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biomedical Engineering, University of California, Davis, California 95616 USA. gmbaer@ucdavis.edu

ABSTRACT

Background: Vascular stents are small tubular scaffolds used in the treatment of arterial stenosis (narrowing of the vessel). Most vascular stents are metallic and are deployed either by balloon expansion or by self-expansion. A shape memory polymer (SMP) stent may enhance flexibility, compliance, and drug elution compared to its current metallic counterparts. The purpose of this study was to describe the fabrication of a laser-activated SMP stent and demonstrate photothermal expansion of the stent in an in vitro artery model.

Methods: A novel SMP stent was fabricated from thermoplastic polyurethane. A solid SMP tube formed by dip coating a stainless steel pin was laser-etched to create the mesh pattern of the finished stent. The stent was crimped over a fiber-optic cylindrical light diffuser coupled to an infrared diode laser. Photothermal actuation of the stent was performed in a water-filled mock artery.

Results: At a physiological flow rate, the stent did not fully expand at the maximum laser power (8.6 W) due to convective cooling. However, under zero flow, simulating the technique of endovascular flow occlusion, complete laser actuation was achieved in the mock artery at a laser power of ~8 W.

Conclusion: We have shown the design and fabrication of an SMP stent and a means of light delivery for photothermal actuation. Though further studies are required to optimize the device and assess thermal tissue damage, photothermal actuation of the SMP stent was demonstrated.

Show MeSH
Related in: MedlinePlus