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TECHNICAL BRIEFS

Mechanical Properties of a Biodegradable Balloon-expandable Stent From Poly(L-lactide) for Peripheral Vascular Applications

[+] Author and Article Information
Niels Grabow

Institute for Biomedical Engineering, University of Rostock, Ernst-Heydemann-Str. 6, D-18057 Rostock, Germanyniels.grabow@medizin.uni-rostock.de

Carsten M. Bünger

Department of Surgery, University of Rostock, Schillingallee 35, D-18057 Rostock, Germany

Katrin Sternberg, Steffen Mews, Kathleen Schmohl, Klaus-Peter Schmitz

Institute for Biomedical Engineering, University of Rostock, Ernst-Heydemann-Str. 6, D-18057 Rostock, Germany

J. Med. Devices 1(1), 84-88 (Aug 10, 2006) (5 pages) doi:10.1115/1.2355683 History: Received February 13, 2006; Revised August 10, 2006

Background: Biodegradable polymeric stents represent a competitive approach to permanent and absorbable metallic stents for vascular applications. Despite major challenges resulting from the mechanical properties of polymeric biomaterials, these stent concepts gain their attraction from their intrinsic potential for controlled biodegradation and facile drug incorporation. This study demonstrates the mechanical properties of a novel balloon-expandable slotted tube stent from PLLA. Method of Approach: Polymeric balloon-expandable slotted tube stents (nominal dimensions: 6.0×25mm) were manufactured by laser machining of solution cast tubes (I.D.=2.8mm, d=270±20μm) from biodegradable (1) PLLA and (2) PLLA/PCL/TEC. The stents were tested in vitro for their mechanical properties: deployment, recoil, shortening, collapse, and creep behavior under a static load of 100mmHg. In vitro degradation was performed in Sørensen buffer solution at 37°C. After 02481224 weeks the remaining collapse stability and molecular weight were assessed. Results: All stents could be deployed by balloon inflation to 8bar at 1barmin (PLLA) and 3barmin (PLLA/PCL/TEC). Recoil, shortening, and collapse pressure were: 2.4%3.4%0.67bar (PLLA), and 8.8%2.3%0.23bar (PLLA/PCL/TEC). A static load of 100mmHg induced pronounced creep processes in the PLLA/PCL/TEC stent. The PLLA stent remained patent and exhibited no creep propensity. During in vitro degradation an increase in collapse pressure was observed (maxima at 12w: 1.3bar (PLLA), 0.7bar (PLLA/PCL/TEC)). At 24 weeks, molecular weight was decreased by 28% (PLLA), and 52% (PLLA/PCL/TEC). Conclusions: Stents fabricated from pure PLLA exhibited adequate mechanical properties. The slow permissible deployment rate, however, limits their potential application range and demands further development.

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Copyright © 2007 by American Society of Mechanical Engineers
Topics: stents , Collapse
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References

Figures

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Figure 1

Balloon-expandable PLLA stent prototype, (a) undeployed configuration, (b) deployed configuration. Note the expansion ratio of 2.1 and the minor shortening of approx. 3%. Bar length=10mm.

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Figure 2

Representative stent profile at different balloon inflation pressures, (a) PLLA stent, (b) PLLA/PCL/TEC stent

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Figure 3

Characteristic pressure-diameter curves of the PLLA and the PLLA/PCL/TEC stents during balloon expansion. The curves reflect the stent diameter measured in the stent midsection.

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Figure 4

Elastic stent recoil and stent shortening after dilation with a balloon pressure of 8bar and subsequent balloon deflation. Bars representing mean values ± standard deviation.

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Figure 5

Superpositioned images from a numerical analysis of stent collapse showing axial views of the stent in the deployed and collapsed configuration. The images illustrate the ovalization of the stent under external pressure, which can be expressed in terms of the radial displacement parameters Δr1 and Δr2.

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Figure 6

Representative radial displacement curves of a PLLA and a PLLA/PCL/TEC stent under increasing external pressure

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Figure 7

Representative curves illustrating the different creep behavior of the PLLA and the PLLA/PCL/TEC stent under a constant static external pressure load of the stents (p=100mmHg). The curves reflect the time dependent radial displacement Δr1 and Δr2.

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Figure 8

Stent collapse pressure as a function of storage time in Sørensen buffer (pH=7.4) at 37°C

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Figure 9

Molecular weight Mw as a function of storage time in Sørensen buffer (pH=7.4) at 37°C

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