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

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 $0∕2∕4∕8∕12∕24$ weeks the remaining collapse stability and molecular weight were assessed. Results: All stents could be deployed by balloon inflation to $8bar$ at $1bar∕min$ (PLLA) and $3bar∕min$ (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.