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Abstract-Safe vascular stent application requires rapid expansion of the stent to minimize the risk of procedural ischemia. While high expansion speeds can be achieved with metallic stents, they are not necessarily feasible with biodegradable polymeric stents due to the viscoelastic material behavior. This study reports on a novel biodegradable polymer blend material based on poly(L-lactide) (PLLA) and poly(4-hydroxybutyrate) (P4HB), and describes the mechanical properties and in vitro degradation behavior of a balloon-expandable slotted tube stent concept. The stent prototypes with nominal dimensions of 6.0 · 25 mm were manufactured by laser machining of solution cast PLLA/ P4HB tubes (I.D. = 2.8 mm, d = 300 lm). The stents were expanded within 1 min by balloon inflation to 8 bar, after 5 min preconditioning in 37°C water. Recoil and collapse pressure were 4.2% and 1.1 bar, respectively. During in vitro degradation collapse pressure initially increased to a maximum at 4 w and then decreased thereafter. After 48 w, molecular weight was decreased by 82%. In summary, the PLLA/P4HB slotted tube stents allowed for rapid balloonexpansion and exhibited adequate mechanical scaffolding properties suitable for a broad range of vascular and nonvascular applications.

Hybrid heart valve scaffolds were fabricated from decellularized porcine aortic heart valve matrices and enhanced with bioresorbable polymers using different protocols: (i) dip coating of lyophilized decellularized matrices, and (ii) impregnation of wet decellularized matrices. The following polymers were evaluated: poly(4-hydroxybutyrate) and poly(3-hydroxybutyrate-co4-hydroxybutyrate). Tensile tests were conducted to assess the biomechanical behavior of valve leaflet strips. Suture retention strength was evaluated for the adjacent conduit. A pulse duplicator system was used for functional testing of the valves under physiological systemic load conditions. The properties of the hybrid structures were compared with native, decellularized, and glutaraldehyde-fixed specimens. Mechanisms of the polymer impregnation process were studied with IR spectroscopy, fluorescent microscopic imaging, and SEM. Altogether this study demonstrates the feasibility and improved biomechanical function of a novel hybrid heart valve scaffold for an application in tissue engineering.

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.

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