Vascular Response Toward an Absorbable Sirolimus-eluting Polymeric Scaffold for Vascular Application in a Model of Normal Porcine Carotid Arteries.

BACKGROUND: Fully absorbable polymeric scaffolds, as a potential alternative to permanent metallic stents, are entering the clinical field. The aim of this study is to assess the in vivo biocompatibility of a novel Sirolimus-eluting (SIR) absorbable scaffold based on poly(L-lactide) (PLLA) and poly(4-hydroxybutyrate) (P4HB) for interventional application. METHODS: Absorbable PLLA/P4HB scaffolds either loaded with SIR coating or unloaded scaffolds were implanted interventionally into common carotid arteries of 14 female. Bare metal stents (BMS) served as control. Peroral dual anti-platelet therapy was administered throughout the study. Stented common carotid arteries segments were explanted after 4 weeks, and assessed histomorphometrically. RESULTS: The absorbable scaffolds showed a decreased residual lumen area and higher stenosis after 4 weeks (PLLA/P4HB: 6.56 ± 0.41 mm² and 37.56 ± 4.67%; SIR-PLLA/P4HB: 6.90 ± 0.58 mm² and 35.60 ± 3.15%) as compared to BMS (15.29 ± 1.86 mm² and 7.65 ± 2.27%). Incorporation of SIR reduced the significantly higher inflammation of unloaded scaffolds however not to a level compared to bare metal stent (PLLA/P4HB: 1.20 ± 0.19; SIR-PLLA/P4HB: 0.96 ± 0.24; BMS: 0.54 ± 0.12). In contrast, the BMS showed a slightly elevated vascular injury score (0.74 ± 0.15), as compared to the PLLA/P4HB (0.54 ± 0.20) and the SIR-PLLA/P4HB (0.48 ± 0.15) groups. CONCLUSION: In this preclinical model, the new absorbable polymeric (SIR-) scaffolds showed similar technical feasability and safety for vascular application as the permanent metal stents. The higher inflammatory propensity of the polymeric scaffolds was slightly reduced by SIR-coating. A smaller strut thickness of the polymeric scaffolds might have been a positive effect on tissue ingrowth between the struts and needs to be addressed in future work on the stent design.

The History of GalaFLEX P4HB Scaffold.

The GalaFLEX Scaffold (Galatea Surgical, Inc., Lexington, MA) for plastic and reconstructive surgery belongs to a new generation of products for soft tissue reinforcement made from poly-4-hydroxybutyrate (P4HB). Other members of this new family of products include MonoMax Suture (Aesculap AG, Tuttlingen, Germany) for soft tissue approximation, BioFiber Scaffold (Tornier, Inc., Edina, MN) for tendon repair, and Phasix Mesh (C.R. Bard, Inc., Murray Hill, NJ) for hernia repair. Each of these fully resorbable products provides prolonged strength retention, typically 50% to 70% strength retention at 12 weeks, and facilitates remodeling in vivo to provide a strong, lasting repair. P4HB belongs to a naturally occurring class of biopolymers and fibers made from it are uniquely strong, flexible, and biocompatible. GalaFLEX Scaffold is comprised of high-strength, resorbable P4HB monofilament fibers. It is a knitted macroporous scaffold intended to elevate, reinforce, and repair soft tissue. The scaffold acts as a lattice for new tissue growth, which is rapidly vascularized and becomes fully integrated with adjacent tissue as the fibers resorb. In this review, we describe the development of P4HB, its production, properties, safety, and biocompatibility of devices made from P4HB. Early clinical results and current clinical applications of products made from P4HB are also discussed. The results of post-market clinical studies evaluating the GalaFLEX Scaffold in rhytidectomy and cosmetic breast surgery demonstrate that the scaffold can reinforce lifted soft tissue, resulting in persistent surgical results in the face and neck at one year, and provide lower pole stability after breast lift at one year.

Poly-4-hydroxybutyrate (P4HB): a new generation of resorbable medical devices for tissue repair and regeneration.

Poly-4-hydroxybutyrate (P4HB) is a thermoplastic, linear polyester, produced by recombinant fermentation, that can be converted into a wide range of resorbable medical devices. P4HB fibers are exceptionally strong, and can be designed to provide prolonged strength retention in vivo. In 2007, the FDA cleared a monofilament suture made from P4HB for general soft tissue approximation and/or ligation. Subsequently, surgical mesh devices for hernia repair, tendon and ligament repair, and plastic and reconstructive surgery have been introduced for clinical use. This review describes the unique properties of P4HB, its clinical applications, and potential uses that are under development.

Development of a sirolimus-eluting poly (L-lactide)/poly(4-hydroxybutyrate) absorbable stent for peripheral vascular intervention.

Fully absorbable drug-eluting stent platforms are currently entering the clinical arena for the interventional treatment of coronary artery disease. This new technology also holds potential for application in peripheral vascular settings. Our study reports on the development of a sirolimus- (SIR) eluting absorbable polymer stent made from a blend of poly(l-lactide) and poly(4-hydroxybutyrate) (PLLA/P4HB) for peripheral vascular intervention. Stent prototypes were laser-cut from PLLA/P4HB tubes (I.D.=2.2 mm, t=250 µm), spray-coated with different PLLA/P4HB/SIR solutions, and bench-tested to determine expansion properties, fatigue, trackability and in vitro drug release kinetics. The stent prototypes were expanded with a 5.0 × 20 mm balloon catheter, and exhibited a recoil of 3.6% upon balloon deflation. Stent collapse pressure of 0.4 bar (300 mm Hg) was measured under external pressure load. Sustained scaffolding properties were observed in vitro over 14 weeks of radial fatigue loading (50 ± 25 mm Hg at 1.2 Hz). Trackability was demonstrated in bench tests with an 8 French contralateral introducer sheath. SIR release kinetics were adjusted over a broad range by varying the PLLA/P4HB ratio of the coating matrix. The newly developed absorbable SIR-eluting PLLA/P4HB stent successfully fulfilled the requirements for peripheral vascular intervention under in vitro conditions.

Characterization of poly-4-hydroxybutyrate mesh for hernia repair applications.

BACKGROUND: Phasix mesh is a fully resorbable implant for soft tissue reconstruction made from knitted poly-4-hydroxybutyrate monofilament fibers. The objectives of this study were to characterize the in vitro and in vivo mechanical and resorption properties of Phasix mesh over time, and to assess the functional performance in a porcine model of abdominal hernia repair. MATERIALS AND METHODS: We evaluated accelerated in vitro degradation of Phasix mesh in 3 mol/L HCl through 120 h incubation. We also evaluated functional performance after repair of a surgically created abdominal hernia defect in a porcine model through 72 wk. Mechanical and molecular weight (MW) properties were fully characterized in both studies over time. RESULTS: Phasix mesh demonstrated a significant reduction in mechanical strength and MW over 120 h in the accelerated degradation in vitro test. In vivo, the Phasix mesh repair demonstrated 80%, 65%, 58%, 37%, and 18% greater strength, compared with native abdominal wall at 8, 16, 32, and 48 wk post-implantation, respectively, and comparable repair strength at 72 wk post-implantation despite a significant reduction in mesh MW over time. CONCLUSIONS: Both in vitro and in vivo data suggest that Phasix mesh provides a durable scaffold for mechanical reinforcement of soft tissue. Furthermore, a Phasix mesh surgical defect repair in a large animal model demonstrated successful transfer of load bearing from the mesh to the repaired abdominal wall, thereby successfully returning the mechanical properties of repaired host tissue to its native state over an extended time period.

A biodegradable stent based on poly(L-lactide) and poly(4-hydroxybutyrate) for peripheral vascular application: preliminary experience in the pig.

PURPOSE: To assess the technical feasibility and biocompatibility of a novel stent based on poly(L-lactide) (PLLA) and poly(4-hydroxybutyrate) (P4HB) for peripheral vascular applications. METHODS: A polytetrafluoroethylene aortobi-iliac graft was implanted in 5 pigs through a midline abdominal incision. After transverse graft limb incision, 5 PLLA/P4HB stents and 5 metal stents (316L stainless steel) were randomly deployed at both iliac anastomotic sites with 6-mm balloon catheters. Angiography was performed to determine patency prior to sacrifice at 6 weeks. Stented segments were surgically explanted and processed for quantitative histomorphometry. Vascular injury and inflammation scores were assigned to the stented iliac segments. RESULTS: No animals were lost during follow-up. All PLLA/P4HB stents were deployed within 2 minutes by balloon inflation to 8 bars without rupture of the stent struts or anastomotic suture. All stents were patent on postprocedural angiography. Histological analysis showed no signs of excessive recoiling or collapse. PLLA/P4HB stents demonstrated decreased residual lumen area and increased neointimal area after 6 weeks (12.27+/-0.62 and 8.40+/-1.03 mm(2), respectively) compared to 316L stents (13.54+/-0.84 and 6.90+/-1.11 mm(2), respectively) as the result of differences in stent areas (PLLA/P4HB: 4.31+/-0.15 mm(2); 316L: 2.73+/-0.29 mm(2)). Vascular injury scores showed only mild vascular trauma for all stents (PLLA/P4HB: 0.41+/-0.59; 316L: 0.32+/-0.47). Inflammatory reaction was slightly higher around PLLA/P4HB stent struts (1.39+/-0.52) compared to 316L (1.09+/-0.50). CONCLUSION: Rapid balloon expansion of PLLA/P4HB stents is feasible without risk of strut rupture. PLLA/P4HB stents provide adequate mechanical stability after iliac anastomotic stenting in pigs. Smaller residual luminal areas in the PLLA/P4HB stents might have been caused by tissue ingrowth into the larger strut interspaces due to higher strut thickness (stent area) in this group. This limitation needs to be addressed in future work on the stent design.

A biodegradable slotted tube stent based on poly(L-lactide) and poly(4-hydroxybutyrate) for rapid balloon-expansion.

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 x 25 mm were manufactured by laser machining of solution cast PLLA/P4HB tubes (I.D. = 2.8 mm, d = 300 microm). The stents were expanded within 1 min by balloon inflation to 8 bar, after 5 min preconditioning in 37 degrees 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 balloon-expansion and exhibited adequate mechanical scaffolding properties suitable for a broad range of vascular and non-vascular applications.