Iliac Anastomotic Stenting With a Biodegradable Poly-L-Lactide Stent: A Preliminary Study After 1 and 6 Weeks

Primary stenting immediatly after surgery in occluded anastomoses of aortoaortic tube graft: a case report

The conventional elective open procedures for abdominal aortic aneurysm repair are reliable and yield durable results. The aortoaortic tube graft has the lowest morbidity incidence when compared with different techniques. Albeit infrequent, thrombosis can be present in the first 30 days. Its treatment consists in thrombectomy and anastomosis evaluation, but with an increase in morbidity, especially in patients with urgent reintervention. This is a case report of a patient with aortoaortic tube graft, who present critical left limb ischemia immediately after surgical procedure. Angiography showed complete occlusion of left common iliac artery, affecting the distal graft anastomosis. The occlusion was resolved with endovascular treatment, and a noncovered, self-expanding, nitinol stent was deployed (primary stenting) covering the distal bypass anastomosis, with no complications and complete lower limb perfusion recovery. One month later, the patient was still asymptomatic, with distal pulse palpable and ankle-brachial index 1.

A new wave in treatment of vascular occlusive disease: biodegradable stents--clinical experience and scientific principles

Stent-based therapies in percutaneous vascular intervention are associated with significant long-term complications related to in-stent restenosis. A growing body of literature demonstrates the feasibility of biodegradable materials for endovascular stents, which may, in theory, circumvent many of the immunologic and inflammatory response issues seen with long-term metallic stent failure in coronary and peripheral applications. This review describes the history of endovascular stents and the challenges encountered with metallic, drug-eluting, and biodegradable stents. A review of the basic engineering principles of biodegradable stents is provided, along with a discussion of the cellular mechanisms of restenosis.

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.

In-vitro assays of polymer-coated stents eluting platelet glycoprotein IIb/IIIa receptor monoclonal antibody

The monoclonal antibody (mAb) to the platelet glycoprotein (GP) IIb/IIIa receptor has potent antiplatelet and antithrombotic characteristics shown to reduce thrombus-related major complications after coronary angioplasty. This mAb can be incorporated in drug-eluting stents capable of releasing single or multiple bioactive agents into the bloodstream and surrounding tissues. Stents eluting the monoclonal mouse anti-human platelet glycoprotein IIb/IIIa antibody SZ-262 were tested for their effectiveness in improving the blood compatibility and the antithrombotic characteristics by immunofluorescence and scanning electron microscopy (SEM). The SEM results convincingly demonstrated that the surface of the mAb eluting-stents was completely free of platelet uptake without any sign of cellular debris or proteinaceous deposits, compared with controls. The deformation index of platelets on the L-polylactic acid (L-PLA) coated stents were higher than bare Nitinol intravascular stents, as shown by SEM images. Monoclonal antibody to the platelet GP IIb/IIIa receptor, when eluting from L-PLA polymer-coated stents, effectively inhibits platelet aggregation in the stent microenvironment, thus demonstrating a potential capacity of reducing thrombosis, improving blood flow and arterial patency rates, and inhibiting cyclic blood flow variations. These results highlight the possibility of such monoclonal antibody-eluting stents to reduce or possibly eliminate thrombosis and in-stent restenosis.

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.

Sirolimus-eluting biodegradable poly-L-lactide stent for peripheral vascular application: a preliminary study in porcine carotid arteries

BACKGROUND

To assess technical feasibility and biocompatibility of a new Sirolimus (SIR)-eluting biodegradable poly-L-lactide (PLLA) stent for peripheral vascular application.

MATERIAL AND METHODS

In 15 pigs, both common carotid arteries (CCA) were surgically exposed and clamped in the proximal segment. After transverse incision, 12 316L stents, 12 unloaded and 6 SIR-loaded PLLA stents mounted on 6.0 x 40-mm balloon catheters were randomly implanted into the CCA and inflated to 8 bar. Angiographic equipment was not available. Stented CCA were explanted after 1 week (6 pigs; 316L versus PLLA) and 6 weeks (9 pigs; 316L versus PLLA versus SIR-PLLA), and processed for quantitative histomorphometry and estimation of vascular inflammation and injury scores.

RESULTS

No animals were lost during follow-up. All stents were patent on histological analysis without any signs of excessive recoiling or collapse. Unloaded PLLA stents showed decreased residual lumen area and increased neointimal area after 1 week (13.16 +/- 0.34, 1.94 +/- 0.26) and 6 weeks (11.57 +/- 0.30, 2.85 +/- 0.24) as compared with 316L stents (15.26 +/- 0.13, 1.27 +/- 0.41 and 13.99 +/- 0.51, 1.54 +/- 0.59). SIR-eluting stents demonstrated comparable neointimal area (1.75 +/- 0.38) and 50% lower intimal thickness as compared with 316L stents after 6 weeks, but a slightly decreased residual lumen (13.06 +/- 0.32) in the consequence of differences in strut thickness (PLLA, 270 microm; 316L, 155 microm). The vascular inflammation score against PLLA-stents could be reduced by Sirolimus. The vascular injury scores were low and similar in all groups.

CONCLUSIONS

PLLA stents showed sufficient mechanical stability after porcine CCA stenting. By incorporation of Sirolimus, a significant reduction of the inflammatory and neointimal response to the PLLA stent was seen without systemic toxicity or thrombotic complications. These findings need to be assessed with longer follow-up to confirm maintenance of efficacy. The greater strut height of PLLA stents is a major limitation and requires modification.

Iliac Anastomotic Stenting With a Sirolimus-Eluting Biodegradable Poly-L-Lactide Stent: A Preliminary Study After 6 Weeks

PURPOSE

To assess technical feasibility and biocompatibility of a new biodegradable sirolimus-eluting poly-L-lactide (PLLA) vascular anastomotic stent.

METHODS

A polytetrafluoroethylene bifurcated graft was implanted in 9 pigs through a midline abdominal incision. After transverse graft limb incision, 6 unloaded PLLAs, 6 sirolimus-loaded PLLAs, and 6 unloaded stainless steel (316L) stents were randomly implanted at both iliac anastomotic sites. Stents were deployed with a 6-mm balloon under direct vision without the use of angiography. Prior to sacrifice after 6 weeks, contrast-enhanced computed tomography (CT) was performed to determine patency of the target vessels. Stented segments were surgically explanted and processed for histology to measure the mean luminal diameter and intimal thickness and to assign vascular injury and inflammation scores.

RESULTS

No animals were lost during the study period. All stented graft limbs were patent on CT and histology. At the anastomotic sites and iliac arteries, the mean luminal diameter of SIR-PLLA stents (4.11+/-0.15 and 4.08+/-0.13 mm, respectively) were comparable to metal stents (4.23+/-0.35 and 4.21+/-0.26 mm, respectively), but significantly higher compared to unloaded PLLA stents [3.32+/-0.56 mm (p<0.001) and 3.29+/-0.39 mm (p=0.013), respectively]. At the iliac arteries, the mean intimal thickness was significantly lower with SIR-PLLA stents (0.09+/-0.02 mm) compared to unloaded PLLA stents (0.31+/-0.15 mm, p<0.001) and metal stents (0.19+/-0.04 mm, p=0.004). Vascular injury scores demonstrated only mild vascular trauma for all stents (SIR-PLLA: 0.42+/-0.63, PLLA: 0.51+/-0.62, metal: 0.50+/-0.62). Only mild inflammatory reaction was noted around SIR-PLLA stent struts (1.14+/-0.46), which was comparable to metal stents (1.27+/-0.45) but significantly lower than PLLA stents (1.79+/-0.56, p<0.001).

CONCLUSION

SIR-PLLA stents showed comparable luminal diameter compared to metal stents, so incorporating sirolimus could reduce the inflammatory and neointimal response to PLLA stents. These findings need to be assessed with longer follow-up to confirm maintenance of efficacy.