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.