A polyhydroxybutyrate biodegradable stent: preliminary experience in the rabbit.

PURPOSE: The lifelong persistence of foreign bodies within the arteries may contribute to restenosis. Thus, biodegradable devices might decrease recurrence rates. METHODS: Eleven polyhydroxybutyrate biodegradable stents and 13 tantalum stents were implanted into the iliac arteries of New Zealand white rabbits for up to 30 weeks. After killing the animals, the specimens were harvested, fixed in formalin, processed in paraffin, and stained. RESULTS: Polyhydroxybutyrate instigated intense inflammatory and proliferative reactions with an increase in collagen (2.4- to 8-fold vs native segments), thrombosis and in-stent lumen narrowing (375.5-606.6 mm vs 655.6 +/- 268.8 mm in native segments). The elastic membranes were destroyed in all specimens. The tantalum stents increased the in-stent lumen progressively (769.7 +/- 366.6 mm vs 1309.9 +/- 695.3 mm), penetrated the external elastic membrane, and increased mural collagen content (6- to 8.6-fold vs native segments). Neither restenoses nor thromboses occurred. CONCLUSIONS: In the rabbit iliac artery, polyhydroxybutyrate stents caused intensive inflammatory vascular reactions which ban them from clinical use.

[First results in an animal model on stents sheathed with a polytetrafluoroethylene membrane]. / Erste tierexperimentelle Ergebnisse eines von einer Polytetrafluoroethylenmembran umhüllten Koronarstents.

OBJECTIVES: Mechanisms of restenosis after coronary stent implantation include marked intimal proliferation as well as vascular tissue protrusion through the meshes. Thus, stent sheathed with membranes may be an alternative to improve the long-term outcome. METHODS: Seventeen cylindric serpentine shaped 316L stainless steel stents (nominal diameter 3.0 mm, length 15 mm) lined and covered by a polytetrafluoroethylene (PTFE) membrane and 10 unsheathed devices were implanted into the iliac arteries of 14 New Zealand White Rabbits for an observation period of 1 - 10, 11 - 20, and 21 - 30 weeks. After sacrificing the animals, specimens were harvested, fixed in formalin, processed in paraffin, serially sliced into 5 microm thick preparations, and stained (hematoxylin & eosin, elastica von Gieson). RESULTS: The polytetrafluoroethylene membrane stents increased the vascular lumen significantly (p < 0.04) to 1185.3 - 1620.4 microm compared with the native segments (655.6 +/- 268.8 microm). In the stainless steel stents the lumen decreased from 1873.1 microm to 719.1 microm. None of the devices penetrated the internal elastic membrane. There was no inflammatory vascular reaction. Compared to the native segments, the amount of elastic fibres was slightly less (native: 8.9 %, PTFE: 2.3 - 3.5 %, without PTFE: 1.9 - 5.5 %) whereas the collagen fibres increased marginally (native: 5.1 %, PTFE: 6 - 6.9 %, without PTFE: 6.4 - 8.4 %). CONCLUSIONS: In the rabbit iliac artery, stents sheathed with a microporous polytetrafluoroethylene membrane showed good tissue compatibility with no restenosis. These results warrant clinical trials.