Bioabsorbable Polymers, Scaffolds Offer Permanent Advantages

SAN FRANCISCO, CALIF.—Compared with permanent polymers and scaffolds, biodegradable polymers and fully erodible stents have the potential to be of greater benefit to patients, given that they result in less long-term toxicity to vessel walls and are less likely to induce a hypersensitivity reaction. Renu Virmani, MD, of the CV Path Institute in Gaithersburg, Md., discussed the reasons why bioabsorbable polymers are the better option during a symposium on next-generation DES and bioabsorbable scaffolds.

BVS Cohort A/B and ABSORB trials

In preclinical and clinical studies, promising results have been observed with biodegradable polymers. Almost full degradation was achieved at 2 and 3 years, with complete degradation at 4 years. “Vessels almost returned to normal morphology with compact contractile smooth muscle cells concentrated towards the lumen and complete endothelialization in animal models,” Virmani said.

Twelve-month data from the ongoing BVS Cohort B trial suggest promising results with a bioresorbable vascular scaffold (BVS; Absorb, Abbott Vascular) when compared with everolimus-eluting stents (Xience V, Abbott Vascular) (see Figure).

Polymer degradation is the result of various factors, such as the chemical stability of the polymer backbone; the presence of a catalyst; and the geometry and location of the device. Other factors that increase polymer degradation include hydrophilic monomers; hydrophilic acidic endgroups; a more reactive hydrolytic group in the backbone; less crystallinity; and small device size.

In other studies that addressed this issue, such as the ABSORB trial that included about 100 patients, results have also been positive. However, these trials were carried out in lesions less than 60% diameter and showed minimal calcification. Virmani said there may be delayed endothelial coverage due to a combination of strut thickness and drug release, which may require long-term DAPT. “These [issues] all have to be worked out,” she said.

Drawbacks of durable polymer

While addressing the composition of durable polymer DES, Virmani said the disadvantages were many. “These stents result in delayed healing and DAPT [is] required for at least 1year, and maybe even longer due to poor endothelialization,” she said.

In addition, permanent, non-erodable polymers may induce inflammation and hypersensitivity vasculitis in patients; coating is permanent, even when not needed. The constant irritation may lead to long-term restenosis and induce neoatherosclerosis within the stented segments. Hence the reason why degradable polymers and scaffolds make more sense, she said.

Knowing that the use of polymers may induce inflammation, Virmani said, “we should always worry about inducing inflammatory reactions.”