9.3 Bio-Resorbable Scaffolds: What is their Future?

These proceedings summarize the educational activity of the 17th Biennial Meeting of the International Andreas Gruentzig Society held January 30 to February 2, 2024 in Chiang Rai, Thailand.

Faculty Disclosures     Vendor Acknowledgments

2024 IAGS Summary Document

Statement of the problem or issue

Metallic stents have certain limitations. For example, there are technical issues and difficulties with placing them in angulated and tortuous vessels, delivering longer stents around bends, or positioning them in vein grafts. Metallic stents have rates of restenosis of up to 5%, stent thrombosis in 0.5%-1%, and stress fracture rates of 1%-8%. Metallic stents may impede or even prevent CABG if too many are placed into far distal sections of coronary arteries, thereby precluding vein graft attachment. Attempts to overcome these limitations led to the development of bioresorbable vascular scaffolds (BVS), stent-like devices that dissolve away slowly over months. The last sizable BVS study was ABSORB III.¹ Unfortunately, long-term results were not favorable. Late-lumen loss was greater with BVS, and TLR, target vessel MI, and very-late scaffold thrombosis rates all were higher with it.²

Gaps in current knowledge

There is incomplete understanding why BVS are inadequate when theoretically they should be superior. Some of these knowledge gaps areas are listed in the Table. Lower radial strength with BVS, which is logarithmically less than metallic stents, seems to be the prime reason for their lack of superiority, contributing to greater mal-apposition and inadequate embedment in the vessel wall. Their greater strut thickness does not overcome this limitation.^3,4 Bioresorbable metallic stents, like those composed of magnesium alloys, do have greater radial strength but still are only a partial solution since they degrade and are resorbed relatively quickly.

Table. Knowledge gap areas for bioresorbable vascular scaffolds.

Possible solutions and future directions

A number of initiatives are underway to overcome BVS limitations. The correct procedural techniques, including use of intravascular imaging, are under investigation. Strut materials and coatings are being developed and examined. Physical and mechanical properties of BVS are being scrutinized, especially radial strength.⁵ The current challenge is how to increase the radial strength of the polymer to bring it closer to that of a metal. For magnesium alloy stents the improved polymer coatings may slow the degradation/resorption process and permit adequate and sustained drug delivery. Newer iron or zinc alloys or a hybrid metallic-polymer material may provide another solution.

References

1. Wykrzykowska JJ, Kraak RP, Hofma SH, et al. Bioresorbable scaffolds versus metallic stents in routine PCI. N Engl J Med. 2017;376(24):2319-2328. doi: 10.1056/NEJMoa1614954. PMID: 28402237.
2. Kereiakes DJ, Ellis SG, Metzger DC, et al. Clinical outcomes before and after complete everolimus-eluting bioresorbable scaffold resorption: Five-year follow-up from the ABSORB III trial. Circulation. 2019;140(23):1895-1903. doi: 10.1161/CIRCULATIONAHA.119.042584. PMID: 31553222.
3. Mishra S. Bioresorbable scaffold -fourth revolution or failed revolution: Is low scaffold strut thickness the wrong target? Indian Heart J. 2017;69(6):687-689. doi: 10.1016/j.ihj.2017.10.004. PMID: 29174242.
4. Mishra S. Structural and design evolution of bio-resorbable scaffolds: The journey so far. Curr Pharm Des. 2018;24(4):402-413. doi: 10.2174/1381612824666171227212737. PMID: 29283053.
5. Mishra S. A fresh look at bioresorbable scaffold technology: Intuition pumps. Indian Heart J. 2017;69(1):107-111. doi: 10.1016/j.ihj.2017.01.006. PMID: 28228292.