Abstract:
Cardiovascular disease manifests in either clogged arteries or in defects within the heart. Implants are used for both opening up and closing cardiovascular vessels or defects. A stent is used for reopening clogged arteries, while an occluder is employed for patching up a defect or hole. Historically, such implants have been made of biostable materials (metal or metal-plastic combinations). I will trace the role of metals in the development of coronary stents and the resulting revolution in cardiology. When first introduced in 1993, bare metal stents (BMS) revolutionized the field of interventional cardiology. However within a few years it became apparent that the use of a permanent stent is not required in most instances of blocked body passageways¹. Hence arose the need for the Disappearing Stent- one that is functional over a specified time period, then dissolves away leaving no local side effects². In our laboratory, we started work on dissolvable stents in 2000, and developed fully-resorbable stents for ureteric³, tracheal⁴ and peripheral vasculature/ coronary artery⁵ applications.

Several aspects of biodegradable stents relevant to its deployment and performance were studied and published: this includes shape memory effects, biodegradation rates, and strength. This work led to the founding of a company, Amaranth Medical, which has since completed several human trials with our stent⁶.

Our experience with the resorbable stent led to other cardiovascular applications such as closure of atrial septal defects (ASD) or patent foramen ovale (PFO). Closure of these defects using permanent occluders (mainly Nitinol-based) leads to long-term complications such as arythmias and thromboembolism⁷, and highlights the need for a biodegradable occluder.

A new occluder design was conceived⁸ and reduced to prototype. This device design is termed a “Chinese Lantern” design. This design is effective in sealing the heart defects temporarily, then allowing for ingrowth of cells.

In the treatment and management of cardiovascular disease, materials innovation plays a pivotal role. Revolutions in cardiology are truly driven by clever use of metallic and polymeric materials. Such innovations lead to minimally-invasive procedures, such as percutaneous deployment of coronary stents, occlusion of defects as well as heart valve replacement. Much remains to be done to make these devices functional and well-tolerated while they degrade in their environment in heart tissue.

References
[1] Kimura et.al., New England J Med., 334, pp.561, 1996
[2] Venkatraman SS, Boey F. Release profiles in drug-eluting stents: Issues and uncertainties, Journal of Controlled Release, 120 (3), pp. 149-160 (2007).
[3] Chan WA, Bini TB, Venkatraman SS, Boey FYC. Effect of radio-opaque filler on biodegradable stent properties, Journal of Biomedical Materials Research Part A, Volume 79A (1), pp. 47-52 (2006).
[4] Zhu GH, Ng AHC, Venkatraman SS, Boey FY, Wee AL, Trasti SL, Yee-Lim LH. A novel drug-eluting tracheal stent, Laryngoscope, 121 (10), pp. 2234–2239 (2011).
[5] Venkatraman SS, Tan LP, Joso JF, Boey YCF, Wang X. Biodegradable stents with elastic memory, Biomaterials, 27 (8), pp. 1573-1578 (2006).
[6] http://amaranthmedical.com/; accessed February 24, 2015.
[7] Carminati M, Giusti S, Hausdorf G, et.al., European multicentric experience using the CardioSEAL(R) and Starflex double umbrella devices to close interatrial communications holes within the oval fossa. Cardiol. Young. 2000;10(5):519-526.
[8] Subramanian Venkatraman; Boey Yin Chiang Freddy; Wu Wei; Tang Yong-dan; Yip Wei Luen James; Duong Hong Duc: Occlusion Device For Closing Anatomical Defects, US Provisional Patent Application No. 61/287,544, filed Dec 18, 2009.