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Tests at SPS Medical, an independent lab in Rush, N.Y., showed PPSU became significantly yellowed and brittle after only 150 Sterrad NX cycles, while Ultem HU1004 showed negligible yellowing or embrittlement after 300 cycles. PPSU showed 10 times greater color shift than Ultem HU 1004 resin significantly yellowing after only 100 Sterrad NX cycles.

With the Ultem HU1004 resin grade, Ultem resins are now one of the few materials that can maintain its key performance properties after exposure to the four most common techniques used in sterilization environments, including:

Autoclave
Low-temperature gas plasma
Ethylene Oxide
Gamma/e-beam radiation

Finally, Abbott Vascular is working to develop a fully bioresorbable polylactic acid (PLA) based stent. While there are three types of bioabsorbable stent technologies under development - including bioabsorbable polymers to coat metal stents, totally bioabsorbable metallic stents that corrode and totally bioabsorbable polymer stents - many stent makers believe that fully dissolving polymer stents are the long term solution. Metal stents are foreign objects that can:

Irritate vessels and cause stent thrombosis
Prevent vessel remodeling
Prevent future surgical interventions
Can fatigue and suffer strut fractures, and impair CT or MR imaging

For these reasons, several stent manufacturers are working on biodegradable stents that do not leave behind any hardware. The main challenge with a fully dissolving polymer stent is to maintain radial strength to keep the vessel open long enough to prevent renarrowing.

Abbott is using stretch blowmolding to enhance physical properties of PLA used to develop its Absorb bioresorbable vascular stent. The stent needs to remain intact for 3-6 months to support artery walls until they can stay open on their own and dispense drugs that maintain artery health. The entire drug is fully eluted in 120 days. The PLA is fully broken down within two years into water and CO2.

PLA degradation rates can be adjusted by changing the ratio of crystalline material in the PLA - the amorphous zones in the PLA breakdown at a different rate than the semi-crystalline zones. Abbott is using strain induced crystallization in the stretch blowmolding process to alter the crystalline material ratio in the PLA. PLA strength is also tailored to provide the necessary vascular wall support and to withstand the sterilization process.

Abbott commercialized the international launch of its Absorb bioresorbable vascular scaffold, now widely available across Europe and parts of the Asia Pacific and Latin America. Abbott is referring to Absorb as a scaffold to indicate that it is a temporary structure, unlike a stent which is a permanent implant.

The international launch of Absorb followed a medical trial program that encompassed five studies in more than 20 countries. Abbott says that study data indicate that Absorb performs similar to a best-in-class drug-eluting stent on tests such as major adverse cardiovascular events (MACE) and target lesion revascularization (TLR).