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Drug-eluting stents (DES), which were introduced in 2000, successfully addressed the issue of restenosis that was associated with bare-metal stents (BMS), and became one of the landmark advancements in the history of coronary artery intervention treatment. Traditional DES utilize permanently coated polymer coatings on the surface, which can cause chronic inflammation of the blood vessel wall and serve as an important trigger for late stent thrombosis (ST). Subsequently developed bioresorbable polymer-coated stents typically employ polylactic acid as the drug carrier coating, allowing the coating to completely degrade 6 to 10 months after the drug is fully released, minimizing the impact on the blood vessel wall and reducing the risk of late stent thrombosis.
However, the development of DES has now entered a bottleneck period, where improvements in stent platform, stent coating, and anti-proliferative drugs have had minimal impact on stent efficacy. In situations where various stents have comparable efficacy, enhancing the safety of stents is undoubtedly a good choice. Stent manufacturers have made numerous attempts in this regard, with technologies such as polymer-free coating, asymmetric coating, surface groove technology, eG™ technology, and Ti-O film among other stent coating technologies, all of which demonstrate the innovative capabilities of stent manufacturers.
To achieve controlled drug release, traditional DES use high molecular weight polymer materials as drug carrier coatings, which can stimulate the stent and adjacent arterial segments to undergo sustained oxidative stress and high sensitivity inflammatory reactions. This could potentially damage the endothelialization process of the stent and impair the endothelial function of the blood vessels neighboring the stent, thereby leading to poor stent apposition in the late phase. These factors could all be predisposing factors for late and very late intrastent thrombosis. Polymer-free coating technology further ensures safety by avoiding the introduction of nonessential foreign materials, favoring late endothelialization, and reducing the likelihood of thrombus formation. Examples include peripheral drug eluting stents.
Past studies have shown no statistically significant difference in the overall rate of thrombus formation between DES and BMS within the first year after stent implantation. However, the rate of very late stent thrombosis in DES significantly increases after 1 year, and this may be attributed to the design of the traditional DES drug carrier coating:
①The drug carrier coating of traditional DES is symmetrically designed, with drug coating present on both the luminal and abluminal sides of the stent. Antiproliferative drugs released gradually from the abluminal side of the stent coating can inhibit excessive proliferation of smooth muscle cells within the vessel wall, significantly reducing the occurrence of intrastent restenosis. However, antiproliferative drugs released gradually from the luminal side of the coating lack beneficial biological effects and instead inhibit the process of stent endothelialization and damage the endothelial function of the stent and adjacent vessel segments.
②The drug carrier coatings of traditional DES are all biologically nondegradable polymers that persist even after complete drug release. These factors could all be predisposing factors for late and very late intrastent thrombosis. Therefore, improvements in coating design may overcome the inherent limitations of traditional DES.
The coating design of the new asymmetric and degradable coating DES involves asymmetrical placement of drug-coated biodegradable polymer coatings only on the luminal side of the stent, with no drug coating on the abluminal side. This avoids the endothelial toxicity caused by drug release from the abluminal side coating.
Unlike traditional drug-eluting stents, surface groove coating technology utilizes lower drug and polymer amounts. The drug coating is solely deposited within the grooves on the outer surface of the stent, and after stent expansion, the drug is only released toward the vessel wall. The drug release rate is effectively controlled by the polymer, allowing for a smaller amount of drug to be maintained in the bloodstream for a longer period at an effective therapeutic concentration. An example is the coronary rapamycin target eluting stent system.
Featuring biodegradable drug coatings and electrografting technology (eG™) inert coating technology, eG™ solves the issue of coating rupture that commonly occurs in conventional stents due to compression or expansion, reduces delayed endothelialization caused by coating rupture, and ensures the efficacy and long-term safety of the product. Clinical studies have shown that after degradation of the biodegradable coating, eG™ can promote the process of endothelialization after stent implantation. An example is the drug eluting stent.
In recent years, Chinese scientists have discovered that n-type semiconductors and rutile structure titanium dioxide (Ti-O) have significant inhibitory effects on the adsorption of fibrinogen and platelet enzyme activation, and Ti-O thin films prepared possess the function of promoting endothelial cell growth and vascular endothelium repair.
At the same time, the design of this coating is based on the "early antirestenosis, late antithrombosis" temporal functionality chart. The early biodegradable polymer drug coating effectively inhibits restenosis, while after the drug coating is fully released, the titanium dioxide film promotes vascular endothelial repair.
Furthermore, the long-term anticoagulant effect of the titanium dioxide film can effectively prevent the occurrence of late stent thrombosis. An example is the drug-eluting stent.
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