Why can the absorbable bracket "deliver" to the metal bracket and sneak out? MIT scientists reveal that their structure is bruised

Release date: 2018-03-28

A few days ago, Dr. Why saw a post in a forum when “surfing the Internet”. The landlord was a confused girl. Her mother was diagnosed with coronary heart disease and her arterial stenosis was 80%. The doctor recommended interventional therapy and placed the stent. The girl’s mother waved her hand: “Do it! Life is the most important thing!”

However, when communicating the problem of what to put on the bracket, the girl’s mother heard that there is a particularly powerful new type of stent that can be naturally degraded. After a few years, it will be gone, not left in the blood vessels, no worries. Although expensive, it is much better than ordinary metal brackets! However, this kind of stent has not been listed in mainland China and has been obtained in Hong Kong. The girl asked someone to inquire, and some acquaintances told her that this absorbable stent is not so good and is prone to thrombosis, so don't go. So, the girl is confused, what should I do?

I believe this girl is not alone. Indeed, as the "fourth revolution" of coronary intervention, absorbable stents have advantages that metal stents cannot match, such as reducing the inflammatory response caused by long-term stent retention, shortening the time taken for dual antiplatelet drugs, and facilitating secondary treatment. Interventional therapy, etc. Because of these outstanding features and the efficacy of the third revolution, drug-eluting stents, in July 2016, the FDA approved the Abbott Absorb market, the first approved absorbable stent, will be Degraded slowly within 3 years.

However, this "future seed player", which everyone is optimistic about, has frequently seen "scandals" after listing. Several highly influential clinical journals such as the Lancet, New England Journal of Medicine, and the Journal of the American College of Cardiology published Absorb in a long-term follow-up of 2 or 3 years. Papers on formation rates and increased incidence of other cardiovascular events [1, 2, 3]. As a result, in September, Abbott announced that Absorb officially withdrew from the market due to sluggish sales.

Although Absorb is on the go, research on absorbable stents continues. What is the reason for its increased incidence of adverse events in long-term use? Do you know if this problem has bothered the majority of cardiologists?

In the recent Proceedings of the National Academy of Sciences, researchers from MIT found that the problem lies in this "degradation" [4]. Absorbable stents are mostly made of poly-L-lactic acid (pLLA), Absorb is no exception. There are still many applications of pLLA in the medical field. Absorbable surgical sutures and orthopedic internal fixation materials have pLLA. A place.

Although pLLA is widely used, in fact, the developer of the stent does not have a clear understanding of its degradation mechanism. In this new study, the researchers pointed out that uneven degradation may be the cause of the "failure" of the absorbable stent.

They used Raman spectroscopy to analyze the microstructure of the scaffold and made an important discovery. We know that the stent is hollow cylindrical, the outer layer contacts the vascular endothelium, the inner layer contacts the blood flow, and the "thickness" structure between the two layers is called the "core".

OS: outer layer; IS: inner layer; Core: inner core

The researchers found that the atomic structure of the inner and outer layers of the stent is different. The inner and outer layers have a regular crystal structure. The arrangement of the molecules is highly ordered, fixed in shape and not easily deformed. The inner core is worse than the core, the molecular arrangement is more disordered, and the structure is less stable. To quantify it, the crystallinity of the inner and outer layers (Crystallinity, the order of molecular chains) reached 61.1%, while the inner core was only 38.3%.

This microstructural difference causes the inner core to be more prone to small deformations of the microstructure under the pressure of the blood vessel wall and blood flow than the inner and outer layers, which often occurs before the scaffold degrades and the hidden seeds are buried. When the stent begins to degrade, the rate of degradation of the inner core that has undergone structural deformation is significantly faster than that of the inner and outer layers, and the uneven degradation rate causes the stent structure to "crash."

At this time, the stent has been obviously deformed. Just like the tunnel collapse, it can not only ensure the normal circulation of blood, but also hinder the effect. It is no wonder that the incidence of cardiovascular events in patients with absorbable stents is higher than that of metal stents. It is.

So why didn't you find this problem? First, because the research strategy of "copying" from the metal bracket neglects the difference in microstructure between the degradable material and the metal material; the second is because the previous preclinical experiment was only carried out for about 6 months, then the stent Microstructural deformation has just begun to occur, too small to be detected [5].

After reading this research, Dr. Why couldn't help but feel the emotion. In scientific research, “copying” is very dangerous (serious sigh. jpg). Later, researchers who can absorb the stent must consider the micro when selecting materials. Structure, and the observation period of preclinical experiments should be extended appropriately so that potential long-term risks can be observed more comprehensively.

Source: DoctorWhy

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