Image courtesy of Pei-Jiang Wang
Bioresorbable coronary scaffolds, designed to avoid the risks associated with the long-term implantation of metal stents, once captured the attention of medtech giants like Abbott (NYSE:ABT) and Boston Scientific (NYSE:BSX).
But companies have since linked the use of these biodegradable polymer-based devices to a heightened risk of myocardial infarction and thrombosis, prompting Abbott to pull its Absorb product from the market and Boston Scientific to terminate its Renuvia scaffold development program last year.
Researchers at Massachusetts Institute of Technology wanted to understand why these stents failed. Funded by Boston Scientific and the National Institutes of Health, they explored the microscopic structure of bioresorbable scaffolds, on the hunt for any clues as to why the devices didn’t hold up in patients.
The team discovered that degradable stents, which are made from the same polymer used in dissolvable sutures, have a heterogeneous (meaning non-uniform) inner structure. When the device is inflated, the internal layer is disrupted and rendered susceptible to structural failure.
“Because the nonuniform degradation will cause certain locations to degrade faster, it will promote large deformations, potentially causing flow disruption,” lead author Pei-Jiang Wang told MIT News.
The researchers, whose work was published last month in the journal Proceedings of the National Academy of Sciences, recommended that companies explore alternative methods to stent development to avoid the microscopic flaws seen with current-gen bioresorbable devices.
The reason this problem evaded companies for so long, according to the research team, is that it takes a long time for the microscopic structural flaws to manifest into visible problems. The companies weren’t using the proper analytical tools to be able to see these tiny problems.
“People have been evaluating polymer materials as if they were metals, but metals and polymers don’t behave the same way,” MIT health sciences and technology professor Elazer Edelman said. “People were looking at the wrong metrics, they were looking at the wrong timescales and they didn’t have the right tools.”
There are two parts in the information you dispatched, one summarizes a tentative explanation to the relative failure of ABBOTT’s BVS and Boston Scientific’s BRS in their stenting and resorption functions, the other indicates the existence of different technologies. Unfortunately, these alternatives are drawn into the giants’ dives in many cardiologists’ vision. This consequence is regrettable because it almost kills the chance to take advantage of the resorption that a technology different from giants’ ones may offer in the future. My other comment concerns the explanation proposed by MIT scientists as you report it. It seems that they rediscover the wheel. Lactic acid-based polymers (only the poly[(S)-lactide)] member of the family was exploited by the giants for their technology) have been known for decades and the relative science is very rich, including the particularities relative to bioresorbable stenting. It has been known for decades that semi-crystalline lactic acid-based polymers are glassy and brittle when rapidly deformed at body temperature, and that degradation in amorphous zones is faster than in crystalline ones, with high risk of breaking when crystallinity is made excessive by drawing. Important too are other factors, including the fact that residual crystallites are very inflammatory and may cause late dramatic reactions. A look at the book entitled “Bioresorbable Scaffolds:From Basic Concept to Clinical Applications” edited By Y. Onuma and P.W.C. Serruys (ISBN: 9781498779777) especially the first chapters, will tell you and the readers of the journal much more than what MIT’s researchers postulate. It will also allow paying credit to the pertinent recent literature and to the tentative alternative technologies.