What is one characteristic of covered stents currently under research?

Covered stents are currently under research and are often considered experimental. This means they are not yet widely recognized for clinical use, as their efficacy, safety profiles, and potential applications are still being evaluated through ongoing studies. The research phase allows for the assessment of their benefits in various medical conditions, particularly in treating vascular obstructions or leaks while minimizing the risk of complications.

The other choices represent characteristics that either do not apply to the current status of covered stents or reflect attributes that are not specifically tied to their ongoing research. For instance, the notion that they are widely available contradicts their experimental status and the rigorous regulatory processes they must undergo before becoming standard practice. Similarly, while flexibility could be a feature of some stents, it does not specifically characterize the covered stents under research, nor is their use limited to emergencies. Thus, recognizing covered stents as experimental aptly reflects their current development stage in interventional radiology.