Biodegradable Smart Stent Repairs Artery-Vein Connection, then Gently Disappears
Personalized cardiovascular treatment has taken a leap forward with research on a new biodegradable smart stent that can be engineered to last only as long as it is needed, avoiding problems such as in-stent blockage, blood clots, and the need for prolonged use of anti-platelet agents that may occur with traditional stents, which cannot be removed. This research is being performed by an interdisciplinary team from the NSF-funded Engineering Research Center (ERC) for Revolutionizing Metallic Biomaterials (RMB), which is headquartered at North Carolina A&T State University (NCAT) with partner institutions including the Universities of Pittsburgh and Cincinnati.
A stent is a mesh tube placed in a blood vessel to widen it and increase blood flow. Stents are used in procedures to prevent restenosis, which is the repeated closure of arteries that are dangerously narrow. Conventional stents stay in the body permanently and cannot be removed, so researchers have been studying biodegradable maturation-enhancing stents (bMES), which degrade in the body and eventually disappear after serving their purpose. The ideal situation is that the stent will function for about 4-6 weeks, and then degrade on command. However, past study and experiments showed that the bMES starts to degrade at the moment it is implanted, so it may not last long enough to do its job. The RMB researchers sought to address this problem by developing a smart stent that can be controlled to start and stop. They found two approaches using polymer coatings on the stent to do just that: (1) coatings that can be heated externally to start and, when its purpose has been served, then dissolve the stent, and (2) coatings that can prevent and then accelerate corrosion on command, based on electrical potential applied to the stent. These smart stent designs, which can be used in other implants, are quite novel do not appear to be reflected in scientific literature.
The induction-heating smart stent was tested in vitro. A magnesium or iron wire to simulate a stent was placed inside of a plastic tube that was routed through a copper coil of an induction heater. Saline water was pumped through the tube, and a thermocouple recorded the water temperature downstream of the wire. Different coatings were tried on the wires and the current in the heater and the heating times were varied. It was determined that the coating on the iron wire was easy to melt at low current (109A) in a short time (100 seconds). The temperature rise of the downstream water was less than 1 degree C. The coating on the magnesium wire was difficult to melt and a higher frequency induction heater may be needed to heat it. Further testing is needed.
The electrochemical corrosion smart stent was tested in a pig for one week. The electrical current corroded the stent faster relative to a reference stent but a problem with the electronics shortened the test. Further testing is needed, and the electronics also need to be made biodegradable.
