Nitinol is a metal with a memory: compressed into a tiny tube, it springs back into shape inside a vessel and keeps it open. But simply inserting a stent isn't enough: it must not clog with clots. To prevent that, a drug is applied, which should be released slowly, like water from a sponge, not all at once.
Scientists treated the nitinol in two steps: first, they used an electric current to grow a uniform layer of pores tens of nanometers in size on the surface; then they coated it with chitosan — a substance derived from crustacean shells that can hold and gradually release drugs. The result was a sponge with a thin film on top.
They tested how heparin comes out of this structure. It turned out that without chitosan, it washes out too quickly, but with chitosan, the release is stretched over time. Cells taken from a human umbilical cord thrived on the coating, indicating that the material is non-toxic.
This "smart" surface is a step toward stents that self-regulate drug dosage and don't harm the body.
Chitosan is derived from chitin — the very substance that makes up the shells of crabs and shrimp. In medicine, it's valued for its ability to slowly release drugs and heal wounds.