Human blood vessels sometimes become occluded or weakened. For example, the vessels can be occluded by a tumour, covered with a plaque, or weakened by an aneurysm. Such a vessel can be either reopened, reinforced, or even replaced with a medical endoprosthesis (stents or stent-grafts). For bare metal stents the in-stent restenosis was a serious problem for a number of patients. This spurred the medical device companies to search for an effective way of preventing restenosis. In late 1990’s the first drug eluting stents (DES) were developed as a solution to the problem.
PBII was used to modify and improve the surface of a NiTi alloy which is interesting for biomedical applications like vascular stents, vena cava filters or osteosynthetic devices. A high concentration of Ni at the surface can be the reason for allergic hazard, toxicity or carcinogenicity. The main goal has been the formation of a Ni-depleted surface, which should serve as a barrier to out-diffusion of Ni ions from the bulk material.
Ion implantation of oxygen or nitrogen was carried out.
The depth profiles of the elemental distribution in the alloy surface region, obtained by Auger electron spectroscopy (AES), confirm the formation a Ni-depleted layer.