Dosimetry of a 188rhenium-labeled self-expanding stent for endovascular brachytherapy in peripheral arteries

PURPOSE

Radioactive stents have been proposed as endovascular irradiation device to prevent in-stent restenosis by inhibiting neointimal proliferation. 32P-stents have been used in several studies so far, but require large-scale labeling procedures and endovascular barotrauma for stent expansion supporting the development of edge restenosis. Purpose of this study was to establish dosimetry of a self-expanding nitinol stent for peripheral vascular disease, which was radiolabeled with 188rhenium (188Re) by a dip coating technique.

METHODS AND MATERIALS

The surface of nitinol Memotherm FLEXX stents was polymer-coated providing functional NH(2) groups for diethylenetriaminepentaacetic acid (DTPA) binding, providing the ligand for the complexation of 188Re onto the stent surface. Stability of radiolabeling was tested over 48 h using an in vitro blood circulation (Chandler Loop). Radial and longitudinal dose distributions of a radiolabeled stent were obtained with a plastic scintillator dosimetry system.

RESULTS

Stents with a length of 30 mm and a diameter of 8 mm were labeled with up to 33 MBq 188Re. A total of 69+/-4% of the labeled 188Re remained stable on the stent surface after 48 h. Ninety-five percent of the infinitely accumulated dose was supplied to the target tissue within 72 h. Including correction for radioactivity washout from the stent, the infinitely accumulated dose at 1 mm radial distance from the stent surface was 1.85+/-0.19 Gy/MBq 188Re/cm stent length.

CONCLUSIONS

We developed a technique for radiolabeling of self-expanding nitinol stents with 188Re by dip coating and formation of 188Re chelate complexes. We provide dosimetry data useful for application of this beta-emitting stent for endovascular brachytherapy in peripheral vascular occlusive disease.

Bioactive immobilization of r-hirudin on CVD-coated metallic implant devices

The poor biocompatibility of metallic coronary stents which leads to un-satisfying restenosis rates is mainly caused by contact activation of blood cells, smooth muscle cells and endothelial cells. Mimicking a metal surface with a biocompatible coating that actively suppresses mechanisms leading to restenosis may overcome today's limitations regarding the complications of metal stents. Nitinol coronary stents were coated by CVD polymerization of functionalized [2.2]paracyclophanes. The monomers 4-amino [2.2]paracyclophane, 4-hydroxy methyl [2.2]paracyclophane and [2.2]paracyclophane-4,5,12,13-tetracarboxylic acid dianhydride were previously synthesized. A suitable installation for the CVD polymerization procedure was designed and used for the polymerization procedures. Physical and chemical properties of the polymers were shown to fulfill the requirements regarding the application as a stent coating material. The functional groups of the polymer coatings were used for the immobilization of the thrombin inhibitor r-hirudin. In vitro results indicate that the bioactively coated stents are less thrombogenic than virgin metallic stents. Surface-bound r-hirudin decreases platelet adhesion drastically due to interactions between platelets and r-hirudin.

Biocompatibility, cell adhesion, and degradation of surface-modified biodegradable polymers designed for the upper urinary tract

OBJECTIVES

The aim of this study was to develop a short bioresorbable ureteric stent and to characterize polymers and their surface modifications with respect to biocompatibility, degradation kinetics, cell adhesion properties, and incorporation of biologically active substances. Poly(D,L-lactide) PDLLA, poly(D,L-lactide-co-glycolide) PDLLA-co-GLY, and poly(D,L-lactide-co-trimethylenecarbonate) PDLLA-co-TMC were chosen as basic polymers. Surface modification was performed by plasma-induced graft polymerization and included grafting with hydroxyethylmethacrylate (HEMA), oligo(ethyleneoxide)-monomethacrylate (OEOMA), and acrylic acid (AAC). Biocompatibility of the polymers was assessed in vitro applying parameters of cell morphology, proliferative activity, and cell adhesion. All polymers were biocompatible and exerted no toxic effect on urothelial cell lines and on primary human urothelial cell cultures. A markedly reduced cell adhesion could be achieved in polymers grafted with HEMA, OEOMA, and AAC. Our results indicate that surface modification of bioresorbable polymers by grafting with HEMA, OEOMA, or AAC is an efficient approach to improve surface properties with respect to biocompatibility and cell adhesion properties.