An experimental study of electrochemical polishing for micro-electro-discharge-machined stainless-steel stents.

This paper reports electrochemical polishing (EP) of 316L stainless-steel structures patterned using micro-electro-discharge machining (µEDM) for application to stents including intelligent stents based on micro-electro-mechanical-systems technologies. For the process optimization, 10 µm deep cavities µEDMed on the planar material were polished in a phosphoric acid-based electrolyte with varying current densities and polishing times. The EP condition with a current density of 1.5 A/cm(2) for an EP time of 180 s exhibited the highest surface quality with an average roughness of 28 nm improved from~400 nm produced with high-energy µEDM. The EP of µEDMed surfaces was observed to produce almost constant smoothness regardless of the initial roughness determined by varying discharge energies. Energy-dispersive X-ray spectroscopy was performed on the µEDMed surfaces before and after EP. A custom rotational apparatus was used to polish tubular test samples including stent-like structures created using µEDM, demonstrating uniform removal of surface roughness and sharp edges from the structures.

Radio aneurysm coils for noninvasive detection of cerebral embolization failures: a preliminary study.

The rupture of a cerebral aneurysm is the most common cause of subarachnoid hemorrhage. Endovascular embolization of the aneurysms by implantation of Guglielmi detachable coils (GDC) has become a major treatment approach in the prevention of a rupture. Implantation of the coils induces formation of tissues over the coils, embolizing the aneurysm. However, blood entry into the coiled aneurysm often occurs due to failures in the embolization process. Current diagnostic methods used for aneurysms, such as X-ray angiography and computer tomography, are ineffective for continuous monitoring of the disease and require extremely expensive equipment. Here we present a novel technique for wireless monitoring of cerebral aneurysms using implanted embolization coils as radiofrequency resonant sensors that detect the blood entry. The experiments show that commonly used embolization coils could be utilized as electrical inductors or antennas. As the blood flows into a coil-implanted aneurysm, parasitic capacitance of the coil is modified because of the difference in permittivity between the blood and the tissues grown around the coil, resulting in a change in the coil's resonant frequency. The resonances of platinum GDC-like coils embedded in aneurysm models are detected to show average responses of 224-819 MHz/ml to saline injected into the models. This preliminary demonstration indicates a new possibility in the use of implanted GDC as a wireless sensor for embolization failures, the first step toward realizing long-term, noninvasive, and cost-effective remote monitoring of cerebral aneurysms treated with coil embolization.