No abstract

ASTM F 2129 test method nor the FDA provides any guidance as to what constitutes an acceptance criterion for the corrosion resistance of implantable medical devices. Neither provide any guidance on how many samples to test or how to handle censored data, i.e. datasets where there are only a few tests that breakdown. The development of both a statistically valid acceptance criterion for corrosion resistance and a method of evaluation would be of significant benefit to the medical device community. This study of 420 nitinol cyclic polarization tests, which builds on previous research that was presented at SMST 2007, investigates the effect of long-term exposure to simulated in vivo environments with differing degrees of aeration. This was accomplished by pre-exposing electropolished (EP) nitinol to phosphate buffered saline (PBS) at 37°C that had been sparged with either ultra high purity nitrogen or laboratory air. Immersion times ranged from 1 h up to 30 days. A total of 290 EP samples were tested in order to obtain a reasonable number of samples with breakdown, i.e. pitted. In addition, a total of 130 mechanical polished (MP) samples were also analyzed. This data allow us to test our statistical model that was presented at SMST 2007. This model takes into account the probability of breakdown per unit of exposed surface area and, if breakdown occurs, predicts the probability that E b 2 E r is greater than some threshold value. Aerated PBS environments were found to have a large influence on the margin of safety against pitting in vivo. Statistical methods for treating highly right censored pitting data are presented.

3′-trifluoropropyl)cyclotrisiloxane (II), and hexamethylcyclotrisiloxane (D 3 ) (III), respectively, in 1,1,3,3-tetramethyldisiloxane (TMDS). Solutions of a UV-sensitive diaryliodonium salt (0.5 wt %) and oligomers VII-IX were cast as uniform layers onto clean glass microscope slides and steel coupons. UV irradiation of these liquid layers rapidly converted them to cross-linked films (X-XII). Thermal stability of these films was determined by thermogravimetric analysis (TGA). Glass transition temperatures (T g s) were measured by dynamic mechanical thermal analysis (DMTA). Static contact angles of distilled water on the air-film interfaces of X-XII have been determined with a goniometer. Dynamic contact angle (DCA) measurements have also been carried out on free-standing films. Corrosion protection of steel coupons by X-XII was evaluated by electrochemical impedance spectroscopy (EIS) during exposure to 0.5 N NaCl. Antifoul and foul-release properties of X-XII were studied by settlement and removal tests with the barnacle Balanus amphitrite and with spores and sporelings of the green alga Enteromorpha.