Accelerated life cycle testing

Once inserted, implants are supposed to stay in the body for life. Implants with active electrodes (cardiac pacemakers, cochlear and retinal implants) in particular tend to display substantially reduced performance after repeat surgery. Newly developed devices, therefore, must remain fully functional in the body for literally 99 years; insertion of cochlear implants, for example, is recommended for deaf children already in their first year of life! The necessary life cycle tests have to reflect such a long service life. So-called accelerated-aging procedures are used for this purpose, making use of the thermal activation that is part of degradation processes. This works well for metal-based and ceramic materials; however, with polymeric starting materials structural changes set limits which reduce the prognostic capability of such activation models. This is why we are exploring new test methods which, on top of only moderately increased temperatures, vary additional physicochemical parameters, as can be realized, for example, in high-pressure reactors. Based on our experience with corresponding theories, for example, about the diffusion of ion-containing fluids along heterogeneous interfaces or the effects of proteins and enzymes in body fluids, we are able to develop accelerated models that enable accurate prediction of an implant’s lifetime functionality in the body.

Publications

Benjamin F, Riedel F, Sendler N, Pohlmann G, Dasenbrock C, Glasmacher B, Lenarz T, Doll T. Accelerated Active Implant Degradation in Proteinated Artificial Body Fluids. Proc. DGBMT, Bremen, 2015

Majaura D, Borrmann F, Stieghorst J, Doll T. Evaluation of the bonding strength between a silicone rubber/polyimide interface for cochlear implants. Engineering of Functional Interfaces EnFI 2015 Proc., Hannover, July 2015