Insights into the mechanical interaction between an active cranial implant and the skull subjected to moderate impact loadings

In the context of cochlear implants, which are now widely used, and innovative active devices, the cranial implantation of electronic devices raises new questions about the mechanical interactions between the implant and the skull. The aim of this study was to build a methodology using experimental data and numerical simulations to evaluate the mechanical interactions between the skull and the WIMAGINE® active cranial implant intended for use for tetraplegic patients. A finite element model of the implant housing and a simplified model of the three-layered skull were developed. 2.5 J-hammer impact tests were performed on implant housings and ovine cadaver heads for model calibration. The two models were then combined to analyze the interactions between the skull and the implant and compared against impact tests. The implant dissipates a certain amount of the impact energy which could be a parameter to include in implant design in addition to the implant integrity, tending to increase the implant stiffness. The non-implanted as well as the implanted lamb heads demonstrated an overall good resistance to the impact tests. The models correlated well with the experimental data, and improvements of the model through more realistic geometry (CT-scans) and more complex material behavior could now be implemented. Such a model could then be used with human head geometries and help for future implant design optimizations using numerical models of the implant-skull and even implant-head complex.