Orthopaedic implants - towards challenges of meta-optimization

Michael Gasik, Aalto University Foundation

Orthopaedic and dental load-bearing implants are one of the famous CAE topics in terms for biomechanics, topology and structural designs as solid 3D bodies. A lot of efforts are being done for optimization of their biomechanical properties, especially in respect to elimination of stress shielding effect and loads distribution improvement. As a result, hundreds of different designs are on the market, yet their versatility does not really reflects into the performance and patient satisfaction. Recently, more attention has been also put in design of the implant surface and living tissue interactions such as combined effect of porosity and its topology, roughness and osteointegration etc. However, there is a great disagreement what is indeed "optimal". Numerous attempts are made for in vitro data connection with 3D structure of the surface, but complexity of the problem is too high.
Furthermore, existing in vitro protocols for biocompatibility (as ISO 10993) are of very limited use, as they do not demonstrate clear connections with realistic in vivo performance. The situation is complicated by external factors biomechanical engineers cannot control (infection, inflammation, aseptic loosening, drug release etc.) which reasons are not even fully understood.
Therefore "meta-optimization" might be a solution - there basic biomechanics is complemented by MODAO (multi-objective design and optimization) approach using data of surface interaction with different cells, factors, extra-cellular matrix, bacteria, viruses and drugs. Altogether such data (with a proper DoE) are shown to be correlating with in vivo tests (animal models), further leading to realistic follow-up conclusions supported by Bayesian analysis, recently recommended by FDA. In the presentation, this concept is presented, discussed and demonstrated with practical examples, including new scientifically based methods for biomaterials evaluation.