Exploiting the advantages of additive manufacturing processes in medical technology

Additive manufacturing processes are playing an increasingly important role in the field of medical technology. They make it possible to meet the demand and need for patient-specific products. The high design freedom of additive manufacturing processes in combination with CAE methods is used to provide approaches to solve the existing stiffness problem in hip endoprosthetics. Using stress adapted geometries and the finite element method, stiffness adapted variants of a short shaft hip endoprosthesis are developed in an iterative process.

One way to vary the stiffness of the implant is the choose of the material. It must be ensured that the selected material not only provides the desired stiffness, but also guarantees the fulfilment of the function by sufficiently good mechanical characteristics. A material that meets the above-mentioned requirements is the
titanium aluminum alloy Ti6-4, which can be processed reliably by selective laser melting. A striking feature is the low Young’s modulus compared to other biocompatible metallic materials, which has a positive influence on the stiffness optimization of implants. The optimization process is carried out by systematically changing the cross-sectional profile of the hip prosthesis for stepwise stiffness adjustment. The result is a more homogeneously stressed bone contact surface, which allows a more extensive transfer of stress to the bone and reduces bone degradation due to stress shielding.

A stiffness-adapted short shaft hip endoprosthesis could be developed by targeted use of the potentials of selective laser melting, in particular the possibility of creating filigree internal grid structures and variable wall thicknesses as well as internal cavities. By numerical analysis of the stress situations of bone and implant, the problem of “stress shielding” and thus potential problems of the patient could be reduced and the expected service life of the prosthesis
increased. The stiffness-adjusted hip endoprostheses were checked for their operational reliability by numerical methods. The findings on stiffness adjustment by exploiting the potential of selective laser melting can now be transferred to other components. Especially for implants, the problem of the stiffness difference between bone and implant is of immense importance, but also technical applications can profit from these considerations.