Additively manufactured metallic hip shaft structures with integral structure and organo-chemically functionalized outer surface (Acronym: AntiStressShielding)

• Applicants: Professor Dr.-Ing. Horst Fischer; Professor Dr.-Ing. Ulrich Krupp
• Subject Area: Materials in Sintering Processes and Generative Manufacturing Processes ; Biomaterials ; Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 567364495

One of the most frequently performed orthopedic surgeries is hip and knee replacement. The main reasons for the failure of endoprostheses are loosening processes. These can be triggered by "stress shielding". Due to the difference between the elastic modulus of the cortical femur (approx. 20 GPa) and the endoprosthesis stem (Ti: approx. 105 GPa, CoCr: approx. 210 GPa), the stress acting on the bone is greatly reduced. This leads to bone tissue loss and prosthesis loosening. The aim of the project is to scientifically test a new design approach to address the problem. The reduction of "stress shielding" is to be achieved by reducing prosthesis stiffness. It has been shown that metallic lattice structures exhibit significantly reduced stiffness. In the project, different lattice structure types (f2bcc,z, gyroid, etc.) are investigated with regard to their structural stiffness and fatigue strength. A pre-selection of suitable structures is made with the help of finite element calculations. These structures are then manufactured using the LPBF process from the β-titanium alloy Ti24Nb4Zr8Sn (Young's modulus approx.50 GPa). To increase the fatigue strength, various post-treatment methods are applied. To enhance the attachment of adjacent bone cells to the implant surface and thus improve osseointegration, chemical conjugations of bioactive ligands or short peptide sequences derived from extracellular matrix (ECM) proteins are used to create a biomimetic microenvironment on the surfaces. In the presence of adhesion ligands, the osteoinductive effect can be significantly enhanced and accelerated differentiation of human mesenchymal stem cells into bone cells can be induced. For this reason, the adhesion peptide c-RGD as well as the growth factor BMP-2 are immobilized on Ti24Nb4Zr8Sn surfaces in different concentrations to be able to evaluate the synergistic effect of both biomolecules. The interaction of both biomolecules will be analyzed by the expression of osteoinductive markers, such as STRO-1, RUNX-2 and osteopontin using immunofluorescence. In addition, the mineralization behavior of mesenchymal stem cells and the secretion of alkaline phosphatase into cell culture supernatant at different time points will be examined. In addition, we will work out how organo-chemical functionalization can be immobilized most efficiently on the outer mantle of a lattice structure.

• DFG Programme: Research Grants