Independent tuning of stiffness and toughness of additively manufactured titanium-polymer composites: Simulation, fabrication, and experimental studies

Abstract Titanium (Ti) alloys are one of the most appropriate metals for bio-medical applications, specifically in making implants. However, the high difference between the stiffness of the Ti alloys and compact bone results in stress shielding of the bone and stress concentration at the implant, both of which are undesirable and could result in implant failure. One method to reduce the stiffness of a dense implants and avoid the stress shielding is adding porosity to the structure. This however results in considerable reduction in the toughness of the structure, which is also undesirable for the long-term success of implants. In this work, we study a new method for independently tuning the stiffness and toughness of the material by adding various polymers to the additively manufactured porous Ti structures. Porous Ti samples with two levels of porosity are fabricated through additive manufacturing. Three different types of thermoplastic polymers are utilized to fill the pores and make the titanium-polymer composite parts. Compression simulations and tests are performed on both porous and composite specimens to compare the mechanical behavior of these structures. Various finite element simulations are conducted on different structures and the results are verified with experiments. Simulation results and experimental findings indicate that filling porous Ti with thermoplastic polymers leads to an increase in the toughness of the structure. The percentage increase of the toughness is assessed as a function of the polymer toughness and the level of porosity in various samples. Our results pave the way for designing polymer-composite structures with independently tunable stiffness and toughness for being employed in a broad range of applications.