Hierarchical cellular structures based on TPMS mimicking cancellous bone

Innovative lightweight materials have significance in various sectors, including biomedical applications, automotive, and aerospace industries. Triply periodic minimal surface (TPMS) structures enhance the performance of these materials by providing consistent energy absorption, high specific strength, and an extensive surface area. Creating hierarchical TPMS structures has emerged as a significant research focus to enhance and optimize these features. This work investigates the mechanical performance and surface-to-volume (S/V) ratio of TPMS-based hierarchical cellular structures modelled inspired by cancellous bone. Specimens with the designated TPMS structures were constructed, systematic production planning was conducted by Taguchi design of experiments (DOE) approach and the specimens were fabricated using bio-resin on a Masked Stereolithography (MSLA) type 3D printer. The mechanical characteristics of the created constructions, including initial peak, maximum peak, and absorbed energy, were investigated using compression tests. Results showed that the DP (main diamond and wall primitive) specimen has a maximum force and initial peak of 1700 N. DP and GP specimens, specifically the main gyroid and wall primitive, exhibit enhanced energy absorption and specific energy absorption capabilities. However, while the S/V ratio, a desirable characteristic particularly in biological applications, was below 0.5 mm^-1 in bulk volumes, it surpassed 0.5 mm^-1 in TPMS structures. In hierarchical structures, this value is approximately 2 mm^-1 for primitive wall structures and around 4 mm^-1 for diamond and gyroid structures. These findings highlight the potential of hierarchical TPMS designs to improve bone integration and tissue compatibility by increasing mechanical properties and surface area.