Multi-objective optimisation of 3D-printed multilayer TPMS osteochondral scaffolds for enhanced mechanical and biological performance

Triply periodic minimal surface (TPMS) architectures offer continuous curvature, a high surface-area-to-volume ratio, and tunable mechanical and mass-transport properties for osteochondral repair. Osteochondral defects have complex multilayered architectures, and conflicting requirements of high porosity and sufficient compressive strength challenge scaffold design. To address these issues, this study introduces a 3D-printed, TPMS-based multilayered osteochondral scaffold, optimised through a multi-objective framework to balance mechanical integrity with structural permeability. The scaffold includes cartilage and subchondral bone zones with independently designed TPMS unit cells, and a transition layer between them to replicate the functional gradient of native tissue. The response surface methodology (RSM) was used to build surrogate models linking geometric parameters to compressive modulus, porosity, and pore size. A Non-dominated Sorting Genetic Algorithm II (NSGA-II) was then applied to maximise compressive modulus and porosity while constraining pore size within a biologically effective range, and knee points on the Pareto front were identified based on their minimum distance from the utopia point, enabling balanced designs. The optimised scaffolds were subsequently manufactured and subjected to integrated structural, mechanical and fluid transport evaluations, confirming good agreement with the model predictions and a favourable internal flow environment. In vitro biological assessments confirmed excellent cytocompatibility. Overall, this work integrates TPMS structural design and multi-objective optimisation with multiscale experimental validation, providing a practical computational-to-physical workflow for osteochondral scaffold development.