Topology-guided shell–truss transition design for additively manufactured TPMS scaffold metamaterials

Additive manufacturing enables complex, interconnected triply periodic minimal surface (TPMS) scaffold metamaterials, but regulating their mechanical properties through relative density or wall thickness alters pore architecture and limits stiffness control at prescribed porosity. A topology-guided shell–truss transition strategy is proposed to achieve topology-assisted stiffness regulation at comparable porosity. Inspired by the morphological continuum from closed-walled through open-walled to truss-like forms in trabecular bone, topology-optimised opening patterns are introduced into closed-walled Schwarz primitive TPMS unit cells. Two representative unit-cell families, ‘D-cross’ and ‘honeycomb’, are constructed to examine how opening topology redistributes load-bearing pathways and reshapes effective stiffness. By coordinating shell thickness and feature width, the proposed metamaterials expand the Young’s modulus–density space from the single trajectory of conventional TPMS shells to a tunable region covering the trabecular-bone range. Selective laser-melted Ti6Al4V specimens confirm manufacturability and demonstrate topology-dependent differences in apparent compressive modulus and first-peak stress at nearly identical porosity. Permeability measurements confirm comparable transport performance between the topology families and trends consistent with numerical predictions. Finite-element analysis reproduces the topology-dependent apparent compressive stiffness trend and reveals distinct early-stage stress redistribution. This work provides a topology-assisted route for balancing mechanical matching, pore connectivity and surface accessibility in bone scaffold design.