Hybrid zirconia epoxy lattice composites fabricated by digital light processing, sintering and infiltration:...

An essential requirement for effective bone implants is the ability to replicate the natural functional gradient of bone, particularly the gradual variation in stiffness across different regions. In this study, graded lattice structures based on triply periodic minimal surface (TPMS) gyroid geometries were designed with a constant overall relative density and varying local volume fractions. Three architectures were investigated: a uniform lattice structure (ULS), a unidirectionally graded lattice (UniGCLS), and a bidirectionally graded lattice (BiGCLS). The lattices were fabricated from 3 mol% yttria-stabilized zirconia (3-YSZ) using vat photopolymerization-based digital light processing (DLP), achieving dimensional accuracy within 1.5% through a shrinkage-compensation strategy. Surface functionalization using KH-570 silane enhanced wettability and interfacial bonding prior to epoxy infiltration. Mechanical testing revealed a strong influence of gradient architecture on compressive behavior, with the UniGCLS exhibiting the highest compressive strength (72.92 MPa) and failure strain (2.79%) due to a smooth porosity gradient and uniform stress distribution, while the BiGCLS showed premature failure from abrupt transitions. Epoxy infiltration transformed the brittle ceramic response into a ductile, energy-absorbing behavior by bridging cracks and redistributing stresses. The UniGCLS/epoxy composite demonstrated the most stable deformation and superior energy absorption, highlighting its potential for durable bone implant applications.