Mechanical and mass-transport design of hybrid TPMS-based metamaterial scaffold for orthopedic implants

Abstract

Orthopedic implants have been widely used to treat massive bone defects in clinical applications. To realize physiological functions after implanting, the mechanical and mass-transport properties of the designed implants should match the properties of the human skeleton. Additive-manufactured titanium lattice scaffolds have aroused great attention due to their superior performances, which can be precisely tuned via cellular structure design. Titanium alloys also show good biocompatibility, which is essential for implants. However, it is still challenging to concurrently design the mechanical and mass-transport properties of metamaterial-infilled implants, which are both of great importance in clinical usage. In this work, a novel series of hybrid triply periodic minimal surface (TPMS)-based lattice unit cells were proposed based on Boolean operations, in which the modulus and permeability can be precisely tuned by adjusting the cellular geometric parameters. The mechanical and mass-transport properties were evaluated numerically, and mechanical experiments were conducted to verify the finite element results. Response surface models of the cellular properties were established based on finite element analysis results to describe influence of geometric parameters, and feasible domains of the geometric parameters for implant design were also calculated. Cell culturing tests were also performed to validate the biocompatibility of the additive-manufactured lattice scaffolds. The proposed hybrid TPMS structure decoupled cellular stiffness from permeability and broadened the accessible design space of TPMS-based microstructure. This work paves the way for the design and clinical application of additive-manufactured metamaterial-infilled orthopedic implants. The results indicated that the proposed hybrid TPMS cells possess great potential for the design of orthopedic implants.