Asymmetric Mechanical Behavior and pre-osteoblast differentiation in Ti-6Al-4V Minimal-Surface Bone-Analogues: The Role of Pore Topology.

Abstract

The manufacturability of the cellular structure-based materials represents one of the most emerging themes in the additive manufacturing of medical implants and devices. This has been more relevant as natural bone possesses a unique porous architecture, which cannot be mimicked in conventional manufacturing. Despite recent advances, a critical knowledge gap persists in connecting scaffold topology and manufacturability with the mechano-biological responses, governed by asymmetric 3D pore structures. In this perspective, the present study focuses on selective laser melting of Schwarz diamond-based triply periodic minimal surface (TPMS) structures in Ti6Al4V, while varying unit cell size from 2.5 to 3.0 mm. The extensive micro-computed tomography analysis of 3D pore topology using customised design evaluation protocols established the efficacy of SLM-based optimised process parameters on dimensional tolerance and manufacturability of the TPMS structures. Intriguingly, an asymmetric mechanical response with a clinically relevant combination of the compressive elastic modulus (14-20 GPa), tensile elastic modulus (38 - 55 GPa), compressive strength (413-547 MPa), and tensile strength (325-475MPa), together with unique 3D pore architecture, closely resembled the properties of human cortical bone. While fitting the strength/modulus to relative density data using the Gibson-Ashby model, the bending-dominated asymmetric microstructural response was revealed with exponents of ∼1.5 in compression and ∼2.0 in tension. Furthermore, in vitro studies demonstrate MC3T3-E1 pre-osteoblasts' adhesion, proliferation, and maturation with modulation of early osteogenic markers and bone mineralisation, both quantitatively and qualitatively. The confocal microscopy observations revealed the cellular bridging, migration, and colonisation, indicating cytocompatibility. The present study conclusively establishes that SDW-TPMS structures offer a compelling combination of cortical bone-mimicking mechanical properties and a favourable biological response. It highlights their potential for reconstructive surgeries of load-bearing joints. STATEMENT OF SIGNIFICANCE: Conventional high-modulus metallic implants can induce periprosthetic bone resorption via stress shielding. While additively manufactured porous biomaterials address this, a robust structure-property-function paradigm has remained elusive. This study presents a Ti-6Al-4V minimal-surface scaffold that achieves the biomechanical fidelity for load-bearing applications while providing a microenvironment suitable for differentiataion of pre-osteoblasts. The central innovation is our use of quantitative pore network modeling to establish a predictive link between the as-manufactured pore topology, the scaffold's pronounced tension-compression asymmetry, and its pro-osteogenic biological response. This work provides a validated framework for the rational design of next-generation bio-integrated orthopedic implants.