[Paper Review] Architectural bone parameters and the relationship to titanium lattice design for powder bed fusion additive manufacturing

Martine McGregor, Sagar Patel+2 more|arXiv (Cornell University)|May 17, 2021

Bone Tissue Engineering Materials169 references102 citations

TL;DR

This review identifies the mismatch between natural trabecular bone microarchitecture and current titanium lattice designs fabricated via powder bed fusion additive manufacturing. It proposes that optimizing porosity, pore size, and lattice topology—particularly through surface-based or hybrid strut-surface lattices—can better match cortical and trabecular bone mechanical properties, reducing stress shielding and improving implant integration.

ABSTRACT

Additive manufacturing (AM) of titanium (Ti) and Ti-6Al-4V lattices has been proposed for bone implants and augmentation devices. Ti and Ti-6Al-4V have favourable biocompatibility, corrosion resistance and fatigue strength for bone applications; yet, the optimal parameters for Ti-6Al-4V lattice designs corresponding to the natural micro- and meso-scale architecture of human trabecular and cortical bone are not well understood. A comprehensive review was completed to compare the natural lattice architecture properties in human bone to Ti and Ti-6Al-4V lattice structures for bone replacement and repair. Ti and Ti-6Al-4V lattice porosity has varied from 15% to 97% with most studies reporting a porosity between 50-70%. Cortical bone is roughly 5-15% porous and lattices with 50-70% porosity are able to achieve comparable stiffness, compressive strength, and yield strength. Trabecular bone has a reported porosity range from 70-90%, with trabecular thickness varying from 120-200 {\mu}m. Existing powder bed fusion technologies have produced strut and wall thicknesses ranging from 200-1669 {\mu}m. This suggests limited overlap between current AM of Ti and Ti-6Al-4V lattice structures and trabecular bone architecture, indicating that replicating natural trabecular bone parameters with latticing is prohibitively challenging. This review contributes to the body of knowledge by identifying the correspondence of Ti and Ti-6Al-4V lattices to the natural parameters of bone microarchitectures, and provides further guidance on the design and AM recommendations towards addressing recognized performance gaps with powder bed fusion technologies.

Motivation & Objective

• To identify the mechanical and architectural parameters of human cortical and trabecular bone relevant to implant design.
• To evaluate the correspondence between natural bone microarchitecture and additively manufactured Ti-6Al-4V lattice structures.
• To identify performance gaps in current powder bed fusion (PBF) AM capabilities for replicating trabecular bone.
• To provide design and manufacturing recommendations for improved titanium lattice implants that better match bone's mechanical behavior.
• To advocate for advanced lattice geometries, such as surface-based or hybrid strut-surface lattices, to better emulate trabecular bone.

Proposed method

• Conducted a comprehensive literature review comparing human bone microarchitecture to Ti-6Al-4V lattice parameters in additive manufacturing.
• Analyzed porosity, strut thickness, pore size, and lattice type across 100+ studies on AM of Ti and Ti-6Al-4V lattices.
• Evaluated mechanical properties (Young’s modulus, compressive strength) of lattices against cortical and trabecular bone using the Gibson-Ashby model.
• Assessed manufacturability limits of powder bed fusion (PBF) AM for achieving trabecular bone-scale features (e.g., 120–200 µm trabecular thickness).
• Explored the potential of stochastic surface-based lattices to better mimic trabecular bone’s complex geometry.
• Proposed a framework for patient- and site-specific lattice design based on bone’s variable porosity and mechanical behavior.

Experimental results

Research questions

• RQ1 To what extent do current Ti-6Al-4V lattice parameters in PBF AM match the porosity and feature dimensions of human cortical and trabecular bone?
• RQ2 Can existing PBF AM technologies produce titanium lattices with mechanical properties comparable to those of human cortical and trabecular bone?
• RQ3 Why is replicating trabecular bone architecture with conventional strut-based lattices particularly challenging?
• RQ4 How can lattice topology (e.g., surface-based, hybrid strut-surface) improve mechanical matching to trabecular bone?
• RQ5 What design and manufacturing strategies are needed to reduce stress shielding in titanium bone implants?

Key findings

• Ti-6Al-4V lattices with 50–70% porosity achieve compressive strength and stiffness comparable to cortical bone (5–15% porosity).
• Trabecular bone porosity ranges from 70–90%, but current PBF AM produces strut thicknesses from 200–1669 µm, overlapping only partially with natural trabecular thickness (120–200 µm).
• Matching feature thickness alone to trabecular bone does not ensure mechanical property similarity due to differences in bulk modulus.
• Surface-based and hybrid strut-surface lattices show greater potential for replicating trabecular bone’s complex microarchitecture than traditional strut-based lattices.
• The Gibson-Ashby model effectively correlates porosity with Young’s modulus and compressive strength in Ti-6Al-4V lattices, but requires refinement for anisotropic, patient-specific designs.
• Patient-specific, site-specific lattice design is essential due to significant variation in bone porosity and microstructure across age, sex, and skeletal location.