Continuous functionally graded porous titanium scaffolds manufactured by selective laser melting for bone implants

Bone implants require mechanical properties that closely match natural bone to ensure long-term stability and integration. Traditional implants often fail to replicate the functional gradient in stiffness that exists within natural bone. Prior research has shown that porous titanium scaffolds can mimic cancellous bone properties, but achieving continuous gradients in porosity remains a challenge. Existing methods struggle with maintaining structural integrity while varying porosity. This gap motivated the development of functionally graded porous scaffolds. No prior work had resolved how to systematically control porosity across a scaffold. The need for a scalable and precise manufacturing method is clear. Selective laser melting (SLM) offers potential for complex geometries but requires validation for graded scaffolds. This study addresses the limitations of current approaches by exploring SLM’s capability for this purpose.

The aim of this study is to evaluate the feasibility of manufacturing continuous functionally graded porous titanium scaffolds using selective laser melting. The specific problem is the lack of methods to produce scaffolds with graded porosity that mimics bone’s natural gradient. The motivation comes from the need to improve implant integration and reduce stress shielding. The study focuses on the Schwartz diamond unit cell as a design framework. It seeks to determine if SLM can fabricate scaffolds with controlled porosity ranges. The goal is to establish a correlation between porosity and mechanical properties. The study also aims to develop predictive equations for scaffold performance. This approach could lead to better-designed implants that support bone tissue growth.

The study uses selective laser melting to fabricate functionally graded porous titanium scaffolds. The Schwartz diamond unit cell is selected as the base geometry. Graded volume fractions are varied from 7.97% to 19.99% across the scaffold. Micro-topology is analyzed using imaging techniques to assess fabrication accuracy. Strut dimensions are measured to evaluate dimensional precision. Mechanical properties, including elastic modulus and yield strength, are tested under compression. Gibson and Ashby models are applied to derive predictive equations. The scaffolds are compared to homogeneous porous structures to assess functional advantages.

The fabricated scaffolds show no defects and accurately reproduce the designed geometry. Strut sizes range from 483 to 905 µm, confirming dimensional control. Elastic modulus is adjustable from 0.28 to 0.59 GPa, matching cancellous bone values. Yield strength ranges from 3.79 to 17.75 MPa, also comparable to cancellous bone. The graded porosity allows for a wide pore size variation from 7.97% to 19.99%. Mathematical relationships between porosity and mechanical properties are established. Two predictive equations are derived from the Gibson and Ashby model. These equations enable estimation of modulus and strength based on design parameters.

The study demonstrates that SLM can produce continuous functionally graded porous titanium scaffolds with controlled porosity. The scaffolds exhibit mechanical properties similar to cancellous bone. The graded structure allows for pore size and porosity variation, which may support bone tissue growth. Predictive equations are developed to estimate mechanical behavior. These findings provide a basis for new design methodologies in scaffold manufacturing. The approach offers potential for tailoring implants to specific patient needs. The results suggest that graded scaffolds may outperform homogeneous ones in bone integration. The study supports further exploration of SLM for advanced implant design.