TY - JOUR

T1 - Fatigue behavior of As-built selective laser melted titanium scaffolds with sheet-based gyroid microarchitecture for bone tissue engineering

AU - Kelly, Cambre N.

AU - Francovich, Jaedyn

AU - Julmi, Stefan

AU - Safranski, David

AU - Guldberg, Robert E.

AU - Maier, Hans J.

AU - Gall, Ken

N1 - Funding information: This study was performed in part at the Duke University Shared Materials Instrumentation Facility (SMIF), a member of the North Carolina Research Triangle Nanotechnology Network (RTNN), which is supported by the National Science Foundation (Grant ECCS-1542015 ) as part of the National Nanotechnology Coordinated Infrastructure (NNCI). Financial support from the German Research Foundation (grant MA 1175/67-1 ) is gratefully acknowledged.

PY - 2019/8

Y1 - 2019/8

N2 - Selective laser melting (SLM) has enabled the production of porous titanium structures with biological and mechanical properties that mimic bone for orthopedic applications. These porous structures have a reduced effective stiffness which leads to improved mechanotransduction between the implant and bone. Triply periodic minimal surfaces (TMPS), specifically the sheet-based gyroid structures, have improved compressive fatigue resistance due lack of stress concentrations. Sheet-based gyroid microarchitectures also have high surface area, permeability, and zero mean curvature. This study examines the effects of the gyroid microarchitectural design in parallel with SLM parameters on structure and function of as-built titanium alloy (Ti6Al4V ELI) scaffolds. Scaffold design was varied by varying unit cell size and wall thickness to produce scaffolds with porosity within the range of trabecular bone (50–90%). Manufacturer's default and refined laser parameters were used to examine the effect of input energy density on mechanical properties. Scaffolds exhibited a stretching-dominated deformation behavior under both compressive and tensile loading, and porosity dependent stiffness and strength. Internal void defects were observed within the walls of the gyroids structure, serving as sites for crack initiation leading to failure. Refinement of laser parameters resulted in increased compressive and tensile fatigue behavior, particularly for thicker walled gyroid microarchitectures, while thinner walls showed no significant change. The observed properties of as-built gyroid sheet microarchitectures indicates that these structures have potential for use in bone engineering applications. Furthermore, these results highlight the importance of parallel design and processing optimization for complex sheet-based porous structures produced via SLM. Statement of Significance: Selective laser melting (SLM) is an additive manufacturing technology which produces complex porous scaffolds for orthopedic applications. Titanium alloy scaffolds with novel sheet-based gyroid microarchitectures were produced via SLM and evaluated for mechanical performance including fatigue behavior. Gyroid structures are function based topologies have been hypothesized to be promising for tissue engineering scaffolds due to the high surface area to volume ratio, zero mean curvature, and high permeability. This paper presents the effects of scaffold design and processing parameters in parallel, a novel study in the field on bone tissue scaffolds produced via additive manufacturing. Additionally, the comparison of compressive and tensile behavior of scaffolds presented is important in characterizing behavior and failure mechanisms of porous metals which undergo complex loading in orthopedic applications.

AB - Selective laser melting (SLM) has enabled the production of porous titanium structures with biological and mechanical properties that mimic bone for orthopedic applications. These porous structures have a reduced effective stiffness which leads to improved mechanotransduction between the implant and bone. Triply periodic minimal surfaces (TMPS), specifically the sheet-based gyroid structures, have improved compressive fatigue resistance due lack of stress concentrations. Sheet-based gyroid microarchitectures also have high surface area, permeability, and zero mean curvature. This study examines the effects of the gyroid microarchitectural design in parallel with SLM parameters on structure and function of as-built titanium alloy (Ti6Al4V ELI) scaffolds. Scaffold design was varied by varying unit cell size and wall thickness to produce scaffolds with porosity within the range of trabecular bone (50–90%). Manufacturer's default and refined laser parameters were used to examine the effect of input energy density on mechanical properties. Scaffolds exhibited a stretching-dominated deformation behavior under both compressive and tensile loading, and porosity dependent stiffness and strength. Internal void defects were observed within the walls of the gyroids structure, serving as sites for crack initiation leading to failure. Refinement of laser parameters resulted in increased compressive and tensile fatigue behavior, particularly for thicker walled gyroid microarchitectures, while thinner walls showed no significant change. The observed properties of as-built gyroid sheet microarchitectures indicates that these structures have potential for use in bone engineering applications. Furthermore, these results highlight the importance of parallel design and processing optimization for complex sheet-based porous structures produced via SLM. Statement of Significance: Selective laser melting (SLM) is an additive manufacturing technology which produces complex porous scaffolds for orthopedic applications. Titanium alloy scaffolds with novel sheet-based gyroid microarchitectures were produced via SLM and evaluated for mechanical performance including fatigue behavior. Gyroid structures are function based topologies have been hypothesized to be promising for tissue engineering scaffolds due to the high surface area to volume ratio, zero mean curvature, and high permeability. This paper presents the effects of scaffold design and processing parameters in parallel, a novel study in the field on bone tissue scaffolds produced via additive manufacturing. Additionally, the comparison of compressive and tensile behavior of scaffolds presented is important in characterizing behavior and failure mechanisms of porous metals which undergo complex loading in orthopedic applications.

KW - Additive manufacturing

KW - Bone tissue scaffold

KW - Fatigue

KW - Selective laser melting

KW - Titanium alloy

KW - Tensile Strength

KW - Stress, Mechanical

KW - Elastic Modulus

KW - Structure-Activity Relationship

KW - Titanium/chemistry

KW - Pressure

KW - Compressive Strength

KW - Cancellous Bone/metabolism

KW - Lasers

KW - Surface Properties

KW - Bone Substitutes/chemistry

KW - Tissue Scaffolds/chemistry

KW - Porosity

KW - Bone and Bones/chemistry

KW - Tissue Engineering

UR - http://www.scopus.com/inward/record.url?scp=85066112221&partnerID=8YFLogxK

U2 - 10.1016/j.actbio.2019.05.046

DO - 10.1016/j.actbio.2019.05.046

M3 - Article

C2 - 31125727

AN - SCOPUS:85066112221

VL - 94

SP - 610

EP - 626

JO - Acta biomaterialia

JF - Acta biomaterialia

SN - 1742-7061

ER -