TY - JOUR
T1 - NiTi-Nb micro-trusses fabricated via extrusion-based 3D-printing of powders and transient-liquid-phase sintering
AU - Taylor, Shannon L.
AU - Ibeh, Amaka J.
AU - Jakus, Adam E.
AU - Shah, Ramille N.
AU - Dunand, David C.
N1 - Funding Information:
The authors acknowledge financial support from the Center, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205); the MRSEC program (NSF DMR-1121262) at the Materials Research Center, the International Institute for Nanotechnology (IIN), the Keck Foundation, and the State of Illinois, through the IIN. This work also made use of the Materials Characterization Laboratory (MatCI) and the Central Laboratory for Materials Mechanical Properties (CLaMMP), which received support from the MRSEC program (NSF DMR-1121262). This work utilized facilities located at the Simpson Querrey Institute for BioNanotechnology at Northwestern University, which is funded by The U.S. Army Research Office, the U.S. Army Medical Research and Material Command, and Northwestern University. The Northwestern University Center for Advanced Microscopy supported by the NCI CCSG P30 CA060553 awarded to the Robert H. Lurie Comprehensive Cancer Center was utilized for confocal live/dead cell imaging. The authors thank Nicholas Geisendorfer (Northwestern University) for assistance with the 3D-printing and Dr. Dinc Erdeniz (Northwestern University) for his numerous, insightful discussions as well as the optical image in National Science Foundation through Grant No. 1207282, a gift from Google, the National Science Foundation Graduate Fellowship Program (for SLT), and The Hartwell Foundation Postdoctoral Fellowship (for AEJ). This work made use of the EPIC, Keck-II, and SPID facilities of Northwestern University’s NU ANCE Fig. 2 a.
Publisher Copyright:
© 2018 Acta Materialia Inc.
PY - 2018/8
Y1 - 2018/8
N2 - We present a novel additive manufacturing method for NiTi-Nb micro-trusses combining (i) extrusion-based 3D-printing of liquid inks containing NiTi and Nb powders, solvents, and a polymer binder into micro-trusses with 0/90° ABAB layers of parallel, ∼600 µm struts spaced 1 mm apart and (ii) subsequent heat-treatment to remove the binder and solvents, and then bond the NiTi powders using liquid phase sintering via the formation of a transient NiTi-Nb eutectic phase. We investigate the effects of Nb concentration (0, 1.5, 3.1, 6.7 at.% Nb) on the porosity, microstructure, and phase transformations of the printed NiTi-Nb micro-trusses. Micro-trusses with the highest Nb content exhibit long channels (from 3D-printing) and struts with smaller interconnected porosity (from partial sintering), resulting in overall porosities of ∼75% and low compressive stiffnesses of 1–1.6 GPa, similar to those of trabecular bone and in agreement with analytical and finite element modeling predictions. Diffusion of Nb into the NiTi particles from the bond regions results in a Ni-rich composition as the Nb replaces Ti atoms, leading to decreased martensite/austenite transformation temperatures. Adult human mesenchymal stem cells seeded on these micro-trusses showed excellent viability, proliferation, and extracellular matrix deposition over 14 days in culture. Statement of Significance: Near-equiatomic NiTi micro-trusses are attractive for biomedical applications such as stents, actuators, and bone implants because of their combination of biocompatibility, low compressive stiffness, high surface area, and shape-memory or superelasticity. Extrusion-based 3D-printing of NiTi powder-based inks into micro-trusses is feasible, but the subsequent sintering of the powders into dense struts is unachievable due to low diffusivity, large particle size, and low packing density of the NiTi powders. We present a solution, whereby Nb powders are added to the NiTi inks, thus forming during sintering a eutectic NiTi-Nb liquid phase which bonds the solid NiTi powders and improves densification of the struts. This study investigates the microstructure, porosity, phase transformation behavior, compressive stiffness, and cytocompatibility of these printed NiTi-Nb micro-trusses.
AB - We present a novel additive manufacturing method for NiTi-Nb micro-trusses combining (i) extrusion-based 3D-printing of liquid inks containing NiTi and Nb powders, solvents, and a polymer binder into micro-trusses with 0/90° ABAB layers of parallel, ∼600 µm struts spaced 1 mm apart and (ii) subsequent heat-treatment to remove the binder and solvents, and then bond the NiTi powders using liquid phase sintering via the formation of a transient NiTi-Nb eutectic phase. We investigate the effects of Nb concentration (0, 1.5, 3.1, 6.7 at.% Nb) on the porosity, microstructure, and phase transformations of the printed NiTi-Nb micro-trusses. Micro-trusses with the highest Nb content exhibit long channels (from 3D-printing) and struts with smaller interconnected porosity (from partial sintering), resulting in overall porosities of ∼75% and low compressive stiffnesses of 1–1.6 GPa, similar to those of trabecular bone and in agreement with analytical and finite element modeling predictions. Diffusion of Nb into the NiTi particles from the bond regions results in a Ni-rich composition as the Nb replaces Ti atoms, leading to decreased martensite/austenite transformation temperatures. Adult human mesenchymal stem cells seeded on these micro-trusses showed excellent viability, proliferation, and extracellular matrix deposition over 14 days in culture. Statement of Significance: Near-equiatomic NiTi micro-trusses are attractive for biomedical applications such as stents, actuators, and bone implants because of their combination of biocompatibility, low compressive stiffness, high surface area, and shape-memory or superelasticity. Extrusion-based 3D-printing of NiTi powder-based inks into micro-trusses is feasible, but the subsequent sintering of the powders into dense struts is unachievable due to low diffusivity, large particle size, and low packing density of the NiTi powders. We present a solution, whereby Nb powders are added to the NiTi inks, thus forming during sintering a eutectic NiTi-Nb liquid phase which bonds the solid NiTi powders and improves densification of the struts. This study investigates the microstructure, porosity, phase transformation behavior, compressive stiffness, and cytocompatibility of these printed NiTi-Nb micro-trusses.
KW - 3D printing
KW - Bone implant
KW - Liquid phase sintering
KW - Nitinol
KW - Porous metal
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U2 - 10.1016/j.actbio.2018.06.015
DO - 10.1016/j.actbio.2018.06.015
M3 - Article
C2 - 29890266
AN - SCOPUS:85048881915
VL - 76
SP - 359
EP - 370
JO - Acta Biomaterialia
JF - Acta Biomaterialia
SN - 1742-7061
ER -