NiTi with 3D-interconnected microchannels produced by liquid phase sintering and electrochemical dissolution of steel tubes

A process was developed for fabricating 3D fully interconnected microchannels in superelastic NiTi-Nb for bone implant applications by combining spaceholder powder metallurgy and liquid-phase sintering. Prealloyed NiTi powders were blended with 3.1 at.% Nb and cold-pressed around a 3D scaffold of carburized steel tubes acting as space-holders. The tubes were then electrochemically dissolved to form orthogonally interconnected microchannels with 400 μm diameter and ∼34% volume fraction. Finally, the powder preform was heated to 1185 °C to form a quasi-binary NiTi-Nb eutectic liquid, which liquid-phase-sintered the NiTi powders without filling the microchannels. The resulting continuously bonded matrix contains an additional 16% porosity, for a total structure porosity of ∼50%. NiTi-Nb micro-architectured structures have excellent potential as bone implant scaffolds due to the high versatility in channel size, fraction, and spatial arrangement. Fully interconnected 3D microchannels also increase fluid transport within the scaffold, assisting in nutrient delivery and waste transport to and from cells deep within the scaffold.