Fabrication of biodegradable porous scaffolds by an extrusion-based additive manufacturing technique

Abstract

As life expectancy is steadily increasing over the years, bone disorders are becoming a prevalent concern among senior citizens. Unfortunately, the main regenerative treatments for bone defects are often associated with a slew of complications and extensive recovery periods. Consequently, the main motive behind this study was to address these limitations by developing a porous metallic scaffold that is composed of pure iron via an extrusion based additive manufacturing technique. A novel fabrication route was adopted for the construction of bone scaffolds. Initially, two separate powder mixtures, one composed of iron and another made of sodium chloride, were prepared. With each individual powder, various binder constituents were added and homogenously mixed until a unique feedstock was created. These mixtures were then extruded in a sequential order to create an alternating pattern of cylindrical struts. Successive layers of these extrudates were deposited at right angles to one another until a three dimensional structure was created. The binder constituents were then removed and the structure was heated to a temperature of 750°C which caused the salt powder to fuse together. Once it cooled, the structure was immersed in water to dissolve the salt and form a porous metallic structure. Subsequently, it was reheated to a temperature of 1200°C where the iron powder sintered and formed the resultant metallic scaffold. In this study, numerous feedstocks were developed and tested in an attempt to find a suitable binder system for each powder. Results indicated that feedstocks with a higher powder to binder ratio produced extrudates with enhanced shape retention after subjected to the final sintering process. Despite that, feedstocks composed of a higher powder loading proved to cause extrusion concerns, particularly with nozzle blockage. The effects of feedstock constituents and heat treatment on powder densification was also studied. Characterisation techniques indicated that satisfactory interparticle bonding was achieved between the powders which resulted in enhanced structural integrity. Nevertheless, small spherical formations were formed in several areas across the microstructure, which were later identified by energy dispersive spectroscopy as contaminants. Collectively, this study made it evident that the novel fabrication route exhibited great potential to develop porous iron scaffolds.