3D printing of metals using biodegradable cellulose hydrogel inks

Additive manufacturing (AM) is a fabrication technique that digitally deposits materials in layers to form a desired 3D structure or shape. It is not as wasteful in materials compared to digital subtractive manufacturing (SM). In 3D printing, complex and unique metallic structures, more energy intensive and expensive techniques such as selective laser melting (SLM) or electron beam melting (EBM) are often used. As metals are an important class of materials used in AM, there is a need for safer and relatively less expensive 3D printing alternatives for widespread adoption. Material extrusion AM methods include fused deposition modeling (FDM) and direct ink writing (DIW), where thermal and viscosity parameters are used to optimize printing. This study presents a materials extrusion precursor route on 3D printing metallic structures with a biodegradable cellulose hydrogel and safer water-based composite ink containing irregularly shaped metallic powders and carboxymethyl cellulose (CMC-Na). Montmorillonite clay and guar gum additives were used to modify the ink viscosity during extrusion and provide post 3D printing structural integrity and stability. By using this composite ink, a part can be made with 75-80% metal composition for sintering. The sintering process at 1050 and 985 degrees C for 316L stainless steel (316L55) and copper (Cu), respectively, removes the cellulose hydrogel, leaving a 100% metal. Large interconnected open and closed pores were formed for both approaches: 316L55 and Cu each had a total of about 31.92% and 32.07% porosity, respectively. Total closure of pores was not achieved and a small shrinkage was observed in both samples. The elastic modulus of the 3D-printed 316L55 structure was measured 0.053 GPa. A number of potential uses for optimized porous metallic structures, particularly in biomedical and energy applications are also discussed.