3D printing of maize protein by fused deposition modeling

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Abstract
Additive Manufacturing (AM) opens new perspectives for biopolymers to obtain functional parts, like biomedical devices, by exploiting their biocompatibility and resorbability. Plasticized materials from zein, a storage protein from maize seed endosperm, display thermomechanical properties that could match with Fused Deposition Modeling (FDM). The objective of this work was to evaluate their thermo-rheological behavior and their structural modifications during processing. 20% glycerol was added to commercial zein, containing naturally about 4% lipids and 5% water. After storage at intermediate relative humidity (RH=59%), its glass transition temperature, measured by DSC, was Tg=42°C. The main mechanical relaxation, measured by DMA, was found at Tα=50°C, leading to a drop of the elastic modulus from E’=1.1GPa, at ambient temperature, to E’=0.6MPa at Tα+100°C. These values are in a similar range as those of standard polymers used for AM-FDM processing, such as PLA and ABS. The structure of zein was characterized at different scales by SDS-PAGE, reversed-phase HPLC, FTIR and WAXS, at each processing stage: (i) the initial formulation of the plasticized powdery material, (ii) after extrusion at 130°C for shaping printable filaments, and (iii) after deposition through the 3D printer nozzle (Ønozzle=0.5mm, Tprinting=130°C, vprinting≈10mm/s). The presence of disulfide bond cross-links was evidenced in extruded filaments and remains at the same level after printing. WAXS showed that, in these conditions, no molecular orientation was obtained in the deposited material. By tuning zein-based printable compositions, these results open the field of their processing as resorbable printed parts, with a controlled geometry and a designed tridimensional structure.

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