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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 Ta=50°C, leading to a drop of the elastic modulus from E'=1.1GPa, at ambient temperature, to E'=0.6MPa at Ta+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. [ABSTRACT FROM AUTHOR]

Additive Manufacturing (AM) of tailored natural biopolymer-based objects by Fused Deposition Modeling (FDM) opens new perspectives for applications such as biomedical temporary devices, or pharmaceutical tablets. This exploits the biocompatibility, resorbability and edibility properties of biopolymers. When adequately plasticized, zeins, storage proteins from endosperm of maize kernels, displayed thermomechanical properties possibly matching FDM processing requirements at a convenient temperature Tprinting=130°C. Indeed, with 20% glycerol added (Tg=42°C), plasticized zeins present a high modulus, E'>1GPa, at ambient conditions, which drops below 0.6 MPa at the processing temperature T=130°C, before flowing in the molten state. The rheological characterization shows that the processing window is limited by a progressive increase of viscosity linked to proteins aggregation and crosslinking by S-S bonding between cysteine amino acid residues, which can lead to gelation. However, for short residence time typical of FDM, the viscosity of plasticized zeins is comparable to the one of standard polymers, like ABS or PLA in their FDM processing conditions: indeed, in presence of glycerol, the molten zeins show a shear-thinning behavior with |η*|≈3kPa.s at 1s-1, decreasing to |η*|≈0.3kPa.s at 100s-1, at 130°C. Moreover, zeins presenting both hydrophilic and hydrophobic domains, amphiphilic plasticizers can be used supplementary to tune their rheological behavior. With 20% oleic acid added to the previous composition, the viscosity is divided down to a ratio about 1/2 at 100s-1 at 130°C, below the value of a standard polymer as PLA at its printing temperature. These results show the possible enhancement of the printability of zein-based materials in the molten state, by combining polar and amphiphilic plasticizers. [ABSTRACT FROM AUTHOR]

The developments of Additive Manufacturing (AM) by Fused Deposition Modeling (FDM) now target new 3D printable materials, leading to novel properties like those given by biopolymers such as proteins: degradability, biocompatibility and edibility. Plasticized materials from zein, a storage protein issued from corn, present interesting thermomechanical and rheological properties, possibly matching with AM-FDM specifications. Thus commercial zein plasticized with 20% glycerol has a glass transition temperature (Tg) at about 42°C, after storage at intermediate relative humidity (RH=59%). Its principal mechanical relaxation at Tα × 50°C leads to a drop of the elastic modulus from about 1.1 GPa, at ambient temperature, to 0.6 MPa at Tα+100°C. These values are in the same range as values obtained in the case of standard polymers for AM-FDM processing, as PLA and ABS, although relaxation mechanisms are likely different in these materials. Such results lead to the setting up of zein-based compositions printable by AM-FDM and allow processing bioresorbable printed parts, with designed 3D geometry and structure. [ABSTRACT FROM AUTHOR]