3D-Printable Sustainable Bioplastics from Gluten and Keratin

Abstract

Bioplastic films comprising both plant- and animal-derived proteins have the potential to integrate the optimal characteristics inherent to the specific domain, which offers enormous potential to develop polymer alternatives to petroleum-based plastic. Herein, we present a facile strategy to develop hybrid films comprised of both wheat gluten and wool keratin proteins for the first time, employing a ruthenium-based photocrosslinking strategy. This approach addresses the demand for sustainable materials, reducing the environmental impact by using proteins from renewable and biodegradable sources. Gluten film was fabricated from an alcohol-water mixture soluble fraction, largely comprised of gliadin proteins. Co-crosslinking hydrolyzed low-molecular-weight keratin with gluten enhanced its hydrophilic properties and enabled the tuning of its physicochemical properties. Furthermore, the hierarchical structure of the fabricated films was studied using neutron scattering techniques, which revealed the presence of both hydrophobic and hydrophilic nanodomains, gliadin nanoclusters, and interconnected micropores in the matrix. The films exhibited a largely (>40%) β-sheet secondary structure, with diminishing gliadin aggregate intensity and increasing micropore size (from 1.2 to 2.2 µm) with an increase in keratin content. The hybrid films displayed improved molecular chain mobility, as evidenced by the decrease in the glass-transition temperature from ~179.7 °C to ~173.5 °C. Amongst the fabricated films, the G14K6 hybrid sample showed superior water uptake (6.80% after 30 days) compared to the pristine G20 sample (1.04%). The suitability of the developed system for multilayer 3D printing has also been demonstrated, with the 10-layer 3D-printed film exhibiting >92% accuracy, which has the potential for use in packaging, agricultural, and biomedical applications.

Keywords: 3D printing; film; gluten; keratin; neutron scattering; protein.

Figure 1

(A) Mechanism of tyrosine cross-linking, and (B) intermolecular dityrosine cross-linking in proteins.

Figure 2

Photographs of photocrosslinked gel films.

Figure 3

(A) FTIR analysis of gluten/keratin hybrid films and (B) quantitative analysis of secondary structure.

Figure 4

DSC thermograms of fabricated gels.

Figure 5

SEM images of (A) G20, (B) G18K2, (C) G16K4, and (D) G14K6 gels.

Figure 6

(A) SANS intensity profile and (B) Kratky plot of the four fabricated gluten/keratin hybrid films/gels (G20, G18K2, G16K4, and G14K6), presented with intensity offset for clarity. Shape-independent form factor models (power law + three Guinier−Porod (GP)) fit to SANS data of (C) G20, (D) G18K2, (E) G16K4, and (F) G14K6 films/gels.

Figure 7

(A) Storage (G′, filled symbols) and loss modulus (G″, open symbols) of films measured as a function of oscillation strain, (B) tan delta of films measured at linear viscoelastic regime, and (C) complex viscosity of films measured as a function of angular frequency.

Figure 8

Hydrolytic degradation behavior of fabricated film.

Figure 9

(A) Photographs of 3D-printed grid structures and (B) corresponding printing accuracy of gluten/keratin (G14K6) hybrid gels.