Electroconductive Bionanocomposites from Black Soldier Fly Proteins for Green Flexible Electronics

Abstract

Printed and flexible electronics hold the potential to revolutionize the world of electronic devices. A primary focus today is their circularity, which can be achieved by using biobased materials. In this study, electrically conductive bionanocomposite materials suitable for flexible electronics were fabricated using proteins from the black soldier fly (BSF, Hermetia illucens). The valorization of BSF biomacromolecules is currently being pursued in the framework of emerging circular economy models for the bioconversion of the Organic Fraction of Municipal Solid Waste (OFMSW), where BSF has been demonstrated to act as an extremely efficient bioconverter to provide lipids, chitin, and proteins. Here, the BSF protein extracts were characterized by proteomic techniques, revealing a pool of myofibrillar proteins able to interact through intermolecular β-sheet interactions. Flexible and electroconductive bionanocomposite materials were next formulated by combining BSF proteins with a conductive carbon black (CCB), either in its pristine form or functionalized with 2-(2,5-dimethyl-1H-pyrrol-1-yl)-1,3-propanediol (serinol pyrrole, SP), using water as the only solvent and incorporating glycerol and carboxymethylcellulose (CMC) as additional green ingredients. A sustainable, low-pressure cold plasma (LPCP) technology was ultimately proposed to achieve high film surface hydrophobicity. Characterized by effective biodegradability, strain-sensing properties, high electrical conductivity (up to 0.9 × 10^-2 S/cm at a filler content of 8% v/v (15% w/w)), and high surface hydrophobicity, the bionanocomposites presented here may be well suited for disposable flexible electronics, as in wearable devices, electrostatic discharge fabrics, or packaging, hence offering new routes toward OFMSW valorization and the development of green flexible electronics.

Figure 1

Schematized pathway going from OFMSW to BSF protein-based networks. OFMSW is used as a rearing substrate for BSF larvae. Protein extracts are obtained from the pupal stage of the insect through a process which can be synthesized in three main steps, as described in a recent publication: freezing and grinding of the insect, defatting of the resulting powder, and protein recovery through isoelectric precipitation. Obtained extracts contain a pool of proteins with different MW, mainly myofibrillar proteins. These proteins can interact through noncovalent interactions between intermolecular β-sheets (H-bonds), thus leading to the formation of a network [Copyright: Galimberti, M. 2024, BioRender.com].

Figure 2

Preparation and characterization of the adduct CCB/SP. (A) Schematic representation of CCB/SP adduct formation and chemical species involved in the functionalization process. (B) Thermogravimetric curves of CCB (black) and CCB/SP (red curve). (C) Graphical representation of the Hansen spheres for CCB and CCB/SP. The polarity increase after functionalization is clearly highlighted by a shift (red arrow) toward higher δ_P and lower δ_D (see Table 2 for numeric values).

Figure 3

Preparation of BSF protein-based bionanocomposite films. (A) Schematization of the lab-scale procedure for the preparation of flexible BSF protein-based electroconductive nanocomposites [Copyright: Galimberti, M. 2025, BioRender.com]. (B) Schematic representation of the chemical species and interactions involved in the formation of the physical network of the nanocomposite. (C) Visual appearance of the prepared bionanocomposite: the material is free-standing and highly flexible.

Figure 4

Evaluation of the filler–matrix interaction and dispersion. (A) Bionanocomposite samples after 2 h of immersion in water evidencing different volumetric variations depending on filler content (0, 10, and 25 phm). (B) Water uptake (% w/w) as a function of the filler content for both sets of bionanocomposite films (black columns for CCB and red columns for CCB/SP). (C) Kraus plots for the evaluation of the filler–matrix interaction in CCB and CCB/SP-containing bionanocomposite films. Continuous lines represent the linear fitting of experimental data (black and red dots) according to the Kraus equation (see Text S9, eq 10). (D) TEM micrographs of micrometric slices (obtained by cryo-ultramicrotome) of CCB and CCB/SP-containing BSF protein-based nanocomposites. Samples with different loadings (5, 10, and 20 phm) of both types of nanofillers are displayed. Scale bar: 1000 nm.

Figure 5

(Bio)degradability test of BSF protein nanocomposites. Visual appearance of the bionanocomposite film containing 25 phm of CBC/SP, before and after the degradation tests: (a) pristine film; (b) after 4 h in a 1 M HCl water solution at 90 °C (c); after 24 h in a 1% pepsin water solution (pH = 4) at 36 °C; (d) after 24 h in a water solution (pH = 4) at 36 °C, without pepsin.

Figure 6

Electrical properties of BSF protein-based nanocomposites. (A) Specimen of the 25 phm CCB/SP bionanocomposite used as a conductive/resistive element in an LED circuit. (B) Electrical conductivity of bionanocomposites as a function of the CCB content (volume fraction, Φ). Electrical percolation thresholds (Φ_C) are reported for both sets of materials. (C) Linear fitting of electrical conductivity data for CCB and CCB/SP-containing nanocomposites according to percolation theory model. Linear regression coefficients are reported in the inset table. (D) Finger bending mimicking test. The graph on the right reports 4-wire resistance measurements of the 25 phm CBC/SP bionanocomposite film under repeated bending at different bending frequencies. [Copyright: Galimberti, M. 2025, BioRender.com]. (E) Frequency counts of the 4-wire resistance measurements recorded during the cyclic bending test on the composite containing 25 phm CBC/SP.

Figure 7

High surface hydrophobicity of BSF protein nanocomposites after LPCP treatment. Static water contact angle (WCA) pictures and calculated angles for the 25 phm CCB/SP-containing bionanocomposite were either submitted or not to the environmentally sustainable hydrophobizing cold plasma treatment.