Bacterially Grown Cellulose/Graphene Oxide Composites Infused with γ-Poly (Glutamic Acid) as Biodegradable Structural Materials with Enhanced Toughness

Abstract

Bioinspired bacterial cellulose (BC) composites are next-generation renewable materials that exhibit promising industrial applications. However, large-scale production of inorganic/organic BC composites by in situ fermentation remains difficult. The methods based on BC mechanical disintegration impair the mechanical property of dried BC films, while the static in situ fermentation methods fail to incorporate inorganic particles within the BC network because of the limited diffusion ability. Furthermore, the addition of other components in the fermentation medium significantly interferes with the production of BC. Here, a tough BC composite with a layered structure reminiscent of the tough materials found in nature (e.g., nacre, dentin, and bone) is prepared using a semistatic in situ fermentation method. The bacterially produced biopolymer γ-poly(glutamic acid) (PGA), together with graphene oxide (GO), is introduced into the BC fermentation medium. The resulting dried BC-GO-PGA composite film shows high toughness (36 MJ m-3), which makes it one of the toughest BC composite film reported. In traditional in situ fermentation methods, the addition of a second component significantly reduces the wet thickness of the final composites. However, in this report, we show that addition of both PGA and GO to the fermentation medium shows a synergistic effect in increasing the wet thickness of the final BC composites. By gently agitating the solution, GO particles get entrapped into the BC network, as the formed pellicles can move below the liquid level and the GO particles suspended in the liquid can be entrapped into the BC network. Compared to other methods, this method achieves high toughness while using a mild and easily scalable fabrication procedure. These bacterially produced composites could be employed in the next generation of biodegradable structural high-performance materials, construction materials, and tissue engineering scaffolds (tendon, ligament, and skin) that require high toughness.