Cellulose nanofibrils (CNFs) have emerged as sustainable alternatives to single-use plastics due to their favorable barrier properties; however, their inherent hydrophilic properties limit their efficacy as water barriers. In this work, we present a novel approach using a CNF matrix and fungal mycelia to grow coatings directly onto a range of paper and textile substrates to enhance their liquid water resistance via a sustainable, low-energy process. We demonstrate that CNF-based mycelial coatings exhibit a water contact angle (CA) of 139.1° ± 3.5° and a water uptake of 29.6 g m–2 ± 3.5 g m–2 after 3 days of growth, compared to a CA of 27.2° ± 5.0° and a water uptake value of 80.0 g m–2 ± 12.8 g m–2 for a CNF coating alone. Furthermore, the CNF-based coating still retained excellent oil and grease barrier properties (Kit Test of 12), air permeability, and oxygen transmission rates even after at least 3 days of mycelial growth. Comparing CNFs and pulp as a matrix for the coating, we find that CNF facilitates faster growth, a higher maximum CA, and a lower water uptake than pulp. Finally, we demonstrate that both the hyphal structure and surface hydrophobicity are playing a role in water barrier functionality by comparing the grown mycelial coating to a coating of fungal hydrophobic surface proteins─hydrophobins─alone. Collectively, our work demonstrates that growing CNF-based mycelial coatings onto paper or textile substrates offers a potentially scalable solution to create water-resistant barriers on diverse substrates, creating more sustainable alternatives to single-use plastics.
Zier et al. (2025) studied this question.