Fungal Nanofibers Turn Aspergillus niger Waste Into Antibacterial Bioplastic

A team of researchers at Tianjin University has developed a scalable process that converts the mycelium of the filamentous fungus Aspergillus niger into partially deacetylated chitin–glucan complex nanofibers, a renewable bionanomaterial with potent antibacterial activity and remarkable mechanical performance. The work, published in Polymer Bulletin, addresses a persistent gap in the emerging field of fungal nanomaterials: while fungal cell walls are known to be rich in chitin and beta-glucan, the path from raw biomass to high-performance nanofibers has remained poorly connected to the practical realities of biomass processing, fiber structure control, and final material properties. By closing that loop, the researchers demonstrate that one of the industrial workhorses of biotechnology can be transformed from a low-value fermentation by-product into a functional nanomaterial feedstock for films, coatings, and packaging applications.

The starting material is deceptively ordinary. Aspergillus niger, the black mold long used to produce citric acid and enzymes at industrial scale, generates large quantities of spent mycelial biomass that is typically discarded or undervalued. Within its cell walls, however, lies a natural composite: chitin microfibrils entangled and covalently associated with glucan polysaccharides. This chitin–glucan architecture is, in effect, a prefabricated nanocomposite produced by biology itself. Unlike crustacean shell waste, which requires energy-intensive demineralization to remove calcium carbonate, fungal biomass is essentially mineral-free, giving it a favorable sustainability profile for chitin extraction. The Tianjin team cultivated A. niger in potato dextrose medium containing 12 grams per liter of potato extract and 60 grams per liter of glucose over 96 hours, producing a dense mycelial mat that served as the raw material for nanofiber fabrication.

The extraction strategy combines three sequential treatments. First, alkaline processing removes proteins and other soluble impurities from the cell wall matrix, enriching the insoluble chitin–glucan fraction. Second, a controlled partial deacetylation converts a proportion of the N-acetyl groups on the chitin backbone into free amine groups, generating chitosan-like character along the fiber surface. This chemical modification is critical: the newly exposed cationic amino groups are responsible for much of the material’s antibacterial behavior and improve its colloidal stability in water. Third, high-pressure homogenization subjects the chemically treated biomass to intense mechanical shear and cavitation forces that disentangle the cell wall architecture into individual nanofibers. The resulting partially deacetylated chitin–glucan complex nanofibers, or CGCNFs, have an average diameter of just 9.86 plus or minus 1.86 nanometers and an aspect ratio of approximately 25, meaning the fibers are slender ribbons a few dozen times longer than they are wide—an ideal geometry for reinforcing polymer films.

The economics of the process may prove as consequential as the science. Compared with conventional routes to chitin nanofibers, the proposed workflow achieved a 15 to 48 percent increase in nanofiber yield and reduced raw material costs by 75 to 81 percent. These gains stem partly from the choice of feedstock and partly from process integration, which avoids the harsh acid treatments and demineralization steps that inflate the cost and environmental footprint of crustacean-derived chitin. In a circular bioeconomy framework, spent microbial biomass from existing fermentation industries could feed directly into nanomaterial production, turning a disposal liability into a revenue stream. The authors position this as a sustainable strategy for biomass conversion and renewable polysaccharide fabrication, with the numbers to back up the claim.

Structural characterization confirmed that the treatment regimen did more than simply defibrillate the cell wall. Fourier-transform infrared spectroscopy, X-ray diffraction, and solid-state carbon-13 nuclear magnetic resonance spectroscopy collectively revealed enhanced surface functionalization of the nanofibers. The spectroscopic signatures showed increased exposure of amine groups alongside the preserved crystalline chitin core, a combination that underpins both the fibers’ reactivity and their mechanical integrity. Solid-state NMR, a technique particularly well suited to probing unlabeled fungal cell walls, allowed the researchers to track the chemical environment of the chitin and glucan carbons through each processing stage, verifying that partial deacetylation proceeded without destroying the glucan–chitin association that makes these fibers a natural composite rather than a mixture of separate polymers.

The most striking result is the antibacterial performance. The CGCNFs inhibited more than 99 percent of Escherichia coli, a Gram-negative bacterium, and Staphylococcus aureus, a Gram-positive pathogen. The mechanism is thought to follow the established antimicrobial behavior of chitosan-like polymers: the protonated amine groups on the fiber surfaces carry a positive charge at physiological pH, promoting electrostatic adhesion to the negatively charged bacterial cell envelope. In Gram-negative organisms this interaction disrupts the outer lipopolysaccharide membrane, while in Gram-positive species it interferes with the thick peptidoglycan layer and the cell membrane beneath, ultimately causing leakage of intracellular contents and loss of viability. Because the antimicrobial functionality is intrinsic to the biopolymer rather than added as a leachable additive, CGCNF-based materials could offer a durable and food-safe alternative to synthetic antimicrobial agents in packaging.

To demonstrate real-world utility, the team blended the nanofibers into polyvinyl alcohol, a water-soluble synthetic polymer widely used in films and coatings. The resulting CGCNF/PVA composite films displayed a tensile modulus of 4.2 gigapascals, a 162.5 percent increase relative to neat PVA films. This dramatic stiffening reflects classic nanocomposite reinforcement physics: rigid nanofibers dispersed at high aspect ratio form an interconnected network within the polymer matrix, efficiently transferring stress and restricting polymer chain mobility. The hydrogen-bonding compatibility between the hydroxyl-rich PVA and the hydroxyl- and amine-bearing surfaces of the nanofibers further strengthens the interface. The outcome is a multifunctional film that is simultaneously stronger, stiffer, and antibacterial—precisely the property combination sought for active food packaging that extends shelf life while resisting microbial spoilage.

The significance of the work extends beyond a single material system. Fungal sources of chitin have attracted growing attention as ecologically preferable alternatives to crustacean shells, with prior studies screening the sustainability and physicochemical properties of chitin and chitin–glucan across dozens of fungal species and assessing the environmental impact of nanofibril isolation from fungi compared with shrimp and crab shells. Previous efforts have produced fungal chitin nanopapers, heavy-metal-adsorbing filtration membranes, hemostatic hydrogels, and chitin nanofibers from mushroom extracts. The Tianjin study contributes a process-technology link that many of these works lacked: a route that is simultaneously high-yielding, low-cost, and compatible with industrially familiar unit operations such as alkaline extraction and high-pressure homogenization, applied to one of the most widely cultivated fungi in existence.

Challenges remain before fungal nanofibers reach commercial films and coatings. Scaling mycelium production and maintaining consistent cell wall composition across fermentation batches will demand tight bioprocess control, and the long-term migration behavior, biodegradation profile, and regulatory status of partially deacetylated chitin–glucan nanofibers in food-contact materials will need thorough evaluation. Nevertheless, the combination of a 9.86-nanometer fiber diameter, stronger-than-neat composite films, near-total bacterial inhibition, and an 81 percent reduction in raw material cost makes a compelling case that the next generation of antibacterial bioplastics may be grown, not drilled. As the biotechnology industry continues to generate mountains of spent fungal biomass, processes like this one suggest that the humble cell wall of Aspergillus niger may become one of the most valuable nanomaterial feedstocks of the coming decade.

Subject of Research: Extraction of antibacterial chitin–glucan nanofibers from Aspergillus niger fungal biomass for sustainable biopolymer films

Article Title: Extraction of nanochitin–glucan composite from Aspergillus niger with enhanced antibacterial activity

Article References: Ba, W., Che, M., Cui, M., Su, R., & Huang, R. (2026). Extraction of nanochitin–glucan composite from Aspergillus niger with enhanced antibacterial activity. Polymer Bulletin, 83(11), Article 637. https://doi.org/10.1007/s00289-026-06692-z

Image Credits: AI Generated

DOI: 10.1007/s00289-026-06692-z

Keywords: Aspergillus niger, chitin-glucan complex, nanofibers, antibacterial activity, fungal biomass, bioplastics, high-pressure homogenization, deacetylation, polyvinyl alcohol, food packaging, waste valorization, Polymers Bulletin