Green synthesis of silver nanoparticle- embedded cellulose nanofibers from mushroom biomass for antibacterial hydrogel applications

Abstract

Underutilized agricultural wastes such as spent mushroom substrate (SMS) offers a significant potential for the development of sustainable biomedical materials. In this study, cellulose nanofibrils (CNFs) were successfully isolated from SMS via a chemomechanical process, while the aqueous extract of SMS (WESMS) was utilized as a green reducing agent for the in-situ synthesis and loading of silver nanoparticles (AgNPs) onto TEMPO-oxidized CNFs (AgNP/ToCNF). ATR-FTIR confirmed the chemical structure of the isolated cellulose, while UV-Vis spectroscopy (λmax = 424 nm) verified successful AgNP synthesis and incorporation. The hybrid nanomaterial exhibited fibril diameters ranging from 273.5–318.5 nm and AgNP sizes averaging 34.04 ± 7.39 nm. Antimicrobial evaluation against Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli using agar diffusion, broth microdilution, time-kill, and membrane leakage assays revealed potent antibacterial activity. AgNP/ToCNF showed MIC₉₀ values of 250 μg/mL for S. aureus and 125 μg/mL for P. aeruginosa and E. coli, while free AgNPs demonstrated lower MIC₉₀ values (62.5–31.25 μg/mL). Despite this, AgNP/ToCNF retained strong bactericidal activity with improved safety as determined by LDH assays that showed minimal cytotoxicity to human dermal fibroblasts at ≤500 μg/mL, in contrast to >67% cytotoxicity was observed from the free AgNPs. The nanocomposite was incorporated into a citric acid–crosslinked hydrogel, which exhibited solid-like rheological properties and high swelling capacity (~1000%), ideal for moist wound environments. Furthermore, the wound scratch assay demonstrated significantly enhanced fibroblast migration in the presence of the crosslinked hydrogel, supporting its potential to accelerate wound healing. Altogether, this study demonstrates the successful upcycling of SMS into a cytocompatible, multifunctional AgNP/ToCNF-based hydrogel with antimicrobial and wound-healing properties, underscoring its potential as a sustainable and effective material for advanced wound dressings.