Functionalization of Metal-Enriched Pleurotus Biomass with γ-Poly-Glutamic Acid for Cytoprotective and Antimicrobial Wound Care

Objectives: Chronic wound dressings require active components that support moisture management, biocompatibility, and local bioburden control. Therefore, in this study, freeze-dried biomass of Pleurotus ostreatus (Po) and Pleurotus djamor (Pdj) was cultivated in vitro under mineral-enriched conditions (calcium, magnesium, zinc) and subsequently modified with poly(γ-glutamic acid) (γ-PGA) to develop a bioactive fungal matrix intended as a functional additive for future wound-care biomaterials. Methods: The elemental content of the biomass was determined using atomic absorption spectroscopy (AAS), and the resulting biomaterial underwent physicochemical analyses—including scanning electron microscopy, X-ray diffraction (XRD), wettability measurements, differential scanning calorimetry (DSC), and thermogravimetric analysis (TG)—as well as biological performance assessments using a disk diffusion assay and cytotoxicity analysis. Results: Mineral enrichment enhanced Pleurotus spp. biomass production and metal accumulation, while γ-PGA coating altered surface properties and cytocompatibility. Zinc supplementation significantly promoted biomass formation in both Pleurotus species, while metal accumulation depended on the specific element and fortification regime. γ-PGA modification reduced the accessible BET surface area and formed a denser polymer-associated layer, confirmed by X-ray photoelectron spectroscopy. While the unmodified Po biomass exhibited the strongest in vitro antibacterial activity against S. aureus and P. aeruginosa, it also displayed dose-dependent cytotoxicity toward HaCaT keratinocytes at high concentrations. The addition of γ-PGA moderately reduced the in vitro bacterial inhibition zones but provided a critical cytoprotective effect, mitigating the cytotoxicity of the concentrated fungal extracts and rescuing HaCaT-cell viability to meet ISO 10993-5 safety thresholds. Conclusions: These findings demonstrate that γ-PGA-modified, metal-enriched Pleurotus biomass exhibits a distinct in vitro trade-off between absolute antimicrobial potency and cellular safety, supporting its further investigation as a biocompatible ingredient for multifunctional wound-dressing systems.