Air-Dried Human Amniotic Membranes: Sterility, Microbial Barrier, and Cytokine Retention

This study aimed to evaluate the long-term structural integrity, sterility, and bioactivity of air-dried human amniotic membranes (AD-hAM) sterilized with gamma radiation after storage for one and two years. hAM were obtained following elective cesarean delivery under sterile conditions, processed using standardized air-drying protocols, and sterilized with gamma radiation at 15, 20, or 25 kGy. Histological examination showed preservation of the stromal matrix, despite partial epithelial detachment and reduced cell density after air-drying compared with frozen hAM (F-hAM). Bioburden testing confirmed the absence of microbial contamination before and after gamma irradiation and after one year of storage at 4°C. Microbial impermeability assays further demonstrated that irradiated membranes remained effective barriers against several bacterial types even after two years of storage at 4°C. Total protein content and levels of basic fibroblast growth factor and transforming growth factor-beta declined significantly in a dose-dependent manner (p < 0.05) following air-drying and irradiation. Despite this decline, key structural features and barrier function were preserved. These findings validate air-drying combined with gamma sterilization as an effective method for producing sterile, shelf-stable hAM grafts with preserved mechanical integrity, supporting their use as safe biological dressings. However, the observed reduction in protein and cytokine content highlights the need to balance sterilization efficacy with bioactivity preservation.