Plasma-activated water in biomedicine: Physicochemical foundations, biomolecular mechanisms, and translational challenges

Plasma-activated water (PAW), an environmentally friendly plasma-treated liquid generated through the interaction of nonthermal plasma with water, has emerged as a promising indirect plasma platform for biomedical applications because it enables the delivery of plasma-generated reactive oxygen and nitrogen species (RONS) in a storable, transferable, and treatment-flexible liquid form. Unlike direct cold atmospheric plasma exposure, PAW can be applied in situations requiring uniform treatment, reduced thermal burden, and improved compatibility with biological systems. Its biological effects are governed by a complex interplay between plasma source characteristics, gas composition, treatment duration, liquid composition, storage conditions, and the resulting physicochemical properties of PAW, including pH, oxidation–reduction potential, conductivity, and the concentrations of long-lived reactive species such as hydrogen peroxide, nitrite, and nitrate. These properties collectively determine the downstream biomolecular responses of cells, including oxidative stress, mitochondrial dysfunction, DNA damage, modulation of redox-sensitive signaling pathways, inflammation control, proliferation, migration, and programmed cell death. This review summarizes the fundamental principles of PAW generation, the physicochemical mechanisms underlying its reactivity, and its emerging biomedical relevance in cell-based systems. Emphasis is placed on the relationship between plasma-liquid interactions and biomolecular outcomes, including anticancer activity, wound healing promotion, anti-inflammatory effects, and the modulation of cell migration, invasion, and stemness-related properties. In addition, this review discusses the current challenges that limit comparison across studies, including inconsistent plasma sources, poorly standardized dose descriptors, differences in storage and liquid matrices, and the frequent conflation of direct plasma treatment with indirect plasma-treated liquids. Finally, future perspectives are proposed for improving mechanistic understanding, energy efficiency, standardization, and translational development of PAW as a redox based industrial innovation.