Surface modification of soft materials (polymers and hydrogels) using plasma: Mechanisms, strategies, and emerging applications

Soft materials such as hydrogels (natural and synthetic), elastomers, and silicone-based polymers commonly suffer from low surface energy, weak interfacial adhesion, and hydrophobic recovery due to surface aging, which restricts their performance in biomedical and functional applications. Plasma-assisted surface modification has emerged as a controllable and solvent-free technique for modifying surface chemistry and topography without changing the bulk properties. This review presents a detailed, mechanism-driven overview of the cold plasma surface modification of soft materials, integrating plasma–material interaction mechanisms with key process parameters, including plasma power, gas type, pressure, treatment time, gas flow rate, and substrate surface chemistry. Both physical (etching, sputtering, nano-roughening) and chemical (crosslinking, radical formation, surface activation, functional-group incorporation, oxidation, and hydrophilization) dominant effects are critically discussed in relation to the surface morphology, wettability, adhesion, and stability of the treated surfaces. Special importance is given to plasma-induced surface modification of natural and synthetic hydrogels, where reactive oxygen and nitrogen species play crucial roles in regulating the surface functionality and bioactivity. Similar mechanistic insights have been extended to soft polymers, including polydimethylsiloxane, silicone rubber, and elastomeric systems, such as styrene–butadiene rubber, nitrile butadiene rubber, natural rubber, and polyurethane. Furthermore, plasma-induced surface structuring strategies, such as nano-roughening, selective material removal, wrinkle formation, and nature-inspired nano-structuring, are systematically reviewed in this paper. Finally, challenges related to surface stability, hydrophobic recovery, and long-term durability are discussed, and future research directions are proposed for the design of robust, application-oriented plasma-modified soft-material interfaces. This review provides a roadmap for designing next-generation plasma-engineered soft-material interfaces.