Permanent Plasma Surface Functionalization of Internal Surface Areas

Surface functionalization technologies of fibrous or porous materials are often considered relatively unstable with a shelf life of several weeks or months at most, evoked by heterogeneous treatment of their internal surface areas. Here, it is demonstrating that the fine balance of plasma etching, deposition, and oxidation involving different reactive species, strongly enhances penetration depth within complex structures. On this basis, capillary wicking is maintained over >10 years after plasma functionalization of a scaffold material used for biomedical engineering. Electrospun membranes of poly(ε-caprolactone) are coated with an oxygen-functional hydrocarbon layer, deposited in a competitive ablation and plasma polymerization process with CO₂ and C₂H₄ as reactive gases. Chemical analysis immediately after coating, 9 months later, and after storing at ambient conditions for over 10 years, indicate a stable surface coating. Using defined geometries such as a cavity and an undercut, the underlying plasma interaction mechanisms are revealed, showing different synergies of energetic particles, depositing species with different surface reactivities, and oxidizing species. A concerted action of such species during plasma functionalization is key to enabling long-term wetting properties. This has a major implication for the surface functionalization of scaffolds, textiles, membranes, or foams used in diverse fields.