Plasma-Induced Graft Polymerization for the In Situ Synthesis of Cross-Linked Nanocoatings

Conventional technology for the modification of surfaces loaded with nanomaterials typically requires a three-step process: (1) the construction of a polymer platform, (2) the synthesis of nanoparticles (NPs), and (3) the immobilization or anchoring of NPs. During the immobilization or anchoring process, there is an unavoidable excess of NPs primarily situated at the top of the surface, resulting in the agglomeration of aggregates. These aggregates can form different shapes and sizes, often creating an uneven distribution of NPs, resulting in an unstable coating that gradually releases NPs over time. In this study, argon plasma technology was used to create an innovative nanocoating consisting of polymer chains that are cross-linked to metal NPs, forming a polymer composite. To do this, argon plasma was employed as both an oxidizing and reducing agent during different steps in the nanocoating fabrication process. More specifically, a "grafting-from" approach, coupled with in situ argon plasma-assisted reduction of Cu²⁺ to Cu⁰, provided an innovative means for the construction of the nanocoating. With this "grafting-from" approach, the covalent binding of acrylic acid monomers to a surface results in a negatively charged nanocoating when exposed to solutions of a pH greater than 4.5. Due to its negative charge, the nanocoating can bind cations from solution, creating a platform for the in situ argon plasma-assisted reduction of Cu²⁺ to primarily Cu⁰ NPs (CuNPs). By controlling grafting conditions, in situ plasma-assisted reduction of NPs, and cross-linking conditions, we can generate nanocoatings with specific (1) polymer graft density and film thickness, (2) NP concentration cross-linked to polymer chains, and (3) NP composition. Under optimal experimental conditions, a nonleaching cross-linkage occurs between the nanocoating and the NPs, with only minimal NP aggregation. We have used this technology to engineer cross-linked nanocoatings possessing extremely low amounts of CuNPs (4.02 μg/cm²), which are distributed within the nanocoating and are capable of preventing infections.