Multifaceted polymeric nerve guidance conduits with distinctive double-layered architecture and plasma-induced inner chemistry gradient for the repair of critical-sized defects

Unraveling Exclusive In-Plasma Initiated Oxidation Processes Occurring at Polymeric Surfaces upon O2 Admixtures to Medium Pressure Ar and N2 DBD Treatments

“…The OES spectrum of the pure Ar plasma, presented in Figure 3b, is primarily characterized by intense atomic Ar I lines associated with the 4p → 4s transition (Racah notation) at: 696.5 nm (2p 2 →1s 5 ), 706.7 nm (2p 3 →1s 5 ), 727.3 nm (2p 2 →1s 4 ), 738.4 nm (2p 3 →1s 4 ), 750.4 nm (2p 1 →1s 2 ), 763.5 nm (2p 6 →1s 5 ), 772.4 nm (2p 2 → 1s 3 ), 794.8 nm (2p 4 → 1s 3 ), 801.5 nm (2p 8 →1s 5 ), 811.5 nm (2p 9 →1s 5 ), 826.5 nm (2p 2 →1s 2 ), 842.5 nm (2p 8 →1s 4 ) and 852.1 (2p 4 →1s 2 ) (Paschen notation) [41,42]. The 1s 2 and 1s 4 states correspond to the Ar resonant states, while the 1s 3 and 1s 5 states are accredited to the Ar metastable [43]. The dominant generation processes of these Ar excited species are the following [42]:…”

“…In the last few decades, intrinsically nonconformant polymeric surfaces have been increasingly subjected to non-thermal plasma activation to impart them with adequate chemistries, enabling their use in a wide range of technological and biomedical applications [ 1 , 2 , 3 , 4 ]. The high-flying position of plasma activation over other surface modification techniques is due, on the one hand, to its simplicity, versatility, solvent-free character, time efficiency, and non-invasive aspect, as its modification depth is limited to a few nanometers, thus not impeding the bulk properties of the used polymer [ 5 , 6 , 7 ]. On the other hand, the plasma capability to improve, amongst others, the surface wettability, printability, cyto- and bio-compatibility, barrier properties, and bonding characteristics of polymers has been widely demonstrated [ 3 , 8 , 9 , 10 ].…”

“…In fact, when plasma is ignited using a noble gas such as argon or helium, the surface radicals are expected to interact with each other, causing a topology change on the polymer surface characterized by the generation of a cross-linked network. On the other hand, when plasma is sustained in a chemically reactive gas such as nitrogen or oxygen, the plasma-ensuing surface radicals are expected to react with the reactive plasma species, causing a surface functionalization theoretically distinguished by the selective incorporation of nitrogen- or oxygen-containing functional groups, respectively [ 5 , 10 , 15 ]. However, most studies involving plasma activation of polymers have revealed that these hypotheses are invalid as an unavoidable insertion of surface oxygen-containing groups on polymers exposed to plasmas sustained in non-oxygen-containing and noble gases has always been observed [ 7 , 13 , 14 ].…”