Comparative study of different nitrogen-containing plasma modifications applied on 3D porous PCL scaffolds and 2D PCL films

Additive manufacturing of 3D-scaffolds and surface modification of 2D-substrates using nitrogen-containing plasmas have separately advanced the tissue engineering field for their cyto-responsive topographical and chemical features. However, their synergistic implementation remains largely unsuccessful because of the non-homogeneous surface treatment throughout porous structures. Therefore, this study focuses on the 3D-printing of polycaprolactone (PCL) scaffolds and the optimization of their surface chemistry via 3 plasma modifications: N2 activation, NH3:He (1:9) activation and allylamine polymerization. For an adequate optimization, a precise surface chemical analysis is performed throughout scaffold cross-sections by local measurements using an X-ray photoelectron spectroscopy (XPS) machine connected to a secondary electron image camera. Overall higher nitrogen incorporation and amino-selectivity are detected after NH3 (5.0%) compared to N2 plasma activation (2.8%). A remarkably high average nitrogen content (12.4%) primarily incorporated as C-N bonds is perceived on plasma polymerized allylamine coatings that exhibit an excellent uniformity throughout the scaffolds. In fact, high energy densities lead to a deposition of coatings with a symmetrical shallow nitrogen gradient towards the scaffold inner struts that still present a much higher nitrogen content (7%) when comparing with the state-of-the-art. Overall, this study constitutes a perfect-picture reference for plasma treatment of porous scaffolds.