Non-thermal plasma jet-assisted development of phosphorus-containing functional coatings on 3D-printed PCL scaffolds intended for bone tissue engineering

The goal of this study was the exclusive deposition of phosphorus-containing coatings via the non-thermal plasma polymerization of triisopropyl phosphate (TIPP) on 3D-printed poly-e-caprolactone (PCL) scaffolds intended for bone tissue engineering. Given the difficulty of implementing a homogeneous surface treatment throughout porous scaffolds, a novel and appropriate atmospheric pressure plasma jet was used. In-situ analysis of the reactive species involved in the polymerization process using optical emission spectroscopy (OES) revealed the presence of P(II) and P(I) ions, CH, C2, O and CO species. X-ray photoelectron spectroscopy (XPS) was carried out at pre-determined locations on the top and throughout the cross-section of the scaffolds, which showed the uniform incorporation of O- and P-containing groups on the whole construct. This resulted in enhanced surface wettability and slightly enhanced surface roughness as perceived by water contact angle (WCA), field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) measurements. The in vivo ability of the scaffolds to promote apatite growth was evaluated via their biomimetic immersion in simulated body fluid (SBF). Interestingly, apatite deposits were successfully formed on the surface of the P-rich coating covering the scaffolds. Overall, one can conclude that this novel plasma-assisted deposition of homogeneous P-containing coatings on complex porous 3D structures enhances their osteo-bioactivity and thus, supporting bone tissue regeneration.