Investigating the stability of cyclopropylamine-based plasma polymers in water

Amino-rich thin coatings, known to show superior cell adhesion, proliferation and viability, are prepared in this study by means of plasma polymerisation. The Yasuda parameter (W/FM) is used as a scaling factor for the deposition of cyclopropylamine based plasma polymer films (CPA-PPFs) making use of a dielectric barrier discharge (DBD) operated at sub-atmospheric pressure. In this paper, the experimental research is focussed on the stability of the CPA-PPFs in water, a property of PPFs which is often overlooked in literature. More specifically, after their plasma-assisted fabrication, the polymerised samples are immersed in water for 24 h after which the coatings are chemically evaluated using Fourier transform infrared (FTIR) and X-ray photoelectron (XPS) spectroscopy. The obtained results reveal that for all W/FM values under study water immersion results in a significant loss in C=N/C equivalent to N groups and a shift of primary to secondary/tertiary amines combined with the incorporation of oxygen at the surface as amides and alcohols/ethers. Moreover, FTIR, XPS chemical depth profiling (by means of C-60 sputtering) and scanning electron microscopy (SEM) results also reveal that at W/FM values <= 288 MJ/kg, the PPFs are gradually dissolving during water immersion, while at W/FM values > 288 MJ/kg, the PPFs are delaminating from the substrate due to their high crosslinking degree. Nevertheless, cell-coating interaction studies reveal no signs of cytotoxicity 1 day after cell seeding and show that the thin coatings remaining on the substrate still strongly increase the adhesion of fibroblasts. In the near future, efforts will be undertaken to avoid the delamination from the substrate of the PPFs prepared at high W/FM values.