# Impact of Nitric Oxide on the Surface Properties of Selected Polymers
## 4 Conclusions  
This paper showed the impact of NO treatment on the surface properties of several polymers and the stability of these effects under liquid contact. The measurements showed that the gas treatment had little to no impact on PMP. The surfaces of MABS became more hydrophilic and chemically heterogeneous, while PU became more hydrophilic and acidic based on both the contact-angle and zeta-potential measurements. The increase in hydrophilicity of both MABS and PU was mainly due to the adsorption of HNO\({}_{3}\). The formation of nitro and nitrate ester groups was stable on both MABS and PU surfaces, with the adsorbed HNO\({}_{3}\) molecules proving less stable. The results discussed in this paper point to an overall positive outlook for applying nitric oxide in the ECMO circuit. The major blood-contacting surface PMP showed little to no changes. The other two blood-contacting surfaces, MABS and PU, developed functional groups largely stable under liquid contact, indicating a low risk for patients during application. However, this is just an initial observation, as blood represents a significantly more complex system than the liquids used in the experiments discussed in this publication. The surfaces became more hydrophilic, potentially improving their liquid contact and hemocompatibility properties [14]. **Supplementary Materials:** The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/app15052646/sl](https://www.mdpi.com/article/10.3390/app15052646/sl)]([https://www.mdpi.com/article/10.3390/app15052646/sl](https://www.mdpi.com/article/10.3390/app15052646/sl)): Figure S1: Complete FTIR-ATR spectra of PMP treated with NO (1000 ppm) for 17 h immersed in either (a) Millipore water or (b) physiological saline solution; Figure S2: Complete FTIR-ATR spectra of MABS treated with NO (1000 ppm) for 17 h immersed in either (a) Millipore water or (b) physiological saline solution; Figure 53: Complete FTIR-ATR spectra of PU treated with NO (1000 ppm) for 17 h immersed in either (a) Millipore water or (b) physiological saline solution; Table S1: Characteristic photograph of the contact-angle measurements of the hollow fiber membranes; Table S2: Individual advancing and receding angles of the untreated hollow fiber membrane (PMP) samples; Table S3: Individual advancing and receding angles of the hollow fiber membrane (PMP) samples treated with NO (1000 ppm) for 17 h; Table S4: Individual advancing and receding angles of the inlet/outlet cap (MABS) samples both untreated and treated with NO (1000 ppm) for 17 h (* no receding angle; continuous decline with decreasing radius); Table S5: Individual advancing and receding angles of the PU material samples both untreated and treated with NO (1000 ppm) for 17 h; Scheme S1: Potential reaction mechanism for the formation of nitro and nitrite ester groups through electrophilic addition of NO\({}_{2}\)[36,37]; Scheme S2:Reaction mechanism for the crosslinking and chain scission reactions of the carbamate group caused by NO\({}_{2}\)[38]; Scheme S3: Potential reaction mechanism for the formation of nitro groups through the electrophilic aromatic nitration reaction, which occurs in a continuum between a polar and a single electron charge transfer (SET) mechanism [40,52,53]; Scheme S4: Potential reaction mechanism for the formation of nitrate ester groups from nitrite ester groups [36,41]; Scheme S5: Potential reaction mechanisms for the formation of nitrate ester groups through the reaction of nitric acid with hydroxy groups [42,54]; Scheme S6: Acid-catalyzed ester hydrolysis mechanism [55]. M.K. : Formal analysis (equal), investigation (equal), methodology (equal), data curation (equal), visualization (lead), writing--original draft (lead). A.C.: Formal analysis (equal), data curation (equal), investigation (equal). S.M. : Formal analysis (equal), data curation (equal), investigation (equal). G.K.A. : Supervision (equal), writing--review and editing (equal). W.K.