Antibacterial coatings are regarded as a necessary tool to prevent implant-related infections. Substrate-independent and widely applicable coating techniques are gaining significant interest to synthesize different types of antibacterial films, which can be relevant from a fundamental and application-oriented perspective. Plasma polymer- and polydopamine-based antibacterial coatings represent the most widely studied and versatile approaches among these coating techniques. Both single- and dual-functional antibacterial coatings can be fabricated with these approaches and a variety of dual-functional antibacterial coating strategies can still be explored in future work. These coatings can potentially be used for a wide range of different implants (material, shape, and size). However, for most implants, significantly more fundamental knowledge needs to be gained before these coatings can find real-life use.

Surface functionalization with biological macromolecules is an important task for the development of sensor materials, whereby the interaction with other biological materials should be suppressed. In this work, we developed a novel multifunctional poly(2-ethyl-2-oxazoline)-dithiolane conjugate as a versatile linker for gold surface immobilization of amine-containing biomolecules, containing poly(2-ethyl-2-oxazoline) as antifouling polymer, dithiolane for surface immobilization, and activated esters for protein conjugation. First, a well-defined carboxylic acid containing copoly(2-ethyl-2-oxazoline) was synthesized by cationic ring-opening copolymerization of 2-ethyl-2-oxazoline with a methyl ester-containing 2-oxazoline monomer, followed by postpolymerization modifications. The side-chain carboxylic groups were then converted to amine-reactive pentafluorophenyl (PFP) ester groups. Part of the PFP groups was used for the attachment of the dithiolane moiety, which can efficiently bind to gold surfaces. The final copolymer contained 1.4 mol% of dithiolane groups and 4.5 mol% of PFP groups. The copolymer structure was confirmed by several analytical techniques, including NMR spectroscopy and size-exclusion chromatography. The kinetics of the PFP ester aminolysis and hydrolysis demonstrated significantly faster amidation compared to hydrolysis, which is essential for subsequent protein conjugation. Successful coating of gold surfaces with the polymer was confirmed by spectroscopic ellipsometry, showing a polymer brush thickness of 4.77 nm. Subsequent modification of the coated surfaces was achieved using bovine serum albumin as a model protein. This study introduces a novel reactive polymer linker for gold surface functionalization and offers a versatile polymer platform for various applications including biosensing and surface functionalization.

Surface modification of hydrophobic nanofibers (NFs) to introduce cell-interactive chemical functionalities re-mains a challenge in biomedical applications. This study presents a novel three-step plasma-based method for synthesizing coatings with improved chemical selectivity compared to conventional plasma polymers. The process involved hexamethyldisiloxane (HMDSO) plasma polymerization followed by helium plasma activation, both performed in a medium-pressure dielectric barrier discharge. Scanning electron microscopy analysis demonstrated that the plasma-based steps did not cause damage to the NFs. X-ray photoelectron spectroscopy (XPS) and water contact angle measurements revealed the formation of a hydrophilic silanol-rich layer after HMDSO plasma polymerization and helium plasma activation. In the third step, (3-aminopropyl)triethoxysilane (APTES) was grafted onto the plasma polymer to introduce primary amine groups onto the surface, as confirmed by XPS. Although the APTES-based layer exhibited partial removal when exposed to aqueous environments, a stable aminated layer remained on the NF surface, which significantly enhanced Schwann cell responses compared to untreated and HMDSO-based coated NFs. This enhancement was confirmed through fluorescent imaging using live-dead staining, immunostaining, and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazo-lium bromide (MTT) assay. These coatings with a high selectivity in their chemical functionality (amines, or other functionalities via silanization agent selection), offer a promising surface functionalization approach for tissue engineering scaffolds.

Fabrication of strong antibacterial composite nanofibrous yarns (CNYs) for suture applications by using common direct current electrospinning has been technologically challenging. In this work, we have demonstrated a more straightforward and facile approach to fabricate chlorhexidine (CHX)-containing antibacterial nanofibrous sheaths wounded around a polyamide core yarn using a novel collectorless alternating-current electrospinning approach. Scanning electron microscopy results showed that the nanofibrous envelope was completely wrapped around the core yarn for both polymers, polyurethane, and polyamide 6 (PA6), used in this study. High-performance liquid chromatography after dissolving of the CNYs confirmed the presence of CHX in the yarns, while X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy indicated that the amount is relatively low. The tensile properties of all the CNYs were better than of the core yarns and the CHX addition resulted in a lower envelope linear density and envelope adhesion force. Thermal gravimetric analysis showed that all CNYs are thermally stable within the temperature range of interest. Cytocompatibility tests with 3T3-SA mouse fibroblast cells and antibacterial evaluations with Escherichia coli and Staphylococcus aureus showed that the CHX-containing PA6-based CNYs are biocompatible and have antibacterial properties, suggesting that these yarns can be used as functional and mechanically performant sutures.

The aging of plasma activated plasma polymer films has been studied to a limited extent, despite the recent application-oriented interest for these coatings. Therefore, the aging of plasma polymerized hexamethyldisiloxane (ppHMDSO) coatings that were subjected to helium or dry air plasma activation was investigated and compared to the aging of plasma activated silicone elastomer (S184) in this work. Water contact angle (WCA) measurements indicated that both materials reached a super-hydrophilic state after both plasma treatments. X-ray photoelectron spectroscopy (XPS) illustrated that this was the result of the introduction of a variety of oxygen-containing functionalities, while atomic force microscopy highlighted that the morphology was not significantly changed. The WCAs of the plasma activated ppHMDSO coating and S184 showed similar aging behavior, as the wettability of both materials significantly decreased. XPS measurements after 11 days of aging indicated that multiple aging processes were occurring in S184, while migration of oxidized short chain fragments was most important for the ppHMDSO coating. All these aged coatings could be silanized with 3-aminopropyltriethoxysilane, although differences in stability were observed. As such, this study provides additional insight in the chemical nature of activated plasma polymers and provides design principles for synthesizing plasma polymers with selective chemical functionalities.

Plasma polymerization has emerged as an appealing technique for surface modification because of its advantages over a variety of conventional techniques, including ease-of-use and the possibility to modify nearly any substrate. One of the main challenges of plasma polymer-based surface modification, however, is having control over the coating chemistry, as plasma deposition generates a diversity of chemical structures. Therefore, this study presents an alternative plasma-based method for the fabrication of coatings that contain selective functionalities. In a first step, hexamethyldisiloxane (HMDSO) plasma polymerization is performed in a medium-pressure dielectric barrier discharge (DBD) to deposit polydimethylsiloxane (PDMS)-like coatings. In a second step, this coating is exposed to an air plasma in a similar DBD setup to introduce silanol groups on the surface. These groups are used in a third and final step as anchoring points for grafting of (3-aminopropyl)triethoxysilane (APTES) and (3-bromopropyl)trichlorosilane (BrPTCS) to selectively introduce amino or bromo groups, respectively. X-ray photoelectron spectroscopy (XPS) and water contact angle (WCA) measurements indicated that the first two steps were successful. Moreover, the coating could be synthesized on three different surfaces, namely, glass, ultrahigh-molecular-weight polyethylene, and polytetrafluoroethylene, indicating the wide applicability of the developed procedure. Afterward, XPS also proved that the APTES and BrPTCS grafting resulted in the formation of a coating containing primary amines and alkyl bromides, respectively, in combination with an organosilicon matrix containing silanol groups as remaining reactive groups, proving the successful synthesis of selective functional plasma-based coatings. The intermediate air-plasma-activation step was demonstrated to be necessary for successful and stable grafting of the final layer. In conclusion, this study established a general procedure for the development of coatings with selective functionality that can be applied on a wide variety of substrates for, e.g., biosensor applications, biomolecule, or polymer immobilization or for the synthesis of antibacterial coatings.

Recently, new plasma polymerization-based techniques emerged to deposit chemically functional coatings for various applications.However, little is known on the aging of these layers.Therefore, this study aims to investigate the physicochemical properties of aerosol-assisted atmospheric pressure plasma deposited (3-aminopropyl)triethoxysilane-based (AAPD-APTES) coatings and compare their aging behavior to APTES-modified plasma polymerized hexamethyldisiloxane-based coatings (ppHMDSO-APTES).X-ray photoelectron spectroscopy (XPS), attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), water contact angle (WCA) and atomic force microscopy (AFM) measurements indicated that the applied power had an insignificant impact on the wettability, chemistry and morphology of the AAPD-APTES films.A complex nitrogen-containing organosilicon layer was obtained with significant preservation of the Si-O-C-bonds.For the ppHMDSO-APTES coatings, XPS indicated that these layers had a significantly higher amount of preserved primary amines and a different surface morphology.Oxidation and hydrolysis of Si-O-C-bonds were the most prevalent aging processes for the AAPD-APTES coatings, while protonation of primary amines was most important for the ppHMDSO-APTES films.This study indicates that further research is needed to examine the differences in coating chemistry and aging of other AAPD-based and conventional plasma polymers.Additionally, it provides a reference to decide which coating type and associated aging processes are preferred for certain applications.

Plasma activation and polydopamine (PDA) coating deposition on nanofibrous tissue engineering (TE) scaffolds have emerged as two easy and inexpensive methods to improve their cell-material interactions. This work is the first one to compare the cytocompatibility of both surface modification techniques on polycaprolactone nanofibers (NFs). First, the argon plasma treatment (PT) and PDA coating deposition were optimized based on water contact angle (WCA) measurements and visual observation, respectively. It was shown that employing the optimized PT before the PDA layer deposition enables a more homogeneous PDA deposition in comparison to the untreated counterpart. Subsequently, scanning electron microscopy showed that the treatments did not damage the fibers. X-ray photoelectron spectroscopy indicated that the PT resulted in the introduction of O-containing functionalities, while the PDA coating introduced a complex C-, N-, and O-based chemistry. The changed surface chemistry also led to a significant increase in wettability for both surface treatments in comparison to the untreated NFs. Different human foreskin fibroblast-based cell tests indicated that the PDA coating outperformed the PT with regard to cell adhesion and proliferation, although the latter still resulted in a significant improvement in comparison to the untreated NFs. Thereby, this study indicates that a careful surface modification selection is necessary to obtain the desired performance of TE scaffolds.

Polyolefins are well-known and the most commonly used polymers worldwide. Advantages like outstanding mechanical properties, chemical resistance, low cost, and processability are neighboring with some drawbacks like relatively high gas and vapor permeability, low surface energy. This chapter introduces surface plasma modification as an environmentally friendly, fast, and versatile technique. Details regarding different plasma reactor designs, generation methods, working parameters suitable for treating polyolefins are presented. Furthermore, plasma activation, grafting, and etching are described as the most commonly used techniques for surface energy modification to enhance polyolefins' biocompatibility, printability, adhesion to materials, and other parameters. For instance, plasma activation cross-linking of the polymer chains can be achieved, which leads to gas and vapor permeability improvement. Choice of working conditions allows controlling the degree of cross-linking, the type, and the concentration of the incorporated functional groups on the surface. Plasma polymerization is introduced as a technique for coating deposition with different properties and functionality depending on the operating parameters and monomer selection. Improvement of barrier layer performance and modification of the surface energy are the main applications of plasma polymerization of polyolefins.

Electrospun polycaprolactone (PCL) nanofibers (NFs) have been extensively researched for tissue engineering purposes, despite their hydrophobic surface properties which compromise their cell interactivity. To enhance this interactivity, within this study, the surface of PCL NFs was first modified by acrylic acid plasma polymerization. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) confirmed that the plasma process did not damage the NFs. Water contact angle (WCA) and zeta potential measurements showed a significant wettability increase and surface charge decrease, respectively. X-ray photoelectron spectroscopy (XPS) confirmed that the NFs were coated with a plasma polymer containing O-based functional groups, which could be related to the aforementioned changes in surface wettability and charge. Additionally, a post-plasma grafting step of ethylene diamine on the surface carboxylic acid groups was performed to investigate the influence of COOH-groups on bone marrow mesenchymal stem cell (BMST) adhesion and proliferation. WCA, zeta potential and XPS measurements confirmed the successful conversion of carboxylic acid into primary amine groups, while SEM indicated that the NF morphology did not change upon the reaction. PCL NFs subjected to this post-plasma grafting evoked the best BMST behaviour, indicating that minor changes in the surface chemistry can have a significant effect on cell-biomaterial interactions.

Plasma activation is an attractive and widely used technique for the surface modification of polymeric substrates. Despite being extensively explored, the fundamentals of plasma activation processes remain not completely unraveled yet, mainly because of the complex physicochemical changes occurring at the polymer surface. In general, plasma treatment leads to a surface functionalization and/or polymer structure modification. The occurrence of plasma surface functionalization was elaborately studied via X-ray photoelectron spectroscopy (XPS), while the second process was in contrast investigated to a much lower extent. Therefore, this study aims at investigating the relative importance of polymer degradation and cross-linking upon standard plasma treatment conditions via size-exclusion chromatography (SEC). To do so, poly(methyl methacrylate) (PMMA) was subjected to different low and medium pressure dielectric barrier discharge (DBD) plasma treatments sustained in three different gases (Ar, He, N-2), and poly(2-ethyl-2-oxazoline) (PEtOx) was treated with Ar plasma at medium pressure. Water contact angle (WCA) measurements were carried out to determine the surface chemistry equilibrium region for Ar plasma treatment at both pressures, after which WCA and XPS measurements were used to evaluate the surface chemistry modification upon the different treatments. The wettability of both PMMA and PEtOx increased for all treatments, which could be linked to the introduction of polar functionalities on the surface, as observed by XPS. By taking into consideration these chemistry changes, all SEC measurements indicated that polymer degradation was the dominant process, while some polymer coupling was observed for Ar plasma treatment at medium pressure. For PMMA treatment at low pressure, a similar degradation was observed for all gases. This was in contrast to the medium pressure treatments for which the Ar plasma induced a more significant chain scission in comparison to N-2 and He. This could probably be attributed to the plasma properties, as Ar DBDs at medium pressure are known to consist of highly energetic microdischarges which are typically absent for the other treatments. Additionally, the different degradation behavior of PMMA and PEtOx highlighted the prominent influence of the initial chemical polymer structure on the plasma activation response. As such, this study further establishes the effective use of SEC in the evaluation of polymer degradation and cross-linking upon plasma activation. (C) 2021 Elsevier Ltd. All rights reserved.

The plasma polymerization of amide-based precursors is a nearly unexplored research area, which is in contrast with the abundance of reports focusing on amide based surface modification using wet chemistry. Therefore, this study aims to profoundly investigate the near-atmospheric pressure plasma polymerization of N,N-dimethylacrylamide (DMAM) to obtain stable coatings. In contrast to the unstable coatings obtained at lower discharge powers, the stable coatings that were obtained at higher powers showed a lower hydrophilicity as assessed by water contact angle (WCA). This decrease in hydrophilicity with increasing plasma power was found to be related to a reduced preservation of the monomer structure, as observed by Fourier transform infrared (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and XPS C-60 depth profiling, a rarely used but effective combination of techniques. Furthermore, the chemical composition of the coating was found to be in good agreement with the plasma active species observed by optical emission spectroscopy. Additionally, XPS C-60 depth profiling indicated a difference between the top layer and bulk of the plasma polymer due to spontaneous oxidation and/or postplasma coating deposition. Finally, the stable coatings were also found to have cell-interactive behavior toward MC3T3 as studied by in vitro live/dead fluorescence imaging and (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) (MTS) assays. With the latter technique, a cell viability of up to 89% as compared with tissue culture plates after 1 day of cell culture was observed, indicating the potential of these coatings for tissue engineering purposes.

Plasma polymerization is gaining popularity as a technique for coating surfaces due to the low cost, ease of operation, and substrate-independent nature. Recently, the plasma polymerization (or deposition) of 2-oxazoline monomers was reported resulting in coatings that have potential applications in regenerative medicine. Despite the structural versatility of 2-oxazolines, only a few monomers have been subjected to plasma polymerization. Within this study, however, we explore the near atmospheric pressure plasma polymerization of a range of 2-oxazoline monomers, focusing on the influence of the aliphatic side-chain length (methyl to butyl) on the plasma polymerization process conditions as well as the properties of the obtained coatings. While side-chain length had only a minor influence on the chemical composition, clear effects on the plasma polymerization conditions were observed, thus gaining valuable insights in the plasma polymerization process as a function of monomer structure. Additionally, cytocompatibility and cell attachment on the coatings obtained by 2-oxazoline plasma polymerization was assessed. The coatings displayed strong cell interactive properties, whereby cytocompatibility increased with increasing aliphatic side-chain length of the monomer, reaching up to 93% cell viability after 1 day of cell culture compared to tissue culture plates. As this is in stark contrast to the antifouling behavior of the parent polymers, we compared the properties and composition of the plasma-polymerized coatings to the parent polymers revealing that a significantly different coating structure was obtained by plasma polymerization.