Cold atmospheric pressure plasma: simple and efficient strategy for preparation of poly(2-oxazoline)-based coatings designed for biomedical applications

Abstract

Poly(2-oxazolines) (POx) are an attractive material of choice for biocompatible and bioactive coatings in medical applications. To prepare POx coatings, the plasma polymerization represents a fast and facile approach that is surface-independent. However, unfavorable factors of this method such as using the low-pressure regimes and noble gases, or poor control over the resulting surface chemistry limit its utilization. Here, we propose to overcome these drawbacks by using well-defined POxbased copolymers prepared by living cationic polymerization as a starting material. Chemically inert polytetrafluoroethylene (PTFE) is selected as a substrate due to its beneficial features for medical applications. The deposited POx layer is additionally post-treated by non-equilibrium plasma generated at atmospheric pressure. For this purpose, diffuse coplanar surface barrier discharge (DCSBD) is used as a source of "cold" homogeneous plasma, as it is operating at atmospheric pressure even in ambient air. Prepared POx coatings possess hydrophilic nature with an achieved water contact angle of 60°, which is noticeably lower in comparison to the initial value of 106° for raw PTFE. Moreover, the increased fibroblasts adhesion in comparison to raw PTFE is achieved, and the physical and biological properties of the POx-modified surfaces remain stable for 30 days. Surface modification of polymers is crucial in many applications, where material must fulfill specific requirements concerning the surface wettability 1 , stiffness 2 , topology 3 as well as chemical reactivity 4. Adjusting the individual surface properties is critical, especially in medicine. Implantable devices or scaffolds must exhibit not only long-term stability in contact with the biological environment but also provide specific interactions with tissues, possess required mechanical or antibacterial properties, or release drugs on demand. Some applications require the material to be non-adhesive and rigid; in other cases, the good cell adhesion is desirable 5. Such control of the specific surface properties of medical implants or devices can be ensured by surface modification 6. The basic strategy for surface modification of low-cost polymers often used in medicine (polypropylene, polyethylene, polytetrafluoroethylene) includes chemical coating by a thin layer of a biocompatible polymer. Besides the polyethylene glycol (PEG) considered being a gold standard for many biomedical applications including surface modification, poly(2-oxazolines) (POx) are gradually more discussed as an available alternative 7,8. POx are accessible via cationic ring-opening polymerization (CROP), which is well controllable process providing the defined polymers with desired architecture, functional moieties, and adjustable properties. Their relevance for employing as biomedical coatings is supported by extensive biological studies of biocompatibility 9,10 , immunotoxicity 11,12 , and control of protein and cell adhesion 13 with positive results. Up to now, many different modification techniqu...

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