Synthesis and structure of antibacterial coatings formed by electron-beam dispersion of polyvinyl chloride in vacuum
Introduction
Nosocomial infection is a cause of serious postoperative complications, which in some cases may lead to the death of a patient [[1], [2], [3], [4], [5], [6]]. The control of its consequences requires significant financial costs. Acute infections occur, in prosthetics, when the implants are introduced into the human body.
Currently, the main directions of the fight against bacterial adhesion and the subsequent formation of biofilms on the surfaces of the implants are formulated [1,2,5]. The most effective way of preventing postoperative complications is to use coatings maintaining a prescribed concentration of antibacterial substance near the implant surface for a long time. There are a number of requirements to these coatings, such as, biocompatibility, self-cleaning, programmable release of the drug component, strong adhesion to the implant surface, resistance to abrasion by soft tissues, etc. The deposition of antibacterial drugs onto a metal implant is not effective, since it may lead to bacterial resistance [5]. This is caused by the inability to maintain the drug concentration above the minimal inhibitory (MIC) for a particular microorganism near the implant surface over a long period of time.
The water-soluble (e.g., PEG) or biodegradable (e.g., polyactide) antibacterial polymeric coatings possess a good self-cleaning function, and can prolong release of the drug component, protect metal nanoparticles from leaching and reduce their cytotoxicity [7]. Physical processing methods, e.g., plasma make it possible to give the polymer coatings the surface energy necessary to stimulate the processes of tissue regeneration [8]. They make it easy to control the structure and, hence, the kinetics of the release of the drug component. The disadvantage of polymer coating systems is the low wear resistance and weak adhesion with metal surfaces, which probably leads to a rapid loss of coatings during the implant introduction into the body. One should note that all medical devices must undergo the obligatory standard procedure of thermal sterilization before being introduced into the body. This heat treatment may lead to notable structural changes of polymeric coating and thus the properties as well.
Carbon coatings (e.g., DLC) are characterized by high adhesion strength to metal surfaces, wear resistance and biocompatibility [[9], [10], [11]]. Only particles of metals (silver, copper, zinc, etc.) may be act as antimicrobial components of DLC coatings [[9], [10], [11], [12], [13]]. These metals are potentially toxic for cell cultures [1,3,5]. DLC coatings cannot be used as layers with programmable release of the drug component.
Many researchers have pursued various ways to deposit thin layers based on the advantages of carbon and polymer coatings. In particular, one of the methods for preparing such coatings is presented previously [6]. However, this technology cannot be effectively used to modify implants in a wide range of sizes and shapes because of the complexity and multi-stage processes.
The electron-beam polymers dispersion allows the formation of thin antibacterial layers with prolonged release of the drug component [7,14,15]. The plasma pre-treatment of metal substrates provides strong adhesion of coatings with the substrates.
In the work presented, the method of electron-beam formation of antibacterial coatings characterized by high adhesion and wear resistance is proposed. It is suggested to use mix condensed products of electron-beam dispersion of polyvinyl chloride PVC with medicinal compound as a target material. The deposited layer structure is midway between the structure of the polymer hydrocarbon and the DLC layers. Thus, the advantages of both polymer antibacterial layers and carbon layers can be preserved.
Section snippets
Methodology of forming coatings
The coatings were formed from the active gas phase generated by the action of a low-energy electron beam with 800–1600 eV energy and 0.01–0.03 A/cm2 density on the target material in a vacuum. The initial pressure of the residual gases in the vacuum chamber was ≈4 · 10−3 Pa.
The composite coatings were deposited from the gas phase formed by the action of electron beam on mechanical mixtures of PVC1 and ciprofloxacin powders, as well as polyurethane and ciprofloxacin in a 1:1 weight ratio.
It
Results of differential scanning calorimetry
Two periods of intensive mass loss were observed in thermogravimetric curves of PVC powder in Fig. 2. At the indicated time intervals, the processes of dehydrochlorination and the subsequent thermal destruction of the formed conjugated system take place [[17], [18], [19]]. The initial noticeable decrease in polymer mass was observed near 300 °C, with the subsequent one near 450 °C. The thermogravimetric curve of the condensed products of PVC electron-beam decomposition lacks the areas of
Conclusions
Electron-beam exposure to PVC initiates dehydrochlorination processes. Condensed in a vacuum, the products of PVC destruction contain practically no chlorine. The repeated action of electron flow on the condensed dispersion products is followed by a poly-conjugated structure formation, which is completely free of chlorine.
Heat treatment of a coating based on PVC2 initiates the exothermic interaction processes of double unsaturated bonds. The consequence of these interactions is the formation of
Acknowledgement
This work was supported by the Intergovernmental Cooperation Projects in the national key research and development plan of the Ministry of Science and Technology of PRC (No. 2016YFE0111800), and the National Natural Science Foundation of China (No. 51373077).
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