Elsevier

Surface and Coatings Technology

Volume 354, 25 November 2018, Pages 38-45
Surface and Coatings Technology

Synthesis and structure of antibacterial coatings formed by electron-beam dispersion of polyvinyl chloride in vacuum

https://doi.org/10.1016/j.surfcoat.2018.09.013Get rights and content

Highlights

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    A new material for implants' antibacterial coating is proposed.

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    The impact of low-energy electron flow on PVC forms a polyconjugate structure.

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    The polyene fragments of the coating reach 8 bonds length.

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    The coating is capable of prolonged release of ciprofloxacin.

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    Heat treatment of the coating does not affect the kinetics of ciprofloxacin release.

Abstract

A new antibacterial coating has been synthesized to modify implants with prolonged release of a medicinal antibacterial component (ciprofloxacin). Condensed in vacuum, the products of electron beam dispersion of PVC were used as one of the components of the target. It is shown that the repeated action of the electron flow on condensed destruction products of PVC is accompanied by the formation of poly-conjugated structures devoid of chlorine. Thermal treatment of the hydrocarbon layer (500 °C) leads to the formation of graphite-like structures and polyene fragments up to 8 units in length. The antibacterial coating (PVC2-ciprofloxacin) is formed by the action of a low-energy electron flow on a mechanical mixture of ciprofloxacin and condensed PVC destruction products. It is shown that in comparison with the antibacterial layer PU - ciprofloxacin, the proposed coating is characterized by a higher resistance to abrasion. The PU - ciprofloxacin layer is completely worn out after 17 cycles. The worn-out areas of the proposed coating after 17 and 25 wear cycles are 47% and 53% respectively. Heat treatment of the coating, including standard sterilization, does not affect the kinetics of the release of ciprofloxacin from the hydrocarbon matrix. Unlike the PU layer - ciprofloxacin, the prolonged release (sustained release) of ciprofloxacin in PVC2-ciprofloxacin is not ensured by intermolecular interaction but by the mechanical containment (confinement) of ciprofloxacin using a hydrocarbon matrix. Microbiological studies showed high antibacterial activity of the proposed composite layer in relation to P. aeruginosa and E. coli. The activity was maintained after abrasive coating treatment for 24 h.

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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