On the Origin of Reduced Cytotoxicity of Germanium-Doped Diamond-Like Carbon: Role of Top Surface Composition and Bonding.

Josef Zemek,Miroslav Jelinek,Tomas Kocourek,Martin Ledinsky,Petr Jiricek,Jana Houdkova

doi:10.3390/nano11030567

Abstract

This work attempts to understand the behaviour of Ge-induced cytotoxicity of germanium-doped hydrogen-free diamond-like carbon (DLC) films recently thoroughly studied and published by Jelinek et al. At a low doping level, the films showed no cytotoxicity, while at a higher doping level, the films were found to exhibit medium to high cytotoxicity. We demonstrate, using surface-sensitive methods—two-angle X-ray-induced core-level photoelectron spectroscopy (ARXPS) and Low Energy Ion Scattering (LEIS) spectroscopy, that at a low doping level, the layers are capped by a carbon film which impedes the contact of Ge species with tissue. For higher Ge content in the DLC films, oxidized Ge species are located at the top surface of the layers, provoking cytotoxicity. The present results indicate no threshold for Ge concentration in cell culture substrate to avoid a severe toxic reaction.

Highlights

This work attempts to understand the behaviour of Ge-induced cytotoxicity of germaniumdoped hydrogen-free diamond-like carbon (DLC) films recently thoroughly studied and published by Jelinek et al At a low doping level, the films showed no cytotoxicity, while at a higher doping level, the films were found to exhibit medium to high cytotoxicity
Apparent composition data derived from the C 1s, O 1s, and Ge 3d spectra recorded at the normal photoelectron emission angle from the air-exposed surfaces of the samples, summarized in Table 1, are compared to the bulk-like Ge concentration values averaged within the whole layer derived from a wavelength dispersive X-ray spectroscopy spectra (WDS) [20]
We proved the formation of the capping carbon film on the top of the low-doped sample that hindered the contact of Ge species with a tissue, explaining the absence of cytotoxicity

Summary

Introduction

This work attempts to understand the behaviour of Ge-induced cytotoxicity of germaniumdoped hydrogen-free diamond-like carbon (DLC) films recently thoroughly studied and published by Jelinek et al At a low doping level, the films showed no cytotoxicity, while at a higher doping level, the films were found to exhibit medium to high cytotoxicity. Ion Scattering (LEIS) spectroscopy, that at a low doping level, the layers are capped by a carbon film which impedes the contact of Ge species with tissue. In biological and medical applications, DLC coatings are often used as barrier layers to prevent corrosion phenomena manifesting themselves by releasing toxic ions from the surfaces of metallic implants into the surrounding tissue [5,6]. A weak property of the undoped DLC layers with a high sp component is a relatively high internal stress resulting in a poor adhesion. This deficiency can be overcome by doping suitable element(s) during a DLC layer deposition. DLC layers is no or weak cytotoxicity, which should be carefully tested for each dopant element and dopant concentration used

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