In vitro analysis of cell compatibility of TiCuN films with different Cu contents

https://doi.org/10.1016/j.surfcoat.2020.126790Get rights and content

Highlights

  • As Cu content increases, columnar structure of the TiN film gradually transforms into a dense and featureless structure.

  • When the Cu content reaches 11.1 at.%, Cu nanocrystals are formed in the TiCuN film.

  • TiCuN film with a Cu content of 2.4 at.% promoted osteoblast viability and reduced the macrophage inflammatory response.

Abstract

TiN film has been used in the surface modification of orthopaedic implants due to its favorable biocompatibility and tribological properties. Copper ions have low toxicity and biological functions. In this study, copper was doped to TiN film to enhance the viability of osteoblast and decrease the inflammatory response of macrophages for TiCuN film applications in orthopaedic implants. TiCuN films with different Cu contents were deposited on Si wafers by direct current (DC) magnetron sputtering technique. The effects of Cu content on the TiCuN film structure, surface morphology, and surface energy were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and contact angle measurements. The results demonstrated that Cu doping could suppress the columnar structure of TiN films, change the surface of the TiN film from hydrophilic to hydrophobic, and reduce its surface energy. When the Cu content reached 11.1 at.%, Cu nanocrystals were formed in the TiCuN film. The biocompatibility of the TiCuN films with different Cu contents was analyzed based on osteoblasts and macrophages. The results demonstrated that the viability and morphology of osteoblasts on the TiCuN films with a Cu content of 2.4 at.% were significantly improved compared with those of the CoCrMo alloy and TiN film. The inflammatory response induced by the TiCuN films with Cu contents of 2.4 and 4.2 at.% was lower than that induced by the CoCrMo alloy and TiN film without Cu doping. The TiCuN film with optimum Cu content of 2.4 at.% promoted the viability of osteoblasts and reduced the inflammatory response of macrophages.

Introduction

TiN film is an excellent surface modification material for medical implants. Owing to its favorable biocompatibility and tribological properties, it has been used for the surface modification of artificial joints and oral implants [1,2]. On the other hand, copper is a necessary trace element in the human body, and important in physiological activities [3]. Ewald et al. [4] found that copper ions can promote the differentiation of bone marrow mesenchymal stem cells into osteoblasts, enhance the activity of osteoblasts, and promote the proliferation and collagen deposition of osteoblasts. Studies by Lin et al. [5] have shown that copper ion can promote the proliferation and maturation of chondrocytes, and induce macrophages shifting to anti-inflammatory phenotype. Huang et al. [6] proved that the copper ions released from TiCu films can improve the viability of endothelial cells (EC). In addition, copper is a metal recognized as having antibacterial properties and is widely used in antibacterial coatings [7].

Considering the low toxicity and biological functions of copper, it is often chosen as a doping element to improve the antibacterial properties of bio-implants [8]. It has been reported that doping Cu atoms into the TiN film can improve the antibacterial properties of the TiN film [[9], [10], [11]]. In addition, a small amount of Cu doping can increase the hardness and toughness of the TiN films and reduce the wear rate [12,13]. Although Cu is required for human body health, it becomes toxic once the concentration of Cu ions exceeds a certain threshold [14]. Excessive amounts of copper can result in Fenton-type redox reactions, resulting in oxidative cell damage and cell death [15]. Therefore, the influence of Cu content in Cu-doped films on biosafety must be considered when applying in vivo.

In this study, copper is doped to TiN to enhance the viability of osteoblast and decrease the inflammatory response of macrophages for TiCuN potential applications in orthopaedic implants. Silicon wafer is often used as the substrate for studying surface morphology, composition, structure, and biocompatibility of biomedical films due to its smooth surface and easy-to-cut characteristics. Compared with biomedical metals for artificial joints and oral implants (such as CoCrMo, Ti alloy etc.), Si has good corrosion resistance. In order to avoid the influence of extra ions originated from substrate on the inflammation reaction of TiCuN films, Si material was selected as the substrate in this study. The direct current (DC) magnetron sputtering technology was used to prepare TiCuN films with different Cu contents, and the Cu content in TiN films was controlled by varying the number of copper rods embedded in the sputtering target. The effects of the Cu content in the Cu-doped TiN film on its microstructure, surface properties, behavior in mouse osteoblast culture, and macrophage inflammatory response were studied.

Section snippets

Preparation of TiCuN films with different Cu contents

Using a four-target unbalanced magnetron sputtering system (UBMS500, SKY Technology Development, Shenyang, China), TiN films with various Cu atomic contents were prepared. Commercially available N-type Si (100) was used as the substrate. A rectangular titanium target (170 mm × 134 mm, 99.9%) embedded with different number of Cu rods (ø6 mm) was used as the sputtering target. The distance between the target and substrate was set at 80 mm. The base pressure of the system was 2 × 10−3 Pa. The

Material characterization of TiCuN films with different Cu contents

The microstructures of the TiCuN films with different Cu contents were investigated by XRD analysis (Fig. 1). The Ti (101) diffraction peak at 39.7° can be attributed to the titanium interlayer for all TiCuN films. The Cu (200) diffraction peak at 50.3° appeared for the TiCuN film with 11.1 at.% Cu, while the peak cannot be observed for the TiCuN films with 2.4 and 4.2 at.% Cu. Zhang et al. [12] found that when Cu content was 5.2 at.%, Cu atoms in TiCuN film existed in the form of solid

Conclusions

In this study, copper is doped to TiN to enhance the viability of osteoblasts and decrease the inflammatory response of macrophages. The Cu-doped TiN films with different Cu contents (0–11.1 at.%) were deposited by DC magnetron sputtering. The effects of Cu content on the physicochemical properties and on the cell compatibility of TiCuN films were analyzed. The addition of Cu suppresses the columnar structure and achieves a compact structure of the TiN films. As the Cu content increased, Cu

CRediT authorship contribution statement

X.Y. Luo: Conceptualization, Methodology, Investigation, Formal analysis, Writing – original draft, Writing – review & editing. D.L. Ma: Investigation, Writing – original draft. P.P. Jing: Investigation, Formal analysis. Y.L. Gong: Methodology, Investigation. Y. Zhang: Investigation, Formal analysis. F.J. Jing: Formal analysis, Writing – review & editing, Project administration. Y.X. Leng: Conceptualization, Formal analysis, Supervision, Funding acquisition.

Declaration of competing interest

No conflict of interest is associated with the publication of this manuscript, and the manuscript was approved by all the coauthors for publication.

Acknowledgment

This work was supported by NSFC (52072312), Sichuan Science and Technology Program (2020YFH0044), and Chengdu Science and Technology Program (2020-GH02-00050-HZ).

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