Abstract

1. Introduction

2. Experimental

3. Results and discussion

4. Conclusion

Conflict of Interest

Supplementary Information

References

Abstract

     This study investigates the effect of graphene oxide (GO) on the mechanical and corrosion behavior, antibacterial performance, and cell response of Mg—Zn—Mn (MZM) nanocomposite. MZM/GO nanocomposites with different amounts of GO (i.e., 0.5wt%, 1.0wt%, and 1.5wt%) were fabricated by the semi-powder metallurgy method. The influence of GO on the MZM nanocomposite was analyzed through the hardness, compressive, corrosion, antibacterial, and cytotoxicity tests. The experimental results showed that, with the increase in the amount of GO (0.5wt% and 1.5wt%), the hardness value, compressive strength, and antibacterial performance of the MZM nanocomposite increased, whereas the cell viability and osteogenesis level decreased after the addition of 1.5wt% GO. Moreover, the electrochemical examination results showed that the corrosion behavior of the MZM alloy was significantly enhanced after encapsulation in 0.5wt% GO. In summary, MZM nanocomposites reinforced with GO can be used for implant applications because of their antibacterial performance and mechanical property.

Introduction

     Currently, because magnesium (Mg) alloys have more benefits than common metallic materials, ceramics, and biodegradable polymers, their biomedical applications have been increasing. In terms of mechanical features, metals have higher mechanical strength and fracture toughness than ceramics or polymers; thus, metals are more appropriate for load-bearing usages than ceramics or polymers [1–2]. The density of human cortical bone (1.75 g/cm3 ) is similar to the density of Mg (1.738 g/cm3 ) and Mg alloys (1.75–1.85 g/cm3 ) but lower than the density of biomedical titanium alloy Ti6Al4V (4.47 g/cm3 ) [3–4]. In terms of biocompatibility, certain amounts of Mg ions in the human body are connected with many metabolic reactions and biological mechanisms [5–6]. Mg alloys are suitable orthopedic and cardiovascular implants because further surgery to remove them is not needed [7–8]. However, an important drawback of Mgbased implants is that they do not have good resistance against corrosion in physiological environments [9]. Mechanical strength could be significantly reduced by rapid and uncontrollable corrosion processes, which leads to premature failure [10]. Moreover, the health of patients who have such implants could be at risk because of the evolution of hydrogen gas and alkalinization of the environments close to the interface between implant and tissue [11]. Therefore, to achieve the secure deployment of biomedical devices, the degradation/corrosion rate of Mg alloys needs to be controlled [12]. In this context, several methods, such as alloying, powder metallurgy (PM), and surface modification strategies, have been used in an extensive number of studies that aimed to solve the problem of corrosion in Mg alloys [13–14]. Among the best methods to enhance the corrosion resistance of porous Mg are PM processes, such as mechanical alloying [15–17].

Conclusion

     In this study, using the semi-powder metallurgy method, different contents of GO were embedded in the Mg–Zn–Mn (MZM) matrix to prepare MZM/xGO nanocomposites for orthopedic applications. The corrosion performance and the 24 20 16 12 8 4 0 0 −0.5 −1.0 −1.5 −2.0 Extension / mm MZM/GO Graphene oxide Graphene oxide Graphene oxide Graphene oxide Crack Crack (a) (c) 1.5GO 0.5GO 1GO MZM (b) MZM composite MZM/0.5GO MZM/1GO MZM/1.5GO 49 59 63 64 Compression strength / N 4820 17810 19960 9620 1.12 1.31 1.44 0.72 Force / (10 3 N) Micro hardness, HV Extension / mm Material nanocomposite Fig. 10.    (a) Typical compressive curves and (b) hardness and compressive strength values of the MZM/xGO nanocomposites; (c) schematic diagram of the crack deflection toughening mechanisms of GO in the MZM/xGO nanocomposites. S. Jabbarzare et al., Effect of graphene oxide on the corrosion, mechanical and biological properties of Mg-based … 317 mechanical and biological characteristics of the MZM/xGO nanocomposites were analyzed. The microstructural assessment showed that a uniform distribution was achieved in the MZM/0.5GO and MZM/1GO nanocomposite specimens. However, agglomeration was observed in the MZM/1.5GO nanocomposite specimen. The results showed that the GO content, hardness value, and compressive strength are positively associated. In this context, the MZM/1GO nanocomposite has higher hardness value and compressive strength than the Mg-based nanocomposite without GO. The MZM/ 0.5GO nanocomposite exhibited a nearly comparable corrosion resistance to the MZM/1GO nanocomposite, even though the incorporation of more GO has an unfavorable effect on the Rct value of the MZM matrix. The MTT assay results showed that the MZM/1GO nanocomposite increased the MG63 cell viability and ALP activity, indicating the increasing level of osteogenesis. The results of the analysis of antibacterial activity showed that the MZM/1.5GO nanocomposite had a noticeable effect on antibacterial effectiveness toward bacteria, including Salmonella–Shigella and Klebsiella pneumoniae. In summary, the results indicate the possibility of utilizing the MZM/1GO nanocomposite for implant applications with effective anti-infection characteristics.

Previous studies showed that Mg-Al layered double hydroxides (Mg-Al LDHs) had well anti-ultraviolet (anti-UV) aging properties when used in the asphalt materials, but it cannot contribute to improve the self-healing properties to repair cracks caused by UV aging under the microwave radiation. Fe3O4 has well microwave absorption and based on the layered structure and large surface area of Mg-Al LDHs, the primary objective of this work was to synthesize Fe3O4-decorated Mg-Al layered double hydroxides magnetic nanosheets, to envisage that the added bitumen modifier has both enhanced anti-UV aging properties and microwave absorption properties. Three modifiers were obtained by the adhesion of Fe3O4 magnetic particles on the surface of Mg-Al LDHs nanosheets, and named as L1F1 (the mass ratio of LDHs: Fe3O4 = 1:1), L2F1 (the mass ratio of LDHs: Fe3O4 = 2:1) and L1F2 (the mass ratio of LDHs: Fe3O4 = 1:2). Morphology, phase composition, chemical structure, anti-UV aging properties, static magnetic properties and microwave absorption properties of them were detected by different analytical methods. Results demonstrate that all magnetic nanosheets present the ferromagnetic behavior, L2F1 shows the lowest MS value among three types of magnetic nanosheets, and the value increases from 28.67 emug1 to 56.78 emug1 with augmented Fe3O4-LDHs ratio. Additions of Fe3O4 significantly enhance the anti-UV aging properties and microwave absorption properties of Mg-Al LDHs. The maximum RL value of L1F2 is recorded as more than two times of that of LDHs, and L1F2 shows the best anti-UV aging properties and microwave absorption properties among all magnetic nanosheets.

Introduction

Layered double hydroxides (LDHs) is a type of multifunctional inorganic supramolecular materials, which is formed by the orderly assembly of positively charged metal cation twodimensional laminate and interlayer anions [1–3]. The nanometer two-dimensional laminates of LDHs are arranged in a longitudinal order to form a three-dimensional crystal structure, which mainly composed of Mg2+ and other metal cations [4,5]. The chemical formula of LDHs can be represented by [M2+ 1xM3+ x (OH)2] x+(An)x/n- mH2 O, where M2+ and M3+ represent divalent and trivalent metal cations, respectively [6–9]. Studies have shown that the layered structure of LDHs has well shielding effect on ultraviolet rays, and can effectively improve the anti-ultraviolet (anti-UV) aging properties of the asphalt materials [5,10]. Zeng added 3% of Mg-Al layered double hydroxides (Mg-Al LDHs) into AH-90, AH-90 and SBS modified bitumen as anti-UV aging agent. The comparisons of equivalent brittle point and fatigue parameters showed that LDHs could effectively reduce the photo-oxidative aging rate of bitumen [11]. This is because when ultraviolet light passes through LDHs, the main layer of metal hydroxide can reflect and absorb ultraviolet light for multiple times. To a certain extent, it can also absorb ultraviolet rays, and the physical shielding effect of the layers on ultraviolet rays is dominant.

Twin-roll casting is an energy-efficient technology for the magnesium strip production consisting of casting and rolling combined in one process step. Producing magnesium strips in an adequate quality-price ratio requires the application of material flow cost accounting to identify hidden improvement potentials. In the following, a material flow cost accounting analysis is carried out for the twin-roll casting process of AZ31 twin-roll-cast strips. Based on the findings, inefficient process steps of the twin-roll casting process are to be revealed, and actions for cost reduction from the point of a stable process management are to be assessed. Overall, an economic process and efficient material consumption can be designed for twin-roll casting considering the strip property development.

Introduction
Value for money is an important criterion for the acceptance of magnesium components by Original Equipment Manufacturers for an industrial application. Beside external business process optimization in the context of supply chain quality individual process steps need to be further improved to achieve the required quality-price ratio [1]. Especially in case of the twin-roll casting technology for the production of magnesium strips [2] the detection of saving potentials is considerable challenging. Compared with other production routes it is an economic and resource-saving procedure combining casting and rolling in one process step [3, 4].To realize additional cost savings, hidden material and energy inefficiencies need to be detected deriving measures for improvement. Supporting transparency of material and energy consumptions and its environmental and financial consequences material flow cost accounting is a useful tool to identify concealed inefficiencies [5, 6]. Therefore, the objective of this paper is to carry out a material flow cost accounting analysis for the twin-roll casting of magnesium AZ31 twin-roll-cast strips at the pilot plant of the Institute of Metal Forming at the TU Bergakademie Freiberg [7]. For this purpose, the twin-roll casting process is initially briefly described. Building on this, the material flow cost accounting analysis is conducted enabling a detailed view of all material and energy flows during twin-roll casting via material flow models. In the next step, the identified energy and material flows are illustrated as Sankey diagram proportional to their mass and energy content. To identify weak points, cost drivers and optimization potentials a material flow cost matrix was developed, whose results will be evaluated in this paper. Based on the technology’s limitations appropriate improvement actions are proposed for further research.