Cytocompatibility and early inflammatory response of human endothelial cells in direct culture with Mg-Zn-Sr alloys

Abstract

Crystalline Mg-Zinc (Zn)-Strontium (Sr) ternary alloys consist of elements naturally present in the human body and provide attractive mechanical and biodegradable properties for a variety of biomedical applications. The first objective of this study was to investigate the degradation and cytocompatibility of four Mg-4Zn-xSr alloys (x = 0.15, 0.5, 1.0, 1.5 wt%; designated as ZSr41A, B, C, and D respectively) in the direct culture with human umbilical vein endothelial cells (HUVEC) in vitro. The second objective was to investigate, for the first time, the early-stage inflammatory response in cultured HUVECs as indicated by the induction of vascular cellular adhesion molecule-1 (VCAM-1). The results showed that the 24-h in vitro degradation of the ZSr41 alloys containing a β-phase with a Zn/Sr at% ratio ~1.5 was significantly faster than the ZSr41 alloys with Zn/Sr at% ~1. Additionally, the adhesion density of HUVECs in the direct culture but not in direct contact with the ZSr41 alloys for up to 24 h was not adversely affected by the degradation of the alloys. Importantly, neither culture media supplemented with up to 27.6 mM Mg2+ ions nor media intentionally adjusted up to alkaline pH 9 induced any detectable adverse effects on HUVEC responses. In contrast, the significantly higher, yet non-cytotoxic, Zn2+ ion concentration from the degradation of ZSr41D alloy was likely the cause for the initially higher VCAM-1 expression on cultured HUVECs. Lastly, analysis of the HUVEC-ZSr41 interface showed near-complete absence of cell adhesion directly on the sample surface, most likely caused by either a high local alkalinity, change in surface topography, and/or surface composition. The direct culture method used in this study was proposed as a valuable tool for studying the design aspects of Zn-containing Mg-based biomaterials in vitro, in order to engineer solutions to address current shortcomings of Mg alloys for vascular device applications.

Magnesium ion leachables induce a conversion of contractile vascular smooth muscle cells to an inflammatory phenotype

“…Our work highlight that vSMCs would undergo phenotypic adaptation to the leachables of the Mg‐based stents, especially to the liberated magnesium ions. Previously, Mg ions were found to affect the differentiation of the undifferentiated human cells, mesenchymal stem cells and endothelial cells . Under the calcifying condition, the Mg ions were anti‐osteogenic for vSMCs .…”

In vitro and in vivo cytocompatibility evaluation of biodegradable magnesium-based stents: a review

“…In contrast, there was no stimulating effect of the Mg 2+ ions for SMCs [25,51,80,81]. This has been traced down to cell cycle regulation and proliferation-associated genes, which showed only minor changes in ECs but were down-regulated in SMCs, indicating that Mg inhibits SMC proliferation without a major influence on EC proliferation [25,82].…”

“…However, these available standards do not consider the physiological clearance of the ions released from the implanted Mg-based biomaterials by circulation in vivo [64]. The standards not only neglect the impact of the different accumulated ions in the extracts on the cytotoxicity results [62,81,82,95,96], the accumulation also contributes to the difference and even contradictive results of in vitro and in vivo studies [12,86,87,97]. There are two feasible approaches to reduce the accumulation of Mg and alloy ions in the extracts.…”

“…Nevertheless, it is difficult to identify the factors causing a reduction of cell viability and adhesion. These factors include the local increase in alkalinity, the change of surface topography, and/or the surface composition [12,81,[98][99][100]. Herein, it has to be emphasized that the "dynamic environment" in direct culture assay is formed in the process of the degradation of Mg alloys accompanied by the hydrogen generation, product diffusion, as well as pH changes.…”

Influence of heat treatment and hot extrusion on the microstructure and tensile properties of rare earth modified Mg-Zn based alloy

“…Then a series of new magnesium alloys for biomedical application were developed [13][14][15]. The research of Zhang et al [10] exhibited that Zn addition in Mg could increases the mechanical performance and biocompatibility, and the Mg-6Zn (wt.%) alloy was the best choice.…”