Page 13 - Magnesium-based supports for stem cell therapy of vascular disease - Mónica Echeverry Rendón

The main aim of this project was to develop a new formulation of biodegradable stent based on c.p Mg (chemically pure Mg), surface-modified by PEO and loaded with therapeutic cells. Along this line of ideas, the material will act as temporal platform to deliver stem cells and with time the material will gradually disappear addressing the healing of damaged cardiovascular tissues (Fig.1).
In order to provide the sufficient information about the context of this topic in Chapter 2 an overview of the state of the art around this topic is summarized. The thesis consists of two parts: part one includes development and optimization of the processing and characterization of the coatings of so-called commercial pure magnesium (c.p Mg) and in the second part contains all the biological validation. The contents of this thesis are summarized in Fig. 2
Fig.2 Structure of the thesis according to the chapters and their contents
In this specific project, c.p Mg was modified by plasma electrolytic oxidation (PEO), also known as micro-arc oxida- tion (MAO). In this process, c.p Mg was used as anode in an electrolytic cell and it was immersed in a conductive solu- tion through which a current was applied during a specific time controlling the growth of a protective hybrid coating consisted of magnesium oxide (MgO) and magnesium hydroxide (Mg(OH)2). These oxidation products are poorly soluble yet not insoluble which is a major advantage because this allows to tune the degradation rate of future stents. Details about the processing and optimization of the Mg anodization is describe in Chapter 3, where organic compounds, hexamethylenetetramine or mannitol, instead of traditional anorganic additives, where added to the electrolytic anodizing solution and compared to fluoride. In Chapter 3, we also describe the influence of voltage and current density on the characteristics of the coatings.
The purpose of the surface modifications was to generate a protective layer that decreases the rate of degradation and improve the corrosion resistance of the material and with this improve its biological performance. In Chapter 4, five formulations, three from the previous work and two new in which a two-step anodized was obtained were characterized. All these coatings differ with respect to morphology, thickness and surface energy. A physicochemical analysis of the coating was performed in which topography, contact angle, surface energy and hydrogen evolution was assessed to determine the corrosion resistance in comparison to untreated Mg.
Additionally, in Chapter 5, the effect of different sterilization methods of coated Mg was studied including steam autoclaving, UV irradiation, dry heat treatment and steam-formaldehyde sterilization. Because Mg is a highly reac-
INTRODUCTION AND AIMS OF THE THESIS
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