IN VITRO CHARACTERIZATION OF ANODIZED MAGNESIUM ALLOY AS A POTENTIAL BIODEGRADABLE MATERIAL FOR BIOMEDICAL APPLICATIONS

MARIA R. KATUNAR; JULIETA MORENO; JULIETA MERLO; ANA CLAUDIA RENNO; JESICA CANIZO; FRANCISCO BOUCHELLY; PASTORE, JUAN IGNACIO; SILVIA CERE

San Pablo

Congreso; XI COLAOB and XVII LASAO XI Latin American Congress of Artificial Organs and Biomaterials; 2021

Metals are increasingly being used to partially or completely restore bone fractures. Biodegradable metals emerged as promissory candidates for fracture fixation devices since they are able to self-degrade in the body environment. The main challenge of the devices is to reach an adequate degradation ratio relative to the bone healing having safe degradation by-products. Magnesium alloys have become popular mainly because they exhibit good biodegradable characteristics (1,2). Although Mg alloys have advantages compared to inert metallic biomaterials, e.g., good mechanical properties and biocompatibility, these alloys also have poor corrosion resistant properties in aggressive solutions (e.g., biological medium) (3). The high degradation rate of Mg in aqueous media releases hydrogen gas, which causes pain and local swelling. Surface treatments, such as anodizing technique, emerged as a potential solution to this limitation. This work assesses the effects of the anodizing process at constant potential (5 V) in two concentrations of KOH solution (0.1 and 5 mol/L) of an extruded Mg-alloy (AZ91D; named ?0.1A-AZ91? and ?5A-AZ91?, respectively) on surface topography, electrochemical response, hydrogen evolution and cell attachment with the aim of generating a potential material for fracturefixation devices. The surface modifications were evaluated by Raman spectroscopy, scanning electron microscopy (SEM) and profilometry to evaluate surface roughness. The hydrogen evolution was monitored as a function of immersion time and electrochemical tests were performed in simulated body fluid solution (SBF). Finally, to assess cell viability and proliferation; primary culture bovine embryonic fibroblasts (BEFs) and mouse pre-osteoblastic MC3T3-E1 cell line were used. Surface analyses of the anodized AZ91 alloy by SEM evidenced the presence of a homogeneous oxide covering the samples, both for the 0.1 and the 5 mol/L KOH solutions, and porous and cracks could be observed on the formed oxide. The oxides formed on both anodized systems increased the roughness of the surface which could be promising for cell attachment Regarding Raman analyses, the corrosion products formed on the surface were principally Mg(OH)2, MgO and MgCO3 and they could act as protective layers which would degrade in a time dependent way. Anodizing increased corrosion resistance and reduced cathodic currents. This is markedly beneficial considering the need of a reduction in the generation of hydrogen in the initial stages of implantation. The electrochemical impedance spectroscopy results confirmed this fact by the lack of an inductive loop compared to the control (non-anodized AZ91), which indicates that the coating behaves as a good barrier in the first moments of immersion. Regarding cell behaviour, there was an increase of MC3T3-E1 viability on 5A-AZ91 samples compared with control ones. This results is in concordance with the results obtained for BEFs cells, which showed better adhesion in 5A-AZ91 samples compared with control AZ91. Thus, the results show that the electrochemical treatment of anodizing at low voltage in 5 mol/L KOH solution generates a surface magnesium oxide which could act as a barrier to prevent fast degradation, and consequently to control hydrogen release allowing a better interaction with cells and surrounding tissues.