Page 52 - Magnesium-based supports for stem cell therapy of vascular disease - Mónica Echeverry Rendón

CHAPTER 3
Under potentiostatic mode for NAF (Fig. 4), bigger thickness were obtained in comparison with those obtained under galvanostatic mode. NAF P1 was homogeneous and nearly defect free, however NAF P2 showed even more holes with an average diameter of 5.8±1.4μm, which were bigger in comparison which the defects on samples under galvanostatic mode. These features could have relationship with the large oscillations observed in the curves of Fig. 2. Higher magnification images of the surface, revealed a particular texture on both samples, similar to that observed on NAF-G1. The morphology of these defects are not similar to what is normally observed in PEO coatings. It is not ap- parent for neither sample, presence of smaller porosity. Also for these samples the same structure of layers one over another can be observed, with a barrier layer of a about 0.3μm for NAF-P1 and 0.4μm for NAF-P2. Looking at these cross sections, it is not clear the existence of passing through porosity, it seems that the defects penetrate only the first layers of anodic material. This could be an indication that this layered morphology is related with the electrolyte composition employed.
Fig. 4 Top-view SEM image of the surface (1000X and 5000X) and cross-section for samples of c.p Mg anodized under potentiostaic mode in NAF solution.
On the other hand samples treated with HMT (Fig. 5), showed a different behavior compared with NAF. Under gal- vanostatic mode, surfaces of the samples treated with HMT showed a morphology consisted of well-defined pores, with volcano shape as typically observed in PEO coatings. The surface of HMT G1 presented pores with a size of 1.2 ± 0.1μm, which are not uniformly distributed on the sample. In sample HMT-G2 were the coating present a
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