Page 72 - Magnesium-based supports for stem cell therapy of vascular disease - Mónica Echeverry Rendón

CHAPTER 4
Fig. 6 AFM pictures (50x50μm scans) of the Mg surfaces anodized. NAF(A); HMT(B), MAN(C), NAF HMT (D) and NAF MAN (E) and c.p Mg (F).
3.2 Wettability and surface energy
Wettability or contact angle is a feature of surfaces that is important for use in biomedical applications in particular when cells need to be adhered. Hydrophilicity allows to deposit proteins and growth factors on the surface promot- ing the attraction and adhesion of cells in the area. The contact angle of c.p Mg was 81° which means it has a hydro- phobic surface. The generation of surface coatings reduced the contact angle. The reduction was approximately 50% for coating after single anodizing, NAF, HMT and MAN, two-step coatings, NAF-HMT and NAF MAN had an even larger decrease which yielded ‘superhydrophilic’ contact angles. According with this, at lower values of contact angle, a higher surface energy and more affinity with interaction with liquids was facilitated (Table 4). It is observed how there is not relationship between roughness values and contact angle, this latter parameter appears to only depend on anodizing conditions. It is, although HMT and MAN showed different contact angle values for the single layer coat- ings, these electrolytes generated quite similar values when two layer anodic films were produced.
Table 4. Surface characteristics of the coatings of Mg obtained by PEO
3.3 Corrosion resistance
The corrosion resistance of the coatings, were assessed by hydrogen evolution in NaCl for 1 month (Fig. 7). All sam- ples with surface modification had a lower corrosion rate in comparison to control c. p Mg. The degradation of c.p Mg showed a typical behavior with an initially fast degradation of up to 0.10 mm/year, with a slope of 0.02 mm.year-1.
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