Page 67 - Magnesium-based supports for stem cell therapy of vascular disease - Mónica Echeverry Rendón

IMPROVEMENT OF CORROSION RESISTANCE OF COMMERCIAL PURE MAGNESIUM AFTER ITS MODIFICATION BY SINGLE AND TWO-STEP ANODIZATION
parameters for roughness are Ra and Rq, Ra (Arithmetic Mean Roughness) is the average of the heights calculated on the entire measurement of the length or area. Ra is frequently used to describe the roughness of machined surfaces. This is useful to detect general variations in the characteristic heights of the profile and to monitor and establish manufacturing processes. On the other hand, Rq or RMS (Mean root mean square) is the quadratic mean of the devia- tions of the roughness profile from the midline along the evaluation length, this parameter is more sensitive than Ra due to the large deviations from the mean. AFM image analysis was carried out with Asylum Research Software to obtain Ra and Rq values.
2.4 Surface energy
Wettability of samples was measured by using a Goniometer/Tensiometer Ramé-hart Model 250 Standard. For this
purpose, a droplet of deionized water was deposited on each surface. After the deposition five consecutive measure- 4 ments were taken and an image was acquired. This process was performed in three different samples. For the surface
energy calculations, the average of the measurements of contact angle for water were used. Surface energy (γS) was
calculated based on the Neuman method (Eq. 1) ,
Where β = 0.0001247 (m2/mJ)2, γ_(L )=72.8 mJ/m2 and θ (contact angle) was as measured previously and with the respective numerical iterations required.
2.5 Evaluation of corrosion resistance
The hydrogen evolution test was used to measure the corrosion resistance of the different specimens. For this pur- pose, a sample was placed in an inverted burette filled with 0.1 M NaCl. The displacement of the liquid by production of hydrogen gas was read daily during one month. Hydrogen evolution rate VH (mL[cm-2.day-1]) was converted into the degradation rate PH(mm.year-1) using the equation PH = 2.279VH. Finally, the samples were analyzed in both top and cross-section views by SEM at the end of the hydrogen evolution test.
2.6 Biological assays
2.6.1 Cytotoxicity test
Dermal fibroblasts (PK48) were seeded in 24-well plates in DMEM (Lonza) supplemented with 10%SBF (Lonza), 1% penicillin/streptomycin (Gibco) and 2 mM l-glutamine (Lonza) until confluency. Next, samples were added to each well and incubated at 37°C, 5% CO2 and 98% humidity. Cell proliferation was measured at 24 and 72 h with the Alamar Blue assay. For this, Alamar Blue (Invitrogen) solution was added to each well at a 1:10 ratio with respect to the volume of the medium and incubated at 37°C for 90 min. Then the supernatant was transferred to another plate and fluorescence was read in a fluorometer (Varioskan, Thermo scientific) at an excitation wavelength of 530 nm and an emission of 590 nm. Fresh medium was added to the cells. Each experiment was performed in triplicate and the values were normalized according the measurement obtained at 24 h to calculate the percentage of increasing/ decreasing population after 72 h.
2.6.2 Cell-material interaction
Human osteoblastic cell line Saos-2 (HTB-85, ATCC, USA) growing in McCoy medium (Sigma-Aldrich, Missouri, USA) supplemented with 10%SBF (Lonza, NJ, USA), 1% penicillin/streptomycin (Gibco, Massachusetts, USA) and 2 mM
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