Barbieri Thesis - BioMedical Materials program (BMM)

Chapter 5 – Alkali surface treatment effects
exposure. Part of the granules of the materials were also embedded in epoxy resin
(Sigma–Aldrich), sectioned to have cross–sections of the granules and observed in
backscattered modality (BSEM) to evaluate their bulk and the effect of alkali
treatment at their surface. To evaluate the extent of apatite exposure caused by the
etching, at least twenty random granules were considered in BSEM images. Using the
software ImageJ (v1.43u, NIH, USA), the average thickness of these apatite layers
was measured with the help of the scale bar. As the sectioning plane was random
respect to the granules, it is expected that the measureable characteristics of the
layers (i.e. their thickness) had a normal distribution of probability and thus,
statistically speaking, the method here proposed might be used to evaluate the
materials.
5.2.3.2 Surface properties
The surface characteristics of the three materials (in the form of discs) were evaluated
with an atomic force microscope (AFM, Bioscope Catalyst AFM, Bruker AXS,
Wormer, the Netherlands) in tapping mode using an ESP cantilever (total tip height
from 10 to 15 m, probe tip radius 12 nm, full type cone radius 25°, spring constant
0.2 N m –1 ). The images were taken with a scan frequency of 1 Hz performing dual
scans over an area of 50×50 m and analysed with SPIP software (v5.1.11, Image
Metrology A/S, Hørsholm, Denmark) after correcting the plane and removing
background/measurement noise using proper digital filters. In this way, two–
dimensional and three–dimensional height maps were obtained, which allowed us
evaluating the surface topographical features. Besides visual results, measurements
were taken on average roughness (Ra), root mean square (Rq) and average ten
largest top–bottom heights (Rz). The distribution of the measured heights compared
to a zero–plane (i.e. a flat plane positioned at middle height of the surface profile of
the sample) was also obtained. Static water contact angle measurements were
performed to evaluate the surface hydrophilicity on the surface of the composites. At
room temperature a drop of 0.6 l of distilled water was placed on the surface of the
discs. Pictures were taken with a digital camera (PowerShot SX200 IS, Canon
Nederland NV, Amstelveen, the Netherlands) immediately after the drop placement.
Measurements of the contact angle from the pictures were done with the software
ImageJ (v1.43u, NIH, USA) using the freely distributed plugin Drop–Shape Analysis
working on the snake–based approach. [335]
5.2.3.3. Remarks
It should be mentioned that AFM and hydrophilicity measurements have been done
on discs instead of granules (for experiment design needs). Thus the numerical
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