Influence of the Processes Parameters on the Properties of The ...

Chapter 4.
Experimental Procedures and Protocols for Analyses
In <strong>the</strong> Sessile drop technique, <strong>the</strong> solid surface is wetted by single drops <strong>of</strong> <strong>the</strong> probe liquid. A
high resolution camera captures <strong>the</strong> shape <strong>of</strong> <strong>the</strong> drop and processes this by image analyzing s<strong>of</strong>tware. The
contact angle is linked to <strong>the</strong> surface energy and so, one can estimate <strong>the</strong> surface energy and discriminate
between polar and apolar interactions. Organic liquids have surface tensions that are in a similar range as
solid polymer.
Advantages <strong>of</strong> this optical approach are <strong>the</strong> precision and quickness. In addition, placing drops at
different positions gives <strong>the</strong> opportunity to explore <strong>the</strong> diversity <strong>of</strong> <strong>the</strong> surface. The disadvantages <strong>of</strong> this
method are solid sample preparation, camera resolution, toge<strong>the</strong>r with <strong>the</strong> investigation <strong>of</strong> only two contact
points. Especially <strong>the</strong> camera angle to obtain a perfect baseline image is important. Baseline inaccuracy is
<strong>the</strong> primary contributor <strong>of</strong> a lower repeatability [Lander et al., 1993]. Contact angle was measured, by using
a contact angle meter (GBX Digidrop) apparatus, by a liquid at six different points on <strong>the</strong> surface on both
sides <strong>of</strong> polylactide or composite pellets. Contact angles were measured on <strong>the</strong> surface for 4 minutes as after
3 minutes, it was observed that measured angle remained stable.
Contact angle measurements are influenced by several factors. First, <strong>the</strong> shape <strong>of</strong> <strong>the</strong> drop is an
important influence. Measurement should take place immediately after <strong>the</strong> drop is placed on <strong>the</strong> solid
material. This should cover <strong>the</strong> errors made due to interaction with <strong>the</strong> material which must be chemically
and physically homogeneous. It is assumed that <strong>the</strong> liquid does not react with <strong>the</strong> solid and that <strong>the</strong> solid
surface is perfectly smooth and rigid. Secondly, surface roughness and surface impurities are influential
parameters. As a result <strong>the</strong> drop can have various metastable states, which automatically influence <strong>the</strong>
contact angle. Finally, relative humidity and temperature are factors that provide contact angle variance
[Rudawska and Jacniacka, 2008].
4 Protocols for Porosity and Pore Size Measurement
4.1 Average Geometric Porosity
The thickness and diameter <strong>of</strong> pellets and scaffold dimensions were measured at eight different
points with an electronic vernier caliper. Mass <strong>of</strong> <strong>the</strong> pellets and foams was measured on an electronic
digital balance to four decimal points. The observed dimensional data values were used to calculate radius
and volume and <strong>the</strong>n utilize <strong>the</strong> mass obtained to calculate density <strong>of</strong> <strong>the</strong> pellet or foam. Then finally relative
density and geometric porosity <strong>of</strong> <strong>the</strong> foam was calculated. As example, we present in Table 4.2 measured
data <strong>of</strong> PLGA 50:50 pellets and foam before and after sc CO 2 foaming.
Table 4.2: Dimensional data <strong>of</strong> PLGA 50:50 pellets and foams for geometric porosity.
Pellet Foam Geometric
S/N Diameter Thickness Mass Density Diameter Thickness Mass Density Porosity
d p (mm) Ø p (mm) (mg) d f (mm) Ø f (mm) (mg) P(%)
1 12.9 0.6 85.0 1074.0 25.0 1.9 96.0 101.1 90.6
2 13.0 0.6 91.6 1103.4 23.5 2.1 84.2 93.1 91.6
3 12.9 0.6 96.0 1184.2 25.1 2.1 96.1 94.4 92.0
4 12.9 0.6 94.0 1137.6 31.6 1.9 93.5 62.7 94.5
5 12.9 0.6 83.8 1066.5 27.7 1.7 84.6 83.5 92.2
6 12.9 0.7 100.0 1171.2 24.9 2.0 100.4 101.1 91.4
7 12.9 0.6 95.8 1144.8 25.9 1.7 84.0 96.3 91.6
8 12.9 0.6 101.0 1242.1 26.3 2.3 100.1 81.2 93.5
9 13.0 0.6 84.2 1022.7 32.0 2.0 90.7 55.7 94.6
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