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

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Chapter 4. Experimental Procedures and Protocols for Analyses During <strong>the</strong> commissioning <strong>of</strong> <strong>the</strong> metalizing high voltage, low current passes through a gold foil, ionize <strong>the</strong> atoms and <strong>the</strong>y are deposited on <strong>the</strong> surface <strong>of</strong> <strong>the</strong> sample. The thickness <strong>of</strong> <strong>the</strong> gold layer deposited depends on <strong>the</strong> time <strong>of</strong> filing but does not exceed 10 Å. The gas pressure was less than 50 mTorr and <strong>the</strong> current was about 40 mA. The coating time was 120 s. The metalizing chamber is <strong>the</strong>n reduced to atmospheric pressure and <strong>the</strong>n <strong>the</strong> samples are introduced into <strong>the</strong> microscope chamber. Complete schematic procedure is shown in Figure 4.22. A working distance between <strong>the</strong> bottom <strong>of</strong> <strong>the</strong> barrel and <strong>the</strong> sample between 30 and 37 mm is recommended. An acceleration voltage <strong>of</strong> electrons between 10 and 15 kV is generally accepted, and a probe current <strong>of</strong> between 50 and 150 Å. 4.2.2 SCION Image Analysis Image analysis <strong>of</strong> SEM micrographs was used for <strong>the</strong> observation <strong>of</strong> <strong>the</strong> internal pore morphology <strong>of</strong> <strong>the</strong> freeze-dried foams. Polymeric and composite foams images are taken on <strong>the</strong> surface, at <strong>the</strong> cross section and inside <strong>the</strong> pores. Cross sectional images are taken at five different points (<strong>the</strong> centre, top left, bottom left, top right and bottom right) to verify homogeneity <strong>of</strong> pores and <strong>the</strong>ir distribution (cf. Figure 4.23). Normally magnifications <strong>of</strong> image are (25, 40, 100, 200, 300, 400, 500) depending on <strong>the</strong> pore size. Higher magnification up to 1K, 2K and 3K is recorded, if internal surface <strong>of</strong> <strong>the</strong> pores walls is to be observed. The SEM micrographs were treated and statistically analyzed using <strong>the</strong> s<strong>of</strong>tware SCION ® Image analysis. The images were digitized on a matrix <strong>of</strong> 1024 1024 pixels with 256 gray levels. The foams were duplicated and five images <strong>of</strong> different areas <strong>of</strong> <strong>the</strong> same foam were analyzed. Effect <strong>of</strong> <strong>the</strong> successive image transformations can be seen in Figure 4.24. Scaffold surface Top left-50× Top Right-100× Scaffold cross- section-20× Bottom left-100× Bottom right-100× Centre-100× Figure 4.23: SEM Images <strong>of</strong> cross sectional foam. An example <strong>of</strong> <strong>the</strong> data obtained after SCION ® image analysis is presented in Table 4.3. From <strong>the</strong> data, it is possible to define three pores categories (cf. Table 4.4): Micro, meso and macro pores are pores with dimension <strong>of</strong> equivalent diameter less than 25 m, 25−150 m and above 150 m respectively. The micro pores are necessary for movement <strong>of</strong> <strong>the</strong> liquids and nutrients in <strong>the</strong> scaffold. Meso pores are for <strong>the</strong> accommodation <strong>of</strong> <strong>the</strong> human mesenchymal stem cells, as <strong>the</strong>ir size varies from 100−150 m. Macro pores - 104 -
Chapter 4. Experimental Procedures and Protocols for Analyses are necessary for <strong>the</strong> movement <strong>of</strong> <strong>the</strong> mesenchymal cells. Data <strong>of</strong> pores was extracted from SCION ® images s<strong>of</strong>tware and calculation was done by using MS Excel calculation sheets. The retrieved data is presented in Table 4.3. 01-SEM Image 02-After threshold 03-After Binary transformation 04-Opening transformation 08-Analyzing pores 07-Opening + closing + dilating + eroding + manual transformation 06-Opening + closing transformation 05-Erodeing transformation Figure 4.24: Various steps <strong>of</strong> transformation <strong>of</strong> SEM image by SCION ® . Table 4.3: Example <strong>of</strong> data obtained from SCION® image analysis. The frequency <strong>of</strong> pores and respective areas <strong>of</strong> <strong>the</strong> pores obtained (cf. Table 4.3) thus helps in calculating <strong>the</strong> pore equivalent circular diameter (d e ). Pore morphology and pore area ratios, pore volume ratios, minimum and maximum equivalent pore diameter. - 105 -
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Institut National Polytechnique de
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Publications and Conferences The wo
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Nomenclature and Abbreviations Abbr
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Chapter 2 .........................
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