Influence of the Processes Parameters on the Properties of The ...
Influence of the Processes Parameters on the Properties of The ...
Influence of the Processes Parameters on the Properties of The ...
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Chapter 2.<br />
<str<strong>on</strong>g>Processes</str<strong>on</strong>g> to Manufacture Foams and to Functi<strong>on</strong>alize <str<strong>on</strong>g>the</str<strong>on</strong>g> Surface<br />
porogen used to prepare 3D scaffolds remains. <strong>The</strong>refore, <str<strong>on</strong>g>the</str<strong>on</strong>g> c<strong>on</strong>venti<strong>on</strong>al method <str<strong>on</strong>g>of</str<strong>on</strong>g> porogen leaching by<br />
washing with water is replaced by freeze-drying, facilitating <str<strong>on</strong>g>the</str<strong>on</strong>g> removal <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> porogen and making<br />
removal more complete. <strong>The</strong> method <str<strong>on</strong>g>of</str<strong>on</strong>g> porogen leaching by using ice particulates as <str<strong>on</strong>g>the</str<strong>on</strong>g> porogen material<br />
can be employed to fabricate porous 3D scaffolds for tissue engineering. Using ice particulates as <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
porogen material, scaffolds are prepared by mixing a polymer soluti<strong>on</strong> in a solvent with ice particulates,<br />
freezing <str<strong>on</strong>g>the</str<strong>on</strong>g> mixture in liquid nitrogen, and freeze-drying. This method can be applied to biodegradable<br />
polymers like polylactides that are soluble in a solvent such as chlor<str<strong>on</strong>g>of</str<strong>on</strong>g>orm or methylene chloride. Sieved ice<br />
particles are dispersed in a polymer/chlor<str<strong>on</strong>g>of</str<strong>on</strong>g>orm soluti<strong>on</strong>. <strong>The</strong> ice particles are eventually leached out by<br />
selective dissoluti<strong>on</strong> in water or by freeze-drying to produce a porous 3D scaffold as described in Figure 2.2:<br />
(a)<br />
(b)<br />
(c)<br />
(d)<br />
(e)<br />
(f)<br />
Ice particulates are prepared by spraying dei<strong>on</strong>ised water into liquid nitrogen [Figure a].<br />
Polymer soluti<strong>on</strong>s <str<strong>on</strong>g>of</str<strong>on</strong>g> various c<strong>on</strong>centrati<strong>on</strong>s are prepared by dissolving different amounts <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
polymer in solvent (e.g. methylene chloride or chlor<str<strong>on</strong>g>of</str<strong>on</strong>g>orm) and cooling. <strong>The</strong> sizes <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> ice<br />
particulates are c<strong>on</strong>trolled by <str<strong>on</strong>g>the</str<strong>on</strong>g> desirable sieving <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> soluti<strong>on</strong> to −20°C [Figures b and c]. Ice<br />
particulates are added to <str<strong>on</strong>g>the</str<strong>on</strong>g> precooled polymer soluti<strong>on</strong>.<br />
<strong>The</strong> dispersi<strong>on</strong> is gently vortexed [Figure d].<br />
It is <str<strong>on</strong>g>the</str<strong>on</strong>g>n poured into a precooled designed mould [Figure e].<br />
Subsequently, <str<strong>on</strong>g>the</str<strong>on</strong>g> mould with dispersi<strong>on</strong> is frozen by placing at low temperature [Figure f].<br />
<strong>The</strong> mould with dispersi<strong>on</strong> is freeze-dried for a desirable time under low temperature [Figure g].<br />
Often, fur<str<strong>on</strong>g>the</str<strong>on</strong>g>r drying at elevated temperatures is required to completely remove <str<strong>on</strong>g>the</str<strong>on</strong>g> solvent after<br />
freeze-drying.<br />
(a) Spraying (b) Sieving (c) Sieved Ice<br />
particles<br />
(d) Vortexing<br />
(e) Moulding (f) Freezing (g) Freeze-drying<br />
Figure 2.2: Procedure <str<strong>on</strong>g>of</str<strong>on</strong>g> ice particle–leaching.<br />
[Kim et al., 2007b]<br />
2.3 Gas-Foaming/Salt-Leaching Technique<br />
<strong>The</strong> biodegradable scaffolds prepared by <str<strong>on</strong>g>the</str<strong>on</strong>g> particulate-leaching method <str<strong>on</strong>g>of</str<strong>on</strong>g>ten exhibit a dense<br />
surface skin layer, which hampers in vitro cell seeding into <str<strong>on</strong>g>the</str<strong>on</strong>g> scaffolds and tissue ingrowth after in vivo<br />
implantati<strong>on</strong>. Additi<strong>on</strong>ally, poor interc<strong>on</strong>nectivities between macropores lower cell viability and result in<br />
n<strong>on</strong>-uniform distributi<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> seeded cells throughout <str<strong>on</strong>g>the</str<strong>on</strong>g> matrix. Sodium bicarb<strong>on</strong>ate salt or amm<strong>on</strong>ium<br />
bicarb<strong>on</strong>ate salt with acidic excipients such as citric acid has been used for effervescent gas-evolving oral<br />
tablets, due to its carb<strong>on</strong> dioxide – evolving property up<strong>on</strong> c<strong>on</strong>tact in acidic aqueous soluti<strong>on</strong>. Thus, various<br />
alkalinising analgesic oral tablets are commercially available. In particular, amm<strong>on</strong>ium bicarb<strong>on</strong>ate salt –<br />
up<strong>on</strong> c<strong>on</strong>tact in an acidic aqueous soluti<strong>on</strong> and/or incubated at elevated temperature – evolves gaseous<br />
amm<strong>on</strong>ia and carb<strong>on</strong> dioxide by itself.<br />
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