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 />
(f)<br />
(g)<br />
And <str<strong>on</strong>g>the</str<strong>on</strong>g>n put into a freezer.<br />
<strong>The</strong> manufactured microspheres are freeze-dried under low temperature and pressure.<br />
(a) Dissolving (b) Dropping (c) Stirring (d) Centrifuging (e) Washing (f) Freezing (g) Freeze-Drying<br />
Figure 2.5: Schematic procedure <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> processing <str<strong>on</strong>g>of</str<strong>on</strong>g> PLGA microsphere scaffolds.<br />
[Ko et al., 2007]<br />
2.6 Particle-Aggregated Scaffolds Technique<br />
<strong>The</strong> particle aggregati<strong>on</strong> method described herein allows <strong>on</strong>e to obtain scaffolds with high<br />
mechanical properties (thus assuring scaffold stability) and full three-dimensi<strong>on</strong>al interc<strong>on</strong>nectivity, which is<br />
assured in a 3D perspective by <str<strong>on</strong>g>the</str<strong>on</strong>g> c<strong>on</strong>tact points between <str<strong>on</strong>g>the</str<strong>on</strong>g> particles. <strong>The</strong> described technique is based <strong>on</strong><br />
<str<strong>on</strong>g>the</str<strong>on</strong>g> random packing <str<strong>on</strong>g>of</str<strong>on</strong>g> prefabricated microspheres with fur<str<strong>on</strong>g>the</str<strong>on</strong>g>r aggregati<strong>on</strong> by physical or <str<strong>on</strong>g>the</str<strong>on</strong>g>rmal means to<br />
create a three-dimensi<strong>on</strong>al porous structure. <strong>The</strong> polymer (at desired c<strong>on</strong>centrati<strong>on</strong>) is dissolved in a good<br />
solvent. For <str<strong>on</strong>g>the</str<strong>on</strong>g> producti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> composite particles, hydroxyapatite (HAp) is added at an adequate<br />
c<strong>on</strong>centrati<strong>on</strong> to <str<strong>on</strong>g>the</str<strong>on</strong>g> soluti<strong>on</strong> and dispersed homogeneously. <strong>The</strong> detailed procedure (cf. Figure 2.6) is <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
following:<br />
(a)<br />
(b)<br />
(c)<br />
(d)<br />
(e)<br />
<strong>The</strong> polymer or composite (polymer plus HAp) soluti<strong>on</strong> is left overnight to assure complete<br />
dissoluti<strong>on</strong> [Figure a]. <strong>The</strong> polymer/composite soluti<strong>on</strong> is filtered to eliminate any residual particles.<br />
<strong>The</strong> polymer/composite soluti<strong>on</strong> is extruded through a syringe in a dispenser (syringe pump) at a<br />
c<strong>on</strong>trolled and c<strong>on</strong>stant rate in order to shape <str<strong>on</strong>g>the</str<strong>on</strong>g> particles into a NaOH soluti<strong>on</strong> [Figure b]. <strong>The</strong><br />
particle size can be c<strong>on</strong>trolled by tailoring <str<strong>on</strong>g>the</str<strong>on</strong>g> polymer soluti<strong>on</strong> c<strong>on</strong>centrati<strong>on</strong>, needle diameter, and<br />
dispensing rate.<br />
<strong>The</strong> particles are <str<strong>on</strong>g>the</str<strong>on</strong>g>n exhaustively washed to remove all exceeding reagents, namely from <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
precipitati<strong>on</strong> bath [Figure c]. To produce composite particles, cross-linking can be used with<br />
appropriate polymer cross-linkers. <strong>The</strong> particles are immersed in <str<strong>on</strong>g>the</str<strong>on</strong>g> cross-linking soluti<strong>on</strong> for a<br />
determined short period and <str<strong>on</strong>g>the</str<strong>on</strong>g>n washed again.<br />
For producti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> scaffolds, appropriate particles are press-fitted into a specific mould [Figure d].<br />
And left in <str<strong>on</strong>g>the</str<strong>on</strong>g> oven for a necessary time for aggregati<strong>on</strong> to take place [Figure e].<br />
(a) (b) (c) (d) (e)<br />
Figure 2.6: Schematic procedure for manufacturing <str<strong>on</strong>g>of</str<strong>on</strong>g> scaffolds with <str<strong>on</strong>g>the</str<strong>on</strong>g> particle-aggregated technique.<br />
[Malafaya and Reis, 2007]<br />
2.7 Freeze-Drying Method<br />
Porosity can be acquired in <str<strong>on</strong>g>the</str<strong>on</strong>g> first step <str<strong>on</strong>g>of</str<strong>on</strong>g> freeze-drying (lyophilising) <str<strong>on</strong>g>the</str<strong>on</strong>g> soluti<strong>on</strong> c<strong>on</strong>taining<br />
polymeric biomaterials, when <str<strong>on</strong>g>the</str<strong>on</strong>g> ice crystals <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> solvents are formed within <str<strong>on</strong>g>the</str<strong>on</strong>g> soluti<strong>on</strong>. <strong>The</strong> ice crystals<br />
serve as a porogen whose size can be easily c<strong>on</strong>trolled by adjusting <str<strong>on</strong>g>the</str<strong>on</strong>g> freezing temperature and <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
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