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 5.<br />
Characterizati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> Scaffolds for C<strong>on</strong>nective Tissue Engineering<br />
(A)-dP/dt = 1 bar/s<br />
d e = 264μm<br />
(B)-dP/dt = 20 bar/s<br />
d e = 100μm<br />
PLGA 85:15 scaffold manufactured at, T sat = 35°C ; t sat = 60 min ; P sat = 100 bar<br />
Figure 5.25: Micrographs revealing <str<strong>on</strong>g>the</str<strong>on</strong>g> effect <str<strong>on</strong>g>of</str<strong>on</strong>g> dP/dt and dT/dt <strong>on</strong> pore size.<br />
Pore size decreases with increasing <str<strong>on</strong>g>the</str<strong>on</strong>g> dP/dt. A rapid drop in temperature implies faster<br />
vitrificati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> polymer that blocks <str<strong>on</strong>g>the</str<strong>on</strong>g> growth <str<strong>on</strong>g>of</str<strong>on</strong>g> pores and <str<strong>on</strong>g>the</str<strong>on</strong>g> average pore diameter decreases. It remains<br />
<strong>on</strong>e important phenomen<strong>on</strong> which deserves a proper c<strong>on</strong>siderati<strong>on</strong>. As menti<strong>on</strong>ed previously in secti<strong>on</strong> 2.3,<br />
when <str<strong>on</strong>g>the</str<strong>on</strong>g> same dP/dt is applied from two different saturati<strong>on</strong> pressures, a difference occurs between <str<strong>on</strong>g>the</str<strong>on</strong>g> final<br />
temperatures measured at <str<strong>on</strong>g>the</str<strong>on</strong>g> gas output. This can be explained by <str<strong>on</strong>g>the</str<strong>on</strong>g> increasing heating effect. Indeed, <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
same rate <str<strong>on</strong>g>of</str<strong>on</strong>g> depressurizati<strong>on</strong> from different saturati<strong>on</strong> pressures, does not give <str<strong>on</strong>g>the</str<strong>on</strong>g> same depressurizati<strong>on</strong><br />
time. Thus, <str<strong>on</strong>g>the</str<strong>on</strong>g> depressurizati<strong>on</strong> time from a high saturati<strong>on</strong> pressure is greater and it causes an increase <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
<str<strong>on</strong>g>the</str<strong>on</strong>g> heating time <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> pressure chamber. Hence, <str<strong>on</strong>g>the</str<strong>on</strong>g> vitrificati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> scaffolds is encouraged by <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
sudden temperature drop from smaller saturati<strong>on</strong> pressures. This can be <str<strong>on</strong>g>the</str<strong>on</strong>g> reas<strong>on</strong> why <str<strong>on</strong>g>the</str<strong>on</strong>g> effect <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
saturati<strong>on</strong> pressure is found to be smaller than <str<strong>on</strong>g>the</str<strong>on</strong>g> effect <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> depressurizati<strong>on</strong> rate in <str<strong>on</strong>g>the</str<strong>on</strong>g> analysis <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
Doehlert’ design. On <str<strong>on</strong>g>the</str<strong>on</strong>g> o<str<strong>on</strong>g>the</str<strong>on</strong>g>r hand, since <str<strong>on</strong>g>the</str<strong>on</strong>g> desorpti<strong>on</strong>-diffusi<strong>on</strong> coefficients are lower with lower<br />
saturati<strong>on</strong> pressures than higher saturati<strong>on</strong> pressures (cf. Table 5.8), <str<strong>on</strong>g>the</str<strong>on</strong>g> polymer processed with lower<br />
saturati<strong>on</strong> pressures vitrifies later.<br />
4.7 Effect <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> Geometry <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> Pressure Chamber<br />
We have to remember that <str<strong>on</strong>g>the</str<strong>on</strong>g> PLGA 50:50 exposed to high pressurized CO 2 , changes its state from<br />
glassy to rubbery. When <str<strong>on</strong>g>the</str<strong>on</strong>g> depressurizati<strong>on</strong> occurs from high pressurized saturati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> polymer, <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
polymer swells as <str<strong>on</strong>g>the</str<strong>on</strong>g> CO 2 desorbs and expands as a result <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> phase separati<strong>on</strong>.<br />
Figure 5.26: Representati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> effect <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> geometry <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> pressure chamber <strong>on</strong> <str<strong>on</strong>g>the</str<strong>on</strong>g> porous structure.<br />
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