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 ...
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
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 />
(h)<br />
(i)<br />
Scaffolds are processed to fabricate a tubular or sheet-types.<br />
After evaporati<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> solvent, <str<strong>on</strong>g>the</str<strong>on</strong>g> salt particles in <str<strong>on</strong>g>the</str<strong>on</strong>g> c<strong>on</strong>struct are leached out to make an openpore<br />
structure.<br />
Scaffolds are freeze-dried for a desired time under low temperature.<br />
Scaffolds are obtained by finally under <str<strong>on</strong>g>the</str<strong>on</strong>g> return to <str<strong>on</strong>g>the</str<strong>on</strong>g> room temperature.<br />
Polymer soluti<strong>on</strong><br />
Salt (NaCl)<br />
(a) Mixing (b) Polymer soluti<strong>on</strong> (c) Evaporati<strong>on</strong> (d) Moulding (e) Gel pressing<br />
(f) Shaping (g) Salt leaching (h) Freeze-drying (i) Scaffolds<br />
Figure 2.4: Procedure <str<strong>on</strong>g>of</str<strong>on</strong>g> scaffolds by gel-pressing method.<br />
[Kim, 2007]<br />
2.5 PLGA Microspheres for Tissue-Engineered Scaffold<br />
PLGA-based microspheres are biodegradable particulate delivery systems providing both drug<br />
protecti<strong>on</strong>, encapsulated inside a polymeric matrix, and its release at a slow and c<strong>on</strong>tinuous rate.<br />
Microsphere manufacturing usually involves (1) <str<strong>on</strong>g>the</str<strong>on</strong>g> c<strong>on</strong>trolling <str<strong>on</strong>g>of</str<strong>on</strong>g> a disintegrated polymer, (2) cell toxicity,<br />
and (3) a suitable envir<strong>on</strong>ment for cell culture. <strong>The</strong> size and degradable pr<str<strong>on</strong>g>of</str<strong>on</strong>g>ile can be easily managed by<br />
c<strong>on</strong>trolling <str<strong>on</strong>g>the</str<strong>on</strong>g> molecular weight <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> polymer and <str<strong>on</strong>g>the</str<strong>on</strong>g> process <str<strong>on</strong>g>of</str<strong>on</strong>g> fabricati<strong>on</strong>.<br />
PLGA microspheres are particularly attractive for tissue regenerati<strong>on</strong> approaches ei<str<strong>on</strong>g>the</str<strong>on</strong>g>r as an<br />
injectable system or as <str<strong>on</strong>g>the</str<strong>on</strong>g> integral part <str<strong>on</strong>g>of</str<strong>on</strong>g> a replacement clinical c<strong>on</strong>struct. <strong>The</strong> small, spherical nature <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
<str<strong>on</strong>g>the</str<strong>on</strong>g>se polymers enables <str<strong>on</strong>g>the</str<strong>on</strong>g> encapsulati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> growth factors or o<str<strong>on</strong>g>the</str<strong>on</strong>g>r drugs, and <str<strong>on</strong>g>the</str<strong>on</strong>g>ir subsequent delivery to a<br />
specific and designated area. C<strong>on</strong>trolled release <str<strong>on</strong>g>of</str<strong>on</strong>g> bioactive molecules, such as cytokines and growth<br />
factors, has become an important aspect <str<strong>on</strong>g>of</str<strong>on</strong>g> tissue engineering because it allows modulati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> cellular<br />
functi<strong>on</strong> and tissue formati<strong>on</strong> at <str<strong>on</strong>g>the</str<strong>on</strong>g> afflicted site. Cell cultures using microspheres have an advantage <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
passage abbreviati<strong>on</strong> to improve cell activity. <strong>The</strong> PLGA microspheres regulate many aspects <str<strong>on</strong>g>of</str<strong>on</strong>g> cellular<br />
activity, including cell proliferati<strong>on</strong>, cell differentiati<strong>on</strong>, and extracellular matrix metabolism, in a time- and<br />
c<strong>on</strong>centrati<strong>on</strong>-dependent fashi<strong>on</strong>. <strong>The</strong> procedure to prepare PLGA microsphere scaffolds is presented in<br />
Figure 2.5.<br />
(a)<br />
(b)<br />
(c)<br />
(d)<br />
(e)<br />
<strong>The</strong> polymer is dissolved in a solvent, and is ready to add to a soluti<strong>on</strong> in surfactant.<br />
<strong>The</strong> polymer soluti<strong>on</strong> is dropped into an aqueous soluti<strong>on</strong> in surfactant by a pipette.<br />
This soluti<strong>on</strong> is stirred at 400 rpm for 7 h using a mechanical stirrer.<br />
<strong>The</strong> fabricated microspheres are collected from <str<strong>on</strong>g>the</str<strong>on</strong>g> bottom by a centrifugal separator.<br />
<strong>The</strong> hardened microspheres are centrifuged, washed with dei<strong>on</strong>ised water.<br />
- 32 -