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

Chapter 2.
<strong>Processes</strong> to Manufacture Foams and to Functionalize <strong>the</strong> Surface
(f)
(g)
(h)
(i)
Scaffolds are processed to fabricate a tubular or sheet-types.
After evaporation <strong>of</strong> <strong>the</strong> solvent, <strong>the</strong> salt particles in <strong>the</strong> construct are leached out to make an openpore
structure.
Scaffolds are freeze-dried for a desired time under low temperature.
Scaffolds are obtained by finally under <strong>the</strong> return to <strong>the</strong> room temperature.
Polymer solution
Salt (NaCl)
(a) Mixing (b) Polymer solution (c) Evaporation (d) Moulding (e) Gel pressing
(f) Shaping (g) Salt leaching (h) Freeze-drying (i) Scaffolds
Figure 2.4: Procedure <strong>of</strong> scaffolds by gel-pressing method.
[Kim, 2007]
2.5 PLGA Microspheres for Tissue-Engineered Scaffold
PLGA-based microspheres are biodegradable particulate delivery systems providing both drug
protection, encapsulated inside a polymeric matrix, and its release at a slow and continuous rate.
Microsphere manufacturing usually involves (1) <strong>the</strong> controlling <strong>of</strong> a disintegrated polymer, (2) cell toxicity,
and (3) a suitable environment for cell culture. The size and degradable pr<strong>of</strong>ile can be easily managed by
controlling <strong>the</strong> molecular weight <strong>of</strong> <strong>the</strong> polymer and <strong>the</strong> process <strong>of</strong> fabrication.
PLGA microspheres are particularly attractive for tissue regeneration approaches ei<strong>the</strong>r as an
injectable system or as <strong>the</strong> integral part <strong>of</strong> a replacement clinical construct. The small, spherical nature <strong>of</strong>
<strong>the</strong>se polymers enables <strong>the</strong> encapsulation <strong>of</strong> growth factors or o<strong>the</strong>r drugs, and <strong>the</strong>ir subsequent delivery to a
specific and designated area. Controlled release <strong>of</strong> bioactive molecules, such as cytokines and growth
factors, has become an important aspect <strong>of</strong> tissue engineering because it allows modulation <strong>of</strong> cellular
function and tissue formation at <strong>the</strong> afflicted site. Cell cultures using microspheres have an advantage <strong>of</strong>
passage abbreviation to improve cell activity. The PLGA microspheres regulate many aspects <strong>of</strong> cellular
activity, including cell proliferation, cell differentiation, and extracellular matrix metabolism, in a time- and
concentration-dependent fashion. The procedure to prepare PLGA microsphere scaffolds is presented in
Figure 2.5.
(a)
(b)
(c)
(d)
(e)
The polymer is dissolved in a solvent, and is ready to add to a solution in surfactant.
The polymer solution is dropped into an aqueous solution in surfactant by a pipette.
This solution is stirred at 400 rpm for 7 h using a mechanical stirrer.
The fabricated microspheres are collected from <strong>the</strong> bottom by a centrifugal separator.
The hardened microspheres are centrifuged, washed with deionised water.
- 32 -