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