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
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
(i)
Salt particulates are prepared by sieving. The sizes <strong>of</strong> <strong>the</strong> salt particulates are controlled by <strong>the</strong>
desirable sieving.
Polymer solutions are prepared by dissolving different amounts and types <strong>of</strong> polymers in solvent
(e.g. methylene chloride or chlor<strong>of</strong>orm).
Sieved salt particulates are added to <strong>the</strong> polymer solution, and <strong>the</strong> dispersion is gently vortexed.
The solution is poured into <strong>the</strong> designed silicon mould.
Subsequently, <strong>the</strong> mould with dispersion is pressed (~ 6 MPa) by pressure apparatus.
The formed samples are taken out <strong>of</strong> <strong>the</strong> mould.
Samples are dissolved for a desirable time (48 h) in deionised water.
Salt-removed samples are freeze-dried for a desirable time (about 48 h) at low temperature and
reduced pressure (around 8 Pa,−55°C).
The scaffolds are dried in a vacuum oven at 25°C for 1 week to remove <strong>the</strong> residual solvent.
Scaffolds are kept under vacuum until use.
(a) Salt
(b) Preparing <strong>of</strong> polymer,
solvent, salt
(c) Mixing <strong>of</strong> polymer,
solvent, salt
(d) Moulding
(e) Pressing
(f) Removal from (g) Dissolution <strong>of</strong> salt (h) Freezing & freeze
drying
(i) Removal <strong>of</strong> residual
solvent and storage
Figure 2.1: Procedure <strong>of</strong> solvent casting/particulate leaching.
[Khang et al., 2007]
Porosity is independent <strong>of</strong> particle diameters, but increases with <strong>the</strong> quantity <strong>of</strong> salt. A minimum
<strong>of</strong> 70% <strong>of</strong> salt particles is needed to create interconnected pores [Mikos et al., 1994]. When particle diameter
increases, pore size increases. Mechanical properties, such as compressive strength or modulus, are
independent <strong>of</strong> pore size but decrease when porosity increases. Porosity up to 90-95%, with varying pore
size, and a compressive modulus <strong>of</strong> 0.15 to 150 MPa, depending on porosity can be achieved. This method
is only applicable to <strong>the</strong> preparation <strong>of</strong> thin films since all <strong>the</strong> salt particles on <strong>the</strong> bulk must be leached out
completely. To obtain thicker scaffolds <strong>of</strong> desired shape, an improved porogen salt-leaching technique has
been proposed [Gross and Rodríguez-Lorenzo, 2004]. By adding small hydroxyapatite (HAp) fibres to a
PLGA solution, it is possible to create composite foams with a controlled porosity [Hou et al., 2003; Chen et
al., 2001b; Thomson et al., 1998; Widmer et al., 1998].
2.2 Ice Particle-Leaching
Previous scaffold manufacturing usually involves (1) dissolving <strong>the</strong> polymer in organic solvent,
(2) incorporating porogens, and (3) leaching porogens. Despite <strong>the</strong>se advantages, <strong>the</strong> problem <strong>of</strong> residual
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