Biomedical Engineering Reference
In-Depth Information
17.4.1 Solvent casting and particulate leaching
Organic solvent casting and particulate leaching is an easy method that has
been widely used to fabricate biocomposite scaffolds (Mikos et al., 1994).
This process involves the dissolution of a polymer in an organic solvent,
mixing with nanofillers and porogen particles, and casting the mixture into a
predefined 3D mold. The solvent is subsequently allowed to evaporate, and
the porogen particles are subsequently removed by leaching (Lu et al., 2000).
However, residual solvents in the scaffolds may be harmful to transplanted
cells or host tissues. To avoid any toxicity effect of the organic solvent, gas
foaming can be used to prepare a highly porous biopolymer foam
(Okamoto, 2006b). Kim et al. (2007) fabricated PLGA/nHA scaffolds by
carbon dioxide (CO
2
) foaming and solid porogen (i.e. sodium chloride
crystals) leaching (GF/PL) without the use of organic solvents. Selective
staining of the nHA indicated that nHA particles exposed to the scaffold
surface were observed more abundantly in the GF/PL scaffold than in the
conventional solvent casting and particulate leaching scaffold. The GF/PL
scaffolds exhibited significant enhanced bone regeneration when compared
with a conventional scaffold.
In recent work (Sakai et al., 2012), highly porous cross-linked PLA
scaffolds were successfully prepared through particulate leaching and
foaming or simple leaching methods. The scaffolds were porous with
good interconnectivity and thermal stability. SEM images confirm the pore
connectivity and structural stability of the cross-linked PLA scaffold (Fig.
17.5). The scaffolds (Lait-X/b and Lait-X/c) have the same percentage of
salt particulates of similar particle size; the former was turned into a scaffold
through simple leaching while the latter went through a process of batch
foaming followed by leaching. Qualitative evaluation of the SEM images of
Lait-X/b and Lait-X/c showed a well-developed porosity and interconnec-
tivity with pore sizes spanning a very wide range, from a few microns to
hundreds of microns.
Figure 17.6 shows the relation between pore diameter and the cumulative
and differential intrusions of mercury in Lait-X/b and Lait-X/c scaffolds.
The maximum intrusion and interconnectivities of Lait-X/b occurred for 0.1
to 1
m. The
porosity, total intrusion volume, total pore area and median pore diameter
(volume) of Lait-X/b calculated by mercury porosimetry were 43%,
0.511 ml/g, 13.4 m
2
/g and 0.520
μ
m pore diameter and for Lait-X/c it was from 0.1 to 10
μ
m, respectively; for Lait-X/c, the values
were 49%, 0.688 ml/g, 27.6 m
2
/g and 1.26
μ
m. The shift in values of Lait-X/
b and Lait-X/c was due to the effect of batch foaming, which led to the
movement of salt particulates, resulting in increased porosity and total
intrusion volume. The in-vitro cell culture demonstrated the ability of the
scaffold to support human mesenchymal stem cells (hMSCs) adhesion,
μ
