Biomedical Engineering Reference
In-Depth Information
composite are strongly affected by the volume fraction and morphology
of the inclusions.
The availability of nano-sized bioactive fillers, for example, bioactive
glass nanoparticles, has led to the recent development a new family
of nanostructured composites for tissue engineering [6]. The higher
specific surface area of nanostructured bioactive glasses allows not only
for a faster release of ions from the glass and more rapid HCA layer
formation but also a better distribution of particles through the polymer
matrix and a better interface between the glass particles and the polymer.
Nanoscale bioactive glass particles will induce nanotopographic features
on scaffold surfaces, which may improve the attachment of osteoblasts
(bone-forming cells), which are known to attach well to surfaces with
nanoscale roughness. Bone cells are not keen on attaching directly
to hydrophobic polymers like PLA, so good distribution of bioactive
phases on the surface of the scaffold is paramount to the success of the
composites.
The major factor affecting the mechanical properties and structural
integrity of scaffolds is, however, their porosity, for example, pore
volume, size, shape, pore orientation and pore interconnectivity. Hence
it is very important to consider suitable fabrication technologies for
production of 3D scaffolds with controlled porosity.
9.4 PROCESSING TECHNOLOGIES FOR POROUS
BIOACTIVE COMPOSITES
Porous composite scaffolds have been prepared by numerous tech-
niques, including thermally induced phase separation (TIPS), compres-
sion moulding and particulate leaching, gas foaming, and sintering of
composite microspheres. Table 9.3 provides a list of typical processing
techniques developed for production of highly porous bioactive compos-
ite scaffolds, including their relative advantages and disadvantages. The
main techniques considered for production of bioactive-glass-containing
composites are discussed in this section.
The most common method for making porous materials is the space
holder or porogen leaching technique, where sacrificial particles are used
as a pore template. In the case of polymer or composites, the particles
(or spheres) are usually removed by washing through with a solvent that
removes the template particles without affecting the polymer matrix,
for example, salt crystals in a polylactide matrix. In this example, the
polylactide would be dissolved in its solvent and salt particles would
