Fabrication Techniques and Properties of Scaffolds - Biodegradable Polymer-Based Scaffolds for Bone Tissue Engineering - page 22

which is created by CAD into the corresponding real three-dimensional (3D)
objects. Sequentially this object is built layer by layer of slices. The desired 3D
interconnectivity and structure can be accurately controlled by the highly repeat-
able computer controlled fabrication process. The key features of the RP technolo-
gies are the combination of computed design and computer controlled fabrication
of complex 3D architecture. Moreover, the complicated scaffold architecture can
be tailored to fit into the individual tissue defect (Pfister et al. 2004 ). The exam-
ples of available RP techniques are stereolithography apparatus (SLA), selective
laser sintering (SLS), laminated object manufacturing (LOM), fused deposition
modeling (FDM), and three dimensional printing. As each RP technique has its
own advantages and disadvantages, it is necessary to understand the conditions of
each RP techniques before an RP process has been selected in order to achieve the
requirements of the application.
2.1.5 Polymer-Ceramic Composite Foams
There are some interesting and unique challenges in scaffold design (Lanza et al. 2007 ):
• Almost all bone defects are irregularly shaped; any proposed scaffold process-
ing technique must be sufficiently versatile to allow the formation of porous
polymer-based materials with irregular three-dimensional shape.
• The scaffold must have high strength to replace the structural function of bone
temporarily until it is regenerated.
For many orthopedic applications, poly( α -hydroxyesters) were used in a solid
form, but the compressive strength of foam scaffolds constructed of these mate-
rials rapidly decreased with increasing porosity (Thomson et al. 1996 ). In order
to formulate polymer/ceramic composites, an alternative method was proposed
using a novel phase transition technique (Wei and Ma 2004 ). Hydroxyapatite pow-
der was added to a PLGA/dioxane solution according to this process. The mixture
was then frozen for several hours to induce phase separation and then freeze dried
to sublimate the solvent. The composite foams thus produced, exhibited intercon-
nected irregular pore morphology with a polymer/hydroxyapatite skeleton. The
compressive strength of these foams was significantly higher than that of foams
made from pure PLGA. The porosity, pore size, and pore structure could be con-
trolled by changing the polymer concentration, hydroxyapatite amount, solvent
type and phase separation temperature. Composite foams with porosity of up to
95 % and pore size in the range of 30-100 μ m were fabricated with this method.
2.1.6 Melt Molding
Another alternative method of constructing three-dimensional scaffolds is melt
molding. By using this technique, PLGA scaffolds were produced by leaching