ADDITIVE MANUFACTURING FOR BONE LOAD BEARING APPLICATIONS - 3D Bioprinting and Nanotechnology in Tissue Engineering and Regenerative Medicine - page 230

as Young's modulus and compressive strength, since these properties may cause short-term failure of
implant ( Oh et al., 2003 ).
11.4.2 AM OF METALS FOR BONE SUBSTITUTES
Historically, conventional techniques were used to fabricate porous metals for several industrial applica-
tions. Once porous metal was introduced in early 1972 in the orthopedic field ( Weber and White, 1972 ),
scientists looked for ways to control and improve the properties of this metal foam. Consequently,
several conventional techniques emerged. However, these techniques are not capable of precisely con-
trolling the porosity and producing a scaffold with a predefined microstructure. Also, these techniques
cannot produce a scaffold with a contoured external shape. In order to overcome these obstacles, addi-
tive manufacturing (AM) techniques are considered the most promising alternative for precise fabrica-
tion of internal and external features of scaffold architecture.
There are many AM techniques that have been used in the fabrication of metal scaffolds, such as
three-dimensional printing (3DP), electron beam melting (EBM), selective laser melting (SLM), direct
metal deposition (DMD), and selective laser sintering (SLS) ( Ryan et al., 2008; Murr et al., 2009; Mul-
len et al., 2009 ; Dinda et al., 2008 ; Shishkovsky et al., 2008 ). Each technique has different opportuni-
ties and limitations. Some of these techniques rely on laser technology, and others rely on the injection
of the slurry. The costs of production through these techniques are varied according to complexity. For
example, the laser sintering methods are highly expensive due to their use of laser technology and the
capability of producing a precise microstructure. Other techniques appropriate for fabricating a scaf-
fold have acceptable microstructure details, such as fiber deposition and 3DP.
SLS is an AM technique ( Figure 11.1 ) that works by sintering very fine layers of metal powders
layer over layer using a CO 2 laser beam, either directly or indirectly. In direct SLS, the powder mix-
ture is a compound of two metals: a low sintering temperature metal and the main metal ( Campanelli
FIGURE 11.1
Schematic presentation of working principle of SLS technique.