Biomedical Engineering Reference
In-Depth Information
4.1.2 Rapid Prototyping Techniques Applied for Scaffolds Fabrication
The principle of rapid prototyping, also known as solid free form fabrica-
tion, is the generation of scaffolds through layer-by-layer construction of 3D
structures with predefined inner and outer geometry. Basis for the CAD/
CAM data sets can be computer tomography or magnetic resonance tomog-
raphy of the defect region, which are used to generate a virtual 3D model
that is then converted into a sequence of slices that are used to build the cor-
responding real 3D object in layer-by-layer fashion (Hutmacher et al. 2004;
Pfister et al. 2004). In contrast to conventional methods used for scaffold fab-
rication, the preparation of molds as well as subsequent machining steps for
shaping are not necessary. Thus, the main advantage of RP techniques is the
possibility to design and control the architecture of a scaffold, not only with
respect to the external geometry predetermined by size and shape of the
patient-specific defect but also a defined pore structure including channels
for nutrient supply and vascularization can be realized.
A number of RP techniques has been successfully adapted for processing
of biomaterials into 3D scaffolds such as systems based on laser technol-
ogy (stereolithography and selective laser sintering), devices using printing
technology (3D powder printing), and extrusion-based systems (Hutmacher
et al. 2004; Pfister et al. 2004). 3D plotting as well as fused deposition mod-
eling, which belong to the last group, function by dispensing strands of a
pasty or molten material through a moving nozzle to build a 3D structure in
layered fashion (Hutmacher et al. 2004). However, whereas fused deposition
modeling is restricted to thermoplastic materials with good melt viscosity,
a wide variety of synthetic and natural materials can be processed by using
the technique of 3D plotting.
Examples for materials that can be used for scaffold preparation apply-
ing the 3D plotting technique, originally developed by Muehlhaupt and
coworkers at the Freiburg Materials Research Center (Germany), are hydro-
gels (Landers et al. 2002; Fedorovich et al. 2008; Maher et al. 2009), hydroxy-
apatite (HA) ceramic slurries (Detsch et al. 2008), polycaprolactone (Kim and
Son 2009; Oliveira et al. 2009), and starch-based blends (Martins et al. 2009).
In contrast to other 3D extrusion technologies, the mild process conditions
(room or physiological temperature and no usage of organic solvents) allow
simultaneous plotting of biological components such as antibiotics, growth
factors, and even living cells that are suspended in the respective plotting
material (Fedorovich et al. 2008; Lode et al., forthcoming).
4.1.3 Rapid Prototyping of Bioceramics
A lot of work has been invested in the fabrication of CaP scaffolds by 3D
printing, also referred to as powder printing. In this process, calcium phos-
phate particles are bonded using a liquid binder that is delivered by an inkjet
printing head (Sachs et al. 1993). After the printing process, the binder-free
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