Biomedical Engineering Reference
In-Depth Information
and inflexible processing procedures meaning the processes are not easily
scalable.
8
Rapid prototyping is a general term that covers a number of techniques
that convert a digital blueprint of an item into a three-dimensional (3D)
model. These techniques are either additive (where material is added to
build a model) or subtractive (where material is removed to reveal a model).
Solid freeform fabrication and 3D printing are both terms used to describe
AM technologies. AM is the o
cial industry standard term (ASTM F2792) for
all applications of the technology, defined by Wohlers Associates as the
process of joining materials to make objects from 3D model data, usually
layer upon layer.
9
The two methods of AM explored in this chapter will be
fused deposition modelling (FDM) and melt extrusion (ME); these are the
most well investigated additive techniques for bone tissue engineering.
Over the past two decades, AM technologies have been developed and
commercialised with focus on the rapid manufacturing of prototypes for
non-biomedical applications. As the field of tissue engineering has evolved,
AM technologies have been adopted. These techniques offer precise control
over the matrix architecture (size, shape, interconnectivity, branching,
geometry and orientation), yielding biomimetic structures varying in design
and even material composition. Through this the ability to control mech-
anical properties, biological integration and degradation kinetics of the
scaffolds has been advanced. AM techniques are easily automated and in-
tegrated with imaging techniques with the potential to generate patient and/
or application-specific scaffolds.
10
A review by Melchels et al.
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has exten-
sively discussed AM for tissue and organ printing.
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9.2.1 Principles of Additive Manufacturing: Fused Deposition
Modelling and Melt Extrusion
Typical AM processes use a number of methods to generate layer parameters
that are translated into tool paths. The most common involve digitally
slicing a computer aided design (CAD) model, digitally slicing computerised
tomography (CT) data or direct generation of tool paths using mathematical
algorithms. Using a CAD method provides the most hands-on approach as
the final product can be visualised on a computer screen and easily ma-
nipulated. This also allows the generation of complex shapes with ease.
Using CT data has the advantage of being the most physiologically accurate
when generating implants. However, both these methods rely on pre-defined
generic algorithms to translate the data into layer parameters and ultimately
tool paths. While powerful and enabling, these algorithms have the limi-
tation that they lack precise control of the scaffold geometry and archi-
tecture. If this is an important requirement then direct mathematical
generation of tool paths is the most flexible and tailorable.
Various types of code can be used to communicate tool paths. Most
commercial systems rely on confidential approaches through which CAD
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