Biomedical Engineering Reference
In-Depth Information
the computer-aided design and manufacturing (CAD/CAM), complex
physical objects of the anatomical structure can be fabricated in a
variety of shapes and sizes. In a typical application, an image of a
bone defect in a patient can be taken and used to develop a three-
dimensional (3D) CAD computer model [161-164]. A computer
can then reduce the model to slices or layers. The 3D objects are
constructed layer-by-layer using rapid prototyping techniques such
as fused deposition modeling [165, 166], selective laser sintering
[167-169], laser cladding [170], 3D printing [171-180], solid
freeform fabrication [181-185] and/or stereo lithography [186-
189]. Furthermore, a thermal printing process of melted calcium
orthophosphates has been proposed as well [190]. A custom-made
implant of actual dimensions would reduce the time it takes to
perform the medical implantation procedure and subsequently lower
the risk to the patient. Another advantage of a prefabricated, exact-
fitting implant is that it can be used more effectively and applied
directly to the damaged site rather than a replacement, which is
formulated during surgery from a paste or granular material [182,
191, 192]. In some cases, laser processing might be applied as well
[193].
The manufacturing technique depends greatly on the ultimate
application of the bioceramic device, whether it is for a hard-tissue
replacement or an integration of the device within the surrounding
tissues. In general, three types of the processing technologies might
be used: (1) employment of a lubricant and a liquid binder with
ceramic powders for shaping and subsequent firing; (2) application
of self-setting and self-hardening properties of water-wet molded
powders (cementation—see Chapter 5); (3) materials are melted to
form a liquid and are shaped during cooling and solidification [194-
197]. Since calcium orthophosphates are either thermally unstable
(MCPM, MCPA, DCPA, DCPD, OCP, ACP, CDHA) or have a melting point
at temperatures exceeding ~1400°C with a partial decomposition
(α-TCP, β-TCP, HA, FA, TTCP), only the first and the second
consolidation approaches are used to prepare bulk bioceramics
and scaffolds. The methods include uniaxial compaction [198, 199],
isostatic pressing (cold or hot) [200-206], granulation [207, 208],
loose packing [209], slip casting [210-213], gel casting [188, 189,
214-219], pressure mold forming [220], injection molding [221],
polymer replication [222-225], extrusion [226-228], slurry dipping
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