Biomedical Engineering Reference
In-Depth Information
printing technology, due to the technical di
culties in keeping
dimensionalprecision and mechanical strength atonce. Aswemen-
tioned above, the postfabrication sintering process is usually used
to increase the mechanical strength of the implants made from
calcium phosphates; however, postfabrication sintering inevitably
causes contraction in size by up to as much as 27%, compromis-
ing the greatest advantage of the inkjet printing technology, that is,
theexcellentshapecontrol.
24
Postfabricationsinteringalsocompro-
mises biodegradability by increasing the crystallinity of the calcium
phosphates, leading to poor resorption by osteoclasts.
25
-
27
There-
fore,itisnecessarytofindawaytofabricatethecalciumphosphates
without postfabrication sintering. We have focused on the finding
that the addition of water turns
α
-tricalcium phosphate (TCP) pow-
der into hydroxyapatite and solidifies it.
7
Although this finding was
paid attention to by other groups and adopted as a fabrication
principle, their final products failed to exhibit su
cient mechanical
strength for clinical use, calling for postfabrication sintering.
28
By
systematically going over fabrication parameters, we succeeded in
optimizingthediameterofthe
α
-TCPparticlesandtheviscosityand
pH of the curing solution for inkjet printing so that, without post-
fabrication sintering, we could obtain the mechanical strength suf-
ficient for surgical handling and non-weight-bearing applications in
dogs.
23
Basedonthistechnologicalbreakthrough,westartedfabricating
custom-made artificial bones from
α
-TCP powder using the inkjet
printing technology and implanted them in 10 patients with max-
illofacial deformities.
29
The artificial bones had good dimensional
compatibility to deformities due to the excellent shape control by
the fabrication method, thereby requiring minimum dimensional
adjustment for several minutes before implantation and minimum
fixation by suturing at several points after implantation. In contrast,
the conventional artificial bones typically require at least an hour
for dimensional adjustment and another hour for fixation. Thus,
theinkjet-printedcustom-madeartificialboneshelpeddramatically
reduce the operation time and the corresponding invasiveness to
the patients. The initial clinical evidence of bone union between
the artificial bones and host bone tissues was seen as early as at 6
months, and all the patients had partial union at 12 months. This
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