Biomedical Engineering Reference
In-Depth Information
staining.Bonegrowthwasobservedinsidetheporesofthescaffolds,
and the bone mineral density of the new bone was measured and
found to be approximately 500 mg/cm
3
, which is in the middle of
the typical bone mineral densities of normal cortical and trabecu-
lar bone. These SLS-developed scaffolds had compressive moduli of
approximately 60 MPa and yield strengths in the range of 2-3 MPa,
which is within the range of normal trabecular bone. Mechanical
propertiesofthescaffoldareimportantaspectsfortwoprimaryrea-
sons. First, the scaffold must support the normal loading of the tis-
sue.Ifnot,excessivedeformationofthescaffoldandthecellsseeded
on it will inhibit proper bone formation. Second, bone remodeling
is naturally influenced by mechanical forces; thus proper mechani-
cal properties of the scaffold may enhance both the amount of bone
ingrowth and osteoinduction of the scaffold.
1
,
14
,
71
In a final aspect
ofthestudy,aporousPCLcondylescaffoldwascreatedfromCTdata
takenfromacondyleofaminipig.Thefabricatedscaffoldsreplicated
theactualcondyleandthusdemonstratedanimportantproofofthe
principle of creating a custom-made bone tissue engineering scaf-
fold from patient CT data.
SLS is hampered by many of the same shortcomings as 3DP,
including unreacted powder in pores and limitations on the pore
size, depending on powder size. Changing SLS parameters such as
laser power and altering particle processing can overcome some of
these limitations and give the user more control, but some techni-
callimitationsstillexist.
2
Gapsresultingfromirregularparticlescan
create porosity, but this porosity is not completely controllable.
61
Resolution is also limited by the laser dimensions. Unreacted pow-
der has been shown to have negative effects on cell survival and
reduce the overall porosity of the scaffold.
68
SLS often involves high
heat, which makes inclusion of biomolecules directly into the scaf-
fold impossible. The biomaterial needs to be readily available in
a highly controlled powder form, which can restrict the materials
that can be used. On the positive side SLS does not require the
use of potentially harmful solvents, and since the polymer is sin-
tered using heat, a binding agent is not required, which reduces the
risk of any harmful substance remaining in the scaffold. Relatively
few cell-based tissue engineering studies utilizing SLS have been
completed,perhapsbecausemanystudieshavefocusedontheeffect
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