Biomedical Engineering Reference
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gradient. The scaffolds were implanted into rabbit cranial defects
and bone ingrowth was measured by histology using Stevenel's
Blue and van Gieson's Picro Fuschin (SVG stain). Histomorpho-
metric analysis was used to quantify new bone area, and results
demonstrated that the high-molecular-weight PLGA scaffolds with
macroscopic channels had a higher new bone area than both
the scaffolds without channels and the defect without any scaf-
fold. The lower-molecular-weight PLGA groups rapidly hydrolyti-
cally degraded and collapsed before the eight-week study was com-
pleted. The higher-molecular-weight PLGA scaffolds were shown to
beosteoconductiveandonlymildlyinflammatoryassignificantbone
growth was observed after eight weeks, as shown by histology. The
scaffolds guided bone growth down the channels, and the poros-
ity gradient of the scaffold had an effect on the type of tissue that
was produced, as only soft tissue was produced outside the radial
channelsofthescaffold.Theseresultsareimportantastheydemon-
stratedthatscaffoldchannels,porosity,andporesizeinfluencebone
growth. In another study HA scaffolds were formed using 3DP in
two architectures, channeled and porous and porous, and the scaf-
folds once again implanted into rabbit cranial defects. Using histol-
ogyextensiveamountofbonegrowthwasobservedinthechanneled
scaffolds and the channels were shown to guide bone growth from
differentareas.Thechanneledscaffoldsguidedboneformationfrom
the edges of the defect into the center of the scaffold. The HA scaf-
foldswereshowntoinducemoreboneformationthanthePLGA-TCP
scaffolds. These studies not only demonstrated the e
cacy of using
scaffolds designed through 3DP in a tissue engineering strategy to
treat cranial defects but showed that the osteoconduction of a scaf-
fold can be greatly influenced by its architecture. Scaffold material
properties and architecture must both be taken into account when
designing scaffoldsfor bonetissueengineering.
Three-dimensional printing has several disadvantages that
hinder its use to manufacture porous scaffolds. In highly porous
scaffolds unreacted powder becomes trapped in the pores and is
di
cult to remove. Second, the pore size is limited by the size
of the printer head and particle size, which make it di
cult to
achieve scaffolds with optimal porosities to enhance bone forma-
tion. Void spaces within fused particles have been shown to create a
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