Biomedical Engineering Reference
In-Depth Information
composed of PEO bound by printing binder solutions. The local microstructure of
the device could be controlled by either changing the binder or by changing the
printing parameters (velocity). Typical powder particle size ranged from 45 to
75 mm for PCL and 75-150 mm for PEO. The binder droplets had a diameter in the
order of 60-80 mm. After 20 h, significant swelling of the PEO was experimentally
observed.
Landers et al. [
177
] studied the use of water-soluble polymers which are bonded
together by means of water-based saccharide glues. Although the choice of pow-
ders and the corresponding adhesives appears to be unlimited, this technology
requires post-sintering or post-curing to improve mechanical as well as environ-
mental stability.
Lam et al. [
221
] developed a blend of starch-based powder containing cornstarch
(50 wt.%), dextran (30 wt.%) and gelatin (20 wt.%). Distilled water was used as a
suitable binder material. Cylindrical scaffolds (Ø 12.5 × 12.5 mm) were produced
having either cylindrical (Ø 2.5 mm) or rectangular (2.5 × 2.5 mm) pores. Using
water as the binder means that the problem of a toxic fabrication environment was
eliminated and the problem of residual solvent in the construct was solved. Other
advantages of using a water-based binder include the possibility to incorporate bio-
logical agents (e.g. growth factors) or living cells. Post-processing of the scaffolds
was necessary to enhance the strength of the scaffolds and increase the resistance
against water uptake. The scaffolds were dried at 100 °C for 1 h after printing and
infiltrated with different amounts of a copolymer solution consisting of 75 % poly(L -
lactide) acid and 25 % PCL in dichloromethane.
Sanjana et al. [
226
] report on the use of ink-jet printing to fabricate neuron-
adhesive patterns such as islands and other shapes using poly(ethylene) glycol
(PEG) as cell-repulsive material and a collagen/poly-D-lysine (PDL) mixture as
cell-adhesive material. They worked with a positive relief: PEG used as background
and cell-repulsive material was bonded covalently to the glass surface while the col-
lagen/PDL mixture was used as the printed foreground and cell-adhesive material.
They also suggest that the ink-jet printing technique could be extrapolated to build-
ing 3D structures in a layer-by-layer fashion.
Xu et al. [
227
] use the inkjet printing technology for the construction of three-
dimensional constructs, based on fibrin gel. Fibrin was used as a printable hydrogel
to build 3D neural constructs. The fibrin is formed by the enzymatic polymerization
of fibrinogen by addition of thrombin and CaCl
2
. First, a thin sheet of fibrinogen
was plated and subsequently, thrombin droplets were ejected from the print car-
tridge onto the pre-plated fibrinogen layer. Fibrin gel formation was observed imme-
diately after thrombin ejection. Subsequently, NT2 neurons were printed on the
gelled fibrin. The whole procedure was repeated five times, resulting in a 3D neural
sheet.
Koegler et al. [
228
] described the fabrication of 3DP scaffolds based on poly(L -
lactide-co-glycolide). Surface chemistry of these scaffolds was modified by reprint-
ing the top surface with a solution of Pluronic F127 in CHCl
3
.
Cui et al. [
229
] reported on the fabrication of micron-sized fibrin channels using
a drop-on-demand polymerization. A thrombin/Ca
2+
solution together with human
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