Page 30 - IJB-5-1

Shuai C
in resin and photopolymerized in the SLA before burning A B
up the resin and sintering the ceramics particles together.
Thavornyutikarn et al. [161] produced bioceramic scaffolds
using suspensions, which contain 41 vol.% of bioglass
and 49 vol.% of an acrylate-based photopolymer resin
together with 10 vol.% of a dispersing agent. The binder C D
was removed after heating to 550°C for 3 h, and the
scaffolds were then sintered at 950°C for 2 h. Du et al.
[162] also successfully fabricated customized ceramic
scaffolds using SLA based on a rabbit femoral segment
model. After culturing in oscillatory perfusion for 5 days,
the cells attached and proliferated homogenously on the
scaffolds. Similarly, Levy et al. [163] successfully produced
HA ceramic scaffolds for orbital floor prosthesis by SLA.
Of particular note is that SLA of such a composite resin
is extremely difficult, due to its significantly increased
viscosity. Moreover, the particle size of the added ceramic
should be less than the curing thickness, so as to avoid a
damage of the processing accuracy. Figure 10. (A) A diagram showing an electrospinning setup.
Indirect method has also been reported to produce (B) Electrospun PCL/gelatin-blended scaffolds, and the measured
scaffolds through SLA. For example, Sabree et al. [164] used fiber thickness at various parameters [179] . PG73 means the PCL/
SLA to create an epoxy mold designed from the negative gelatin ratio of 70:30, and PG55 means the PCL/gelatin ratio of
50:50. (C) Confocal laser microscopy of scaffolds under basal or
images of implants. Then, a highly loaded HA-acrylate osteogenic conditions [177] . (D) Representative 3D reconstructions
suspension was filled into the mold. Subsequently, for the implants at 2, 4, and 8 weeks’ post-implantation.
both the mold and the acrylic binder were removed
by pyrolysis. The remaining HA scaffolds were then collector. Once the potential within the solution breaks
sintered to improve the densification rate. The obtained through the surface tension of the obtained droplets, the
scaffolds possessed a porosity of approximately 42% and polymer solution ejects from the spinneret. After the
pore sizes of 300–600 μm. They presented an average solvent evaporates, the polymer fibers are subsequently
crushing strength of 10–25 MPa, which were close to collected onto the grounded collector. As a result, a
other ceramic scaffolds with similar porosity produced fibrous polymer scaffold with fiber diameter ranging
by different fabrication approaches. Kim et al. also used from a 100 nm to several micrometers is constructed.
such an indirect method to produce HA scaffolds [165] . Similar to FDM, electrospinning uses a nozzle to deliver
Compare to other AM techniques, the main advantage the molten polymer for 3D structure construction. Thus,
of SLA is that it has high accuracy and resolution. SLA electrospinning is also described as “electrostatically
using two-photon curing method can build parts with an assisted FDM” [138] . Significantly, electrospinning produces
accuracy of 200 nm [166] . Therefore, SLA is also reported much thinner filaments by applying high voltage supply.
to be used to prepare vascular scaffolds with a smaller During electrospinning, it is of great importance to form
pore structure. Nevertheless, the limited material use a stable fiber, which in turn demands the polymer chains
of photo resins and time-consuming post-processing extensively entangling in the original solution. Otherwise,
remain challenges for the further application of SLA in the solution will be ejected into a series of small droplets
biomedical application. or aggregates into large bead-shaped fibers. From this

3.6. Electrospinning view, low molecular weight polymers with a relative
small molecular size are usually difficult to electrospin,
In decades, electrospinning has gained intensive attention due to their poor ability to entangle with each other.
from the researchers in tissue engineering field, due to On the other hand, polymers with an extremely high
its powerful ability to fabricate scaffolds with micro- and molecular weight usually have a considerably increased
nano-scale structure [167-169] . A typical electrospinning solution viscosity, which inevitably increases the surface
apparatus generally includes a capillary tube with a tension of the formed droplet-thus reducing the ability
spinneret, a high-voltage power supply, and a collector, to form a jet fluid [170] . Based on the above consideration,
as shown in Figure 10A. During electrospinning, the researchers commonly introduce a second polymer to
polymer solution is extruded from the electrically enhance the chain entanglement without an increase of
conductive spinneret to obtain droplets. The high voltage the viscosity or use of amphiphilic molecules to reduce
is imposed between the spinneret and the grounded the surface tension [171] .

International Journal of Bioprinting (2019)–Volume 5, Issue 1 13