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Solvent-based extrusion 3D printing
structure, mechanical properties, and mechanical biodegradables material with ceramics or polymers
properties of the printed scaffolds. has also been investigated [65,66] . For example, Wong
et al. developed a biodegradable composite
[66]
4.2 SBE 3D printed scaffold degradation and composed of PCL and magnesium; they indicated
biocompatibility that magnesium hydroxide was formed during

Degradation and biocompatibility are important the degradation of magnesium microparticles.
parameters that affect the use of SBE 3D printed This process may help to neutralize the pH since
scaffolds for tissue repair. The degradation rate acidic by-products are produced during PCL
of scaffold material should be controllable, degradation. The scaffolds containing magnesium
allowing the scaffold to be gradually replaced by microparticles exhibited low scaffold degradation
an extracellular matrix that is released by nearby rates; in addition, the elastic modulus of the
cells. The degradation rate can be manipulated composite scaffolds showed no differences after a
by optimizing the cell/hydrogel ratio. Lowering 2-month immersion period. The biological results
the cell density and increasing the hydrogel level showed significantly higher specific ALP activity
can extend the degradation time. Controlling and upregulation of bone-related markers in the
the cross-linking procedure is another approach Mg/PCL scaffold than in the pure PCL scaffold.
for optimizing the degradation rate . A slower 5 Summary and future perspective
[53]
degradation rate can also be obtained by increasing
the degree of cross-linking in the polymer [54,55] . Despite the remarkable achievements of SBE
Mixing the polymer with other polymers can 3D printing in TE, challenges remain that have
also alter the polymer degradation rate [15,56,57] . prevented the translation of 3D printed scaffolds
Collagen, gelatin, and alginate hydrogel constructs for clinical applications. First, new types of
were printed with human corneal epithelial cells biomaterials, particularly bio-composite materials,
incubated with a medium containing sodium would facilitate the clinical use of SBE 3D printing.
citrate to obtain degradation-controllable cell- The use of a single type of material is currently not
laden tissue constructs. The results indicate that able to produce a suitable environment for more than
the degradation time of the bioprinting constructs one functional cell type. The use of bio-composite
can be controlled by altering the mole ratio of materials in an organized pattern that matches the
sodium citrate to sodium alginate. The results of biodegradability, biocompatibility, and mechanical
this study showed that the printed cells exhibited a properties of natural tissue may be a more effective
higher proliferation rate and greater cytokeratin-3 approach to create a suitable environment for more
expression . than one functional cell type .
[58]
[67]
For cell-free scaffolds, the degradation rate Second, the ink rheology and processing
can be controlled by incorporating various parameters should be adjusted carefully so
combinations of hydrophobic and hydrophilic that multiple biomaterials and cell types can
synthetic polymers [59-61] . Bioceramics can provide a be simultaneously processed during scaffold
range of degradation rates; in addition, these materials fabrication . The ink should exhibit a shear-
[18]
are capable of stimulating biomineralization for thinning behavior and recover quickly after the
bone tissue repair [62,63] . Kolan et al. plotted PCL/ extrusion from the nozzle. The filament formation
[64]
bio-glass composite scaffolds with and without the process should be evaluated to confirm that the
presence of hydrogel; the biodegradation rate was printed filament diameter is close to the needle
investigated by soaking the scaffold in the culture diameter. The processing parameters should be
medium. A consistently higher weight loss was investigated to confirm the scaffold stackability. In
noted over one week for PCL/bio-glass scaffolds addition, the shear stress that the cell experiences
printed with hydrogel in comparison to those should be evaluated. A cell damage model should
printed without hydrogel. The combination of be developed to investigate the cell damage caused

38 International Journal of Bioprinting (2020)–Volume 6, Issue 1