Page 246 - IJB-9-1

International Journal of Bioprinting 3D printing of smart constructs for precise medicine

Table 1. Comparison of performances of commonly used 3D bioprinting techniques.
Technique Advantages Drawbacks References
Inkjet based • Low cost • Low cell density (<10 cells mL ) [45,154-157]
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• High cell viability (75% – 90%) • Low‑viscosity bioinks (~3 – 12 mPa·s)
• Fine printing resolution (~30 μm) • Risk of nozzle clogging
• Rapid printing speed (up to 10,000 droplets per second)
Microextrusion • High cell density (~10 cells mL , e.g., cell spheroids) • Low resolution (~100 μm) [158-162]
-1
8
• High viscosity bioinks (30 mPa·s‑6×10 mPa·s×10 mPa·s) • Slow printing speed (~10 – 50 μm s )
7
7
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• Medium cell viability (40% – 95%) • High shear stress
• Nozzle clogging
Light assisted • Ultrafine printing resolution • High cost [159,163,164]
• High cell viability (>95%) • Post‑printing cell damage
• High cell density (10 cells mL ) • Difficulty in assembling multiple types of bioinks
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• Low‑viscosity cell suspensions (1 – 300 mPa·s),
• Free from nozzle clogging
3.2. pH-responsive biomaterials
The development of pH-sensitive biomaterial inks
to improve the efficiency of drug release for tumor
therapy is underway [72,73] . Polymers that are used
to study pH responsiveness include polyacrylate,
poly(N-isopropylacrylamide), n-vinylcaprolactam, sodium
alginate, and carrageenan . Bivalent copper can be used
[74]
in combination with alginate to form biomaterial ink.
Notably, it has proven in this study that the encapsulation
system is able to retain its structural integrity at pH = 1.2.
The contents were then released slowly only at a pH > 5,
Figure 5. Stimulation-responsive biomaterials in tissue engineering.
suggesting slow release of the contents in the intestinal
formulated with polyvinyl alcohol (PVA), which is capable tract [75,76] . Furthermore, novel biomaterial inks have been
of interpenetrating with chemically cross-linked PEG developed using a gelation mechanism that crosslinks
during crystallization. After three cycles of freezing and polyvinylpyrrolidone polymer and crotonic acid under
[76]
thawing, the hydrogel composed of 70% PVA and 30% PEG gamma (γ) radiation . The drug release rate from the
exhibited a stable helical morphology. The results of these resulting gel was much lower in an acidic medium than
studies showed that the degree of thermoresponsiveness in a neutral medium. Some biomaterial inks must also
was affected by the crystallinity of the polymers. Xu et al. include the stability of their pores to avoid swelling. Silica
[71]
merged dynamic ionic and covalent bonds to formulate a nanocomposites on top of poly(N-isopropylacrylamide)
[77]
novel thermally responsive polybutadiene (PB) rubber. have been employed for this purpose . The pH-responsive
More specifically, the ionic bonds were formed through the biomaterial inks depend on the ionic side chains, that is, they
combination between PB-COOH and PB-NH . Afterward, depend on the protonation of electrostatic repulsion with
2
[78]
they were cross-linked with different concentrations of the surrounding environment . pH-responsive cellulose
the trithiol cross-linker. The SPB-6% hydrogel exhibited biomaterial inks have also been used in wound dressings
a permanent spiral-like structure when the SPB film was for better skin tissue engineering. These are biomaterial
photocrosslinked after rolling on a rod. As the spiral inks that can be degraded on acidic skin and have the
[79]
biomaterial ink was heated to 60°C, the structure was ability to self-heal. For example, Akhlaghi et al. revealed
changed into a temporary flat shape, which reverted to that the functionalized cellulose nanocrystals (CNCs) with
spiral shape on cooling. This transformation may have amine (CNC-NH ) moieties could lead to pH-responsive
2
been caused by the thermoreversibility of the ionic characteristics. The biomaterial ink was degraded at a low
bonds. Different types of thermoresponsive materials are pH. This ink can be added into a poly(vinyl acetate) to
widely utilized in various tissue engineering applications. obtain pH-responsive composite nanofilms. In addition,
Therefore, they have great potential in smart 3D bioprinting, pH-responsive characteristics can be used to improve
in which the shape of biomaterial ink can be transformed micropores within a biomaterial ink [80,81] . For example,
by altering the temperature within ideal ranges. Bao et al. manufactured micropore-forming viscoelastic
[80]

Volume 9 Issue 1 (2023) 238 https://doi.org/10.18063/ijb.v9i1.638