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International Journal of Bioprinting Bioprinting cell-laden protein-based hydrogel

the regulations on tissue and organ donation specific to is another problem impairing their capability to form
each of the countries. All in all, a shift toward allogeneic stable constructs; this matter can be solved by blending
sourcing necessitates collaboration among research them with other biopolymers. Besides, the fundamental
groups, companies, and regulatory bodies in defining challenges in bioprinting of keratin, elastin, and resilin
more standardized regulations on tissue and organ are poor extensibility, possibility of contaminations after
donation. Besides, biological, physical, and biochemical the purification process, and difficulty in determining the
requirements of cartilage and bone tissues in designing molecular sequence and primary sequence of resilin owing
PBHs are sometimes overlooked, representing an issue to the diminished stability during the purification.
that should be addressed in order to obtain accurate Despite the rapid advances of bioprinting approaches
experimental results in this field. in recent years, the above-mentioned obstacles should be
Natural proteins, including collagen, gelatin, silk surmounted to move this field forward. Regarding the
fibroin, fibrin, keratin, elastin, and resilin, are in the PBHs, successful examples on the development of cartilage-
spotlight of investigations on PBHs. However, each and bone-engineered constructs employing bioprinting
displays several drawbacks that should be overcome to strategies have been described. As stated, several factors,
achieve favorable outcomes. In the case of collagen-based including biophysical and biochemical parameters, and
bioinks, bioprinting of pure collagen is rather complex PBHs’ process considerations must be taken into account,
because of its low viscosity; a suggested solution in this and multiple challenges with respect to these subjects
regard is combining it with viscous polymers. Additionally, are required to be overcome to ultimately translate these
to enhance its shape fidelity, physical crosslinking and concepts into clinics in the foreseeable future.
blending with other polymers can be employed. Other
hindrances in the bioprinting of collagen that need to 6. Conclusion
be addressed are poor mechanical strength and rapid In bioprinting, there is a paramount need to address
hydrolysis. A common problem of pure gelatin bioinks the cell damage caused by shear stress and to develop
at physiological temperature is their low viscosity, which bioinks with ideal cell protection. Researchers have been
can be also improved when blending them with viscous employing experimental investigations and probabilistic
polymers. Another obstacle, again solvable via combining models to understand cell encapsulation in droplets
with other polymers, is associated with the low bioprinting and to design bioinks with suitable characteristics.
resolution of these bioinks. Notably, to augment their poor Notably, current single-cell bioprinting techniques have
shape fidelity, post-printing crosslinking and utilizing limitations in terms of throughput and deviation in the
external support for the bioinks have been demonstrated printing process. In addition, reproducing complex cell–
as effective methods. Unfortunately, the stress shielding matrix and cell–cell interactions is a significant challenge
features of gelatin bioinks are low; a complication that for other bioprinting methods. Future directions include
can be tackled by nozzle temperature optimization during developing tissue repair printers, equipping bioprinters
bioprinting to increase cellular survival. Pure silk bioinks with microfluidic heads, and designing gradient scaffolds.
have the disadvantage of high viscosity, resulting in Of note, combining different bioprinting approaches,
nozzle clogging at the time of bioprinting; one efficacious evaluating cellular functions, and optimizing factors like
strategy involves using recombinant silk that possesses imaging and bioink formulations are ongoing trends to
lower viscosity compared to that of the native silk. advance the bioprinting field. Protein-based materials
Furthermore, lacking cell binding domains which can display promise for bioinks but may have batch-to-batch
limit cellular attachment, low cellular growth and function variations. It is important to mention that establishing
support, and the absence of an established protocol for the strict protocols for protein concentration, purification, and
optimization of silk-based bioinks are other obstacles that extraction is crucial to ensure reliable and reproducible
need to be taken into account. Particularly, scholars should outcomes in bioprinting. Selecting the best method of
address the high rate of enzymatic degradation and poor sterilization is also critical for the safety and properties
mechanical parameters related to the silk fibroin bioinks of the final bioink. In addition, ethical concerns and
as well as the weak structural integrity associated with pathogen transmission risks arise when using proteins
the silk sericin bioinks. The chief challenge of employing from xenogeneic sources, while allogeneic sources are
fibrin as a bioink is its irreversible and rapid gelation at limited in availability due to regulations on tissue and
the body temperature, making its bioprinting intricate. organ donation. In this regard, a collaboration between
As an alternative, fibrinogen and thrombin blends can be research groups, companies, and regulatory bodies is
printed together at low temperatures in order to inhibit required to standardize regulations on tissue and organ
early crosslinking. The fast degradation of fibrin bioinks donation for allogeneic sourcing. Natural proteins such

Volume 9 Issue 6 (2023) 489 https://doi.org/10.36922/ijb.1089