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International Journal of Bioprinting Hydrogels for 3D bioprinting

provides a suitable 3D microenvironment for cell growth. 6. Conclusion and outlooks
SMCs and UCs survive and proliferate well in the In the field of 3D bioprinting, the design and improvement
printed urethra.
of biomaterials with better performance, vascularization
5.3. Complex organ simulation of organs/tissues, chip functionalization to
At present, in many industrialized countries in the world, simulate the physiological environment in vivo, and how
cardiovascular and cerebrovascular diseases become the to construct the culture conditions of organs/tissues, etc.
most common non-communicable diseases that threaten are the directions of most research focus [82,161,162] . However,
human health and life. These diseases are the leading in recent years, more and more attention has been paid to
causes of death in the middle-aged and elderly, who are various process parameters from 3D printers to hydrogels.
the most commonly affected by these diseases [154] . The Because the parameters have a great impact on the printing
cost of performing a heart transplant in patients with resolution and the fidelity of biological materials, some
cardiovascular diseases is expensive, and there are not many researchers have specifically studied the printability of
donors. The emergence of tissue engineering provides a biomaterials and the printing process parameters. With the
new method for the construction of heart tissues/organs. help of a series of explorations on the printing of gelatin/
However, the most difficult part is to build a blood vessel SA hydrogel, they found that the most important factors
network that matches the patient’s blood vessel anatomy [155] . affecting print quality are air pressure, squeeze rate, and
Based on the previously proposed strategy, printed bioink print distance. Combined with the test results, a suitable
in the support medium can make it stably exist [156] . Noor printing process parameter scheme was determined [161] .
et al. [155] developed a support medium mixed with SA and Ouyang et al. [163] studied the effects of gelatin/SA hydrogel
xanthan gum, which is a completely transparent and cell- characteristics and printing parameters on the printability
friendly microparticle formulation. The medium supports of the hydrogel and the viability of embryonic stem cells
the printing of large-size intact tissues and/or organs with (ESCs). They evaluated the rheology of Gel-SA hydrogel to
thick vascularization and high complexity. Of course, optimize the hydrogel formulation, printing temperature,
bioinks are still the focus of our attention. They removed gel time, and other parameters. They also proposed the
omentum tissue from the body and separated the cells influence of factors such as differences in cell types and
from the matrix. Cell recoding can differentiate into CMs printing time on cell-loaded bioink printing. Therefore,
and endothelial cells, and the acellular matrix is processed for a successful 3D bioprinting technology platform, it
into personalized hydrogels. Then, the two kinds of cells are depends not only on the printing process and biological
mixed with hydrogel to prepare bioinks. This self-extracted materials but also on the cells. Specifically, these factors
material will not cause immune rejection in the patient. A include printing speed, shear stress, printing temperature,
huge breakthrough of 3D bioprinting was achieved when nozzle diameter, etc.; suitable biomaterials, concentration
the world’s first complete heart organ (height: 20 mm; ratio, extrusion state, crosslinking method, etc.; cell
diameter: 14 mm) containing a blood vessel network and source, density, and survival state; high-fidelity scaffold
perfusion was successfully printed (Figure 7C). Although structure and ideal three-dimensional microenvironment,
the printed blood vessel network is limited, we can still learn etc. [18,28,163-165] . A complete tissue construction process
from this personalized printing strategy. The construction generally includes imaging, model design, selection of
of organ models is necessary for guiding the transplantation biological materials, selection of cells, determination of
treatment of complex organs/tissues such as heart, kidney, printing methods, and in vivo and in vitro applications [166] .
and lung. Especially in urology, the phantom of the kidney Therefore, any factors can affect the success of complete
in vivo provides detailed anatomical data for replicating tissue/organ construction. The bioinks’ materials used
the bionic model in vitro. Adams et al. [157] used a soft mold for printing, rather than the bioprinting technologies,
technology combining 3D wax printing and polymer are usually the challenges in the development of tissue
molding to obtain modeling data through CT scanning of engineering. In other words, the current limited number of
the anatomical structure of the human kidney. This design bioinks can meet the requirements of printing biophysics
mimics the detailed anatomical structure of a real kidney, and at the same time provide an ideal 3D environment
using soft materials with a tensile modulus of 0.8 to 1.5 MPa for cells [41,80,167] . Therefore, the development of new
and biocompatible hydrogel to simulate human kidney biomaterials and the design of new bioink formulations
tissue. The preparation method is low cost and has good are currently the main focus areas, which are also the main
robustness and high reproducibility of organs. It is a means challenges facing researchers in printing.
to obtain a repeatable and robust model suitable for surgical This article reviews the research progress of the
simulation and training purposes (Figure 7D). performance of hydrogel bioinks for 3D bioprinting, as

Volume 9 Issue 5 (2023) 230 https://doi.org/10.18063/ijb.759