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International Journal of Bioprinting 3D printing and bioprinting in urology

Park et al. fabricated a polymeric anti-reflux flap valve via excellent biocompatibility, but their mechanical properties
3D printing technology, which can be attached to a ureteral are poor compared to synthetic materials. The popular
stent and can effectively resist reflux . To improve anti- biomaterials are mainly hydrogels, gelatin, alginate,
[54]
reflux, Lee et al. created extraluminal anti-reflux diodes decellularized extracellular matrix (dECM), and their
with various shapes, which can be used in ureteral stents , mixtures. As the most widely used synthetic material in
[55]
as shown in Figure 7D–F. 3D bioprinting [75-79] , hydrogel can mimic the extracellular
matrix (ECM) and provide a physiologically similar
5. 3D bioprinting in urology environment for cell growth. Gelatin, alginate, and dECM
3D bioprinting is commonly defined as the process of are acceptable natural materials. The basic biomaterials
fabricating cell-loaded biological materials into tissue- provide carriers for the placement of live cells, and they
engineered scaffolds. Although 3D printing provides can undergo biological reactions. Viscoelastic bioinks are
technical support for the construction of urological usually processed using an extrusion strategy and can
tissue-engineered scaffolds with similar shapes, only 3D be handled equally well using a light-curing strategy by
bioprinting can endow them with biological functions by adding a photoinitiator.
incorporating biomaterials, live cells, and growth factors.
The essence of bioprinting is the processing of living cells, 5.2. Cell types
which requires that the whole process of 3D printing Bioprinting revolves around the processing and
should be friendly or non-invasive to living cells. Common manufacturing of cell-loaded bioink. The cells represent
3D bioprinting technologies include extrusion-based one of the keys to bioprinting, and their selection endows
bioprinting (single-, multi-, and coaxial-nozzle), inkjet- the sample with specific functions. To mimic the biological
based bioprinting (piezoelectric and thermal), and light- microenvironment of natural urological organs in vitro
based bioprinting (UV light and laser light) . Although as much as possible, cells from the target organ, such as
[13]
current technologies are not feasible to reconstruct organs human urothelial cells (HUCs) from urinary tract ,
[74]
in vitro that are fully capable of normal human activity human renal progenitor cells (hRPCs) and human
for clinical transplantation, 3D bioprinting offers the embryonic kidney 293 cells (HEK293) from the kidney ,
[63]
possibility to reconstruct biologically active and functional human bladder smooth muscle cells (HBSMCs) and T24
urological organs. cell from bladder [59,60] , are usually used, according to the
Our search revealed a total of 73 research papers reviewed literature. In addition, stem cells are one of
on bioprinting in urology based on search strategy #3. important cells for 3D bioprinting in urology due to their
Of these, 19 research articles were selected for detailed ability to differentiate into other cells, such as human bone
[61]
study [56-74] (as shown in Table 3) after excluding literature marrow-derived mesenchymal stem cells (hBMSCs) .
reported works that used only urological cells, or some 5.3. Structure design
review articles that were incorrectly categorized as The printing method determines the strategy of structure
research article. Among these articles, 11 are about the design and the type of bioinks. The most widely accepted
kidney [56-58,62,63,65,67,69-72] , 6 about the bladder [59-61,64,66,73] , 1 3D bioprinting technology is the extrusion strategy, which
about the glomerular , and 1 about the urinary tract . relies on bioink deposition to form fibers to build the
[68]
[74]
Of these papers, extrusion bioprinting is the most widely sample layer by layer. In addition, the extrusion strategy
used 3D bioprinting technology, due to its advantages such is carried out with the help of a three-coordinate printer
as low device cost, a wide range of applicable materials, and or a six-degree-of-freedom robot arm to control the
cell-friendliness. To present the advances of 3D bioprinting nozzle movement, and the viscoelastic bioink extrusion is
in urology, we divide this section into four parts: bioinks, achieved by screw, pneumatic, or piston.
cell types, structure design, and urological scaffolds, as
shown in Figure 8. According to the fluid process of the ink flow through
the nozzle, we can get D = 2×(Q/πv) , where D, Q, and v
0.5
5.1. Bioinks are the ideal diameter of the fiber, bioink flow, and printing
Bioink is the raw material for 3D bioprinting, which is speed, respectively . It can be obtained that there is a
[80]
processed into samples according to the structure design functional relationship between the printing speed and
with the aid of printing equipment. Currently, there are the ideal diameter of the deposited fibers. Specifically,
various formulations of bioink, which is mainly composed with a fixed print head size and printing parameters, the
of basic biomaterials and bioadditives. The 3D bioprinting printing speed determines the size of the ideal diameter
method determines the type of basic biomaterial required. of the fiber and the printability of the bioink. During 3D
The commonly used biomaterials include natural and bioprinting, a very high printing speed will result in fiber
synthetic materials. Generally, natural materials have breakage and discontinuity, while a very low speed will

Volume 9 Issue 6 (2023) 333 https://doi.org/10.36922/ijb.0969