Page 217 - IJB-9-6

International Journal of Bioprinting Multi-Cellular tissues/organoids manufacturing strategies

However, Kenzan method has some challenges. The been explored to overcome these challenges [78,79] . Acoustic
first is the low-resolution problem. Since the needle spacing holography technology holds promise for larger length
defines a relatively narrow spheroid diameter range, the scales, as it allows for modulating the phase and shaping
resolution depends on the size of the spheroids. Therefore, the acoustic intensity distribution.
this may prove challenging for an optimal spheroid Electrophoresis- and magnetofluid-based manipulations
generation when considering unknown cell combinations rely on electrophoresis and magnetophoresis, respectively,
and culture conditions . However, Murata et al. believed to move and levitate cells, as shown in Figure 5B.
[60]
[43]
that the Kenzan method could quickly expand and fuse Paramagnetic chelates like gadolinium are commonly
external cells. Compared with the scaffold-based strategy, used in these techniques , but concerns regarding
[80]
its resolution can be further reduced by the migration and biocompatibility have been raised. Mitigating cytotoxic
fusion of cells inside the spheroid so that the mechanism can effects can be achieved using low-toxicity salts, increasing
be further reduced, thereby improving the resolution [65,66] . magnetic field strengths, or conducting magnetic
The second challenge is that spheroid size, uniformity, and bioassembly in microgravity environments . Notably,
[81]
compaction issues can alter the physiological conditions microgravity experiments conducted on the International
for oxygen and metabolite diffusion . Ozbolat et al. Space Station have shown the successful construction of 3D
[68]
[67]
proposed that cells can be cultured by secondary tissue using implant-grade human chondrocytes.
attachment to the surface of spheroids or hydrogel beads
to improve spatial heterogeneity. Consider developing Optically induced dielectrophoresis (ODEP) technology
aggregate spheroids that continuously release oxygen and employs focused light to generate a dielectrophoresis
[82]
nutrients and integrate them into the tissues they build . field . ODEP devices consist of a fluid medium
[69]
The third challenge is that the Kenzan method is similar sandwiched between a photoconductive material and
to the aspiration biosystem method, which also faces the separate electrodes , as shown in Figure 5B. By altering
[83]
inefficiency of manual positioning in the configuration of the illumination position, various electrode patterns can
heterogeneous structure spheroids at the single-cell scale. be formed, enabling precise manipulation tasks such as
cell aggregation, isolation, pairing, and fusion. However,
3.2. Fluid-based manipulation ODEP devices have a relatively small vertical size due to the
Assembling spheroids or tissue building blocks into MTOs requirement of electrodes on both sides of the fluid domain.
is challenging, as MTOs typically involve complex biological
interfaces, such as cardiac organoids and osteochondral Fluid-based manipulation techniques offer unique
constructs. In this regard, fluid-based manipulation advantages for cell manipulation and assembly.
has emerged as effective means for spatially organizing Acoustophoresis provides microscale accuracy,
spheroids . Fluid-based manipulation is commonly magnetophoresis enables controlled cell movement
[70]
used with microfluidic devices to sort, capture, pattern, through magnetic fields, and optically induced
and encapsulate cells with high biocompatibility [71,72] . This dielectrophoresis allows precise cell manipulation using
technology is characterized by a contactless and label- focused light. However, limitations such as challenges
free cell manipulation method, which is increasingly with large cell numbers, biocompatibility issues, and size
used in organ-on-a-chip devices and is an essential constraints exist within each technique.
technique for aligning and patterning cells in structural 3.3. Suspended-based techniques
fabrication. According to different mechanisms, there are Suspension-based techniques encompass two main
acoustophoresis, magnetophoresis, and optically induced approaches: support bath bioprinting and sacrificial
dielectrophoresis techniques. These techniques utilize bioprinting. In the support bath technique, as shown in
fluid flow, acoustic waves, magnetic fields, or light-induced Figure 5C, a suspension medium containing tightly packed
electric fields to manipulate and position particles or cells granular hydrogel microgels is used as a liquid-like solid
in a fluidic environment. support for the printed structure. This medium allows for

Acoustophoresis, as shown in Figure 5B, involves the use the deposition of individual cells or cell aggregates while
of surface acoustic wave (SAW) actuators to create precise enabling the diffusion of nutrients and waste through the
and localized sound fields, enabling the manipulation and interstitial spaces between the microgels . This approach
[84]
alignment of cells in 3D space . However, limitations has demonstrated high-resolution printing, capable of
[73]
arise when dealing with large numbers of cells or thicker reproducing personalized tissues and organs . It has
[85]
target tissues, and the high natural frequency of SAW also been applied to support the bioprinting of bone and
devices can lead to temperature increases and unnecessary cartilage, where cellular condensations are maintained
fluid movement [74–77] . On the other hand, bulk acoustic within a mechanically stable support medium for long-
wave transducers operating at lower frequencies have term culture .
[86]
Volume 9 Issue 6 (2023) 209 https://doi.org/10.36922/ijb.0135