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Liu, et al.
A B

C D

E F

Figure 3. Bio-assembling powered by micromanipulations. (A) Building microvessels by pick-and-place of the cell spheroids and the
piezo-driven two-finger microhand for high speed pick-and-place assembly (Republished with permission from Ramadan AA, Takubo T,
Mae Y, et al., IEEE Trans Ind Electron, 56:1121–35. ). (B) Construction of the microvessels by wrapping a cell sheet . (C) A 4-layer
[60]
[58]
PDMS microfluidic device for microfluidic self-assembly of ring-shaped modules (left, reproduced from ref 63 with permission from The
Royal Society of Chemistry), and automated assembly of microvascular structures using a multimicromanipulator system (Republished
with permission, from Liu X, Shi Q, Wang H, et al. IEEE/ASME Trans Mechatron, 2018, 23:667–78 ). (D) Semi-automatic fabrication
[65]
of microvascular structures by spinning fibers containing cells (Reproduced from ref. 66 with permission from the Royal Society of
Chemistry). (E) Construction of microvessels using cell origami based on the self-folding driven by cell traction force (from ref. licensed
[39]
under Creative Commons Creative Commons Attribution License). (F) The cells are electrically assembled to a microvascular structure on
the capillary surface by applying an electrical potential and extracting the rods from the collagen gel [22,76] .
muscle cells, regardless of their ability to synthesize up along the micropipette utilizing the micropipette fixed
extracellular matrix. on another micromanipulator. Depending on the specific
shape, the assembly process can also be carried out in
4.3. Rotation and alignment of rings the microchannels using microfluidic forces. On-chip

Cell-embedded 2D ring-shaped units are important assembly driven by fluidic force is a promising efficient
building blocks for engineering the microvessels from method for fabricating artificial microvessels with ring-
the bottom up. Du et al. first realized the efficient shaped modules [22,63,64] . Figure 3C shows the assembly of
assembly of the ring-shaped micromodules utilizing the ring-shaped micromodules conducted in the 4-layer PDMS
surface tension force to drive rotation and alignment of microfluidic device. The microfluidic device provides
the modules during the interaction between each other . a closed environment for biological applications while
[61]
The interaction was initialed by manually swiping a allowing integration with other functional components
needle to generate physical forces and fluidic shear. for multiple tasks, including the rotation area, aligning
Wang et al. developed a dual-micromanipulator system area, and collection area. However, the whole assembly
to achieve the automated rotation and alignment of the process is not as flexible as the robotic assembly using
ring-shaped modules . The modules were rotated based on the micromanipulator. It can only assemble the
[62]
and picked up using the micropipette fixed on one ring-shaped modules with fixed sizes. Liu et al. integrated
micromanipulator to press the modules and then pushed robotic assembly and fluidic assembly in the bubble-

International Journal of Bioprinting (2021)–Volume 7, Issue 3 9