Page 381 - IJB-10-3

International Journal of Bioprinting Multi-physical field control inkjet bioprinting

a shape. As shown in Figure 6E, at this stage , when the point above the isothermal surface was selected for the
GelMA microdroplet began to assemble, its kinetic and test in the cell-laden structure printing experiment. In
gravitational potential energies were converted into surface the printing test process, first, we adjusted the voltage
tension potential energy and viscous dissipation, and there amplitude and pulse width to achieve the suitable diameter
was no elastic potential energy in the equation. Because and velocity of the microdroplet. Then, the corresponding
the GelMA microdroplet showed liquid properties, it was air temperature was found on the fitted surface in Figure
prone to collapse during assembly. This phase did not meet 6I. Moreover, according to the air temperature control
the requirements for printing. relationship obtained above, the temperatures of the upper
and lower floors of the temperature controlled chamber
The second phase was the printable phase, as shown
in Figure 6H(Ⅱ). When the internal air temperature were adjusted. Finally, we controlled the final assembly
temperature of the microdroplets at 16°C.
was between 4.9°C and 1.7°C, the GelMA microdroplet
temperature was between 17°C and 15°C. The microdroplet This study aims to expand the scope of the proposed
did not collapse on the baseplate and bonded to form a method by conducting printability tests of GelMA at
hemisphere. As shown in Figure 6E, and were similar at different concentrations. Specifically, printability tests
this stage. When the GelMA microdroplet touched the were conducted on 3% and 10% GelMA, which are widely
bottom plate, its kinetic and gravitational potential energies adopted concentrations in printing experiments (Figure
were converted into surface tension, elastic potential S1 in Supplementary File). Therefore, we accurately
energy, and viscous dissipation. The properties of the controlled the temperature of the GelMA microdroplets
microdroplets were between those of a liquid and a solid, and realized the MFCPIB. Next, we performed a series of
and they characterized a glassy phase. During assembly, printing experiments using MFCPIB.
the microdroplet was glassy at the initial assembly stage
and rapidly became solid after completion of assembly. 3.3. Printing 3D structures with MFCPIB
To verify the printing effect of the MFCPIB method, we
Therefore, the GelMA microdroplet in this phase was
suitable for printing. performed a series of printing tests using 5% GelMA. First,
we printed a pyramid (Figure 7A) to demonstrate the 3D
The third phase was the excessive gelation phase, printing capability of the MFCPIB method. The top of
as shown in Figure 6H(Ⅲ). When the internal air Figure 7A shows the computer-aided design (CAD) model
temperature dropped below 1.7°C, the gelation of the of the design; the pyramid was 20 mm long, 16 mm wide,
GelMA microdroplet was complete, and the microdroplet and 20 mm high. Using the MFCPIB method in printing
exhibited the properties of a solid. When the microdroplet for 1.5 h, the top of the pyramid structure had well-defined
reached the floor, it bounced. At this stage, , and elastic edges and did not collapse. It was not easy to achieve this
potential energy and viscous dissipation were generated level of performance with the previous inkjet molding
during assembly. The kinetic and gravitational potential method. The MFCPIB method could form structures from
energies decreased, and there was no surface tension temperature-sensitive materials such as GelMA.
potential. When the elastic potential energy reached Next, we fabricated a stereoscopic letter structure
its maximum value, it was converted into gravitational (Figure 7B) to verify the ability to adapt the MFCPIB
potential and kinetic energies. Therefore, the GelMA method to DOD printing using a printhead that started
microdroplet bounced, and the assembly could not and stopped. In inkjet printing, many structures cannot be
be achieved.
completed; for example, the pyramid model can be printed
Based on the above experimental results, we at one time, but it is necessary to pause several times during
determined that the optimal printing temperature of the DOD printing. When printing is paused, this significantly
GelMA microdroplet was 16°C. As in a previous study, challenges the use of thermosensitive materials because
we adjusted the microdroplet diameter and velocity by they easily gel and clog the nozzle. Additionally, after the
adjusting the pressure field. After obtaining the desired printing is stopped, material that is in the temperature-
microdroplet diameter and velocity, we controlled the controlled chamber for a long time undergoes excessive
temperature during assembly at 16°C by controlling gelation, which affects the assembly of the microdroplets of
the air temperature. According to the results of the the gel. The MFCPIB technique should solve this problem
temperature calculation, we obtained the relationship of by applying temperature control to the printing process.
MFCPIB, as shown in Figure 6I. The surface was fitted by Since the printhead is kept at 37°C, the material will not
the microdroplet diameter, velocity, and air temperature, clog the nozzle when the printing process is suspended
which controlled the temperature at 16°C. The gray plane for a long time. Although the deposited microdroplets
in Figure 6I is a 0°C isothermal surface. The appropriate stay in the temperature-controlled chamber for 1 h, the

Volume 10 Issue 3 (2024) 373 doi: 10.36922/ijb.2120