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3D-printed bioreactors for in vitro modeling and analysis
complex microfabrication processes. Another carrier , have been shown to stimulate microbial
[63]
group developed a 3D-printed smartphone assemblages for improved organic matter removal
platform integrated with an optoelectrowetting- and better performance of biofilm reactors. Other
operated microfluidic device for on-site detection studies employed SLA-printed miniature anaerobic
of viable algae cells . The collected data were digester reactors as a process screening tool for
[52]
wirelessly transmitted to a central host for real-time sustainable treatment of wastewater and biowaste .
[62]
monitoring of water quality with reduced analysis
time. Given its sensitivity, this chip allowed 3 Conclusions and future directions
sample preparation methods such as droplet
immobilization and mixing, target cell counting, In recent years, significant advances have been
and fluorescent detection. made in 3D-printed bioreactor technologies.
Bioreactors have been tailored to easy online
2.2.3 3D-printed bioreactor for pathogen monitoring and automated bioprocesses, thereby
phenotypic analysis closing the gap between conventional bioreactors

Profiling pathogen phenotypes is important in and their miniature 3D-printed counterparts.
decoding the virulence and interaction of pathogen However, in addition to their basic functions, other
with its surroundings. A propidium monoazide design aspects, such as flexible operation and
(PMA) pretreatment was carried out in a 3D- process optimization, should be taken into account,
printed bioreactor to efficiently discriminate live especially for devices used to study complex
waterborne bacterial pathogens in natural pond physiological phenomena. It is noteworthy to
water samples . The material jetted bioreactor mention that there has been limited clinical
[60]
was designed with an inlet, splitter, and mixers translation of 3D-printed bioreactors. This could
for proper sample-PMA mixing followed by be attributed to the lack of optimized protocols that
incubation in serpentine channels containing are fine-tuned to respective 3D-printing methods
herringbone structures for alternating dark and and materials. The reproducibility of certain 3D-
light incubation. The results obtained from this printing processes is suboptimal.
3D-printed bioreactor suggested the need for At present, 3D-printing research for in vitro
species-specific optimization of pretreatment biological applications focuses mostly on relatively
performance. Elsewhere, an SLA-printed simple systems that only incorporate a limited
incubation/diffusion chamber was designed for number of cells and cell types. Future studies
culturing bacteria from soil samples to study their should aim to attend to relatively complex tissues
interaction dynamics. The chamber facilitated and organs. Moreover, several concerns such as
diffusion of soil components with target cells and 3D-printing compatible design, removal of support
also allowed single-cell and ensemble bacterial structures, the choice of appropriate cell lines, better
phenotypic analyses .
[61]
cocultivation concepts, establishment of optimal
2.2.4 3D-printed bioreactor for wastewater conditions, and protocol standardization remain to be
treatment resolved and should be the focus of future research.

Several 3D-printed bioreactors have demonstrated With advances in various aspects of 3D-printing,
great potential in water treatment applications one would be able to design and manufacture
that were difficult to be achieved by conventional customized bioreactors with tailored functionalities
wastewater treatment systems. Cylindrical using 3D-printing in laboratory settings, which
microrobots printed by SLA conveyed would significantly drive future biomedical research
excellent water purification capability and great by offering on-demand in vitro testing.
biocompatibility with mammalian cells . Other Conflicts of interest
[26]
intricate 3D-printed bioreactor designs, including
fullerene-shaped bio-carriers and gyroid-shaped The authors declare no conflicts of interest.
[21]
92 International Journal of Bioprinting (2020)–Volume 6, Issue 4