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International Journal of Bioprinting Bioprinting of PDAC microtissues for drug screening

beads to support the co-culture of tumor cells and stromal is because the abundant fibroblasts within the stroma-rich
fibroblasts. First, the proposed DEP system is different from model secreted related factors that further promoted the
the conventional continuous extrusion mode. Discrete tumor development, as many other works reported [49,50] .
hydrogel bead units could be printed with the pneumatic Future efforts should be concentrated at illustrating the
extrusion printhead under intermittent pressure-driven detailed molecular mechanisms involved in the complex
printing mode. We noticed that this kind of bioprinting tumor-stoma interactions.
system has the ability to print uniform-sized GelMA beads Finally, we demonstrated that the engineered PDAC
in an effective manner. Besides, the hydrogel beads were microtissues with stromal barrier surrounding the cancer
directly printed in gel state, which reduces GelMA droplets cells within GelMA beads could serve as a drug screening
splashing and evaporation in the process of droplet-based platform for in vitro prediction of chemotherapy efficacy.
bioprinting . Therefore, the proposed DEP system has
[42]
the potential to construct independent tumor microtissue The printed PDAC microtissues are ECM-biomimetic,
array samples for large-scale drug testing. stroma-tunable, and resistant to chemotherapeutic drugs
and can be used in in situ analysis. Here, our drug screening
GelMA material was applied to support the embedded results showed that the formed PDAC microtissue with
cells. Several advantages of using GelMA include good dense fibrous barrier was obviously resistant to gemcitabine.
printability, rapid crosslinking ability and remarkable The engineered PDAC microtissue can be used to optimize
biocompatibility . SEM analysis further confirmed novel treatment strategies, for example, combined therapy
[43]
porous honeycomb structures within the 8% GelMA containing chemotherapeutic and stroma-targeted drugs,
hydrogel, which have been proven to facilitate the because of the stromal barrier formed. On the other hand,
diffusion of and culture medium and provide space for in addition to fibroblasts, other cellular components such
proliferating encapsulated cells [44-46] . Additionally, we as immune cells and endothelial cells are also vital for
printed GelMA hydrogel into microbead structure, which PDAC progression and drug resistance [51,52] . Therefore, we
serves as microcarrier for cell growth. The hydrogel beads envision a more complicated microenvironment of our
that encapsulate cells within a limited spherical structure model by precise and controllable deposition of multiple
(hundred microns in size) have been proved to promote cell types in the future.
the nutrient entry and waste removal . To further verify
[47]
the advantages of the microbead structure, we fabricated 5. Conclusion
pancreatic cancer models including mono-tumor, stroma-
poor and stroma-rich microtissues by culturing cells Taken together, we engineered 3D pancreatic tumor-
in a bulk GelMA hydrogel for 7 days. According to our stroma ECM biophysical microtissues that recapitulate
results, cells encapsulated in the bulk hydrogel showed a the key features of PDAC by utilizing the DEP system to
poor proliferation status, especially in the central region print cell-laden GelMA hydrogel beads. The hydrogel
of the bulk hydrogel, where cells proliferated more slowly beads provided a suitable ECM-mimetic environment that
when compared to cells in the surrounding region, and facilitates the growth of cells. A dense fibroblastic network
cell viability was lower than that of cells encapsulated in with pancreatic cancer cells embedded was formed during
hydrogel beads after cultured for a week (Figure S3). 1-week co-culture, which recapitulates the desmoplastic
PDAC structure in vivo. Importantly, the stroma-rich PDAC
Through printing GelMA beads to encapsulate microtissue developed resistance to gemcitabine, which is
pancreatic cancer cells and stromal fibroblasts with typically observed in clinical practice, confirming the effect
tunable cell densities, we constructed 3D PDAC models of stromal barrier on drug sensitivity. The proposed model
with features of stroma-poor and stroma-rich fibroblastic is easy to construct and yields highly reproducible results,
networks. Further, we demonstrated that there were making it a valuable drug screening platform for rapid
interactions between cancer cells and normal fibroblasts. evaluation of cancer drug treatment and thereby narrowing
Notably, while stromal cells within the PDAC model the gap between drug development and clinical trials.
could be patient-derived PSCs, relevant report pointed
out that PSCs isolated from patient specimens are at least Acknowledgments
partially activated and are not suitable for co-culture with
pancreatic cancer cells aiming at exploring the process of The authors acknowledge the SEM testing service from
normal fibroblasts induction to CAFs . In our PDAC Zhejiang University.
[48]
models, the normal fibroblasts changed their morphology Funding
when the CAF-relevant markers were expressed. On the
other hand, we found that cancer cells proliferated with a This work was supported by the National Key Research
rapid rate as the fibroblast density increased. Probably, this and Development Program of China (2018YFA0109000)

Volume 9 Issue 3 (2023) 10 https://doi.org/10.18063/ijb.v9i3.676