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International Journal of Bioprinting Single-step bioink deposition and maturation of human epidermis

used in a clinical setting. To that end, in addition to the Acknowledgments
obvious requirement that the bioink enables the formation
of an epidermis, we identified the following key criteria: The authors would like to acknowledge Associate Professor
the formulation should be defined, using no complex Hao Li, Amy for her contribution of N/TERT keratinocyte
mixtures such as serum; it should be compatible with cells cell line.
before gelation, during the estimated handling time of an Funding
hour within the operating theatre (Figure 4D); and the
deposition of the bioink should be controlled and visible. We This research is supported by Agency for Science,
systematically characterized different media formulations Technology and Research (A*STAR) under its RIE2020
based on these criteria, and arrived at the serum-free, Advanced Manufacturing and Engineering (AME)
defined PDβ + collagen bioink described above, which Programmatic Grant no. A18A8b0059 titled Additive
we have demonstrated to be able to produce epidermis Manufacturing for Biological Materials (AMBM).
on an artificial dermal substrate. The airlift step, crucial in
triggering stratification in typical RHE protocols [28,39,40] , is Conflict of interest
achieved in the resulting epidermis as the collagen gel dries The authors declare that they have no competing interests.
starting from the top toward the dermis. We surmise that
this reduction in volume, coupled with cell proliferation, Author contributions
is sufficient to create cell-cell contact that can induce
differentiation (Figure S3 in Supplementary File). Based Conceptualization: Cyrus Weijie Beh
on our experience with modifying the bioink formulation Formal analysis: Ruth Jinfen Chai, Wan Ling Wong
to favor either proliferation or differentiation (Figure S2 in Funding acquisition: Cyrus Weijie Beh
Supplementary File), we believe that we will be able to Investigation: Ruth Jinfen Chai, Wan Ling Wong
achieve the goal of a bioprintable epidermis for clinical use. Methodology: Cyrus Weijie Beh, Ruth Jinfen Chai, Wan
Compared with STSG or CEA, which typically result in Ling Wong
visible scars and boundaries, a bioprinted epidermis can be Writing – original draft: Cyrus Weijie Beh, Ruth Jinfen
deposited in a contiguous layer, which may yield improved Chai, Wan Ling Wong
cosmetic outcome. In the meantime, this protocol can Writing – review & editing: Cyrus Weijie Beh
also serve as a relatively easy way to obtain donor-specific Ethics approval and consent to participate
skin models for testing purposes. To achieve an even more
realistic model, work on incorporation of other cell types, Not applicable.
especially melanocytes, is ongoing [18,24] .
Consent for publication
5. Conclusion
Not applicable.
We have developed a serum-free, defined bioink
formulation that can promote maturation of keratinocytes Availability of data
into a functional epidermis through an elegant one- Not applicable.
step deposition process. Based on careful histological
and immunofluorescence analysis, we determined that Further disclosure
the N/TERT RHE formed with our formulation was
largely indistinguishable from established protocols. Part of the findings has been presented in the International
Furthermore, using the general principles gleaned from Conference of Additive Manufacturing for a Better World
the N/TERT experiments, we were able to tweak the (AM Conference) 2022 and the conference abstract has
formulation to achieve similar results with primary been published in Materials Today: Proceedings.
keratinocytes, which will be needed for clinical application. References
We have systematically identified and addressed the
unique challenges that would affect the feasibility of 1. World Health Organization, 2018, Burns. World Health
the bioprinting workflow, including the handling time Organization, Geneva: Available: from: https://www.who.
and the single-media requirement. While we will need int/news-room/fact-sheets/detail/burns [Last accessed on
to deploy this material on various animal models in the 2022 Sep 06].
near future to verify its utility as an alternative to existing 2. Chacon MA, Haas J, Hansen TC, et al., 2019, Thin and ultra-
burn treatments, the current protocol can already produce thin split-thickness skin grafts are safe and efficacious in the
donor-specific models for testing purposes. burn population. J Burn Care Res, 41: 849–852.

Volume 9 Issue 4 (2023) 446 https://doi.org/10.18063/ijb.738