Large-Scale, Automated Production of Adipose-Derived Stem Cell Spheroids for 3D Bioprinting
Summary
Here, we describe the large-scale production of adipose-derived stromal/stem cell (ASC) spheroids using an automated pipetting system to seed the cell suspension, thus ensuring homogeneity of spheroid size and shape. These ASC spheroids can be used as building blocks for 3D bioprinting approaches.
Abstract
Adipose-derived stromal/stem cells (ASCs) are a subpopulation of cells found in the stromal vascular fraction of human subcutaneous adipose tissue recognized as a classical source of mesenchymal stromal/stem cells. Many studies have been published with ASCs for scaffold-based tissue engineering approaches, which mainly explored the behavior of these cells after their seeding on bioactive scaffolds. However, scaffold-free approaches are emerging to engineer tissues in vitro and in vivo, mainly by using spheroids, to overcome the limitations of scaffold-based approaches.
Spheroids are 3D microtissues formed by the self-assembly process. They can better mimic the architecture and microenvironment of native tissues, mainly due to the magnification of cell-to-cell and cell-to-extracellular matrix interactions. Recently, spheroids are mainly being explored as disease models, drug screening studies, and building blocks for 3D bioprinting. However, for 3D bioprinting approaches, numerous spheroids, homogeneous in size and shape, are necessary to biofabricate complex tissue and organ models. In addition, when spheroids are produced automatically, there is little chance for microbiological contamination, increasing the reproducibility of the method.
The large-scale production of spheroids is considered the first mandatory step for developing a biofabrication line, which continues in the 3D bioprinting process and finishes in the full maturation of the tissue construct in bioreactors. However, the number of studies that explored the large-scale ASC spheroid production are still scarce, together with the number of studies that used ASC spheroids as building blocks for 3D bioprinting. Therefore, this article aims to show the large-scale production of ASC spheroids using a non-adhesive micromolded hydrogel technique spreading ASC spheroids as building blocks for 3D bioprinting approaches.
Introduction
Spheroids are considered a scaffold-free approach in tissue engineering. ASCs are capable of forming spheroids by the self-assembly process. The spheroid's 3D microarchitecture increases the regenerative potential of ASCs, including the differentiation capacity into multiple lineages1,2,3. This research group has been working with ASC spheroids for cartilage and bone tissue engineering4,5,6. More importantly, spheroids are considered building-blocks in the biofabrication of tissues and organs, mainly due to their fusion capacity.
The use of spheroids for tissue formation depends on three main points: (1) the development of standardized and scalable robotic methods for their biofabrication7, (2) the systematic phenotyping of tissue spheroids8, (3) the development of methods for the assembly of 3D tissues9. These spheroids can be formed with different cell types and obtained through various methods, including hanging drop, reaggregation, microfluidics, and micromolds8,9,10. Each of these methods has advantages and disadvantages related to the homogeneity of size and shape of the spheroids, recovery of the spheroids after formation, the number of spheroids produced, process automation, labor intensity, and costs11.
In the micromold method, the cells are dispensed and deposited at the bottom of the micromold because of gravity. The non-adhesive hydrogel does not allow the cells to adhere to the bottom, and cell-to-cell interactions lead to the formation of a single spheroid per recession8,12. This biofabrication method generates spheroids of homogeneous and controlled size, can be robotized for large-scale production in a time-efficient manner with minimal effort, and has good cost-effectiveness-critical factors in the design of a biofabrication of tissue spheroid7,8. This method can be applied to form spheroids of any cell lineage to prepare a new tissue type with predictable, optimal, and controllable characteristics8.
Biofabrication is defined as "the automated generation of biologically functional products with structural organization …"13. Therefore, the automated production of spheroids is considered the first mandatory step for developing a biofabrication line, which continues in the 3D bioprinting process and finishes in the full maturation of the bioprinted tissue by spheroid fusion. In this study, to improve the scalability of ASC spheroid biofabrication, we use an automated pipetting system to seed the cell suspension, thus ensuring the homogeneity of spheroid size and shape. This paper shows that it was possible to produce a large number (thousands) of spheroids needed for 3D bioprinting approaches to biofabricate more complex tissue models.
Protocol
Representative Results
Discussion
This paper presents the large-scale generation of ASC spheroids using an automated pipette system. The critical step of the protocol is to precisely set up the software to ensure the correct volume of cell suspension, speed, and distance for pipetting. The parameters described in the protocol were determined after a number of trials to optimize the dispensing of the ASC cell suspension into the wells of 12-well plates containing the micromolded, non-adherent hydrogels. The optimization was evaluated by measuring the diam…
Divulgazioni
The authors have nothing to disclose.
Acknowledgements
We thank the National Institute of Metrology, Quality and Technology (INMETRO, RJ, Brazil) for the use of their facilities. This study was partially supported by the Carlos Chagas Filho Foundation for Research Support of the State of Rio de Janeiro (Faperj) (finance Code: E26/202.682/2018 and E-26/010.001771/2019, the National Council for Scientific and Technological Development (CNPq) (finance code: 307460/2019-3), and the Office of Naval Research (ONR) (finance code: N62909-21-1-2091). This work was partially supported by the National Center of Science and Technology on Regenerative Medicine-INCT Regenera (http://www.inctregenera.org.br/).
Materials
| 12-well plastic plate | Corning | 3512 | |
| 50 mL centrifuge tube | Corning | CLS430828 | |
| EpMotion 5070 | Eppendorf | 5070000282 | |
| epT.I.P.S. Motion | Eppendorf | 30015231 | |
| ethylenediaminetetraacetic acid (EDTA) | Invitrogen | 15576028 | |
| fetal bovine serum (FBS) | Gibco | 10082147 | |
| Low Glucose Dulbecco's Modified Eagle Medium (DMEM LOW) | Gibco | 31600034 | |
| MicroTissues 3D Petri Dish micro-mold spheroids – 16 x 16 array | Sigma | Z764000 | |
| MicroTissues 3D Petri Dish micro-mold spheroids – 9 x 9 array | Sigma | Z764019 | |
| phosphate saline buffer (PBS) | Sigma | 806552 | |
| sodium chloride (NaCl) | Sigma | S8776 | |
| tissue culture flask | Corning | 430720U | |
| trypan | Lonza | 17-942E | |
| trypsin | Gibco | 27250018 | |
| ultrapure agarose | Invitrogen | 16500100 |
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