Engineering solutions are desired to create three-dimensional (3D) cell structures to fill the need for physiologically relevant *in vitro* models. Using a unique bottom-up approach, we rapidly form 3D cell clusters by exploiting the diamagnetic property of cells. Through the addition of gadopentatic acid (Gd-DTPA), cell culture medium is transformed into a paramagnetic solution to establish a magnetic susceptibility difference between the cells and their liquid counterpart. The presence of a magnetic field gradient displaces the suspended cells towards regions of relatively lower magnetic field strength. This movement of cells followed by the movement of the culture medium seeds the formation of scaffold-free 3D cell clusters in a contactless, label-free manner. Using this method, various geometries and dimensionalities of cellular structures are produced. The influence of the paramagnetic salt on cell viability, cell morphology, and ability of cells to adhere to each other to stabilize the printed structures on both ultra-low attachment (ULA) and tissue culture treated (TCT) surfaces is investigated to determine exposure limits (time and concentration) of Gd-DTPA required to facilitate magnetic printing. MCF-7, a human breast cancer cell line, can be printed into 3D cell structures on ULA surfaces in 6 hours. Alternatively, MCF-7 cells can be printed on a TCT surface, forming a unique cell landscape where a 3D printed spheroid coexists with a two-dimensional (2D) cell monolayer, the composite of which is termed as a 2.5D structure. Printing with magnetic assistance promotes intercellular interactions between monotypic cells that do not otherwise form 3D cellular structures readily. The magnetic printing of 3D MDA-MB-231 cellular structures occurs within 24 hours without the use of additional reagents or matrices, whereas it takes 48 hours to form a similar structure through gravitational settling alone. The presence of a co-culture introduces new printing abilities and cell morphologies. Increasing the relative amounts of fibroblasts mixed with the MDA-MB-231 cells decreases the time taken to form the structures and further improves their reproducibility. Structures produced through gravitational settling have larger maximum projected areas and total cellular adenosine triphosphate (ATP), but are deemed less reproducible. The distribution of individual cell lines in the co-cultured 3D cellular structures shows that printing with magnetic assistance yields 3D cellular structures that resemble *in vivo* tumors more closely than those formed through gravitational settling alone. This engineering solution has the potential to overcome limitations in bioprinting to expedite efforts in drug discovery, tissue engineering and regenerative medicine.


Rapid Magnetic Printing of 3D Cell Structures

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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