Poster M17 - Electromagnetic Control and Self-assembly of Cell Clusters for Applications in Tissue Engineering and Regenerative Medicine

Introduction: Cell aggregation as a tool for cancer research and tissue engineering has grown in popularity over the past decade. Cell aggregates is a large category encompassing different types of multicellular structures––mainly clusters, spheroids, and organoids. Cell aggregates have become an exceptionally useful tool for a variety of applications such as personalized drug screenings, with aggregate response closely mimicking patient response to different drug cocktails. Several labs for whole-exome sequencing have developed cancer organoid collections and to study tumor heterogeneity. Additionally, aggregates are used as scaffold-free fundamental building blocks for more complex tissue constructs and regenerative medicine research. While there exist many methods for the generation of cell aggregates and organoids, including bioprinting, magnetic assembly, directed assembly, and microfluidics, these methods often require expensive equipment, extensive training, or long timescales in order to produce consistent aggregates for downstream usage.

In response to this issue, we have developed a 5-minute simple and scalable method to generate cell clusters using our new Electro-LEV apparatus. The Electro-Lev system is a novel magnetic levitation platform combining permanent magnets with electromagnets to achieve spatial and temporal control over samples. Cells or particles are suspended in a paramagnetic medium with Gadavist (a FDA-approved contrast reagent containing gadolinium (Gd)) and levitate at a consistent height between two permanent magnets based primarily on their density. Then, by applying an oscillating current to the electromagnets bracketing the device, the cells are quickly moved up and down multiple times until they form tight cell aggregates.

Materials and

Methods: The Electro-LEV levitation device consisted of two permanent bar magnets with poles facing each other and iron core inductors. In the center is a 1 mm channel where the capillary or flow-based system would fit.

NIH-3T3, MDA-MB-231, and SK-MEL-28 cells were cultured in Dulbecco’s Modified Eagle’s Medium, high glucose with L-glutamine, supplemented with 10% Fetal Bovine Serum and 1% Penicillin/Streptomycin. Cells were cultured at 37°C and 5% CO2.

For magnetic levitation experiments, cell and Gd concentration were precisely calculated to make a 100 uL solution, and 30 uL was loaded into a 1 mm square capillary for each levitation experiment. Cells were given 10 minutes to reach their levitation equilibrium height in the device before pictures were taken and the indicated current was applied to the electromagnets. Current switches between the positive and negative indicated value every 4 seconds, and each change in current applied to the electromagnets is counted as one “up and down iteration”. Videos were taken of every levitation experiment, and screenshots at the highest resolution were taken of all cell aggregates for quantification using ImageJ.

Results, Conclusions, and Discussions: The Electro-LEV system is a substantial improvement over standard magnetic levitation devices. Using the MagDense levitation platform, the levitation height of particles in the capillary can only be adjusted by changing the solution inside the capillary, such as increasing the [Gd] to increase levitation height. However, using the Electro-LEV system, by applying current to the electromagnets, the levitation height of particles inside the device can be precisely and quickly adjusted (Fig 1A). When we tracked the levitation height and velocity of single cells and cell clusters as the magnetic field was adjusted every 10 seconds, we observed that cell clusters were more sensitive to changes in the magnetic field, responding quicker with higher initial velocities and reaching greater levitation heights than single cells (Fig 1B-C). Therefore, Electro-LEV opens up a new dimension to analyze seemingly homogenous cell populations, by tracking their response to changes in the magnetic field.

After observing how cell clusters responded to the magnetic field inside the device, we found that using higher cell or polyethylene bead concentrations, we could generate consistent clusters by rapidly moving the particles up and down. As the particles rapidly oscillate within the capillary, they conglomerate, forming tight, consistent clusters throughout the length of the capillary (Fig 2A-D). By quantifying the dimensions of the clusters using ImageJ, we found that there were significant differences in cluster area based on the cell and Gd concentration in the solution, and that the aspect ratios of the clusters were very consistent and between 1-3 for all conditions tested (Fig 2E-F). By further adjusting several of the parameters, including cell and Gd concentration, current amplitude, oscillation frequency, and number of oscillations, we could conceivably generate large quantities of clusters with a specific size and dimensions in a short period of time.

We have demonstrated the ability of the Electro-LEV system to generate large quantities of cell clusters quickly and consistently, in a scalable manner. These cell clusters can then be pushed out of the device to be used for a variety of applications, including drug screenings and biofabrication.

Acknowledgements (Optional): Naside Gozde Durmus acknowledges funding support from the Career Award at the Scientific Interface (CASI) from the Burroughs Wellcome Foundation (BWF), Gordon and Betty Moore Foundation, McCormick and Gabilan Faculty Award from Stanford University, and the Donald E. and Delia B. Baxter Foundation.