Abstract
A contactless label-free method using a diamagnetophoretic ink to rapidly print three-dimensional (3D) scaffold-free multicellular structures is described. The inks consist of MCF-7 cells that are suspended in a culture medium to which a paramagnetic salt, diethylenetriaminepentaacetic acid gadolinium (III) dihydrogen salt hydrate (Gd-DTPA), is added. When a magnetic field is applied, the host fluid containing the paramagnetic salt is attracted towards regions of high magnetic field gradient, displacing the ink towards regions with a low gradient. Using this method, 3D structures are printed on ultra-low attachment (ULA) surfaces. On a tissue culture treated (TCT) surface, a 3D printed spheroid coexists with a two-dimensional (2D) cell monolayer, where the composite is termed as a 2.5D structure. The 3D structures can be magnetically printed within 6 hours in a medium containing 25 mM Gd-DTPA. The influence of the paramagnetic salt on MCF-7 cell viability, cell morphology, and ability of cells to adhere to each other to stabilize the printed structures on both ULA and TCT surfaces is investigated. Gene expressions of hypoxia-inducible factor 1-alpha (HIF1α) and vascular endothelial growth factor (VEGF) allow comparison of the relative stresses for the printed 3D and 2.5D cell geometries with those for 3D spheroids formed without magnetic assistance. This magnetic printing method can be potentially scaled to a higher throughput to rapidly print cells into 3D heterogeneous cell structures with variable geometries with repeatable dimensions for applications such as tissue engineering and tumour formation for drug discovery.
Highlights
Two-dimensional (2D) environments, where cells are grown on a tissue culture treated (TCT) surface, have limited clinical relevance since they do not correctly mimic the interactions that influence living cells
The paramagnetic culture medium consists of Gd-DTPA salt dissolved in DMEM supplemented with 10% FBS, as described in Materials and Methods
Since the salt is toxic at high concentrations and prolonged exposures [18, 27, 28, 31], we assess the proliferation of MCF-7 monolayers incubated with 0, 1, 10, 25, 50, 75, 100, and 125 mM Gd-DTPA dissolved in the cell culture medium
Summary
Two-dimensional (2D) environments, where cells are grown on a tissue culture treated (TCT) surface, have limited clinical relevance since they do not correctly mimic the interactions that influence living cells. Three-dimensional (3D) models provide more accurate representations of physiologic environments. For 3D cell geometries composed of human carcinoma cells, these interactions involve cell-cell signaling, presence of extracellular matrix (ECM), mechanical cues, hypoxic environments, gene expressions, and drug resistance [1,2,3,4]. Examples include multicellular tumours [5, 6], mammospheres formed with mammary cells [7], and tissue spheroids that are embedded in a hydrogel matrix as building blocks to produce larger cell structures [8]
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