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Magnetic 3D Bioprinting
Magnetic 3D bioprinting is a methodology that employs biocompatible magnetic nanoparticles to print cells into 3D structures. In this process, cells are tagged with magnetic nanoparticles (Nanoshuttle) are used to render them magnetic. Once magnetic, these cells can be rapidly printed into specific 3D patterns using external magnetic forces that mimic tissue structure and function. What separates this system over other 3D bioprinting modalities are: the rapid bioprinting process (15 min - 1 h) compared to the days-long processes of others ; the endogenous synthesis of extracellular matrix (ECM) without the need of an artificial protein substrate; and fine spatial control. Using this system, 3D cellular models can be rapidly printed, from simple spheroids and rings, to more complex organotypic models, like of the lung, aortic valve , and fat.

Recently, Nano3D Biosciences, Inc. launched the BiO Assay kit, which is the first commercially available 3D bioprinting system designed for high-throughput and high-content drug screening. In this system, cells are magnetically printed into 3D patterns (rings or dots), and after printing, interact with surrounding cells and ECM to migrate and proliferate and ultimately shrink the structure, typically within 24 h. This shrinkage varies with drug concentration and is a label-free metric of cell function that can be easily captured and measured with brightfield imaging. In the BiO Assay, the size of the pattern is captured using an iPod-based system, which is programmed using a freely available app (Experimental Assistant) to image whole plates of up to 96 structures at small intervals (as small as 1 s) to efficiently capture pharmacodynamics. We are currently developing the 384 version of this system.

Results using this assay were recently published in Scientific Reports in October 2013 (http://www.nature.com/srep/2013/131021/srep03000/full/srep03000.html). More recently, we have used the BiO Assay to screen for cardiovascular toxicity, which accounts for 30% of drug withdrawals Vascular smooth muscle cells are magnetically printed into 3D rings to mimic blood vessels that can contract and dilate. This system could potentially replace experiments using ex vivo tissue, which are costly and yield few data per experiment. Furthermore, the BiO Assay can use human cells to approximate a human in vivo response better than with an animal model. Together, the BiO Assay combines the benefits of 3D bioprinting in building tissue-like structures for study with the speed of magnetic printing.

The main customers of the BiO Assay are in the pharmaceutical and CRO industries, where this system can be integrated early in the drug discovery process as a compound screen for toxicity and efficacy. The integration of the BiO Assay into existing screening laboratories would require minimal turnover, as magnetic 3D bioprinting uses standard cell culture supplies and few additional equipment (iPod, magnets, and NanoShuttle). In the future, magnetic 3D bioprinting could be applied to the burgeoning field of regenerative medicine and organogenesis. Overall, magnetic 3D bioprinting is a powerful tool to create faithful models of native tissue.