Heterogeneity is a facet of biology; even single-celled organisms differ between individuals due to slight genetic mutations and the influence of their environment. Humans, of course, are no different, and it is known that mutations and person-to-person heterogeneity drive differences in disease progression. This is especially true with cancer, where the rapid replication of cancer cells and their impacts on the surrounding microenvironment create a cascade of opportunities for further mutation. Taking this into account, there is a paradigm shift occurring in the research community toward the widespread adoption of 3D culture methods. When compared to 2D methods, based around monolayers of often identical cells, 3D techniques offer significantly more opportunities to capture this innate heterogeneity and the complexity of natural systems. To this end, the co-culture of patient-derived explants with autologous immune cells has proven to be the most physiologically relevant method available for modeling human disease and including the idiosyncrasies of the patient.
The stochastic nature of biology means that with complex in vitro systems comes some level of unpredictability between experiment constituents. For example, in a CAR T-cell killing assay there may be a subset of cells that is particularly aggressive. Or, perhaps in trying to model metastasis, only a subset of cancer cells migrate to and spread within the target tissue despite others being nearby. Cells which behave differently are of particular interest as the mechanisms behind their actions may comprise important puzzle pieces required to solve pertinent problems in the clinic. With the increasing power and accessibility of tools like high resolution single-cell RNA sequencing and CRISPR-based lineage tracing, there exists the ability to decode the gene expression of collected cells and investigate these behaviors. The challenge, then, is the collection of samples, both in situ and in real-time, when these rare or anomalous events occur.
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Unlike other 3D culture mediums, like basement membrane extract gels, samples cultured in Liquid-Like Solids (LLS™) can be extracted from culture without disturbing the rest of the experiment, and without any sort of enzymatic degradation. The granular nature means that anything held within can be plucked out via a syringe needle, pipette tip, or other similar device and the microgel will heal upon removal. Leveraging this property and the optical transparency of LLS™, Aurita has developed the BioPelle, a microscope mounted hydraulic micromanipulator with analog controls. The BioPelle print head can be mounted in the microscope condenser turret where the tip is aligned with the optical axis, or on an adjacent platform with the tip located in the field of view, and in either case the microscope stage controls are employed for motion of the sample with respect to the collection/deposition tip of the BioPelle. Fluidly connected to the tip through a thin tube is the control module with both coarse and fine knobs having resolutions of 100 µl per revolution and 0.5 µl per revolution, respectively. The combination of precise fluid actuation and the calibrated stage controls of most microscopes makes the BioPelle a highly versatile manipulation and collection tool that requires no new electronics to integrate into pre-existing systems.
