Advances in immuno-biomaterials are providing increasing control of immunity both in vitro and in vivo. Organoids and 3D cultures begin to mimic functions such as antibody production, while biomaterials-based immunotherapies modulate immune responses in animals, often acting directly in the lymph node. A critical element of the immune system that is challenging to incorporate into the design of such materials is tissue-level spatial organization. Cells and extracellular matrix elements in the lymph node, spleen, and thymus are all highly organized. It is thought that spatial proximity, coupled with diffusion and interstitial flow, ensures that secreted signals such as cytokines and chemokines arrive at their target cell in the time required for immunity. Therefore, methods are needed to control the spatial patterning of 3D cultures and to test the role of spatially targeted biomaterials-based therapies.
Here, we report the development of a microfluidic method for chemical stimulation of engineered 3D cultures and live tissue sections on the regional scale. A microfluidic chip was built with 1 – 10 parallel channels running beneath a tissue culture chamber. Each channel connected to a single vertical port, providing focal stimulation to a hydrogel slab or tissue sample in the culture chamber. This system enabled precise control over quantity delivered and timing of delivery to the sample, as demonstrated by delivering fluorescent dextrans with 200 – 300 micron resolution into a live slice of murine lymph node. This resolution was sufficient to target functional regions such as a B cell follicle or the T cell zone. The method was compatible with live fluorescent imaging, making it possible to deliver fluorescently-labeled bioactive proteins into live tissue in order to measure diffusion coefficients and tissue tortuosity. More recently, we have redesigned the device to make the port mobile beneath the tissue, so that the region of stimulation could be chosen on-demand and even moved during the experiment by the user. We anticipate that microfluidic local delivery will be used to create spatially patterned protein distributions in engineered 3D cultures, as well as to test the effects of immuno-modulating materials in specific regions of the lymph node. Combining engineered biomaterials with the fluidic and spatial control of microfluidics promises a new level of insight and control over the spatiotemporal dynamics of inflammation and immunity.