The Modular µSiM: a Mass Produced, Rapidly Assembled, and Reconfigurable Platform for the Study of Barrier Tissue ModelsIn Vitro

Abstract

Advanced in vitro tissue chip models can reduce and replace animal experimentation and may eventually support 'on-chip' clinical trials. To realize this potential, however, tissue chip platforms must be both mass-produced and reconfigurable to allow for customized design. To address these unmet needs, we introduce an extension of our μSiM (microdevice featuring a silicon-nitride membrane) platform. The modular μSiM (m-μSiM) uses mass-produced components to enable rapid assembly and reconfiguration by laboratories without knowledge of microfabrication. We demonstrate the utility of the m-μSiM by establishing an hiPSC-derived blood-brain barrier (BBB) in bioengineering and non-engineering, brain barriers focused laboratories. We develop and validate in situ and sampling-based assays of small molecule diffusion as a measure of barrier function. BBB properties show excellent interlaboratory agreement and match expectations from literature, validating the m-μSiM as a platform for barrier models and demonstrating successful dissemination of components and protocols. We then demonstrate the ability to quickly reconfigure the m-μSiM for co-culture and immune cell transmigration studies through addition of accessories and/or quick exchange of components. Because the development of modified components and accessories is easily achieved, custom designs of the m-μSiM should be accessible to any laboratory desiring a barrier-style tissue chip platform.

The Modular μSiM Reconfigured: Integration of Microfluidic Capabilities to Study in vitro Barrier Tissue Models under Flow

“…Although we used HUVECs in our experiments as a proof-of-concept, the m-µSiM is compatible with other cell populations including iPSC derived endothelial cells in co-cultured environments. [44] Furthermore, the reversible latching mechanism offers the potential to add other functional modules including TEER measurement and passive pumping modules.…”

“…The membrane and m-μSiM components were assembled in a layer-by-layer manner as described in detail in a companion paper ( Figure 2A ). [44] The porous region of the membrane (yellow) is surrounded by silicon support (blue) ( Figure 2B ). As shown in Figure 2C , the membrane separates two compartments of the m-μSiM into luminal and abluminal sides while allowing soluble factor communication between compartments to occur over length scales that are consistent with the ~100 nm thick basement membrane found in vivo.…”

“…immunostaining and barrier permeability measurements using standard experimental protocols as described in the companion paper. [44] The user also has the option to keep the channel in place and use microfluidic assay protocols if desired.…”

“…[26,[29][30][31] As shown in a companion paper, barriers can be established in the m-µSiM using familiar open-well protocols with excellent reproducibility across engineering and bioscience focused laboratories. [44] To highlight the flexible nature of our approach, we seed and establish an endothelial monolayer in the open-well format and reconfigure the platform into a fluidic system. Using particle image velocimetry (PIV), we experimentally validate the computational model of the flow path and demonstrate the shearinduced alignment of endothelial cells.…”

“…Here, we introduce a reconfigurable platform that combines the ease-of-use and standard protocols found in open-well formats with the controlled dynamic flow capabilities provided by microfluidics. Building from our open-well modular-μSiM (m-μSiM; micro physiological system enabled by a si licon m embrane) platform described in a companion paper, [44] we use a tool-free magnetic latching approach to insert a microfluidic flow module onto an established endothelial barrier in the m-μSiM and introduce luminal flow for shear conditioning and leukocyte introduction. The m-μSiM features an ultrathin culture membrane with molecular level thinness (100 nm), high porosity (15%), and excellent live imaging capability that addresses problems with track-etched membranes materials used in commercial membrane-based culture systems ( Figure 1B ).…”