now clear that architectures that reproduce tissue organization in 3D are favored for studying function as first shown by Bissell and co-workers nearly 30 years ago. [5,6] Another emerging concept is the capacity for multiple cell types to auto-organize when given the appropriate mechanical cues. [7] A large variety of 3D models have been developed, with the major subtypes being spheroids/organoids, multilayered tissue like models, and scaffold models. [8] 3D tissues are frequently constructed as spheroids using hydrogel-like matrices such as Matrigel, [9] or PuraMatrix, [10] with a highly desirable degree of mechanical softness, however, there can be problems related to cost and inhomogeneity of the materials. [11] Multilayer models hold a lot of promise for applications such as skin toxicology measurements, [12] however, they cannot be easily applied for more complex tissue or organ constructs including vasculature. Considerable attention has thus focused on the development of biocompatible scaffold materials for hosting cells in 3D. A variety of synthetic and bio-derived polymers (some resorbable, some not) have been used to mimic the ECM or connective tissue. In terms of technology integration, the major advances so far for 3D cell biology have been related to materials and methods used for scaffold preparation, and integration of microfabrication techniques, for example for fluidics. As might be expected, a challenge of 3D culture over 2D is associated with the difficulty of oxygenation of tissues in the absence of vasculature. Microfluidics have gained favor for a number of reasons, including for perfusion, reduction in reagent volumes, and the fact that flow induced stress This work reports the design of a live-cell monitoring platform based on a macroporous scaffold of a conducting polymer, poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate). The conducting polymer scaffolds support 3D cell cultures due to their biocompatibility and tissue-like elasticity, which can be manipulated by inclusion of biopolymers such as collagen. Integration of a media perfusion tube inside the scaffold enables homogenous cell spreading and fluid transport throughout the scaffold, ensuring long term cell viability. This also allows for co-culture of multiple cell types inside the scaffold. The inclusion of cells within the porous architecture affects the impedance of the electrically conducting polymer network and, thus, is utilized as an in situ tool to monitor cell growth. Therefore, while being an integral part of the 3D tissue, the conducting polymer is an active component, enhancing the tissue function, and forming the basis for a bioelectronic device with integrated sensing capability.

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We report development of the first biomimetic transistor in a tube for continuous monitoring of 3D cell cultures.

Transmembrane proteins (TMPs) regulate processes occurring at the cell surface and are essential gatekeepers of information flow across the membrane. TMPs are difficult to study, given the complex environment of the membrane and its influence on protein conformation, mobility, biomolecule interaction, and activity. For the first time, we create mammalian biomembranes supported on a transparent, electrically conducting polymer surface, which enables dual electrical and optical monitoring of TMP function in its native membrane environment. Mammalian plasma membrane vesicles containing ATP-gated P2X2 ion channels self-assemble on a biocompatible polymer cushion that transduces the changes in ion flux during ATP exposure. This platform maintains the complexity of the native plasma membrane, the fluidity of its constituents, and protein orientation critical to ion channel function. We demonstrate the dual-modality readout using microscopy to characterize protein mobility by single-particle tracking and sensing of ATP gating of P2X2 using electrical impedance spectroscopy. This measurement of TMP activity important for pain sensing, neurological activity, and sensory activity raises new possibilities for drug screening and biosensing applications.

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