Enhancing the Scalability and Functionality of Soft Bioelectronic Materials Through Emulsion-Based Techniques

Despite significant progress in recent decades, fundamental differences between biological tissues and conventional electronics create challenges in material design and manufacturing for the next generation of bioelectronics. For example, the human body comprises a diverse array of soft tissues with variable mechanical properties and high water content, while most commercially available and lab-level bioelectronic devices primarily use stiff, dry electronic components like silicon and metals. Additionally, natural tissues are hierarchal in structure, whereby cells act as building blocks for larger networks of tissues and organs, but traditional bioelectronic devices are often monolithic, resulting in spatially homogeneous devices with limited regional control of functionalities. Droplet-based assembly techniques, such as the Droplet Interface Bilayer, harness the natural compartmentalization observed in cells, offering precise spatial control and modular manipulation of chemical and biological processes, along with selective transport across their membrane interfaces, enabling functionalities such as signal processing and molecular detection. Current strategies for constructing droplet-based materials involve the dispensing and positioning of individual droplets, which is time-consuming and demands meticulous coordination of timing and spatial precision. Also, while a liquid-in-liquidfilled structure more closely models the uniquely wet environment of natural tissues, it lacks the mechanical robustness needed in many applications. Thus, an alternative approach is necessary for the rapid and scalable assembly of soft, compartmentalized bioelectronic materials. This study introduces a novel protocol utilizing emulsification and centrifugation to enhance the scalability of soft compartmentalized tissues. In this approach, lipids or amphiphilic block copolymers such as poly(Butadiene)-b-poly(ethylene oxide) (PBPEO) act as emulsifiers to stabilize a water-in-oil emulsion. By emulsifying an aqueous buffer, a selective oil solvent, and the surfactant, individual compartments (5-50 µm) are formed, each stabilized by a monolayer of the surfactant and connected with their neighbor via a biomimetic bilayered hydrophobic membrane. Centrifugation then removes excess oil and condenses the surfactant-coated droplets into a densely packed network of interconnected aqueous compartments. The resulting tissue-like material has a suitable consistency for 3D bioprinting in that it has shape-holding abilities but is viscous enough to be extruded at low pressures. Additionally, the presence of biomimetic membranes allows for the incorporation of transmembrane proteins and ion channels. For example, the voltage-gated ion channel, Alamethicin, can be reconstituted into the hydrophobic membranes, providing discrete control of ionic current. The overall mechanical, electrical, and selective transport properties of the emulsions are not yet well-defined, though. Thus, a comprehensive examination of the material is performed herein. Rheological measurements are obtained to evaluate the material’s viscoelasticity and self-healing abilities. Electrophysiology is used to reveal equivalent circuits and characterize membrane selectivity, and the print fidelity is assessed across various 3D geometries. Overall, this innovative protocol offers a rapid and scalable approach for creating compartmentalized tissue-like materials. The compartmentalized architecture enhances the functionality of bioelectronic devices by enabling precise spatial control and customization of individual compartments. Ionic conductance can be regionally manipulated via selective channels to enable localized filtration, absorption, and/or secretion of distinct species, holding great promise for applications such as advanced biosensing, drug delivery, and biohybrid systems.