Designing bioelectronic devices that seamlessly integrate with the human body is a technological pursuit of great importance. Bioelectronic medical devices that reliably and chronically interface with the body can advance neuroscience, health monitoring, diagnostics, and therapeutics. Recent major efforts focus on investigating strategies to fabricate flexible, stretchable, and soft electronic devices, and advances in materials chemistry have emerged as fundamental to the creation of the next generation of bioelectronics. This review summarizes contemporary advances and forthcoming technical challenges related to three principal components of bioelectronic devices: i) substrates and structural materials, ii) barrier and encapsulation materials, and iii) conductive materials. Through notable illustrations from the literature, integration and device fabrication strategies and associated challenges for each material class are highlighted.
Ionically conductive hydrogels are gaining traction as sensing and structural materials for use bioelectronic devices.. Hydrogels that feature large mechanical compliances and tractable ionic conductivities are compelling materials that can...
Hydrogels are promising materials for soft and implantable strain sensors owing to their large compliance (E < 100 kPa) and significant extensibility (ε max > 500%) compared with other polymer networks. Further, hydrogels can be functionalized to seamlessly integrate with many types of tissues. However, most current methods attempt to imbue additional electronic functionality to structural hydrogel materials by incorporating fillers with orthogonal properties such as electronic or mixed ionic conduction. Although composite strategies may improve performance or facilitate heterogeneous integration with downstream hardware, composites complicate the path for regulatory approval and may compromise the otherwise compelling properties of the underlying structural material. Herein, hydrogel strain sensors composed of genipin‐crosslinked gelatin and dopamine‐functionalized poly(ethylene glycol) for in vivo monitoring of cardiac function are reported. By measuring their impedance only in their resistive regime (>10 kHz), hysteresis is reduced and the resulting gauge factor is increased by ≈50× to 1.02 ± 0.05 and 1.46 ± 0.05 from ≈0.03 to 0.05 for PEG‐Dopa and genipin‐crosslinked gelatin, respectively. Adhesion and in vivo biocompatibility are studied to support implementation of strain sensors for monitoring cardiac output in porcine models. Impedance‐based strain sensing in the kilohertz regime simplifies the piezoresistive behavior of these materials and expands the range of hydrogel‐based strain sensors.
Intestinal retentive devices have applications ranging from sustained oral drug delivery systems to indwelling ingestible medical devices. Current strategies to retain devices in the small intestine primarily focus on chemical anchoring using mucoadhesives or mechanical coupling using expandable devices or structures that pierce the intestinal epithelium. Here, the feasibility of intestinal retention using devices containing villi‐inspired structures that mechanically interlock with natural villi of the small intestine is evaluated. First the viability of mechanical interlocking as an intestinal retention strategy is estimated by estimating the resistance to peristaltic shear between simulated natural villi and devices with various micropost geometries and parameters. Simulations are validated in vitro by fabricating micropost array patches via multistep replica molding and performing lap‐shear tests to evaluate the interlocking performance of the fabricated microposts with artificial villi. Finally, the optimal material and design parameters of the patches that can successfully achieve retention in vivo are predicted. This study represents a proof‐of‐concept for the viability of micropost‐villi mechanical interlocking strategy to develop nonpenetrative multifunctional intestinal retentive devices for the future.
Low‐profile and transient ingestible electronic capsules for diagnostics and therapeutics can replace widely used yet invasive procedures such as endoscopies. Several gastrointestinal diseases such as reflux disease, Crohn's disease, irritable bowel syndrome, and eosinophilic esophagitis result in increased intercellular dilation in epithelial barriers. Currently, the primary method of diagnosing and monitoring epithelial barrier integrity is via endoscopic tissue biopsies followed by histological imaging. Here, a gelatin‐based ingestible electronic capsule that can monitor epithelial barriers via electrochemical impedance measurements is proposed. Toward this end, material‐specific transfer printing methodologies to manufacture soft‐gelatin‐based electronics, an in vitro synthetic disease model to validate impedance‐based sensing, and tests of capsules using ex vivo using porcine esophageal tissue are described. The technologies described herein can advance next generation of oral diagnostic devices that reduce invasiveness and improve convenience for patients.
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The interface between nanoscale electronic devices and biological systems enables interactions at length-scales natural to biology, maximizing communication between these two diverse yet complementary systems. Nanostructures and nanostructured substrates show enhanced coupling to artificial membranes, cells, and tissue. Such nano-bio interfaces offer better sensitivity and spatial resolution as compared to conventional planar structures. I will present the electrical properties of silicon nanowires (SiNWs) interfaced with embryonic chicken hearts and cultured cardiomyocytes. Utilizing the bottom-up approach enabled subcellular electrical recordings using the smallest reported device ever and thus exceeded the spatial and temporal resolution limits of other electrical recording techniques. I will discuss the synthetic breakthrough and novel fabrication required to realize the first new electronic measurement tool for intracellular measurements since patch-clamp of the 1970s – a truly three-dimensional nanoscale transistor. Finally, I will discuss my group’s current efforts to overcome the limits of cell-nanodevices interfaces. We are tackling these challenges through unique materials synthesis and device platform geometries. The exceptional synthetic control and flexible assembly of nanomaterials provides powerful tools for fundamental studies and applications in life science, and opens up the potential of merging active transistors with cells such that the distinction between nonliving and living systems is blurred.
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