The gastrointestinal (GI) tract is a complex environment comprised of the mouth, esophagus, stomach, small and large intestines, rectum and anus, which all cooperate to form the complete working GI system. Access to the GI using endoscopy has been augmented over the past several decades by swallowable diagnostic electromechanical devices, such as pill cameras.Research continues today and into the foreseeable future on new and more capable miniature devices for the purposes of systemic drug delivery, therapy, tissue biopsy, microbiome sampling, and a host of other novel ground-breaking applications. The purpose of this review is to provide engineers in this field a comprehensive reference manual of the GI environment and its complex physical, biological, and chemical characteristics so they can more quickly understand the constraints and challenges associated with developing devices for the GI space. To accomplish this, the work reviews and summarizes a broad spectrum of literature covering the main anatomical and physiological properties of the GI tract that are pertinent to successful development and operation of an electromechanical device. Each organ in the GI is discussed in this context, including the main mechanisms of digestion, chemical and mechanical processes that could impact devices, and GI motor behavior and resultant forces that may be experienced by objects as they move through the environment of the gut.

Microinjection protocols are ubiquitous throughout biomedical fields, with hollow microneedle arrays (MNAs) offering distinctive benefits in both research and clinical settings. Unfortunately, manufacturing‐associated barriers remain a critical impediment to emerging applications that demand high‐density arrays of hollow, high‐aspect‐ratio microneedles. To address such challenges, here, a hybrid additive manufacturing approach that combines digital light processing (DLP) 3D printing with “ex situ direct laser writing (esDLW)” is presented to enable new classes of MNAs for fluidic microinjections. Experimental results for esDLW‐based 3D printing of arrays of high‐aspect‐ratio microneedles—with 30 µm inner diameters, 50 µm outer diameters, and 550 µm heights, and arrayed with 100 µm needle‐to‐needle spacing—directly onto DLP‐printed capillaries reveal uncompromised fluidic integrity at the MNA‐capillary interface during microfluidic cyclic burst‐pressure testing for input pressures in excess of 250 kPa (n = 100 cycles). Ex vivo experiments perform using excised mouse brains reveal that the MNAs not only physically withstand penetration into and retraction from brain tissue but also yield effective and distributed microinjection of surrogate fluids and nanoparticle suspensions directly into the brains. In combination, the results suggest that the presented strategy for fabricating high‐aspect‐ratio, high‐density, hollow MNAs could hold unique promise for biomedical microinjection applications.

Ingestible devices have been gaining attention from the medical community due to their noninvasive use in diagnostics and treatment of the gastrointestinal (GI) tract. However, their passive locomotion limits their GI residency period. Ingestible sensors residing in the GI tract are capable of providing continuous data, while long-acting ingestible drug delivery systems can reduce medication nonadherence. This paper presents a comprehensive overview of the state-of-the-art, long-term ingestible devices (LTIDs). Additionally, this review summarizes the current status of ingestible devices that persist in the GI tract for a prolonged period, as well as their inhabitance mechanisms and applications. Also included are relevant information about the GI structure and design considerations for understanding the significance and challenges associated with LTIDs. Finally, we discuss several potential applications of the LTIDs for therapeutic intervention in the GI tract and monitoring the physiology and pathophysiology of the GI tract for an extended period.

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