In a recent review published in the journal Gut, researchers discussed using smart and robotic capsules for sampling and sensing the gut. They described the benefits and limitations of these miniaturized devices while identifying their potential applications in personalized medicine, diet, and the early diagnosis of several chronic gut ailments, including cancer.
The human gastrointestinal (GI) tract is up to nine meters long, with four structurally and functionally distinct segments, namely the esophagus, the stomach, the small intestine, and the large intestine. The tract is colonized by diverse bacteria, fungi, and archaea, a collection of about 1013 microorganisms. The gut microbiota ferment fiber, provide essential nutrients and are now known to be markers of health.
Dysbiosis of these organisms is reported to be associated with inflammation, aging, as well as diseases such as diabetes, obesity, metabolic diseases, arterial dysfunction, and cancer. Fecal sample collection is the most common noninvasive method employed to study gut microbiota.
However, the sample collected from feces may not accurately describe the microflora of the disease site, thus missing major spatiotemporal information. Biopsies may not be reliable methods for sampling microorganisms and are limited by procedural risks.
Since the advent of tiny, ingestible capsule endoscopes in the early 2000s, our understanding of the gut, the associated microflora, and their links to overall health has greatly improved. This review focuses on the latest advances in gut sensing and sampling and their potential role in diagnosing and treating diseases and monitoring health.
Smart capsules for gut sensing
While the diagnosis of gut-related diseases in the earlier era widely relied upon the use of X-rays, endoscopy, and surgery, the field gradually progressed to the use of swallowable capsules about 3 cm x 1 cm in size, that could transmit information on the pH, temperature, and pressure of the gut. These devices have evolved greatly since then, overcoming the challenges related to their movement inside the gut as well as their adverse effects.
Today’s commercially available smart capsule endoscopes can transmit images of the gut lining, finding clinical applications in sensing, drug delivery, and monitoring gut diseases. Smart capsules, including the Bravo reflex capsule, the alphaOne capsule, and the Heidelberg pH capsule, have been used to measure the pH of various sections of the GI tract. Smart capsules such as eCelsius and myTemp can be used to continuously measure the core temperature of the gut, especially in athletes during exercise, which is not possible conventionally.
The measurement of peristaltic forces (which also govern the in vivo movement of the capsules) is easily possible using these devices. SmartPill and Bravo capsules have been used to measure pressure and the transit time of food inside the gut to sense conditions such as constipation, achalasia, and dysmotility. The Atmo Gas Capsule was tested in humans for its ability to measure gases and identify the origin of gas generation inside the gut.
Robotic capsules for gut-sampling
Despite these benefits, smart capsule-based imaging does not capture the wealth of information available inside the human gut. Robotic capsules address this gap by enabling sample collection in the form of tissues and/or fluids and allowing their detailed examination post-retrieval.
Robotic capsules, equipped with blades and razors in cylindrical, barb-based, scissor-based, and magnet-based designs, have been used to collect small tissue samples via biopsy of the intestinal wall, providing an edge over traditional tethered devices.
Additionally, robotic capsules may be designed to extract content samples from the gut in the form of fluids, mucus, microflora, and exfoliates. Several of these designs have been patented since 1957.
Laboratory and commercial prototypes
Three kinds of laboratory prototypes are described in the literature: passive, active, and dynamic. Passive capsules may be osmotic or gelatin-based; their coating dissolves when contacting the target fluid in the gut lumen. However, they are limited by a longer sampling time and lack of control within the gut.
Active sampling capsules use microelectromechanical systems (MEMS) that trigger the sampling process at the target site. They may be motor-based, vacuum suction-based, or magnetic actuation-based in their mechanism of action. While active and passive capsules sample content from the gut lumen, dynamic capsules can also sample the intestinal wall.
Although dynamic capsules can scrape and extract microbial samples from the mucosal layer, a site previously unexplored, in vivo trials are yet to be conducted to gauge their effectiveness.
Smart and robotic capsules have allowed minimally invasive, rapid, and accurate measurement of various gut parameters. However, multitasking capsules that can sense and sample various sites and measure several gut parameters in a single run are yet to be developed and tested. Further, auto-location of the target site and functioning in a stand-alone manner are desirable features that could be introduced in these capsules. Developing low-cost options and easing their operation via computers and the internet could lower the healthcare burden associated with using these devices in medical facilities and at-home settings.
In conclusion, the development of advanced ingestible capsules in the future for sensing and sampling the gut could aid the early diagnosis of diseases while allowing easy monitoring of health among patients, thereby improving clinical outcomes.