Bioinspired Kirigami Capsule Robot for Minimally Invasive Gastrointestinal Biopsy

TL;DR

The paper tackles the lack of biopsy capability in wireless capsule endoscopy by introducing the Kiri-Capsule, a swallowable capsule that employs kirigami-based PI-film flaps actuated by a dual-cam mechanism to achieve depth-controlled GI tissue sampling with rotary scraping. The device integrates a compact, swallowable shell with a front-end dual-cam actuator that deploys sharp kirigami protrusions and captures tissue within internal cavities for histology-ready analysis. Through benchtop tensile and angular tests, motor calibration, and ex vivo porcine validation, the authors demonstrate a penetration depth of about $0.61$ mm and biopsy yields of approximately $10.9$ mg for stomach and $18.9$ mg for intestine, with tissue integrity preserved. The work establishes a safe and repeatable biopsy-capable capsule platform that bridges imaging and histology, while outlining paths toward untethered operation and multi-site sampling for clinical translation.

Abstract

Wireless capsule endoscopy (WCE) has transformed gastrointestinal (GI) diagnostics by enabling noninvasive visualization of the digestive tract, yet its diagnostic yield remains constrained by the absence of biopsy capability, as histological analysis is still the gold standard for confirming disease. Conventional biopsy using forceps, needles, or rotating blades is invasive, limited in reach, and carries risks of perforation or mucosal trauma, while fluid- or microbiota-sampling capsules cannot provide structured tissue for pathology, leaving a critical gap in swallowable biopsy solutions. Here we present the Kiri-Capsule, a kirigami-inspired capsule robot that integrates deployable PI-film flaps actuated by a compact dual-cam mechanism to achieve minimally invasive and repeatable tissue collection. The kirigami surface remains flat during locomotion but transforms into sharp protrusions upon cam-driven stretching, enabling controlled penetration followed by rotary scraping, with specimens retained in internal fan-shaped cavities. Bench tests confirmed that PI films exhibit a Young's modulus of approximately 20 MPa and stable deployment angles (about 34$^\circ$ at 15% strain), while ex vivo porcine studies demonstrated shallow penetration depths (median $\sim$0.61 mm, range 0.46--0.66 mm) and biopsy yields comparable to standard forceps (mean $\sim$10.9 mg for stomach and $\sim$18.9 mg for intestine), with forces within safe ranges reported for GI biopsy. These findings demonstrate that the Kiri-Capsule bridges passive imaging and functional biopsy, providing a swallowable, depth-controlled, and histology-ready solution that advances capsule-based diagnostics toward safe and effective clinical application.

Figures (11)

• Figure 1: Overview of the proposed kiri-capsule system. (a) The capsule is ingested and performs biopsy in the stomach and small intestine. (b) Working principle: the kirigami skin deploys via dual-cam expansion, followed by rotational scraping for tissue detachment. (c) Bioinspired kirigami scales mimic snake skin, enabling tissue collection on the flap surface and storage within fan-shaped internal cavities for subsequent histological analysis.
• Figure 2: Design and structural assembly of the kiri-capsule. (a) Fabrication of capsule body parts using a J826 stereolithography printer. (b) Exploded view showing major components, including fastener, cam 1, cam 2, rotating shell, stepper motor, back shell, central shell, rotating shaft, blade, and connecting rod. (c) Cross-sectional view of the assembled capsule with the anterior actuator driven by dual cams and a miniature stepper motor, while the posterior shells protect the motor and electronics.
• Figure 3: Working principle and cam kinematics of the kiri-capsule. (a) Initial top view. (b) Deployment and stretching of the kirigami flaps via cam-driven plate translation. (c) Rotational scraping as the plates follow the cam groove. (d) Kinematic model and geometric parameters of the profiled cam–expansion plate mechanism.
• Figure 4: Design and fabrication of the kirigami biopsy surface. (a) Kirigami pattern with parameters $\delta_0 = 0.5$ mm, $l_1 = 3$ mm, and $\gamma = 40^{\circ}$. (b) CAD model with strip dimensions $h = 7.5$ mm and $w = 50$ mm. (c) Laser cutting and engraving process using PI film. (d) Fabricated kirigami sheets with four different PI thicknesses ($t = 0.05, 0.1, 0.15, 0.2$ mm).
• Figure 5: Fabricated prototype of the kiri-capsule. All manufactured parts are displayed, including fastener, cam 1, cam 2, rotating shell, stepper motor, back and central shells, rotating shaft, blade, and connecting rod. The fully assembled capsule with kirigami skin and testing motor is also shown. The capsule dimensions are 17 mm in diameter and 22 mm in length, with a scale bar of 1 cm for reference.