Untethered Microgrippers for Biopsy in the Upper Urinary Tract

Abstract

Untethered microrobots offer the possibility to perform medical interventions in anatomically complex and small regions in the body. Presently, it is necessary to access the upper urinary tract to diagnose and treat Upper Tract Urothelial Carcinoma (UTUC). Diagnostic and treatment challenges include ensuring adequate tissue sampling, accurately grading the disease, achieving completeness in endoscopic treatment, and consistently delivering medications to targeted sites. This work introduces microgrippers (µ-grippers) that are autonomously triggered by physiological temperature for biopsy in the upper urinary tract. The experiments demonstrated that µ-grippers can be deployed using standard ureteral catheters and maneuvered using an external magnetic field. The μ-grippers successfully biopsied tissue samples from ex vivo pig ureters, indicating that the thin-film bilayer springs' autonomous, physiologically triggered actuation exerts enough force to retrieve urinary tract tissue. The quality of these biopsy samples is sufficient for histopathological examination, including hematoxylin and eosin (H&E) and GATA3 immunohistochemical staining. Beyond biopsy applications, the µ-grippers' small size, wafer-scale fabrication, and multifunctionality suggest their potential for statistical sampling in the urinary tract. Experimental data and clinical reports underscore this potential through statistical simulations that compare the efficacy of µ-grippers with conventional tools, such as ureteroscopic forceps and baskets.

Keywords: biopsy microrobot; microgripper; microrobotics; microsurgery; shape changing device.

Figure 1.. Conceptual schematics showing microgrippers (μ-grippers) operating as biopsy tools in the upper urinary tract.

(a) Biopsy μ-grippers are deployed into the ureter of the upper urinary tract using a ureteroscopy procedure. A long, flexible ureteroscope traverses through the urethra and bladder, reaching the pathological site in the ureter. (b) At the pathological site, the μ-grippers are distributed into the ureter lumen from a catheter or the working channel of a ureteroscope. (c) After the μ-grippers self-fold and capture tissue samples, a magnet-mounted ureteroscope retrieves them. (d) The μ-grippers self-fold in response to body temperature grasp on the ureter. On retrieval by a magnet, the μ-grippers sample a cluster of urothelial tissue. The tissue samples are collected and sent for (e) histopathology studies, including histological slices and genomic analysis to diagnose diseases such as Upper Tract Urothelial Carcinoma (UTUC).

Figure 2.. Design, fabrication, and actuation of biopsy μ-grippers.

(a) Schematic showing the structural multilayer design of a μ-gripper consists of three major components: differentially stressed bilayer, panel layer, and thermo-responsive layer. (b) Photograph of tweezer holding a piece of a silicon wafer section with multiple as-fabricated μ-grippers. This wafer section with an area of around 2 cm² accommodates about 143 μ-grippers. (c). Microscopic image of μ-grippers after stress and panel layer patterning showing the arrangement of the rigid panels and foldable hinges. (d). Microscopic image of as-fabricated μ-grippers after wax trigger patterning and the entire fabrication process. (e) Microscopic image of released μ-grippers in saline. (e) Microscopic image of actuated μ-grippers in saline after being warmed to body temperature. The μ-grippers self-folded into hexagonal cage-like structures. Scale bars are 200 μm.

Figure 3.. Autonomous operation and tissue penetration of the biopsy μ-grippers on ex vivo pig urothelial tissue.

Microscopic images of (a) μ-grippers on ex vivo pig urothelial tissue next to a ureteroscopic biopsy forceps (Piranha^™, Boston Scientific) with open jaws. The forceps are significantly (5x) larger than a μ-gripper. Microscopy images of (b) μ-grippers on ex vivo pig urothelial tissue before actuation, (c) μ-grippers gripping onto ex vivo pig urothelial tissue after being warmed to body temperature, (d) biopsy forceps gripped a cluster of pig urothelial tissue. Scale bars for panels a-d are 1 mm. (e) Top view microscopy image of an actuated μ-gripper with arms penetrating the urothelial tissue; the white dashed lines marked the insertion boundary. (e) Side view of an actuated μ-gripper with arms penetrating the urothelial tissue; the white dashed lines marked the insertion boundary. Scale bars from panels e and f are 200 μm.

Figure 4.. Delivery studies of biopsy μ-grippers through ureteral catheters.

(a) Conceptual schematic showing the μ-gripper deployment system used to transport μ-grippers to the upper urinary tract. The μ-grippers were delivered through a ureteral catheter at a controlled air pressure using a microfluidic flow control system (MFCS). (b). Photograph showing around 200 μ-grippers in an MFCS vial with a ureteral catheter attached. The scale bar is 5 mm. (c). Plot showing the μ-grippers passage rate when being delivered through three different types of ureteral catheters. The schematics on each bar depict the size and shape of the corresponding ureteral catheter. Each test contains 3 samples (n =3), and a t-test was used to determine the difference. Differences were labeled as ns if not significant.

Figure 5.. Magnetically controlled μ-gripper multimodal motion and biopsy transportation.

(a) Conceptual schematic illustrating remote control of a μ-gripper in the upper urinary tract via an external magnetic field. Before actuation, the μ-gripper can be moved and tumbled magnetically. After gripping tissue, the μ-gripper can tear and transport samples under magnetic control. (b) A series of microscopic snapshots showing μ-gripper moves on ex vivo pig urothelial tissue controlled by an external moving magnet. (c) A series of microscopic snapshots showing μ-gripper tumbles on ex vivo pig urothelial tissue controlled by an external rotating magnet. Scale bars in panels b and c are 1 mm. (d) A series of microscopic snapshots showing a gripped μ-gripper holds and transports a cluster of pig urothelial tissue under the control of an external moving magnet. The insert in the first panel shows the zoomed view of the μ-gripper gripping the tissue cluster. The scale bar for panel d is 2 mm; for insert, the scale bar is 500 μm.

Figure 6.. Biopsy of the ex vivo pig ureter using untethered μ-grippers.

(a) Photo of a piece of blue-stained ex vivo pig ureter with μ-grippers deployed within it. The scale bar is 1 cm. (b). Microscopic image showing actuated μ-grippers gripped on the blue-stained urothelial tissue. The insert shows a zoomed-in view. We selected one of the ureter samples, cut it open, and examined the μ-grippers gripping performance. The scale bar for panel b is 1 cm; for insert, the scale bar is 200 μm. (c) Microscopic image showing a magnet cylinder with μ-grippers retrieved from the ureter sample. (d) Microscopic image of a group of μ-grippers holding blue-stained urothelial tissue samples. Scale bars for panels c and d are 1 mm. (e) Microscopic image of a μ-gripper captures a cluster of blue-stained urothelial tissue. (f) Fluorescent microscopic image of a μ-gripper captures a cluster of DAPI-stained urothelial tissue. The massive amount of blue fluorescent nuclei suggests that the μ-grippers capture adequate tissue samples. (g) Microscopic image of H&E-stained urothelial tissue sample. This sample shows urothelial cells with clearly visible purple nuclei, pink extracellular matrix, and cytoplasm. Blue staining from the tissue marking dye applied earlier on the surface of the ureter lumen was observed, indicating the μ-grippers’ capacity to penetrate and capture multiple layers of urothelial cells. (h) Microscopic image of GATA3 immunohistochemical stained urothelial tissue sample. The brown dots in the nuclei indicate a weakly positive result for GATA3 expression, confirming the biopsy’s urothelial origin.

Figure 7.. Simulation comparison of μ-grippers statistical biopsy performance with existing upper urinary tract biopsy tools.

(a) Schematic showing the concept of statistical sampling using μ-grippers in the ureter. A single μ-gripper can obtain a biopsy with a similar size to the μ-gripper. A large number of μ-grippers distributed on the ureter mucosa increases the chance of hitting the lesion, especially for small and invisible lesions. (b). Schematics showing the existing ureteroscopic biopsy tools and their corresponding biopsy sample sizes reported from clinical studies. (c, d) Plots showing the simulated percentage sampling success rate by different sampling tools as a function of lesion sizes. The μ-grippers are assumed to be randomly distributed. For the existing tools, 3 biopsies were taken for each sampling procedure per clinical study. (c). Simulation results for spotted sampling from a 5 cm section of the ureter. (d). Simulation results for statistical sampling in the whole ureter (25 cm). In this simulation, we included a combined 60% failure rate, the results representing only 40% of the delivered μ-grippers collected tissue samples.