Application of robotic technologies in lower gastrointestinal tract endoscopy: A systematic review

Table 1 Summary of the included studies reviewing robotic lower gastrointestinal endoscopy devices with electromechanical actuation

Ref.	Design and actuation components of evaluated robotic system(s)	Endoscope and/or capsule dimensions	Mode(s) of actuation	Mode(s) of illumination and luminal visualisation	Capabilities evaluated	Degree of robot navigational assistance	Study methodology	Main findings
Rösch et al[21], 2008 (Germany)	InvendoscopeTM SC40 (Invendo Medical, Kissing, Germany): Colonoscope with an inverted sleave mechanism, propulsion connector, endoscope driving unit, hand-held control unit, 3.2 mm working channel	18 mm diameter, 170-200 cm length.	Electromechanical	Three white LEDs, CMOS vision chip with a field of view of 114 degrees	Visualisation	Direct Robot control	In vivo: n = 34 Human, heathy volunteers	CIR of 82%. Pain free procedure in 92% of cases. Mean pain score 1.96/6. 0% required sedation. No complications
Groth et al[23], 2011 (Germany)	InvendoscopeTM SC40 (Invendo Medical, Kissing, Germany): Colonoscope with an inverted sleave mechanism, propulsion connector, endoscope driving unit, hand-held control unit, 3.2 mm working channel	18 mm diameter, 170-200 cm length	Electromechanical	Three white LEDs, CMOS vision chip with a field of view of 114 degrees	Visualisation, Diagnosis, Treatment	Direct Robot control	In vivo: n = 61 Human, Asymptomatic individuals at average risk of CRC willing to undergo CRC screening	CIR of 98.4%. Sedation required in 4.9%. Median CIT of 15 min. Mean pain/discomfort score: 2.6. 32 of 36 polyps successfully removed with snare or forceps. 1 flat polyp required referral for conventional colonoscopy and 3 polyps seen on introduction could not be found on withdrawal
Eickhoff et al[24], 2007	The NeoGuide Endoscopy System (NeoGuide Endoscopy System Inc., Los Gatos, CA United States): Scope with 16 actuator segments, steering dials to control the tip and Tip position sensor. External position sensor, support arm, 3.2 mm working channel, video processor and control unit. Computed 3D mapping of the colon	173 cm in length, 14-20 mm in diameter	Electromechanical	Conventional CCD camera	Visualisation, safety and ease of use	Semi-autonomous	In vivo: n = 10 Humans requiring screening or diagnosis	CIR is 100%. Median CIT is 20.5 min. Adenomas successfully removed with snare or forceps. No acute colonic trauma (bleeding, perforation, submucosal petechiae). No complications at 30 d follow up. Detection and correction of looping is 100%. Physician satisfaction is 100%
Valdastri et al[25], 2009 (Italy)	Legged capsule consisting of two leg sets (six legs each with hooked round tips), 2 motors, bidirectional communication platform, HMI in LabVIEW	11 mm diameter by 25 mm long	Electromechanical	No camera in this prototype	Locomotion and safety	Semi-autonomous	Ex vivo- Porcine colon between two fixtures and 140 cm porcine colon placed in an abdominal phantom	Porcine colon between two fixtures: The 12-legged capsule distended the colon in a uniform manner. Maximum pulling force of the capsule on the colon wall: 0.2 N. Porcine colon in abdominal phantom: Capsule was able to traverse the complete length of the colon, Average speed was 5 cm/min
Lee et al[26], 2019 (Korea)	Legged robotic colonoscope, reel controller with external motor, Bowden cable and control system. The robot has 6 legs covered with silicone	Robot: 16 mm diameter (33 mm with legs deployed) by 49 mm in length. Bowden cable: 5 mm diameter by 1 m length	Electromechanical	Not described	Locomotion and safety	Autonomous	Ex vivo: Excised porcine colon	Locomotion velocities: Straight path: 9.5 mm/s. Incline at 30 degrees: 7.1 mm/s. Incline at 60 degrees: 5.1 mm/s. No mucosal damage or perforations
Trovato et al[27], 2010 (Japan)	Robotic colonic endoscope consisting of a front body with a clockwise helical fin, DC motor and rear body with an anti-clockwise helical fin; Reinforcement learning algorithm (Q-learning and State-Action-Reward-State-Action)	170 mm in length, 30 mm in diameter	Electromechanical	Not described. No Visualisation module in this prototype	Locomotion and safety	Semi-autonomous	Ex vivo: < 1 m Swine colon (6 specimens) attached to the inside of a cylindrical plastic tube. In vivo: Swine colon–10 trials, 5 min each	Ex vivo: Best travelled distance around 70 cm. Average velocity with Fixed input (15 trials): 21.47 mm/min. Average velocity with SARSA (18 trials): 40.71 mm/min (P = 0.02). Average velocity with Q-learning (21 trials): 36.05 mm/min (P = 0.039). Robot with learned algorithms are more likely to pass through bends/tight passages. In vivo: Speed 11 mm/min. Best travelled distance is 55 mm. No acute mucosal damage
Kim et al[28], 2010 (Korea)	Paddling-based capsule endoscope: Capsule with camera module, DC motor and 6 paddles. Tether consisting of 4 cables extend from the capsule to the external controller	Capsule: 15 mm in diameter and 43 mm in length. Tether: 2 m	Electromechanical	A camera module with 125 degree field of view and which transmits images at 10 frames per second	Locomotion and safety	Semiautonomous	Ex vivo: Porcine colon set up in 2 positions (sloped 27.5 degrees, straight length 35 cm or sloped 37.5 degrees, straight length 62 cm). In vivo: 1 pig–8 trials	Ex vivo: Velocity in sloped 27.5 degrees, straight length 35 cm colonic segment: 36.8 cm/min. Velocity in sloped 37.5 degrees, straight length 62 cm colonic segment: 37.5 cm/min. In vivo: Mean velocity: 17 cm/min over 40 cm length. Complications: Pinpoint erythema on colonic mucosa seen
Wang et al[29], 2006 (China)	Worm like robotic endoscope system consisting of a microrobot, controller and personal computer. The microrobot consists of a head cabin with the visualisation module and 3 mobile cells connected to the controller by an electric cable. Each mobile cell contains a linear electromagnetic driver	9.5 mm in diameter, 120 mm in length	Electromechanical	CCD camera and lights	Locomotion	Semi-autonomous	Ex vivo: Porcine colon	Robot travels the colon length (112 cm) in 7.3 min. Robot able to move forward, backward or remain static based on controller commands
Wang et al[30], 2007 (China)	Worm like robotic endoscope system consisting of a microrobot, controller and personal computer. The microrobot consists of a head cabin with the visualisation module and 3 mobile cells connected to the controller by an electric cable. Each mobile cell contains a linear electromagnetic driver. Additional deflection mechanism after the head cabin controls the camera’s pose	10 mm in diameter, 110 mm in length	Electromechanical	CCD camera and lights	Locomotion	Semi-autonomous	Ex vivo: Porcine colon	Robot travels the colon length (112 cm) in 7.3 min
Wang et al[31], 2017 (China)	Worm like robotic endoscope consisting of a head cabin and three independent segments; each segment is composed of a linear locomotor with micromotor, turbine-worm and wire wrapping-sliding mechanism. The robot is entirely covered by an external soft bellow	13 mm diameter, 105 mm in length	Electromechanical	Not described	Locomotion and safety	Semi-autonomous	In vivo: Porcine colon	Greater speed in straight rather than curved paths. Speed ranges from 1.62-2.2 mm/s. Robot travels the entire colon in 119 s. Distance is not specified. No breakage or damage to the colonic mucosa
Naderi et al[32], 2013 (Iran)	Robot with a camera, 2 clampers, 5 discs and 15 springs allowing bending and steerability, 3 motors; Driving kit, HMI in MATLAB and Joystick	19 mm in diameter, 180 mm in length.	Electromechanical	Camera	Locomotion and safety	Semi-autonomous	Ex vivo: Sheep colon, 2 positions: Straight or with an 84 degree bend	Velocity: Straight path: 18.4 cm/min. Curved path: 10.5 cm/min. No significant trauma
Lee et al[26], 2019 (Korea)	3 elastic PTFE caterpillars with worm gear, steering module, camera module, flexible shaft with steering knobs and wires, external motor and controller	130 mm in length, 55 mm maximum diameter	Electromechanical	LED lamps and camera	Locomotion and visualisation	Direct robot operation	Ex vivo: 1 m excised porcine colon placed in an abdominal phantom. In vivo: 1 mini pig	Ex vivo: Velocity of the robotic colonoscope: 3.0 mm/s; CIR is 50%; CIT is 8.55 min. In vivo: Failed caecal intubation with difficulty travelling through fluid and faecal material
Formosa et al[34], 2020 (United States)	Endoculus- treaded (4) robotic capsule endoscope consisting of an inertial measurement unit, two motors, air/water channels, a tool port, flexible tether connected to a control board and laptop with controller	2 m tether	Electromechanical	CMOS camera with adjustable LEDs	Locomotion, visualisation and channel function	Direct robot operation	Ex vivo: 40 cm excised porcine colon. In vivo: 1 pig	Ex vivo: Able to move in forward/reverse directions at 40 mm/s and whether the colon was collapsed or inflated. Also able to pass tight haustra and make turns. In vivo: Camera, insufflation, irrigation and biopsy tools functioned as expected

LEDs: Light emitting diodes; CMOS: Complementary metal-oxide-semiconductor; CIR: Caecal intubation rate; CIT: Caecal intubation time; CCD: Charged coupled device; HMI: Human machine interface.