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.

Table 2 Summary of the included studies reviewing robotic lower gastrointestinal endoscopy devices with pneumatic or hydraulic 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
Vucelic et al[35], 2006 (Israel)	Aer-O-scope (GI View Ltd, Ramat Gan, Israel): Workstation and Disposable unit consisting of a rectal introducer, supply cable, scanning balloon, scope and rectal balloon. The supply cable connects the disposable unit to the workstation with its joystick and is able to transmit air, water and suction	5.5 mm diameter, 2.5 m length	Pneumatic	White LED, 360 panoramic vision system with CMOS camera with a field of view of 57 degrees	Visualisation and safety	Semi-autonomous	In vivo: n = 12 Human, healthy volunteers	CIR is 83%. Median CIT is 14 min with an average procedure duration of 23 min. Analgesia required in 2 patients. 4 patients had submucosal petechial lesions. No complications at 30 d follow up
Gluck et al[36], 2016 (Israel)	Aer-O-scope (GI View Ltd, Ramat Gan, Israel): Workstation and Disposable unit consisting of a rectal introducer, supply cable, scanning balloon, scope and rectal balloon. The supply cable connects the disposable unit to the workstation with its joystick and is able to transmit air, water and suction	5.5 mm diameter, 2.5 m length	Pneumatic	White LED, 360 panoramic vision system with CMOS camera with a field of view of 57 degrees	Visualisation and safety	Semi-autonomous	In vivo: n = 56 Human, CRC screening	CIR is 98.2%. Mean withdrawal time is 14 min. Polyp detection rate of 87.5%. 0 patients had submucosal damage. No complications at 48 h follow up. Rated as excellent visualisation by endoscopists
Gluck et al[37], 2015 (Israel)	Aer-O-scope (GI View Ltd, Ramat Gan, Israel): Workstation and Disposable unit consisting of a rectal introducer, supply cable, scanning balloon, scope and rectal balloon. The supply cable connects the disposable unit to the workstation with its joystick and is able to transmit air, water and suction	5.5 mm diameter, 2.5 m length	Pneumatic	White LED, 360 panoramic vision system with CMOS camera with a field of view of 57 degrees	Visualisation and detection	Semi-autonomous	In vivo: n = 12 pigs with surgically simulated colonic ‘polyps’	A total of 36 Aer-O-scope and 24 colonoscopy procedures were performed. The Aer-o-scope visualised 94.9% of polyps compared to 86.8% with colonoscopy. This was significant (P = 0.002). Miss rates for polyps was 5.1% with Aer-O-scope and 13.2% (P = 0.002) with conventional colonoscopy. This significant difference is true for > 6 mm polyps
Cosentino et al[38], 2009 (Italy)	Endotics System [ERA Endoscopy S.r.l., Peccioli (Pisa), Italy]: Workstation with console and disposable flexible probe. The probe has 2 clampers to aid locomotion and a head (contains the camera, LEDs and channels for suction, irrigation and insufflation) a body and a tail	23-37 cm in length, 17 mm in diameter	Pneumatic	LED light source and CMOS camera with a field of view of 110 degrees	Visualisation and Safety	Semi-autonomous	Ex vivo: n = 1 porcine colon fixed to a human adult abdominal phantom. In vivo: n = 40 Humans, with a family Hx of CRC, known previous polyps and FOB positive requiring investigation	Ex vivo: The stress pattern was 90% less than with colonoscopy. In vivo: CIR was 27% for the endotics system compared to 82% with colonoscopy. The mean CIT was 57 min. The endotics system was described as less painful (0.9 vs 6.9). The endotics system has a higher diagnostic accuracy as it detected 2 polyps and 2 angiodysplastic lesions not identified with colonoscopy
Tumino et al[39], 2010 (Italy)	Endotics System (ERA Endoscopy S.r.l., Peccioli (Pisa), Italy): Workstation with console and disposable flexible probe. The probe has 2 clampers to aid locomotion and a head (contains the camera, LEDs and channels for suction, irrigation and insufflation) a body and a tail	25-43 cm in length, 17 mm in diameter	Pneumatic	LED light source and CMOS camera with a field of view of 110 degrees	Visualisation, sensitivity and specificity	Semi-autonomous	In vivo: n = 71 Humans, with a family Hx of CRC or polyps	Endotics system versus colonoscopy: CIR: 81.6% vs 94.3%. The average time for procedure completion: 45 min vs 23 min (P < 0.001). Patients requiring sedation: 0% vs 19.7% (P < 0.001). Endotics system for detecting polyps: Sensitivity: 93.3%; Specificity: 100%; Positive predictive value: 100%; Negative predictive value: 97.7%
Trecca et al[40], 2020 (Italy)	Endotics System [ERA Endoscopy S.r.l., Peccioli (Pisa), Italy]: Second generation system- Workstation with console and disposable flexible probe. The probe has 2 clampers to aid locomotion and a head (contains the camera, LEDs, chromoendoscopy and channels for suction, irrigation and insufflation) a body and a tail	23-37 cm in length, 17 mm in diameter	Pneumatic	LED light source, chromoendoscopy and CMOS camera with a field of view of 140 degrees	Learning curve, visualisation and diagnostic accuracy, safety	Semi-autonomous	In vivo: n = 55 Humans, requiring diagnosis, CRC screening or surveillance. Training progress was evaluated by comparing two consecutive blocks of patients i.e. group A (first 27) and group B (last 28)	CIR is 92.7%. Median CIT is 29 min. Median withdrawal time is 18 min. Polyp detection rate: 40%; Adenoma detection rate: 26.7%; Advanced neoplasm: 0%; Complication: 1.8%-bleeding with polypectomy; Successful polypectomy and hot biopsy coagulation for bleeding. Mean VAS pain/discomfort: 1.8. Learning curve assessment, Group A vs Group B: CIR: 85.2% vs 100%. Median CIT: 55 min vs 22 min (P = 0.0007). Median withdrawal time: 21 min vs 16 min
Tumino et al[41], 2017 (Italy)	Endotics System (ERA Endoscopy S.r.l., Peccioli (Pisa), Italy): Workstation with console and disposable flexible probe. The probe has 2 clampers to aid locomotion and a head (contains the camera, LEDs and channels for suction, irrigation and insufflation) a body and a tail	25-43 cm in length, 17 mm in diameter	Pneumatic	LED light source and CMOS camera with a field of view of 110 degrees	Visualisation and performance	Semi-autonomous	In vivo: n = 102 Humans, previously failed caecal intubation on colonoscopy	CIR was 93.1% and therefore had a 95% performance. Mean CIT was 51 min
Shike et al[42], 2008 (Italy/Israel/United States)	Sightline ColonoSight (Stryker GI, Dallas, Tex, Haifa, Israel): A reusable scope with LEDs and camera at the tip and steering dials proximally. Tips is covered by a disposable sleeve with 3 working channels for suction, irrigation, insufflation and instruments. Electropneumatic unit, control unit and video monitor	Not described	Pneumatic	LED light source and camera	Visualisation, diagnosis and treatment	Semi-autonomous	In vivo: 2 pigs–To assess safety in terms of bacterial transmission to the reusable scope with a disposable sleeve covering. In vivo: 178 Humans, healthy volunteers and various clinical indications for colonoscopy	In vivo, Pigs: E.coli and E. Fergusonii from scope handle, shaft and tip before the procedure: Nil growth. E.coli and E. Fergusonii from scope handle, shaft and tip after the procedure: Nil growth. E.coli and E. Fergusonii from sheath covering after the procedure: Heavy growth. In vivo, Humans: CIR is 90%. Mean CIT is 11.2 min. Diagnoses of diverticulosis, polyps, colitis, haemorrhoids, normal or other was given. Successful polypectomy, biopsy and argon plasma coagulation. No complications at 2 wk follow up
Ng et al[43], 2000 (Singapore)	EndoCrawler: Longitudinal and circumferential rubber bellow actuators joined in four segments with a bending tube to allow steering between the first two segments and vision module; Central hollow cavity for instruments, insufflation, irrigation and suction channels and CCD cables. These exit the proximal end as a flexible cable similar to a colonoscope; LabWindows user interface and joystick	28 mm in diameter, 420 mm length	Pneumatic	CCD camera and light source	Locomotion and visualisation	Direct robot operation	Ex vivo- Cadaveric colon. In vivo-Pig	Ex vivo: Clear visualisation of colonic wall. Speed: 200 mm/min however required external pushing and couldn’t progress beyond bends unless the head was deflected away from the colonic wall. In vivo: ‘Red out’ images throughout most of the robot’s journey. Average speed: 150 mm/min with external pushing. Unable to progress beyond an acute bend
Dehghani et al[44], 2017 (United States)	Pneumatically driven colonoscopy robot consisting of the robot (tip with camera, latex tubing, tethered camera and anal fixture) and external pneumatic circuit and electric circuit with laptop	Not described	Pneumatic	Camera	Locomotion feasibility and safety	Semi-autonomous	Ex vivo: 1.5 m porcine colon in human phantom. Tests repeated 5-14 times depending on analysis performed	Able to traverse the entire length 71.4% (10/14 trials). Able to traverse the entire length with additional bends 90.9% (10/11 trials). Robot speed of 28 mm/s (5 trials). Average CIT is 54.2 s. (5 trials). Maximum propulsive force is 6 N (44 mmHg) which is less than the safe intraluminal pressure of 80 mmHg. Balloon rupture led to damage including tearing of the porcine colon
Chen et al[45], 2019 (China)	Soft endoscopic device which consists of two gripper segments and one propulsion segment. Each segment contains two soft pneumatic balloons and two rigid connectors. The balloons are twisted in the gripper segments but linear in the propulsion segment. The connectors contain inner channels for air flow and instruments; Lab view interface. Air compressor with regulators, pressure sensors, valves and air pipes connected to the endoscopic device and a power source	The unactuated device is 95 mm in length and 22 mm in diameter.	Pneumatic	CCD camera	Locomotion and visualisation capability	Semi-autonomous	Ex vivo: Pig colon-one end fixed to a pipe, the other free. Colon placed in a horizontal position	Velocity to traverse the colon: 1 mm/s. Clear visualisation of the colonic mucosa
Coleman et al[47], 2016 (United Kingdom)	Hydraulic colonoscope system: A CV connected to extra-corporeal pumps and valves via a tether. The CV contains a magnetic tracker and is surrounded by a balloon which is flexible and may be inflated or deflated. The pump system is used to pump water into the colon behind the CV; Anal port and control system on HMI	CV dimensions not described. Tether: 1.8 m long, 6 mm in diameter	Hydraulic	No camera in this prototype however a dummy with a diameter if 11 mm and length of 25 mm is incorporated to simulate its presence	Comparison of CV locomotion under manual control or automatic control to colonoscopy	Direct or semi-autonomous	Ex vivo: Two 120 cm porcine colon placed in human abdominal phantom–6 trials per manual control, automatic control and colonoscopy	100% CV reached the caecum. CV vs colonoscopy: CIT: 3.95 vs 4.91 min (P = 0.43). Maximum force to the colon: 0.63 vs 2.2 N (P = 0.004). Maximum anal pressure: 1.53 vs 4.53 kPa (P = 1 × 10-7). Mean anal pressure: 0.65 vs 1.5 kPa (P = 0.0003). No difference in maximum or mean caecal pressure. Manual CV versus Auto CV: CIT: 2.11 vs 5.79 min (P = 0.02). Mean anal pressure: 1.86 vs 1.31 kPa (P = 0.03). No difference maximal anal pressure and maximum or mean caecal pressure

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; CV: Colonic vehicle.

Table 3 Summary of the included studies reviewing robotic lower gastrointestinal endoscopy devices with magnetic or hybrid 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
Valdastri et al[49], 2008 (Italy)	Swallowable wireless capsule with surgical clip, electromagnetic motor, 4 IPMs and a bidirectional communication platform. The EPM on a passive hydraulic arm is controlled manually by the user. A HMI controls clip deployment	Diameter of 12.8 mm and a length of 33.5 mm	Magnetic	No camera in this prototype however 300 mm3 space was left for future integration. Throughout the experiments the capsule was monitored with a flexible endoscope	Therapeutic clip application for bleeding	Direct robot operation	Ex vivo- Porcine colon placed in a model of the abdomen–10 trials. In vivo-1 pig	Ex vivo: Clip release: 100%; Clip release occurred instantly, and moving of the capsule was effective and fast. It took 2-3 min to position the capsule against the mucosa to be clipped. In vivo: Good locomotion and positioning with the EPM. The clip was released successfully onto the desired target. The clip remained in situ. The amount of tissue grasped was satisfactory
Ciuti et al[50], 2010 (Italy)	Magnetic wireless capsule with inertial and vision sensors and a set of IPM; External robotic arm with EPM and human machine interface. The working distance is 150 mm. The HMI is used to control the robotic arm and receives input from the capsule	Capsule: 40 mm in length, 18 mm in diameter	Magnetic	CMOS camera and 4 white LEDs	Visualisation, locomotion and learning curve	Intelligent teleoperation	Ex vivo: 500 mm porcine colon in human phantom model–40 trials (some insufflated and collapsed colons)	Insufflated colon: 100% of success rate in traversing the entire colon. Short learning curve (descriptive analysis) to drive the robotic arm. The average time required to traverse the colon was approximately 10 min. Collapsed colon: Capsule was able to travel only really short distances and manual assistance was required
Ciuti et al[51], 2009 (Italy)	Wired capsule with 3 IPMs and vision module; EPM either controlled manually or robotically via a robotic arm controlled by a HMI and controller. The working distance is 150 mm	14 mm in diameter and 38 mm in length	Magnetic	CMOS camera with illumination system	Robotic versus manual steering	Direct or Intelligent teleoperation	Ex vivo: 480 mm porcine colon in human phantom model–10 trials each for robot and manual arm steering. In vivo: 2 Pigs–5 trials each for robot and manual arm steering	Ex vivo: Robot versus manual steering: The mean completion time: 423 s vs 201 s (P < 0.01). The mean percentage of ‘4 mm white spherical targets’ reached: 87% versus 37% (P < 0.01). In vivo: Manual steering was usually faster, whereas manoeuvrability was better with robotic movement of the EPM (Descriptive analysis)
Carpi et al[52], 2011 (Italy/United States)	PillCam (Given Imaging Ltd, Israel) capsule covered in a magnetic shell; Two EPMs, a magnetic navigation system (Niobe, Stereotaxis, Inc, United States), a remote computer work-station and mouse. Fluoroscopic images were continuously acquired by means of a digital scanner to provide visual feedback regarding capsule manoeuvres	13 mm in diameter and length	Magnetic	Not described	Steering and localisation capability	Intelligent teleoperation	In vivo: Pig (Number of pigs and trials not described)	The capsule was freely moved within the colon. No complications
Gu et al[53], 2017 (China)	The MCCE system (Chongqing Jinshan Science & Technology Group Co, Ltd): Ingestible colon capsule with IPM and battery, an external magnetic manipulator with an EPM, and an image transmission system	Capsule measures 27.9 mm in length by 13.0 mm in diameter	Magnetic	Not described	Manoeuvrability, visualisation, diagnosis and safety	Direct robot operation	In vivo: n = 52 Human, CRC screening volunteers. Capsule movement was visualised via colonoscopy 5 h after ingestion	Average CIT: 3.63 h. Maneuverability of the capsule was good (94.3%) or moderate (5.77%). MCCE provided good-quality pictures and identified 6 positive findings (polyps, diverticulum) which were confirmed by colonoscopy. 78% reached the rectosigmoid colon in 25 min. All 57 volunteers were able to swallow the capsule and excreted the capsule within 2 d. Complications: 7 mild adverse events (abdominal discomfort, nausea, and vomiting) lasting 24 h. No complications at one week follow up
Valdastri et al[13], 2012 (Italy)	MAC consists of capsule-like frontal unit and a compliant multi-lumen tether. The frontal unit contains a vision module, an IPM, a magnetic field sensor, and two channels, one for lens cleaning and the other for insufflation/suction/irrigation or instrument passage. The IPM is controlled by an EPM mounted on a robotic platform. A control device allows the user to directly control the position of the EPM. The working distance is 150 mm. The tether connects to an external control box	Capsule: 11 mm diameter, 26 mm in length. Tether: 5.4 mm diameter, 2 m length	Magnetic	CCD camera with 120 degree field of view and 4 white LEDs	Diagnostic and treatment ability, safety, usability	Intelligent teleoperation	Ex vivo: 850 mm porcine colon in human phantom model–12 trials. In vivo: 2 Pigs–3 trials each	Ex vivo: Mean percentage of 5 mm coloured beads (polyps) detected was 85%. 100% successful removal (polypectomy loop) of identified beads. Mean completion time (inspection and bead removal) was 678 s. Mean bead removal time was 18 s. Good manoeuvrability, low friction from the tether on the colon wall and reliable feedback from the vision module. In vivo: No mucosal damage or perforation. Able to navigate around bends and folds, retroflexion of the camera and successful operation of the tools (loop, forceps, retrieval basket, grasper) without loss of magnetic link
Arezzo et al[54], 2013 (Italy)	Robotic arm with EPM controlled by HMI and controller; Wired capsule with 3 IPMs, camera, LEDs and magnetic sensor. The working distance is 150mm. The wired sheath allows transmission from the vision module and electric energy	Capsule: 13.5 mm in diameter and 29.5 mm in length. Wired sheath: 2 mm in diameter	Magnetic	CCD camera with 120 degree view and 6 white LEDs	Visualisation and diagnostic ability compared to colonoscopy	Intelligent teleoperation	Ex vivo: 850 mm porcine colon in human phantom model–22 trials each for capsule and colonoscope	Robot vs colonoscopy: CIR: 100% for both. Pin detection rate: 80.9% vs 85.8%. Procedure completion time (visualisation and diagnosis): 556 s vs 194 s (P = 0.0001). No difference in intuitiveness score
Slawinski et al[55], 2018 (United States/United Kingdom)	MFE with IPM, camera, illumination module, working channel for instruments, channel for irrigation and insufflation, EPM on robotic arm and HMI. Additional sensing, retroflexion and software control systems	Tip: 20.6 mm in diameter and 18.1 mm in length. Body: 6.5 mm in diameter	Magnetic	Camera and illumination module	Retroflexion ability	Intelligent teleoperation with task autonomy	In vivo: 1 Pig–30 trials	100% successful retroflexion manoeuvres with a mean time of 11.3 s. No acute tissue trauma or perforation
Martin et al[14], 2020 (United Kingdom)	MFE with an IPM, camera, an insufflation channel, irrigation channel, working channel for instruments and localisation circuit; A robotic arm with EPM; Robot operating system and joystick	Capsule: 20.6 mm in diameter and 18.1 mm in length. Tether: 6.5 mm in diameter	Magnetic	Camera and LED	Comparison of different degrees of autonomy for locomotion and novice usability	Direct robot or intelligent teleoperation or semi-autonomous	In vivo: 2 Pigs–3 trials for each MFE control and colonoscopy in the first pig and 4 trials for each in the second pig	First porcine model–colon distance of 45 cm: Task completion times for direct robot operation, teleoperation, semi-autonomous operation and conventional colonoscopy were 9 min 4 s, 2 min 20 s and 3 min 9 s and 1 min 39 s, respectively. Second porcine model-colon distance of 85 cm: Task completion times for, teleoperation, semi-autonomous operation and conventional colonoscopy were 8 min 6 s, 9 min 39 s and 3 min 29 s, respectively. It was not possible to reach the marker with direct robotic operation. Intelligent and semi-autonomous had NASA task force mean Index ratings lower/less demanding than colonoscopy or direct robot operation
Verra et al[57], 2020 (Italy)	Endoo system: An Endoo capsule with a IPM, soft tether connection with 4 working channels for suction, insufflation, irrigation and instruments; An external robot with EPM, force-torque sensor and movable platform, localisation system and medical workstation with a joystick complete the system. The robot with EPM is controlled via the workstation but can also be steered manually. The localisation system provides information on the capsule position and orientation	Tether: 160 cm long	Magnetic	Two CMOS cameras with 170 degree field of view, 4 white LEDs and 4 green/blue UV-LEDs	Visualisation, locomotion, diagnosis and safety	Semi-autonomous	Ex vivo: 100-120 mm porcine colon in human phantom model	Ex vivo Endoo alone: 100% success rate in operating channel (use of polypectomy snares, biopsy forceps and needles). 100% success rate for target approach tests (using these instruments to target a polyp). Ex vivo Endoo (21 trials) vs colonoscopy (13 trials): Completion rate: 67% vs 100%. Interaction forces: 1.17 N vs 4.12 N. Polyp detection rate: 87% vs 91% (P = 0.16). Mean CIT: 9.5 min vs 3.5 min. The magnetic link was lost an average of 1.28 times per complete procedure, but it was restored in 100% of cases
Simi et al[58], 2010 (Italy)	Wireless endocapsule with legged mechanism (3 legs), DC motor, battery, small IPMs which interacts with an EPM. LabVIEW HMI is present and is also compatible with voice commands	14 mm in diameter, 44 mm in length.	Hybrid- Electromechanical and Magnetic	No camera in this prototype however 450 mm3 space was left for future integration. Throughout the experiments the capsule was monitored with a gastroscope	Locomotion and lumen dilatation	Semiautonomous	Ex vivo: 20 cm porcine colon–10 trials. In vivo: 4 pigs–10 trials. Capsule was placed 40 cm from the anus and expected to travel towards the anus	Ex vivo: Ability to travel 20 cm in 10 min: 70%. Average time to traverse 20 cm and number of leg activations: 4 min and 5 mechanism activations. Average speed: 5 cm/min. In vivo: Ability to travel 40 cm in 20 min: 60%. Average time to traverse 40 cm and number of leg activations: 5 min and 5 activations. Average speed: 8 cm/min
Nouda et al[59], 2018 (Japan)	Self-propelling capsule endoscope (SPCE) consisting of a silicon resin fin with micro-magnet connected to the PillCam SB2 capsule; External magnetic field generating controller (Minimermaid System), human interface with joystick	45 mm in length and 11 mm in diameter	Hybrid- Mechanical and Magnetic	Camera with 156 degree field of view	Locomotion and safety	Semi-autonomous	In vivo: 1 Human	The SPCE could swim smoothly in forward and backward directions but had difficulty bypassing bends. No acute complications

IPM: Internal permanent magnet; EPM: External permanent magnet; HMI: Human machine interface; LEDs: Light emitting diodes; CMOS: Complementary metal-oxide-semiconductor; CIT: Caecal intubation time; CIR: Caecal intubation rate; CCD: Charged coupled device; MCCE: Magnetic controlled capsule endoscopy; MFE: Magnetic flexible endoscope.