Development and applicability of a soft and flexible robotic arm in digestive surgery

Introduction The oncologic adequacy of laparoscopy in digestive surgery is still controversial, especially in some technically demanding operations like Total Mesorectal Excision (TME). Even if standard robotic platforms, i.e. the da Vinci Surgical System, can improve dexterity and manouvrability of surgical instruments, there is no evidence supporting its use in digestive and rectal cancer surgery. The only multi-centre prospective RCT (ROLARR trial) suggests that robotic TME has no advantages compared to laparoscopic TME in terms of clinical and oncologic outcomes. A possible explanation of this lack of real advantages is that the articulation is possible only on the tip of the instrument. The opportunity to have a robotic platform with modular flexibility on the whole length of the arm could overcome technical limitations, improving results and allowing standardization and diffusion of the procedures. Methods The 7FP STIFF FLOP project was financed by the European Commission in order to develop a STIFFness controllable Flexible and Learn-able manipulator for surgical operations. Engineers were inspired by the tentacles of an octopus. A prototype was realized, consisting of multiple soft, pneumatically actuated threechamber segments. Additional chambers are integrated within the segments to allow their stiffening, employing an approach based on the concept of granular jamming. The STIFF-FLOP segments are actuated using pressure regulators and the stiffening chambers are interfaced via valves, applying a vacuum to the granules in the chambers. Sensors are embedded in the STIFF-FLOP modules to measure interaction forces (between the robot and its environment) and the robot’s configuration. A newly developed user interface, based on a Delta robot design, is used to move and position the tip of the STIFF-FLOP arm inside the abdomen. Signals obtained from sensors are fed back to the user interface console providing the operator with force feedback. The entire soft robot is equipped with a 4 mm in diameter centre-free lumen, which allows the passage of the electrical wires needed for the laparoscopic miniaturized optic system positioned at the tip of the robot. Phantom test The prototype was tested in order to assess learnability and satisfaction of the operators. The test was designed as a spatial motion task, consisting of movements between predefined target points clockwise and counter clockwise in a 3D phantom of the abdominal cavity. The participants were asked to conclude the task for the first time with the STIFF-FLOP prototype (SF1), then to repeat the task using conventional laparoscopic instrumentation (LAP) and finally to perform the task once more with the STIFF-FLOP arm (SF2). Surface EMG signals from the forearm muscles were recorded during the test. Results SF1 took a longer time than the other tasks, i.e. 36.4% more than LAP (p=0.0071). However, from SF1 to SF2 there was a 32.1% time reduction (p=0.0232). EMG amplitude analysis showed a higher overall average muscle activity during LAP. Moving from LAP to SF2 there was a 25.9% reduction in average muscle activity (p=0.0128). Cadaver test. The main objective of the test was to validate the compatibility of the system with human anatomy for laparoscopic TME and to determine whether the soft robot could represent a potential improvement compared to standard rigid laparoscopic instrumentation. The study was performed on two cadavers prepared according to the method described by Thiel. Results The use of the STIFF-FLOP camera allowed the surgeon to clearly visualize the inferior mesenteric vessels and the autonomic nerves that were subsequently spared from injury. The ability to smoothly follow the sacral curve due to the flexibility of the manipulator allowed the surgeons to perform a very precise dissection of the posterior part of the mesorectum. The same procedure was performed on both human cadavers, demonstrating the ease of use of the system. Completion times of the procedure were 165 and 145 min, respectively. No intraoperative complications were recorded. No technical failures were registered. Conclusion The STIFF FLOP flexible robotic arm is an intuitive technology that can be easily learned. The prolonged use of the STIFF FLOP manipulator is more comfortable than standard laparoscopic instrumentation and can be used for a long time without exhaustion. The system is compatible with human anatomy and allows to perform a standard surgical abdominal operation. The STIFF FLOP arm seems to improve visualization of the operatory field especially in narrow spaces like the pelvis.