Design and Fabrication of an Elastomeric Unit for Soft Modular Robots in Minimally Invasive Surgery

Summary

This paper describes the design and fabrication of a soft unit for surgical manipulators. The base module includes three flexible fluidic actuators to achieve omnidirectional bending and elongation, and a granular jamming-based mechanism to enable stiffness control. A complete mechanical characterization is also reported.

Abstract

In recent years, soft robotics technologies have aroused increasing interest in the medical field due to their intrinsically safe interaction in unstructured environments. At the same time, new procedures and techniques have been developed to reduce the invasiveness of surgical operations. Minimally Invasive Surgery (MIS) has been successfully employed for abdominal interventions, however standard MIS procedures are mainly based on rigid or semi-rigid tools that limit the dexterity of the clinician. This paper presents a soft and high dexterous manipulator for MIS. The manipulator was inspired by the biological capabilities of the octopus arm, and is designed with a modular approach. Each module presents the same functional characteristics, thus achieving high dexterity and versatility when more modules are integrated. The paper details the design, fabrication process and the materials necessary for the development of a single unit, which is fabricated by casting silicone inside specific molds. The result consists in an elastomeric cylinder including three flexible pneumatic actuators that enable elongation and omni-directional bending of the unit. An external braided sheath improves the motion of the module. In the center of each module a granular jamming-based mechanism varies the stiffness of the structure during the tasks. Tests demonstrate that the module is able to bend up to 120° and to elongate up to 66% of the initial length. The module generates a maximum force of 47 N, and its stiffness can increase up to 36%.

Introduction

Recent trends in the medical field are pushing for a reduction in the invasiveness of surgical operations. Minimally Invasive Surgery (MIS) has been successfully improved in the last few years for abdominal operations. MIS procedures are based on the use of tools introduced through four or five access points (trocars) placed on the abdominal wall. In order to reduce the number of trocars, the instruments can be inserted by Single Port Laparoscopy (SPL) or Natural Orifice Translumenal Endoscopic surgery (NOTES)¹. These procedures prevent external visible scars, but increase the difficulty for the clinicians in executing the surgery. This limitation is mainly....

Protocol

Note: This protocol describes the fabrication phases of a single module, which includes the fluidic chambers, stiffening channel, actuation pipelines and external sheath. The following procedure has to be executed under a fume hood and wearing lab coat and gloves for safety reasons. As previously mentioned, the fabrication process of the elastomeric unit is based on the sequential use of molds designed with CAD software. They are composed of the 13 pieces shown in Figure 2 and listed in Table 1.

1. Preparation of the Silicone

1. Weigh 12 g of part A and 12 g of part B in the same plastic glass or P....

Results

The various phases of the fabrication, described in the Protocol, are illustrated in Figure 3.

In order to evaluate the effectiveness of the technique and the outcomes of the final prototype, the module was tested in different working conditions. An external setup allows control of both the actuation and stiffness of the module. It includes an air compressor that activates three valves. They are connected to the siliconic tubes integrated in the chambers and allow their pressu.......

Discussion

The technique described in this protocol enables the fabrication of a pneumatically actuated soft unit usable for modular compliant structures. Thanks to the design of the molds and their simple assembly, it is possible to fabricate one complete module in about 4 hours with 7 main steps. The process of fabrication involves specific materials, which are easily available, and work should be carried out under a fume hood. An external set up including air valves, air compressor and vacuum pump is necessary to activate the mo.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Ecoflex 00-50 Trial Kit	SmoothOn		Used for the fabrication of the soft unit, combining equal amounts of liquid parts A (the base) and B (the catalyst)
Latex	Antichità Belsito		Used for the fabrication of the granular jamming membrane
Peroxide-Cured Silicone Tubing	Cole Parmer	T-06411-59	Used for actuating the chambers and applying vacuum
PET expandable braided sleeving	RS	408-249	Used for the fabrication of the external braided sheath
Silicone Rubber	Momentive	127374	Used to fix the actuation tubes to the module
Parafilm	Cole Parmer	EW-06720-40	Used to fix the latex membrane to the vacuum tube
Fume hood Secuflow	Groupe Waldner		Working space
Precision scale	KERN EW		Used to weight silicone, latex and coffee powder
Oven/degasser	Heraeus		Used to degass the silicone and reduce its cure time
Vacuum pump	DVP Vacuum Technology		Used to apply vacuum to the latex membrane