Abstract
In the medical field and in soft robotics, flexible devices are required for safe human interaction, while rigid structures are required to withstand the force application and accuracy in motion. This paper aims at presenting controllable stiffness mechanisms described in the literature for applications with or without shape-locking performances. A classification of the solutions based on their working principle is proposed. The intrinsic properties of these adaptive structures can be modified to change their mechanical characteristics from a geometrical point of view or equivalent elastic properties (with internal mechanisms or with a change in material properties). These solutions are compared quantitatively, based on selected criteria linked to the medical field as the stiffness range, the activation time and the working conditions. Depending on the application and its requirements, the most suitable solution can be selected following the quantitative comparisons. Several applications of these tunable stiffness structures are proposed and illustrated by examples of the literature.
Highlights
Soft tools with controllable stiffness performances can have applications in the medical field, as in Minimally-Invasive Surgery (MIS) in which the endoscopic tools are mainly used [1]
Some solutions can be deformed in the flexible state and locked in this configuration by switching to the stiff state, while others are limited to a given shape
Two main families of controllable stiffness solutions based on intrinsic properties of the structure can be defined: the first is based on the change of the second moment of the area of the structure, and the second is based on the change of elastic properties of the structure
Summary
Soft tools with controllable stiffness performances can have applications in the medical field, as in Minimally-Invasive Surgery (MIS) in which the endoscopic tools are mainly used [1]. Rigid tools are required during medical interventions to transmit force during punctures, biopsies or grasping tasks, for supporting other tools and to bring accuracy in positioning [2]. These needs can be illustrated with the problems encountered during colonoscopies when the colonoscope forms loops in the colon [3]. The guidewire has to be flexible enough to reach the stenosis, having followed a possible tortuous path through the blood vessels Once it has reached the stenosis and in order to pass through the occlusion, it requires a rigid support to avoid buckling or deformation due to the force application.
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