Multi Jet Fusion of Nylon-12: A Viable Method to 3D-print Concentric Tube Robots?

Abstract

Concentric Tube Robots (CTRs) are needle-sized flexible manipulators well suited for minimally invasive surgery. The body of a CTR consists of a set of pre-curved tubes nested telescopically within each other, as shown in Fig. 1. Each tube can be translated and rotated independently. During actuation, the tubes interact elastically with each other, creating tentacle-like bending motions. CTRs are usually made of superelastic Nickel-Titanium (Nitinol), a metal alloy capable of withstanding large amounts of strain (typically up to 6-8%) without undergoing plastic deformation. Strain recovery is key for the operation of a CTR, as it enables the body of the robot to undergo substantial yet reversible bending. In recent years, different groups have investigated the viability of 3D-printing CTRs using materials other than Nitinol [1-2]. This research is motivated by the fact that Nitinol can be a challenging material to work with: to build CTRs, Nitinol tubing must first be formed into a prescribed curved shape through an annealing treatment, which, as previous work has shown, can be complex, time-consuming, and error-prone [3]. Correct execution of this process requires specialized expertise as well as equipment that may not be readily available in a robotics laboratory. 3D-printing promises to overcome these challenges by providing a way to rapidly prototype CTRs. This would not only benefit CTR research, but it would also enable new appealing capabilities, such as the ability to create patient- or procedure-specific robots. In this paper, we present a study on the viability of fabricating CTRs using Multi Jet Fusion (MJF) of Nylon- 12, a type of elastic polymer commonly used in additive manufacturing [4]. We note that Nylon-12 was already evaluated for the purpose of building CTRs in [2], but fabrication was performed with Selective Laser Sintering (SLS), which produced unsatisfactory results. Our study is the first study to evaluate the suitability of MJF to 3D- print CTRs.