Shape control of continuum robots requires a means of sensing the the curved shape of the robot. Since continuum robots are deformable, they take on shapes that are general curves in space, which are not fully defined by actuator positions. Vision-based shape-estimation provides a promising avenue for shape-sensing. While this is often facilitated by fiducial markers, sometimes fiducials are not feasible due to either the robot's application or its size. To address this, we present a robust and efficient stereo-vision-based, shapesensing algorithm for continuum robots that does not rely on fiducials or assume orthogonal camera placement. The algorithm employs self-organizing maps to triangulate threedimensional backbone curves. Experiments with an object with a known shape demonstrate an average accuracy of 1.53 mm on a 239 mm arc length curve.

Innovations in the field of continuum robotics are enabling increasingly thin and dexterous slave robots in surgical telemanipulation systems. Actuation of these robots is a challenge, because many degrees of freedom must be controlled simultaneously in a compact and unobtrusive package in the operating room. While significant progress in designing these actuation units has been made for both larger, non-medical continuum robots, and for certain types of surgical continuum robots, the design of clinically-relevant actuation units for concentric tube robots is a comparatively understudied area of research. To address this, in this paper we present the design of a robot intended to deliver four concentric tube manipulators simultaneously through a single nostril. We present the considerations that motivated the design and the prototype we have constructed to meet these needs.

Polymorph screening is a crucial step in the characterization and development of pharmaceuticals. The 1998 recall of ritonavir upon the unexpected appearance of the more stable Form II polymorph remains a notorious case of disappearing polymorphs as the presence of Form II inhibited the ability to grow the original Form I. This study presents the characterization of Form III of ritonavir grown from melt/cool crystallization. While Form III was observed in 2014, it was not characterized as a unique polymorph until 2022 when, coincidentally, a team at AbbVie and the authors of this manuscript independently discovered Form III via melt/cool crystallization. This study builds upon the discovery through a thorough characterization and novel thermal profile for quicker nucleation and crystallization of the new form.

Polymorph screening is a crucial step in the characterization and development of pharmaceuticals. The 1998 recall of ritonavir upon the unexpected appearance of the more stable Form II polymorph remains a notorious case of disappearing polymorphs as the presence of Form II inhibited the ability to grow the original Form I. This study presents the characterization of Form III of ritonavir grown from melt/cool crystallization. While Form III has been observed by researchers in 2014 and 2022, this study presents a thorough characterization and novel thermal profile for quicker nucleation and crystallization of the new form. In this work, we expand upon past thermal methods examining the polymorphic landscape of ritonavir to shed light on the crystallization of Form III from the melt.

An active cannula is a surgical device capable of dynamically changing its curved shape in response to rotation and translation of the several precurved, concentric, superelastic tubes from which it is made. As the tubes move with respect to one another in response to input motion at their bases (outside the patient), they elastically interact, causing one another to bend. This bending can be harnessed to direct the cannula through winding trajectories within the human body. An active cannula has the potential to perform a wide range of surgical tasks, and it is especially well suited for guiding and aiming an optical fiber (e.g. BeamPath from OmniGuide, Inc.) for laser ablation. Controlling the trajectory of the laser requires control of the shape of the active cannula, and in particular the position and orientation of its tip. Prior work has shown that beam mechanics can be used to describe the shape of the cannula, given the translations and axial angles of each tube base. Here, in order to aim the laser, we invert this relationship (obtaining the “inverse kinematic”), solving for the translations and axial angles of each tube, given a desired position and orientation of the cannula tip. Experimental evaluation of inverse kinematics was carried out using a prototype consisting of three tubes. The outermost tube is straight and rigid (stainless steel), with an outer diameter (OD) of 2.4 mm. The 1.8 mm OD middle tube is superelastic Nitinol, with a preshaped circular tip. The 1.4 mm OD innermost tube is Nitinol and is not precurved, representing the straight trajectory of a laser emanating from the tip of the cannula. We assessed the accuracy of the inverse kinematics by computing the necessary tube translations and rotations needed to direct the beam of the “laser” to sequential locations along a desired trajectory consisting of two line segments that meet at a corner. These inputs were then applied at tube bases to direct the laser to thirty points along the trajectory on a flat surface 100 mm away the cannula base. The position of the tip of the simulated laser was measured using an optical tracker (Micron Tracker H3-60, Claron, Inc.). Mean error between desired and actual positions was 3.1 mm (maximum 5.5 mm). This experiment demonstrates proof of concept for laser guidance, and establishes the accuracy of the inverse kinematic model. We note that these results are applicable to guidance of a wide range of medical devices in addition to lasers. Relevant references, as well as images of our prototype and experimental data described here can be found in an online version of this abstract at http://research.vuse.vanderbilt.edu/MEDLab/. This work was supported by NSF grant #0651803, and NIH grant #1R44CA134169-01A1.