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Introduction

J. Med. Devices. 2015;9(3):030201-030201-1. doi:10.1115/1.4030777.

The following technical briefs were submitted, peer reviewed, and accepted for presentation at the 2015 University of Minnesota's Design of Medical Devices (DMD) Conference (www.dmd.umn.edu) held April 13–16, 2015 at The Commons Hotel & McNamara Alumni Center in Minneapolis, MN. The conference had another successful year with attendance reaching over 1100 and raised $158,000 from 42 sponsors. The money raised will support medical devices education at the University of Minnesota, the University of Minnesota Medical Devices Center, and the DMD Conference expenses.

Commentary by Dr. Valentin Fuster

Special Section Technical Briefs

Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
J. Med. Devices. 2015;9(3):030911-030911-2. doi:10.1115/1.4030607.
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
J. Med. Devices. 2015;9(3):030919-030919-2. doi:10.1115/1.4030597.
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster

Research Papers

J. Med. Devices. 2015;9(3):031001-031001-8. doi:10.1115/1.4030274.

The aim of this study is to focus on the effect of probe-to-specimen distance in kidney stone treatment with hydrodynamic bubbly cavitation. Cavitating bubbles were generated by running phosphate buffered saline (PBS) through stainless steel tubing of inner diameter of 1.56 mm at an inlet pressure of ∼10,000 kPa, which was connected to a 0.75 mm long probe with an inner diameter of 147 μm at the exit providing a sudden contraction and thus low local pressures. The bubbles were targeted on the surface of nine calcium oxalate kidney stones (submerged in a water pool at room temperature and atmospheric pressure) from three different distances, namely, 0.5 mm, 2.75 mm, and 7.75 mm. The experiments were repeated for three different time durations (5 min, 10 min, and 20 min). The experimental data show that amongst the three distances considered, the distance of 2.75 mm results in the highest erosion amount and highest erosion rate (up to 0.94 mg/min), which suggests that a closer distance does not necessarily lead to a higher erosion rate and that the probe-to-specimen distance is a factor of great importance, which needs to be optimized. In order to be able to explain the experimental results, a visualization study was also conducted with a high speed CMOS camera. A new correlation was developed to predict the erosion rates on kidney stones exposed to hydrodynamic cavitation as a function of material properties, time, and distance.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2015;9(3):031002-031002-6. doi:10.1115/1.4029924.

Traditional hand-suturing for vascular connection techniques is time consuming, expensive, and requires highly complex instruments and technical expertise. The aim of this study is to develop a new vascular coupler that can be used in end-to-end anastomosis surgery in an easier and more efficient way for both arteries and veins. The vascular coupler has four rotatable wings and one translatable spike in each wing. Prototypes were manufactured using polytetrafluoroethylene (PTFE) and high-density polyethylene (HDPE). A set of installation tools was designed to facilitate the anastomosis process. Proof-of-concept testing with the vascular coupler using plastic tubes and porcine cadaver vessels showed that the coupler should work as designed. A simplified finite element (FE) model assisted in the evaluation of the tearing likelihood of human vessels during installation of the coupler. Results of tests on the coupler showed that the vascular coupler could be efficiently attached to blood vessels, did not leak after the anastomosis was performed, had sufficient joint strength, and had little impact on flow in the vessel. The entire anastomosis process can be completed in 3 min when using the vascular coupler to join porcine cadaver vessels.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2015;9(3):031003-031003-7. doi:10.1115/1.4030083.

Otologic surgery often involves a mastoidectomy, which is the removal of a portion of the mastoid region of the temporal bone, to safely access the middle and inner ear. The surgery is challenging because many critical structures are embedded within the bone, making them difficult to see and requiring a high level of accuracy with the surgical dissection instrument, a high-speed drill. We propose to automate the mastoidectomy portion of the surgery using a compact, bone-attached robot. The system described in this paper is a milling robot with four degrees-of-freedom (DOF) that is fixed to the patient during surgery using a rigid positioning frame screwed into the surface of the bone. The target volume to be removed is manually identified by the surgeon pre-operatively in a computed tomography (CT) scan and converted to a milling path for the robot. The surgeon attaches the robot to the patient in the operating room and monitors the procedure. Several design considerations are discussed in the paper as well as the proposed surgical workflow. The mean targeting error of the system in free space was measured to be 0.5 mm or less at vital structures. Four mastoidectomies were then performed in cadaveric temporal bones, and the error at the edges of the target volume was measured by registering a postoperative computed tomography (CT) to the pre-operative CT. The mean error along the border of the milled cavity was 0.38 mm, and all critical anatomical structures were preserved.

Commentary by Dr. Valentin Fuster

Design Innovation Paper

J. Med. Devices. 2015;9(3):035001-035001-6. doi:10.1115/1.4030505.

A lower limb prosthesis is able to restore mobility to patients who have lost a limb; however, no current replacement is as moveable and adaptable as the limb that was lost. Therefore, all amputees suffer from a reduction in function at some level. Movement in the transverse plane of a lower limb prosthesis is often negated in a traditional prosthesis, and those devices that do allow for transverse plane motion are set to a single, fixed stiffness, and incapable of adapting to the varying activities of the user. A prototype device has been created that allows for varying stiffness in the transverse plane of a lower limb prosthesis. The variable stiffness torsion adapter (VSTA) functions by way of a movable pivot lever arm that can actively modify the mechanical advantage between the outer housing and the internal spring. The motion of the pivot is perpendicular to the external torque allowing for low power adjustments of the stiffness. Bench tests were performed and demonstrate the ability of the VSTA to vary torsional stiffness between 0.12 and 0.91 N m/deg over a ±30 deg rotational range of motion. The device also includes a mode for fully locked operation. The VSTA may improve the mobility of lower limb amputees by allowing for activity-dependent transverse plane stiffness.

Commentary by Dr. Valentin Fuster

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