Research Papers

J. Med. Devices. 2018;12(2):021001-021001-6. doi:10.1115/1.4039209.

Current techniques for diagnosing skin cancer lack specificity and sensitivity, resulting in unnecessary biopsies and missed diagnoses. Automating tissue palpation and morphology quantification will result in a repeatable, objective process. LesionAir is a low-cost skin cancer diagnostic tool that measures the full-field compliance of tissue by applying a vacuum force and measuring the precise deflection using structured light three-dimensional (3D) reconstruction. The technology was tested in a benchtop setting on phantom skin and in a small clinical study. LesionAir has been shown to measure deflection with a 0.085 mm root-mean-square (RMS) error and measured the stiffness of phantom tissue to within 20% of finite element analysis (FEA) predictions. After biopsy and analysis, a dermatopathologist confirmed the diagnosis of skin cancer in tissue that LesionAir identified as noticeably stiffer and the regions of this stiffer tissue aligned with the bounds of the lesion. A longitudinal, full-scale study is required to determine the clinical efficacy of the device. This technology shows initial promise as a low-cost tool that could rapidly identify and diagnose skin cancer.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2018;12(2):021002-021002-9. doi:10.1115/1.4039390.

This paper investigates the energy transmitted to and harvested by a camera pill traveling along the gastrointestinal (GI) tract. It focuses on the transmitted electromagnetic (EM) energy in the frequency range of 0.18 to 2450 MHz and compares it to the mechanical energy due to the motion of the pill and the force exerted from the intestine in its peristalsis onto the pill, and the electrochemical energy due to the change of pH along the path of the pill. A comprehensive multilayer EM power transmission model is constructed and implemented in a numerical code, including power attenuation through each layer and multireflections at material interfaces. Computer simulations of EM power transmission through a multilayer abdomen to a pill traveling in the intestine are presented for the human abdominal cavity as well as phantom organs and phantom environments, coupled with corresponding experimental studies using these phantom components and environments. Two types of phantom abdomen are investigated: a ballistic gel and a multilayer duck breast. Phantom small intestine involves gelatin gel layers with embedded phantom chyme. Due to limitations related to the energy safety limit of skin exposure and energy losses in the transmission through the abdomen and intestines, inductive range frequencies are recommended which may yield energy harvesting of 10–50 mWh during 8 h of pill journey, complemented by about 10 mWh of mechanical energy and 10 mWh of electrochemical energy harvesting, in addition to about 330 mWh typically stored in the coin batteries of a camera pill.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2018;12(2):021003-021003-10. doi:10.1115/1.4039389.

A system was developed for computed tomography (CT)-guided needle placement in the thorax and abdomen, providing precise aiming of a needle guide (NG) to reach a user-specified target in a single manual insertion. The objective of this work is to present its technical design and analyze its performance in terms of placement error in air. The individual contributions to the placement error of a fiducial marker based system-to-CT registration system, a two degrees-of-freedom (2DOFs) drive system to aim the NG, and a structural link between NG and CT table were experimentally determined, in addition to the placement error of the overall system. An error contribution of 0.81 ± 0.34 mm was determined for the registration system, <1.2 mm and <3.3 mm for the drive system, and 0.35 mm and 0.43 mm for two load cases of the structural link. The overall unloaded system achieved 1.0 ± 0.25 mm and 2.6 ± 0.7 mm at 100 mm and 250 mm depth, respectively. The overall placement errors in air do not exceed the 5 mm error specified as a clinical user requirement for needle placement in tissue.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2018;12(2):021004-021004-6. doi:10.1115/1.4039593.

Manufacturers are constantly seeking to design new, better performing transvenous cardiac leads to prevent perforation of the heart by the lead tip. Currently, there is no standardized test method to measure the buckling load of leads, a major factor in the propensity of the lead to perforate the heart. This study further investigates the effect of boundary conditions on buckling loads at the lead tip of different transvenous cardiac leads achieved using different variations of our initial physiologically relevant test method. The goals of the test are to create the maximum buckling load with high repeatability and the simplest possible design. A buckling test was performed to capture maximum buckling load using three leads of each model (five currently available cardiac lead models) and were tested in each of six test setups. The buckling test methodology had a substantial effect on the load-displacement profiles, regardless of whether the lead was a pacemaker or defibrillator lead. By adding the right ventricular (RV) constraint, the buckling load more than doubled for most leads. The use of a lubricant reduced friction between the lead body and the RV surface, and thereby subsequently lowered the buckling load in those setups that used the RV constraint. In addition, the use of the lubricant reduced the variability in the results. The addition of both the RV constraint and the lubricant substantially influences the mechanical behavior of transvenous cardiac leads and is recommended for buckling testing of transvenous cardiac leads.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2018;12(2):021005-021005-11. doi:10.1115/1.4039434.

This presents the influence of gamma irradiation on Pharmacopeia specifications, mechanical and flow parameters of polypropylene (PP) syringes. There has been significant progress in the terminal sterilization of single-use, disposable medical devices with gamma radiation sterilization due to the growing awareness of toxic residues during the ethylene oxide (EtO) sterilization. PP is a widely used polymer for the production of syringes because of its excellent mechanical and thermal properties and has expanded continuously over the last decade. Although 25 kGy was generally recommended for the gamma radiation sterilization of medical products, this radiation dose is high enough to produce substantial damage. Electron spin resonance (ESR) characteristics of irradiated syringes were also studied at normal (25 °C, 60% relative humidity) and accelerated (40 °C, 75% relative humidity) stability test conditions. It was found that the chemical and radiolytic changes and sterility assurance levels (SAL) after gamma radiation sterilization were different in PP syringes. It was shown that for two commercial syringes, E1 and E3, a SAL of 10−4 could be attained with only 10 kGy, with there being less detrimental radiation effects on E1. The differences in the radiosensitivity of the propylene syringes could be due to the different formulations and manufacturing processes. The results indicated that a commercial syringe, identified as E1 could be safely sterilized with gamma irradiation as the radicals decay over a period of days under normal conditions and quenched much faster under stability conditions. Furthermore, ESR technique could be used successfully in monitoring the radiosterilization of this material. Additionally, the confirmation and validation of the SAL doses which are below 25 kGy, will decrease the time and cost of the sterilization with less damaging effects of ionizing irradiation.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2018;12(2):021006-021006-8. doi:10.1115/1.4039592.

The distal head of the natural orifice transluminal endoscopic surgery (NOTES) platform commonly uses the structure of a snake bone, which cannot rotate, and the manufacturing is often time-consuming. A novel rotatable, one-element snake bone for NOTES is proposed. This paper first describes the movement mechanism and actuation. The new structure, which is composed of hinge pairs for bending and track-sled rings for rotation, was designed to reach a 90 deg bending angle and 62 deg rotational angle. The workspace of the snake bone was derived using screw theory and was simulated on matlab. The relationship between the angle and wire displacement was analyzed in detail. The new snake bone system bent and rotated by manipulating control wires that were actuated by DC motors, and its angular movements were measured by motion sensors with an angle error within ±2.6 deg. The snake bone was mounted on a flexible tube, inserted into a colonoscopy model, and navigated by motor actuation to eventually reach the cecum. The experimental results demonstrate the new snake bone's ability to travel through a natural orifice by rotating and bending, which satisfies the mobility requirement for NOTES.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2018;12(2):021007-021007-7. doi:10.1115/1.4040043.

Design by Dragging (DBD) [1] is a virtual design tool, which displays three-dimensional (3D) visualizations of many simulation results obtained by sampling a large design space and ties this visual display together with a new user interface. The design space is explored through mouse-based interactions performed directly on top of the 3D data visualizations. Our previous study [1] introduced the realization of DBD with a simplistic example of biopsy needle design under a static bending force. This paper considers a realistic problem of designing a vacuum-assisted biopsy (VAB) needle that brings in more technical challenges to include dynamic tissue reaction forces, nonlinear tissue deformation, and progressive tissue damage in an integrated visualization with design suggestions. The emphasis is placed on the inverse design strategy in DBD, which involves clicking directly on a stress (or other output field parameter) contour and dragging it to a new (usually preferable) position on the contour. Subsequently, the software computes the best fit for the design variables for generating a new output stress field based on the user input. Three cases demonstrated how the inverse design can assist users in intuitively and interactively approaching desired design solutions. This paper illustrates how virtual prototyping may be used to replace (or reduce reliance on) purely experimental trial-and-error methods for achieving optimal designs.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Med. Devices. 2018;12(2):024501-024501-5. doi:10.1115/1.4039753.

Endoscopic closure is an essential procedure in gastrointestinal (GI) surgery, but currently it is difficult to close large defects endoscopically because of the lack of an appropriate device. Previously, we developed an endoscopic clipping device that has multifiring function and is equipped with an independent clamp. The goal of this study is to provide a new closure method with this device and 4S-modified Roeder (4SMR) slipknot. The feasibility of the closure method is examined by deploying two clips during one insertion onto the 4SMR slipknot to close a 5 cm full-thickness linear defect of an ex vivo porcine stomach from the center. Mechanical strengths of clip-knot closure and the slipknot as regards to tensioning forces are also evaluated. Specifically, the mechanical strength of the 4SMR slipknot is verified by mean peak forces to failure, while the knot is tensioning by 2.5, 5, 7.5, and 10 N force (n = 20 for each group), respectively. Experimental results indicate the clip-slipknot closure can withstand a distracting force of 6.3 ± 5.6 N. Tensioning force has a great influence on the mechanical strength of slipknot, with the mean peak force (tensioning force) being 7.1± 6.5, 16.3 ± 9.3, 18.9 ± 10.4, and 24.2 ± 12.0 N, respectively. The proposed closure method can be used for large defects. Tensioning force higher than 5 N is suitable to ensure a stronger 4SMR slipknot.

Commentary by Dr. Valentin Fuster

Design Innovation Paper

J. Med. Devices. 2018;12(2):025001-025001-3. doi:10.1115/1.4039208.

Tube thoracostomy (TT) insertion can serve as a life-saving adjunct for thoracic trauma. Unfortunately, suboptimal positioning using the open, standard of care technique is associated with complications resulting in impaired TT function. Using a porcine model, we aimed to determine whether a magnetic chest tube positioning system (MCTPS) could be utilized to direct the intrathoracic TT position. Using recently deceased cross-bred domestic swine, we performed TT using our MCTPS and the standard of care open technique. The operator held one magnet outside of the thorax. The second magnet was positioned at the distal aspect of the TT. The operator was tasked with positioning the TT to distinct premarked intra-thoracic locations under blinded conditions. The experiment was video-recorded through an open sternotomy incision. As a control, TT was inserted using the standard of care open technique. The utilization of MCTPS successfully directed TT from one premarked location to another in 4 of 5 attempts (80%). Conversely, the control TT without magnetic guidance failed to navigate the premarked intra-thoracic locations with 0 of 5 attempts successful (p = 0.05). Positional flaws after TT placement are common. We demonstrate the feasibility of the MCTPS as an alternative to traditional hand-guided technique under simulated TT insertion conditions. The MCTPS is possibly superior to the current standard of care technique of TT. Additional studies are needed to develop this emerging technology in humans.

Commentary by Dr. Valentin Fuster

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