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Editorial

J. Med. Devices. 2015;9(2):020201-020201-1. doi:10.1115/1.4030353.

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.

Commentary by Dr. Valentin Fuster

Special Section Technical Briefs

J. Med. Devices. 2015;9(2):020901-020901-2. doi:10.1115/1.4030151.
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
J. Med. Devices. 2015;9(2):020915-020915-2. doi:10.1115/1.4030123.
Commentary by Dr. Valentin Fuster
J. Med. Devices. 2015;9(2):020919-020919-2. doi:10.1115/1.4030188.
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
J. Med. Devices. 2015;9(2):020928-020928-3. doi:10.1115/1.4030139.
Topics: Adhesion , Design
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
J. Med. Devices. 2015;9(2):020931-020931-2. doi:10.1115/1.4030142.
Topics: Pressure , Electrodes
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(2):020939-020939-3. doi:10.1115/1.4030191.
Topics: Design , Membranes , Trachea
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
J. Med. Devices. 2015;9(2):020947-020947-2. doi:10.1115/1.4030126.
Topics: Electrodes , Design
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
J. Med. Devices. 2015;9(2):020950-020950-2. doi:10.1115/1.4030129.
Topics: Design , Catheters
Commentary by Dr. Valentin Fuster

Research Papers

J. Med. Devices. 2015;9(2):021001-021001-8. doi:10.1115/1.4029706.

Bioimpedance spectroscopy (BIS) has shown significant potential in many areas of medicine to provide new physiologic markers. Several acute and chronic diseases are accompanied by changes in intra- and extracellular fluid within various areas of the human body. The estimation of fluid in various body compartments is therefore a simple and convenient method to monitor certain disease states. In this work, the design and evaluation of a BIS instrument are presented and three key areas of the development process investigated facilitating the BIS measurement of tissue hydration state. First, the benefit of incorporating DC-stabilizing circuitry to the standard modified Howland current pump (MHCP) is investigated to minimize the effect of DC offsets limiting the dynamic range of the system. Second, the influence of the distance between the bioimpedance probe and a high impedance material is investigated using finite element analysis (FEA). Third, an analytic compensation technique is presented to minimize the influence of parasitic capacitance. Finally, the overall experimental setup is evaluated through ex vivo BIS measurements of porcine spleen tissue and compared to published results. The DC-stabilizing circuit demonstrated its ability to maintain DC offsets at less than 650 μV through 100 kHz while maintaining an output impedance of 1 MΩ from 100 Hz to 100 kHz. The proximity of a bioimpedance probe to a high impedance material such as acrylic was shown to increase measured impedance readings by a factor of 4x as the ratio of the distance between the sensing electrodes to the distance between the bioimpedance probe and acrylic reached 1:3. The average parasitic capacitance for the circuit presented was found to be 712 ± 128 pF, and the analytic compensation method was shown to be able to minimize this effect on the BIS measurements. Measurements of porcine spleen tissue showed close correlation with experimental results reported in published articles. This research presents the successful design and evaluation of a BIS instrument. Specifically, robust measurements were obtained by implementing a DC-stabilized current source, investigating probe-material proximity issues and compensating for parasitic capacitance. These strategies were shown to provide tissue measurements comparable with published literature.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2015;9(2):021002-021002-11. doi:10.1115/1.4029557.

Needle insertion is used in many diagnostic and therapeutic percutaneous medical procedures such as brachytherapy, thermal ablations, and breast biopsy. Insufficient accuracy using conventional surgical cannulas motivated researchers to provide actuation forces to the cannula's body for compensating the possible errors of surgeons/physicians. In this study, we present the feasibility of using shape memory alloy (SMA) wires as actuators for an active steerable surgical cannula. A three-dimensional (3D) finite element (FE) model of the active steerable cannula was developed to demonstrate the feasibility of using SMA wires as actuators to bend the surgical cannula. The material characteristics of SMAs were simulated by defining multilinear elastic isothermal stress–strain curves that were generated through a matlab code based on the Brinson model. Rigorous experiments with SMA wires were done to determine the material properties as well as to show the capability of the code to predict a stabilized SMA transformation behavior with sufficient accuracy. In the FE simulation, birth and death method was used to achieve the prestrain condition on SMA wire prior to actuation. This numerical simulation was validated with cannula deflection experiments with developed prototypes of the active cannula. Several design parameters affecting the cannula's deflection such as the cannula's Young's modulus, the SMA's prestrain, and its offset from the neutral axis of the cannula were studied using the FE model. Real-time experiments with different prototypes showed that the quickest response and the maximum deflection were achieved by the cannula with two sections of actuation compared to a single section of actuation. The numerical and experimental studies showed that a highly maneuverable active cannulas can be achieved using the actuation of multiple SMA wires in series.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Med. Devices. 2015;9(2):024501-024501-4. doi:10.1115/1.4029707.

Sterilization is a vital component of the manufacturing process for any medical device. However, some sterilization techniques may alter device properties. While it is known that electron beam sterilization can change the mechanical properties of solid polymethylmethacrylate (PMMA) constructs, its effect on porous PMMA has not been explored. Therefore, porous PMMA space maintainer constructs designed for the treatment of craniofacial bone defects were sterilized at dosages of 30 kGy and 40 kGy. Electron beam sterilization was shown to increase the compressive properties of porous PMMA space maintainer devices.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2015;9(2):024502-024502-4. doi:10.1115/1.4029810.

Studies have suggested that elevated cerebrospinal fluid (CSF) pressure can have a damaging effect on the optic nerve and visual acuity. There is need for a noninvasive CSF pressure measurement technique. A portable device for noninvasive intracranial pressure (ICP) monitoring would have a significant impact on clinical care. A proof-of-concept prototype is used to test the feasibility of a technique for monitoring ICP changes. The proposed methodology utilizes transcranial Doppler ultrasonography to monitor blood flow through the ophthalmic and central retinal arteries while forces are applied to the cornea by a controlled actuator. Control algorithms for the device were developed and tested using an integrated experimental platform. Preliminary results using tissue-mimicking materials show the ability to differentiate between materials of differing stiffness that simulates different levels of ICP. These experiments are an initial step toward a handheld noninvasive ICP monitoring device.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2015;9(2):024503-024503-5. doi:10.1115/1.4030152.

Intramedullary nails are the gold standard of fracture fixation, yet problems can still arise due to their manufacture in discrete lengths. Patient outcomes are less favorable when implanted with an improper length nail, and the wide range of discrete length options can increase the size hospital inventory. Prototypes of adjustable-length intramedullary nails were developed and tested in axial compression, torsion, and four-point bending. These prototypes are comparable to conventional nails in axial and bending stiffness. The torsional stiffness of the prototypes is less than that of conventional nails, but may be sufficient for clinical use.

Commentary by Dr. Valentin Fuster

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