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Editorial

J. Med. Devices. 2014;8(2):020201-020201-1. doi:10.1115/1.4027158.

The following technical briefs were submitted, peer reviewed, and accepted for presentation at the 2014 University of Minnesota's Design of Medical Devices (DMD) Conference (www.dmd.umn.edu) held April 7–10, 2014 at The Commons Hotel & McNamara Alumni Center in Minneapolis, MN.

Commentary by Dr. Valentin Fuster

Technical Brief

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
J. Med. Devices. 2014;8(2):020923-020923-2. doi:10.1115/1.4027024.
Topics: Design , Simulation
Commentary by Dr. Valentin Fuster
J. Med. Devices. 2014;8(2):020924-020924-2. doi:10.1115/1.4027023.
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
J. Med. Devices. 2014;8(2):020927-020927-2. doi:10.1115/1.4027027.
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. 2014;8(2):020934-020934-2. doi:10.1115/1.4026996.

Endochondral fracture healing, the process in which callus bridges a fracture, can be enhanced using a brace with a deforming element. This deforming element acts to locally increase pressure at the fracture site. In this paper, we describe a bracing device, which has the capability of controlling blood flow in targeted regions of an extremity. Controlling the blood flow around a fracture site induces a mechanism that enhances fracture healing. We hypothesize that, since local oxygen tension is lowered by means of controlling the blood flow at the fracture site, fracture healing is accelerated and bony union is more likely. Using the results of several previous studies, we will show that increased mechanical pressure in the soft tissues over the fracture site enhances fracture healing.

Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
J. Med. Devices. 2014;8(2):020938-020938-2. doi:10.1115/1.4026995.
Topics: Knee
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
J. Med. Devices. 2014;8(2):020942-020942-2. doi:10.1115/1.4027049.
Commentary by Dr. Valentin Fuster
J. Med. Devices. 2014;8(2):020944-020944-2. doi:10.1115/1.4027051.
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
J. Med. Devices. 2014;8(2):020947-020947-2. doi:10.1115/1.4027062.
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
J. Med. Devices. 2014;8(2):024501-024501-5. doi:10.1115/1.4026633.

One way to provide powered lower limb prostheses with greater adaptability to a wearer's intent is to use a neural signal to provide feedforward control of prosthesis mechanics. We designed and tested the feasibility of an experimental powered ankle-foot prosthesis that uses pneumatic artificial muscles and proportional myoelectric control to vary ankle mechanics during walking. The force output of the artificial plantar flexor muscles was directly proportional to the subject's residual gastrocnemius muscle activity. The maximum force generated by a pair of artificial muscles fixed at nominal length was 3513 N. The maximum planter flexion torque that could be generated during walking was 176 Nm. The force bandwidth of the pneumatic artificial muscles was 2 Hz. The electromechanical delay was 33 ms, the time to peak tension was 48 ms, and the half relaxation time was 50 ms. We used two artificial muscles as dorsiflexors and two artificial muscles as plantar flexors. The prosthetic ankle had 25 deg of dorsiflexion and 35 deg of plantar flexion with the artificial muscles uninflated. The intent of the device was not to create a commercially viable prosthesis but to have a laboratory prototype to test principles of locomotor adaptation and biomechanics. We recruited one unilateral transtibial amputee to walk on a treadmill at 1.0 m/s while wearing the powered prosthesis. We recorded muscle activity within the subject's prescribed prosthetic socket using surface electrodes. The controller was active throughout the entire gait cycle and did not rely on detection of gait phases. The amputee subject quickly adapted to the powered prosthesis and walked with a functional gait. The subject generated peak ankle power at push off that was similar between amputated and prosthetic sides. Our results suggest that amputees can use their residual muscles for proportional myoelectric control to alter prosthetic mechanics during walking.

Commentary by Dr. Valentin Fuster

Research Papers

J. Med. Devices. 2014;8(2):021001-021001-7. doi:10.1115/1.4026508.

Silicone-based tissue-mimicking phantom is widely used as a surrogate of tissue for clinical simulators, allowing clinicians to practice medical procedures and researchers to study the performance of medical devices. This study investigates using the mineral oil in room-temperature vulcanizing silicone to create the desired mechanical properties and needle insertion characteristics of a tissue-mimicking phantom. Silicone samples mixed with 0, 20, 30, and 40 wt. % mineral oil were fabricated for indentation and needle insertion tests and compared to four types of porcine tissues (liver, muscle with the fiber perpendicular or parallel to the needle, and fat). The results demonstrated that the elastic modulus and needle insertion force of the phantom both decrease with an increasing concentration of mineral oil. Use of the mineral oil in silicone could effectively tailor the elastic modulus and needle insertion force to mimic the soft tissue. The silicone mixed with 40 wt. % mineral oil was found to be the best tissue-mimicking phantom and can be utilized for needle-based medical procedures.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2014;8(2):021002-021002-7. doi:10.1115/1.4026560.

In endovascular interventions, thin, flexible instruments are inserted through the skin into the blood vessels to diagnose and treat various diseases of the vascular system. One drawback is that the instruments are difficult to maneuver in the desired direction due to limitations in shape and flexibility. Another disadvantage is that the interventions are performed under intermittent fluoroscopy/angiography imaging. Magnetic resonance imaging (MRI) may offer advantages over X-ray guidance. It presents a good soft tissue contrast without the use of nephrotoxic media or ionizing radiation. The aim of this study is to develop a guidewire that is compatible with MRI and includes a steerable segment at the tip. This added degree-of-freedom may improve the maneuverability of the devices thereby the efficiently and safety of the navigation. A 1.6 m (5 ft, 3 in.) long and 0.035 in. diameter guidewire that consists of MR compatible materials and has a flexible tip was designed. The only metallic part was a nitinol rod that was implemented at the distal flexible tip. To limit the risk of heating in the MRI, this rod was kept shorter than 30 mm. The tip could be deflected in one direction by pulling on a Dyneema wire that was placed in the lumen of the shaft of the guidewire. To drive the steerable tip, a handle that could be easily attached/detached from the instrument was designed and implemented. Using the handle, the tip of the 1.60 m long guidewire prototype could be actuated to reach angles from 30 deg to 250 deg. The handle could easily be placed on and removed from the guidewire, so conventional 0.035 in.–compatible catheters could slide over from the proximal end. However, in order to make the guidewire more efficient to enter a bifurcation, the stiffness of the tip should progressively increase from its proximal to its distal end. The guidewire was imaged in a 1.5T MRI using real-time imaging without producing artifacts that would have shaded the anatomy. It was possible to assemble a guidewire with a steerable segment in the required size, using MR compatible materials. Therefore, the current design is a promising proof of concept and allowed us to clearly identify the features that need to be improved in order to come to a clinically applicable instrument.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2014;8(2):021003-021003-6. doi:10.1115/1.4026577.

Thyroid nodules are a frequent clinical finding and the most common endocrine malignancy is thyroid cancer. The standard of care in the management of a patient with a thyroid nodule is to perform a preoperative fine needle aspiration (FNA) biopsy of the suspect nodule under ultrasound imaging guidance. In a significant percentage of the cases, cytological assessment of the biopsy material yields indeterminate results, the consequence of which is diagnostic thyroidectomy. Unfortunately, 75–80% of diagnostic thyroidectomies following indeterminate cytology result in benign designation by post-surgery histopathology, indicating potentially unnecessary surgeries. Clearly, the potential exists for the improvement in patient care and the reduction of overall procedure costs if an improved preoperative diagnostic technique was developed. Elastic scattering spectroscopy (ESS) is an optical biopsy technique that is mediated by optical fiber probes and has been shown to be effective in differentiating benign from malignant thyroid tissue in ex vivo surgical tissue samples. The goal of the current research was to integrate the ESS fiber optic probes into a device that can also collect cells for cytological assessment and, thus, enable concurrent spectroscopic interrogation and biopsy of a suspect nodule with a single needle penetration. The primary challenges to designing the device included miniaturizing the standard ESS fiber optic probe to fit within an FNA needle and maintaining the needle’s aspiration functionality. We demonstrate the value of the fabricated prototype devices by assessing their preliminary performance in an on-going clinical study with >120 patients. The devices have proven to be clinically friendly, collecting both aspirated cells and optical data from the same location in thyroid nodules and with minimal disruption of clinical procedure. In the future, such integrated devices could be used to complement FNA-based cytological results and have the potential to both reduce the number of diagnostic thyroidectomies on benign nodules and improve the surgical approach for patients with thyroid malignancies, thereby, decreasing healthcare costs and improving patient outcomes.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2014;8(2):021004-021004-8. doi:10.1115/1.4026561.

Bone transport distraction osteogenesis (BTDO) is a surgical procedure that has been used over the last 30 years for the correction of segmental defects produced mainly by trauma and oncological resections. Application of BTDO has several clinical advantages over traditional surgical techniques. Over the past few years, several BTDO devices have been introduced to reconstruct mandibular bone defects. Based on the location and outline of the defect, each device requires a uniquely shaped reconstruction plate. To date, no biomechanical evaluations of mandibular BTDO devices have been reported in the literature. The present study evaluated the mechanical behavior of three different shaped prototypes of a novel mandibular bone transport reconstruction plate and its transport unit for the reconstruction of segmental bone defects of the mandible by using numerical models complemented with mechanical laboratory tests to characterize strength, fatigue, and stability. The strength test evaluated device failures under extreme loads and was complemented with optimization procedures to improve the biomechanical behavior of the devices. The responses of the prototypes were characterized to improve their design and identify weak and strong regions in order to avoid posterior device failure in clinical applications. Combinations of the numerical and mechanical laboratory results were used to compare and validate the models. In addition, the results remark the importance of reducing the number of animals used in experimental tests by increasing computational and in vitro trials.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2014;8(2):021005-021005-6. doi:10.1115/1.4026451.

This paper presents an implantable device concept with applications for treating ocular diseases such as glaucoma, age-related macular degeneration (AMD), diabetic retinopathy, and retinitis pigmentosa. The design of a biodegradable drug delivery device concept consisting of a polydimethylsiloxane (PDMS) shell with a fluid reservoir and micro/nanofluidic tubes that allow the drug to be stored and delivered at a specified rate is discussed. Computational fluid dynamics simulations were conducted through various tube configurations in order to obtain the drug diffusion characteristics. The results from the simulation studies revealed information related to drug transport under varying design parameters. The design simulations were conducted with a desired rate. Based on results from several simulations, an optimization study was conducted to achieve the required dosage for about 2 years. The results obtained from the optimization study shows that the device concept can be extended for different drugs to treat ocular diseases.

Commentary by Dr. Valentin Fuster

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