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Review Article

J. Med. Devices. 2015;10(1):010801-010801-8. doi:10.1115/1.4031718.

Implantation of drug-eluting stents (DESs) via percutaneous coronary intervention is the most popular treatment option to restore blood flow to occluded vasculature. The many devices currently used in clinic and under examination in research laboratories are manufactured using a variety of coating techniques to create the incorporated drug release platforms. These coating techniques offer various benefits including ease of use, expense of equipment, and design variability. This review paper discusses recent novel DES designs utilizing individual or a combination of these coating techniques and their resulting drug release profiles.

Commentary by Dr. Valentin Fuster

Research Papers

J. Med. Devices. 2015;10(1):011001-011001-7. doi:10.1115/1.4031799.

The CardioMEMS heart failure (HF) system was tested for cardiac output (CO) measurement accuracy using an in vitro mock circulatory system. A software algorithm calculates CO based on analysis of the pressure waveform as measured from the pulmonary artery, where the CardioMEMS system resides. Calculated CO was compared to that from reference flow probe in the circulatory system model. CO measurements were compared over a clinically relevant range of stroke volumes and heart rates with normal, pulmonary hypertension (PH), decompensated left heart failure (DLHF), and combined DHLF + PH hemodynamic conditions. The CardioMEMS CO exhibited minimal fixed and proportional bias.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2015;10(1):011002-011002-8. doi:10.1115/1.4031798.

This paper presents a design of a passive spine exoskeleton which implements a “push–pull” external assistive strategy. The spine exoskeleton was designed for reducing the risk of back injury. It applies a pulling force on thoracic region and a pushing force on lumbar region during spine flexion/extension. The design was inspired by previous simulation work, where the results highly supported benefits of the push–pull strategy on reducing the back muscular efforts and bending moment for the sagittal spine flexion/extension. A passive physical prototype was designed and constructed to test the push–pull strategy on human subjects. Three subjects were able to repeat the identical dynamic spine flexion and extension tasks with the spine exoskeleton prototype. The surface electromyography showed a reduction of up to 24% at lumbar and 54% at thoracic level muscle for the human subjects wearing the exoskeleton suit to accomplish the same static tasks without any external assistance. The muscle force and intervertebral bending moment were estimated to be reduced by up to 479 N and 36 N · m, respectively.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2015;10(1):011003-011003-7. doi:10.1115/1.4031810.

Currently, end-to-end anastomosis of blood vessels is performed using suturing, which is time consuming, expensive, and subject to large degrees of human error. One promising alternative is a ring–pin coupling device. This device has been shown to be useful for venous anastomosis, but lacks the versatility necessary for arterial applications. The purpose of this study was to optimize a vascular coupling design that could be used for arteries and veins of various sizes. To achieve this, finite-element (FE) analysis was used to simulate the vessel–device interaction during anastomosis. Parametric simulations were performed to optimize the number of pins, the wing pivot point, and the pin offset of the design. The interaction of the coupler with various blood vessel sizes was also evaluated. Maximum strain in the vessel wall increased with the number of pins. The positions of the wings and pins were also important in dictating maximum strain, and improper dimensions lead to failure of the installation process. Extra force applied to the distal end of the vessel, or a supplementary tool, will be required during the coupler installation process to prevent vessels less than 3 mm inner diameter (0.5 mm wall thickness) from slipping off the coupler.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2015;10(1):011004-011004-11. doi:10.1115/1.4031811.

There is an increasing need to incorporate an actively controlled drug delivery system (DDS) into the next generation of capsule endoscopy in order to treat diseases in the gastrointestinal tract in a noninvasive way. Despite a number of attempts to magnetically actuate drug delivery mechanisms embedded in endoscopic capsules, longer operating distances and further miniaturization of on-board components are still drawbacks of such systems. In this paper, we propose an innovative magnetic system that consists of an array of magnets, which activates a DDS, based on an overly miniaturized slider–crank mechanism. We use analytical models to compare the magnetic fields generated by cylindrical and arc-shaped magnets. Our experimental results, which are in agreement with the analytical results, show that an optimally configured array of the magnets enhances the magnetic field and also the driving magnetic torque and subsequently, it imposes a high enough force on the piston of the DDS to expel a required dose of a drug out of a reservoir. We conclude that the proposed magnetic field optimization method is effective in establishing an active DDS that is designed to deliver drug profiles with accurate control of the release rate, release amount, and number of doses.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2015;10(1):011005-011005-10. doi:10.1115/1.4031800.

Dental caries, the breakdown of tooth enamel by bacteria infection that causes cavities in the enamel, is the most common chronic disease in individuals 6–19 years of age in the U.S. Optical detection of caries has been shown to be sensitive to the presence of bacteria and the resulting demineralization of enamel. The scanning fiber endoscope (SFE) is a miniature camera system that can detect early stages of caries by performing high-quality imaging and laser fluorescence spectroscopy with 405 nm excitation. Because optical imaging of caries does not involve radiation risk, repeated imaging of the teeth is acceptable during treatment of the bacterial infection to monitor healing. A disposable handpiece was designed and fabricated to position the flexible fiber optic SFE probe for quantitative measurements. Plastic 3D-printed handpiece prototypes were tested with the SFE and a fluorescence calibration standard to verify mechanical fit and absence of signal contamination. Design feedback was provided by pediatric dentists and staff engineers to guide iterations. The final design configuration was based on the need to image interproximal regions (contact surfaces between adjacent teeth), ergonomics, and probe safety. The final handpiece design: (1) is safe for both the patient and the probe, (2) allows easy SFE insertion and removal, (3) does not interfere with spectral measurements, (4) standardizes the SFE's positioning during imaging by maintaining a consistent distance from the target surface, and (5) is significantly less expensive to produce and use than purchasing sanitary endoscope sheaths. The device will be used to help determine if new medicinal therapies can arrest caries and repair early interproximal demineralization under the clinical monitoring program. Ultimately, we anticipate that this handpiece will help us move closer toward widespread implementation of a dental diagnostic laser system that is safer and more sensitive than conventional methods for early caries detection.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2016;10(1):011006-011006-9. doi:10.1115/1.4032614.

The accuracy of many freehand medical procedures can be improved with assistance from real-time localization. Magnetic localization systems based on harnessing passive permanent magnets (PMs) are of great interest to track objects inside the body because they do not require a powered source and provide noncontact sensing without the need for line-of-sight. While the effect of the number of sensors on the localization accuracy in such systems has been reported, the spatial design of the sensing assembly is an open problem. This paper presents a systematic approach to determine an optimal spatial sensor configuration for localizing a PM during a medical procedure. Two alternative approaches were explored and compared through numerical simulations and experimental investigation: one based on traditional grid configuration and the other derived using genetic algorithms (GAs). Our results strongly suggest that optimizing the spatial arrangement has a larger influence on localization performance than increasing the number of sensors in the assembly. We found that among all the optimization schemes, the approach utilizing GA produced sensor designs with the smallest localization errors.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2016;10(1):011007-011007-6. doi:10.1115/1.4032633.

A premature infant needs a stable thermal environment. This paper studies if the infant weight can be employed in the standard heat regulation system in incubators. This was done in two stages. First, a weight sensor was designed by means of using strain gauge in order to provide weight measurement. Later, a heat regulation circuit was designed and implemented by means of using a microcontroller. The humidity, environmental and skin temperature, and infant's weight are measured and used as inputs. The experiments showed that infant's weight can be successfully added to the control circuit in the incubator instrument. The results showed that infant's weight can productively contribute in temperature control with good confidence. The average standard error was equal to 0.48 °C. The results reveal that the infant's weight can contribute to increase quality assurance of incubators.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2016;10(1):011008-011008-7. doi:10.1115/1.4032615.

Magnetic compression based anastomoses use magnetic force to necrose tissue between two magnets to create an anastomosis. Nickel-plated neodymium–iron–boron magnets are used in our study. The compression pressure between the magnets depends on the distance between the magnets, which is determined by the thickness of the compressed tissue and depends on bowel wall thickness and elasticity. It is critical to know the distance between the magnets once the tissue is compressed because the magnets must be within a critical distance of each other in order to create enough compressive force to necrose the tissue. We have developed an inductance sensor to detect the distance (tissue thickness) between the two magnets after the surgeon has deployed them. Inductance sensing is a contact-less sensing method that enables precise short-range detection of conducting surfaces. The inductor coil mounted on one magnet detects the second magnet by measuring the change in inductance due to eddy current induced on the nickel-plated surface of the second magnet. The change in the inductance is proportional to the change in distance between the magnets. The sensor was first calibrated by using polycarbonate sheets to simulate the intestine tissue. We are able to detect up to 6 mm of spacing between the magnets. Pig intestine from Yorkshire pigs was used to characterize the sensor. We are able to distinguish up to five distinct layers of the intestine from the large intestine. This sensing mechanism can indicate the operating surgeon the exact thickness of the tissue compressed between the two magnets. The surgeon can thus be sure of formation of a clean anastomosis and avoid the likelihood of the magnets sliding away or uncoupling.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Med. Devices. 2016;10(1):014501-014501-3. doi:10.1115/1.4032106.

Naegleria fowleri is a free-living amoeba; it is a protist pathogen that is known to cause a fatal encephalitis in humans known as “primary amoebic meningoencephalitis” (PAM). The peak season for the cases admitted to the hospital is in the summers, and all the reported cases have a history of exposure to the warm waters. Mostly, PAM is reported in recent swimmers and people who perform ablution and/or nasal cleansing. Much has been done for vaccination and treatment without any success in past 60 years, but the mortality has remained 99%. Here, we propose a prophylaxis for this disease by introducing a device “Naegleriopel.” This device is noninvasive and requires insertion into the nostrils at times of swimming or water sports related activities. This device, made up of synthetic plastic or silicone, could be adapted to the contours of the interior of the nose. It is expected to reduce the sporadic and seasonal incidences of PAM.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2016;10(1):014502-014502-4. doi:10.1115/1.4032107.

Ex vivo high-resolution measurement of highly crosslinked (HXL) polyethylene hip liner wear is necessary to characterize the in vivo performance of these polymers that exhibit increased wear resistance. Current studies focus on using a coordinate measuring machine (CMM) to acquire data representing the bearing surface(s) of HXL hip liners and use this data to determine linear and volumetric wear. However, these current techniques are subject to error in both data acquisition and data analysis. The purpose of this study was to identify these sources of error and present a novel method for HXL wear measurement that minimizes these contributions to error: our novel methods use a CMM to measure both the articular and backside surfaces of HXL hip liners for subsequent data analysis in Geomagic Control and matlab. Our method involves a vertical orientation of the hip liner to enable one CMM scan of both sides of the hip liner. This method minimizes identified sources of error and proves to be an effective approach for data acquisition of HXL hip liner wear. We also find that our data analysis technique of calculating changes in wall thicknesses is effective in accounting for errors associated with data analysis. Validation of this technique occurred via measurement of two never-implanted HXL hip liners of different sizes (28 mm and 32 mm). In comparing the 32 mm hip liner to its corresponding computer-aided design (CAD) model, we found that our data acquisition technique led to a 0.0019 mm discrepancy between the scanned liner and its CAD model in measured thickness at the pole. We calculated 0.0588 mm and 0.0800 of linear wear for the 28 mm and 32 mm hip liners, respectively, based on our data analysis algorithm. We hypothesize that these reported linear wear values of the never-implanted hip liners are due to machining tolerances of the hip liners themselves.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2016;10(1):014503-014503-5. doi:10.1115/1.4032616.

Deep vein thrombosis (DVT) is a severe medical condition that affects many patients around the world, where one of the main causes is commonly associated with prolonged immobilization. Current mechanical prophylaxis systems, such as the compression stockings and intermittent pneumatic compression devices, have yet to show strong efficacy in preventing DVT. The current study aimed to develop a soft pneumatic sock prototype that uses soft extension pneumatic actuators to provide assisted ankle dorsiflexion–plantarflexion motion, so as to prevent the occurrence of DVT. The prototype was evaluated for its efficacy to provide the required dorsiflexion–plantarflexion motion by donning and actuating the prototype on simulated ankle–foot models with various ankle joint stiffness values. Our results showed that the soft extension actuators in the sock prototype provided controllable assisted ankle plantarflexion through actuator extension and ankle dorsiflexion through actuator contraction, where in our study, the actuations extended to 129.9–146.8% of its original length. Furthermore, the sock was able to achieve consistent range of motion at the simulated ankle joint across different joint stiffness values (range of motion: 27.5 ± 6.0 deg). This study demonstrated the feasibility of using soft extension pneumatic actuators to provide robot-assisted ankle dorsiflexion–plantarflexion motion, which will act as an adjunct to physiotherapists to optimize therapy time for bedridden patients and therefore may reduce the risk of developing DVT.

Commentary by Dr. Valentin Fuster

Errata

J. Med. Devices. 2016;10(1):017001-017001-1. doi:10.1115/1.4032373.

The author names in the publication are incorrect. The correct author names are given below:

Commentary by Dr. Valentin Fuster

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