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Research Papers

J. Med. Devices. 2018;12(3):031001-031001-12. doi:10.1115/1.4040183.

To improve the balance of individuals with lower limb amputation on coronally uneven terrain, a coronally clutching ankle (CCA) was developed to actively adapt through ±15 deg of free coronal foot rotation during the first ∼60 ms of initial contact. Three individuals with lower limb amputations were fit with the CCA and walked across an instrumented walkway with a middle step that was either flush, 15 deg inverted, or 15 deg everted. An opaque latex membrane was placed over the middle step, making the coronally uneven terrain unpredictable. Compared to participants' clinically prescribed prosthesis, the CCA exhibited significantly more coronal angular adaption during early stance. The CCA also improved participants' center of mass (COM) path regulation during the recovery step (reduced variation in mediolateral position) and reduced the use of the hip and stepping recovery strategies, suggesting it improved participants' balance and enabled a quicker recovery from the disturbance. However, use of the CCA did not significantly affect participants' ability to regulate their coronal angular momentum during the disturbance, suggesting that the CCA did not improve all elements of dynamic balance. Reducing the distance between the CCA's pivot axis and the base of the prosthetic foot might resolve this issue. These findings suggest that actively adapting the coronal plane angle of a prosthetic ankle can improve certain elements of balance for individuals with lower limb amputation who walk on coronally uneven and unpredictable terrain.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2018;12(3):031002-031002-11. doi:10.1115/1.4040184.

Radiofrequency ablation (RFA) is an increasingly used, minimally invasive, cancer treatment modality for patients who are unwilling or unable to undergo a major resective surgery. There is a need for RFA electrodes that generate thermal ablation zones that closely match the geometry of typical tumors, especially for endoscopic ultrasound-guided (EUS) RFA. In this paper, the procedure for optimization of an RFA electrode is presented. First, a novel compliant electrode design is proposed. Next, a thermal ablation model is developed to predict the ablation zone produced by an RFA electrode in biological tissue. Then, a multi-objective genetic algorithm is used to optimize two cases of the electrode geometry to match the region of destructed tissue to a spherical tumor of a specified diameter. This optimization procedure is then applied to EUS-RFA ablation of pancreatic tissue. For a target 2.5 cm spherical tumor, the optimal design parameters of the compliant electrode design are found for two cases. Cases 1 and 2 optimal solutions filled 70.9% and 87.0% of the target volume as compared to only 25.1% for a standard straight electrode. The results of the optimization demonstrate how computational models combined with optimization can be used for systematic design of ablation electrodes. The optimization procedure may be applied to RFA of various tissue types for systematic design of electrodes for a specific target shape.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2018;12(3):031003-031003-8. doi:10.1115/1.4040187.

Noninvasive ventilator support using bi-level positive airway pressure/continuous positive airway pressure (BiPAP/CPAP) is commonly utilized for chronic medical conditions like sleep apnea and neuromuscular disorders like amyotrophic lateral sclerosis (ALS) that lead to weakness of respiratory muscles. Generic masks come in standard sizes and are often perceived by patients as being uncomfortable, ill-fitting, and leaky. A significant number of patients are unable to tolerate the masks and eventually stop using their devices. The goal of this project is to develop custom-fit masks to increase comfort, decrease air leakage, and thereby improve patient compliance. A single-patient case study of a patient with variant ALS was performed to evaluate the custom-fit masks. His high nose bridge and overbite of lower jaw caused poor fit with generic masks, and he was noncompliant with his machine. Using desktop Stereolithography three-dimensional (3D) printing and magnetic resonance imaging (MRI) data, a generic mask was extended with a rigid interface such that it was complementary to the patient's unique facial contours. Patient or clinicians interactively select a desired mask shape using a newly developed computer program. Subsequently, a compliant silicone layer was applied to the rigid interface. Ten different custom-fit mask designs were made using computer-aided design software. Patient evaluated the comfort, extent of leakage, and satisfaction of each mask via a questionnaire. All custom-fit masks were rated higher than the standard mask except for two. Our results suggest that modifying generic masks with a 3D-printed custom-fit interface is a promising strategy to improve compliance with BiPAP/CPAP machines.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2018;12(3):031004-031004-12. doi:10.1115/1.4040185.

An automated surgical device, the ventilator tube applicator (VTA), enables a grommet insertion surgery for patients with otitis media with effusion (OME) to be completed in a short time automatically and precisely, eliminating the use of general anesthesia (GA) typically required in such procedure. However, its current design limits the usefulness of the device as it is restricted by the properties of the tympanic membrane (TM), such as angle, thickness, and strength. Therefore, a novel design was conceptualized and the insertion control algorithm was improved to overcome the current challenges of the VTA. This innovative cover-cutter instrument design allows three-dimensional (3D) motion on an oblique surface using a single axis actuator. Experimental results on mock membranes showed great improvements in terms of robustness and success rate. The new design allowed the procedure to be performed on wider range of TM angles and hence increased the effectiveness of VTA. Grommet insertion force was reduced by an average of 66%, and the overall peak force reduced by an average of 14%. Finite element (FE) analysis on a cadaveric TM model further validated the usefulness of the cover-cutter instrument, and showed some interesting insights in the grommet insertion process.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2018;12(3):031005-031005-13. doi:10.1115/1.4040188.

Premature infants often require respiratory support with a varying concentration of the fraction of inspired oxygen FiO2 to keep the arterial oxygen saturation typically measured using a peripheral sensor (SpO2) within the desired range to avoid both hypoxia and hyperoxia. The widespread practice for controlling the fraction of inspired oxygen is by manual adjustment. Automatic control of the oxygen to assist care providers is desired. A novel closed-loop respiratory support device with dynamic adaptability is evaluated nonclinically by using a neonatal respiratory response model. The device demonstrated the ability to improve oxygen saturation control over manual control by increasing the proportion of time where SpO2 is within the desired range while minimizing the episodes and periods where SpO2 of the neonatal respiratory model is out of the target range.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2018;12(3):031006-031006-7. doi:10.1115/1.4040635.

Skin cancer represents one of the most common forms of cancer in the U.S. This and other skin disorders can be effectively diagnosed by performing a punch biopsy to obtain full-thickness skin specimens. Their quality depends on the forces exerted by the punch cannula during the cutting process. The reduction of these forces is critical in the extraction of high quality tissue samples from the patient. During skin biopsy, the biopsy punch (BP) is advanced into the lesion while it is rotated alternately clockwise and counterclockwise generating, therefore, a rotary vibrational motion. No previous studies analyzed whether this motion is effective in soft tissue cutting and if it could be improved. In this study, the BP procedure is investigated in detail. First, the steady cutting motion of the BP is analyzed. Then, the superimposition of several vibrational motions onto the rotary motion of the BP is investigated. Analytical models, based on a fracture mechanics approach, are adopted to predict the cutting forces. Experimental studies are performed on phantom tissue, usually adopted in medical investigations. The results demonstrate that the application of rotary vibrational motions determines the increase of the force and penetration depth necessary to fracture soft tissue, while the implementation of axial vibrations can lead to 30% decrease of the axial force. The outcome of this study can benefit several clinical procedures in which a cannula device is used to cut and collect soft tissue samples.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2018;12(3):031007-031007-6. doi:10.1115/1.4040492.

Polymer needles for medical injections offer a range of opportunities like compatibility with magnetic resonance scanning and simultaneous delivery of more than one drug. However, the lower stiffness property of polymers compared to steel is a challenge for penetration. This paper explores strategies for higher penetration success, which include impulse insertion, tissue stretching, and different tip geometries. The strategies are experimentally examined using three layers of nitrile rubber gloves and sticking glue to create an artificial skin model. It is demonstrated that polymer needles have higher penetration rates when the strategies are applied. Penetration rates were only 10–20% when using slow speed insertion (0.2 mm/s) but 100% penetration rates was achieved using impulse insertion. Penetration forces are similar for slow insertion speed and high speed (impulse insertion) and for needles made out of different material (polymer or steel). Conical and pyramidal tips were studied for polymer needles and a commercial bevel steel needle tip. The result was lower penetration forces and 100% penetration success was possible using the pyramidal polymer needles. For the model in study was observed a similar behavior (penetration force and rate of penetration success) for steel and polymer pyramidal needles. An analysis of variance statistical analysis show significance when using springs and strain, as well for the combination of both.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2018;12(3):031008-031008-8. doi:10.1115/1.4040638.

Natural orifice translumenal endoscopic surgery (NOTES) has offered significant advantages of less pain, reduced recovery time, and minimized scar after operation, demonstrating a promising development prospect. However, the large-size specimen extraction remains challenging for NOTES, due to the narrow space of the human natural orifices. To address such difficulties, a specimen extraction method that utilizes the braided fiber tube (BFT) structure with excellent retractility to accommodate and bind the bulky specimen has been proposed. Based on the theory of helical spring, the geometric model and the mechanical model of the BFT are established, and experiments have been performed to verify the accuracy of the derived mechanical model. In addition, a tensile test of using the BFT to extract large specimens via a small channel is carried out, which verifies the stable extraction performance of the proposed design. The BFT will not be damaged when extracting the specimen with a diameter less than 1.75 times of the channel diameter. A NOTES-specific specimen extraction instrument is designed according to the characteristics of NOTES, and it has three degrees-of-freedom and is able to actively capture different specimen by using a suction cup. Finally, specimen extraction experiments on NOTES multitasking platform phantom have been conducted using the prototyped instrument to validate its feasibility and effectiveness.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2018;12(3):031009-031009-10. doi:10.1115/1.4040699.

This paper describes a control approach for a lower limb exoskeleton intended to enable stair ascent and descent of variable geometry staircases for individuals with paraplegia resulting from spinal cord injury (SCI). To assess the efficacy of ascent and descent functionality provided by the control approach, the controller was implemented in a lower limb exoskeleton and tested in experimental trials on three subjects with motor-complete SCI on three staircases of varying geometry. Results from the assessments indicate that subjects were able to capably ascend and descend step heights varying from 7.6 to 16.5 cm without changing control settings; the controller provided for step time consistency highly representative of healthy subjects (9.2% variation in exoskeleton step time, relative to 7.7% variation in healthy subjects); and the exoskeleton provided peak joint torques on average 110% and 74% of the healthy-subject peak joint torques during stair ascent and descent, respectively. Subject perceived exertion during the stair ascent and descent activities was rated between “light” and “very light.”

Commentary by Dr. Valentin Fuster

Technical Brief

J. Med. Devices. 2018;12(3):034501-034501-4. doi:10.1115/1.4040637.

Surgical needles are commonly used to reach target locations inside of the body for percutaneous procedures. The major issues in needle steering in tissues are the insertion force which causes tissue damage and tissue deformation that causes the needle path deviation (i.e., tip deflection) resulting in the needle missing the intended target. In this study, honeybee-inspired needle prototypes were proposed and studied to decrease the insertion force and to reduce the tissue deformation. Three-dimensional (3D) printing technology was used to manufacture scaled-up needle prototypes. Needle insertion tests on tissue-mimicking polyvinyl chloride (PVC) gel were performed to measure the insertion force and the tip deflection. Digital image correlation (DIC) study was conducted to determine the tissue deformation during the insertion. It was demonstrated that the bioinspired needles can be utilized to decrease the insertion force by 24% and to minimize the tip deflection. It was also observed that the bioinspired needles decrease the tissue deformation by 17%. From this study, it can be concluded that the proposed bee-inspired needle design can be used to develop and manufacture innovative surgical needles for more effective and less invasive percutaneous procedures.

Commentary by Dr. Valentin Fuster

Expert View

J. Med. Devices. 2018;12(3):034701-034701-8. doi:10.1115/1.4040489.

Rare diseases (RD) affect approximately 30 million Americans, half of whom are children. This study is the first to comprehensively evaluate their medical device needs via a survey of physicians. The study sought to identify and document the presumed unmet diagnostic and therapeutic device needs for RD management; clarify the magnitude of the potential unmet need; and generate meaningful data to inform medical device stakeholders. A cross-sectional nonprobability survey was conducted. The study population was drawn from the membership files of four groups: FDA Medical Devices Advisory Committee, Pediatric Advisory Committee, Pediatric Device Consortia, and National Institutes of Health (NIH) Rare Diseases Clinical Research Network. Only physician respondents with experience or knowledge regarding RD were eligible. Among eligible respondents, 90% confirmed the need for innovative devices to care for people with RD. Over 850 device needs were identified for 436 RD, with 74% of needs related to children. Pediatric physicians (OR = 2.11, 95% CI 1.01–4.39, P = 0.046) and physicians with more RD experience reflected greater dissatisfaction with existing devices (OR = 4.49, 95% CI 2.25–8.96, P < 0.0001). Creation of entirely new devices is the top recommendation for mitigating needs. This study demonstrates a major public health need for innovative medical devices to care for children and adults with RD. FDA and NIH support and seek opportunities to accelerate device development for these vulnerable patients.

Commentary by Dr. Valentin Fuster

Design Innovation Paper

J. Med. Devices. 2018;12(3):035001-035001-9. doi:10.1115/1.4040186.

Wide mesh or tape sutures are used to close high-tension wounds such as in hernia or tendon repair. However, wide sutures produce large knots that are susceptible to increased palpability, infection, and foreign body response. To prevent such adverse events, we developed a small suture anchor to replace wide suture knots. The suture anchor was iteratively developed using three-dimensional (3D) design software and produced via 3D printing. Anchor prototypes underwent monotonic, cyclic fatigue, and stress-life testing in a benchtop soft tissue suture model. Results were compared to a standard of care knot and alternative suture fixation devices. The final anchor design was selected based on minimal size and mechanical performance. The size of the final anchor (200 mm3) was 33% smaller than a tape suture knot and 68% smaller than a mesh suture knot. Monotonic testing of mesh and tape sutures revealed a significantly greater anchor failure load compared to knot and alternative fixations (p < 0.05). Additionally, all anchors successfully completed cyclic fatigue testing without failure while other fixations, including knot, failed to complete cyclic fatigue testing multiple times. Stress-life testing demonstrated durable anchor fixation under varying tensile stresses. Failure mode analysis revealed anchor fracture and tissue failure as modes of anchor failure, each of which occurred at supraphysiologic forces. We created a small suture anchor that significantly outperforms knot and alternative suture fixations in benchtop testing and addresses concerns of increased palpability, infection, and foreign body response from large suture knots.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2018;12(3):035002-035002-9. doi:10.1115/1.4040636.

Even though technological advances have increased the application area of minimally invasive surgery (MIS), there are still hurdles to allow for widespread adoption for more complex procedures. The development of steerable instruments, in which the surgeon can alter the tip orientation, has increased the application area of MIS, but they are bulky, which limits their ability to navigate through narrow environments, and complex, which complicates miniaturization. Furthermore, they do not allow for navigating through complex anatomies. In an effort to improve the dexterity of the MIS instruments, while minimizing the outer dimensions, the previously developed cable-ring mechanism was redesigned, resulting in the thinnest, Ø 2 mm (Ø 1 mm lumen), eight degrees-of-freedom (DOF) multisteerable tip for MIS to date. The multisteerable tip consists of four steerable segments of 2DOF stackable elements allowing for ±90 deg articulation, as well the construction of complex shapes, actuated by 16 Ø 0.2 mm stainless steel cables. In a proof-of-principle experiment, an ultrasound transducer and optical shape sensing (OSS) fiber were inserted in the lumen, and the multisteerable tip was used to perform scanning motions in order to reconstruct a wire frame in three-dimensional (3D). This configuration could in future be used to safely navigate through delicate environments and allow for tissue characterization. Therefore, the multisteerable tip has the potential to increase the application area of MIS in future, as it allows for improved dexterity, the ability to guide several tip tools toward the operation area, and the ability to navigate through tight anatomies.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2018;12(3):035003-035003-9. doi:10.1115/1.4040639.

Optical molecular imaging is an emerging field, and high-resolution optical imaging of the distal lung parenchyma has been made possible with the advent of clinically approved fiber-based imaging modalities. However, currently, there is no single method of allowing the simultaneous imaging and delivery of targeted molecular imaging agents. The objective of this research is to create a catheterized device capable of fulfilling this need. We describe the rationale, development, and validation in ex vivo ovine lung to near clinical readiness of a triple lumen bronchoscopy catheter that allows concurrent imaging and fluid delivery, with the aim of clinical use to deliver multiple fluorescent compounds to image alveolar pathology. Using this device, we were able to produce high-quality images of bacterial infiltrates in ex vivo ovine lung within 60 s of instilling a single microdose of (<100 mcg) imaging agent. This has many advantages for future clinical usage over the current state of the art.

Commentary by Dr. Valentin Fuster

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