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Review Article

J. Med. Devices. 2017;11(4):040801-040801-11. doi:10.1115/1.4037258.

Cardiovascular disease (CVD), as the most prevalent human disease, incorporates a broad spectrum of cardiovascular system malfunctions/disorders. While cardiac transplantation is widely acknowledged as the optional treatment for patients suffering from end-stage heart failure (HF), due to its related drawbacks, such as the unavailability of heart donors, alternative treatments, i.e., implanting a ventricular assist device (VAD), it has been extensively utilized in recent years to recover heart function. However, this solution is thought problematic as it fails to satisfactorily provide lifelong support for patients at the end-stage of HF, nor does is solve the problem of their extensive postsurgery complications. In recent years, the huge technological advancements have enabled the manufacturing of a wide variety of reliable VAD devices, which provides a promising avenue for utilizing VAD implantation as the destination therapy (DT) in the future. Along with typical VAD systems, other innovative mechanical devices for cardiac support, as well as cell therapy and bioartificial cardiac tissue, have resulted in researchers proposing a new HF therapy. This paper aims to concisely review the current state of VAD technology, summarize recent advancements, discuss related complications, and argue for the development of the envisioned alternatives of HF therapy.

Commentary by Dr. Valentin Fuster

Research Papers

J. Med. Devices. 2017;11(4):041001-041001-9. doi:10.1115/1.4037259.

Three-dimensional (3D) bioprinting offers innovative research vectors for tissue engineering. However, commercially available bioprinting platforms can be cost prohibitive to small research facilities, especially in an academic setting. The goal is to design and fabricate a low-cost printing platform able to deliver cell-laden fluids with spatial accuracy along the X, Y, and Z axes of 0.1 mm. The bioprinter consists of three subassemblies: a base unit, a gantry, and a shuttle component. The platform utilizes four stepper motors to position along three axes and a fifth stepper motor actuating a pump. The shuttle and gantry are each driven along their respective horizontal axes via separate single stepper motor, while two coupled stepper motors are used to control location along the vertical axis. The current shuttle configuration allows for a 5 mL syringe to be extruded within a work envelope of 180 mm × 160 mm × 120 mm (X, Y, Z). The shuttle can easily be reconfigured to accommodate larger volume syringes. An attachment for a laser pen is located such that printing material may be light-activated pre-extrusion. Positional fidelity was established with calipers possessing a resolution to the nearest hundredth millimeter. The motors associated with the X and Y axes were calibrated to approximately 0.02 mm per motor impulse. The Z axis has a theoretical step distance of ∼51 nm, generating 0.04% error over a 10 mm travel distance. The A axis, or pump motor, has an impulse distance of 0.001 mm. The volume extruded by a single impulse is dictated by the diameter of the syringe used. With a 5 mL syringe possessing an inner diameter of 12.35 mm, the pump pushes as little as 0.119 μL. While the Z axis is tuned to the highest resolution settings for the motor driver, the X, Y, and A axes can obtain higher or lower resolution via physical switches on the motor drivers.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2017;11(4):041002-041002-10. doi:10.1115/1.4037441.

Orthostatic intolerance in patients can occur secondary to concomitant venous pooling and enhanced capillary filtration when standing upright, and is one of the principle causes of syncope or fainting. Compression therapy is commonly recommended for the management of syncope based on the assumption that it increases venous return. Technologies currently used include compression stockings, whose efficacy has, however, been challenged, and intermittent pneumatic pressure devices, which highly restrict the patients' mobility. This paper therefore investigates a novel active compression brace (ACB), which could potentially provide intermittent pressure while not restricting movements. The ACB, actuated by shape memory alloy (SMA) wires, in this work was tested with twelve healthy individuals in a seated position. The experimental observation showed that the ACB can apply a constant initial pressure to the leg similar to commercial compression stockings and also produce intermittent pressure exceeding 30 mmHg. A comparison between analytical and experimental results showed a maximum of 2.08 mmHg absolute averaged difference among all the participants. A correlation analysis showed that the normalized root-mean-square deviation (NRMSD) between the experimental and analytical results had a significant negative correlation with the estimated total calf circumference minus the calf fat cross-sectional area (CSA). A calibration formula, accounting for fat and circumference of the leg, was introduced to account for these two parameters. The comfort of the ACB was also compared to two other available compression devices using questionnaires. No participants reported discomfort in terms of pressure, skin irritation, or heat generated by the ACB.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2017;11(4):041003-041003-10. doi:10.1115/1.4037349.

Chronic obstructive pulmonary disease (COPD) is the fourth leading cause of morbidity in aging populations worldwide. One of the most debilitating effects of COPD is hyperinflation, which restricts the function of healthier portions of the lung, diaphragm, and heart. Bronchoscopic lung volume reduction (BLVR) is a minimally invasive technique to reduce hyperinflation, consisting of one-way valves inserted bronchoscopically that slowly drain the diseased lobe of its accumulated air. Presented here is a novel redesign of current BLVR devices using pop-up microelectromechanical systems (MEMS) manufacturing to create microscale check valves. These operate more reliably than current polymer valves and allow tunable airflow to accommodate widely varying patient physiologies. Analysis and ex vivo testing of the redesigned valve predicted the valve should outlast current valves with a lifetime of well over 8 yr and showed airflow controllability within desired physiological ranges of up to 1.2 SLM. The valve resists backflow twice as well as the current standard valves while permitting comparable forward flow.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2017;11(4):041004-041004-6. doi:10.1115/1.4037257.

Improperly designed medical devices can induce unwanted biomechanical stressors on their users, impacting health and career longevity. Despite this, manufacturers struggle to balance device design with the growing female surgeon population. We have applied anthropometry to a population of surgeon hands as an alternative to preferred glove size. Correlations to physical dimensions of two laparoscopic staplers were assessed. Five anthropometric measurements were taken from dominant hands of surgeons. These measurements were selected with the goal of comparing resulting data to published anthropometry studies and assessing correlation to preferred glove size and instrument design. The trigger reach of the two laparoscopic staplers were measured to assess suitability among the surgeon population surveyed. Fifty eight surgeons (50 male, 8 female), average glove size 7.5 and 6.0, were measured. Data indicate that male surgeons had significantly larger hands than female. Hand circumference displayed a relatively strong positive correlation with preferred glove size (0.799, R2 = 63.9%); other measurements did not. The trigger span of one stapler was found suitable for only 78.2% of male and 30.9% of female surgeons, based on comparisons with anthropometry of the surveyed population. Anthropometry should be used to characterize surgeon hands instead of preferred glove size. Also, from the limited scope of this research, discrepancies exist between the size of the surgeon hand and the devices designed for their use. The use of inappropriately designed instrumentation can cause musculoskeletal injury, decreased productivity, and shortened careers. Manufacturers would benefit by consulting anthropometry databases to develop products.

Commentary by Dr. Valentin Fuster

Design Innovation Paper

J. Med. Devices. 2017;11(4):045001-045001-7. doi:10.1115/1.4037260.

An adjustable-length intramedullary (IM) nail may reduce both complications secondary to fracture fixation and manufacturing costs. We hypothesized that our novel nail would have suitable mechanical performance. To test this hypothesis, we manufactured three prototypes and evaluated them in quasi-static axial compression and torsion and quasi-static four-point bending. Prototypes were dynamically evaluated in both cyclic axial loading and four-point bending and torsion-to-failure. The prototypes exceeded expectations; they were comparable in both quasi-static axial stiffness (1.41 ± 0.37 N/m in cervine tibiae and 2.30 ± 0.63 in cadaver tibiae) and torsional stiffness (1.05 ± 0.26 N·m/deg in cervine tibiae) to currently used nails. The quasi-static four-point bending stiffness was 80.11 ± 09.360, greater than reported for currently used nails. A length-variance analysis indicates that moderate changes in length do not unacceptably alter bone-implant axial stiffness. After 103,000 cycles of axial loading, the prototype failed at the locking screws, comparable to locking screw failures seen clinically. The prototypes survived 1,000,000 cycles of four-point bend cyclic loading, as indicated by a consistent phase angle throughout cyclic loading. The torsion-to-failure test suggests that the prototype has adequate resistance to applied torques that might occur during the healing process. Together, these results suggest that our novel IM nail performs sufficiently well to merit further development. If brought to market, this adjustable-length IM nail could reduce both patient complications and healthcare costs.

Commentary by Dr. Valentin Fuster

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