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Research Papers

J. Med. Devices. 2011;5(3):031002-031002-6. doi:10.1115/1.4004416.

A challenge is always presented when attempting to measure the pain an individual patient experiences. Unfortunately, present technologies rely nearly exclusively on subjective techniques. Using these current techniques, a physician may use a manually operated algometer and a series of questionnaires to gauge an individual patient’s pain scale. Unfortunately these devices and test methods have been suggested to introduce error due to variability and inconsistent testing methods. Some studies have shown large variability, while others have shown minimal variability, both between patients and within the same patient during multiple testing sessions. Recent studies have also shown a lack of correlation between pain threshold and pain tolerance in pain sensitivity tests. Hand-held algometer devices can be difficult to maintain consistent application rates over multiple test periods, possibly adding to widespread variability. Furthermore, there are limited test results that correlate pain ratings with biological measures in real time. The computer-controlled pressure algometer described is not hand-held or dependent on significant examiner input. This new device is capable of recording electrocardiograph (ECG), blood pressure (BP), pressure pain threshold (PPT), and pressure pain tolerance (PPTol) in real time. One major goal is the capability of correlating pain stimuli with algometer pressure, heart rate, and blood pressure. If a predictable correlation between vital signs and pain could be established, significant gains in the understanding of pain could result. Better understanding of pain will ultimately lead to improvements in treatment and diagnosis of pain conditions, helping patients and physicians alike.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2011;5(3):031003-031003-9. doi:10.1115/1.4004417.

This paper presents the authors’ investigation results of applying the pneumatic artificial muscle actuation to above-knee prostheses. As a well-known muscle actuator, the pneumatic artificial muscle actuator features a number of unique advantages, including high power density, and similar elastic characteristics to biological muscles. Despite multiple applications in related areas, the application of pneumatic artificial muscle in above-knee prostheses has not been explored. Inspired by this fact, the research presented in this paper aims to develop a pneumatic artificial muscle-actuated above-knee prosthesis, with three specific objectives: (1) demonstrate the pneumatic artificial muscle actuation’s capability in generating sufficient torque output to meet the locomotive requirements; (2) develop an effective control approach to enable the restoration of locomotive functions; (3) conduct preliminary testing of the prosthesis prototype on a healthy subject through a specially designed able-body adaptor. In the prosthesis design, an agonist–antagonist layout is utilized to obtain a bidirectional motion. To minimize the radial profile, an open-frame structure is used, with the purpose of allowing the expansion of the muscle actuators into the center space without interference. Also, the muscle actuator parameters are calculated to provide sufficient torque capacity (up to 140 N m) to meet the requirements of level walking. According to this design, the fabricated prototype weighs approximately 3 kg, with a range of motion of approximately 100°. For the control of the prosthesis, a model-based torque control algorithm is developed based on the sliding mode control approach, which provides robust torque control for this highly nonlinear system. Combining this torque control algorithm with an impedance-based torque command generator (higher-level control algorithm), the fabricated prosthesis prototype has demonstrated a capability of providing a natural gait during treadmill walking experiments.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2011;5(3):031004-031004-6. doi:10.1115/1.4004316.

Although hemodiafiltration is presumed to be a gold standard for higher convective therapy for kidney failure patients, the repetition of forward and backward filtration during hemodialysis increases the total filtration volume and convective clearance. Hence, the authors describe a new method of enhancing forward filtration and backfiltration. The devised method, named pulse push/pull hemodialysis (PPPHD), is based on the utilization of dual pulsation in a dialysate stream; namely, pulsatile devices in the dialysate stream both upstream (a dialysate pump) and downstream (an effluent pump) of the dialyzer. Fluid management accuracy of the unit was assessed using fresh bovine blood, and its hemodialytic performance was investigated in a canine renal failure model. Forward filtration rates during PPPHD were maintained at the levels of dialysate flow rates. Fluid balancing error was less than ±0.84% of total dialysate volume, when 97.4 ± 1.66L of pure dialysate was circulated for 4 hs. The animal remained stable without any complication. Urea and creatinine reductions were 56.9 ± 1.6 and 52.8 ± 2.3%, respectively, and albumin levels remained uniform throughout treatment. The devised PPPHD unit offers a simple, but efficient strategy of combined simultaneous diffusive and convective solute transport for ESRD patients, without the need for external replacement infusion.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2011;5(3):031005-031005-9. doi:10.1115/1.4004418.

Endoscopy is a minimally invasive procedure using instruments that pass through the body for diagnostic purposes and minimizes the risks associated with open surgery. Colonoscopy can viewed as an endoscopic procedure of the colon. Colonoscopy may cause extreme discomfort to the patient and also carries the risks of perforating the lining of the colon, splenic ruptures, or bleeding. The technology is an endoscope that has an exoskeleton structure of controllable stiffness and a highly flexible stem. The device saves the patient from the pain caused by the shaft of a colonoscope when it is guided from the anus to the end of the sigmoid colon. The stiffenable sheath guides the shaft of the colonoscope up to the end of the sigmoid colon to avoid looping the shaft of the colonoscope. A prototype of the device was built and tested to validate its effectiveness. In order to further improve the performance of the device, skilled endoscopists tested and validated the device using a colonoscopy training model. The colonoscopy training model is comprised of a configurable rubber colon, a human torso, a display, and sensing part. It measures the forces caused by the distal tip and the shaft of the colonoscope and the pressure to open up the lumen. The force sensors at the rubber colon constraints measure the forces, and the real-time display panel will show the results to the colonoscopist and record the data for analysis. The endoscopy sheath device improves the process of endoscopy by reducing the mechanical trauma and loops caused by the shaft of the endoscope. With the guide provided by the colonoscope sheath, the forces to the constraints of a colon are significantly decreased in the sigmoid colon. The colonoscope sheath helps to reduce the force to constraints of the colon and isolates the direct contact between the shaft of a colonoscope and a colon wall up to the end of the sigmoid colon. For the complicated shape of the colon, the endoscopy sheath also solved possible looping problems. The colonoscope training model effectively measures the forces and makes it possible to validate the effectiveness of the endoscopy sheath.

Topics: Force , Endoscopes , Stiffness
Commentary by Dr. Valentin Fuster
J. Med. Devices. 2011;5(3):031006-031006-9. doi:10.1115/1.4004648.

This paper presents the design and simulation of a cyclic robot for lower-limb exercise robots. The robot is designed specifically for cyclic motions and the high power nature of lower-limb interaction—as such, it breaks from traditional robotics wisdom by intentionally traveling through singularities and incorporating large inertia. Such attributes lead to explicit design considerations. Results from a simulation show that the specific design requires only a reasonably sized damper and motor.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2011;5(3):031007-031007-7. doi:10.1115/1.4004654.

Finite Element Analysis (FEA) of Nitinol medical devices has become prevalent in the industry. The analysis methods have evolved in time with the knowledge about the material, the manufacturing processes, the testing or in vivo loading conditions, and the FEA technologies and computing power themselves. As a result, some common practices have developed. This paper presents a study in which some commonly made assumptions in FEA of Nitinol devices were challenged and their effect was ascertained. The base model pertains to the simulation of the fabrication of a diamond shape stent specimen, followed by cyclic loading. This specimen is being used by a consortium of several stent manufacturers dedicated to the development of fatigue laws suitable for life prediction of Nitinol devices. The FEA models represent the geometry of the specimens built, for which geometrical tolerances were measured. These models use converged meshes, and all simulations were run in the FEA code Abaqus making use of its Nitinol material models. Uniaxial material properties were measured in dogbone specimens subjected to the same fabrication process as the diamond specimens. By convention, the study looked at computed geometry versus measured geometry and at the maximum principal strain amplitudes during cyclic loading. The first aspect studied was the effect of simulating a single expansion to the final diameter compared to a sequence of three partial expansions each followed by shape setting. The second aspect was to ascertain whether it was feasible to conduct the full analysis with a model based on the electropolished dimensions or should an electropolish layer be removed only at the end of fabrication, similar to the manufacturing process. Finally, the effect of dimensional tolerances was studied. For this particular geometry and loading, modeling of a single expansion made no discernable difference. The fabrication tolerances were so tight that the effect on the computed fatigue drivers was also very small. The timing of the removal of the electropolished layer showed an effect on the results. This may have been so, because the specimen studied is not completely periodic in the circumferential direction.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2011;5(3):031008-031008-8. doi:10.1115/1.4004650.

This work proposes a small, light, valveless pump design for a portable renal replacement system. By analyzing the working principle of the pump and exploring the design space using an analytical pump model, we developed a novel design for a cam-driven finger pump. Several cams sequentially compress fingers, which compress flexible tubes; thus eliminating valves. Changing the speed of the motor or size of the tube controls the flow rate. In vitro experiments conducted with whole blood using the pump measured Creatinine levels over time, and the results verify the design for the portable renal replacement system. The proposed pump design is smaller than 153 cm3 and consumes less than 1 W while providing a flow rate of more than 100 ml/min for both blood and dialysate flows. The smallest pump of a portable renal replacement system in the literature uses check valves, which considerably increase the overall manufacturing cost and possibility of blood clotting. Compared to that pump, the proposed pump design achieved reduction in size by 52% and savings in energy consumption by 89% with the removal of valves. This simple and reliable design substantially reduces the size requirements of a portable renal replacement system.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2011;5(3):031009-031009-7. doi:10.1115/1.4004653.

This paper describes the design and performance of a new prosthetic hand capable of multiple grasp configurations, and capable of fingertip forces and speeds comparable to those used by healthy subjects in typical activities of daily living. The hand incorporates four motor units within the palm, which together drive sixteen joints through tendon actuation. Each motor unit consists of a brushless motor that drives one or more tendons through a custom two-way clutch and pulley assembly. After presenting the design of the prosthesis, the paper presents a characterization of the hand’s performance. This includes its ability to provide eight grasp postures, as well as its ability to provide fingertip forces and finger speeds comparable to those described in the biomechanics literature corresponding to activities of daily living.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2011;5(3):031010-031010-6. doi:10.1115/1.4004793.

Actuators for physical human-robot interaction (pHRI) such as rehabilitation or assistive systems should generate the desired torque precisely. However, the resistive and inertia loads inherent in the actuators (e.g., friction, damping, and inertia) set challenges in the control of actuators in a force/torque mode. The resistive factors include nonlinear effects and should be considered in the controller design to generate the desired force accurately. Moreover, the uncertainties in the plant dynamics make the precise torque control difficult. In this paper, nonlinear control algorithms are exploited for a rotary series elastic actuator to generate the desired torque precisely in the presence of nonlinear resistive factors and modeling uncertainty. The sliding mode control smoothed by a boundary layer is applied to enhance the robustness for the modeling uncertainty without chattering phenomenon. In this paper, the rotary series elastic actuator (RSEA) is installed on the knee joint of an orthosis, and the thickness of the boundary layer is changed by gait phases in order to minimize the torque error without the chattering phenomenon. The performance of the proposed controller is verified by experiments with actual walking motions.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2011;5(3):031011-031011-11. doi:10.1115/1.4004647.

The development of nanoceramics-polymer composites and bioactive materials such as calcium phosphates and bioglasses and ceramics especially hydroxyapatite (HAp) and β-tricalcium phosphate (TCP) for bone regeneration has been carried out for bone regeneration. Due to their resorption in the body and direct contact with tissues, it is necessary to sterilize the dental graft before administration to the patient. Three different dental graft materials including TCP, bioglass, and equine bone tissue (G1, G2, and G3, respectively) were studied in this study. The effects of γ irradiation were evaluated with different analytical methods (organoleptic analysis, FTIR, DSC, TGA, and SEM) and microbiological analysis (sterility, pyrogenity, and sterility assurance level (SAL) determination). The physicochemical results indicated that G1 is the most γ stable (optimum) dental graft material for γ radiation sterilization with minimum changes in chemical and physical properties in comparison with other two dental graft materials. G3, was the most sensitive dental graft material according to organoleptic investigations, TGA and SEM analysis. Another aspect of this study was, to investigate the effect of ethylene oxide (EtO) sterilization on optimum dental graft material, G1 and the comparison of two sterilization methods with analytical and microbiological examinations. The resorption times and resorption characteristics of γ sterilized dental graft material (G1G ) and EtO sterilized one (G1E ) were evaluated on New Zealand rabbits for 12 weeks. Histological studies showed that TCP containing dental graft material, G1, did not induce inflammation in bone and soft tissue. Resorption and bone formation of G1G was faster than G1E . Total resorption time of G1 was 12 weeks for both sterilization groups. The analytical, microbiological and in vivo results suggest that the dental graft G1 can be sterilized with γ radiation safely with validated doses lower than medical γ sterilization dose, 25 kGy.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2011;5(3):031012-031012-5. doi:10.1115/1.4004833.

Microneedles have been an expanding medical technology in recent years due to their ability to penetrate tissue and deliver therapy with minimal invasiveness and patient discomfort. Variations in design have allowed for enhanced fluid delivery, biopsy collection, and the measurement of electric potentials. Our novel microneedle design attempts to combine many of these functions into a single length of silica tubing capable of both light and fluid delivery terminating in a sharp tip of less than 100 μm in diameter. This paper focuses on the fluid flow aspects of the design, characterizing the contributions to hydraulic resistance from the geometric parameters of the microneedles. Experiments consisted of measuring the volumetric flow rate of de-ionized water at set pressures (ranging from 69 to 621 kPa) through a relevant range of tubing lengths, needle lengths, and needle tip diameters. Data analysis showed that the silica tubing (∼150 μm bore diameter) adhered to within ±5% of the theoretical prediction by Poiseuille’s Law describing laminar internal pipe flow at Reynolds numbers less than 700. High hydraulic resistance within the microneedles correlated with decreasing tip diameter. The hydraulic resistance offered by the silica tubing preceding the microneedle taper was approximately 1–2 orders of magnitude less per unit length, but remained the dominating resistance in most experiments as the tubing length was > 30 mm. These findings will be incorporated into future design permutations to produce a microneedle capable of both efficient fluid transfer and light delivery.

Commentary by Dr. Valentin Fuster

Technical Briefs

J. Med. Devices. 2011;5(3):034501-034501-5. doi:10.1115/1.4004646.

A new and miniature imaging device is being developed to allow flexible endoscopy in regions of the body that are difficult to reach. The scanning fiber endoscope employs a single scanning optical fiber to illuminate a target area, while backscattered light is detected one pixel at a time to build a complete image. During each imaging cycle the fiber is driven outward in a spiral pattern from its resting state at the image center to the outer fringe of the image. At this point, the fiber is quickly driven back to its initial position before acquiring a subsequent frame. This work shortens the time between successive images to achieve higher overall frame rates by applying a carefully timed input, which counteracts the tip motion of the scanning fiber, quickly forcing the scanning fiber to the image center. This input is called motion braking and is a square wave function dependent upon the damped natural frequency of the scanning fiber and the instantaneous tip displacement and velocity. Imaging efficiency of the scanning fiber endoscope was increased from 75–89% with this implementation.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2011;5(3):034502-034502-6. doi:10.1115/1.4004651.

Recently, microneedles (or microneedle arrays) for transdermal drug delivery have received increasing attention because they can provide painless, minimal invasiveness and time-released drug delivery. However, it is very difficult to design such an eligible microneedle that meets all the requirements for mechanical strength, small insertion force, and good biocompatibility. In this paper, we investigate a biomicroneedle: caterpillar spine. It is found that this type of biomicroneedle can pierce mouse skin using a very small force (about 173 μN) without fracture and buckling failures. Such excellent properties are mainly a result of its optimal geometry evolved by Nature, the high hardness, and the reasonable high elastic modulus near the tip end. This finding may provide an inspiration for the development of improved transdermal drug delivery microneedles.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2011;5(3):034503-034503-6. doi:10.1115/1.4004649.

As minimally invasive operations are performed through small portals, the limited manipulation capability of straight surgical instruments is an issue. Access to the pathology site can be challenging, especially in confined anatomic areas with few available portals, such as the knee joint. The goal in this paper is to present and evaluate a new sideways-steerable instrument joint that fits within a small diameter and enables transmission of relative high forces (e.g., for cutting of tough tissue). Meniscectomy was selected as a target procedure for which quantitative design criteria were formulated. The steering mechanism consists of a crossed configuration of a compliant rolling-contact element that forms the instrument joint, which is rotated by flexural steering beams that are configured in a parallelogram mechanism. The actuation of cutting is performed by steel wire that runs through the center of rotation of the instrument joint. A prototype of the concept was fabricated and evaluated technically. The prototype demonstrated a range of motion between −22° and 25° with a steering stiffness of 17.6 Nmm/rad (min 16.9 – max 18.2 Nmm/rad). Mechanical tests confirmed that the prototype can transmit an axial load of 200 N on the tip with a maximum parasitic deflection of 4.4°. A new sideways steerable mechanical instrument joint was designed to improve sideways range of motion while enabling the cutting of strong tissues in a minimally invasive procedure. Proof of principle was achieved for the main criteria, which encourages the future development of a complete instrument.

Commentary by Dr. Valentin Fuster

Design Innovation

J. Med. Devices. 2011;5(3):035001-035001-6. doi:10.1115/1.4003674.

Persistence of the ductus arteriosus (DA) after birth leads to the congenital heart disease known as patent ductus arteriosus (PDA). The objective of this study is to develop an evaluation protocol and to propose a new and innovative intraductal design for a PDA occluder in order to conform to the varied morphology of the DA and to overcome the problems associated with devices relying on the anchorage mechanism. The new design, an assembly of 36 planar thermally treated Nitinol wires called Novel Device 36 (ND36), is in the shape of a frustum of a cone with a larger diameter of 12 mm, smaller diameter of 6 mm, and length of 11 mm. In-vitro biomimetic evaluations, namely, hemolysis tests and platelet adhesion studies, were conducted to ascertain the biocompatibility of the thermally treated Nitinol wires. These tests were also conducted on two different dimensions of Dacron fibers, which were to be sutured onto the device to induce thrombogenesis while in the duct, thereby facilitating better occlusion. Flow dynamics tests, which help simulate the dynamic conditions prevalent in the duct, were carried out on the ND36 and a commercially used PDA occlusion device. An analysis of the scanning electronic microscopy images showed no platelet adhesion on the Nitinol wires. The tested wires also showed nearly 0% hemolysis. Dacron fibers 0.2 mm thick and having an area density of 77 GSM proved to be best suited. Comparative analysis carried out with the commercially available Amplatzer duct occluder during the flow dynamics tests showed that the ND36 was capable of effectively occluding the duct as well as remaining stable under the dynamic conditions encountered in the duct. The ND36 has the potential to efficiently serve as a simplistic and cost effective alternative for PDA occlusion.

Commentary by Dr. Valentin Fuster

Errata

J. Med. Devices. 2011;5(3):037001-037001-1. doi:10.1115/1.4004929.
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The following figures have been corrected:

Commentary by Dr. Valentin Fuster

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