Research Papers

J. Med. Devices. 2011;5(1):011001-011001-7. doi:10.1115/1.4002901.

In this paper, we present the design, analysis, and testing of an ankle rehabilitation device (ARD), the purpose of which is to improve the efficacy of ankle joint complex (AJC) injury diagnosis and treatment. The ARD enables physicians to quantitatively measure the severity of an injury. This is done by measuring deficiencies in the joint’s range of motion, as well as force, torque, and power output. Evaluation of the relative degree of recovery over time can also reduce the error associated with current methodologies for rehabilitation, which rely on measurements based on the patient’s verbal response. A Wheatstone bridge circuit is used for the measurement of the various parameters as applied to the blades of complementary rotational flexures; the device is designed to measure motion about three axes of rotation in the ankle joint: pitch, roll, and yaw. A full bridge circuit is applied to each axis of rotation, and the use of multiple axes increases anatomically accurate measurement, enabling characterization of coupled motions. The device has flexibility and a range of motion such that it can be adjusted to take measurements of multiple different degrees of plantar or dorsiflexion of the AJC. The ARD is able to measure both range of motion, force, and torque output simultaneously. Experimental results show that there is significant coupled motion among the ankle joint rotations but that it is highly dependent on a subject’s own physical development.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2011;5(1):011002-011002-10. doi:10.1115/1.4003329.

Gravity balancing is often used in industrial machines to decrease the required actuator efforts during motion. In this paper, we present a new design for gravity balancing of the human leg using an external orthosis. This external orthosis is connected to the human leg on the shank and its other end is fixed to a walking frame. The major issues addressed in this paper are as follows: (i) design for gravity balancing of the human leg and the orthosis, (ii) kinematic compatibility of the human leg and the external orthosis during walking, and (iii) comparison of the joint torque trajectories of the human leg with and without external orthosis. We illustrate feasible 2D and 3D designs of the external orthosis through computer simulations. Our results show that the 3D design has smaller inertia with respect to 2D design, which can be more helpful for typical stroke patients to walk in a balanced position.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2011;5(1):011003-011003-9. doi:10.1115/1.4003117.

Biodegradable magnesium-calcium (Mg–Ca) implants have the ability to gradually dissolve and absorb into the human body after implantation. The similar mechanical properties to bone indicate that Mg–Ca is an ideal implant material to minimize the negative effects of stress shielding. Furthermore, using a biodegradable Mg–Ca implant prevents the need for a secondary removal surgery that commonly occurs with permanent metallic implants. The critical issue that hinders the application of Mg–Ca implants is the poor corrosion resistance to human body fluids. The corrosion process adversely affects bone ingrowth that is critical for recovery. Therefore, sequential laser shock peening (LSP) of a biodegradable Mg–Ca alloy was initiated to create a superior surface topography for improving implant performance. LSP is an innovative treatment to fabricate functional patterns on the surface of an implant. A patterned surface promotes bone ingrowth by providing a rough surface texture. Also, LSP imparts deep compressive residual stresses below the surface, which could potentially slow corrosion rates. Unique surface topographies were fabricated by changing the laser power and peening overlap ratio. The resultant effects on surface topography were investigated. Sequential peening at higher overlap ratios (75%) was found to reduce the tensile pileup region by over 40% as well as compress the overall surface by as much as 35μm.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2011;5(1):011004-011004-7. doi:10.1115/1.4003435.

This paper describes the development of an articulating endoscopic screw driver that can be used to place screws in osteosynthetic plates during thoracoscopic surgery. The device is small enough to be used with a 12 mm trocar sleeve and transmits sufficient torque to fully secure bone screws. The articulating joint enables correct screw alignment at obtuse angles, up to 60 deg from the tool axis. A novel articulating joint is presented, wherein a flexible shaft both transmits torque and actuates the joint; antagonist force is provided by a superelastic spring. Screws are secured against the driver blade during insertion with a retention mechanism that passively releases the screw once it is securely seated in the bone. The prototype has been fitted with a blade compatible with 2.0 and 2.3 mm self-drilling screws, though a different driver blade or drill bit can be easily attached. Efficacy of the tool has been demonstrated by thoracoscopically securing an osteosynthetic plate to a rib during an animal trial. This tool enables minimally invasive, thoracoscopic rib fixation.

Topics: Torque , Screws , Design
Commentary by Dr. Valentin Fuster
J. Med. Devices. 2011;5(1):011005-011005-7. doi:10.1115/1.4003536.

A viscoelastic artificial disc may more closely replicate normal stiffness characteristics of the healthy human disc compared with first-generation total disc replacement (TDR) devices, which do not utilize viscoelastic materials and are based on a ball and socket design that does not allow loading compliance. Mechanical testing was performed to characterize the durability and range of motion (ROM) of an investigational viscoelastic TDR (VTDR) device for the lumbar spine, the Freedom® Lumbar Disc. ROM data were compared with data reported for the human lumbar disc in the clinical literature. Flexibility and stiffness of the VTDR in compression, rotation, and flexion/extension were within the parameters associated with the normal human lumbar disc. The device constrained motion to physiologic ranges and replicated normal stress/strain dynamics. No mechanical or functional failures occurred within the loads and ROM experienced by the human disc. Fatigue testing of the worst case VTDR device size demonstrated a fatigue life of 50 years of simulated walking and 240 years of simulated significant bends in both flexion/extension and lateral bending coupled with axial rotation, with no functional failures. These results indicate that the VTDR evaluated in this mechanical study is durable and has the ability to replicate the stiffness and mechanics of the natural, healthy human lumbar disc.

Commentary by Dr. Valentin Fuster

Technical Briefs

J. Med. Devices. 2011;5(1):014501-014501-5. doi:10.1115/1.4002932.

In cochlear-implant (CI) insertion experiments, scala-tympani (ST) phantoms are often used in place of in vivo studies or cadaver studies. During the development of novel CI technology, a scaled-up phantom is often desirable. In this paper, we create a scalable model of the human ST by synthesizing published anatomical data and images. We utilize the model to fabricate an accurate, inexpensive, and reproducible ST phantom at a 3:1 scale.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2011;5(1):014502-014502-6. doi:10.1115/1.4003436.

There is a very large need for prosthetic components in developing countries, where such devices are imported and prohibitively expensive. This work explores the possibility of developing and manufacturing prosthetic components locally in Venezuela while preserving high quality and function. We aimed at developing a kit of plastic modular adaptors for external transtibial prostheses. The project covers design, stress analyses, and function assessment of the components. Design criteria were established from the state-of-the-art of prosthetic adaptors in commercial models and international patents. The resulting kit comprises four adaptors of simple design. Their response was studied with stress analysis, using the finite element method, applying static loads for different instants of gait during the stance phase. The simulation of the adaptors shows that the stresses presented for a person weighing up to 980 N (100 kg) do not reach the yield strength of nylon 6.6. Then, five kits of adaptors were manufactured with this thermoplastic material using conventional metal-working machines. The resulting components are lighter and cheaper than equivalent imported metallic ones. The kits were adapted to four patients and assessed via gait analysis and questionnaire. A very good function is observed, with neither significant difference in most of spatiotemporal gait parameters compared to normal values (p<0.05) nor significant asymmetries between prosthetic and sound sides. From the questionnaire, stiffness, maneuverability, and comfort ability of the manufactured kits was found high by all the patients. A 3 months adaptation period was also completed by the patients prior to performing the gait analyses. This period is considered a first field trial of the adaptors; however, these results will be complemented in the future, as the kits were not tested to structural fatigue.

Commentary by Dr. Valentin Fuster

Design Innovation

J. Med. Devices. 2011;5(1):015001-015001-7. doi:10.1115/1.4003330.

A jet injector platform technology that provides improved performance over existing jet injectors through the use of a controllable linear Lorentz-force actuator and software-based control system has been developed. Injectors designed on this platform are capable of delivering injections using arbitrary pressure pulse shaping. Pulse shaping has been shown to allow a wide degree of control over the depth to which the injection is delivered. A software-based injector control system improves repeatability and allows for automatic reloading of the injector, a task that would be difficult to implement using existing jet injector platforms. A design for a prototype autoloading controllable jet injector (cJI) based on this platform is detailed. The injection capability of this cJI was evaluated both in-vitro and in-vivo using a tissue analog, excised porcine tissue, and ovine tissue. An analysis of the cJI’s performance indicates that this design is capable of delivering a controllable volume of fluid to a controllable depth based entirely on the parameter’s input into the control software.

Commentary by Dr. Valentin Fuster

Book Review

J. Med. Devices. 2011;5(1):016501-016501-1. doi:10.1115/1.4003637.
The Role of Biofilms in Device-Related Infections,. Springer-Verlag, Berlin, Heidelberg, ISBN: 978-3-540-68113-7; e-ISBN: 978-3-540-68119-9
Commentary by Dr. Valentin Fuster

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