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Showing papers in "Journal of Medical Devices-transactions of The Asme in 2010"


Journal ArticleDOI
TL;DR: In this article, a unique, robust, robotic transtibial prosthesis with regenerative kinetics was successfully built and a 6-month human subject trial was conducted on one male below-the-knee amputee under linear walking conditions.
Abstract: A unique, robust, robotic transtibial prosthesis with regenerative kinetics was successfully built and a 6-month human subject trial was conducted on one male below-the-knee amputee under linear walking conditions. This paper presents the quasistatic system modeling, DC motor and transmission modeling and analyses, design methodology, and model verification. It also outlines an approach to the design and development of a robotic transtibial prosthesis. The test data will show that the true power and energy requirement predicted in the modeling and analyses is in good agreement with the measured data, verifying that the approach satisfactorily captures the physical system. The modeling and analyses in this paper describes a process to determine an optimal combination of motors, springs, gearboxes, and rotary to linear transmissions to significantly minimize the power and energy consumption. This kinetic minimization allows the downsizing of the actuation system and the battery required for daily use to a self-portable level.

189 citations


Journal ArticleDOI
TL;DR: Through this prototype, the strategy of cam-actuated BVM compression is proven to be a viable option to achieve low-cost, low-power portable ventilator technology that provides essential ventilators features at a fraction of the cost of existing technology.
Abstract: This paper describes the design and prototyping of a l ow-cost portable mechanical ventilator for use in mass casualty cases and resource-poor environments. The ventilator delivers breaths by compressing a conventional bag-valve mask (BVM) with a pivoting cam arm, eliminating the need for a human operator for the BVM. An initial prototype was built out of acrylic, measuring 11.25 x 6.7 x 8 inches (285 x 170 x 200 mm) and weighing 9 lbs (4.1 kg). It is driven by an electric motor powered by a 14.8 VDC battery and features an adjustable tidal volume up to a maximum of 750 ml. Tidal volume and number of breaths per minute are set via user-friendly input knobs. The prototype also features an assist-control mode and an alarm to indicate overpressurization of the system. Future iterations of the device will include a controllable inspiration to expiration time ratio, a pressure relief valve, PEEP capabilities and an LCD screen. With a prototyping cost of only $420, the bulk-manufacturing price for the ventilator is estimated to be less than $200. Through this prototype, the strategy of cam-actuated BVM compression is proven to be a viable option to achieve low-cost, low-power portable ventilator technology that provides essential ventilator features at a fraction of the cost of existing

84 citations



Journal ArticleDOI
TL;DR: A proof-of-concept prototype of the new minimally invasive surgical tool design paradigm, referred to as FlexDex ™, is tested by a focused end-user group to evaluate its performance and obtain feedback for the next stage of technology development.
Abstract: This paper presents a new minimally invasive surgical (MIS) tool design paradigm that enables enhanced dexterity, intuitive control, and natural force feedback in a low-cost compact package. The paradigm is based on creating a tool frame that is attached to the surgeon's forearm, making the tool shaft an extension of the latter. Two additional wristlike rotational degrees of freedom (DoF) provided at an end-effector that is located at the end of the tool shaft are manually actuated via a novel parallel-kinematic virtual center mechanism at the tool input. The virtual center mechanism, made possible by the forearm-attached tool frame, creates a virtual two-DoF input joint that is coincident with the surgeon's wrist, allowing the surgeon to rotate his/her hand with respect to his/her forearm freely and naturally. A cable transmission associated with the virtual center mechanism captures the surgeon's wrist rotations and transmits them to the two corresponding end-effector rotations. This physical configuration allows an intuitive and ergonomic one-to-one mapping of the surgeon's forearm and hand motions at the tool input to the end-effector motions at the tool output inside the patient's body. Moreover, a purely mechanical construction ensures low-cost, simple design, and natural force feedback. A functional decomposition of the proposed physical configuration is carried out to identify and design key modules in the system—virtual center mechanism, tool handle and grasping actuation, end-effector and output joint, transmission system, tool frame and shaft, and forearm brace. Development and integration of these modules leads to a proof-of-concept prototype of the new MIS tool, referred to as FlexDex ™ , which is then tested by a focused end-user group to evaluate its performance and obtain feedback for the next stage of technology development.

73 citations


Journal ArticleDOI
TL;DR: In this article, two commercially available stents (the Palmaz-Schatz (PS) and S670 stents) with reported high and low restenosis rates, respectively, have been investigated.
Abstract: Two commercially available stents (the Palmaz-Schatz (PS) and S670 stents) with reported high and low restenosis rates, respectively, have been investigated in this paper. Finite element models simulating the stent, plaque, and artery interactions in 3 mm stenosed right coronary arteries were developed. These models were used to determine the stress field in artery walls after stent implantation. The material properties of porcine arteries were measured and implemented in the numerical models. The stress concentration induced in the artery by the PS stent was found to be more than double that of the S670 stent. It demonstrated a good correlation with the reported restenosis rate. The effects of stent structures, compliance mismatch, plaque geometry, and level of stenosis were studied. Results suggested that stent designs and tissue properties cause alterations in vascular anatomy that adversely affect arterial stress distributions within the wall, which impact vessel responses such as restenosis. Appropriate modeling of stent, plaque, and artery interactions provided insights for evaluating alterations to the arterial mechanical environment, as well as biomechanical factors leading to restenosis.

58 citations


Journal ArticleDOI
TL;DR: A thermodynamically consistent constitutive model for materials undergoing deformation-induced degradation was applied to a commonly employed biodegradable polymer system, poly(L-lactic acid), and its specific form was determined by corroboration against experimental data.
Abstract: The use of biodegradable polymers in biomedical applications has been successful in nonload bearing applications, such as biodegradable implants for local drug delivery, and in simple load bearing situations such as surgical sutures and orthopedic fixation screws. The desire to incorporate these materials in more complex load bearing situations, such as tissue engineering scaffolds and endovascular or urethral stents, is strong, but the lack of constitutive models describing the evolution of biodegradable polymers over the course of degradation has severely hampered the rational design process for these more complex biodegradable medical applications. With the objective of predicting biodegradable stent behavior, we incorporated constitutive models of biodegradable polymeric materials in a computational setting and the mechanical response of three different stent designs were analyzed as degradation progressed. A thermodynamically consistent constitutive model for materials undergoing deformation-induced degradation was applied to a commonly employed biodegradable polymer system, poly(L-lactic acid), and its specific form was determined by corroboration against experimental data. Depreciation of mechanical properties due to degradation confers time-dependent characteristics to the response of the biodegradable material: the deformation imparted by a constant load increases over time, i.e. the body creeps, and the stress necessary to keep a fixed deformation decreases, i.e. the body relaxes. Biodegradable stents, when subjected to constant pressure in its exterior, deflect inwards and ultimately fail as the structure loses its mechanical integrity. The complex geometry of endovascular stents and their physiological loading conditions lead to inhomogeneous deformations, and consequently, inhomogeneous degradation ensues. Degradation is mostly confined to the bends of the stent rings and junction points, which are the locations that carry most of the deformation, whereas mostly undeformed connector bars remain less degraded. If failure occurs, it will occur most likely at those sensitive locations and large, nondegraded pieces can provoke severe embolic problems. Highly nonuniform degradation indicates that some stent designs are at higher risk for complications. Deformation patterns of stents made of a material that loses its integrity are different than those of permanent stents. Blind adaptation of permanent stent design concepts is ill-suited for biodegradable stent design. The time-dependent aspect of the implant not only must be taken into account but should also be used to interact with the body’s reaction and to enhance healing.

44 citations


Journal ArticleDOI
TL;DR: A simple instrument for noninvasive in vivo evaluation of arterial compliance using a single element ultrasound transducer that can measure arterial distension with a precision better than 5 and the end-diastolic arterial diameter with an accuracy of 1%.
Abstract: Measurement of arterial distensibility is very important in cardiovascular diagnosis for early detection of coronary heart disease and possible prediction of future cardiac events. Conventionally, B-mode ultrasound imaging systems have been used along with expensive vessel wall tracking systems for estimation of arterial distension and calculation of various estimates of compliance. We present a simple instrument for noninvasive in vivo evaluation of arterial compliance using a single element ultrasound transducer. The measurement methodology is initially validated using a proof of concept pilot experiment using a commercial ultrasound pulser-receiver. A prototype system is then developed around a PXI chassis using LABVIEW software. The virtual instrument employs a dynamic threshold algorithm to identify the artery walls and then utilizes a correlation based tracking technique to estimate arterial distension. The end-diastolic echo signals are averaged to reduce error in the automated diameter measurement process. The instrument allows automated measurement of the various measures of arterial compliance with minimal operator intervention. The performance of the virtual instrument was first analyzed using simulated data sets to establish the maximum measurement accuracy achievable under different input signal to noise ratio (SNR) levels. The system could measure distension with accuracy better than 10 μm for positive SNR. The measurement error in diameter was less than 1%. The system was then thoroughly evaluated by the experiments conducted on phantom models of the carotid artery and the accuracy and resolution were found to meet the requirements of the application. Measurements performed on human volunteers indicate that the instrument can measure arterial distension with a precision better than 5%. The end-diastolic arterial diameter can be measured with a precision better than 2% and an accuracy of 1%. The measurement system could lead to the development of small, portable, and inexpensive equipment for estimation of arterial compliance suitable in mass screening of "at risk" patients. The automated compliance measurement algorithm implemented in the instrument requires minimal operator input. The instrument could pave the way for dedicated systems for arterial compliance evaluation targeted at the general medical practitioner who has little or no expertise in vascular ultrasonography.

37 citations


Journal ArticleDOI
Wei Wei1, Claire Popplewell1, Stanley Chang1, Howard F. Fine1, Nabil Simaan1 
TL;DR: This pioneering work is the first to demonstrate successful stent deployment in a scale suitable for retinal surgery and has the promise of enabling effective vascular treatments for blinding conditions such as central and branch retinal vein occlusion.
Abstract: Microstenting is a potentially revolutionary approach to surgical treatment of microvascular retinal disorders that do not resolve using pharmaceutical treatment. This article presents a novel device called a stent deployment unit (SDU) that aims at enabling microstent placement in ophthalmic surgery. The clinical motivation for this work is highlighted in context of microvascular retinal surgery. The proposed SDU is designed for intraocular adjustment of the approach angle and the position of the stent with respect to the retina. The feasibility of this device is experimentally evaluated on chick chorioallantoic membranes and on agar vascular models. Experiments show dependency on the approach angle with respect to the vasculature and on the mobility of the vasculature. Successful placement of stents was achieved in both experimental media. To the best of our knowledge, this pioneering work is the first to demonstrate successful stent deployment in a scale suitable for retinal surgery. We believe that this technique has the promise of enabling effective vascular treatments for blinding conditions such as central and branch retinal vein occlusion.

37 citations


Journal ArticleDOI
TL;DR: Micropatterned treads that may enable mobile capsule crawlers inside the body are explored, including initial drawbar force generation experimental results, dynamic finite element analysis with these tread designs, and in vivo porcine evaluation and comparison of two leading tread designs.
Abstract: Despite revolutionary advances in many fields of medicine, there are no active mobile in vivo devices commercially available, or in use, today. Several research groups are actively looking at a number of mobility methods in a number of lumens but little commercial work has been done. While robotic surgery is available today thanks to ex vivo robots, such as the da Vinci surgical system, these methods are very expensive, require heavy external equipment, and are still constrained by entry incisions. An alternative approach may be to place the robot completely inside the patient. Such devices may enable noninvasive imaging and diagnostics. These devices may be significantly less expensive than current minimally invasive methods, without extensive support equipment, which may allow them to be also used routinely in the emergency room (ER)/trauma sites and remote locations. This work explores micropatterned treads that may enable mobile capsule crawlers inside the body. Current research efforts into providing contact locomotion using micro-tread tracks are explored including initial drawbar force generation experimental results, dynamic finite element analysis with these tread designs, and in vivo porcine evaluation and comparison of two leading tread designs.

35 citations


Journal ArticleDOI
TL;DR: The results in this article show that the plastolock concept can offer simple, scalable solutions for medical situations that desire stiffness at one instance and flexibility at another.
Abstract: Flexible endoscopes are used for diagnostic and therapeutic interventions in the human body for their ability to be advanced through tortuous trajectories. However, this very same property causes difficulties as well. For example, during surgery, a rigid shaft would be more beneficial since it provides more stability and it allows for better surgical accuracy. In order to keep the flexibility and to obtain the rigidity when needed, a shaft-guide with controllable rigidity could be used. In this article, we introduce the plastolock shaft-guide concept, which uses thermoplastics that are reversibly switched from rigid to compliant by changing their temperatures from 5°C to 43°C. These materials are used to make a shaft that can be rendered flexible to follow the flexible endoscope and rigid to guide it. To find polymers that are suitable for the plastolock concept, an extensive database and internet search was performed. The results suggest that many suitable materials are available or can be custom synthesized to meet the requirements. The thermoplastic polymer Purasorb ® PLC 7015 was obtained and a dynamic mechanical analysis showed that it is suitable for the plastolock concept. A simple production test indicated that this material is suitable for prototyping by molding. Overall, the results in this article show that the plastolock concept can offer simple, scalable solutions for medical situations that desire stiffness at one instance and flexibility at another. DOI: 10.1115/1.4002494

23 citations


Journal ArticleDOI
TL;DR: In this article, a computer-aided design of 3D porous tissue scaffolds with spatial control of encapsulated biomolecule distributions is proposed to control release kinetics spatially for tissue engineering and drug release.
Abstract: This paper presents a computer-aided design (CAD) of 3D porous tissue scaffolds with spatial control of encapsulated biomolecule distributions. A localized control of encapsulated biomolecule distribution over 3D structures is proposed to control release kinetics spatially for tissue engineering and drug release. Imaging techniques are applied to explore distribution of microspheres over porous structures. Using microspheres in this study represents a framework for modeling the distribution characteristics of encapsulated proteins, growth factors, cells, and drugs. A quantification study is then performed to assure microsphere variation over various structures under imaging analysis. The obtained distribution characteristics are mimicked by the developed stochastic modeling study of microsphere distribution over 3D engineered freeform structures. Based on the stochastic approach, 3D porous structures are modeled and designed in CAD. Modeling of microsphere and encapsulating biomaterial distribution in this work helps develop comprehensive modeling of biomolecule release kinetics for further research. A novel multichamber single nozzle solid freeform fabrication technique is utilized to fabricate sample structures. The presented methods are implemented and illustrative examples are presented in this paper.

Journal ArticleDOI
TL;DR: A 6-DOF steerable laparoscopic grasping forceps incorporating a novel and very simple “cable-ring” mechanism consisting out of a ring of cables surrounded by two coil springs suitable for commercialization is described.
Abstract: Laparoscopic surgery is carried out using long and slender endoscopes and instruments that are inserted through small incisions in the abdominal wall. Current endoscopes and instruments are rigid and have the drawback that their motion is restricted to 4-degrees of freedom (DOF). This paper describes a 6-DOF steerable laparoscopic grasping forceps incorporating a novel and very simple “cable-ring” mechanism consisting out of a ring of cables surrounded by two coil springs. Methods are described to increase stiffness and to improve manual control, resulting in a well-working prototype suitable for commercialization. The paper ends with a discussion on a number of cable-ring variants suitable for challenging new steerable designs in the future.

Journal ArticleDOI
TL;DR: A novel mobility interface for the robot to explore the environment when infants are placed in a prone position that can be trained to drive a robot purposefully and how such self-generated locomotion affects their long-term development is described.
Abstract: Many infants with special needs, such as with Down syndrome, cerebral palsy, and autism have delayed independent mobility due to weak musculature and/or poor coordination. Children with mobility impairments often do not use powered chairs until the age of five, as per current medical practice. Consequently, these children spend considerably less time moving independently around in their environment compared with typically developing children of the same age. Lack of independent mobility may result in delays in their cognitive, perceptual, social, and emotional development, which are well correlated with locomotion. This paper describes a novel mobility interface for the robot to explore the environment when infants are placed in a prone position. Infants can maneuver the robot through a drive interface that utilizes a camera to detect the motion of markers attached to their legs. We expect that infants will learn to drive the device by swinging their legs. Specifically, this paper demonstrates feasibility of this drive interface using data from two infants. Future studies will determine how infants can be trained to drive a robot purposefully and how such self-generated locomotion affects their long-term development. DOI: 10.1115/1.4002322

Journal ArticleDOI
TL;DR: The home lift, position, and rehabilitation (HLPR) chair has a unique design and novel capabilities when compared with conventional powered wheelchairs as mentioned in this paper, it provides lift and can transfer patients.
Abstract: The home lift, position, and rehabilitation (HLPR) chair has a unique design and novel capabilities when compared with conventional powered wheelchairs. In addition to mobility, it provides lift and can transfer patients. Even though medical devices are developing at a rapid pace today, an aspect that is often overlooked in these developments is adherence to "rider safety standards. " The contributions of this paper are threefold: (i) novel design of a lift and transfer system, (ii) experiments and results toward improved stability test designs that include HLPR-type devices to meet rider safety standards, and (iii) autonomous navigation and control based on nonlinear system theory of dynamic feedback linearization. Stability experimental results show promise for multipurpose patient mobility, lift, and transfer devices such as HLPR. A method for autonomous maneuvers was tested in simulation and experiments. We also expect the autonomous or semi-autonomous mobility mode of the vehicle to be useful for riders who have potential neural and cognitive impairments.

Journal ArticleDOI
TL;DR: The overall scope of research and in vitro test method to develop biocompatible RFID tag components for use in a "pharmaceutical supply chain system" beginning with the manufacturer, continuing through distribution, and ending at the point of interest within the patient's body.
Abstract: Advances in medical technology rely heavily on the collection and analysis of measured data to facilitate patient diagnosis and business decisions. The healthcare industry, particularly pharmaceuticals and diagnostic processes, has an ongoing need to improve item tracking and data collection to improve the quality of care while reducing cost. The remote, non-invasive characteristics of radio frequency identification (RFID) can facilitate the information needs of healthcare without imposing additional burden onto the patient or the staff. Properly deployed RFID enabled devices can provide convenient and accurate data for disease diagnosis, evaluation of prescription noncompliance, and identification of medication dosage errors. This paper describes an overview of the concept of an all-encompassing RFID pharmaceutical tracking system that begins with compliance documentation from the drug manufacturer and continues through the confirmation of patient compliance by capsule extraction from the bottle into a pill case and ultimately ingested or inserted into the body. This system also facilitates compliance with Food and Drug Administration proposed e-pedigree requirements and provides data for healthcare decision making. An introduction to healthcare trends is provided in order to communicate the need for such a biocompatible RFID pharmaceutical tracking system. Also presented in this paper is the overall scope of research and in vitro test method to develop biocompatible RFID tag components for use in a "pharmaceutical supply chain system" beginning with the manufacturer, continuing through distribution, and ending at the point of interest within the patient's body.

Journal ArticleDOI
TL;DR: An integrated collaborative modular architecture method for medical device design and development focused on analyzing the input of stakeholder data from existing products and components to achieve an optimal number of modules to reduce product cycle time and improve market competitiveness among other factors.
Abstract: In this paper, we present an integrated collaborative modular architecture method for medical device design and development. The methodology is focused on analyzing the input of stakeholder data from existing products and components to achieve an optimal number of modules. The methodology starts by defining a product’s functional and physical decompositions. Product parameters are selected such as quality, reliability, ease of development, and cost. These are prioritized using analytical hierarchy process (AHP) to determine the medical device manufacturers’ focus area. The parameters’ subsequent metrics are selected for performance requirements. Next, we evaluate the candidate modules by acquiring stakeholder data and converting them to crisp values by applying the Sugeno fuzzy-based method. Finally, we determine the subsequent optimal module values using a multi-optimization goal programming model. We present here a proof of concept using a typical glucometer. The implication of this work is the determination of the optimal number of product modules based on stakeholder constraints. Hence, an original equipment manufacturer (OEM) can work on fewer components per module without adversely affecting the integrity, quality, and reliability of the final product. Next is the improved quality of patient care by enabling cost reductions in product design and development, thereby improving patient safety. This methodology helps reduce product cycle time, thereby improving market competitiveness among other factors.

Journal ArticleDOI
TL;DR: This work attempts to optimize stents that are implanted at the neck of coronary or cerebral aneurysms to effect a flow diversion and finds that placing struts in the proximal region of the neck gives the best flow diversion.
Abstract: This work attempts to optimize stents that are implanted at the neck of coronary or cerebral aneurysms to effect a flow diversion. A two-dimensional version of the stent, which is a series of struts and gaps placed at the neck, is considered as the first step. Optimization is carried out based on the principles of exploration of design space using reductions in velocity and vorticity in the aneurysm dome as the objective functions. Latin hypercube sampling first develops 30-60 samples of a strut-gap arrangement. Flow past an aneurysm with each of these samples is computed using the commercial software FLUENT and the objective functions evaluated. This is followed by a Kriging procedure that identifies the nondominated solutions to the system, which are the optimized candidates. Three different cases of stents with rectangular or circular struts are considered. It is found that placing struts in the proximal region of the neck gives the best flow diversion.

Journal ArticleDOI
TL;DR: The activation parameter computed for the tilting disc valve, at the time of closure was found to be 2.7 times greater than that of the bi-leaflet mechanical valve and was finding to be in the vicinity of the minor orifice region mainly due to the migration of vortical structures from the major to the minorOrifice region during the leaflet rebound of the closing phase.
Abstract: The fluid dynamics during valve closure resulting in high shear flows and large residence times of particles has been implicated in platelet activation and thrombus formation in mechanical heart valves. Our previous studies with bi-leaflet valves have shown that large shear stresses induced in the gap between the leaflet edge and the valve housing results in relatively high platelet activation levels whereas flow between the leaflets results in shed vortices not conducive to platelet damage. In this study we compare the result of closing dynamics of a tilting disc valve with that of a bi-leaflet valve. The two-dimensional fluid-structure interaction analysis of a tilting disc valve closure mechanics is performed with a fixed grid Cartesian mesh flow solver with local mesh refinement, and a Lagrangian particle dynamic analysis for computation of potential for platelet activation. Throughout the simulation the flow remains in the laminar regime and the flow through the gap width is marked by the development of a shear layer which separates from the leaflet downstream of the valve. Zones of re-circulation are observed in the gap between the leaflet edge and the valve housing on the major orifice region of the tilting disc valve and are seen to be migrating towards the minor orifice region. Jet flow is observed at the minor orifice region and a vortex is formed which sheds in the direction of fluid motion as observed in experiments using PIV measurements. The activation parameter computed for the tilting disc valve, at the time of closure was found to be 2.7 times greater than that of the bi-leaflet mechanical valve and was found to be in the vicinity of the minor orifice region mainly due to the migration of vortical structures from the major to the minor orifice region during the leaflet rebound of the closing phase.

Journal ArticleDOI
TL;DR: A device design comprising a continuous miniature motor-driven distractor with a controller and an on-board lithium-ion battery enables completely automated and continuous distraction by the application of a low strain magnitude with multiple steps potentially leading to enhanced osteogenic activity.
Abstract: Distraction osteogenesis is a method of generating new bone formation by the gradual application of tensile stress across an osteotomy site (a complete cut through the bone). Internal or intraoral distraction devices have become the most common clinical apparatus in craniofacial distraction osteogenesis, although actuating the distraction devices relies upon manual length adjustment under patients' compliance, introducing inconvenience and potential error in the procedure. To realize a fully implantable automatic distraction device, we propose a device design comprising a continuous miniature motor-driven distractor with a controller and an on-board lithium-ion battery. A benchtop prototype was fabricated to demonstrate the device's structural design capable of transmitting sufficient loads with sufficient strain accuracy; it is capable of using a battery selection algorithm to determine an appropriate electrochemistry temperature, sealability, and form factor and a control algorithm and a testing protocol with a laboratory-fabricated control circuit. This new distraction osteogenesis device enables completely automated and continuous distraction by the application of a low strain magnitude with multiple steps potentially leading to enhanced osteogenic activity.

Journal ArticleDOI
TL;DR: A new specimen collection device is designed to collect aerosol specimens selectively from the lower lung generated during deep coughing, which may aid in the diagnosis of specific pathogens causing pneumonia.
Abstract: The pathogens causing pneumonia are difficult to identify because a high quality specimen from the lower lung is difficult to obtain A new specimen collection device is designed to collect aerosol specimens selectively from the lower lung generated during deep coughing The PneumoniaCheck device utilizes a separation reservoir and Venturi valve to segregate contents from the upper and lower airways The device also includes several specially designed features to exclude oral contaminants from the sample and a filter to collect the aerosolized pathogens Verification testing of PneumoniaCheck demonstrates effective separation of upper airway gas from the lower airway gas (p <00001) and exclusion of both liquid and viscous oral material (p<00001) from the collection chamber The filters can collect 999997% of virus and bacteria sized particles from the sampled lower lung aerosols The selective collection of specimens from the lower airway may aid in the diagnosis of specific pathogens causing pneumonia

Journal ArticleDOI
TL;DR: A novel knee joint fixation/distraction system that uses an external fixator to apply a cyclic distraction of the knee joint while monitoring the resultant force developed across the joint, thus providing a temporal indication of structural changes during the healing process of the bone-tendon-bone reconstruction.
Abstract: We designed and validated a novel knee joint fixation/distraction system to study tendon-to-bone healing in an in vivo rat model of anterior cruciate ligament (ACL) reconstruction. The system uses an external fixator to apply a cyclic distraction of the knee joint while monitoring the resultant force developed across the joint, thus providing a temporal indication of structural changes during the healing process of the bone-tendon-bone reconstruction. The validation was performed using an optical kinematic tracking system to determine the local displacement of the knee. The average system compliance was determined to be 42.4 +/- 8.8 mum/N with a coefficient of variation of 20.7%. The compliance was used to obtain a best fit correction factor which brought the total root mean square error of knee joint distraction to within 179 mum (16.1%) of the applied distraction. We performed a pilot study using 15 rats that had ACL reconstructions using a flexor digitorum longus tendon autograft and found that the animals tolerated the indwelling fixator and daily anesthesia over a 10 day loading protocol. Our knee joint fixation/distraction system provides a valuable tool to study how mechanical stimuli affect in vivo bone-tendon-bone healing.

Journal ArticleDOI
TL;DR: In this paper, the lateral deflection of thin Kirschner wires is studied both theoretically and computationally, in which the bone was modeled as a hollow cylinder, and the wire-bone interaction was assumed to be frictionless.
Abstract: The mechanical behavior of the transosseous elements is a defining factor in the overall stiffness, stability, and reliability of an external fixation system. Mechanics involving the application of thin Kirschner wires in Ilizarov apparatus is yet to be fully explained. To address this problem, load-deflection behavior of the pretensioned thin wires laterally loaded by the bone is necessary to be studied. In this paper, the lateral deflections of thin Kirschner wires are studied both theoretically and computationally. Fully three dimensional finite element (FE) modeling and analyses were performed in which the bone was modeled as a hollow cylinder, and the wire-bone interaction was assumed to be frictionless. The mathematical solution resulted in new exact solutions for the deflection as well as final tension in the wires subjected to the lateral loading under a cylinder representing the bone. Results from the FE analyses turned out to be very close to those from the mathematical solution. The results obtained from theory and FE method are comparable to published experimental findings. Some aspects of the pretensioned thin wire behavior in ring fixation systems, e.g., stiffness-tension proportionality, were revealed in the results. The current study adds to the existing knowledge on the general behavior of tensile elements.

Journal ArticleDOI
TL;DR: The results represent a strong agreement between the two systems in measuring the lowest point during swing, suggesting the OPS could be used instead of a camera system to record foot clearance, opening up opportunities for data collection over long periods of time, in natural settings.
Abstract: Foot clearance is an important measurement variable in understanding trip falls. Current methods for measuring foot clearance are limited by their inability to capture multiple steps and confinement to a laboratory. Given that variation in this parameter is considered a factor in trip falling, it's measurement in the field over multiple steps would be valuable. The development of an optical proximity sensor (OPS) has created the opportunity to collect this type of data. This study aimed to test the validity of an OPS through comparison with a motion capture system. Twenty subjects aged 33(+/−10) years, with a height of 174(+/−6) cm and a weight of 75(+/−12) kg, walked at three self selected velocities (preferred, slow, and fast). The OPS was mounted on the shoe of each subject. The motion of the shoe was recorded with a motion analysis system which tracked three markers attached to the shoe and outer casing of the OPS. Both systems were sampled at 50 Hz. The lowest point of the foot during the swing phase was recorded from each system and compared using intraclass correlation coefficients (ICCs). There was excellent agreement between the two systems. ICCs of 0.925 (all speeds), 0.931 (preferred), 0.966 (slow), and 0.889 (fast) were recorded. These results represent a strong agreement between the two systems in measuring the lowest point during swing. The OPS could thus be used instead of a camera system to record foot clearance, opening up opportunities for data collection over long periods of time, in natural settings. These results should be interpreted in context of the young healthy sample.

Journal ArticleDOI
TL;DR: Th thin polyvinyl alcohol (PVA) cryogel membranes were tested for their ability to stretch with uniaxial tension tests and for puncture strength with a modified ASTM method, and PVA cryogels are mechanically suitable for covered stent membranes.
Abstract: Covered stents could reduce restenosis rates by preventing cellular migration with a physical barrier and may have reduced thrombotic complications if an appropriate material is selected. Previous Dacron™ or poly(tetrafluoroethylene) (PTFE) covered stents have had mixed clinical results in part because they are too thick and too thrombogenic at small diameters. Ideally, the covering should be as thin as a stent strut, mechanically able to expand as much as a stent, and durable enough to withstand deployment. As an alternative to PTFE, thin polyvinyl alcohol (PVA) cryogel membranes were tested for their ability to stretch with uniaxial tension tests and for puncture strength with a modified ASTM method. Additionally, PVA cryogel covered stents were made by coating expanded bare metal stents. These covered stents were then hand-crimped onto a balloon catheter and expanded. PVA cryogel membranes were made as thin as 100 μm—thinner than some stent struts—and stretched to approximately 3.0 times their original diameter (similar to a stent during deployment). PVA cryogel membranes resisted puncture well with an average push-through displacement of 4.77 mm—allowing for safe deployment in vessels of up to 9 mm in diameter. Push-through displacement did not depend on membrane thickness in the range tested—a trait that could reduce stent profile without increased risk of puncture. All the PVA cryogel covered stents tolerated the crimping and expansion process well and there was little to no visible membrane damage. In conclusion, based on the results of these mechanical tests, PVA cryogels are mechanically suitable for covered stent membranes. This work represents a first step toward the creation of a new class of covered stent, which could prevent complications from both restenosis and thrombosis.

Journal ArticleDOI
TL;DR: A holistic conception of simulation-based engineering, including abilities to not just simulate with unprecedented accuracy but also to visualize and interact with simulation results, is critical to making simulation- based engineering practical as a tool for major innovation in medical devices.
Abstract: This paper presents a framework and detailed vision for using immersive virtual reality (VR) environments to improve the design, verification, validation, and manufacture of medical devices. Major advances in medical device design and manufacture currently require extensive and expensive product cycles that include animal and clinical trials. The current design process limits opportunities to thoroughly understand and refine current designs and to explore new high-risk, high-payoff designs. For the past 4 years, our interdisciplinary research group has been working toward developing strategies to dramatically increase the role of simulation in medical device engineering, including linking simulations with visualization and interactive design. Although this vision aligns nicely with the stated goals of the FDA and the increasingly important role that simulation plays in engineering, manufacturing, and science today, the interdisciplinary expertise needed to realize a simulation-based visual design environment for real-world medical device design problems makes implementing (and even generating a system-level design for) such a system extremely challenging. In this paper, we present our vision for a new process of simulation-based medical device engineering and the impact it can have within the field. We also present our experiences developing the initial components of a framework to realize this vision and applying them to improve the design of replacement mechanical heart valves. Relative to commercial software packages and other systems used in engineering research, the vision and framework described are unique in the combined emphasis on 3D user interfaces, ensemble visualization, and incorporating state-of the-art custom computational fluid dynamics codes. We believe that this holistic conception of simulation-based engineering, including abilities to not just simulate with unprecedented accuracy but also to visualize and interact with simulation results, is critical to making simulation-based engineering practical as a tool for major innovation in medical devices. Beyond the medical device arena, the framework and strategies described may well generalize to simulation-based engineering processes in other domains that also involve simulating, visualizing, and interacting with data that describe spatially complex time-varying phenomena.

Journal ArticleDOI
TL;DR: It is demonstrated that the use of dynamically shaped beams results in greatly improved dose homogeneity compared with standard techniques, which use a single static beam shape.
Abstract: A novel translating bed total body irradiation treatment delivery technique that employs dynamically shaped beams is presented. The patient is translated along the floor on a moving bed through a stationary radiation beam and the shape of the radiation beam is changed dynamically as the patient is moved through it, enabling compensation for local variations in patient thickness and tissue density. We demonstrate that the use of dynamically shaped beams results in greatly improved dose homogeneity compared with standard techniques, which use a single static beam shape. Along a representative dose profile through the lungs of a mock-human body, the maximum range of dose deviation from the average is 5.6% (from +2.7% to -2.9%) for the dynamic beam technique compared with 12.8% (from +3.6% to -9.2%) for the static beam technique. A novel, dual-interlock system that prevents bed motion when the radiation beam is stopped and stops the radiation beam when the bed motor is stopped has also been developed. The dual-interlock not only enhances the safety of the treatment but also ensures accuracy in the delivery of the treatment.

Journal ArticleDOI
TL;DR: The design of a cooling guide catheter that can provide rapid, local cooling to heart tissue during emergency angioplasty is described, showing 18 W of cooling delivered by the catheter can reduce heart tissue temperatures rapidly, approximately 3° in 5 min in some locations.
Abstract: Cardiovascular disease is the leading cause of death in the United States. Despite decades of care path improvements approximately 30% of heart attack victims die within 1 year after their first heart attack. Animal testing has shown that mild hypothermia, reducing tissue temperatures by 2-4°C, has the potential to save heart tissue that is not adequately perfused with blood. This paper describes the design of a cooling guide catheter that can provide rapid, local cooling to heart tissue during emergency angioplasty. Using standard materials and dimensions found in typical angioplasty guide catheters, a closed-loop cooling guide catheter was developed. Thermal fluid modeling guided the interior geometric design. After careful fabrication and leak testing, a mock circulatory system was used to measure catheter cooling capacity. At blood analog flow rates ranging from 20 ml/min to 70 ml/min, the corresponding cooling capacity varied almost linearly from 20 W to 45 W. Animal testing showed 18 W of cooling delivered by the catheter can reduce heart tissue temperatures rapidly, approximately 3° in 5 min in some locations. Future animal testing work is needed to investigate if this cooling effect can save heart tissue.

Journal ArticleDOI
TL;DR: In this article, a new procedure utilizing computer aided design and the finite element method can be employed to develop a customized weight-bearing dynamic orthotic, which is composed of soft foam interior layers and a polymer supportive exterior layer.
Abstract: Clubfoot is a common pediatric orthopaedic deformity. Despite the popularity of Ponseti’s method and night splints such as the Denis–Browne method, there is still an 11–47% rate of deformity relapse reported in the literature. The technique to make traditional orthotics is dependent on a nonweight-bearing casting or foot imprint. These splints outdate clinical treatment trends and only apply to patients who are of nonwalking age. This study shows that a new procedure utilizing computer aided design and the finite element method can be employed to develop a customized weight-bearing dynamic orthotic. In addition, the plantar pressure distribution and the trajectory of the center of this pressure distribution are used to design the orthotic. It is shown that the trajectory of the center of pressure, traditionally used in gait analysis, can be used not only to quantify the severity of the foot deformity but to design a custom orthotic as well. Also, the new procedure allows the custom orthotic to be designed and analyzed within a day. The new orthotic design is composed of soft foam interior layers and a polymer supportive exterior layer. It is proved that rapid prototyping technologies employing selective laser sintering can be used to construct these layers to produce a custom orthotic within a 24 h time frame.

Journal ArticleDOI
TL;DR: In this article, a low-cost prosthetic knee joint that uses a compliant member for stance-phase control was proposed. But the compliant member concept was not considered in this paper.
Abstract: This paper is concerned with the feasibility and design of a low-cost prosthetic knee joint that uses a compliant member for stance-phase control. A mechanical locking mechanism was used in conjunction with a compliant control axis to achieve automatic stance-phase locking. The concept was developed with the aid of computer-aided engineering software and was validated through the fabrication and testing of a simplified prototype made of an injection moldable polymer. A prosthetic knee joint was then designed, incorporating the compliant member concept. After modeling, fabrication, and laboratory testing, a pilot study was conducted in a clinical setting. A simple gait analysis showed asymmetric gait patterns that demonstrated the need for improved swing-phase control and damping, while qualitative feedback indicated the desire to reduce the noise produced by the knee. The knee provided the automatic stance-phase control for which it was designed and shows significant potential to evolve into a highly functioning, low-cost knee.

Journal ArticleDOI
TL;DR: The special features of the proposed robot make it well suited for use with new surgical tools and micro-robots for a range of medical interventions and enable it to perform and interact efficiently with the constrained and limited workspace of surgical environments.
Abstract: An actuated robot arm is designed for use as a gross positioning macro-manipulator that can carry, appropriately orient, precisely position, and firmly "lock" in place different types of micro-robots and surgical tools necessary for applications in minimally invasive therapy. With a simple manipulation protocol, the clinician can easily operate the robot in manual mode. A remote control mode can also be enabled for teleoperation of the robot. The robot's normally locked braking system and the simple quick-release joint enhance its safety features for emergencies and power shutdown. Robot workspace analysis showed that the singularity regions are outside the usable work envelope of the robot. Performance analysis showed that the robot operates with an average displacement accuracy of 0.58 mm and a roll, pitch, and yaw angular accuracies of 0.26 deg, 0.26 deg, and 0.38 deg, respectively. The sophisticated configuration and joint architecture of the arm enable it to perform and interact efficiently with the constrained and limited workspace of surgical environments. The special features of the proposed robot make it well suited for use with new surgical tools and micro-robots for a range of medical interventions.