bluuebunny/crossref_metadata_2025 huggingface dataset:
A High-Throughput In Vitro Model Illustrating Potential Microbiological Interactions During Treatment of Pseudomonas Aeruginosa Biofilm Associated Infections
Authors: El-Khatib Walid , Haynes Virginia , Noreddin Ayman
Published: July 2008

Objective: Amend a real-time, high-throughput method of bacterial growth detection for use as a model of biofilm response to co-administered pharmaceuticals during the treatment of devise associated infections. Background: Biofilms are the root etiology for chronic infections, particularly in regard to infections in patients with implanted medical devices. Calcium channel blockers (CCBs) are used for control of hypertension and angina and are commonly prescribed to elderly patients. We address potential interference of commonly prescribed CCBs with levofloxacin for treatment of Pseudomonas aeruginosa biofilms. Methods: Inoculum of 1–3×106CFU∕mL in the log phase were seeded into each well of a polystyrene plate. Biofilms developed over 6h at 37°C, was washed and medium containing various CCBs plus levofloxacin was added to the biofilm. OD measurements were obtained at 1h intervals over 90h at 37°C. Changes in turbidity were kinetically measured with a vertical photometer with a wide-band filter. Results: Mibefradil and diltiazem appear to be strongly antagonistic toward levofloxacin where both of them decrease antibiofilm effect of levofloxacin and they encourage the selection of resistant mutants from biofilm. Discussion: Implanted medical devices are quite common and are subjected to biofilm infections. Increasing multi-drug resistance underscores the need to conserve current antibiotics by judicious use. This necessitates consideration of evidence regarding antagonistic or synergistic activity of commonly prescribed drugs of different classes toward commonly used antibiotics. The combinations described here show vital and previously unreported effects of some CCBs when co-prescribed with levofloxacin on Pseudomonas aeruginosa biofilm.
Characterization of Chitosan Coated Magnetoelastic Materials for Use in Percutaneous Implants
Authors: Janka L. P. , Jang-Stewart S. , Hembolt A. , Ong K. G. , Rajachar R. M.
Published: July 2008

There are upwards of 250,000 cases of infections due to the use of percutaneous devices in the US every year, with an estimated cost of $25,000 per incident. Improving the longevity of these devices is thus of significant clinical and economic importance. Current antimicrobial and junctional healing approaches do not allow for in situ modulation of therapeutic effects. In this work we are developing bioactive vibrational magnetoelastic (ME) materials for use as a remotely activated tunable coating promoting cell differentiation and inhibition of bacterial adhesion at the tissue-implant interface. ME sensors are currently used as an in situ method of measuring biological processes. The objective of this study was to develop an ME antimicrobial coating conducive to cell growth and characterize the antimicrobial and cell inductive response towards frequency-amplitude modulated vibrations. A thin film of Chitosan, a natural polymer with antimicrobial properties, was applied to the material using spin coating and quantified with profilometry and scanning electron microscopy. Custom built activation coils were constructed measuring resonant frequencies and amplitudes of coated and uncoated ME material. Based upon collected data a representative curve was created modeling the changes in resonant frequency and amplitude. Tunable vibrations induced a 30% decrease in bacterial adhesion when compared to non-vibrated controls. Currently we are testing the effectiveness of these coatings at promoting epithelial cell differentiation in addition to inhibition of bacteria adhesion.
A Novel Halo Orthosis to Reduce Pin Loosening
Authors: Karnes G. Joshua , Stamper Richard E. , Hofmann Brittiney N.
Published: July 2008

Pin loosening is a frequent complication associated with the use of halo orthoses. Efforts to reduce pin loosening incidence include increasing the number of halo pins, increasing the torque specification, and proactively retightening the halo pins. Although these approaches lower pin loosening incidence rates, none addresses the cause of pin loosening, which is the inability of current halo ring designs to accommodate changes in geometry of the skull. A novel four-pin adaptive halo ring is introduced that can accommodate changes in geometry of the skull and provide a nearly constant pin force. To quantify pin loosening in a halo ring, tests were performed using a fixture that was capable of simulating the changes in skull geometry that are responsible for pin loosening. Both the four-pin adaptive halo and a conventional halo were tested. After 1.1mm of radial recession of the skull at the pin site, the average halo pin force in the conventional halo decreased by 78% while the average halo pin force in the four-pin adaptive halo decreased by 12%. In addition, the four-pin adaptive halo had significantly less variation in initial halo pin force (p-value <0.0001) than that of the four-pin adaptive halo.
A Novel Approach to Drug Delivery for Hepatities C Virus (HCV) for High Immune Responses
Authors: Chen W. T. , Zhang C.
Published: July 2008

Hepatities C Virus (HCV) is a significant health problem worldwide due to the lack of effective vaccines. HCV plasmid DNA (pDNA) vaccine represents a promising means to induce a Th1-biased cell-mediated response which tends to be associated with HCV clearance. However, the immune responses induced by naked pDNA vaccine in large animals as well as in humans are usually too weak to show sufficient protection against new infections. Therefore, it is interesting to look for new ways to deliver HCV pDNA vaccine. In this research, carbon nanotube (CNT) is used as a carrier to deliver the pDNA vaccine of HCV to induce high immune responses, because CNT has some excellent properties such as high strength and good biocompatibility. One of the key approaches to make this idea work is to treat CNT so that it can bind with HCV pDNA with good stability. An approach called 1, 3-dipolar cycloaddition of azomethine ylides was modified. We analyzed the complex of f-CNTs combined with pDNA vaccines expressing HCV E2 protein by using Enzyme-linked immunospot (ELISPOT) or Enzyme-linked immunosorbent assay (ELISA) assay in vitro. The result showed that the CNT approach can induce stronger protective immune responses than the needle delivery of naked pDNA vaccine. We have also found an optimal way to treat CNT in light of the highest immune response in the same testing environment. The success of this research will warrant testing HCV vaccine in large animal models and human clinical trials.
TI Low-Leakage130nm Digital Process with Nonvolatile FRAM for Ultra-Low-Power Medical Electronics
Authors: Landers A. Robert , Elkind B. Jerry , Aggarwal C. Rajni
Published: July 2008

Both external and implantable devices are becoming more sophisticated and are requiring more on-chip memory to store data from biological sensors. To deal with this complexity, chip designs are moving toward smaller process geometries, which provide added functionality, reduced size, or both, often along with a reduction in dynamic power. However, leakage power begins to increase significantly at the 130nm node if steps are not taken to mitigate the increased transistor leakage. Lower operating voltages and careful transistor design can offset some of this increase. These very changes, however, make it difficult to design a dense, stable low-power SRAM. Nonvolatile memories like FRAM (F-RAM) avoid these difficulties and save power by simply turning off the memory when not in use. This is particularly valuable since many medical devices have very low duty cycle. FRAM provides the added benefit of providing SRAM-like active power, unlike competing nonvolatile technologies. To meet the challenging power requirements of medical devices, a new ultra-low-power 130nm process has been developed. The new process includes a very-high-density, SER-resistant, nonvolatile FRAM and an ultra-low-leakage transistor, coupled with a library that is optimized for low-power operation. This paper compares the power, area and performance of competing process technologies for a typical implantable medical design and highlights the advantages that FRAM provides in low static power through a transparent power-down capability and in low SRAM-like active power.
Vision-Based Patient Body Tracking in Helical Tomotherapy
Authors: Bird Nathaniel , Santos Troy Dos , Hui Susanta , Papanikolopoulos Nikolaos
Published: July 2008

Radiation therapy using state-of-the-art helical tomotherapy treatment is largely automatic after the doctor creates the dosage plan. The system currently has no method to detect if the patient moves out of alignment during treatment, a capability that could improve treatment accuracy. This cross disciplinary project combines the fields of computer vision with medical physics. The creation of a minimally invasive, vision-based, total-body tracker that can interact with the helical tomotherapy system to detect when a patient becomes misaligned has been explored. The tolerances are tight, by measuring when the patient moves just 5mm out of alignment, the uncertainty in radiation dose delivery can be greatly reduced. A stereoscopic vision system uses infrared reflective markers to track the patient. Using these data points, boney structures, such as the head, can be tracked independently, providing roll, pitch, and yaw information about their pose. Initial results compared vision-based patient-positioning tolerances with those of traditional megavoltage CT-scans. Simulation-based results have explored the efficacy of tracking large portions of the patient’s body.
Robotic Scrub Nurse for Otolaryngology
Authors: Agovic Amer , Levine Samuel , Papanikolopoulos Nikolaos , Tewfik Ahmed
Published: July 2008

A typical operation in otolaryngology takes place under the microscope. The surgeon works with a large set of very delicate tools, which are managed by a scrub nurse∕tech. In practice, the surgeon is intimately familiar with all instruments, which can number into hundreds but the nurse might not be. This situation can lead to miscommunication and longer operations. Any delay is a costly proposition. Typical costs during procedures can be $250 per 15minute interval and every minute counts. Scrub nurse responsibilities include organization of instruments and their sterilization. During operation the surgeon requests an instrument, the technician must be able to identify it from a list of hundreds and place it correctly in the surgeon’s hand. The instruments might be microscopically different and look very similar. Each instrument is several hundred dollars and difficult to replace or repair. This study looks at the steps needed to automate the activities of a scrub nurse. First step towards this goal is the study of haptic and spoken language interfaces. The robot must know when to pick up a new instrument and when to release it. Next the robot must be able to plan out a stable and collision free motion and grasping movement. To enable all of this vision based localization of surgeon’s hands, instrument palette and any obstacle movement is necessary.
A Computational Approach to Muscle Modeling of the Human Tongue via the Finite Element Method Along With Motion Control Correlations With MRI Tracking Data for Simple Speech Patterns
Authors: Buscemi Paul , Carlson Mark , Tricarico Reiner Wilhelms
Published: July 2008

Tongue motion control results from a complicated series of interactions between multiple tongue muscles. Surgical intervention could possibly affect speech while at the same time producing positive benefits as reduction of retro-palatal collapse. The goal of the study was to represent the tongue as a quantifiable structured geometry specifying the various muscle regions as locally varying directional fields and use this model to determine the affect of altered muscle structure on tongue motion. A quantitative computer simulation of the human tongue was constructed around a finite element model. Muscle morphology was generated from segmentation of images from the Visible Human project and MRI images. The extrinsic and intrinsic muscles were represented as directional fields at a large number of elements. Muscle contraction was produced as a stress controlled region of a locally varying directional field. A Lagrangian formulation of an Ogden hyperelastic material was used for the passive isotropic components and muscle fibers were represented by strain energy and pressure functions. Validation of the model was obtained by comparing tongue displacement or strain patterns generated with various muscle activation patterns with those obtained from tracked MRI images. Quantifiable differences in the motion of the tongue caused by alteration of specific muscle morphology or activation patterns were used to identify regions of the tongue that may be affected by surgical implants and may help in the understanding of patterns of muscle activation in the study of speech and sleep apnea.
Human Joint Simulation Using LifeMOD Co-Simulation
Authors: Fahlgren Eric , Carlson Mark , Elliott Andrew S.
Published: July 2008

Advanced design of human artificial joints requires an in-depth understanding of the dynamic interaction between the very stiff bone replacement material and the softer viscoelastic cartilage replacement material. It must take into account both the large displacement gross motions as well as the small displacement elastic responses. A co-simulation methodology has been developed in BRG LifeMOD, connecting Adams∕Solver, a large displacement multi-body dynamics code, to Marc, a nonlinear finite element code. This efficient co-simulation approach allows for each code to handle that portion of the system for which it is most capable, while adding the potential to work across multiple CPUs and operating systems as desired. The method was applied using LifeMOD∕KneeSIM to simulate an artificial knee joint, containing cobalt chromium steel and ultra-high molecular weight polyethylene contact elements, undergoing a normal walking gait to predict kinematics, forces and the resulting wear patterns.
Synthetic Soft Tissue Characterization of the Mechanical Analogue Lumbar Spine
Authors: Avidano Eugene E. , LaPierre Leighton J. , Friis Elizabeth A. , James John E. , Johnson Amy E.
Published: July 2008

Evaluation of spinal implants is limited by difficulties in testing biological structures. Soft tissues primarily control spinal biomechanical responses. The objective of this study is to show controllability of the synthetic soft tissue properties of the mechanical analogue lumber spine. The development of an analogue spine would answer a multitude of clinical questions and improve implant design. Polyester fibers in a wave pattern were embedded in a shore-A F55 polyurethane matrix to mimic the nonlinear properties of human ligaments. Ligaments with four different volume fractions (Vf) of fibers were tested to failure in tension using specially designed jigs in a MTS MiniBionix. Polyester fibers oriented at +∕−30degrees were embedded in F55 polyurethane to simulate the annulus fibrosis (AF). Discs with three different Vf’s and F5 polyurethane for the nucleus pulposus were tested in compression to 1.25mm using a self-aligning jig. Displacement control was used for all specimens at a rate of 0.04230mm∕sec. For the ligaments, the initial stiffness and strain at toe was similar and the mean secondary stiffness in MPa was 187±5%, 307±5%, 422±2%, and 511±3% as the Vf increased. For the discs, the mean initial and (secondary) stiffness in N∕mm was 158±14%(658±6%), 150±5%(666±8%), and 74±3%(1230±2%) as the AF Vf increased. The results showed that synthetic soft tissue properties are controllable and properties measured fall within the range of human cadaveric literature values. A wide variety of analogue models can be developed utilizing the control of soft tissues.
Custom TMJ Hemi-joint Fabrication Process
Authors: Kuhlmann Joel L. , McEligot Sean
Published: July 2008

Temporomandibular joint disorder afflicts 10 million Americans, many of whom have osteoarthritis of the temporomandibular joint (TMJ). This condition can inflict severe pain and disrupt the lives of sufferers in many ways. Partial or total replacement of the temporomandibular joint is a last resort treatment option. Surgeons at Mayo Clinic believe a new hemijoint implant design coupled with unique surgical technique can improve joint kinematics and reduce pain. They are currently investigating a patent-pending implant design in a series of patient trials. The Division of Engineering at Mayo Clinic has developed a novel process for fabricating TMJ implants for this study. Computed Tomagraphy (CT) images of the surgical site are first converted into a 3D computer model of the mandibular fossa and condyle area. A fused deposition modeling process is used to create a plastic model of the anatomy, and the surgeons use that model to create a wax mold of the implant. The wax mold is laser scanned to create a 3D CAD model that can be machined with a standard four axis milling machine out of implant grade CoCrMo material. Because of the unique shape of the implant, the machining takes place in two phases, with the implant being refixtured between machining phases using a high strength industrial adhesive. Finally, the implant is polished, inspected, passivated and sterilized for surgery. This fabrication process has allowed Mayo Clinic surgeons to quickly and accurately test their unique implant design.
A New External Fixator Design for Femoral Fracture Reduction
Authors: Cucinotta Michael J. , LeBlon Courtney E. , Rahimi Nima , Paliwal Manish
Published: July 2008

Objective: To design an external fixator for femoral fracture reduction with improved angulation and adjustability, reduced bulk, and comparative stiffness. Background: The use of external fixator for femoral shaft fixators in children has been a device of choice. The use though satisfactory, the occurrences of wire∕pin tract infections has been widely reported. Moreover, The use of Ilizarov external fixator in adults has been limited due to its bulk. Hence there is a need for improvement on the current external fixators for femoral fractures. Methods: The finite element models of four-ring Ilizarov and hybrid two-ring fixators were developed. These designs were improved upon by incorporating a “modular sliding joint design,” and by reducing the bulk by reducing the number of rings and adding guide plates. Wire length optimization feature was also added in the design. Axial stiffness of the new design was compared with the hybrid design using finite element analysis (FEA). Results and Discussion: The new design has reduced bulk at the proximal region allowing its application in adults. The axial stiffness of the proposed design was found to be comparable with the two-ring hybrid design, as determined from FEA. Sliding joint design allows reduced inventory, quick assembly, and improved angulation over current designs. Wire length optimization may reduce the occurrences of wire tract infections.
Novel re-entrant porous composite structure: a potential for orthopaedic applications
Authors: Jaumard Nicolas V. , Friis Elizabeth A. , Smay James , Xu Jian
Published: July 2008

It was hypothesized that the nonlinear load-displacement relationship displayed by bone could be conferred on an implant by tailoring its structure, yielding an enhanced mechanical stimulation of the tissues. Composite structures would feature piezoelectric properties that could also stimulate osteogenesis. Preliminary mechanical and electromechanical investigations of such porous structures are presented. Initial trial bowtie specimens with various aspect ratii were made from Nickel powder via a solid free form process and from stainless steel shim stocks. Poled Barium Titanate plates were sandwiched between stainless steel bowtie cells to create composite structures.Results: Under quasi-static compression, the Nickel structures displayed a nonlinear mechanical behavior at small strains and an overall strain-stress relationship similar to bone. Under cyclic compressive tests to 0.6 percent strain, all structures presented a repeatable nonlinear strain-stress behavior. The curves were fitted by a second-order polynomial whose coefficients are function of the relative density of the structure to a power n. Composite stainless steel/BaTiO3 bowtie structures confirmed that their electromechanical properties can be tailored.Discussion: Certain patients present metabolic degeneration that hamper bone healing. A ductile and tough structural material with piezoelectric properties such as the new composite structures in development presents the potential to overcome those limitations. They could have the advantages of existing devices without some of the drawbacks. Those porous implants may reduce the needs, costs, and risks linked to the additional use and implementation of an electrical stimulator and BMPs. Furthermore, the solid free form technique gives control over the mechanical properties of the structure. Thus, the mechanotransduction activity of biologic cells can be fully exploited to trigger a faster implant-tissue bonding, which could lead to reduction of surgical cost and time.
Development of Polymeric Nerve Guidance Conduits That Contain Anisotropic Cues Including Aligned Microfibers and Gradients of Adsorbed Laminin-1
Authors: Cregg Jared M. , Wang Han Bing , Mullins Michael E. , Gilbert Ryan J.
Published: July 2008

Structures that direct neurite extension are important for regeneration following spinal cord injury and peripheral nerve injury. Within the spinal cord, neurons encounter a glial scar environment that impedes regeneration. In the peripheral nervous system, endogenous regeneration cannot occur across nerve gaps greater than 2mm. Current repair strategies use guidance conduits to channel axonal growth towards distal targets. While showing promise, conduit walls do not provide a suitable environment for neuronal attachment or extension, and axonal growth within conduits remains tortuous. Hence, there is a need for development of three-dimensional (3D) structures that use contact guidance—rather than confinement—as a means of guided regeneration. Our laboratory has developed aligned, electrospun fiber matrices that have been shown to direct neurite extension in vitro. In addition, a gradient of the glycoprotein laminin-1 has been adsorbed onto aligned microfiber matrices to stimulate directional growth. These matrices were then manipulated into 3D conduit structures. Novel polymeric conduits that utilize contact guidance and contain gradients of molecules that stimulate directional growth have the potential to foster fast, directed regeneration into and through conduit structures.
The Effect of Stent Design on the Restenosis Rate
Authors: Muttyam Aswini K. , Gu Linxia
Published: July 2008

Within 6months from the initial procedure, restenosis is observed in 40% of the cases treated with coronary stenting. Exact reasons for restenosis are yet to be explored. Stenting is a mechanical process which causes large stress in the arterial wall. This may lead to the activation of stent related stenosis. The primary objective of this study is to investigate the relation between the stresses developed in the arterial wall and the restenosis rate. A three-dimensional model based on finite element method has been built which includes the stent, the plaque and the artery. The simulated result shows high stress concentrations at the contact areas of the stent and the plaque. The over flaring of the end struts causing arterial trauma may lead to restenosis.
Nanofiber Covered Stent (NCS) for Vascular Diseases
Authors: Dong Yixiang , Eong Teo Wee , Liao Susan , Chan Casey , Ramakrishna S.
Published: July 2008

Introduction: A covered stent is one whose length and circumference is enclosed with a membrane or fabric like material. Current covered stents have been used in the treatment of failed saphenous vein grafts in coronary bypass and coronary artery perforations. Covered stents have also been proposed in treating brain aneurysm. However, none of these applications showed satisfactory results. The deficiencies of the covered stents are 1) Large wall thickness 2) Rigidity 3) Non-biodegradable polymer with poor endothelialization. Materials and methods: Aligned poly(L-lactide-co-epsilon-caprolactone) [P(LLA-CL)] nanofiber was lon-gitudinally deposited on to a bare metal stent (BMS) by a patent pending electrospinning technique. The NCS were deployed following the instruction to evaluate the expandability. Biocompatibility of the nanofiber was characterized by cell culture, degradation and drug eluting study. Results: The cell viability of Porcine smooth muscle cells (PSMC) on the nanofiber was initially low but caught up after 2weeks. SEM images showed 100% of cell confluence on the nanofiber after 2months. Significant amount of ECM protein was detected on P(LLA-CL) nanofiber (0.07mg∕cm2 at day 70). Complete degradation of P(LLA-CL) is expected within 6months. Paclitaxel released from drug loaded nanofiber was shown to inhibit PSMC growth but kill Hela cells. NCS was successfully fabricated and deployed without tearing the nanofiber. Conclusions: NCS was successfully fabricated. P(LLA-CL) was chosen for the “cover” with proved superiorities on biocompatibility, cell viability, degradability and drug loading capacity. Future work will be animal study to prove that NCS can reduce in-stent restenosis and promote endothelialization.
Dynamic Behavior of SMA Actuated Catheter
Authors: Veeramani Arun S. , Buckner Gregory D. , Owen Stephen B. , Crews John H. , Cook Richard C. , Bolotin Gil
Published: July 2008

Introduction: While catheters have proven effective in numerous cardiovascular procedures, their functionality and versatility can be greatly improved by incorporating active steering capabilities to the catheter tip. Shape memory alloy (SMA) actuation is ideally suited to this application, as these materials offer superior power density, energy density and biocompatibility. In this research, we investigate the transient behavior of an SMA-actuated active catheter to optimize its design and enable precise computer-controlled navigation. Methods: The active catheter prototype consists of a central beam actuated by a single SMA tendon, both enclosed by an outer Teflon sleeve. Joule heating is used to generate tip deflections, which are measured in real time using a dual-camera imaging system. SMA actuation is described using the Seelecke-Muller-Achenbach single-crystal model whose parameters are experimentally derived from stress-strain characteristics of the SMA tendon measured at different temperatures. These characteristics are used to optimize the design parameters of the catheter to maximize the bending response. The effects of outer sleeve thickness on the transient behavior of the catheter are also studied. Results: The catheter’s bending mechanics are described using a circular arc model, which is experimentally validated. Catheter actuation is found to be slower with increased sleeve thickness, as explained by heat transfer analysis. Dynamic simulation of the system model shows excellent correlation to experimental data for low frequency actuation.
Radiopaque Nano-Porous Ta Coatings for Nitinol Medical Devices
Authors: Bell Brent C. , Glocker David A.
Published: July 2008

Nano-porous Ta coatings have been developed to render Nitinol medical devices fully radiopaque. These coatings are deposited atom by atom in a unique PVD process that utilizes a cylindrical cathode and operates at conditions that produce low substrate temperatures. As a result, complex 3D shapes are coated with high uniformity and the critical Nitinol mechanical properties are unchanged. Because these coatings consist of a nano-porous columnar structure they are able to withstand strains of at least 8% without delamination or cracking. X-ray and fluoroscopic imaging shows that Nitinol stents with these coatings are highly visible and reveal the entire 3D shape of the device instead of only point markers. The benefits of these coatings are easier, faster and more reliable implantation procedures, especially for difficult to visualize medical devices such as bifurcated stent-grafts. Ta is extremely biocompatible. Thirty-day and 6‐month porcine studies have shown that there is no difference in stenosis, intimal thickness, injury score or inflammation score for stents with this nano-porous Ta coating compared to a bare Nitinol stent. In addition, measurement of corrosion breakdown potential show higher values for Ta on Nitinol than Nitinol alone. Aside from radiopacity, these Ta coatings, hold the potential for other highly desirable functions such as controlled drug delivery without polymers and enhanced re-endothelialization. Studies are currently underway to understand the drug loading and release kinetics as a function of a pore size and aspect ratio.
Electromyogram-Triggered Functional Electrical Stimulation-Assisted Walking After Partial Paralysis
Authors: Dutta Anirban , Kobetic Rudi , Triolo Ronald
Published: July 2008

Objective: Functional Electrical Stimulation (FES) triggered by manual switch provides brace-free ambulation to wheelchair dependent individuals with spinal cord injuries. An electromyogram (EMG)-based trigger can enhance the coordination between FES-assisted and volitional actions. This study evaluated the gait speed modulation and coordination of the actions of the EMG-triggered FES with the volitional movements during stand-to-walk transition after incomplete spinal cord injury. Methods: two incomplete spinal cord injured (iSCI) subjects (iSCI1: 24years, C7 motor & C6 sensory; iSCI2: 34years, T1 motor & C5 sensory) volunteered for this study. Four able-bodied volunteers provided the normative gait data. The Vicon WorkstationTM (Vicon Peak, USA) software acquired lower-body kinematics data using a seven camera motion capture system during stand-to-walk transition. The FES-assisted swing-phase in iSCI subjects was triggered with three command interfaces—manually triggered with a switch, triggered with EMG-based GED, triggered automatically at a user-selected rate. Results and Discussion: The Euclidean distance from origin of the perturbations of 18 joint angles and 18 joint velocities during stand-to-walk transition converged towards zero. It was found from the Mahalanobis distances between each pair of group means that the EMG-triggered FES-assisted iSCI gait was closest to the able-bodied normative gait clusters.
A Minimally Invasive Device for Continuous Glucose Monitoring in Infants
Authors: Erdman Christopher P. , Goldman Stephen M. , Lynn Patrick J. , Ward Matthew C.
Published: July 2008

Blood sugar management is particularly critical in the neonatal intensive care unit where the incidence of hypoglycemia is high and patients run the risk of brain damage. The staff at most hospitals obtain glucose levels in infants by drawing blood from the heel, which is a cause for recurrent pain. Some infants undergo this procedure every 1–3hours for up to a few months. Our goal is to design a minimally invasive device that allows for real-time glucose monitoring in very low birth weight infants in the neonatal intensive care unit (NICU). This glucose monitor will reduce the amount of pain and physiological stress on the infants, decrease the risk of hypoglycemia in neonates and reduce the workload on hospital staff. There is currently much room for emerging technologies in this market as it trends towards less pain and faster responses. The device should only slightly hinder the infant’s motion, be as painless as possible, and all materials used in contact with the body need to be biologically inert and cause no irritation or allergic reaction. The device will utilize a microneedle array to extract interstitial fluid and draw it through a hydrophilic polyurethane membrane and into a polarimetry chamber. Circularly polarized light will be passed through the chamber and the differential absorbance of left and right polarized light will be used to calculate the glucose concentration. A literature and patent review showed that each separate portion could be used in an effective device for minimally invasive, continuous glucose monitoring.
Continuous In Vivo Monitoring of a Flexible Subcutaneous Sensor in Freely Moving Diabetic Rats
Authors: Thomas Spencer , Hitchcock Robert
Published: July 2008

Subcutaneous tissue is frequently the target site for placement of continuous, real-time metabolic sensors. Since the 1960s, numerous research groups have developed needle-like sensor designs, patterned after the Clarke Electrode, to monitor glucose in subcutaneous tissue. These designs perform well in vitro but often fail in vivo due to sensor instability and tissue response. None of these studies focused on the mechanical properties of implanted sensors and how these properties may affect in vivo performance. To investigate the role of sensor stiffness on short term functionality we developed a low stiffness subcutaneous sensor patterned after the Clarke Electrode and tested it in rodents. The purpose of this study was two-fold. The first goal was to demonstrate the in vivo functionality of the flexible sensor. The second goal was to evaluate the effect of stiffness on functionality by co-implanting stiff and flexible sensors. In the first series of studies the low stiffness sensors provided glucose level measurements that fell within the A and B regions of the Clarke Error Grid 93.0% of the time. The results of the second study yielded similar accuracy; however, no performance difference was seen between the stiff and flexible sensors. We concluded that the flexible sensor works for at least 3days after implantation in the subcutaneous tissue of freely moving rats and that the key property of low stiffness has no differential effect on the accuracy of the sensor in the freely moving rodent model of these studies.
Diagnostics of Human Body Cavities Using Diode Laser Gas Spectroscopy
Authors: Cassel-Engquist M. , Persson L. , Svanberg K. , Svanberg S.
Published: July 2008

We have developed a technique to measure gas non-intrusive in scattering media, such as human tissue. The technique was first demonstrated for test samples in 2001 by our group and utilizes diode laser absorption spectroscopy to monitor molecular oxygen and water vapor. The focus of medical application has been on sinuses, both maxillary and frontal sinuses and the potential of the technique has been shown on volunteers. A spin-off company named GasPorOx AB has been formed with the aim to develop a product used to improve the diagnosis of the sinus infections. A portable fiber-guided system has been developed and is used in an ongoing initial clinical trial in collaboration with the Ear, Nose and Throat Clinic, the Oncology and Diagnostic radiology clinics at the Lund University Hospital.
Modal Parameter Extraction of a Turboset From High Speed Balance Data
Authors: Dhingra Anoop K. , Hidalgo Juan I.
Published: July 2008

Turbosets used in power generation industry are frequently placed on flexible foundations, which significantly influence the overall dynamics. Establishment of structural models that capture the rotor and foundation effects reliably using finite element modeling or modal analysis is difficult because of model complexity and/or costs involved. This paper presents a method to extract modal parameter information of a turboset using frequency response function data recorded during high speed balancing. The main advantage of the present method over the others is the low cost and small effort involved, so that it is of practical use in an industrial setting. A real life example dealing with parameter extraction for a large generator rotor is presented to demonstrate its implementation.
Experimental Blowout Limits and Computational Flow Field of Axial Single and Multijet Flames
Authors: Shebl Khaled M.
Published: July 2008

Measurements of the lean blowout equivalence ratio (Φoverall,b) along with the numerical simulations of flame structure and dynamics of the flow field for coaxial burner configurations are reported. The burner comprises central mixture (air+liquefied petroleum gas) issuing either through six holes distributed radially each of 2mm diameter or through a circular single port of area equal to the total areas of the six holes. A bluff-body stabilizer is attached to provide recirculation of the coaxial air surrounding the central flame. The study covers the effect of the central injection configuration with emphasis on the multijet on the overall lean equivalence ratio at which flame is extinguished. The dynamics of the flow field for the multiflame configurations were identified and compared with the single flame, using the generalized finite-rate chemistry model of FLUENT 6.2 with the detailed chemical reaction mechanism defined by GRI-MECH 3.0 and other mechanisms for the higher carbon species. The computed flow field of the multijet flame provides an extra intermediate vortex in addition to the two counter-rotating vortices observed for cases of the single central stream configuration. Such a vortex is believed to enhance the stability characteristics for all the test flames in the form of reduced experimental Φoverall,b-values.
On Scaling Down Turbines to Millimeter Size
Authors: Deam R. T. , Lemma E. , Mace B. , Collins R.
Published: July 2008

The purpose of this work is to establish the maximum theoretical efficiency that a viscous flow turbine (such as a Tesla turbine) can achieve. This is very much in the spirit of the Betz limit for wind turbines. The scaling down of viscous flow turbines is thought not to alter this result, whereas the scaling down of conventional turbines, whether axial or radial flow, results in an ever lowering of their efficiencies. A semiempirical scaling law is developed for conventional gas turbines using published machine performance data, which is fitted to a simple boundary layer model of turbine efficiency. An analytical model is developed for a viscous flow turbine. This is compared to experimental measurements of the efficiency of a Tesla turbine using compressed air. The semiempirical scaling law predicts that below a rotor diameter of between about 11mm and 4mm, a practical Brayton cycle is not possible. Despite that, however, and for rotor diameters less than between about 7mm and 2mm, a viscous flow turbine, compressor, or pump will be more efficient than a conventional design. This may have a significant impact on the design of microelectromechanical system devices.
Autoignition of Hydrogen and Air Inside a Continuous Flow Reactor With Application to Lean Premixed Combustion
Authors: Beerer D. J. , McDonell V. G.
Published: July 2008

With the need to reduce carbon emissions such as CO2, hydrogen is being examined as potential “clean” fuel for the future. One potential strategy is lean premixed combustion, where the fuel and air are allowed to mix upstream before entering the combustor, which has been proven to curb NOx formation in natural gas fired engines. However, premixing hydrogen and air may increase the risk of autoignition before the combustor, resulting in serious engine damage. A flow reactor was set up to test the ignition delay time of hydrogen and air at temperatures relevant to gas turbine engine operations to determine maximum possible mixing times. The results were then compared to past experimental work and current computer simulations. The current study observed that ignition is very sensitive to the initial conditions. The ignition delay times follow the same general trend as seen in previous flow reactor studies: ignition within hundreds of milliseconds and relatively low activation energy. An experimentally derived correlation by Peschke and Spadaccini (1985, “Determination of Autoignition and Flame Speed Characteristics of Coal Gases Having Medium Heating Values,” Research Project No. 2357-1, Report No. AP-4291) appears to best predict the observed ignition delay times. Homogenous gas phase kinetics simulations do not appear to describe ignition well in these intermediate temperatures. Therefore, at the moment, only the current empirical correlations should be used in predicting ignition delay at engine conditions for use in the design of gas turbine premixers. Additionally, fairly large safety factors should still be considered for any design to reduce any chance of autoignition within the premixer.
A Comparison Between Combustion Phase Indicators for Optimal Spark Timing
Authors: Pipitone Emiliano
Published: July 2008

The closed-loop control of internal combustion engine spark timing may be accomplished by means of a combustion phase indicator, i.e., a parameter, derived from in-cylinder pressure analysis, whose variation is mainly referable to combustion phase shift and assumes a fixed reference value under optimal spark timing operation. The aim of the present work is a comparison between different combustion phase indicators, focusing on the performance attainable by a feedback spark timing control, which uses the indicator as pilot variable. An extensive experimental investigation has been carried out, verifying the relationship between indicators’ optimal values and the main engine running parameters: engine speed, load, and mixture strength. Moreover, assessment on the effect of the most common pressure measurement problems (which are mainly related to pressure referencing, sampling resolution, top dead center determination, and cycle-by-cycle variations) on the indicators’ values and on the performance attainable by the spark timing control is included. The results of the comparison point out two indicators as the most suitable: the location of pressure peak and the location of maximum heat release rate. The latter, not available in literature, has been introduced by the author as an alternative to the 50% of mass fraction burned.
A Review of H∞ Robust Control of Piezoelectric Smart Structures
Authors: Iorga Lucian , Baruh Haim , Ursu Ioan
Published: July 2008

Robust vibration control of piezoelectric actuated smart structures has attracted substantial interest in recent years. Such control laws are desirable for systems where guaranteed stability or performance is required despite the presence of multiple sources of uncertainty. In this work, we review the principal problems that the structural control engineer has to address when designing robust control laws: structural modeling techniques, uncertainty modeling, controller order reduction, and robustness validation. A comprehensive literature review is presented and the different techniques employed are discussed in detail in a tutorial manner for the case of a piezoelectric smart plate, with the aim of providing a comprehensive and unitary methodology for designing and validating robust H∞ controllers for active structures.
A Two-State Cell Damage Model Under Hyperthermic Conditions: Theory and In Vitro Experiments
Authors: Feng Yusheng , Tinsley Oden J. , Rylander Marissa Nichole
Published: July 2008

The ultimate goal of cancer treatment utilizing thermotherapy is to eradicate tumors and minimize damage to surrounding host tissues. To achieve this goal, it is important to develop an accurate cell damage model to characterize the population of cell death under various thermal conditions. The traditional Arrhenius model is often used to characterize the damaged cell population under the assumption that the rate of cell damage is proportional to exp(−Ea∕RT), where Ea is the activation energy, R is the universal gas constant, and T is the absolute temperature. However, this model is unable to capture transition phenomena over the entire hyperthermia and ablation temperature range, particularly during the initial stage of heating. Inspired by classical statistical thermodynamic principles, we propose a general two-state model to characterize the entire cell population with two distinct and measurable subpopulations of cells, in which each cell is in one of the two microstates, viable (live) and damaged (dead), respectively. The resulting cell viability can be expressed as C(τ,T)=exp(−Φ(τ,T)∕kT)∕(1+exp(−Φ(τ,T)∕kT)), where k is a constant. The in vitro cell viability experiments revealed that the function Φ(τ,T) can be defined as a function that is linear in exposure time τ when the temperature T is fixed, and linear as well in terms of the reciprocal of temperature T when the variable τ is held as constant. To determine parameters in the function Φ(τ,T), we use in vitro cell viability data from the experiments conducted with human prostate cancerous (PC3) and normal (RWPE-1) cells exposed to thermotherapeutic protocols to correlate with the proposed cell damage model. Very good agreement between experimental data and the derived damage model is obtained. In addition, the new two-state model has the advantage that is less sensitive and more robust due to its well behaved model parameters.
Experimental Surface Strain Mapping of Porcine Peripapillary Sclera Due to Elevations of Intraocular Pressure
Authors: Girard Michaël J. A. , Downs J. Crawford , Burgoyne Claude F. , Suh J.-K. Francis
Published: July 2008

To experimentally characterize 2D surface mapping of the deformation pattern of porcine peripapillary sclera following acute elevations of intraocular pressure (IOP) from 5mmHgto45mmHg. Four porcine eyes were obtained within 48h postmortem and dissected to the sclera. After the anterior chamber was removed, each posterior scleral shell was individually mounted at the equator on a custom-built pressurization device, which internally pressurized the scleral samples with isotonic saline at 22°C. Black polystyrene microspheres (10μm in diameter) were randomly scattered and attached to the scleral surface. IOP was incrementally increased from 5mmHgto45mmHg(±0.15mmHg), and the surface deformation of the peripapillary sclera immediately adjacent to the dural insertion was optically tracked at a resolution of 2μm∕pixel one quadrant at a time, for each of four quadrants (superior, nasal, inferior, and temporal). The 2D displacement data of the microsphere markers were extracted using the optical flow equation, smoothed by weighting function interpolation, and converted to the corresponding Lagrangian finite surface strain. In all four quadrants of each eye, the principal strain was highest and primarily circumferential immediately adjacent to the scleral canal. Average maximum Lagrangian strain across all quadrants for all eyes was 0.013±0.005 from 5mmHgto10mmHg, 0.014±0.004 from 10mmHgto30mmHg and 0.004±0.001 from 30mmHgto45mmHg, demonstrating the nonlinearity in the IOP-strain relationship. For each scleral shell, the observed surface strain mapping implied that the scleral stiffness was relatively low between 5mmHg and 10mmHg, but dramatically increased for each IOP elevation increment beyond 10mmHg. Peripapillary deformation following an acute IOP elevation may be governed by the underlying scleral collagen microstructure and is likely in the high-stiffness region of the scleral stress-strain curve when IOP is above 10mmHg.
Enzymes Without Borders: Mobilizing Substrates, Delivering Products
Authors: Forneris Federico , Mattevi Andrea
Published: July 2008

Many cellular reactions involve both hydrophobic and hydrophilic molecules that reside within the chemically distinct environments defined by the phospholipid-based membranes and the aqueous lumens of cytoplasm and organelles. Enzymes performing this type of reaction are required to access a lipophilic substrate located in the membranes and to catalyze its reaction with a polar, water-soluble compound. Here, we explore the different binding strategies and chemical tricks that enzymes have developed to overcome this problem. These reactions can be catalyzed by integral membrane proteins that channel a hydrophilic molecule into their active site, as well as by water-soluble enzymes that are able to capture a lipophilic substrate from the phospholipid bilayer. Many chemical and biological aspects of this type of enzymology remain to be investigated and will require the integration of protein chemistry with membrane biology.