bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of Photoinitiated Nitric Oxide Releasing Polymer Films for Controlled Drug Delivery
Authors: Smeenge D. M. , Barron M. J. , Nielsen M. T. , Goldman J. , Frost M. C.
Published: July 2009

Nitric Oxide (NO) is small, free radical gas that has been shown to have a wide variety of physiological functions, including the ability to hinder tumor angiogenesis at high, but non lethal, concentrations [1]. Previous work suggests that if NO could be effectively delivered in vivo to tumors of patients currently undergoing chemotherapy treatments at the appropriate levels, less damaging chemotherapy treatments could be used against cancer [2]. This could increase the overall survivability of cancer patients, especially in those prone to the harmful effects of chemotherapy: children, elderly, and those of weak immune systems. If NO is especially successful at preventing and eliminating tumor growth, angiogenesis, and carcinogenesis the need for stressful chemotherapy treatments could be eliminated altogether. This project is focused on developing novel photosensitive NO donors that can be incorporated into polymeric systems and used in a fiber optic drug delivery system. Development of these NO-releasing polymers will allow continued investigation of NO's role in tumor death by precisely controlling the surface flux of NO that cells are exposed to. Generating specific surface fluxes of NO from polymer films has been demonstrated by using polymer films that contain photoinitiated NO donors [3], prepared by synthesizing S-nitrosothiol (RSNO) derivitized polymer fillers that are blended into hydrophobic polymers and cast into a film. These films generate and sustain a surface flux of NO based on the wavelength and intensity of light used [3]. Polymers releasing NO are more promising as an NO donor than simply injecting NO into samples because they allow for spatial and temporal control of NO delivery. The specific concentration of NO needed to produce desirable effects on tumor cells (i.e., apoptosis) is not known. Data will be presented that show the synthesis and NO-release properties of novel RSNOs based on the nitrosation of benzyl mercaptan thiols. Specifically, UV-Vis spectrum of benzyl mercaptan in toluene and S-nitrosobenzyl mercaptan after the addition of t-butyl nitrite will be presented. We are currently investigating the effects of varying NO-surface fluxes generated from photolytic NO donating polymer films on aortic smooth muscle cell cultures obtained from mice. Once we have established that we can quantitatively determine the effects of different levels of NO on the proliferation of smooth muscle cell cultures, work will begin to apply this methodology and these novel NO-releasing polymeric systems to begin investigating what durations and surface fluxes of NO are necessary to have tumorcidal effects on specific cancer cells.
Visualization and Hemo-Dynamic Evaluation of Edge-to-Edge Mitral Valve Repair Within Reanimated Swine Hearts
Authors: Bateman M. G. , Quill J. L. , St. Louis J. , Iaizzo P. A.
Published: July 2009

This project aims to investigate the performance of edge-to-edge mitral valve repair (MVR) within reanimated swine hearts. Direct imaging and hemodynamic data of the mitral valve during normal cardiac function (Normal), after an induced prolapse (Prolapse), and post surgical repair (E2E) was obtained. Isolated swine hearts (n=6) were reanimated using a clear Krebs–Henseleit buffer. Mitral prolapse, and regurgitation, in the P2 region was induced by cutting chordae tendinae of the posterior leaflet. An edge-to-edge MVR procedure was performed, suturing the prolapsed P2 region to the A2 region of the anterior leaflet. The mitral valve was imaged using endoscopic cameras in the left atrium and ventricle allowing verification of stitch placement and leaflet coaptation. Analysis of the endoscopic images provided measures of annulus area, orifice area, and regurgitant area. Echocardiography, the standard clinical imaging modality, was used to determine the hemodynamic performance of the valve. Additionally, ECG and left chamber pressures were recorded at a sample rate of 5 kHz. Prolapse of the P2 region was consistently created, and edge-to-edge repair of the mitral leaflet showed full leaflet coaptation. The annulus area of the valve was tracked throughout the procedure and did not show significant variation. The orifice area, defined as the area of the annulus that does not contain leaflets, normalized to the corresponding annulus area for Normal, Prolapse and E2E were: 41±13%, 44±14% and 21±13%, p=0.02. The regurgitant area, normalized to the corresponding annulus area, increased from 2±2% for Normal to 8±3% for the Prolapse and then decreased to 1±1% for the E2E group. The regurgitant fraction, normalized against the maximum observed, for Normal, Prolapse and E2E was 10±6%, 57±26% and 13±13%, p<0.01. Over the course of the experiment the left ventricular (LV) systolic pressure and negative dP/dt reduced from 95 to 54 mm Hg and 743 to 402 mm Hg/s, respectively. Our results show that orifice area was significantly smaller after MVR when compared to Normal and Prolapse periods. There was no significant change in regurgitant area and regurgitant fraction from the Normal to repaired valve as compared to a significant increase in regurgitant area and regurgitant fraction during Prolapse. Low gradients were observed for all three groups, with no indications for symptomatic stenosis. The reduction of LV function was caused by global ischemia and the progressive onset of edema. In this acute assessment of edge-to-edge repair of P2 prolapse, repair does not affect annulus area, decreases orifice area, and successfully eliminates regurgitant area with no evidence of mitral stenosis.
Medtech Design in Interdisciplinary Clinical Innovation Teams
Authors: Lund K. , Norell-Bergendahl M. , Oddsson L.
Published: July 2009

Interdisciplinary settings have been highlighted for creative user-close development of products and services. Similarly, user involvement in the actual design process has been presented as a way to make attractive products that will earn market shares. But will an interdisciplinary setting in itself generate the beneficial spin-offs we expect? Will including the end-user on the development team ensure better products that are more successful on the market? A study has been set up to create a work model for Clinical Innovation Teams (CIT) at the Sister Kenny Research Center in Minneapolis, MN, to facilitate the research and development process, and provide guidance to work in a creative and innovative way around rehabilitation technology development. The CITs consist of clinicians, such as nurses, occupational therapists, physical therapists, physicians, engineers and engineering students, and in some cases patients. The CITs combine the interdisciplinary setting and end-user involvement with a custom work-model. The work-model emphasizes the strengths of the teams and provides tools to overcome the obstacles and challenges that these kind of teams face. The technological depth and clinical experience is combined with a structured project work-model. The teams work interdisciplinary by pairing research with actual patient needs to develop rehabilitation technology and medical devices to address those needs. The first tool in the work model is an Innovation Handbook for development projects at the Sister Kenny Research Center, especially written for this specific setting. The second tool is a report with recommendations to the management on how to create a work environment where innovation can occur and where creative ideas are welcome, as well as how to engage clinicians into research. The report also addresses aspects of workplace design, recommendations on how to deal with uncertainties that come when moving between clinical care and research and ideas of how to ensure quality of care and maintain productivity when clinicians engage in research activities. The third tool in the work model is a schematic illustration of how the important elements of innovation management is paired with the design process, and how a project will benefit from good management and where it will suffer from insufficient support. This project has been supported by the City of Minneapolis, the Sister Kenny Research Center and the Product Innovation Engineering Program of Sweden (PIEp). Corresponding author: L. Oddsson; e-mail: lars.oddsson@allina.com
Microfabrication of a Device to Evaluate the Swelling of Glucose Sensitive Hydrogels Under Isochoric Conditions
Authors: Barriet D. , Siegel R. A.
Published: July 2009

Diabetes has been the focus of intense research for more than half a century both in academia and in industry. The number of diabetes cases (especially type II) continues to increase due to the obesity pandemic in western societies and the cost of treatment of diabetes and its severe side effects will undoubtedly continue to drive development of wide ranging technological means to better understand and treat diabetes. Tight blood sugar regulation has been shown to delay or limit side effects and prolong lifespan in patients. Continuous glucose monitoring (CGM) is expected to provide information that can be used in better regulating patient behavior, or as part of a closed loop feedback control system for administering insulin at appropriate times. Our approach to CGM involves a hydrogel whose swelling depends on glucose concentration, coupled to an LC microresonator circuit, whose resonant frequency depends on hydrogel swelling due to impingment of the hydrogel on one plate of the microcapacitor. The whole sensor is microfabricated and implantable. Wireless determination of the resonant frequency permits continuous glucose sensing without chronic skin breach. We are in the process of designing hydrogels that swell/shrink with decreasing/increasing glucose concentration to test for hypoglycemia or hyperglycemia. In collaboration with Professor Babak Ziaie's group at Purdue, a first generation microdevice was fabricated. Since the full sensor requires a significant investment in time and money for its fabrication, the incorporation and testing of diverse hydrogel systems in the full device is unrealistic at the present stage of development. We are currently fabricating a testbed device to allow for the selection of lead hydrogels, which will evaluate quantitatively the relationship stimuli/pressure. Few examples exist in the literature to measure the swelling pressure of hydrogels under isochoric conditions (V=constant) experimentally. We will describe our progress toward the fabrication of a test device to evaluate the pressure developed by a hydrogel sample inside a cavity. We used a commercial pressure die with a very small piezoresistive element (500μm by 500μm), and packaged it such that the pressure sensitive membrane was in contact with a hydrogel sample a few tens of μm thin separated from the external environment by a commercial Anodisc? membrane (0.02 and 0.2 μm pore diameter). Details of design and preliminary results will be presented.
Effects of Design Parameters on the Sensitivity of a Micro-Cantilever Based Biosensor
Authors: Vidhya S. , Mathew L.
Published: July 2009

Piezo-resistive actuation of a microcantilever induced by biomolecular binding such as DNA hybridization and antibody-antigen binding is an important principle useful in biosensing applications. As the magnitude of the forces exerted is small, increasing the sensitivity of the microcantilever becomes critical. In this paper, we are considering to achieve this by geometric variation of the cantilever. The sensitivity of the cantilever was improved so that the device can sense the presence of antigen even if the magnitude of surface-stresses over the microcantilever was very small. We consider a `T-shaped' cantilver that eliminates the disadvantages while improving the sensitivity simultaneously. Simulations for validation have been performed using Intellisuite software (a MEMS design and simulation package). The simulations reveal that the T-shaped microcantilver is almost as sensitive as a thin cantilever and has relatively very low buckling effect. Simulations also reveal that with an increase in thickness of the cantilever, there is a proportional decrease in the sensitivity. This paper presents an analytical modeling and simulation studies of a piezoresistive cantilever used as MEMS based biosensor for the detection of cardiac markers. Diagnosis of Myocardial Infarction was achieved by the nanomechanical deflection of the microcantilever due to adsorption of the Troponin I complex. The deflection of the microcantilever was measured in terms of the piezoresistive changes by implanting boron at the anchor point where there is maximum strain due to the adsorption of the analyte molecules. The biochemical interactions between the Cardiac Troponin I (cTnl) complex and the immobilized antibodies would cause change in resistance of the piezoresistor integrated at the anchor point. A ‘T’ shaped microcantilever design was proposed for the study. The distal end of the device was coated with gold. The sensitivity of the cantilever was improved so that the device can sense the presence of antigen even if the magnitude of surface-stresses over the microcantilever was very small. To obtain an application specific optimum design parameter and predict the cantilever performance. The miniaturization of the cantilever-based biosensor leads to significant advantages in the absolute device sensitivity.
Robotic Scrub Nurse for Otolaryngology-Integrating an Assistive Robot in the Operating Room
Authors: Agovic A.
Published: July 2009

Over the past year we have studied the challenges that must be overcome before we can introduce assistive robots in an operating room. We consider top among the issues a human-robot interface and an instrument-robot interface. In order for an autonomous mechanism to serve up instruments it must have domain specific knowledge about the instrument nature. The robot must be able to track the state of each instrument under its management. To this end we examine technical requirements of an instrument server. The second area of interest, and the one more unpredictable, is the problem of interaction between a human and a machine. In the past we have looked at the human speech as a medium of communication with the robot. Going beyond that we also examine the interaction that occurs at the haptic level. Here we would like to know what precisely could be conveyed to the robot and frmo the robot just by a touch? In microscope is undesirable and touch becomes a valuable means of communication.
Ambulatory Device for Urinary Incontinence Detection in Female Athletes
Authors: Wang D. , Timm G. W. , Erdman A. G. , Tewfik A. H.
Published: July 2009

Urinary incontinence (UI) has been known as a prevalent concern among parous and elderly women. However, recent studies have shown an unexpectedly high occurrence of UI in young physically fit female athletes who are actively participating in vigorous physical activities. Those study results motivated us to explore the relationship between daily intensive exercise and the occurrence of UI. As the first step to advance our understanding of this problem, an ambulatory device was developed for recording urological response to the intense force levels to which female athletes are subjected. The device consists of three types of wearable sensors, including 1) a +/– 25g tri-axial accelerometer, 2) a 360° biaxial inclinometer and 3) a urinary leakage detector or ULD. It also contains a compact data logger for real-time data recording with high frequency and precision (125 Hz, 16-bit A/D converter). The accelerometer and inclinometer help to determine the force levels developed in the body during physical activities at which urinary leakage occurs. Two types of ULD sensors have been designed: (1) copper lattice ULD, and (2) thermistor array ULD. Copper lattice ULD senses the UI based on the fact that urine drops reduce the resistance of the copper lattice resulting in a voltage change. The thermistor array ULD makes use of the finding that leaked urine is warmer than the surface of the skin, such that the integrated thermal components respond to urine leakage differently. In addition, a thermoelectric cooler is applied to produce a constant reference temperature. The entire device is small, lightweight, nonintrusive, and can be worn comfortably by subjects on their wrists or low back for at least 3 hours of continuous data recording. The test results from the recruited female athletes show that the three sensors can simultaneously record the intensity of activity and the corresponding urine leakage. However, for the copper lattice ULD, substantial sweat developed during the vigorous activity which produced an artifact and prevented the device from detecting the occurrence of urine leakage. The recently designed thermistor array ULD is less sensitive to sweat, resulting a more reliable sensor than is provided by the copper lattice ULD. The wearable sensor based device enables us to determine if urinary incontinence in female athletes occurs during vigorous physical activities or as a result of the fatigue caused by these activities. This conclusion facilitates the understanding of the mechanism of UI and assists trainers and coaches with the design of an appropriate training program that reduces the occurrence of UI in these female athletes.
Numerical Study of Shear-Induced Thrombus Formation Over Aterial Stent Struts
Authors: Bark D. L. , Ku D. N.
Published: July 2009

Thrombosis remains an important problem in both bare-metal and drug eluting stents. Platelet accumulation appears to be highly shear dependent in uniform parallel plate and stenosis models. This study was performed to evaluate thrombus formation location and size with respect to time for a stent. A three-dimensional laminar flow field was modeled via computational fluid dynamics through a stent-containing coronary sized vessel. Platelet deposition and accumulation was then simulated using a shear dependent accumulation function. The platelet deposition rate is given by the function: 3.2γ̇+67 platelets/mm2/s, where γ̇ is the shear rate, which comes from a linear regression to data presented in Ku and Flannery 2007. A three-dimensional stent with a helical strut matrix design and a pitch of 21 mm was designed around a 3 mm diameter vessel. Square strut designs of 0.15mm×0.15mm and 0.30mm×0.30mm were considered, with each strut embedded halfway into the vessel. A 30° section of the stent was modeled because of stent symmetry. The inlet was set at a mean Reynolds number of 200 by specifying a pressure differential across the length of the vessel. Thrombus growth based on shear rate was set through the equation: dΦ/dt=(3.2γ̇+67)(Vplatelet/V)∑n=0MAn. V is volume, Φ is the volume fraction of thrombus, M is the number of surrounding faces that are either a wall face or are neighboring a computational cell denoted as occluded by thrombus, associated with area, A. Each term without a subscript pertains to the local computational cell prescribed as undergoing thrombus growth. Thrombus cell occlusion was assumed to occur when thrombus filled 80% of the cell's volume. Maximum shear rates occur near the edges along the inner blood surface side of the stent struts. Thrombus growth increases more in the axial direction of the stent relative to the radial direction for the larger strut size. Conversely, the thrombus growth is more uniform in all directions along the smaller struts. The difference emanates from the two distinctly localized high shear contours near the edges of the larger stent struts, while the high shear regions were less distinct for the smaller strut size. Quadrupling the cross sectional area of a strut increases the initial maximum shear rate along the strut by 50%, in addition to doubling the available surface area for platelet deposition. Therefore, increasing strut size has a threefold effect on platelet deposition rate, leading to faster vessel occlusion. This computational technique may be extended to approximate where thrombus may grow to completely occlude a blood vessel and the length of time occlusion would take. The CFD modeling technique may also be used to evaluate thrombus deposition on medical devices such as heart valves and ventricular assist devices.
Wireless Vibrotactile Trainer for Balance Rehabilitation
Authors: Lee B. C. , Sienko K. H.
Published: July 2009

During balance rehabilitation, physical therapists typically provide verbal instruction and/or physically reposition a patient to demonstrate proper postural position and movements. We have developed a wireless device that enables an expert (such as a physical therapist) to map his/her movements to a trainee in a hands-free fashion. The trainee is subsequently able to mimic the motion of the expert by interpreting positional cues presented via vibrotactile feedback to the relevant body segments. This device will potentially enable a therapist to aid multiple patients simultaneously and/or remotely, or enable a trainee (such as an athlete or student) to replicate expert movements. The device comprises an Expert Module (EM) and Trainee Module (TM). Both the EM and TM are composed of six degree-of-freedom inertial measurement units, microcontrollers, and batteries. The TM also has an array of vibrating actuators that provides the user with vibrotactile biofeedback. The expert dons the EM, and his/her relevant body position is computed by an algorithm based on an extended Kalman filter that provides asymptotic state estimation. The captured body position information is transmitted wirelessly to the trainee, and directional instructions regarding the desired motion/position are displayed via vibrotactile feedback. The trainee is instructed to move in the direction of the vibration sensation until the vibration is eliminated. While prior work has demonstrated the use of vibrotactile stimulation for improved motor learning, this portable and wireless device is suitable for use outside of a laboratory environment. Five healthy young blindfolded subjects were instructed to mimic recorded expert anterior-posterior trunk tilt motion using the aforementioned device in a series of proof-of-concept studies designed to investigate the effects of changing the feedback activation threshold and varying the nature of the feedback. To characterize the efficacy of the system, we performed a cross correlation of expert and trainee trunk tilt angle while varying the threshold angle difference at which vibrotactile feedback was applied. Preliminary results showed that subjects performed best at 0.5 and 0.75 degree thresholds among those tested (0.5, 0.75, 1.0, 1.25, 1.5). The normalized mean cross correlations for the 0.5 and 0.75 threshold conditions were 0.96 and 0.97 respectively, while the mean differences between expert and trainee trunk tilt angles were 1.1 and 1.2 degrees respectively. Further studies at 0.5 and 0.75 threshold conditions confirmed that proportional plus derivative feedback of the angle difference resulted in superior performance compared to proportional or derivative feedback alone. Repetition of the task was not significant suggesting that trainees could immediately use the device to accurately replicate expert anterior-posterior trunk tilt movements.
Thermochemical Ablation: A Novel Technique for Solid Tumor Therapy
Authors: Shenoi M. , Cressman E.
Published: July 2009

To overcome the limitations of existing ablation techniques, we propose a novel combinatorial approach that would utilize the thermal and chemical destructive effects of exothermic chemical reactions, such as an acid/base neutralization reaction, to treat solid tumors. Thermochemical ablation is a potential technique for percutaneous probe-based tumor therapy. It involves simultaneous intratumoral delivery of multiple reagents resulting in thermal energy released by an exothermic reaction to ablate tumor tissue with concurrent generation of a hyperosmolar byproduct that could accentuate tumor destruction. Besides the benefit of synergistic thermal and chemical effects for tumor tissue destruction, this technique is potentially highly cost-effective, easy to implement, and able to treat larger sized tumors. Our hypothesis is that thermochemical ablation can create an evenly distributed zone of coagulation in tumor tissue without systemic toxicity. A prototype device assembled using off-the-shelf components is being investigated in our lab for concurrent intraparenchymal delivery of an acid and a base. The distal portion of the multi-lumen device allows for passive mixing of the reagents before entering the tissue. The prototype device also satisfies other desirable design criteria such as rigidity to penetrate body tissue, reduced diameter, chemical stability to reagents, etc. However, the device can be improved upon by incorporating additional characteristics such as optimized imaging characteristic for real-time visualization and localization within tumor tissue, MRI compatibility, thermal insulation, improved mixing at the tip, etc. Our lab is currently working on improving the design of the infusion device as well as assessing the feasibility of the thermochemical ablation technique in vitro and in vivo. While currently being targeted conservatively for palliative therapy of unresectable or late-stage aggressive malignancies such as hepatocellular carcinoma, thermochemical ablation has potential use in the therapy of a majority of solid tumors such as breast cancer, lung cancer, prostate cancer, renal cancer, sarcomas, etc.
Novel Transaortic Double Barrel Ventricular Cannula
Authors: Cezo J. D. , Day S W.
Published: July 2009

A novel transaortic ventricular cannula, known as the ‘double barrel’ cannula (DBC), is designed to minimize the invasiveness of Ventricular Assist Device (VAD) implantation by combining the inlet and outlet cannulae into a single dual lumen cannula. Both flows will pass through a single opening in the apex of the Left Ventricle with the outflow then continuing past the aortic valve, into the aortic arch. This design offers several potential advantages over the current state-of-the-art. These include less invasive surgery and providing mechanical support to the septum. By routing the outflow through the aortic valve, the need to access the external structure of the ascending aorta is eliminated thereby eliminating the need for open heart surgery. In determining the DBC's design, close attention has been paid to the outflow portion of the cannula, which passes through the aortic valve. It was anticipated that this portion of the DBC could have the largest impact on the device's usability in practice. The object of this study was to test the performance of the valve with the cannula passing through it. Three different geometries are circular, equilateral triangular, and one-third semicircular. Experiments measuring aortic insufficiency during the diastolic phase were conducted. The experiment was designed to analyze several geometries passing through an aortic valve under diastolic flow conditions. All experiments used a simple flow loop which allows a natural porcine aortic valve to be viewed from downstream. The loop was driven with a pneumatic ventricular simulator in order to produce a cyclic flow. Three cannulae cross-sections were molded from RTV11 Silicone. During this test, High Speed Cinematography and flow rate measurement were used to quantify valve sealing and leakage. All data was collected and analyzed for the three cross-sectional geometries during diastole. The performances of the three geometries were compared using American Heart Association guidelines of aortic insufficiency (Al) diagnosis. The flow rate data was integrated in order to determine the volume of ventricle ejection and valve regurgitation. All three geometries exhibit low and acceptable levels of Al (⩽15%Al), with the circular geometry causing the least amount of Al at 7.1%. The experimental control (Porcine aortic valve with no cannulae) exhibited an Al or 2.4%, validating both the harvested aortic valve and experimental flow loop for further testing. Using the high speed cinematography, several phenomena were observed during the sealing of the porcine valve; including leaflet folding leaflet bunching, and cannula displacement due to valve closure.
Transcatheter Aortic Valve Deployment: Interactions Between Native Leaflets and Coronary Ostia
Authors: Quill J. L. , Geeslin A. G. , Iaizzo P. A.
Published: July 2009

During the delivery of a transcatheter aortic valve, the native leaflets are pressed toward the vessel wall when the stented valve is deployed, but the proximity of the native leaflets to the coronary ostia following deployment is not fully understood. Fluoroscopic (F) and endoscopic (E) video footage was gathered from isolated human hearts (n=3). Balloon valvuloplasty (BAV) was performed with a non-compliant balloon, followed by contrast injection into the coronary ostia. Images (F) captured the perpendicular distance from the balloon to the ostia (ostium depth). A nitinol stent was delivered to the aortic position trans-apically. Images (E) measured the distance between the native aortic leaflet and the lowest point of the coronary ostium (ostium height). Additionally, cadaveric hearts (n=23) underwent extensive anatomical analyses using a 3D digitizing arm in addition to the described procedures. BAV in perfusion fixed hearts gave left and right ostium depths of 5.28±1.49 and 5.34±1.85. Images (E) from the perfusion fixed human hearts showed left and right ostium heights of 3.2±2.9 mm and 4.3±2.4, respectively. 2 of the 23 perfusion fixed human hearts studied had negative ostia heights, but the effect on coronary flow is not known.
High-Density Transcranial Direct Current Stimulation (HD-tDCS): Skin Safety and Comfort
Authors: Patel J. , Bansal V. , Minha P. , Ho J. , Datta A. , Bikson M.
Published: July 2009

Transcranial Direct Current Stimulation (tDCS) is a non-invasive procedure where a weak electrical current (260 μA to 2 mA) is applied across the scalp to modulate brain function. tDCS has been applied for therapeutic purposes (e.g., addiction, depression, mood and sleep disorders) as well as cognitive performance enhancement (e.g., memory consolidation, motor learning and language recall). Despite safety and cost advantages, the developments of tDCS therapies have been restricted by spatial targeting concerns using existing two-channel systems. We have developed novel technology for High-Density tDCS (HD-tDCS) that improves spatial focality. Integral to the system are specialized HD-tDCS electrodes (<12 mm diameter) which allow safe and comfortable passage of current across the scalp. Here we evaluate a range of HD-tDCS electrode designs for comfort as well as test electrode over-potential, pH, and temperature. Passing 2 mA current for 22 minutes, both anodal and cathodal stimulations were evaluated independently. Subjective sensation during forearm stimulation was evaluated in 8 subjects. The benefits of skin electrical or chemical pre-conditioning were tested. Conductive Rubber, Ag, AgCl, pellet electrodes and AgCl ring electrodes were evaluated in combination with salty gels (Signa and CCNY4) and nominally electrolyte free gel (Lectron). The use of AgCl ring electrodes in combination with CCNY4 gel resulted in no significant pH, temperature, or over-potential changes under either polarity stimulation and was well tolerated by subjects. HD-tDCS may thus be applied with 2 mA per electrode for up to 22 minutes without skin irritation. Moreover, skin pre-conditioning can eliminate sensation such that HD-tDCS can be applied in a blinded fashion and under a broad range of therapeutic and performance enhancement applications. Our HD-tDCS system allows non-invasive, safe, and targeted modulation of selected cortical structures for electrotherapies that are individualized as well as optimized for a range of therapeutic applications.
Intra-Operative Pulse Oximetry
Authors: Oliveira L. , Servais E. , Rizk N. , Adusumilli P. , Bikson M.
Published: July 2009

Bowel resection surgery is a commonly performed operation used to treat a variety of gastro-intestinal tract disorders, including cancer. The surgery entails excising the diseased portion of intestine, and then creating a surgical anastomosis, or reattachment of the remaining ends. One of the major complications following bowel resection surgery is breakdown or leakage from the anastomosis, which affects 20% of patients, with an associated 10-15% mortality rate. The surgical creation of anastomosis frequently involves dividing blood vessels and can introduce unrecognized twists and tension on the intestine. As a result, the blood supply to the site of anastomosis is often hampered, limiting the oxygen supply that is essential for adequate anastomotic healing. We are proposing a device that enables surgeons to obtain real-time feedback on local tissue oxygen saturation (SpO2) during operative procedures. Such data will not only help surgeons realize any bowel oxygenation compromising maneuvers, but also help perform an anastomosis at the site of maximal tissue oxygenation, thus minimizing the occurrence of postoperative anastomotic leakage and improve patient outcomes. This report details the specifications, fabrication, operation and performance of a handheld wireless pulse oximeter suitable for the intraoperative measurement of tissue SpO2 during bowel surgery. The device adapts principles and technology developed for non-invasive pulse oximetry, and introduces tissue interface, physician tools, and signal processing algorithms for intra-operative application. The handheld device includes local display of SpO2 level (<1 s refresh) at the contacted tissue, and signals the operator on degraded signal quality/faults. An onboard micro-controller digitizes and processes signals transduced through a controlled LED array. Signal processing and display parameters were optimized for operating room conditions. A disposable functionally-transparent cover provides both device and tissue protection. Through serial or Bluetooth wireless transmission (250 Kbps), SpO2 and pulse signals can be processed on a PC or operating room VI. The incorporation of a pressure sensor to increase accuracy and robustness is explored. The device was validated intra-operatively on rodent and bovine surgical models.
Stimuli-Responsive Triblock Polymers for Multipulse Drug Delivery
Authors: Gaumet M. , Xi J. , Barriet D. , Siegel R. A.
Published: July 2009

Temperature and pH-sensitive ABC triblock polymers were prepared to form hydrogel membranes capable of changing their structure in response to environmental stimuli, allowing drug release, from a micro implantable device, in short and repetitive pulses. We have previously investigated the capacity of hydrogels to sustain open loop oscillatory behavior, with application in rhythmic hormone release. This novel oscillator is mediated by feedback instability between swelling/shrinking of the hydrogel and an enzyme reaction, whose product modifies pH in the hydrogel. The objective of this work was to prepare and characterize triblock polymer-based hydrogels, to overcome limitations of conventional hydrogels. Our strategy involves reversible arrangement of A and C thermosensitive domains within a strong network, whereas B block is also pH-sensitive. The triblock was mainly based on the use of NIPAAm (N, isopropylacrylamide) and AA (acrylic acid) monomers. Polymers were synthesized by reversible addition fragmentation chain transfer (RAFT) polymerization. Polymers molecular weight (Mn) and polydispersity index (PDI) were determined by matrix-assisted laser desorption ionization/mass spectrometry (MALDI). Monomers conversion was assessed by NMR and copolymers composition by NMR and pH-titration. Temperature and pH responsiveness was studied by turbidity and light scattering experiments. ABC triblock presented Mn close to 40,000 Da and was nearly monodisperse (PDI<1.1). The monomers conversion was 92%, 97% and 39% for A, B and C blocks, respectively. The opposing effects of hydrophobicity and ionization on the aggregation behavior of the diblock have been highlighted through the turbidity and light scattering data. AB diblock cloud points were 32, 34, 35.5 and 37.5°C for 3, 5, 10 and 20% of AA, respectively. Micelles or aggegrates were observed depending on pH and temperature. ABC triblock polymers with controlled architecture and Mn distribution were synthesized and fully characterized. The results suggest that these block polymers are promising materials for stimuli-responsive hydrogel membranes applied to medical devices. Work supported by the Swiss National Fund for Scientific Research and an NSF-funded MRSEC (DMR#0819885) at the University of Minnesota.
A Lattice Boltzmann Method Based Numerical Scheme for Microchannel Flows
Authors: Fu S. C. , Leung W. W. F. , So R. M. C.
Published: July 2009

Conventional lattice Boltzmann method (LBM) is hyperbolic and can be solved locally, explicitly, and efficiently on parallel computers. The LBM has been applied to different types of complex flows with varying degrees of success, and with increased attention focusing on microscale flows now. Due to its small scale, microchannel flows exhibit many interesting phenomena that are not observed in their macroscale counterpart. It is known that the Navier–Stokes equations can still be used to treat microchannel flows if a slip-wall boundary condition is assumed. The setting of boundary conditions in the conventional LBM has been a difficult task, and reliable boundary setting methods are limited. This paper reports on the development of a finite difference LBM (FDLBM) based numerical scheme suitable for microchannel flows to solve the modeled Boltzmann equation using a splitting technique that allows convenient application of a slip-wall boundary condition. Moreover, the fluid viscosity is accounted for as an additional term in the equilibrium particle distribution function, which offers the ability to simulate both Newtonian and non-Newtonian fluids. A two-dimensional nine-velocity lattice model is developed for the numerical simulation. Validation of the FDLBM is carried out against microchannel and microtube flows, a driven cavity flow, and a two-dimensional sudden expansion flow. Excellent agreement is obtained between numerical calculations and analytical solutions of these flows.
Effect of Liquid Transparency on Laser-Induced Motion of Drops
Authors: Shukla R. , Sallam K. A.
Published: July 2009

An experimental investigation of the role of liquid transparency in controlling laser-induced motion of liquid drops is carried out. The study was motivated by application to manipulation of liquid drops over a solid substrate. Droplets with diameters of 1–4 mm were propelled on a hydrophobic substrate using a pulsed-laser beam (532 nm, 10 Hz, 3–12 mJ/pulse) with a 0.9 mm diameter fired parallel to the substrate. The test liquid was distilled water whose transparency was varied by adding different concentrations of Rhodamine 6G dye. Motion of the drops was observed using a video camera. Measurements include direction of motion and the distance traveled before the drops come to rest. The present results show that the direction of the motion depends on the drop transparency; opaque drops moved away from the laser beam, whereas transparent drops moved at small angles toward the laser beam. The motion of both transparent and opaque drops was dominated by thermal Marangoni effect; the motion of opaque drops was due to direct heating by the laser beam, whereas in the case of transparent drops, the laser beam was focused near the rear face of the transparent drops to form a spark that pushed the drops in the opposite direction. Energies lower than 3 mJ were incapable of moving the drops, and energies higher than 12 mJ shattered the drops instead of moving them. A phenomenological model was developed for the drop motion to explain the physics behind the phenomenon.
An Experimental Investigation of the Flowfield and Dust Resuspension Due to Idealized Human Walking
Authors: Kubota Yoshihiro , Hall Joseph W. , Higuchi Hiroshi
Published: July 2009

In order to address how human foot movement causes particles to be resuspended from the floor, particle flow visualization and particle image velocimetry (PIV) measurements were performed on a simplified model of the human walking motion; a disk moving normal to the floor. Flow visualization of particles, seeded initially on the ground, indicates that particles are resuspended by both the downward and upward motions of the walking process. On both the upstep and the downstep, particle resuspension occurs due to a high velocity wall jet, forming between the wall and the disk in general accord with the mechanism for particle resuspension put forth by Khalifa and Elhadidi (2007, “Particle Levitation Due to a Uniformly Descending Flat Object,” Aerosol Sci. Technol., 41, pp. 33–42). Large-scale ring vortex structures were formed on both the downstep and the upstep, and did not cause particle resuspension, but were extremely effective at quickly moving the already resuspended particles away from the wall. By varying the seeding of the particles, it was determined that only particles underneath and toward the outer edge of the disk are resuspended.
Development and Design of a Cost-Efficient Tire Mechanics Testing Apparatus
Authors: Chan Brendan J. , Sandu Corina , Hissong Erin , Southward Steve
Published: July 2009

Most tire models need experimentally obtained data as input for simulation purposes. The study of tire mechanics requires the accuracy and repeatability of a controlled environment. However, the accessibility and cost of tire testing machines make it prohibitive for exploring tire mechanical properties for academic studies. Moreover, most industrial tire testing machines are designed for general tire testing, and would require an extensive amount of time and resources to adapt for academic research. To study tire mechanical behavior for modeling purposes, a tire mechanics test apparatus has been developed at the Center for Vehicle Systems and Safety (CVeSS), Virginia Tech. The tire mechanics test apparatus has been designed as an interchangeable attachment to an existing modular quarter car test rig developed at the Institute for Advanced Learning and Research (IALR) in Danville, Virginia, to save on cost, as well as to maintain repeatability of testing. The physical limitations of maximum tire vertical load for various tire testing machines are also among the main motivations for developing the tire mechanics test apparatus. The current configuration of the tire mechanics test apparatus provides the capability to study the vertical load - deflection characteristics of the tire, as well as the static footprint of the tire under various vertical loads. Future planned enhancements to the setup include the addition of a soil bin and an instrumented rolling drum for tire shear force studies.
Mechanism Analysis Using Implicit Constraints
Authors: Sutherland George H.
Published: July 2009

This paper introduces an approach to kinematic and dynamic mechanisms analysis where one or more joints are modeled using joint component relative displacements that approximate real joint behavior. This approach allows for the simultaneous nonrecursive solution for both mechanism kinematic parameters and selected dynamic joint reaction forces. Also, for closed loop mechanisms, the approach eliminates the need for forming explicit loop closure constraint equations, so that the dynamic equations of motion, derived using either the Newtonian or Lagrangian method, have a simplified unconstrained form. The key element underlying the approach is the formation of axioms for the standard mechanism joint types that describe the form of the joint reaction force and/or moment in terms of a virtual (or real) displacement between the joint components.
Dynamic Observer Method Based on Modified Green’s Functions for Robust and More Stable Inverse Algorithms
Authors: Sousa Priscila F. B. , Fernandes Ana P. , Borges Vale´rio Luiz , Dulikravich George S. , Guimara˜es Gilmar
Published: July 2009

This work presents a modified procedure to use the concept of dynamic observers based on Green’s functions to solve inverse problems. The original method can be divided in two distinct steps: i) obtaining a transfer function model GH and; ii) obtaining heat transfer functions GQ and GN and building an identification algorithm. The transfer function model, GH, is obtained from the equivalent dynamic systems theory using Green’s functions. The modification presented here proposes two different improvements in the original technique: i) A different method of obtaining the transfer function model, GH, using analytical functions instead of numerical procedures, and ii) Definition of a new concept of GH to allow the use of more than one response temperature. Obtaining the heat transfer functions represents an important role in the observer method and is crucial to allow the technique to be directly applied to two or three-dimensional heat conduction problems. The idea of defining the new GH function is to improve the robustness and stability of the algorithm. A new dynamic equivalent system for the thermal model is then defined in order to allow the use of two or more temperature measurements. Heat transfer function, GH can be obtained numerically or analytically using Green’s function method. The great advantage of deriving GH analytically is to simplify the procedure and minimize the estimative errors.
Monte Carlo Optimization of Two-Stage Cascade R134A Refrigeration System With Flash Chamber
Authors: Abdel-Rahim Yousef M.
Published: July 2009

Present paper studies the optimal characteristics of the two-stage cascade R134A refrigeration system with flash and mixing chambers over its operating ranges of all cycle controlling parameters. The COP, total heat rate in Qin, total work rate in Win and second law efficiency ηII are used as cycle performance parameters. Compared to the practically-limited other rate-based optimization methods and to other experimentally-optimized specific cases of cycle parameters, the application of Monte Carlo method has proved to be very effective for optimizing the cycle performance in its global sense over all cycle controlling parameters. Correlations relating performance and cycle controlling parameters are presented and discussed. Study shows that COP of the cycle can reach a value of 8 at intermediate pressure P2 of about 200 kPa, and a maximum value of 9.92 at about 370 kPa and 720 kPa, beyond which COP goes as low as 4.2. P2 alone has no significant effect on Qin, Win and ηII unless values of other controlling parameters are specified. Values of Qin, Win and ηII can reach as high as 94 kW, 23 kW and 0.85 and as low as 6.8 kW, 1.1 kW and 0.57 respectively depending on other cycle parameters. Neither pressure ratio nor volume ratio of the HP compressor has any effect on Qin, Win or ηII. However, the ratio of inlet to exit temperatures of the condenser has the greatest effect on both ηII and the volumetric specific work of the HP compressor, which is about double the value of the volumetric specific work of the LP compressor. Study shows an almost linear relationship between the two mass flow rates in the upper and lower loops of the cycle, where its value in the lower LP loop is about 75% that in the upper HP loop. Findings of the present work as well as the elaborate application of Monte Carlo method to real cycles can greatly open the way for reducing the trade-off design methods currently used in developing such systems as well as direct the useful experimentations and assessment of such designed systems.