Bioengineering Seminar Schedule
Spring 2007
Friday, January 19, 12:00 - 1:00 p.m., Room 210 Hallowell, CG624E Hershey
Andrew Webb
"Welcome"
Peter Butler
"Professional Development Opportunities for BIOE Graduate Students"
Abstract
In order to enhance graduate student training, I will be presenting opportunities for professional development that are available around campus. These include, workshops for public speaking, presentations, and writing, as well as internship opportunities and mechanisms for job searches. I welcome student input on which workshops and internships they have participated in and what their impressions are.
Friday, January 26, 12:00 - 1:00 p.m., Room 210 Hallowell, CG624E Hershey
Edward Guo
Columbia University
"Mechanics and Mechanobiology of Bone"
Abstract
Bone is one of the most clinically important components in human skeleton, which is affected by many metabolic diseases such as osteoporosis or bone loss in space. In addition, bone adapts in response to its mechanical environment. A quantitative characterization of the relationship between bone adaptation and mechanical loading and establishment of underlying cellular and molecular mechanism of bone adaptation are important in the understanding of the etiology of age-related bone fractures, optimal design of total joint replacements, and prevention of bone loss due to microgravity. In this presentation, mechanics of bone will be emphasized from both modeling and biological perspectives. Mechanical properties of trabecular bone will be examined from continuum to microstructural level. Both idealized and micro computed tomography (µCT) based models of trabecular bone will be discussed in understanding mechanical properties of trabecular bone and their clinical and biological application. Three model systems for the study of mechanobiology of bone will be reviewed: an in vivo rat tail vertebrae model, an in vitro trabecular bone explant model, and an in vitro micropatterned osteocytic network model. In the first model system, an intact vertebral bone is subjected to controlled mechanical loading while in the in vitro trabecular bone explant model, osteocytes in their native trabecular bone matrix are maintained alive in vitro and allowed for controlled seeding of osteoblasts and/or osteoclasts. Combining with high-resolution micro image based finite element modeling techniques, a quantitative assessment of mechanotransduction mechanisms involving all three types of bone cells can be examined. In the second in vitro system, 2D and 3D osteocytes networks have been developed using modern microfabrication techniques while allowing controlled interactions with osteoblasts and/or osteoclasts. New experimental findings from these new in vivo and in vitro models regarding a century old hypothesis of trabecular bone adaptation: Wolff's Law, will be presented.
Friday, February 2, 12:00 - 1:00 p.m., Room 210 Hallowell, CG624E Hershey
Student Presentations
Shankar Shastry
"Site Specific Kinesin Labeling to Study FRET Between Motor and Microtubules"
Abstract
Kinesins are a class of molecular motors that are essential for intracellular transport and they also play a
major role in cell division. These motors utilize the energy released by the hydrolysis of ATP to translocate along
microtubules. Understanding how they function and mapping out the individual steps in the biochemical cycle is
a fundamental goal of cell biology. With the current data available it is known that ATP is hydrolyzed, phosphate
is released and the motor steps 8nm in the ‘+’ direction. ATP binding changes motor affinity for microtubule and
induces the trailing head to release and move forward. During the cycle, how long is the kinesin bound to the microtubules
with both heads and how fast does the rear head dissociate from the microtubule is not determined. To study this
we have made kinesin constructs with mutations such that a fluorescent label can bind specifically to the inserted
amino acid sequence. FlAsH is a fluorescein derivative which flroresces only when it binds to a tetra-cysteine
motif. We have introduced an amino acid sequence CCPGCC in the kinesin head at different locations and expressed
the proteins and labeled with FlAsH reagent. FRET experiments between motors and rhodamine labeled microtubules
enable us to study the motor biochemistry.
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Pranav Soman
"Molecular Detection of Fibrinogen on Poly (dimethyl siloxane) by Atomic Force Microscopy"
Abstract
The success of long-term blood-contacting devices is largely dependent upon the interaction of the blood components
with the device biomaterial surface. The ability to study these interactions has been hindered by a lack of methods
to measure single-molecule interactions in complex multi-protein environments similar to those found in-vivo. Atomic
force microscopy (AFM) methods typically utilize sub-monolayer distributions of a single protein type from dilute
solutions onto model material surfaces. In vivo however, multiple proteins can adsorb onto rough polymeric biomaterial
surfaces thereby making AFM identification of specific proteins at the molecular level a difficult task.
Gold nano-labels were conjugated to an anti-fibrinogen polycolonal antibody to produce a unique identifier tag
to detect fibrinogen from a dual protein layer on model ultrasmooth mica surface and model polymer, poly (dimethy
siloxane) PDMS. Bovine serum albumin (BSA) was patterned on these substrates and subsequently backfilled with fibrinogen
to get a smooth protein layer. Following infusion of anti-fibrinogen conjugated nanogold, proteins were easily
detected by AFM mechanical property imaging with little nonspecific binding.
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Yanghui Xing
"Different Responses of Non-Differentiated and Differentiated ATDC5 Cells to Fluid Flow"
Abstract
TDC5 is a cell line derived from mouse embryonal carcinoma cells. It expresses a fibroblast phenotype in normal condition and its chondrogenic differentiation can be induced by culturing in the presence of insulin. In our current research, we are trying to use this cell line to investigate the influence of fluid flow on chondrocyte differentiation and end plate cartilage growth. During the study, we found that differentiated ATDC5 cells have a much stronger response to fluid flow than non-differentiated ATDC5 cells in terms of Phos-ERK and calcium release. We also found that differentiated ATDC5 cells expressed more G-protein coupled P2Y2 receptor mRNA and less GRK 2/3 proteins (G-protein coupled receptor kinase) than those of non-differentiated ATDC5 cells. In order to study the role of P2Y2 and GRK 2 in the mechanotransduction process, we tried to overexpress them in ATDC5 cells and the results in terms of Phos-ERK were evaluated.
Friday, February 9, 12:00 - 1:00 p.m., Room 210 Hallowell, CG624E Hershey
Alan Hunt
University of Michigan
"Breaking the Diffraction Limit: Committing an Optical Misdemeanor for Microfluidics and Cell Biology"
Abstract
Damage produced by lasers through optical breakdown becomes very precise for pulse durations less than a picosecond, a property which allows damage to be limited to regions below the diffraction limit. Taking advantage of this property near the critical breakdown intensity (Optics at Critical Intensity, or OCI), enables machining and ablation even at the nanoscale, producing surface features on the order of 10 nm on a wide variety of materials. This competes with the resolution of e-beam or ion-beam lithography, but is more straightforward and less material-specific, and is not limited to the surface if transparent substrates are used. These makes OCI nanomachining ideal for creating submicron features on or within a substrate, such as channels in arbitrary 3D patterns in transparent dielectric materials. We have also used this method to machine solid 3D objects such as cones, spheres, and cantilevers. OCI nanomachining of analytical devices in hard materials enables rapid "art to part" construction of micro and nanofluidic devices, with potential to dramatically accelerate development of micro-total analysis (µTAS) applications such as integrated HPLC devices, micro scale sensors, and integrated nanopores for patch-clamp studies of cells. Likewise, the ability to selectively ablate nanoscale structures within a material enables "structural knockouts" a powerful tool for basic cell biology.
Friday, February 16, 12:00 - 1:00 p.m., Room 210 Hallowell, CG624E Hershey
Student Presentations
Amit Ailiani
"Analysis of Segmental Gastrointestinal Motion in an Animal Model Using Dynamic MRI"
Abstract
The gastrointestinal (GI) tract functions via deformations of the lumen resulting from neurophysiologically
induced changes in muscle fiber tone. Peristaltic contractions underlie transport, while segmental contractions
facilitate macro mixing in bulk flow. These processes are affected significantly by pathologies of the intestinal
tract such as irritable bowel syndrome. The aim of this work is to quantify GI motility in a rat model using dynamic
MRI. Although it is known that peristalsis is reduced during anesthesia, segmental contractions still occur. Segmental
motions of the rat gut were quantified from dynamically acquired MR images, image segmentation using live-wire
and gradient vector flow (GVF) methods and image characterization using active shape models (ASM). Future work
will concentrate on analyses of the effects of different types of anesthesia on gut motility, the incorporation
of more sophisticated data analysis techniques such as space-time proper orthogonal decomposition, and potential
application to different disease models.
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Joy Matsui
"Characterizing the Interface Between Functioning Implantable Neural Probes and Their
Surrounding Cortical Tissue"
Abstract
When neural probes are chronically implanted into a brain, there is always a concern for how the immune response of brain tissue will affect probe recording quality. Many groups have done histological studies on the tissue surrounding implanted probes to detect the immune response. Signs of an active immune response consist of the presence of activated microglia, astrocytes, and other phagocytic cells that encapsulate probes and inhibit the ability to record neural activity. However, the probes used in previous studies were not capable of recording neural activity and thus did not produce neural recordings that could be compared to the histology results. The purpose of this work is to uncover any correlations between histology results, impedance measurements, and recording capabilities of functioning neural probes chronically implanted into the cortical brain tissue of rat models. This will be executed by chronically implanting probes into cortical tissue of rat models, collecting impedance and electrical neural activity for six weeks, and then detecting the aforementioned cells associated with the immune response. The results of this study will help in devising techniques that inhibit the immune response and lengthen the time chronically implanted probes remain active.
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Gayatri Muthukrishnan
"Uncovering Differences in the Processivity and Dissociation Constants of Kinesin-2
and Kinesin-1 Motors"
Abstract
Kinesins are motor proteins that 'walk' on microtubule tracks using energy derived from ATP hydrolysis. Of the
14 kinesin families, Kinesin-2 motors are unique for having two different motor domains. These motors are involved
in intraflagellar transport as well as cytoplasmic transport of melanosomes. The difference in the motor domains
make Kinesin-2 a natural candidate to understand coordination between the two heads of kinesins in general. We
use optical tweezers to manipulate and observe single motor interactions with the microtubule. By adsorbing motors
to beads and using low optical trap forces, we measured run lengths and velocities of single KIF3A/B (mouse ortholog
of Kinesin-2) motors and conventional Kinesin-1 motors. The velocity of KIF3A/B (0.37 ± 0.22 µm/s)
is slightly less than conventional kinesin (0.56 ± 0.21 µm/s), while the run lengths of KIF3A/B (0.63
± 0.05 µm) motors are less than a third that of Kinesin-1 (1.9 ± 0.08 µm). The difference
in run lengths indicate a higher off-rate for Kinesin-2 motors compared to Kinesin-1. These data are consistent
with results from single-molecule fluorescence assays. The next steps will be to determine step-sizes, stall forces
and force-velocity relationships for these motors.
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Ning Yang
"Turbulence Modeling of Blood Flow at the End-to-Side Anastomosis of a Left Ventricular
Assist Device"
Abstract
The end-to-side anastamosis of a left ventricular assist device (LVAD) strongly complicates the blood flow in the aorta. Often, transitional and turbulent flow are observed, so that laminar flow modeling is inappropriate. To study the effect of the configuration of the LVAD end-to-side anastomosis on the flow patterns in the aorta, several different turbulence models including a k-e model, a k-w model and Reynolds stress models (RSM) are used. Neither the aortic sinus nor the secondary vessels are included in our initial, simplified aortic model. LVAD outflow conduit angles of 15o, 30o, 45o, 60o, and 75o referenced to the aorta mid-line, are investigated for connections both proximal and distal of the aortic arch. The effect of the phase difference between the aortic flow and LVAD outflow are also considered. The numerical results obtained from each of the turbulence models were compared in terms of overall flow, Reynolds stresses, wall shear stress, turbulence intensity and vorticity. Preliminary results suggest that the Reynolds stress models gives the best predictions for major turbulent features of this highly curved three-dimensional aortic flow, including damping of turbulence near the convex wall, enhancement of turbulent near the concave wall, and the subsequent separation downstream of the aortic arch. Experimental measurements were performed with laser Doppler velocimetry, using an acrylic model, to test the computations. This work will help to better understand the causes of LVAD-induced thrombosis and thromboembolism.
Friday, February 23, 12:00 - 1:00 p.m., Room 210 Hallowell, CG624E Hershey
BIOENGINEERING Research Day in HUB
Friday, March 2, 12:00 - 1:00 p.m., Room 210 Hallowell, CG624E Hershey
Nathan McDannold
Harvard Medical School
"Noninvasive Therapies Using Focused Ultrasound Under MRI Guidance"
Abstract
Focused ultrasound (FUS) exposures produced by an externally located transducer can be used to locally heat deep-seated tissue and noninvasively create discrete lesions. This technology is currently being used in several ongoing clinical studies for tumor treatment in sites around the world, and it appears to be poised to enter widespread use. Magnetic Resonance Imaging (MRI) based monitoring has been shown in recent years to effectively guide thermal ablation techniques. MRI's soft tissue contrast and ability to image in any orientation make it extremely useful for treatment planning and for imaging the tissue response to the therapy. The temperature sensitivity of several intrinsic parameters enables MRI to visualize and quantify the progress an ongoing thermal treatment. The most useful temperature-sensitive parameter appears to be the water proton resonant frequency, which allows for precise and accurate temperature measurements. Our experience with these techniques, both in experimental studies and in our ongoing treatments of uterine and breast tumors will be reviewed. The experimental studies have shown the usefulness of thermal imaging for targeting the ultrasound beam, monitoring the temperature rise, and predicting the threshold and extent of the thermal damage. The promise of the method appears to be largely realized in the clinical studies in uterine fibroids. The monitoring is more limited in the breast, due to the presence of fatty tissue, but it still allows for localization of the ultrasound beam and temperature measurements within the tumor. The brain offers several future applications for FUS, both in our ability to noninvasively create discrete lesions and in ultrasound's ability to act on tissue in other ways. A system for noninvasive, trans-cranial FUS thermal ablation in the brain will be reviewed as well as our ongoing research on using FUS for other applications in the CNS, such as targeted drug delivery.
Friday, March 9, 12:00 - 1:00 p.m., Room 210 Hallowell, CG624E Hershey
C. Forbes Dewey, Jr.
MIT
"Awash in a Sea of Data: The Paddle is Ontologies"
Abstract
For a number of years, we have struggled with sharing data between databases and have used several solutions
to overcome the inability of separate databases to interoperate. One method is warehousing, where all the data
are written to a single database which is a monolithic system of poor performance and problematic maintenance.
Another solution is database federation, wherein queries are sent to the individual databases using unique "stovepipes"
between each database and the query engine. These approaches fail because they are difficult to implement on the
one hand, and cannot support changes on the other. Real databases morph over time.
We propose a different solution: Interpolation between different data repositories should be conducted at the level
of descriptions of the schema rather than at the level of schema implementation. We will demonstrate that the schema
and the interconnections between different elements of the database can be captured in ontologies, and that the
ontologies can be compared, edited and normalized with relative efficiency. From that level, the connections between
databases becomes clear and software can be written to maintain and connect them.
Friday, March 16, 12:00 - 1:00 p.m., Room 210 Hallowell, CG624E Hershey
SPRING BREAK
Friday, March 23, 12:00 - 1:00 p.m., Room 210 Hallowell, CG624E Hershey
Qiuhong He
University of Pittsburgh
"Magnetic Resonance Spectroscopy and Imaging in Cancer Diagnosis and Therapy"
Abstract
Cancer cells display heterogeneous genetic characteristics, depending on the tumor dynamic microenvironment. Abnormal tumor vasculature and poor tissue oxygenation generate a fraction of hypoxic tumor cells that have selective advantages in metastasis and invasion, and often resist chemo- and radiation therapies. The genetic alterations acquired by tumors modify their biochemical pathways, which results in abnormal tumor metabolism. Magnetic resonance spectroscopy (MRS) has been used to study tumor metabolism in preclinical animal models and in clinical research on human cancers. This technique can identify specific genetic and metabolic changes that occur in malignant tumors. When combined with the contrast-enhanced Magnetic Resonance Imaging (MRI), in vivo magnetic resonance spectroscopic imaging (MRSI) improves the diagnostic specificity of malignant human cancers and is becoming an important clinical tool for cancer management and care. We have developed the MR techniques to detect and quantify metabolic changes in breast cancer, or any extracranial tumor tissues that contain high concentrations of fat. MRI/MRSI methods have been used to characterize tumor physiology and microenvironment using animal tumor models. A novel bacterial-based cancer therapy studied in our laboratory using diffusion-weighted MRI techniques will be presented as an example. The capability of the MR technology in probing molecular information non-invasively in tumor tissues illustrates a great potential for studying molecular mechanisms of human cancer in physiological conditions.
Friday, March 30, 12:00 - 1:00 p.m., Room 210 Hallowell, CG624E Hershey
Ajit Yoganathan
Georgia Tech
"Surgical Planning of the Total Cavopulmonary Connection Using MRI, Experimental and Computational
Fluid Mechanics"
Abstract
The total cavopulmonary connection (TCPC) is the current procedure of choice for palliative surgical repairs of single ventricle congenital heart diseases. Despite major improvements in patient outcome over the past three decades, single ventricle patients are still subjected to numerous long-term complications. One parameter over which there may be some kind of control is the surgically created TCPC geometry. The superior (SVC) and inferior (IVC) venae cavae are anastamosed in stages onto the right (RPA) and left (LPA) pulmonary arteries, thus bypassing the right side of the heart and separating the pulmonary and systemic circuits. In order to achieve configurations that result in optimal surgical outcome, the determining fluid dynamics must be understood and controlled.
A database of MRI/PCMRI data of over 200 patients aged 2-25 who have undergone the TCPC procedure has been developed. The stacks of axial patient MRI images are used to reconstruct accurate TCPC geometries. The images are interpolated in the out-of-plane direction using an adaptive control grid interpolation technique to achieve isotropic voxel size. The TCPC blood volume is segmented out and reconstructed into a smooth 3D geometry (Figure 1a). Using rapid prototyping with the recently available transprent resins, anatomically accurate experimental models of selected TCPC anatomies are manufactured (Figure 1b), ensuring that the numerical and experimental simulations are run on the same geometries. Qualitative flow visualization and quantitative flow assessment (power loss calculation, particle image velocimetry, PIV, and phase contrast magnetic resonance, PCMRI) are performed experimentally and used to validate the results obtained from computational fluid dynamics (CFD) .
Friday, April 6, 12:00 - 1:00 p.m., Room 210 Hallowell, CG623 Hershey
Yingxiao (Peter) Wang
UIUC
"Live-Cell Visualization of Molecular Signaling in MechanoBiology"
Abstract
Tyrosine kinases have been shown to play critical roles in a variety of cellular processes, including cell motility/migration, mechanotranduction, and cancer development. Based on fluorescent resonance energy transfer (FRET), we have developed and characterized a genetically encoded single-molecule Src reporter, which enables the imaging and quantification of tempo-spatial activation of Src in live cells. We introduced a local mechanical stimulation by applying laser-tweezer-traction on fibronectin-coated beads adhered to the cells. Using the Src reporter, we observed a rapid Src activation and a slower directional wave propagation of Src activation along the plasma membrane. This Src reporter was also applied to visualize the dynamic Src activation at subcellular levels in a variety of cellular processes and functions, including the interplay between cell-cell and cell-ECM adhesions, the epherin-induced growth cone collapse of hippocampal neuronal cells, and the cancer development. With a similar strategy, we have developed a new reporter for focal adhesion kinase (FAK). Pilot studies revealed that there is a hot zone with high FAK activities at the base of lamellipodium in spreading cells, suggesting an important role of focal adhesion turnover in cell motility. In summary, our novel reporters have made it possible to monitor key signaling transduction cascades in live cells with tempo-spatial characterization in Mechanobiology.
Monday, April 9, 10:00 - 11:00 a.m., Room 210 Hallowell CG Hershey
Ketul Popat
"Micro/Nano-Engineering of Material Surfaces for Applications in Biology and Medicine"
Abstract
Surfaces that contain micro- and nanoscale features in a well-controlled and "engineered" manner have been shown to significantly affect cellular and subcellular function of various biological systems. Our research is focused towards using the tools of micro- and nanotechnology for application in orthopedic biomaterials and drug delivery. The goal of current research is to design implants that induce controlled, guided, and rapid healing. In addition to acceleration of normal wound healing phenomena, these implants should result in the formation of a characteristic interfacial layer with adequate biomechanical properties. To achieve these goals, however, a better understanding of events at the bone-material interface is needed, as well as the development of new materials and approaches that promote osseointegration. Our work proposes the use of well controlled nanostructured interfaces to enhance implant osseointegration. We hypothesize that controlled nanoscale architectures can promote osteoblast differentiation and matrix production, and enhance short-term and long-term osseointegration. Moreover, the ability to create model nano-dimensional constructs that mimics physiological systems can aid in studying complex tissue interactions in terms of cell communication, response to matrix geometry, and effect of external chemical stimuli. By understanding how physical surface parameters influence cellular adhesion and differentiation, we can more effectively design biomaterial interfaces that can be used in a clinical setting. Further these novel nanostructured surfaces can reliably deliver therapeutic substances from the surface of an implanted medical device. Current delivery methods after implantation include release of protein adsorbed directly on implant surface, in collagen sponges, or in porous coatings and controlled release of protein encapsulated in a biodegradable polymer. These conventional technologies for drug-eluting devices have been successful, but limited in the range of control it provides in terms of release and loading. The short biological half-life, the lack of long-term stability and tissue-selectivity, and their potential toxicity demand platforms that can deliver drugs in a localized and controlled manner. The delivery of drugs from the surface of load bearing orthopedic implants such as total joint replacements is ideal. Complications associated with orthopedic implants can be quite severe. The ability to design implant interfaces which simultaneously enhance osseointregration and deliver therapeutics which may enhance bone growth or fight off infection can have large clinical benefit and help reduce the need for costly and traumatic surgery. Thus, in this work we have also explored the possibility of using these nanostructured surfaces as drug eluting coatings.
Friday, April 13, 12:00 - 1:00 p.m., Room 210 Hallowell, CG624E Hershey
Charla Triplett
Biomedical Career Center
"CANCELLED"
Friday, April 20, 12:00 - 1:00 p.m., Room 210 Hallowell, CG624E Hershey
David Vorp
University of Pittsburgh
"Developments in Stem Cell-Based Vascular Tissue Engineering"
Abstract
Lack of functional small-diameter synthetic vascular grafts remains an important clinical barrier. This need can potentially be met via tissue engineering approaches. To be successful, a tissue engineered vascular graft (TEVG) should include adequate cell sourcing, scaffold, seeding, and culture methods. This presentation will describe our approach of developing a TEVG, which includes the bulk-seeding of multipotent stem cells inside a porous, tubular biodegradable scaffold and implanting them in vivo. Also to be presented will be the results of our related investigations into the responsiveness of stem cells to biomechanical forces consistent with the vasculature, and the implications therein vis-à-vis vascular tissue engineering.
Friday, April 27, 12:00 - 1:00 p.m., Room 210 Hallowell, CG624E Hershey
Student Presentations:
Florly Ariola
"Ultrafast Dynamics Imaging of Lipid Analogue Interactions in Engineered Biomembranes"
Abstract
Biomembranes are complex systems that regulate numerous biological processes including cell signaling and permeability.
These membranes consist of lipid phases (i.e. microdomains) that dictate their mechanical properties and transport
characteristics. Here we use a newly developed ultrafast fluorescence dynamics imaging assay to investigate lipid-marker
interactions in giant unilamellar vesicles (GUVs) as a function of lipid composition. The central thesis of this
approach is to use the exquisite sensitivity of excited-state dynamics, to changes in the molecular conformations
and to the surrounding environment, as a contrasting factor for lipid microdomains. Phase-specific lipid analogues,
such as Bodipy-PC and DiI-C12, are used to investigate liquid-disordered and gel phases in GUVs. Two-photon fluorescence
lifetime (2P-FLIM) and polarization anisotropy imaging of these lipid analogues are phase specific and allow for
modeling the lipid-marker interactions in engineered biomembranes. These results on synthetic lipid bilayers will
be compared with in vivo biomembranes. The proposed experimental approach will ultimately help in our understanding
of the structure-function relationship of biomembranes in vivo. ============================================================================================
Byeong-Yeul Lee
"In vivo Measurement of Iron Deficiency in Restless Legs Syndrome (RLS) with Voxel-Based
MRI Relaxometry"
Abstract
Restless legs syndrome (RLS) is a neurodegenerative disorder characterized by involuntary, unbearable urges
to move the legs. R2 maps were used to evaluate the overall brain iron deficiency in RLS. We introduced the voxel-based
relaxometry (VBR) method, which allows for an unbiased statistical analysis of iron concentration. A significant
reduction in R2 was found in the subtantia nigra, putamen, red nucleus, thalamus, and globus pallidus in RLS (n=16).
There was a significant negative correlation between clinical symptomatology and R2 in the substantia nigra and
putamen. These results suggest that the VBR can be a potential biomarker for RLS.
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Varun Reddy
"Fluid Dynamic Studies of a Polymeric Trileaflet Heart Valve"
Abstract
While mechanical heart valves (MHVs) remain the most widely implanted prosthetic valves, polymeric valves have
inherent advantages. These include their unobstructed orifice and lower leaflet closing velocities which minimize
their hemolytic, platelet activating and cavitation potential, relative to MHVs. Currently, most polymeric valves
are used as part of left ventricular assist devices and total artificial hearts. There is interest to implant these
valves clinically, and characterizing the fluid dynamics of polymeric heart valves will help achieve this goal.
An in vitro laser Doppler velocimetry study was conducted on a 25 mm polymeric trileaflet heart valve (Abiomed
Inc), in the aortic position. The valve is housed in an acrylic conduit with aortic sinuses that allows for optical
access upstream and downstream of the valve. A sodium/iodide/glycerin fluid that matches the kinematic viscosity
of blood and the index of refraction of the model was used as a blood analog. Flow was driven using a ventricular
assist device at a heart rate of 90 bpm, a flow rate of 4.5 l/min, and an aortic pressure of 130/90 mmHg.
Mean velocity data was collected in four planes: one diameter upstream, one diameter downstream of the commissural
plane, within the sinuses, and at the tip of the commissures. High velocity jets and high Reynolds stresses were
measured near the orifice at the leaflet tips and between the leaflets. Lastly, recirculation occurs in the aortic
sinuses, reducing the potential for thrombus formation.
Friday, May 4, 12:00 - 1:00 p.m., Room 210 Hallowell, CG624E Hershey
Student Presentations:
Mattahew Raab
"Detachment Kinetics of Single-headed Kinesins"
Abstract
Eukaryotic cells use kinesins to transport intracellular cargo to the periphery of the cell by walking along
protein filaments of tubulin called microtubules. Processivity is the favorable property that allows the kinesin
to move along microtubules significant distances by taking many steps before dissociating off the microtubule.
Kinesins are able to take multiple steps because there are two motor heads, and one remains bound to the microtubule
while the other is in the process of taking a step. A potential explanation for the kinesin's ability to take multiple
steps is that there exists intersubunit strain-dependant coordination between the two motor head domains. Conventional
kinesin is a homodimer which has two identical motor heads. By engineering the kinesin protein so that it has one
head instead of two, we can perform binding experiments which could prove that there is coordination between the
two heads. The one-headed kinesin was attached to 200 nm silica beads and the binding events of the kinesin-bead
were investigated. Preliminary results show that the Koff rate of the single-headed kinesin is significantly slower
than the estimated Koff rate of each head in the homodimer. This evidence suggests that there exists one head of
the kinesin affects the other through internal molecular strain, preventing the kinesin from microtubule dissociation.
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Rachna Sah
"Inhibition of Inflammation Induced Shedding of Glycocalyx using MMP Inhibitors"
Abstract
Endothelial glycocalyx plays an important role in various biological processes such as leukocyte adhesion, mechanotransduction,
micro-vascular permeability and capillary resistance. It serves as a barrier to leukocyte adhesion and its shedding
is an essential part of the inflammatory response. In this study, BS-1 Lectins were covalently linked to fluorescently
labeled microspheres (0.1-µm diameter) and infused systemically into the rat circulation. Adhesion of lectins
specific for galactose residues (chondrotin sulfate) of glycosaminoglycans (GAGs) decreased significantly after
superfusion of the mesentery with the chemoattractant N-formylmethionyl-leucyl-phenylalanine (fMLP, 10 -7M).
These reductions were significantly attenuated by superfusion of the tissue with MMP (Matrix metalloproteinases)
inhibitors like Doxycycline and GM6001. These findings suggest that the integrity of the glycocalyx may be controlled
by the ECs and WBCs through an MMP pathway. From this study, we can conclude that glycocalyx composition changes
dynamically in various physiological and pathophysiological states which could be quantified using microspheres
labeled with lectins. It also suggests that there is a balance between the rate of biosynthesis of GAGs by the
endothelial cell and their shedding to maintain the integrity of the layer.
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Qianru Yu
"Molecular Dynamics Imaging of Autofluorescence in Human Breast Cells at the Single
Cell Level"
Abstract
Reduced nicotinamide adenine dinucleotide (NADH) is a major electron donor in both the oxidative phosphorylation and glycolysis pathways in live cells. As a result, there has been an increasing interest in exploiting cellular NADH as an intrinsic molecular probe for energy metabolism and cell pathology. Here we provide experimental and theoretical analysis of intrinsic NADH using ultrafast dynamics in live, intact human breast cancer (Hs578T) and normal (Hs578Bst) cells, at the single-cell level and with polarization selectivity. In addition to the mitochondrial distribution and morphological differences, two-photon FLIM indicates that the average lifetime of intrinsic NADH is faster in breast cancer cells than in the normal ones. Moreover, we have also developed a new algorithm using FLIM and intensity images to accurately calculate the NADH concentration in cells. This is in contrast with traditional biochemical protocols, which require lysing the cells. Our comparative studies of rotational diffusion and modeling, at the single-cell level, provide the structural basis (e.g., free versus enzyme-bound) of the observed differences of intrinsic NADH dynamics. The autofluorescence results are compared with NADH binding dynamics using relevant enzymes such as mitochondria malate dehydrogenase (mMDH) and lactate dehydrogenase (LDH) in solution. Further, the cellular NADH dynamics are distinctive from flavin adenine dinucleotide (FAD), which can be assessed using different excitation and detection windows. These studies demonstrate the sensitivity of intrinsic NADH dynamics to cell physiology and pathology.
For additional information, contact Ms. Doretta Garvey, Dept of Bioengineering, Tel: 814.865.1407 or E-Mail: bioe@engr.psu.edu