Bioengineering Seminar Schedule, Fall 2008
"Integrated Experimental, Computational and Theoretical methods to study the Molecular Dynamics of Stressed Membranes"
Ramachandra Gullapalli, Penn State University
Thursday, August 21, 2008, 10:00 - 11:00 am, Room 210 Hallowell Building, CG628 Hershey
Final Defense
Abstract
Cells transduce forces into biochemical signals through a process termed mechanotransduction. This process involves transmembrane proteins, the activity of which is modulated by the lipid solvent surrounding them. The goal of this work was to develop the experimental, computational and theoretical infrastructure to study the direct interrelationship between force and lipid dynamics. First, fluorescence correlation spectroscopy (FCS) and fluorescence lifetime methods based on time-correlated single photon counting (TCSPC) instrumentation were developed in order to capture the force-induced change in lipid dynamics on spatial and temporal scales relevant to mechanotransduction. In tandem, the infrastructure was developed and tested for micropipette aspiration of giant unilamellar vesicles (GUV's) stained with lipoid dyes such as DiI-C18(3). These systems will be used for direct interrogation of the relationship between membrane tension and molecular dynamics. Second, we developed atomistic computational molecular dynamics (MD) simulations of a lipoid fluorescence dye, DiI-C18(3), in a DPPC bilayer. From these simulations, we clarify, for the first time, the location of DiI-C18(3) within a bilayer and compare the computational data to experimentally available data. Third, a generalized analytical model was developed that shows an exponential relationship between membrane lateral stretch and lipid diffusion; a relationship that can be tested directly on stressed GUVs using single molecule fluorescence methods. This infrastructure provides tools to determine, from atomic to continuum scale and from nanosecond to minute time scales, the role of plasma membrane lipids in mechanotransduction.
"Ultrasound: 1 Million and One Uses"
Nadine Smith, Penn State University
Friday, August 29, 2008, 12:00 - 1:00 pm, Room 210 Hallowell Building, CG624E Hershey
"Orientation for New Students"
Herbert H. Lipowsky
Friday, September 5, 2008, 12:00 - 1:00 pm, Room 210 Hallowell Building, CG624E Hershey
"Drag Reducing Polymers: A New Treatment for Coronary Artery Disease" - CA NCELLED
John J. Pacella, University of Pittsburgh
Friday, September 12, 2008, 12:00 - 1:00 pm, Room 210 Hallowell Building, CG624E Hershey
Cancelled
Drag reducing polymers (DRPs) are linear, blood soluble macromolecules that reduce fluid friction in turbulent flow and provide a higher flow for a given driving pressure. Using myocardial contrast echocardiography (MCE) and radiolabeled microsphere flow analysis, we have previously shown that DRPs reduce microvascular resistance and improve myocardial capillary perfusion in a canine model of severe LAD coronary artery stenosis. In an effort to discern the microvascular level in which DRPs exert their primary flow enhancing effect, we used mathematical modeling and MCE and determined that DRPs lowering capillary resistance and increase capillary blood volume. To further uncover the mechanism of action of these intriguing polymers, we used intravital microscopy of the rat cremaster muscle microcirculation to study microvascular hemodynamics during DRP infusion. We found that DRPs increased microvasular RBC velocity in all three microvascular compartments. In addition, we found that DRPs were associated with a 10% increase in arteriolar diameter. Since vasodilation could also explain their resistance lowering and flow enhancing effects, we attempted to pharmacologically control vasomotor tone in 2 different animal models. We then determined whether DRPs had additional resistance lowering effects. These studies were conducted in rabbit in which we locally infused adenosine to cause maximal VD and then infused DRP measured R to determine whether there was a further reduction. Then, in rats, to exclude changes caused by nitric oxide (NO), we used LNAME to block endogenous NO and cause VC. DRP infusion was again found to cause a further reduction in VR. Interestingly, in 2 different animal species employing 2 different pharmacologic means to control vascular tone, the DRP-induced magnitude of resistance reduction was similar at 14%. The current mechanistic investigations of DRPs are centered around determining whether DRPs enhance microvascular perfusion via favorable alterations in blood flow hydrodynamics or whether DRPs enhance the distribution of RBCs within the microcirculation. To address the former, the servonull micopressure technique will be brought to bear on this question as we will attempt to cannulate precapillary arterioles to determine whether DRPs increase capillary driving pressure. Thus, DRPs appear to not only have tone-independent resistance lowering effects, but also, they favorably alter the microvascular distribution of RBCs. Both of these properties could have important therapeutic implications for any condition that results in compromised microvascular perfusion.
"Aerodynamics of the Voice"
Mike Krane, Applied Research Lab, Penn State University
Friday, September 19, 2008, 12:00 - 1:00 pm, Room 210 Hallowell Building, CG624E Hershey
Abstract
The voice we hear is sound produced by flow-induced vibration of the vocal folds, filtered through the vocal tract resonator. Traditionally, the aerodynamic action of the vocal folds has been modeled as a simple aerodynamic resistance element, due to the separation loss. Other, additional aerodynamic effects, such as glottal jet formation and instability, as well as motion of the vocal fold walls, have been neglected, even though their dynamic relevance is not clear. This seminar describes research that seeks to rank aerodynamic effects in terms of their dynamic relevance. Equations of motion reformulated to explicitly include each aerodynamic effect are presented. The terms in these equations are then estimated using measurement and computer simulation. Experiments were performed in a scaled up model in water, using DPIV. These show the development of the glottal jet and its instability Computational Fluid Dynamics simulations of the same problem were also performed on the same geometry in order to estimate the forces on the vocal fold walls. The results show that the simple resistance model is oversimplified.
"Molecular Interactions in Biomaterial-Induced Thrombosis"
Chris Siedlecki, Penn State Hershey Medical Center
Friday, September 26, 2008, 12:00 - 1:00 pm, Room 210 Hallowell Building, CG624E Hershey
Abstract
Thrombosis and coagulation remain major impediments to the successful use of blood-contacting medical devices. Thrombosis is initiated by the interaction of plasma proteins with biomaterial surfaces, leading to protein activation, fibrin formation and platelet adhesion/activation/aggregation. Despite decades of research, the mechanisms that lead to biomaterial-induced thrombosis remain largely unclear, although the surface properties of the material are known to influence these events. This seminar will discuss experiments to elucidate the material-induced activation mechanisms for Hageman Factor (Factor XII) which triggers the coagulation cascade, and fibrinogen which is the principal protein involved in mediating blood platelet interactions with materials. The work utilizes a combination of high resolution probe microscopy techniques, chromogenic substrates for enzyme detection, and traditional measures of blood compatibility such as clot formation and platelet adhesion. Studies are conducted using both model surfaces with well-defined properties and clinically-relevant biomaterials that are much more complex and harder to characterize. Taken together, results provide insight into the dynamic environment that is present at the blood-biomaterial interface and may eventually offer new approaches towards developing materials specifically designed for use in blood-contacting applications.
NO SEMINAR, BMES Conference
Friday, October 3, 2008, 12:00 - 1:00 pm, Room 210 Hallowell Building, CG624E Hershey
"Microfluidics for Continuous Clinical Monitoring"
Jeffrey Zahn, Rutgers University
Friday, October 10, 2008, 12:00 - 1:00 pm, Room 210 Hallowell Building, CG624E Hershey
Abstract
The focus of research conducted in the Zahn laboratory is the design and fabrication of microfluidic technologies for the clinical diagnosis and treatment of disease. Batch fabricated microfluidic platforms that can mimic conventional sample preparation techniques performed in laboratories hold great potential to enable both research and healthcare advances. These miniaturized diagnostic devices have been termed micro total analysis systems (mTAS) or biochips and combine sensing mechanisms (physical, optical, electrical or chemical) with microfluidics. While microfluidics promises to have an impact in many research fields, one of the more attractive applications has been towards biomedical and life science diagnostics. There is a growing market for point of care diagnostic devices for both bedside and outpatient monitoring. Research on approaches towards developing devices which can separate blood plasma from whole blood and measure the concentration of the clinically relevant proteins in a continuous, real time fashion will be reviewed. This is especially important for monitoring inflammatory responses in patients undergoing cardiac surgery when cardiopulmonary bypass (CPB) is used. An approach for improving DNA purification from cells using a two phase liquid extraction will also be discussed.
"Tissue Engineering Approaches to Cardiac Repair and Regeneration"
George Engelmayr, Jr., Harvard-MIT Division of Health Sciences & Technology,
Massachusetts Institute of Technology
Monday, October 20, 2008, 3:30 - 4:30 pm, Room 210 Hallowell Building, CG623 Hershey
Abstract
Congenital and acquired lesions of the heart persist among the leading causes of death, encompassing pathologies of the cardiac vessels, valves and myocardium. Tissue engineered grafts comprised of living cells cultivated on bioresorbable scaffolds represent a promising potential alternative to current prosthetics used in cardiac repair. In this talk, I will focus on quantitative design aspects of cardiac tissue engineering, beginning with studies on tissue engineered heart valves for pediatric applications, and continuing with studies on tissue engineered heart muscle. The design of physiologically-appropriate scaffolds and bioreactor conditioning regimens will be emphasized. Mathematical models developed to instruct the design and assessment of scaffold and engineered tissue mechanical properties will also be discussed. I will conclude by summarizing the current state-of-the-art, including the emerging role of microfabrication in cardiac tissue engineering for basic science and clinical applications.
"Thrombosis and Cardiovascular Risk in Cardiovascular Devices, CVS Pathologies, and Due to Smoking"
Danny Bluestein, SUNY - Stony Brook
Friday, October 24, 2008, 12:00 - 1:00 pm, Room 210 Hallowell Building, CG624E Hershey
Abstract
Cardiovascular devices expose recipients to enhanced risk of thrombosis and cardioembolic stroke. In most cases anticoagulation regimen is mandated for these patients, that does not eliminate the risk. Thrombus formation in prosthetic cardiovascular devices and in arterial pathologies is associated with elevated hemodynamic stresses that may induce platelet activation, thrombus formation, and potentiate their interaction with the endothelium. In vitro studies were conducted to estimate the thrombogenic potential of various Prosthetic Heart Valve (PHV) designs. A new polymer trileaflet design was tested for its thrombogenic potential and compared to that of existing prosthetic heart valves (PHVs) routinely implanted in patients: a St. Jude Medical bileaflet mechanical heart valve (MHV) and a St. Jude porcine bioprosthetic tissue valve. The valves were mounted in a left ventricular assist device (LVAD) and the procoagulant activity of the platelets was measured using an innovative platelet activation state (PAS) assay. Complementary in vivo studies were conducted in the sheep model to study the effects of valve implantation on platelet activity and the risk of cardioembolic stroke. Sheep with implanted valves had increased level of platelet activity, as measured with the PAS assay. Transcranial Doppler measurements indicated a significant increase in the amount of microembolic signals, as measured in the carotid artery of the sheep after valve implantation.
Mechanisms of thrombus formation were investigated using numerical simulations of transient non‑Newtonian turbulent blood flow patterns and Direct Numerical Simulations (DNS) in various PHVs. Platelet damage accumulation model incorporating damage history (senescence) was developed to estimate platelet activation resulting from the combined effect of flow induced stresses and exposure time in the device. Additionally, Fluid Structure Interaction (FSI) simulations of flow past ATS and SJM bileaflet valves were conducted and platelet activation damage averaged over a large number of trajectories within the flow field.
FSI simulations were conducted in a model of a vulnerable plaque‑ a pathology that prompts strokes and fatal heart attacks (sudden cardiac death), and in abdominal aortic aneurysms (AAA) reconstructed from patients CT images, in order to predict plaque vulnerability and AAA risk of rupture. For the vulnerable plaque the analysis indicates regions where a combination of elevated strains in the vessel wall and shear stresses induced by the flow, combined with the fibrous cap thickness, enhance the plaque vulnerability and may lead to rapid thrombus formation. The role of calcification in the plaque was examined, indicating that it significantly increases the plaque vulnerability. For the AAA, the role of intraluminal (ILT) thrombus in the AAA was examined and used to predict potential rupture locations, using hyperelastic and anisotropic (orthotropic) material models.
Thrombus formation in arterial pathologies is associated with elevated hemodynamic stresses that may induce platelet activation and potentiate their interaction with the endothelium. In‑vitro platelet measurements were conducted in a Hemodynamic Shearing Device (HSD) which is driven by a computer‑controlled motor that is fed with dynamic waveforms that can mimic any stress loading combination in the vasculature. Platelet activity was measured in the HSD using a Platelet Activation State (PAS) assay in the presence and absence of cultured endothelial cells (EC) in order to investigate the effect of platelet concentration on platelet activity, and the potential antithrombotic effect EC on platelet activity.
Cigarette smoke is recognized as a primary risk factor for an increased vulnerability to cardiovascular diseases. Previous studies clearly indicate that cigarette smoke adversely affects platelet function, in smokers as well as nonsmokers exposed to Second Hand Smoke (SHS). Recently marketed low/zero‑nicotine cigarettes that are promoted by the tobacco industry as safer to smokers, were tested in smokers and non‑smokers volunteers exposed to SHS, and in in vitro studies. Enhanced platelet activity was found in the subjects exposed to smoke from these cigarettes, as expressed by platelet activity markers measured with flow cytometry.
NO SEMINAR
Friday, October 31, 2008, 12:00 - 1:00 pm, Room 210 Hallowell Building, CG624E Hershey
FINAL DEFENSE - CANCELLED
Don Bigler, Penn State Hershey Medical Center
Friday, November 7, 2008, 12:00 - 1:00 pm, Room 210 Hallowell Building, CG624E Hershey
Student Presentations: Shankar Shastry, Qianru Yu
Friday, November 14, 2008, 12:00 - 1:00 pm, Room 210 Hallowell Building, CG624E Hershey
"Kinesin Neck-Linker and Neck-Coil Both Contribute to Motor Processivity"
Shankar Shastry, Advisor: Will Hancock
Abstract
Kinesins are microtubule-based molecular motors involved in intracellular transport. A principle question in understanding motor function is: What are the structural determinants of processivity. In contrast to homodimeric motors in the canonical Kinesin-1 family, Kinesin-2 motors have two different head domains and a three amino acid extension in their neck linker. We showed previously that Kinesin-2 motors are slower than Kinesin-1 and are roughly four-fold less processive. These differences could result from biochemical differences in the head domains, reduced inter-head coordination due to differences in the neck-linker domains, or diminished electrostatic interactions between the coiled-coil domain and the microtubule track. To test the influence of the coiled-coil domain, we engineered motors containing the Kinesin-2 head and neck linker domains fused to the Kinesin-1 coiled-coil. Single-molecule fluorescence experiments of GFP-labeled motors showed enhanced processivity compared to Kinesin-2, indicating a role for the coiled-coil in motor processivity. When the Kinesin-1 neck-linker domain was extended by three amino acids, processivity fell by a factor of three, suggesting that the neck-linker domain is an important determinant of processivity.
"Concentrations and Molecular-Conformations of Cellular NADH and FAD are Sensitive to Cell Physiology: A Nonlinear-Fluorescence Dynamics Perspective"
Qianru Yu, Advisor: Ahmed Heikal
Abstract
The native reduced nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD) in eukaryotic cells are key metabolic cofactors in redox reactions and energy metabolic pathways. Recently, there is resurgence in employing cellular autofluorescence as a natural probe for diagnostic purposes in cancer, diabetes, apoptosis, and neurodegenerative diseases. Here, I will present quantitative, fluorescence-based biochemistry of intrinsic NADH and FAD at the single-cell level. Cancerous (Hs578T) and normal (Hs578Bst) breast cells were used as a model system. This quantitative fluorescence dynamics assay includes two-photon fluorescence lifetime and polarization anisotropy imaging for contrast, concentration measurements, and analysis of the free-to-enzyme-bound molar fraction. Such non-invasive assay on living cells provides an alternative approach for (i) probing mitochondrial anomalies associated with cell pathology (without the need for exogenous dyes) and (ii) avoiding cell destruction required in conventional biochemical techniques (i.e., loss of the morphological context). The sensitivity of this fluorescence dynamics assay has also been examined in primary and Ras-activated keratinocytes as well as MCF-7 breast cancer cells.
FINAL DEFENSE - CANCELLED
Amit Ailiani, Penn State University
Friday, November 21, 2008, 12:00 - 1:00 pm, Room 210 Hallowell Building, CG624E Hershey
FINAL DEFENSE - "Novel Approaches to Quantifying, Tracking and Enhancing the Performance of the Electrode-Tissue Interface in Microwire Brain Implants"
Kunal Paralikar, Penn State University
Monday, November 24, 2008, 2:00 - 3:00 pm, Room 210 Hallowell Building, CG628 Hershey
Abstract
Intracortical microwire electrodes record extracellular multi-unit activity that is essential to drive neuroprosthesis systems as well to develop our understanding of various brain functions like learning and memory. Implantation of the electrode arrays in the brain is a complex and invasive undertaking that requires excision of bone and meninges. Recordings obtained from electrodes are random in nature. Typically, neuronal spiking events are detected by their relatively large amplitudes as compared to the rest of the signal or by their typical shapes. This process is extremely subjective, time consuming and requires trained experts. Presence of microwire implants in the brain triggers an immune response that leads to degradation and eventual loss of recordings. The extent and nature of this response is unpredictable and is currently known only by end-point histology studies.
This dissertation documents the development of techniques to help the processes of implantation, neuronal spike detection, and real-time interface monitoring. It reports an objective approach to neuronal spike detection that uses information of electrode spacing and modeling studies to increase the probability of neuronal event detection. Minor addition to standard implantation techniques is reported that uses enzyme enabled disruption of meninges in order to reduce the implantation trauma, reduce electrode insertion forces and improve chronic recording. In the last part of this dissertation, the safety of employing magnetic resonance imaging as a non-invasive imaging modality for real-time tracking of the longitudinal tissue changes around the electrode is demonstrated.
NO SEMINAR - Thanksgiving Break
Friday, November 28, 2008, 12:00 - 1:00 pm, Room 210 Hallowell Building, CG624E Hershey
FINAL DEFENSE - "Evaluation of Fluid Mechanics and Cavitation Generated by Mechanical Heart Valves During the Closing Phase"
Luke Herbertson, Penn State University
Friday, December 5, 2008, 12:00 - 1:00 pm, Room 210 Hallowell Building, CG624E Hershey
Abstract
Significant advances have been made in the field of heart valve replacement, especially in terms of anticoagulation therapy and valve design. However, heart valve patients remain more susceptible to complications involving hemolysis and thrombosis. For this thesis work, the closing dynamics of mechanical heart valves have been dissected to better understand the roles of valve design and environmental conditions on local fluid mechanics. Flow visualization and measurement techniques, such as laser Doppler velocimetry (LDV), were applied to analyze the near-valve fluid structures that may impact hemolytic rates. Modifications were made to the valve housing to enable optical measurements in previously inaccessible regions of the flow. The three-dimensional flow patterns presented here reveal regions of turbulence, flow stagnation, vorticity, and flow separation near the leaflet tip.
Mechanisms for blood damage were further investigated by analyzing high frequency pressure fluctuations representative of cavitation. Mitral valve closing sounds were shown to contain characteristics that, when properly isolated, can help to diagnose cavitation potential, asynchronous leaflet closure, and valve impact forces. Potential improvements to implantation techniques, valve design, and flow conditions have evolved from these findings. Creating a dampened valve impact and rebound proved to be the critical factor for minimizing the risk of blood damage in patients with mechanical heart valves.
Student Presentations: Hari Muddana, Amit Vaish
Friday, December 12, 2008, 12:00 - 1:00 pm, Room 210 Hallowell Building, CG624E Hershey
"Photophysical Characterization of Dye-Encapsulated Calcium Phosphate Nanoparticles using Steady-State and Time-Resolved Fluorescence Spectroscopy"
Hari Muddana, Advisor: Peter Butler
Abstract
Organic dyes rapidly photobleach, have low quantum yield, and exhibit random blinking under physiological conditions due their interaction with solvent. Encapsulation of fluorophores in silica or polymeric matrices such as polystyrene or PLGA can minimize these solvent interactions and enhance the dye's chemical- and photo-stability, but use of these nanoparticle systems for in vivo imaging is complicated by their lack of biocompatibility and bioresorbability. Adair's group at Penn State has recently developed a novel sub-50nm nanoparticles using calcium phosphate (CP), a naturally biocompatible material. The objective of this study was to determine whether this encapsulation system imparts increased fluorescence to the organic dye, Cy3, necessary for its utility as an in vivo imaging agent. Particle size on the order of 20 nm and monodispersity were confirmed using fluorescence correlation spectroscopy (FCS)- determination of particle diffusion coefficients and their respective hydrodynamic radii. Brightness of a single CP nanoparticle was found to be ~20 times higher than a single free dye, due to a 4.5 fold increase in quantum efficiency of the encapsulate dye and the presence of about 4 dye molecules per nanoparticle. To elucidate whether enhanced quantum efficiency was due to protection from solvent, we measured the fluorescence lifetime of free and encapsulated dye under different solvent conditions. An increase in viscosity and decrease in hydrogen bonding, each resulted in a 2-fold increase in the radiative decay rate and 2-fold decrease in the non-radiative decay of the free dye. Changing solvents had a negligible effect on the fluorescence lifetime of the encapsulated dye and lifetime of the encapsulated dye was consistently higher than that of the free dye in water suggesting that the CP matrix shielded the dye well. These results support an iterative strategy for development of a new bioresorbable dye encapsulation system involving coordinated materials development and photophysical characterization.
"5-Hydroxytryptophan-Functionalized Self-Assembled Monolayers Capture Native Membrane-Associated Serotonin Receptors"
Amit Vaish, Advisor: Peter Butler
Abstract
We have developed methods to tether small molecules to self-assembled monolayers (SAMs) at necessarily low surface coverages so as to retain sufficient chemical functionality for recognition by large biomolecules. We chose the neurotransmitter serotonin as a prototypical small molecule because of its importance in psychiatric disorders. The amino acid precursor of serotonin, 5-hydroxytryptophan (5-HTP) was covalently bound to oligoethyleneglycol alkanethiol SAMs by carbodiimide coupling chemistry. Surface chemistry was analyzed by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Using quartz crystal microgravimetry, we demonstrate that 5-HTP-functionalized surfaces show low nonspecific binding. They selectively capture anti-5-HTP antibodies or recombinant receptors that natively recognize free serotonin vs. receptors for other neurotransmitters with similar structures. Previously studied serotonin-functionalized surfaces fail to show binding of membrane-associated serotonin receptors. Our findings suggest that the lack of recognition of tethered serotonin itself is due to masking of primary amines by the tethering chemistry.
"Multi-scale approaches to exploring the active regulation of lymphatic function"
Brandon Dixon, Ecole Polytechnique Federal de Lausanne
Monday, December 15, 2008, 11:00 - 12:00 pm, Room 210 Hallowell Building, CG628 Hershey
Abstract
Lymphatics are a specialized vascular tissue that (i) absorb fluid, proteins, and lipid from interstitial spaces and return them to the blood, (ii) provide a conduit for immune cell trafficking to lymph nodes, and (iii) transport postprandial lipids secreted by enterocytes in the form of chylomicrons from the small intestine to the circulation. The lymphatic system is also involved in cancer metastasis. While lymphatics play vital roles in three extremely well-studied areas in modern medicine – immune function, lipid metabolism, and cancer biology – the molecular mechanisms that control these functions are only now being explored. During this talk I will provide two examples of how an integrated bioengineering approach to studying lymphatics has provided new insight into how lymphatics control and modulate their function. First, novel methodologies in imaging, physiology, and image processing have elucidated the first measurements of wall shear stress in contracting lymphatics. These measurements are now allowing researchers to explore the molecular mechanisms that control the shear response to lymphatic pump function. Second, I will present a tissue engineered model of the intestinal lacteal that has been recently developed and characterized and show how this model, in conjunction with in vivo imaging of lipid uptake, is being used to explore the modulation of lymphatic transport of lipid.
FINAL DEFENSE - "Characterization of Protein Films Using Novel Atomic Force Microscopy Techniques"
Pranav Soman, Penn State University
Wednesday, December 17, 2008, 12:00 - 1:00 pm, Room 210 Hallowell Building, CG624E Hershey
Abstract
The success of long-term blood-contacting implanted devices greatly depends upon the interaction of the blood components with the device material. The search for a hemocompatible biomaterial has not yielded success yet, largely due to the incomplete understanding of blood-material interactions, especially at sub-cellular and molecular levels. In this work, critical aspects of blood-material interactions are probed at the molecular scale using Atomic Force Microscopy (AFM). Conventional AFM imaging techniques are not capable of detecting specific plasma proteins on clinically relevant polymeric biomaterials, mostly due to the surface roughness of the biomaterial. This work has developed AFM techniques, which will not require the topographical features otherwise needed by conventional AFM methods to detect proteins. Fibrinogen, the third most abundant plasma protein, plays a crucial role in surface induced thrombosis in blood contacting devices. AFM is used to characterize fibrinogen, in terms of its spatial location, on ultrasmooth mica substrate and a clinically relevant polymer substrate, poly (dimethyl-siloxane). Gold labels are used as immunological tags to detect adsorbed fibrinogen from a dual-protein layer at molecular resolution. Force spectroscopy is used to calculate the time dependent activity of the platelet binding dodecapeptide epitope of fibrinogen. These nanoscale results are corroborated with macroscale platelet adhesion experiments. The effects of concentration and co-adsorption of bovine serum albumin with fibrinogen are studied on hydrophilic mica substrates. Polyethylene glycol (PEG) is investigated as a potential tether to attach proteins to the AFM probe. Modified PEG-probes are more efficient in decreasing non-specific interactions, which is the main problem with glutaraldehyde linkers especially in the case of hydrophobic substrates. Taken together, this work fills the gaps in the current understanding of the blood-material interactions at the molecular level and provides important tools for future studies.
For additional information, contact Ms. Doretta Garvey, Dept of Bioengineering, Tel: 814.865.1407 or E-Mail: bioe@engr.psu.edu