|
Biomedical Engineering Research Grants June 1998 Kenneth A. Barbee, Ph.D. Assistant Professor, Department of Neurosurgery Allegheny University of the Health Sciences (RG-97-0494) Philadelphia, PA Optimization of Angioplasty to Minimize Smooth Muscle Cell Injury and Prevent Restenosis Percutaneous transluminal coronary angioplasty (balloon angioplasty) offers a less invasive alternative to coronary by-pass surgery for patients whose coronary vessels have become occluded due to the process of atherosclerosis. Its potential has not been fully realized due to the high rate of restenosis - the rapid reocclusion of the vessel due to the pathological growth of the vascular smooth muscle (VSM) in response to the trauma of the balloon inflation. Despite the recognition of smooth muscle injury as an initiating event in the process of restenosis, there has been no systematic study to determine the mechanical loading conditions required to produce VSM injury and elicit the restenosis response. The general objectives of this project are to characterize the mechanical and biological response of vascular smooth muscle to injury induced by vessel wall stretch associated with percutaneous translumenal coronary angioplasty (PTCA) procedures. By characterizing the sensitivity of the cells in terms of strain and strain rate, an optimal loading regime can be designed to minimize smooth muscle cell injury, proliferation, and restenosis. The specific aims are to: 1. determine the dependence of injury, characterized by membrane permeability and viability, on strain magnitude, strain rate, and duration of a single dynamic biaxial stretch in normal and cholesterol-enriched vascular smooth muscle. 2. characterize the proliferative response of vascular smooth muscle to mechanical injury. 3. use the stretch injury model to test treatment strategies targeted to injury mechanism itself: nonionic surfactants to increase membrane fluidity, immunoliposomes to promote membrane repair, and B-cyclodextrin tetradecasulphate to complex bFGF released by injured cells. This research project will establish tolerance criteria for smooth muscle cell injury in terms of the magnitude and rate of loading, and develop a culture model to measure biophysical changes in cell structure and function due to the mechanical loading. Victor Barocas, Ph.D. Assistant Professor, Department of Chemical Engineering University of Colorado (98-0157) Boulder, CO Role of Aqueous Humor Dynamics in Glaucoma The PI proposes to develop, validate and apply a computer model to assess the role of aqueous humor (AH) dynamics in glaucoma. He will use computational fluid and solid mechanics to study the flow of AH around the iris in the eye and its contribution to certain forms of glaucoma in which displacement of the iris plays a significant role in the disease. It is hypothesized that this displacement arises from elasto-hydrodynamic interaction between the iris and the aqueous humor, and it is proposed to use computational mechanics to assess the significance of this interaction. Once this extended model has been developed and tested, it will be used to explore the mechanisms underlying pigmentary and angle closure glaucoma and to project the long-term effects of various treatments. The PI will also perform two basic types of experiments. First, mechanical tests of tissue samples will be used to obtain the parameters necessary for the model; second, ultrasound biomicroscopy will provide accurate dimensional data for the model domain. The proposed research consists of six components: 1. Experimental determination of model parameters (i.e., tissue properties). 2. Execution and validation of the existing steady-state simulation. 3. Development and validation of a transient model and simulation method. 4. Evaluation of existing hypotheses on the mechanism of pigmentary glaucoma. 5. Evaluation of possible long-term effects of various treatments of pigmentary glaucoma. 6. Evaluation of the hypothesis that anterior placement of the iridoscleral junction leads to increased angle closure glaucoma susceptibility. Computer simulation offers two advantages in the study of glaucoma. First, one can speed up or slow down time easily in a simulation; and second, one can predict quantities, such as the stress in various portions of the eye, that are inaccessible in patient examination. This work can provide insight into a common disease that is at present treatable but incurable and irreversible. Ravi Bellamkonda, Ph.D. Assistant Professor, Department of Biomedical Engineering Case Western Reserve University (RG-98-0159) Cleveland, OH Engineered Three-Dimensional Substrates for Nerve Regeneration In spite of significant advances in the understanding of the molecular mechanisms of the development, maintenance and aging of the human nervous system, regeneration of injured peripheral and central nerves remains an elusive therapeutic goal. Recently, developmental neurobiologists and neuroscientists have identified potent proteins that either play an important role in development, axon guidance and stimulate nerve regeneration. This research proposal describes a novel bioengineering approach to design and develop biomaterials based on "enabling" technologies that try to make the environment at the site of nerve injury conducive to regeneration. The main objective of the proposed research, therefore, is to design and develop novel 3D biomaterial substrates that are specifically engineered to be optimal "bridges" that facilitate regeneration and reconnection of severed nerve stumps. The research is based on two main hypotheses: 1) the molecular strategies employed by the fetal nervous system in "wiring" the mammalian nervous system are ideally suited to promote peripheral and central nerve regeneration and 2) novel, hydrogel-based, 3D substrates and gel-embedded drug delivery systems can be used to partially recreate the molecular fetal milieu at the site of nerve injury in a well-characterized, controlled manner to stimulate maximal regeneration. The specific aims of this research proposal are to: 1. Develop a fundamental understanding of neurite extension in 3D hydrogel substrates. 2. Develop an in vitro model to probe nerve growth across 3D interfaces. 3. Design and develop a novel controlled release system for site-specific trophic factor delivery. 4. Promote the regeneration of transected sciatic nerves and dorsal roots in a rodent model in vivo. The research is expected to have an important impact on the therapeutic strategies adopted for both peripheral and central nerve injuries and to aid the further evolution and maturing of the emerging discipline of neural tissue engineering. Anuj Bellare, Ph.D. Instructor, Orthopedic Research Lab Brigham and Women's Hospital (RG-98-0006) Boston, MA Engineering Polyethylene to Improve the Performance of Patellar Implants The primary goal of this proposal is to improve the wear performance of total joint replacement prostheses. These orthopedic implants comprise a metal or ceramic component that slides against a polymeric component commonly made of ultra-high molecular weight polyethylene. Despite the excellent wear resistance of this type of polyethylene compared to other polymers, the lifetime of joint replacement prostheses is still limited by wear performance. Among the various joint prostheses, the polyethylene patellar component is associated with the most complications. Several mechanisms of wear have been identified in the knee joint prostheses: adhesive, abrasive and delamination wear. The primary goal of this proposal is to improve the wear performance of total joint replacement prostheses. The specific aims of this proposal are: 1. To fabricate polyethylene components using cross-linked polyethylene 2. To fabricate polyethylene components by self-reinforcement using fibers of oriented polyethylene. 3. To characterize each type of polyethylene and determine their mechanical properties, with particular emphasis on tensile strength, fracture toughness and resistance to creep. 4. To verify the resistance of the new forms of polyethylene to specific wear mechanisms with the use of laboratory patellar wear tests. Development of wear resistant polyethylene will improve the longevity of orthopedic prostheses and reduce the number of costly and complicated revision surgery necessary to replace such implants. Longer lifetimes of such implants would also enable implantation in younger patients who would otherwise be disabled. This proposal uses the engineering approach of improving implant quality as a solution to the biological problem associated with this type of implantation surgery. Brett Bouma, Ph.D. Assistant Professor, Department of Dermatology The General Hospital Corporation (RG-98-0071) Boston, MA Subcellular Resolution Endoscopic Microscopy In the proposed study the PI will investigate and develop new optical imaging technologies for the endoscopic visualization of tissue structures on the cellular level within living subjects. This work will implement innovations for two recently developed imaging techniques, confocal microscopy and optical coherence tomography. Neither of these techniques is currently capable of performing cellular level resolution imaging through endoscopic access. The high resolution afforded by confocal microscopy permits the visualization of intra-cellular structures such as nuclei and can be performed at high (real-time) image acquisition rates. The current scanning methods used in confocal microscopy, however, cannot be adapted to endoscopic technology. Optical coherence tomography (OCT) can readily be adapted to catheter or endoscope implementation but suffers from relatively poor resolution and can only evaluate tissue morphology on the scale of 30 microns. Higher axial resolution OCT has been demonstrated but because the depth of field in current OCT imaging is intrinsically linked to transverse resolution, visualizing subcellular features over an appreciable depth is problematic. The proposed study is comprised of three distinct engineering elements: 1. Eliminating the mechanical primary axis scanning system currently used in confocal microscopy. A unique spatial sampling scheme will replace the standard mechanical scanning by spectral encoding enabling endoscopic confocal microscopy. 2. Increasing the transverse resolution of optical coherence tomography approximately 10-fold while preserving a large depth of field using a unique illumination geometry. 3. Investigating advanced clinically viable optical sources that will enable these new imaging technologies to rapidly acquire high resolution, high dynamic range images of human tissue in vivo. Since the greatest number of cancers of the reproductive, gastro-intestinal and respiratory tracts are epithelial cancers, it is believed that instruments that permit endoscopic microscopy will significantly impact the early diagnosis of these diseases. Ashutosh Chilkoti, Ph.D. Assistant Professor, Department of Biomedical Engineering Duke University (RG-97-0486) Durham, NC Targeted Delivery of Radionuclides to Tumors by Genetically Engineered Thermally-Responsive Polymers Gliomas are the most malignant primary brain tumors. Surgical resection, followed by chemo- and/or radio-therapy are the most common therapeutic modalities indicated for malignant gliomas. However, each of these treatments suffers from significant limitations, leading to dismal long-term prognosis. Motivated by the limitations of current therapeutic approaches, the objective of the proposed research is to develop a local hyperthermia-targeted approach to site-specifically deliver radionuclides to gliomas and other solid tumors. The underlying hypothesis of the proposed research is that intravenously-delivered radionuclide elastin-like protein (ELP) biopolymer conjugates are likely to be rapidly cleared under physiological conditions, while at tumor-related sites, where local hyperthermia is externally-induced, the ELP biopolymer will accumulate because of desolvation and precipitation. Local hyperthermia-induced precipitation of the radionuclide-ELP biopolymer conjugate in the tumor vasculature will directly target the tumor microvasculature, and will thereby circumvent the barriers associated with extravasation, antibody targeting methods for local delivery of radionuclides. The specific aims are: 1. Synthesis and characterization of thermally-responsive ELP) biopolymer. 2. Conjugation of radionuclide to ELP biopolymer. 3. Effect of hyperthermia on tumor targeting of radionuclide-ELP biopolymer conjugate. While the PI has chosen a subcutaneous xenograft of malignant glioma in athymic mice as the model experimental system, the proposed research is not limited to malignant gliomas, but is more broadly relevant as a feasibility study of hyperthermia-targeted delivery of radionuclides to solid tumors by thermally-responsive biopolymers. Michael L. Dustin, Ph.D. Assistant Professor, Department of Pathology Barnes-Jewish Hospital (RG-0019) St. Louis, MO Affinity and Kinetics of Molecular Interactions in Leukocyte Adhesion to Artificial Surfaces The long-term goal of this work is to define the basic physical parameters that are important for immune cell adhesion. Immune cells use the blood stream to obtain rapid access to all tissues of the body where infection can occur. Entry of leukocytes into the tissues from the blood, their movement through the tissues, and cellular actions required for the destruction of pathogens are dependent on cell-cell and cell-substrate adhesion. Too much adhesion results in tissue destruction, while too little adhesion results in profound susceptibility to infection. Appropriate levels of leukocyte adhesion are essential for artificial tissues that are the goal of much work in tissue engineering. The PI has developed an experimental system based on an artificial phospholipid membrane technology that allows quantitative studies of adhesion molecule interactions in cell-artificial substrate contact areas. The hypothesis states that two-dimensional kinetic rate and equilibrium constants depend not only on the intrinsic interaction between receptors and ligands but also on how the two opposing surfaces linked by these molecules are aligned. The specific aims are to: 1. Determine the equilibrium binding constants for the interaction of receptors CD16 and CD2 with their respective ligands and compare these values to those obtained using micropipet based transient adhesion analysis. 2. Determine the kinetic rate constants in cell-phospholipid bilayer contact areas by fluorescence photobleaching recovery methods. 3. Determine what parameters must be considered to understand how disorder of apposing membranes effects the kinetics of adhesion molecule interactions. The PI will determine the kinetic rate constants and equilibrium constants for the interaction of important pro-inflammatory receptor systems. The results of these studies will help in understanding the inflammatory response to IgG deposition on an artificial surface and in the design of new drugs that facilitate acceptance of synthetic materials. Mark W. Grinstaff, Ph.D. Assistant Professor, Department of Chemistry Duke University (97-0497) Durham, NC Biopolymers for Islet Cell Transplantation The long-term objective of this research project is to entrap insulin secreting cells (islets of Langerhans) in an immuno-protected photo-cross-linkable polysaccharide and to implant this device in the peritoneal cavity. In the peritoneal cavity, this "artificial pancreas" will maintain glucose homeostasis, and thus may have the potential to cure insulin dependent diabetes mellitus (IDDM). In order to accomplish this objective, the PI will determine the optimal chemical, physical and biological properties that constitute a suitable biopolymer for encapsulation of islets. A modified hyaluronic acid biopolymer containing photo-polymerizable acrylate groups will be the novel material that was first investigated. The PI will integrate engineering principles and chemical expertise to design, synthesize and evaluate a novel bioploymer for encapsulation of islet cells. The complex interrelationships between chemical structure and resulting transport and rheological properties as well as the biocompatibility of this biopolymer will be investigated. Ultimately, the development of composition-structure-property-function relationships with respect to the polysaccharide biomaterial will not only enable the PI to accomplish this goal, but also to identify other prototype applications for testing. The specific aims are:
Rolf Gruetter, Ph.D. Assistant Professor, Department of Radiology University of Minnesota (98-0153) Minneapolis, MN 13C MRS at 4 Tesla: A Novel Probe of Brain Metabolism Functional magnetic resonance imaging (fMRI), magneto-encephalo-graphy (MEG) and brain mapping (EEG) can be used to measure localized brain activity. 13C MR complements these imaging methods by its capability to map intermediary metabolism with an unparalleled chemical specificity. Despite the enormous potential of this mapping method, 13C MR spectroscopy of the human brain has not found widespread application. The main goal of this project is to establish the necessary instrumentation, experimentation and modeling for clinical use of 13C MRS at very high magnetic field strength. The specific aims are to:
M. Saleet Jafri, Ph.D. Research Associate, Department of Biomedical Engineering The Johns Hopkins University (98-0165) Baltimore, MD Theoretical Analysis of Cardiac Energetics and Ischemia It is proposed to investigate the cellular basis of cardiac myocyte energetics under normal and ischemic conditions by studying the major components for energy production and utilization. This requires an integrative modeling study directed at understanding the interplay between Ca2+ handling, force generation, membrane currents, and glycolytic and mitochondrial respiration. The primary function of cardiac cells is to contract and generate force to pump blood. In response to electrical stimulation, Ca2+ is released from internal stores to activate the myofilaments causing contraction. The process of contraction requires large amounts of adenosine triphosphate (ATP) as the energy supply. After contraction, Ca2+ is resequestered into internal stores by means of additional ATP-dependent processes. Ischemia in the heart occurs when there is significant disruption in the oxygen supply, typically through blockage of the blood supply as occurs with coronary artery disease. In the absence of oxygen, mitochondrial respiration ceases and the energy reserves of the cell diminish quickly. The cell then uses anaerobic metabolism (glycolytic respiration) as an energy source leading to the accumulation of lactic acid and potential damage to the cell. The specific aims are to: 1. Test the hypothesis that increases in mitochondrial respiration are due primarily to increases in the activity of mitochondrial respiratory enzymes by Ca2+. 2. Test the hypothesis that metabolic oscillations are primarily due to oscillations in glycolytic respiration. 3. Test the hypothesis that mitochondrial respiration modulates glycolytic respiration and influences metabolic oscillations. 4. Test the hypothesis that dynamic changes in ATP level can contribute to cardiac arrhythmias through their activation of IK,ATP. These models will be used in network models to identify the arrhythmogenic potential of fluctuations in metabolism, predict the effects of IK,ATP channel openers and inhibitors, and suggest beneficial reaction to drugs. E. Duco Jansen, Ph.D. Assistant Professor, Department of Biomedical Engineering Vanderbilt University (RG-98-0124) Nashville, TN Multispectral in vivo Monitoring of Laser-Induced Injury to Biological Tissue The apparent pulsed laser ablation paradox can be summarized by long pulses causing excessive thermal damage due to thermal diffusion while short pulses cause significant tissue tearing owing to the explosiveness of the ablation event. Researchers have focused their efforts mostly on macroscopic measurements of physical parameters such as temperature, pressure, tissue mass removal, thermal damage, coagulation, denaturation of biological tissue, etc. while studies of the ensuing biological effects have mostly been limited to in vitro experiments or post-mortem analysis and histological studies. This project tries to develop a novel optical method based on bioluminescent reporter genes to monitor the temporal course of gene expression in vivo and to use this technology to correlate specific biological responses to well-characterized physical laser-induced stimuli in vivo. The specific aims of this proposal are as follows:1. Implement and adapt an in vivo model system for gene expression based on the luciferase reporter gene in cultured cells and in transgenic animals (mice). 2. Determine gene expression kinetics and threshold of the HSP-70 promotor by measuring bioluminescence after exposing cultured cells to series of temperatures and pressures. 3. Correlate well-characterized physical stimuli, including laser-induced perturbations, to the specific expression of HSP-70 in vivo. 4. Produce DNA constructs with luciferase as a reporter gene for other factors. 5. Start development of a multiple wavelength/multiple reporter assay using luciferase mutations. 6. Quantify and localize HSP-70 expression in the live animal. Correlations between specific aspects of laser-induced effects and cellular response can be made and quantified and correlated to histologically observed tissue damage. This information is crucial in optimizing the strategies and parameters for laser applications in medicine and biology. Josef A. Kas, Ph.D. Assistant Professor, Department of Physics University of Texas at Austin (98-0011) Austin, TX The Optical Stretcher - Single Cell Elasticity Measurements for Early Diagnosis of Malignant Cells and for Biopolymer Engineering The internal structure and organization of plant and animal cells are largely governed by the cytoskeleton, a filamentous protein network implanted in each cell. Permanent disruption of this cytoskeleton results in the death of the cell while more subtle changes can change the cell's mechanical strength, its ability to move, and other important functions. Conversely, changes in cell function such as transformation into malignant cells affect the structure of the cytoskeleton. Variations in the composition of the cytoskeleton should be reflected in the elasticity of cells. Determining whether cell elasticity is truly a potential way of detecting abnormality in cells could be of great value in the early detection of malignancy. Existing methods of measuring the elasticity of cells are tedious and cannot detect small changes in cellular elasticity. The PI proposes develop an optical stretcher-a unique optical tool to stretch single cells between two laser beams and measure the elongation of the cell. By using a flow chamber for the optical stretcher, large numbers of cells can be handled which will provide more data for more accurate analysis. Fungal toxins that either enhance or reduce the cytoskeleton will be used to test the optical stretcher. Cell elasticity measurements of clonal populations of cells differing only in the expression of key cytoskeletal proteins will determine to which extent the optical stretcher is sensitive to changes in the cytoskeleton. The transformation of fibroblasts into malignant cells by oncogenic vectors will be then investigated by the optical stretcher. In addition, the PI will design a finite element program to extract measurements of the shear modulus from the geometrically complex cell deformation for in vivo rheological measurements. This will allow the PI to gain insight into the viscoelastic function of the cytoskeleton. The long-term goal is to discover whether cancer can be detected at the cellular level by cell elasticity measurements. Since the irregular shape of cancer cells is an indicator of reduced cell elasticity, the optical stretcher could have a potential for use as a diagnostic tool. Konstantinos Konstantopoulos, Ph.D. Assistant Professor, Department of Chemical Engineering The Johns Hopkins University (98-0005) Baltimore, MD Bioengineering Aspects of Cancer Metastasis: Effects of Fluid Mechanical Forces on Blood Cell-Tumor Cell Interactions Modern surgical techniques and chemotherapeutic strategies have succeeded in treating some primary tumors. However, they have been less effective in combating metastasis that represents the most elaborate hurdle to overcome in the cure of the disease. Blood-borne metastasis is a highly regulated and dynamic process in which cancerous cells separate from a primary tumor, migrate across blood vessel walls into the bloodstream and disperse throughout the body to generate new colonies. This study proposed to investigate the effects of fluid mechanical forces due to blood flow on tumor-platelet and tumor-neutrophil interactions relevant to the process of blood-borne metastasis at the molecular level. The overall goal of this project is to elucidate (a) the kinetics of tumor-blood cell adhesion/aggregation, (b) the adhesion receptors involved in these processes, and (c) the sequence of molecular events mediating these interactions. A cone-and-late rheometer and a parallel-plate flow chamber will be employed to create well-defined conditions of shear stress in vitro. Specimens will be exposed to a wide range of physiological and pathophysiological shear stresses, mimicking typical blood flow conditions. Flow cytometry and videomicroscopy/digital image processing will allow determination of the extent of tumor cell-blood cell conjugate formation under shear flow. The specific aims are: 1. Quantitation of tumor-platelet interactions in cell suspensions. 2. Quantitation of tumor-neutrophil interactions in cell suspensions. 3. Development of a mathematical model of heteroaggregation. 4. Quantitation of tumor cell adhesion to surface-adherent platelets and neutrophils. This study will improve our understanding of the mechanisms underlying metastasis and provide insights for the development of therapeutics to effectively treat and prevent metastasis. David S. Lalush, Ph.D. Research Assistant Professor, Department of Biomedical Engineering University of North Carolina at Chapel Hill (98-0158) Chapel Hill, NC Dual-Plane Circular-Orbit Cone-Beam Brain SPECT This proposal develops a new approach to cone-beam single-photon emission computer tomography (SPECT) using two or more cone-beam collimators with different focal planes. The SPECT camera requires a lead collimator that determines if projection views are taken along parallel lines or along converging lines. Cone-beam collimators offer a better resolution/noise trade-off than parallel collimators, but they have one primary disadvantage; views taken with a cone-beam collimator in a single circular orbit about the patient do not constitute complete tomographic data except in the focal plane of the cone. This results in distortion in the reconstructed image that worsens with distance from the focal plane. This proposal improves on circular-orbit cone-beam by taking advantage of available multi-camera SPECT systems. The new approach uses a matched pair of cone-beam collimators with different focal planes so that the two cameras acquire data in two different cones with a single circular rotation of the gantry. This reduces distortion and expands the usable field-of-view. The specific aims are: 1. To evaluate the feasibility of dual-plane cone-beam SPECT by developing a realistic simulation models and implementing iterative reconstruction algorithms. 2. To implement dual-plane cone-beam SPECT on a clinical SPECT system by evaluating various collimator designs, developing methods to characterize the constructed collimators and performing experiments on plastic phantoms. 3. To evaluate dual-plane cone-beam SPECT in terms of quantitative accuracy by generating realistic simulations of dual-plane cone-beam SPECT data for slab and brain phantoms and computing mean, variance, and covariance data from these simulations. 4. To evaluate dual-plane cone-beam SPECT in terms of observer detection performance. The improved spatial resolution expected from the dual-plane system will allow physicians to better visualize smaller tumor and non-tumor structures. The technique can be used on existing multi-detector SPECT systems with only the addition of the special collimator pair and reconstruction software. Lothar Lilge, Ph.D. Assistant Professor, Department of Medical Biophysics Ontario Cancer Institute (RG-98-0144) Toronto, ON Dosimetry for Photodynamic Therapy of Barrett's Esophagus and Non-Resectable Brain Tumors Photodynamic Therapy (PDT) is the use of light-activated drugs or photosensitizers (PS) to produce cytotoxic substances for the treatment of cancers and other diseases. Since the malignant tissue selectively absorbs and retains PS, the treatment is very localized and can be completed in a single session. The project will focus on PDT dysplasia in Barrett's esophagus as an example of a surface/cavity treatment and PDT of non-resectable brain tumor as an example of an interstitial treatment. The Photodynamic Threshold and the Oxygen Consumption Models will be evaluated and/or modified for either of the two treatments. Finally, the benefit(s) of dosimetry-guided PDT in the two applications will be demonstrated through incorporation into ongoing clinical trials. These general objectives translate into the following specific aims. 1. Evaluation of multitasking fiber optical probes for their use in clinical PDT. 2. Design of clinical systems for photosensitizer, molecular oxygen and fluence-rate monitoring during PDT in compliance with clinical requirements for probe and source placement in PDT for dysplasia in Barrett's esophagus or non-resectable brain tumors, with focus on adequate spatial and temporal sampling of three biophysical parameters. 3. Evaluation and/or development of mathematical models of tissue response to PDT for their relevance of PDT dosimetry to guide treatment. 4. Determination of the feasibility and limitations of PDT dosimetry for two different clinical indications by incorporation of the developed PDT-dosimetry into ongoing clinical trials of PDT. There is a large difference in the use of dosimetry for radiotherapy and PDT. The use of average injected drug and administered light doses is most likely the major cause of frequent treatment failure or over-treatment, discouraging physicians from further use of this modality and accepting PDT as a minimally invasive oncological treatment. Engineering approaches to individualized dosimetry, to increase efficacy of PDT, will have an important impact on the success of this treatment modality. Thomas M. Moriarty, M.D., Ph.D. Assistant Professor, Department of Neurological Surgery University of Louisville Research Foundation, Inc. (RG-98-0009) Louisville, KY 3-D Navigation Through the Human Brain: A Computer Vision-Based System for Endoscopic Surgery The goal of this project is to develop a system for image-guided, minimally-invasive neurosurgical technologies. This system will be based on integrating advanced modules for data acquisition, volume segmentation, registration, display, and eventually implementation in the operating rooms of the University of Louisville hospitals. This project specifically addresses one question of registration: can 2-D, high-resolution intra-operative images from a neuroendoscope be rapidly registered to a 3-D representation of the patient's brain, and if so, can this be used as neuronavigational aid in the routine practice of neuroendoscopy? The goals are 1) to develop an accurate registration approach that maps 2-D video images obtained by a miniature endoscopic camera into their corresponding structural position on a 3-D model of the human brain constructed by a pre-operative CT or MRI scan; and 2) to use this 3-D to 3-D registration to interactively guide the miniature surgical tools during minimally invasive surgical procedures. The specific aims are to: 1. Develop a quantitative measure for the quality of segmentation. 2. Develop an accurate registration approach that maps 2-D video images obtained by a miniature endoscopic camera into their corresponding structural position on a 3-D model of the human brain constructed by a pre-operative MRI scan. 3. Use this 2-D to 3-D registration to interactively guide the miniature surgical tools during minimally invasive surgical procedures. The findings of this project will lend themselves to future research and development in image-guided surgery. The concepts will be readily transportable to endoscopic applications in other surgical disciplines. Charles W. Patrick, Jr., Ph.D. Assistant Professor University of Texas M.D. Anderson Cancer Center (98-0147) Houston, TX In vivo Analysis and Control of Neovascularization in a Tissue Engineered Construct Tissue engineered constructs (TECs) for replacement of diseased, non-functioning, or missing tissues need an adequate blood supply. This proposal addresses the seemingly simple, but mechanistically complex, issue of providing TECs a microvascular network. It is hypothesized that the underlying extent and rate of TEC neovascularization can be quantified and enhanced by incorporating microvascular fragments (MVFs) and/or angiogenic factor-loaded micro particles within TECs. Ideally, incorporated MVFs will inosculate rapidly with host capillaries and angiogenic factors released from attempts to mimic a conventional tissue graft, the current gold standard for tissue replacement. The specific aims of this project are to: 1. Determine the temporal and spatial patterns of neovascularization and hypoxia within a model in vivo TEC using a 3D quantitative imaging technique developed in preliminary studies. Two TEC microenvironments will be assessed: poly (lactic-co-glycolitic acid) (PLGA) polymer foam and fibrin. In each TEC microenvironment, microvascular architecture parameters and hypoxia distribution will be measured spatially and temporally. 2. Enhance TEC neovascularization by incorporating MVFs in the model TEC and determine the extent of implanted MVF inosculation with recipient capillaries. 3. Enhance TEC neovascularization further by adding biodegradable micro particles loaded with vascular endothelial growth factor (VEGF). Particle size distribution, cumulative release kinetics, and bioactivity of the micro particles will be assessed prior to use in vivo within TECs. 4. Determine the extent to which model TECs possessing MVFs and VEGF-loaded micro particles ensure the viability of seeded parenchymal cells. Tissue engineering has great potential in extending the quality and extent of patient life and significantly reducing the cost of health care by providing TECs for replacement of diseased, non-functioning, or missing tissues. This can only come to fruition, however, if an adequate blood supply is available to nourish TECs. Bruce Pike, Ph.D. Assistant Professor, Department of Neurology and Biomedical Engineering Montreal Neurological Institute (RG-98-0196) Montreal, QC Magnetic Resonance Imaging of Cerebral Oxygen Consumption and Perfusion Functional MRI (fMRI) techniques attempt to go beyond the study of simple anatomy to detect brain activity noninvasively in living humans. To date, however, fMRI methods have been largely qualitative in nature with the measured signals representing a complex interaction of more fundamental physiological processes. The goal of this proposal is to advance the state-of-the-art in quantitative fMRI methods and to use the newly developed techniques to elucidate the mechanisms that link focal changes in brain activity to changes in blood flow and oxygen metabolism. The specific aims of this project are to: 1. Develop new MRI methods to simultaneously and continuously measure cerebral blood flow and oxygenation. 2. Combine this data with a mathematical model to calculate the metabolic rate of oxygen consumption. 3. Use these techniques to study the physiological response of the brain to specific visual stimuli. Functional information has traditionally been obtained using tracer techniques in which a radioactive substance is injected into the blood stream, or inhaled, and detected as it passes through the brain. The research proposed here would produce alternate, MRI-based techniques that allow repeated and detailed study of normal subjects and patients. The visual stimulation studies will answer important fundamental questions about brain physiology that are also key to the understanding of current qualitative fMRI methods. Functional brain mapping using MRI has tremendous potential as a tool for basic neuroscientific investigation as well as clinical diagnosis and monitoring. However, critical questions regarding the general applicability of the most commonly employed technique remain unanswered. This proposal directly addresses these important issues. David J. Reinkensmeyer, Ph.D. Assistant Professor, Department of Mechanical and Aerospace Engineering University of California at Irvine (RG-98-0004) Irvine, CA Mechatronic Rehabilitation for Arm Movement after Stroke Stroke causes a variety of physiological changes that can limit movement, including changes to neural pathways, reflex circuits, muscle, and connective tissue. The severity of these changes varies from patient to patient. Currently, there exists a need in rehabilitation practice for better techniques for evaluating these changes. In particular, being able to objectively assess the relative contributions of different motor impairments to reduced movement ability would greatly improve treatment planning. The goal of this project is to develop such an improved assessment capability for the arm using a new device. The device, called the "ARM Guide," combines mechanical, electronic and computer (i.e. "mechatronic") technology to allow measurement of hand position and force generation during reaching movements. It can also guide and assist the arm during reaching. The device will allow the PI to determine the relative impact of different motor impairments. The general objective is to assess the relative contributions of neurological and mechanical factors to reduced movement ability after stroke. In particular, the PI will develop techniques for distinguishing the mechanisms of decreased range of motion using a computer-controlled linear bearing that can measure and assist in the movement of the arm. The specific aims are to: 1. Evaluate the effects of impaired multi-joint feed forward control on active range of motion of reaching. 2. Evaluate the effects of intrinsic mechanical and reflexive restraint on active range of motion of reaching. Both the device and the analysis techniques to be developed in this project could significantly improve clinical diagnosis and rehabilitation after stroke. Brian T. Saam, Ph.D. Adjunct Assistant Professor, Department of Physics Washington University (RG-98-0043) St. Louis, MO MRI of Lung Ventilatory Function with Hyperpolarized 3He The goal of this project is to develop magnetic resonance imaging (MRI) using hyperpolarized (HP) 3He gas into a technique which depicts and quantifies the real-time flow of gas into an out of the lungs. The focus on lung ventilatory function is directly tied to the long-range goal of improving the understanding of and treatment for emphysema and, more generally, chronic obstructive pulmonary disease (COPD). This three-year project aims to solve the significant engineering problems in applying HP-3He MRI to real-time lung ventilatory function, and to evaluate both healthy and diseased volunteers with the newly developed MRI techniques as a precursor to a possible future clinical study. The specific aims are: 1. To improve methods for polarization, storage, and administration of HP 3He for use in MRI. 2. To design and optimize the imager hardware and software specific to HP-3He MRI of lung ventilatory function. 3. To develop a method for quantifying regional human-lung ventilation based on HP-3He MRI with temporal resolution of a few tenths of a second. The PI will first determine the wall relaxation mechanism(s) in 3He polarization vessels and find a protocol to consistently produce slowly relaxing and reusable vessels to yield maximum polarizations. Then he will develop, implement, and test a modified echoplanar imaging (EPI) pulse-sequence to optimize the use of a single bolus of inhaled 3He gas for rapid repetitive imaging of lung ventilatory function. Finally, he will separate the effects of oxygen, rf excitation, and diffusion on the 3He magnetization to determine regional 3He concentrations in the lung. Dynamic HP-3He MRI, based on the EPI strategy proposed will provide both good spatial resolution and good temporal resolution, with repetitive cross-sectional images of the entire lung spaced by a few tenths of a second. The technique will assess physiologic function in emphysematous and normal lung regions in under 1s. Ann Marie Sastry, Ph.D. Assistant Professor, Department of Mechanical Engineering and Applied Mechanics The University of Michigan (98-0217) Ann Arbor, MI Investigation of Failure Mechanisms in Peripheral Nerves This research seeks to provide a mechanical explanation and model for the pathology of damage in peripheral nerves, using diabetic neuropathy as a test example for the modeling effort. Complications of diabetic neuropathy and its effects on both rat and human nerve tissue have been well documented, providing an excellent database to test the damage simulations performed in this proposed research. The research will combine experiments that determine material properties of nerve tissue with statistical methods that analyze the damage progression in these materials. The goal is to characterize damage modes and assess the effects of local damage on conduction. The proposed research will consist of the following tasks:1. Atomic For Microscopy (AFM) will be used to mechanically characterize the primary microstructures of diabetic and normal rat sciatic nerve and their interfacial properties. 2. An AFM and a voltage clamp technique will be used to assess the effect of electrophysiological stimulus on mechanical properties of nerve tissue in an unmyelinated squid giant axon. 3. A novel micromechanical model based on transport analysis will be developed to predict the mechanical behavior of nerves under multiaxial loads. 4. Computer simulations of damage progression will be performed, combining the micromechanical models for mechanical damage over time with the transport models to assess loss of conductivity of particular microstructures. 5. Progressive damage simulations will be compared to rat and human databases of damaged and undamaged nerve morphology and conduction velocities. It is anticipated that the proposed research will provide an important link in understanding the mutually exacerbating metabolic and vascular causes of peripheral neuropathy. Christine E. Schmidt, Ph.D. Assistant Professor, Department of Chemical Engineering University of Texas at Austin (RG-98-0158) Austin, TX Quantitative Analysis of Neurite Outgrowth in Response to an Electrical Stimulus Despite the evidence that electrical charges can significantly enhance nerve regeneration, the fundamental cellular mechanisms for this effect are unclear. In the proposed research, the goals are to elucidate the underlying mechanisms of electrically-stimulated neurite outgrowth and to quantify the extent to which neurite outgrowth is enhanced via electrical stimulation. To gain a fundamental mechanistic understanding of how neurite outgrowth and nerve regeneration are affected by an electrical stimulus, the PI will attempt to identify the factors that induce regeneration at the cellular level. Therefore, she will investigate and model the motility of the growth cone, the portion of the axon which actively guides neurite outgrowth. Specifically, she will determine whether electrical conduction through polypyrole (PP) directly modifies various extracellular and intracellular events which are critical for growth cone motility. Furthermore, she will develop a mathematical mode which incorporates results from the fundamental mechanistic studies described below to describe neurite outgrowth in response to an electrical stimulus. The specific aims are:1. Test hypotheses for neurite outgrowth in response to an electrical stimulus. 2. Formulate a model for neurite outgrowth in response to an electrical stimulus. There are 235,000 Americans suffering from debilitating spinal cord injuries and injuries to peripheral nerves are in fact much more common. Unfortunately, there is no effective treatment for paralysis and current therapies for peripheral nerve damage are far from ideal. The proposed studies will be a crucial first step toward the creation of an experimental and quantitative framework for linking the fundamental mechanisms of growth cone motility to neurite outgrowth and nerve regeneration. The ultimate goals of this research are to predict, a priori, the effective level and duration of an electrical stimulus required for nerve regeneration, and to determine key molecular targets for manipulation to improve nerve regeneration. Robin Shandas, Ph.D. Assistant Professor, Department of Pediatrics/Mechanical Engineering University of Colorado Health Sciences Center (97-0162) Denver, CO Fluid Mechanics of Ventricular Filling Diastolic function has been shown to be a good reflector of overall cardiac health, and cardiologists continue to search for parameters that quantify diastolic function. However, current techniques such as measuring the ratio of peak diastolic (E-wave) blood flow velocity to atrial contraction velocity (A-wave) using ultrasound Doppler or examining left ventricular wall motion using echocardiography have been shown to have poor specificity and sensitivity. These methods may also not be able to distinguish between decreasing yet normal diastolic function due to aging and depressed function due to disease until the disease has progressed significantly. The PI proposes to improve these techniques by applying fundamental principles of fluid mechanics to analyze the filling dynamics of the left ventricle, and thereby examine the relationship between the dynamics of the filling vortices to physiological changes in diastolic function. The main hypothesis is that the left ventricular inflow vortex plays a substantial role in efficiently transferring left atrial blood to the left ventricle, and that changes in physiology cause concomitant changes in the properties of the inflow vortex. A sub-goal of this project will be to develop precise metrics of fluid mechanical efficiency in ventricular filling, and to test these metrics on in vitro and animal models. The specific aims of this project will be: 1. Develop fluid mechanics standards for the definition of hydrodynamic filling efficiency during ventricular inflow. 2. Examine the relationship of the above-derived efficiency parameters to flow dynamics of the filling vortex in vitro and animal models of normal and abnormal ventricular inflow. 3. Correlate the above-developed efficiency parameters to a gold standard of diastolic function (the time constant of ventricular relaxation) in normal and diseased conditions. This project will yield a substantial amount of basic and clinically relevant information regarding the role of vortex structures within the heart and the use of vortex properties as clinical parameters of diastolic function. William Tao Shi, Ph.D. Assistant Professor, Department of Radiology Thomas Jefferson University (98-0033) Philadelphia, PA Subharmonic Imaging and Subharmonic-Aided Pressure Estimation with Microbubble-Based Ultrasound Contrast Agents This research project will explore the implementation of subharmonic imaging (SHI) and subharmonic-aided pressure estimation (SHAPE) using microbubble-based ultrasound contrast agents. The aim of SHI is to produce "microbubble-only" images, which will improve the depiction of blood flow in vessels and tissue by enhancing echoes from microbubbles within blood (due to their strong subharmonic response) and suppressing tissue information (due to its weak subharmonic generation). SHAPE has the potential to be a non-invasive technique to measure changes in pressure. The specific aims of the proposed project are: 1. To characterize and identify contrast agents with strong subharmonic response and agents whose subharmonic response is sensitive to changes in ambient pressure. 2. To develop a theoretical model describing the dynamics of contrast microbubbles set in motion by acoustic pulses. 3. To investigate the response of a single microbubble and the collective behavior of a cloud of microbubbles. 4. To explore new transmit and receive strategies and techniques based on the numerical simulation and experimental investigation. 5. To implement SHI and SHAPE with the proposed strategies or strategies to be developed. 6. To evaluate SHI and SHAPE in vitro and in vivo. The non-invasive estimation of pressures in heart cavities and major vessels would provide clinicians with an invaluable tool for assessing patients with valvular heart disease, congestive heart failure as well as portal hypertension and various other vascular diseases. Molly S. Shoichet, Ph.D. Assistant Professor, Department of Chemical Engineering and Applied Chemistry University of Toronto (98-0179) Toronto, Ontario Designing a Synthetic Graft to Enhance Axonal Regeneration After CNS Injury Traumatic spinal cord injury (SCI) is a devastating clinical condition for which there is no effective treatment. In SCI, the communication pathways between the brain and the rest of the body are interrupted because of damage to the nerve fibers that normally carry messages along the spinal cord. This results in a loss of function below the site of injury and lifelong disability for the patient. To overcome injury in the central nervous system (CNS), damaged nerve fibers must be encouraged to regrow across the injured site and to reestablish communication between the brain and the periphery. The overall hypothesis is that regeneration of CNS nerve fibers, across the site of injury and into the CNS tissue, can be enhanced by the use of a synthetic graft that combines 1) an adequate pathway for regeneration with 2) causes for regeneration and 3) molecules to neutralize inhibition. The specific aims include: 1. To provide an adequate pathway for regeneration, a parallel array of guidance fibers will be aligned within a hollow fiber membrane (HFM). 2. To provide cues for nerve regeneration within the HFM, the guidance fibers will be modified with peptides to stimulate nerve fiber regeneration. 3. To overcome the chemical inhibitors of regeneration, antibodies that neutralize the inhibitory factors in the CNS will be released in a controlled manner from the HFM. 4. To assess the significance of the design in vivo, the graft will be implanted in a transected nerve first in the periphery and then in the CNS. If successful, this research may lead to pre-clinical trials with the aim of maximizing potential neurologic recovery after chronic human SCI. In striving to fill the therapeutic void of SCI, this research seeks to better understand the design criteria required for regeneration and re-innervation of CNS axons. David Solomon, M.D., Ph.D. Assistant Professor, Department of Neurology University of Pennsylvania (RG-97-0496) Philadelphia, PA Three-Dimensional Gaze and Posture Control During Turns and Tilts The vestibular system provides sensory information crucial for gaze stabilization, maintenance of equilibrium and navigation, mechanisms important in the control of locomotion. The proposed research will investigate the nature of vestibular signals arising in the labyrinth during turning in human subjects. A unique vestibular stimulator is being developed by the PI to deliver linear and angular accelerations to standing subjects, reproducing components of motion the body undergoes when walking around a corner. Measurement of eye and head position in three dimensions, and monitoring of ground reaction forces will establish the input-output relationships between afferent vestibular and somatosensory information and postural and gaze motor activity. During the everyday act of turning a corner, the head and body undergo a rotation into a new direction and linear accelerations due to translation and gravity. The combination of tangential, centripetal and gravitational accelerations is described by a gravito-inertial acceleration (GIA) vector. The orientation of the GIA must be sensed and appropriate postural compensation must occur in order to avoid falling. The specific aims are to: 1. determine the reference frame in which the head is most stable during pivot turns. 2. characterize head tilt in the frontal plane with respect to the resultant gravito-inertial acceleration (GIA) and ocular motor responses to rotation of the GIA with respect to the head. 3. define the contexts in which changes in linear acceleration result in compensation for translation or tilt. Understanding how head-based labyrinthine information needs to be processed for gaze and postural stability will allow for further development of rational rehabilitation strategies for patients with balance problems and motion intolerance. Beth Sproule, Pharm.D. Scientist, Psychopharmacology Research Program; Assistant Professor, Faculty of Pharmacy, University of Toronto Sunnybrook Health Science Centre (RG-98-0051) Toronto, ON Fuzzy Logic Modeling in Clinical Psychopharmacology: Development and Evaluation of a Novel Approach Understanding the large differences in how people respond to medications is one of the most important goals of drug therapy. Progress in this area, especially for psychiatric medications, has been slow because of the complexity of problem. Fuzzy logic is a new computational approach able to model complex and uncertain data. The PI plans to conduct a series of studies over the next three years to systematically evaluate fuzzy logic modeling in clinical psychopharmacology. Mood stabilizers (lithium, valporic acid, carbamazepine) are widely used to treat patients suffering from bipolar mood disorders (manic-depression). The PI is looking for ways to better predict the response to these medications and determine optimal doses. First, she will collect clinical information from consenting patients receiving mood stabilizer therapy, construct and test fuzzy logic models, and then compare them with other modeling systems. The specific aims are: 1. To evaluate fuzzy logic modeling in the pharmacokinetic analyses of psychotropic drugs. 2. To determine the feasibility of fuzzy logic pharmacokinetic/pharmacodynamic modeling to answer clinical questions based on naturalistic clinical psychopharmacological data. 3. To refine the fuzzy logic modeling process as it applies to psychopharmacology. 4. To compare the performance of the fuzzy logic models developed in the previous three parts to the performance of more established modeling approaches using the same data. It is anticipated this research will significantly contribute to the understanding of the relationships between patient characteristics and drug factors with the goal of improving our ability to effectively and safely use psychotropic medications in the treatment of those suffering from mental illness. This approach could also have a wide applicability to other medications. Weihong Tan, Ph.D. Assistant Professor, Department of Chemistry and UF Brain Institute University of Florida (97-0425) Gainesville, FL Engineering an Optical Patch-Clamp Device for Single Ion Channel Recording Ion channels regulating the flow of ions across cell membranes are intimately involved in the maintenance of cell homeostasis. Ion channel activities and properties are studied using the patch-clamp technique. Recent advances in optical microscopy and spectroscopy have made it feasible to develop an optical patch-clamp (OPC) device to study and manipulate individual ion channels on a cell membrane. In OPC, near-field optics is combined with patch-clamp technique for biomedical applications. The general objective of this proposal is to develop an optical patch clamp for intracellular studies and for ion channel recording, imaging and manipulation. The specific aims are:
Michael Wendt, Ph.D. Assistant Professor, Department of Radiology and Biomedical Engineering Case Western Reserve University (RG-98-0188) Cleveland, OH Active Tip-Tracking for Interventional MRI Procedure Guidance It is the goal of this project to develop a set of magnetic resonance imaging hardware and software tools to permit minimally invasive interventional technology to be utilized in the modern treatment of lung cancer To achieve this goal a new technique will be developed that uses a large standard imaging coil to obtain an image of the region of interest (lung) and a small catheter-tipped micro-coil to provide high-resolution local images. The new active method for visualization and guidance will overcome drawbacks previous methods such as image artifacts, misregistration errors, and errors due to manual control. The PI will use the new devices to acquire images from within the body. The specific aims of this proposal are as follows: 1. Development of a technique to build micro-receive-coils (tip tracking coils - TTC). 2. Development of MR compatible circuit to permit switching between standard receiving coils and micro-coils. 3. Development of software tools for image acquisition and pre-processing. 4. Determining limiting factors, spatial errors, and biocompatibility. The successful completion of this research project will allow precise positioning of interventional tools during MR-guided procedures. This will provide the opportunity to obtain high resolution images of the tissue surrounding the tip of the interventional device to ascertain tissue information prior to biopsies or other medical assessments. |
Copyright 1998 The Whitaker Foundation
1700 North Moore Street, Suite 2200, Rosslyn VA 22209
(703) 528-2430 info@whitaker.org