Flow Induced Cardiovascular Pathologies
Induction of angiogenesis by a biodegradable microparticle VEGF DNA delivery system
A Novel Approach to Identify and Separate Contributions of Autonomic Nervous Systems to Heart Rate Variability Using Principal Dynamic Modes
Discovery of molecular mechanisms in chronic atrial fibrillation
Novel approaches to imaging electrical activity in engineered cardiac cell constructs
Flow patterns and flow coordination in the microcirculation.
Molecular mechanisms of bone regeneration
Genetic variations determine the skeleton's sensitivity to anabolic signals
Biomechanics of Low Back Pain
A non-invasive diagnostic for osteoporosis
Low-level mechanical stimulus may prevent osteoporosis

Flow Induced Cardiovascular Pathologies.
Danny Bluestein, Department of Biomedical Engineering

Despite major progress, cardiovascular diseases remain the leading cause of death in the western world. One of the major culprits in cardiovascular disease and in devices designed to treat or restore impaired cardiovascular function, is the non-physiologic flow patterns that enhance the hemostatic response mainly through platelet activation. Platelets have long been regarded as the preeminent cell involved in physiologic hemostasis and pathologic thrombosis. An innovative technique for measuring flow induced platelet activation has been developed (in collaboration with Dr. Jesty from SOM), and its utility demonstrated in experiments conducted in recirculation devices (models of arterial stenosis, Left Ventricular Assist Device (LVAD), and mechanical heart valves). The mechanisms by which the non-physiologic flow patterns induce platelet activation and generate free emboli, that enhance the risk of cardioembolic stroke, was demonstrated in vivo with mechanical heart valves implanted in the sheep model (in collaboration with Drs. Krukenkamp & Saltman from SOM). The results of this research will aid in elucidating physical forces that regulate cellular function in flowing blood, and may be applied to improve the design of blood recirculating devices and to develop more potent drugs for treating cardiovascular diseases.

Induction of angiogenesis by a biodegradable microparticle VEGF DNA delivery system.
William Chen, Department of Biomedical Engineering

Direct intramuscular injection of VEGF DNA appears to be a promising approach for treating ischemic heart disease. However, repeated injection may be needed to realize the full potential of this experimental therapy. Our recent in vivo experiment has demonstrated that a biodegradable microparticle formulation intended for prolonged VEGF DNA delivery is capable of inducing angiogenesis in hindlimb muscle 6, 12, 18 and 36 weeks after injection. This sustained DNA delivery system will ensure the continual presence of VEGF to facilitate the maturation of newly formed blood vessels and thus their persistence. These results were presented at the October, 2001, meeting of Biomedical Engineers Society. The VEGF DNA microparticles will be used to induce angiogenesis in porcine chronic ischemic myocardium. In collaboration with Drs. Fu-Pen Chiang, Irvin Krukenkamp and Adam Saltman, we will be using two state-of-the-art diagnostic techniques, Computer Aided Speckle Interferometry (CASI) and Multi-Channel Electromapping (MCEM), to evaluate the functional recovery of revascularized myocardial tissue after injecting VEGF DNA microparticle. This will resolve the controversial issues on therapeutic angiogenesis.

A Novel Approach to Identify and Separate Contributions of Autonomic Nervous Systems to Heart Rate Variability Using Principal Dynamic Modes
Ki Chon, Department of Biomedical Engineering

We developed a method, modified Principal Dynamic Modes (PDM) method, which is for the first time able to separate the dynamics of sympathetic and parasympathetic nervous activities. The PDM is based on the principle that among all possible choices of expansion bases, there are some that require the minimum number of basis functions to achieve a given mean-square approximation of the system output. Such a minimum set of basis functions is termed PDMs of the nonlinear system. We found that the first two dominant PDMs have similar frequency characteristics for parasympathetic and sympathetic activities, as reported in the literature. These results are consistent for all nine of our healthy human subjects using our modified PDM approach. Validation of the purported separation of parasympathetic and sympathetic activities was performed by the application of the autonomic nervous system blocking drugs atropine and propranolol. With separate applications of the respective drugs, we found a significant decrease in the amplitude of the waveforms that correspond to each nervous activity. Furthermore, we observed near complete elimination of these dynamics when both drugs were given to the subjects. Comparison of our method to the conventional low/high frequency ratio shows that our proposed approach provides more accurate assessment of the autonomic nervous balance. Our nonlinear PDM approach allows a clear separation of the two autonomic nervous activities, the lack of which has been the main reason why heart rate variability analysis has not had wide clinical acceptance.

Discovery of molecular mechanisms in chronic atrial fibrillation.
Anil Dhundale, Center for Biotechnology and the Department of Biomedical Engineering

Atrial fibrillation is the most common cardiac arrhythmia seen in cardiology practice today. At Stony Brook University Hospital cardiovascular surgeons perform hundreds of open heart surgery each year as well as investigate vascular disease. A collaboration, between Adam Saltman (Surg), Glenn Gaudette (BME and Surg), Kenny Ye (AMS) and Anil Dhundale (BME), is exploring the molecular basis of chronic atrial fibrillation utilizing DNA microarray technology. An initial broad survey of approximately 12,000 genes has offered clues to the genes differentially regulated in a disease which affects over 3 million patients in the United States alone. Beyond characterization of this mechanism is the discovery and validation of potential diagnostic and therapeutic gene targets for drug discovery, and the long term goal to identify pharmaceuticals specifically targeted to treatment of this devastating disease.

Novel approaches to imaging electrical activity in engineered cardiac cell constructs.
Emilia Entcheva, Department of Biomedical Engineering

A novel optical mapping approach was developed - a cost-effective all-solid-state system combining ultra-bright light emitting diodes and thin plastic emission filters in fluorescence measurements of transmembrane potentials and intracellular calcium in cardiac cells. The versatility of the semiconductor light sources is demonstrated through action potential recordings under electronically modulated light - a useful feature for phase-lock detection or excitation-ratiometric measurements. The system is applied to map electrical activity on the millimeter scale in monolayers of cultured neonatal rat ventricular cells, as well as in engineered cardiac fibers grown in custom-made microgrooved biomaterials. Mapping of normal propagation and capturing arrhythmic behavior in the cardiac cell constructs illustrate the use of the developed imaging system, which could be a valuable tool in evaluation of the viability of tissue engineering constructs and the impact of drug prophylaxes. Dr. Entcheva will present this work at the Annual BMES Meeting in Durham, NC in 2001.

Flow patterns and flow coordination in the microcirculation.
Mary D. (Molly) Frame, Department of Biomedical Engineering

Our emerging understanding of oxygen delivery to the tissues is that the blood flow within the smallest arterioles is tightly organized within repeating networks across the tissue. Central to this paradigm are the concepts of vascular communication between the beginning and end of the network (via gap junctions), and its relation to flow sensing by the vascular endothelium. Our work has shown that different types of microvascular flow patterns can be triggered by direct stimulation of the focal adhesions (alpha-v-beta-3 integrins, i.e., wound healing), compared to adenosine (i.e., metabolic change), compared to nitric oxide (i.e., inflammation), hence we can control the flow patterns. Among the goals of this work are in vitro construction of transplantable microvascular networks, using bionanotechnology to create the sturdy scaffolding, and verification of nanofabricated drug delivery units within the vasculature. To this end, equally important are mechanotransduction of the physical forces associated with flow change (i.e., wall shear stress), the pharmacologic signal transduction systems involved (which guide drug discovery and intervention), and the molecular basis for the committed step that ensures healthy flow delivery. Our work employs computational modeling of the fluid mechanics, the physiology of arteriolar network blood flow (in vivo and in vitro), and precise genomic manipulation of key proteins in healthy and vascular disease states.

Molecular mechanisms of bone regeneration.
Michael Hadjiargyrou, Department of Biomedical Engineering

Delayed or non-union of bone fractures is a crippling condition which effects over 200,000 people per year. Dr. Hadjiargyrou's research provides unique insight into the molecular mechanisms that underlie the wound healing (i.e. fracture repair) process, and thus may provide novel approaches to augment, accelerate and/or ensure healing. In an effort to identify the vast array of genes involved in the bone regeneration process, Dr. Hadjiargyrou's group constructed a PCR-select cDNA library consisting of induced clones pooled from RNA isolated from the fracture calluses at day 3, 5, 7, and 10, and subtracted against RNA derived from an intact, control bone (includes cartilage and bone marrow). Over 5,000 cDNA clones were then sequenced and their identities examined using bioinformatic analyses. As reported in the October 2001 meeting of the American Society of Bone and Mineral Research, the simultaneous expression of all genes represented in this callus-specific library were established using custom-spotted cDNA microarrays, and bioinformatic analyses used to functionally cluster the thousands of novel genes identified. This work will facilitate a greater understanding of the process of bone development and regeneration, and help to identify gene candidates for therapeutic intervention to ensure rapid and appropriate repair of musculoskeletal tissues.

Genetic variations determine the skeleton's sensitivity to anabolic signals.
Stefan Judex, Department of Biomedical Engineering

The structure of the adult skeleton is determined, in large part, by its genome. Recent data by Dr. Stefan Judex indicate not only a genetic basis for bone architecture, but also that the sensitivity of bone tissue to both anabolic and catabolic stimuli is influenced by sbutle genetic variations. Using different strains of mice, this study showed that stimuli which are strongly anabolic in the skeletal tissue of one cohort, failed to initiate a response in other strains. Similarly, signals which stimulated resorption of bone from one strain failed to initiative a response in other strains of mice. Extrapolated to humans, these results may in part explain why prophylaxes for osteoporosis are not universally effective, yet also indicate that there may be a genotypic indication of people who are at reduced risk of suffering from the disease.

Biomechanics of Low Back Pain.
Partap Khalsa, Department of Biomedical Engineering

Recent findings from the Somatosensory Spine Research Laboratory have shown that certain spine ligaments could provide a biomechanical basis for spine proprioception. A theory of low back pain due to non-traumatic mechanical causes posits that mechanically sensitive neurons innervating the ligamentous joint capsules in the spine are necessary for accurate encoding of spine motion. Inaccurate "feedback" from these neurons may result in altered coordinated muscle control of the vertebra during normal motions, eventually resulting in pain. Jon Chiu, a PhD candidate in Biomedical Engineering, has just published his Master's Thesis in which he found that joint capsule plane strains provide a reliable code that could be used by proprioceptive neurons to encode spine motion ("Facet Joint Capsule Strains of Human Lumbar Spine Specimens during Physiological Motions, BME Master's Thesis, Sept. 2001). Chiu's co-investigators were Avi Baitner, MD (an orthopaedic resident) and Partap S. Khalsa, D.C., Ph.D. (Chiu's Advisor and Director of the Somatosensory Spine Research Laboratory).

A non-invasive diagnostic for osteoporosis.
Yi-Xian Qin, Department of Biomedical Engineering

Early diagnostic of osteoporosis allows for accurate prediction of fracture risk and effective options for early treatment of the bone disease. A new ultrasound technology, based on focused transmission and reception of the acoustic signal, has been developed by Dr. Qin and his team which represents the early stages of development of a unique diagnostic tool for the measure of both bone quantity (density) and quality (strength). Dr. Qin presented part of this work at the annual meeting of Am. Society of Bone Mineral Research. These data show a strong correlation between non-invasive ultrasonic prediction and micro-CT determined bone mineral density (r>0.9), and significant correlation between ultrasound and bone stiffness (r>0.8). Considering the ease of use, the non-invasive, non-radiation based signal, and the
accuracy of the device, this work opens an entirely new avenue for the early diagnosis of metabolic bone diseases.

Low-level mechanical stimulus may prevent osteoporosis.
Clinton Rubin, Center for Biotechnology and the Department of Biomedical Engineering

Encouraging results show that the application of extremely low levelstrains to animals and humans will increase bone formation, and thus may represent the much sought after "anabolic" stimulus in bone. More than 15 years of research into non-invasive, non-pharmacological intervention to control osteoporosis, was referenced in Dr. Clint Rubin's recent paper published in the journal Nature (August 9, 2001; 412:603-604). Dr. Rubin's studies suggest that gentle vibrations on a regular basis will help strengthen the bones in osteoporosis sufferers and increase bone formation. In his study, adult female sheep treated with gentle vibration to their hind legs for 20 minutes daily showed almost 35% more bone density.