Bone Mechanics
Methods in these studies span a broad range of activities including experimental, theoretical, and computational techniques. One project concerned with bone behavior is focused on understanding the ability of living bone to adapt its form to match its function. Analytical and experimental studies of theoretical bone adaptation models are continuing in parallel with the development of the Finite Element Method as a tool for studying and predicting the shape and material property response of living bone to applied loads and metabolic changes.
Soft Tissue Mechanics / Joint Mechanics
Experimental, theoretical and computational studies in this area begin at the level of the whole joint and range down to the function of the cells within the tissues that guide and stabilize joint motion. Particular emphasis is placed upon the kinematics of joints, the function of soft tissue structures (e.g. ligaments, cartilage) under overall joint loading, the cellular response to mechanical loading, and modelling of the finite and time-dependent deformation of musculoskeletal soft tissues. Current research projects include: the application of multi-DOF sensors and manipulation systems to knee mechanics, determination of the in-situ forces and strains in normal and reconstructed connective tissues, the effect of mechanical stimulation on the metabolic response of articular cartilage, healing mechanisms in damaged cartilage, and current experimental and clinical techniques to promote healing.
Ocular Biomechanics
A long-established collaboration with the LSU Eye Center allows for research into the structure and function of the eye and its tissues. Current projects include coupled experimental and computational studies of the eye subjected to increased internal pressure; various studies related to vision and optics; and fluid mechanics of the blood flow and nutrients in the eye and cornea.
Pulmonary Mechanics
The goal of these studies is to understand the interaction of the fluid and mechanical properties of the pulmonary system. One aim is to explain the role of pulmonary surfactant in influencing the mechanical and geometrical characteristics of the airways. The knowledge gained from these studies may be useful in the development of new therapeutic approaches towards the reversal of deranged pulmonary mechanics caused by airway closure or insufficient surfactant production, and the commensurate decrease in gas exchange. Current topics of interest include (i) studies of mechanics of pulmonary airway reopening, and (ii) studies of the dynamic behavior induced by localized surfactants on the surface of the lung's thin liquid lining. Both theoretical and computational analyses are used in these investigations, and are augmented by results from benchtop and excised-lung experiments.
Another major direction of the research is in the study of the transport of respiratory gases and suspended particles and solutes through the lung. Since such transport is dependent on both convection and diffusion, the understanding of its mechanisms requires knowledge of the flow field in which the transport takes place. Both transport studies and flow measurements are carried out in these experiments, making extensive use of in vitro bronchial airway models.
Brain Biomechanics
Traumatic brain injuries are often fatal and result in a total loss of consciousness or death, and even those who have experienced a mild brain injury are disposed to a risk of progressive sequences leading to secondary neurological disorders, such as retrograde amnesia. Traditionally, brain tissue has been modeled either as an elastic or viscoelastic solid material or as a pure fluid encapsulated in the skull, and such models have been used in most of the theoretical analyses of traumatic brain injuries. Brain tissue, however, is a solid network of neurons saturated with cerebrospinal fluid, and thus it is more plausible to describe brain tissue as a mixture of solid and fluid components rather than as a single phase material. Furthermore, because the brain is completely bathed in the cerebrospinal fluid environment, a solid-fluid interaction at the brain-skull interface would play an important role in governing the mechanics of brain tissue under an impact load. Therefore, the major goal of the study is to develop a physiologically reasonable material and structural model for brain, which is based on the structural composition of brain, i.e., a mixture of solid and fluid components. This model will allow us not only to analyze the solid-fluid interaction in the brain biomechanics but also to study the role of the interstitial fluid component in the material behaviors of the brain tissue during impact.
Brain Physics
Research on EEG and evoked potentials is important to both medicine and psychology. Various brain states are correlated with specific spatial-temporal patterns of electrical activity in the cerebral cortex. The sources of this activity are likely to be nonstationary and distributed over large regions of tissue and may be studied with various computer and statistical methods. One immediate objective is the improvement of spatial resolution so that scalp recordings more accurately represent local neural sources. A number of related projects have been initiated: estimation of local skull resistance in living subjects, development of finite element models of the human head, recording from patients with chronic depth electrodes, computer analysis of auditory and visual evoked potentials, theoretical development of cortical imaging methods, nonlinear dynamic systems and theoretical analysis of the effects of neural interactions on EEG and evoked potentials. Students working in this area are necessarily exposed to a wide variety of experimental and theoretical work.
Cardiac Electrophysiology
Computer modeling is used as a tool to study the significance of cardiac tissue structure on the electrical behavior of the heart. One goal of this work is to understand how the complicated action potential kinetics of heart cells and the pathways for connections between cells interact in normal and pathologic cases. Another goal is to understand how the applied strong electric field interacts with the myocardium in therapeutic procedures such as defibrillation and cardioversion; this research is expected to contribute to the improved design of the future generation of antiarrhythmic devices. Research tools include finite element and finite difference models based on the three-dimensional myocardial fiber geometry of the heart. Projects underway include simulations of action potential propagation in ventricles and atria, modeling the distribution of the transmembrane potential induced in the myocardium during a defibrillation shock, post-shock arrhythmogenesis, and scientific visualization to study current flow paths from simulated and experimental data.
The labs emphases are on development of electronic devices that will improve patient care in the home and hospital environments. Recent projects have included the development of a noninvasive cerebral hypoxia monitor, an implantable early warning system for edema secondary to congestive heart failure, and a new device for rapid delivery of therapeutic agents to the anterior segment of the eye. Ongoing relationships with the clinical departments at Tulane Medical Center present additional opportunities for patient oriented research.
Surgical Implant & Dental Materials
Research in the Surgical Implant and Dental Materials Laboratory is mainly concerned with study of the factors that govern the durability and suitability of materials for use in various surgical applications. Present work is directed primarily toward further understanding of the corrosion behavior and biocompatibility of implant and dental alloys, investigation of bioadhesion, and studies related to environmental science and biosensors. Specific topics being studied include corrosion products released from metals used in orthopaedic applications, investigation of the interaction between applied stresses and implant corrosion processes, electrochemical behavior of dental materials, and cell and bacterial adhesion to orthopaedic materials. Application of chemical analysis, biosensors, and toxicity measurements to biomedical and environmental problems are other areas that are featured. Facilities which are available for biomaterials research include computerized electrochemical and polarographic measurement systems, a computer controlled servo-hydraulic universal mechanical testing apparatus, metallurgical furnaces, metallographic and histologic specimen preparation equipment, microscopic examination and photographic equipment, cell culture apparatus, and a toxicity analyzer.
Pulmonary Function
Research in pulmonary function is directed towards developing sensitive and specific noninvasive indicators of pulmonary and cardiopulmonary status and also concerns the basic nature of air flows and gas transport. Spirometry is currently the method of choice for assessment, diagnosis and monitoring of airways disease. Spirometry, however, requires a high degree of strenuous cooperation by the patient and lacks the ability to detect disease before it becomes irreversible. Acoustic methods, using both natural and induced sounds, provide a means for assessing lung health noninvasively, even in non-cooperative subjects. Present work concentrates on further understanding of how sound travels in the structures of the lung and in relating acoustic measurements to clinically important variables. In addition, work includes mapping and display of sound fields, ultrasound, cardiopulmonary interaction, noninvasive hemodynamic measurement, and other bioacoustic phenomena.
Cell / Tissue Engineering
Cell/tissue engineers combine principles from engineering disciplines with techniques from biology and chemistry in order to control select functions of living cells and tissues. The experimental cell and tissue engineering laboratories at Tulane are the site of multiple, collaborative projects, which can be broadly grouped by tissue type: bone, lung, nerve, eye, and bone/soft tissue interface. Bone-related studies include mechanochemical stimulation of bone cell functions, chemical modification of dental/orthopaedic biomaterials with bioactive ligands to control cell-material interactions, manipulation of bone marrow stromal cell phenotype to produce bone-forming cells, bone-resorbing cells, and the development of polymeric scaffolding materials appropriate for generating bone tissue in vitro. Lung-related studies include experimental models of pulmonary airway opening, assessing lung epithelial cell damage caused by aspects of bubble progression through a fluid-occluded channel. These experimental models are coupled with computational pulmonary mechanics, allowing quantitative analysis of experimentally-induced micromechanical stimuli. The goal of the nerve tissue engineering group is to develop electrically excitable cells from a population of bone marrow derived-adult stem cells using a variety of chemical factors and electrical stimuli. Eye-related studies primarily focus on the use of tissue engineered optic nerve heads as models of glaucomatous degeneration. Combining these experiments with computer models of tissue degeneration will provide us with new insights into the progression of the disease and allow us to develop new interventions. Bone/soft tissue interface studies include the development of a simplified, model tissue-engineered ligament and ligament/bone interface as well as an exploration of the osteogenic capabilities of periosteal tissue applied at the bone/tendon interface.