Benjamin C. Weed

Experimental Evidence of Mechanical Isotropy in Porcine Lung Parenchyma

Pulmonary injuries are a major source of morbidity and mortality associated with trauma. Trauma includes injuries associated with accidents and falls as well as blast injuries caused by explosives. The prevalence and mortality of these injuries has made research of pulmonary injury a major priority. Lungs have a complex structure, with multiple types of tissues necessary to allow successful respiration. The soft, porous parenchyma is the component of the lung which contains the alveoli responsible for gas exchange. Parenchyma is also the portion which is most susceptible to traumatic injury. Finite element simulations are an important tool for studying traumatic injury to the human body. These simulations rely on material properties to accurately recreate real world mechanical behaviors. Previous studies have explored the mechanical properties of lung tissues, specifically parenchyma. These studies have assumed material isotropy but, to our knowledge, no study has thoroughly tested and quantified this assumption. This study presents a novel methodology for assessing isotropy in a tissue, and applies these methods to porcine lung parenchyma. Briefly, lung parenchyma samples were dissected so as to be aligned with one of the three anatomical planes, sagittal, frontal, and transverse, and then subjected to compressive mechanical testing. Stress-strain curves from these tests were statistically compared by a novel method for differences in stresses and strains at percentages of the curve. Histological samples aligned with the anatomical planes were also examined by qualitative and quantitative methods to determine any differences in the microstructural morphology. Our study showed significant evidence to support the hypothesis that lung parenchyma behaves isotropically.

Biomechanical Characterization of Sheep Vaginal Wall Tissue: A Potential Application in Human Pelvic Floor Disorders

Pelvic Organ Prolapse (POP) is a leading women’s health issue affecting a significant portion of the population and has been recently coined as a “silent epidemic”. POP leads to a considerable reduction in women’s quality of life and can cause chronic pelvic pain, sexual dysfunction, and social/psychological issues. The lifetime risk for having surgery for POP is approximately 11% with 200,000 POP procedures performed each year in USA, with an annual direct cost of over

Pelvic Floor Biomechanics from Animal Models

1000 million. Exact etiology of POP is unclear, but it is understood that POP is multi-factorial in nature. Risk factors for POP include increasing age, obesity, multiple vaginal births, gravidity, history of hysterectomy, smoking, chronic cough conditions, frequent heavy lifting, and some genetic factors. POP results due to loss or damage of structural supports that support the pelvic organs (i.e. rectum, bowel, bladder, etc). Vaginal wall prolapse (anterior and posterior) is the most common presentation. This can result from weakening of the levator ani muscle and other connective tissue structures which not only control the mechanical function, but also help support neurological and anatomical function[1].Copyright

Influence Of Microgravity On Left Ventricular Sphericity: A Finite Element Model Of The Heart

Pelvic organ prolapse (POP) is characterized by the failure of vaginal wall support and protrusion of the pelvic organs through the vaginal orifice. The exact etiology of POP remains elusive to date, and one of the primary hurdles is the limited availability of animal models, which provide a means to better understand the weakening of supportive tissues in POP and the mechanisms of treatment failures. Each animal model has its own set of advantages and disadvantages. In this chapter, we review the various animal models of POP and provide an indepth analysis of sheep as a robust large animal model for urogynecological research. The ease of handling, short lifespan, and relatively low costs are major advantages of rodent models, which have been used extensively to investigate connective tissue physiology and pathophysiology as it relates to POP. However, sheep have supporting structures for pelvic organs, as well as structural and mechanical properties more similar to humans. Many of the risk factors for sheep prolapse have close analogues in humans, including high fetal weight, obesity, dystocia, parity, and family history of prolapse. In addition, large animal models, such as sheep, are likely more appropriate for evaluation of novel therapeutic strategies for treatment. Future research using sheep and other animal models will illuminate the pathophysiology of POP as well as provide essential information on pelvic floor biomechanics and treatment efficacy.

Stress State Dependence of Human Placenta Mechanical Behavior

There is concern regarding the effects of microgravity exposure on cardiac function and loss of ventricular mass in astronauts. By Laplace’s law, the geometry of the ventricle is important in determining segmental wall stress and can induce alterations in myocardial mass. If microgravity exposure results in a variation in the ventricular radius of curvature, then we might also expect some cardiac remodeling during extended spaceflights. This study analyzes the theoretical impact of microgravity on changes in the geometric conformation of a finite element mesh model (FEM) created from the 3-dimensional geometry of the human left ventricle (LV) and attributed with material properties consistent with myocardial tissue. The Geometric Aspect Ratios (GAR, length to width quotient) of the LV were calculated and compared during simulations of the upright anatomic diastolic position in Earth’s gravity and in microgravity. The theoretical application of microgravity to the FEM model of the heart resulted in a 3.65% lower GAR of the LV as compared to that calculated for Earth’s gravity. This finding suggests that microgravity exposure could potentially result in changes in ventricular sphericity and radius of curvature and thereby alter the segmental myocardial wall stress.

Recellularization Potential of Acellular Aortic Valve Scaffolds Treated With Collagenase and Acetic Acid

Maternal trauma affects 5–8% of all pregnancies and is the leading nonobstetric cause of maternal death in the United States [1]. The most common cause of trauma is motor vehicle accident (MVA) and the most common pathology is abruptio placentae, detachment of the placenta from uterus, which leads to serious maternal and fetal consequences [2].Copyright

A comparative biomechanical analysis of term fetal membranes in human and domestic species.

It is estimated that five million Americans suffer from moderate to severe aortic valve disease, making it the third most common type of cardiovascular disease. Aortic valve replacement, which is second leading reason for undergoing open heart surgery, is the prevailing treatment for patients with extensive aortic valve pathologies. Currently, substitute valves used to replace the disease valves are classified as either mechanical or biological, each of which carry significant disadvantages. Patients with mechanical valves are at a much higher risk for developing blood clots and therefore must remain on anticoagulants for the remainder of their lifetime; and biological valves, which are typically derived from porcine or cadeveric tissues, will deteriorate over time. The ideal replacement valve is one that presents no thrombogenicity or immunogenecity, provides normal hemodynamics, is free of blood damaging elements, offers a practical mode for implantation, is able to grow and remodel, and does not deteriorate over time.© 2009 ASME