Engineering Commons^™

Assessment Of Material Properties In Bone Surrounding Microdamage, Niovi Dollas

Dissertations and Theses

Bisphosphonates [BPs] are the mainstay for osteoporosis treatment. They suppress bone resorption/remodeling, preventing bone loss. However, BPs also suppress the beneficial bone remodeling that replaces microscopically damaged bone that occurs from normal mechanical wear-and-tear or fatigue, leading to impaired tissue material properties and in some instances atypical femoral fractures.

In these studies, we assessed the effects of acute fatigue, fatigue induced remodeling, and fatigue microdamage with remodeling suppression using the clinical BP, alendronate [ALN], on local bone material properties. Studies were performed on cortical bone sections from rat ulnae into which fatigue damage had been introduced in vivo. Rat …

Mechanically Driven In Vivo Osteocyte Ca2+ Signaling: Aging And Pharmacologic Effects, James Padgett

Dissertations and Theses

Bone’s ability to respond and adapt to mechanical loading declines significantly with age which is a major contributor to bone fragility. It is widely accepted that osteocytes are the key cells responsible for orchestrating the development of the “ideal” skeleton. This ability is attributed to osteocyte’s role as the primary mechanosensing cell that is responsible for maintaining the skeleton’s integrity throughout life. Recent work from our laboratory has shed light into how osteocytes respond to mechanical loading in vivo. The breakthrough approaches that enabled these discoveries were development of: (1) the first ever reporter mouse model with a genetically encoded …

Impact Of Percutaneous Transluminal Intervention On Vascular Hypoxia And The Role Of Micro-Calcifications On Atherosclerotic Plaque Rupture, Andrea Corti

Dissertations and Theses

Atherosclerotic disease is initiated by cholesterol build-up beneath the endothelium, which evolves into a fibroatheroma, a lipid-rich plaque covered by a fibrous cap. Many of these plaques are considered as vulnerable, as they grow to occlude the luminal section of the artery (chronically stenotic) or become mechanically unstable with a higher chance of rupturing (rupture-prone). On one hand, chronically stenotic vulnerable plaques are symptomatic lesions that are often treated with Percutaneous Transluminal Intervention (PTI). Unfortunately, approximately 10% of PTI procedures are followed by severe Neointima Hyperplasia (NH), which causes a new occlusion and failure of the implant. A significant precursor …

Modulation Of Brain Tissue Transport And Endothelial Glycocalyx And Tight Junctions Of The Blood-Brain Barrier By Transcranial Direct Current Stimulation, Yifan Xia

Dissertations and Theses

Transcranial direct current stimulation (tDCS) is a non-invasive approach to treat a broad range of brain disorders and to enhance memory and cognition in healthy individuals. In addition to directly acting on neurons by modulating the membrane potential, inducing neuronal polarization and changing cortical excitability in the brain to achieve its therapeutic effects, prior studies found that tDCS can transiently enhance the permeability (P) of the blood-brain barrier (BBB), the interface between blood circulation and brain tissue. Brain extracellular space (ECS) is a narrow microenvironment which surrounds every cell in the central nervous system (CNS). ECS occupies ~20% of brain …

Development Of A Biaxial Testing System For Research Of Soft Tissue Biomechanics Using Laboratory Models, Tariq Shameen

Dissertations and Theses

The rupture of the cap tissue layer of a fibroatheroma in human coronary vessels is considered the key event leading to the formation of a thrombus and myocardial infarction, resulting in more than half a million deaths in the US every year. In this study, we are interested in investigating the biomechanics of different elastomer materials that can be used as laboratory models to replicate coronary arteries’ ultimate tensile stress (0.2 - 2.08 MPa). To this end, we developed a biomechanical testing system that allows us to characterize the material properties of small samples with high accuracy and precision. We …

Osteocyte Activity And Skeletal Muscle Relative Gene Expression Profiling After Short-Term Muscle Paralysis, Michelle Gelbs

Dissertations and Theses

Mechanical loading is essential for maintaining bone tissue. Reduced mechanical loading has been shown to have a negative effect on bone, and can result in the development of disuse osteoporosis. Disuse models of muscle inactivity and immobilization, like the Botox model used in this study, result in changes in the bone microarchitecture, the mechanisms behind which are not fully understood. In a previous four-week Botox disuse study, skeletally mature 20- week-old rats experienced degradation of intracortical bone, increased vascular porosity, and decreased osteocyte lacunar density in the tibiae. The focus of this study was to explicate a potential source of …

Development Of Light Actuated Chemical Delivery Platform On A 2-D Array Of Micropore Structure, Hojjat Rostami Azmand, Hojjat Rostami Azmand

Dissertations and Theses

Localized chemical delivery plays an essential role in the fundamental information transfers within biological systems. Thus, the ability to mimic the natural chemical signal modulation would provide significant contributions to understand the functional signaling pathway of biological cells and develop new prosthetic devices for neurological disorders. In this paper, we demonstrate a light-controlled hydrogel platform that can be used for localized chemical delivery in a high spatial resolution. By utilizing the photothermal behavior of graphene-hydrogel composites confined within micron-sized fluidic channels, patterned light illumination creates the parallel and independent actuation of chemical release in a group of fluidic ports. The …

Restoration Of Bone Material And Microstructural Properties After Long-Term Remodeling Suppression, Abigail A. Coffman

Dissertations and Theses

Anti-resorptive drugs, principally bisphosphonates (BPs), are the mainstay of osteoporosis treatment. They work by inhibiting bone resorption/remodeling, thus preventing bone loss. However, long-term suppression of bone resorption adversely affects bone tissue mechanical properties, even while conserving bone mass. Lack of remodeling leads to accumulation of fatigue-induced microdamage, altered matrix mineralization and reduction in normal bone tissue heterogeneity, causing impaired strength and fracture toughness. The most severe consequence to patients, while rare, is Atypical Femur Fractures (i.e., complete fatigue fractures of the femoral shaft). To counteract the effects of long-term remodeling suppression, a temporary break in BP treatment (a "drug holiday) …

Characterization Of Bone Pathology In Sickle Cell Disease And Therapeutic Strategies, Mykel D. Green

Dissertations and Theses

Sickle cell disease (SCD) is a genetic hemoglobinopathy that has grown into a global health concern. While the advances in medical treatment and management of SCD during childhood have drastically improved the overall survival of children, the transition from pediatric to adult services is significantly inadequate in comparison. Life expectancies of patients with SCD in first world countries such as the United States are shortened to averages of 42 and 48 years for men and women, respectively. Despite the increasing number of people living with SCD, remarkably, few detailed studies have described the clinical course and complications of the disease …

Diffuse Damage Repair Mechanism In Bone, Leila Mehraban Alvandi

Dissertations and Theses

Bone microdamage is a result of fatigue, creep or ‘wear and tear’ caused by physiological activities and largely contributes to bone fragility. Bone, unlike engineered materials, has the ability to repair the microscopic cracking or microdamage through targeted, osteoclast-mediated bone remodeling. This capability is crucial for preservation of its structural integrity and quality; failure of the skeleton to effectively repair microdamage leads to accumulation of damage, which is one of the main contributors to bone fragility. Linear microcracks (50-100 µm) and diffuse damage (Dif.Dx) (sub-micron) are the two types of microdamage. Recent studies show that Dif.Dx repairs without bone remodeling, …

Design Development And Performance Study Of A Novel Assistive Device For Mobility Of Toddlers And Children With Visual Impairments, Joowon Jun

Dissertations and Theses

Being able to see allows mankind tremendous access to learn about the world, and because so much learning comes visually, children with visual impairments are delayed in developing range of skills: learning own languages, doing activities, socializing with peers, and etc. While children with vision can do virtually all the activities and tasks for granted, children with visual impairment require different types of tools or materials to do same tasks most of time. Amongst all the disadvantages that children with visual impairment have, one of the most critical disadvantageous area that visual impairment brings to toddler is learning to walk. …

Multi-Scale Assessment Of Bone Mechanics And The Mineral Phase Of Intramuscular Bone Of Atlantic Herring Fish, Svetlana Zeveleva

Dissertations and Theses

Bone tissue is a complex composite structure made up of a soft organic phase consisting of collagen I and non-collagenous proteins, and a hard inorganic phase consisting of mineral nanoplatelets. Given it’s compositional properties, bone is a unique stiff, tough, and strong biomaterial, making it exceptionally difficult to synthesize ex vivo. While the complete hierarchical structure may change with age and population, the basic building block components of mineralized collagen fibrils, are preserved. This study uses a model of intramuscular bone of the Atlantic herring fish, which present a simple structure, and no process of remodeling.

A multi-scale approach …

Morphology Of Brain Sulci Trabeculae And Its Effect On Brain During Impacts, Sharlin Anwar

Dissertations and Theses

Traumatic brain injury (TBI) is an intracranial injury caused by direct contact or non-contact head impacts to the brain. TBI is a major problem that accounts for high incidents of hospitalizations each year. Thus, it is important to understand and predict the occurrence of TBI in an impact. It has been shown that the subarachnoid space (SAS) trabeculae play an important role in damping the effect of an impact, thus reducing the injuries. However, the influence of sulci parameters and the sulci trabeculae in TBI due to impact is unexplored. Studies have shown that inclusion of sulci in brain models …

Effect Of Rolling On Viscoelastic Fluids Using A Novel Testing Device, Aswini Mangadu

Dissertations and Theses

The purpose of this research thesis project was to develop a mechanical testing device that could enable us to load articular cartilage with a rolling/sliding motion. This novel device was then used to observe the effect of a rolling motion on the fluid film thickness of different lubricants (motor oil, synovial fluid and Hyaluronic Acid (HA)) to varying loads (1kg, 2,kg, 3kg and 4kg) and speeds (10, 25, 48 and 91 mm/s) applied on the sample fluids for 10 cycles. We were able to examine the effect of different speeds within each load for each of the fluid that was …