Browsing by Subject "biomechanics"
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Item Biomechanical Root Cause Analysis of Complications in Head Immobilization Devices for Pediatric Neurosurgery(ASME, 2018-06) Abdulhafez, Moataz; Zaazoue, Mohamed; Kadry, Karim; Goumnerova, Liliana C.; Bedewy, Mostafa; Neurological Surgery, School of MedicinePrecise and firm fixation of the cranium is critical during craniotomy and delicate brain neurosurgery making head immobilization devices (HIDs) a staple instrument in brain neurosurgical operations today. However, despite their popularity, there is no standard procedure for their use and many complications arise from using HIDs in pediatric neurosurgery. In this paper, we identify biomechanical causes of complications and quantify risks in pin-type HIDs including clamping force selection, positioning and age effects. Based on our root cause analysis, we develop a framework to address the biomechanical factors that influence complications and understand the biomechanics of the clamping process. We develop an age-dependent finite element model (FEM) of a single pin on a cranial bone disc with the representative properties and skull thickness depending on age. This model can be utilized to reduce risk of complications by design as well as to provide recommendations for current practices.Item Can Deterministic Mechanical Size Effects Contribute to Fracture and Microdamage Accumulation in Trabecular Bone?(2010-07) Siegmund, Thomas; Allen, Matthew R.; Burr, David B.Failure of bone under monotonic and cyclic loading is related to the bone mineral density, the quality of the bone matrix, and the evolution of microcracks. The theory of linear elastic fracture mechanics has commonly been applied to describe fracture in bone. Evidence is presented that bone failure can be described through a non-linear theory of fracture. Thereby, deterministic size effects are introduced. Concepts of a non-linear theory are applied to discern how the interaction among bone matrix constituents (collagen and mineral), microcrack characteristics, and trabecular architecture can create distinctively differences in the fracture resistance at the bone tissue level. The non-linear model is applied to interpret pre-clinical data concerning the effects of anti-osteoporotic agents on bone properties. The results show that bisphosphonate (BP) treatments that suppress bone remodeling will change trabecular bone in ways such that the size of the failure process zone relative to the trabecular thickness is reduced. Selective estrogen receptor modulators (SERMs) that suppress bone remodeling will change trabecular bone in ways such that the size of the failure process zone relative to the trabecular thickness is increased. The consequences of these changes are reflected in bone mechanical response and predictions are consistent with experimental observations in the animal model which show that BP treatment is associated with more brittle fracture and microcracks without altering the average length of the cracks, whereas SERM treatments lead to a more ductile fracture and mainly increase crack length with a smaller increase in microcrack density. The model suggests that BPs may be more effective in cases in which bone mass is very low, whereas SERMS may be more effective when milder osteoporotic symptoms are present.Item Influence of Mechanical Stimulation on the Quantity and Quality of Bone During Modeling(2016) Berman, Alycia G.; Wallace, Joseph; Na, Sungsoo; Li, Jiliang; Yoshida, KenSkeletal fractures due to bone disease impact an estimated 1.5 million Americans per year, creating a large economic burden on our society. Treatment of bone diseases prior to fracture often involves bisphosphonates (current gold-standard in osteoporosis care and prevention). Although bisphosphonates decrease fracture incidence, they often improve bone mass without regard for bone quality. Thus, although bisphosphonates increase the amount of bone present, the inherent bone material strength often decreases, creating a trade-off that increases the risk of atypical fractures after long-term use. This trade-off demonstrates the need for a treatment that targets both bone quality AND quantity. Although bone quality is important, the components of bone that contribute to bone quality are incompletely understood, making it difficult to create new pharmacological agents. With this in mind, my particular area of interest is in understanding how mechanical stimuli protects the formation of bone, leading to improved bone quality. Initially, this area was explored through use of tibial loading in a disease mouse model (osteolathyrism, induced by injection of beta-aminoproprionitrile) as a means of assessing how the body is able to compensate for decreased bone quality. The results of the BAPN and tibial loading studies indicated that injecting mice with BAPN may not be the ideal method to induce osteolathyrism. However, other intriguing results from the BAPN studies then led us into an exploration of how tibial loading itself contributes to bone quality.Item Locomotor Kinematics and Kinetics Following High-Intensity Stepping Training in Variable Contexts Poststroke(SAGE, 2020-06-06) Ardestani, Marzieh M.; Henderson, Christopher E.; Mahtani, Gordhan; Connolly, Mark; Hornby, T. George; Physical Medicine and Rehabilitation, School of MedicineBackground and Purpose Previous studies suggest individuals post-stroke can achieve substantial gains in walking function following high-intensity locomotor training (LT). Recent findings also indicate practice of variable stepping tasks targeting locomotor deficits can mitigate selected impairments underlying reduced walking speeds. The goal of this study was to investigate alterations in locomotor biomechanics following three different LT paradigms. Methods This secondary analysis of a randomized trial recruited individuals 18–85 years old and >6 months post-stroke. We compared changes in spatiotemporal, joint kinematics and kinetics following up to 30 sessions of high-intensity (>70% heart rate reserve [HRR]) LT of variable tasks targeting paretic limb and balance impairments (high-variable, HV), high-intensity LT focused only on forward walking (high-forward, HF), or low-intensity LT (<40% HRR) of variable tasks (low-variable, LV). Sagittal spatiotemporal and joint kinematics, and concentric joint powers were compared between groups. Regressions and principle component (PC) analyses were conducted to evaluate relative contributions or importance of biomechanical changes to between and within groups. Results Biomechanical data were available on 50 participants who could walk ≥0.1 m/s on a motorized treadmill. Significant differences in spatiotemporal parameters, kinematic consistency, and kinetics were observed between HV and HF vs LV. Resultant PC analyses were characterized by paretic powers and kinematic consistency following HV, while HF and LV were characterized by non-paretic powers. Conclusion High-intensity LT results in greater changes in kinematics and kinetics as compared to lower-intensity interventions. The results may suggest greater paretic-limb contributions with high-intensity variable stepping training that targets specific biomechanical deficits.Item Muscle contraction induces osteogenic levels of cortical bone strain despite muscle weakness in a mouse model of Osteogenesis Imperfecta(Elsevier, 2020) Berman, Alycia G.; Organ, Jason M.; Allen, Matthew R.; Wallace, Joseph M.; Biomedical Engineering, School of Engineering and TechnologyMechanical interactions between muscle and bone have long been recognized as integral to bone integrity. However, few studies have directly measured these interactions within the context of musculoskeletal disease. In this study, the osteogenesis imperfecta murine model (oim/oim) was utilized because it has both reduced bone and muscle properties, allowing direct assessment of whether weakened muscle is able to engender strain on weakened bone. To do so, a strain gauge was attached to the tibia of healthy and oim/oim mice, muscles within the posterior quadrant of the lower hind limb were stimulated, and bone strain during muscle contraction was measured. Results indicated that the relationship between maximum muscle torque and maximum engendered strain is altered in oim/oim bone, with less torque required to engender strain compare to wild-type and heterozygous mice. Maximum muscle torque at 150 Hz stimulation frequency was able to engender ~1500 μɛ in oim/oim animals. However, even though the strain engendered in the oim/oim mice was high relative to historical bone formation thresholds, the maximum strain values were still significantly lower than that of the wild-type mice. These results are promising in that they suggest that muscle stimulation may be a viable means of inducing bone formation in oim/oim and potentially other disease models where muscle weakness/atrophy exist.Item Phase II – Biomechanics of Smooth Muscle Cell Differentiation: Experimental Study Using an Innovative In Vitro Mechanical System(Office of the Vice Chancellor for Research, 2014-04-11) Collins, Jessica; Sheikh, Zahir; Vipra, Niraj; Yeoh, JosephSmooth muscle cells (SMCs) controls involuntary contractions and express different genotypic and phenotypic traits on specific organs such as blood vessels, bladder and stomach. However, studies have shown different SMC lineages tend to gradually lose specific characteristics due to a static milieu without exerting forces that they would experience naturally when cultured in vitro. The research provided in vivo conditions are mimicked effectively in vitro by applying controlled mechanical loading, SMCs should express their differentiated characteristics. We have validated an innovative mechanical device that simulates the pulsatile stretching SMCs undergo in their in vivo environment. Using the new system and cell and molecular biology techniques, we are evaluating cell differentiation and strain induced alignment when phenotypically modulated SMCs undergo cyclic mechanical loading at 10 and 20 percent strains, for 4, 6, or 8 hours at physiological frequency. We collected proteins after stretch experiments and analyzed via western blot, α-actin, γ-actin, transgelin, and calponin protein expression changes in: coronary SMCs strained 10% and 20% at 4, 6, and 8 hours, bladder SMCs strained 10% at 4, 6, and 8 hours, and BAECs for varying intensities and durations. In order to improvise the machine capability, LabVIEW code is been developed as the user interface providing advantageous of Graphical Approach instead of Cool Muscle Language code. Developed coding provide a complete coverage of acquisition, analysis, reporting, and display features to create modern applications that can scale as system requirements change over time. The next phase of this experiment enable analysis of gene expression using quantitative RT-PCR (qRT-PCR). This facet of research may prove valuable in the analysis of the effect of mechanical stress on maintaining SMC lineage as well as the study of how pathological stretch conditions affect SMC and endothelial cell gene and protein expressions.Item A Qualitative Engineering Analysis of Occlusion Effects on Mandibular Fracture Repair Mechanics(SAGE-Hindawi, 2011-08) Katona, Thomas R,Objectives. The purpose of this analytical study was to examine and critique the engineering foundations of commonly accepted biomechanical principles of mandible fracture repair. Materials and Methods. Basic principles of static equilibrium were applied to intact and plated mandibles, but instead of the traditional lever forces, the mandibles were subjected to more realistic occlusal forces. Results. These loading conditions produced stress distributions within the intact mandible that were very different and more complex than the customary lever-based gradient. The analyses also demonstrated the entirely different mechanical environments within intact and plated mandibles. Conclusions. Because the loading and geometry of the lever-idealized mandible is incomplete, the associated widely accepted bone stress distribution (tension on top and compression on the bottom) should not be assumed. Furthermore, the stress gradients within the bone of an intact mandible should not be extrapolated to the mechanical environment within the plated regions of a fractured mandible.Item Raloxifene Enhances Vertebral Mechanical Properties Independent of Bone Density(2006-11) Allen, Matthew R.; Iwata, Ken; Sato, Masahiko; Burr, David B.Anti-remodeling agents produce similar reductions in vertebral fracture risk despite large differences in BMD changes suggesting the mechanism of fracture risk reduction may differ among these agents. Forty-eight intact (non-ovariectomized) skeletally mature female beagle dogs were treated orally for 12 months with clinically relevant doses of risedronate (RIS, 0.10 mg/kg/day), alendronate (ALN, 0.2 mg/kg/day), raloxifene (RAL, 0.50 mg/kg/day), or saline (VEH, 1 ml/kg/day). After sacrifice, the following measurements were made on vertebral bone: areal (aBMD) and volumetric (vBMD) bone mineral densities, tissue mineralization by ash content, static and dynamic histomorphometric parameters, microdamage, and extrinsic and intrinsic measures of biomechanical strength, stiffness and energy to fracture. At these doses, RAL suppressed bone turnover (-20%) significantly less than the bisphosphonates (-66 and -71%) and did not produce significant differences in aBMD, vBMD, BV/TV or percent ash compared to VEH-treated animals. Microdamage accumulation in RAL-treated animals was not significantly different than VEH; both RIS and ALN had significantly higher crack surface density compared to VEH. Stiffness was significantly higher than VEH in all treatment groups. Ultimate load divided by aBMD, a measure of strength independent of BMD, was significantly higher only in RAL-treated animals compared to VEH (+16%, P = 0.015). Based on these data, we conclude that raloxifene produces improvements in bone mechanical properties in ways that do not involve increases in BMD.Item The roles of wedging and friction in the mechanics of dental occlusal contacts(2019-04) Katona, Thomas R.; Eckert, George J.Objective: The primary aim of this project is to elucidate the basic mechanical engineering principles that govern and explain unexpected and counter-intuitive occlusal contact force measurements. Methods: Forces were measured on matched pairs of first molar denture, ceramic and stainless steel crowns during occlusion and disclusion, with human saliva and dry (control). The weighted maxillary assembly, guided by a precision slide, was lowered onto, and raised from, the mandibular crown. The forces experienced by the mandibular tooth were continuously measured by the load cell that supported it. Statistical analyses included LOESS smoothing splines and generalized additive models. Principles of basic statics and classic friction were applied to explain and validate the results. Results: It was determined that within the span of a single chomp, the in-occlusal plane force component (Flateral) on the tooth is highly variable in direction and/or magnitude. The most salient observations were that Flateral was higher in disclusion than in occlusion, and the largest Flateral did not necessarily occur when the bite force was maximum. Furthermore, saliva significantly affected the results. Conclusions: The results demonstrated that contacting teeth experience complex transient mechanical environments that can be readily explained with elementary engineering principles involving wedging and friction at the occlusal contacts.Item Ultrastructural elastic deformation of cortical bone tissue probed by NIR Raman spectroscopy(2004-07) Finney, William F; Morris, Michael D.; Wallace, Joseph M.; Kohn, David H.Raman spectroscopy is used as a probe of ultrastructural (molecular) changes in both the mineral and matrix (protein and glycoprotein, predominantly type I collagen) components of murine cortical bone as it responds to loading in the elastic regime. At the ultrastructural level, crystal structure and protein secondary structure distort as the tissue is loaded. These structural changes are followed as perturbations to tissue spectra. We load tissue in a custom-made dynamic mechanical tester that fits on the stage of a Raman microprobe and can accept hydrated tissue specimens. As the specimen is loaded in tension and/or compression, the shifts in mineral P-O4v 1 and relative band heights in the Amide III band envelope are followed with the microprobe. Average load is measured using a load cell while the tissue is loaded under displacement control. Changes occur in both the mineral and matrix components of bone as a response to elastic deformation. We propose that the mineral apatitic crystal lattice is deformed by movement of calcium and other ions. The matrix is proposed to respond by deformation of the collagen backbone. Raman microspectroscopy shows that bone mineral is not a passive contributor to tissue strength. The mineral active response to loading may function as a local energy storage and dissipation mechanism, thus helping to protect tissue from catastrophic damage.