Journal of biomechanics
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Journal of biomechanics · Oct 2016
ReviewReview of the fluid flow within intervertebral discs - How could in vitro measurements replicate in vivo?
By maintaining a balance between external mechanical loads and internal osmotic pressure, fluid content of intervertebral discs constantly alters causing fluctuations in disc hydration, height, diameter and pressure that govern disc temporal response. This paper reviews and discusses the relevant findings of earlier studies on the disc fluid flow with the aim to understand and remedy discrepancies between in vivo and in vitro observations. New results of finite element model studies are also exploited in order to help identify the likely causes for such differences and underlying mechanisms observed in vitro. ⋯ In view of much longer periods required to recover disc height and pressure in vitro in ovine, porcine, caprine, bovine and rat discs, concerns have been raised on the fluid inflow through the endplates that might be hampered by clogged blood vessels post mortem. Analyses of discrepancies in the flow-dependent recoveries in vivo and in vitro highlight an excessive fluid content in the latter as a likely cause. To replicate in vivo conditions as closely as possible in vitro, preparation and preconditioning of specimens and/or pressure and osmolarity of the culture media in which specimens are immersed should hence be designed in a manner as to diminish disc hydration level and/or fluid transport.
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Scarring and tissue fibrosis represent a significant source of morbidity in the United States. Despite considerable research focused on elucidating the mechanisms underlying cutaneous scar formation, effective clinical therapies are still in the early stages of development. ⋯ Mechanotransduction, which refers to the mechanisms by which mechanical forces are converted to biochemical stimuli, has been closely linked to inflammation and fibrosis and is believed to play a critical role in scarring. This review provides an overview of our current understanding of the mechanisms underlying scar formation, with an emphasis on the relationship between mechanotransduction pathways and their therapeutic implications.
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Journal of biomechanics · Sep 2013
ReviewWhat have we learned from finite element model studies of lumbar intervertebral discs in the past four decades?
Finite element analysis is a powerful tool routinely used to study complex biological systems. For the last four decades, the lumbar intervertebral disc has been the focus of many such investigations. To understand the disc functional biomechanics, a precise knowledge of the disc mechanical, structural and biochemical environments at the microscopic and macroscopic levels is essential. ⋯ The role of fluid pressurization and collagen fiber stiffening diminish with time during diurnal loading. The endplates permeability influences the time-dependent response of the disc in both loaded and unloaded recovery phases. The transport of solutes is substantially influenced by the disc size, tissue diffusivity and endplates permeability.
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Journal of biomechanics · Jan 2013
ReviewThe Syncardia(™) total artificial heart: in vivo, in vitro, and computational modeling studies.
The SynCardia(™) total artificial heart (TAH) is the only FDA-approved TAH in the world. The SynCardia(™) TAH is a pneumatically driven, pulsatile system capable of flows of >9L/min. The TAH is indicated for use as a bridge to transplantation (BTT) in patients at imminent risk of death from non-reversible bi-ventricular failure. ⋯ To aid in the development of a new "pediatric," TAH an engineering methodology known as "Device Thrombogenicity Emulation (DTE)", that we have recently developed and described, is being employed. Recently, to further our engineering understanding of the TAH, as steps towards next generation designs we have: (1) assessed of the degree of platelet reactivity induced by the present clinical 70 cc TAH using a closed loop platelet activity state assay, (2) modeled the motion of the TAH pulsatile mobile diaphragm, and (3) performed fluid-structure interactions and assessment of the flow behavior through inflow and outflow regions of the TAH fitted with modern bi-leaflet heart valves. Developing a range of TAH devices will afford biventricular replacement therapy to a wide range of patients, for both short and long-term therapy.
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Journal of biomechanics · Sep 1996
ReviewLumbar facet pain: biomechanics, neuroanatomy and neurophysiology.
Idiopathic low back pain has confounded health care practitioners for decades. Although there has been much advance in the understanding of the biomechanics of the lumbar spine over the past 25 years, the cellular and neural mechanisms that lead to facet pain are not well understood. An extensive series of experiments was undertaken to help elucidate these mechanisms and gain a better understanding of lumbar facet pain. ⋯ These studies provide the following evidence to help explain the mechanisms of lumbar facet pain: (1) The facet joint can carry a significant amount of the total compressive load on the spine when the human spine is hyperextended. (2) Extensive stretch of the human facet joint capsule occurs when the spine is in the physiologic range of extreme extension. (3) An extensive distribution of small nerve fibers and free and encapsulated nerve endings exists in the lumbar facet joint capsule, including nerves containing substance P, a putative neuromodulator of pain. (4) Low and high threshold mechanoreceptors fire when the facet joint capsule is stretched or is subject to localized compressive forces. (5) Sensitization and excitation of nerves in facet joint and surrounding muscle occur when the joint is inflamed or exposed to certain chemicals that are released during injury and inflammation. (6) Marked reduction in nerve activity occurs in facet tissue injected with hydrocortisone and lidocaine. Thus, the facet joint is a heavily innervated area that is subject to high stress and strain. The resulting tissue damage or inflammation is likely to cause release of chemicals irritating to the nerve endings in these joints, resulting in low back pain.