Frontiers of Engineering Reports on Leading Edge Engineering from the 1997 NAE Symposium on Frontiers of Engineering (1998) / Chapter Skim
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Biomechanics
Biomechanics
Pages 1-20
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Nonetheless, the progress has been exciting. The focus of these papers from the Biomechanics session of the Third Annual Symposium on Frontiers of Engineering is on bone and cartilage and their mechanical properties.
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In the absence of that we get deterioration. More examples of this type are described in the second paper, "Mechanical Influences on Bone Development and Adaptation." That paper focuses on the mechanical environment in which bone thrives and in which the adaptive responses elicited by physiochemical factors amplify and supplement the responses to mechanical loading.
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Technological developments such as new imaging modalities, microscopic modalities, adaptively analytical finite element models, large-scale numerical modeling ability, and computational power have been critical factors in the intellectual advances in physiology and biomechanics discussed herein.
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In the human body the interaction of living cells with physical forces, such as mechanical stress, is critical to the normal health and function of most organ systems. Cells not only have extraordinary capabilities to generate mechanical forces but also can possess exquisite abilities to detect and respond to mechanical signals in their environment.
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Many recent advances in this field have been made through the application of new theoretical and experimental engineering technologies in combination with techniques in cell biology. In particular, new microscopy and imaging techniques coupled with large-scale numerical modeling have been very useful in providing new information on the micromechanical environment of single cells.
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Validation of these theoretical predictions has been made using three-dimensional confocal scanning laser microscopy to quantify the changes in shape and volume that living chondrocytes undergo as articular cartilage is subjected to physiological levels of compression (Guilak, 1995~. Confocal scanning laser microscopy has also been used to elucidate the earliest intracellular events that occur in response to mechanical stimuli.
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These forces often represent the interactions between individual molecules and are at the limit of detection using current technologies. New advances in engineering technology have enabled measurement and application of extremely low forces in this range using such techniques as atomic force microscopy, optical gradient traps, micropipette manipulation, and microelectromechanical systems.
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FUTURE DIRECTIONS With the development of such techniques as atomic force microscopy, optical gradient traps, and micropipette manipulation, it is now possible to measure the extremely low forces and displacements generated by molecular interactions in living cells. Simultaneously, rapid advances in computational speed and power have made it possible to develop large-scale continuum and structural models of the interactions between tissues and cells.
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1995. Dynamic micromechanical properties of cultured rat atrial myocytes measured by atomic force microscopy.
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The bone tissue of the skeleton consists of a hard mineralized matrix that has living cells embedded in it. These cells produce the extracellular matrix around themselves and enable the skeleton to respond to its environment by altering their matrix production.
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In the past decade, adaptive analytical and finite element models have been developed to simulate the functional adaptation of both the continuum and microstructural features of bone (Beaupre et al., 1990; Mullender et al., 1994; van der Meulen et al., 19931. Whereas the overall nature of the adaptive response of bone has been well documented, the mechanisms that transduce a mechanical stimulus to a biological signal to increase or decrease bone mass are not understood, including the stimulus, signal transduction pathway, and response process (Duncan and Turner, 19951.
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The potential impact of understanding bone adaptation to biophysical stimuli is significant: mechanical factors are implicated in many orthopedic and endocrine skeletal disorders, including total joint replacements, fracture healing, arthritis, and osteoporosis. Osteoporosis is a severe worldwide health problem.
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Transactions of the Orthopaedic Research Society 22:403. van der Meulen, M
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Until about 1960 the normal degradation of joint function with increasing age, or due to systemic disease such as rheumatoid arthritis, was considered a regrettable but essentially nontreatable chronic condition. In about 1960 Sir John Charnley of the United Kingdom developed the idea of replacing the articulating mechanism of the hip with an artificial construct consisting of a stainless steel ball affixed to an implantable stem articulating with a plastic (polyethylene)
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Early cementless implants were made of a cobalt-chromium alloy surfaced with tiny beads to create pores into which the living bone would grow and thus form a mechanical bond and load transferring interface between the femur and the implant. Strategies for placement of the beads varied by design, but it became apparent that in order to achieve bony integration with the implant the relative motion between the implant and the bone had to be reduced to below about 100 ,um.
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Hydroxylapatite-coated stems came onto the U.S. market in the late 1980s and to date have shown a significantly lowered propensity toward bone resorption, presumably because of the enhanced load transfer to the bone as a function of the reduced structural stiffness of the stem coupled with an enhanced interface between the living bone and the calcium phosphate layer.
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While in many areas people no longer believe that technology will rescue them from whatever challenge befalls, in medicine the same people place a trust on the engineer, scientist, and physician that all ailments can be cured or at least substantially mitigated hence, the continued study of artificial prostheses. their material composition.
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