Dimitrije Stamenovi - Academia.edu (original) (raw)
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Papers by Dimitrije Stamenovi
AJP: Cell Physiology, 2002
Cell prestress. I. Stiffness and prestress are closely associated in adherent contractile cells. ... more Cell prestress. I. Stiffness and prestress are closely associated in adherent contractile cells. The tensegrity hypothesis holds that the cytoskeleton is a structure whose shape is stabilized predominantly by the tensile stresses borne by filamentous structures. Accordingly, cell stiffness must increase in proportion with the level of the tensile stress, which is called the prestress. Here we have tested that prediction in adherent human airway smooth muscle (HASM) cells. Traction microscopy was used to measure the distribution of contractile stresses arising at the interface between each cell and its substrate; this distribution is called the traction field. Because the traction field must be balanced by tensile stresses within the cell body, the prestress could be computed. Cell stiffness (G) was measured by oscillatory magnetic twisting cytometry. As the contractile state of the cell was modulated with graded concentrations of relaxing or contracting agonists (isoproterenol or histamine, respectively), the mean prestress (p t) ranged from 350 to 1,900 Pa. Over that range, cell stiffness increased linearly with the prestress: G (Pa) ϭ 0.18p t ϩ 92. While this association does not necessarily preclude other interpretations, it is the hallmark of systems that secure shape stability mainly through the prestress. Regardless of mechanism, these data establish a strong association between stiffness of HASM cells and the level of tensile stress within the cytoskeleton. tensegrity; mechanical stress; traction; cytoskeleton; actin microfilaments CONTROVERSY SURROUNDS the tensegrity hypothesis (23, 28). As described below, some part of this controversy is perhaps attributable to insufficient precision in the use of associated terminology and some part to insufficient emphasis on underlying mechanisms on which tensegrity rests. The major part of the controversy, however, is surely attributable to the fact that tensegrity is a hypothesis that has been rich in opinions but poor in quantitative data.
PM&R, 2013
Objectives: To determine whether a knee brace incorporating inflatable air bladders can alter the... more Objectives: To determine whether a knee brace incorporating inflatable air bladders can alter the net peak external knee adduction moment in persons with medial compartment knee osteoarthritis. Design: Prospective cohort study. Setting: Motion analysis laboratory. Participants: Subjects (n ¼ 18) diagnosed with knee osteoarthritis as defined by the Diagnostic and Therapeutic Criteria Committee of the American Rheumatism Association. Methods: Instrumented gait analysis was performed while subjects walked with and without the knee brace. When subjects wore the knee brace, the air bladders were either uninflated or inflated to 7 psi. The net external knee adduction moment was obtained by subtracting the abduction moment produced by the knee brace (estimated using a finite element analysis model) from the external knee adduction moment (estimated using a camera-based motion analysis system). Main Outcome Measurements: The net external knee adduction moment was compared across all testing conditions. Results: A 7.6% decrease in net peak external knee adduction moment was observed when subjects wore the knee brace uninflated compared with when they did not wear the brace. Inflation of the bladders to 7 psi led to a 26.0% decrease in net peak external knee adduction moment. Conclusions: The results of the study suggest that the effects of an unloading knee brace may be enhanced by incorporating inflatable air bladders into the design of the brace, thus leading to an improved correction of the excessive peak external knee adduction moment observed in patients with medial compartment knee osteoarthritis.
AJP: Cell Physiology, 2002
Cell prestress. I. Stiffness and prestress are closely associated in adherent contractile cells. ... more Cell prestress. I. Stiffness and prestress are closely associated in adherent contractile cells. The tensegrity hypothesis holds that the cytoskeleton is a structure whose shape is stabilized predominantly by the tensile stresses borne by filamentous structures. Accordingly, cell stiffness must increase in proportion with the level of the tensile stress, which is called the prestress. Here we have tested that prediction in adherent human airway smooth muscle (HASM) cells. Traction microscopy was used to measure the distribution of contractile stresses arising at the interface between each cell and its substrate; this distribution is called the traction field. Because the traction field must be balanced by tensile stresses within the cell body, the prestress could be computed. Cell stiffness (G) was measured by oscillatory magnetic twisting cytometry. As the contractile state of the cell was modulated with graded concentrations of relaxing or contracting agonists (isoproterenol or histamine, respectively), the mean prestress (p t) ranged from 350 to 1,900 Pa. Over that range, cell stiffness increased linearly with the prestress: G (Pa) ϭ 0.18p t ϩ 92. While this association does not necessarily preclude other interpretations, it is the hallmark of systems that secure shape stability mainly through the prestress. Regardless of mechanism, these data establish a strong association between stiffness of HASM cells and the level of tensile stress within the cytoskeleton. tensegrity; mechanical stress; traction; cytoskeleton; actin microfilaments CONTROVERSY SURROUNDS the tensegrity hypothesis (23, 28). As described below, some part of this controversy is perhaps attributable to insufficient precision in the use of associated terminology and some part to insufficient emphasis on underlying mechanisms on which tensegrity rests. The major part of the controversy, however, is surely attributable to the fact that tensegrity is a hypothesis that has been rich in opinions but poor in quantitative data.
PM&R, 2013
Objectives: To determine whether a knee brace incorporating inflatable air bladders can alter the... more Objectives: To determine whether a knee brace incorporating inflatable air bladders can alter the net peak external knee adduction moment in persons with medial compartment knee osteoarthritis. Design: Prospective cohort study. Setting: Motion analysis laboratory. Participants: Subjects (n ¼ 18) diagnosed with knee osteoarthritis as defined by the Diagnostic and Therapeutic Criteria Committee of the American Rheumatism Association. Methods: Instrumented gait analysis was performed while subjects walked with and without the knee brace. When subjects wore the knee brace, the air bladders were either uninflated or inflated to 7 psi. The net external knee adduction moment was obtained by subtracting the abduction moment produced by the knee brace (estimated using a finite element analysis model) from the external knee adduction moment (estimated using a camera-based motion analysis system). Main Outcome Measurements: The net external knee adduction moment was compared across all testing conditions. Results: A 7.6% decrease in net peak external knee adduction moment was observed when subjects wore the knee brace uninflated compared with when they did not wear the brace. Inflation of the bladders to 7 psi led to a 26.0% decrease in net peak external knee adduction moment. Conclusions: The results of the study suggest that the effects of an unloading knee brace may be enhanced by incorporating inflatable air bladders into the design of the brace, thus leading to an improved correction of the excessive peak external knee adduction moment observed in patients with medial compartment knee osteoarthritis.