scholarly journals Modelling approaches for evaluating multiscale tendon mechanics

2016 ◽  
Vol 6 (1) ◽  
pp. 20150044 ◽  
Author(s):  
Fei Fang ◽  
Spencer P. Lake
Keyword(s):  
Computational Models ◽  
Mechanical Response ◽  
Helical Structure ◽  
Mechanical Analysis ◽  
Hierarchical Organization ◽  
Organization Model ◽  
Tendon Mechanics ◽  
Modelling Approaches

Tendon exhibits anisotropic, inhomogeneous and viscoelastic mechanical properties that are determined by its complicated hierarchical structure and varying amounts/organization of different tissue constituents. Although extensive research has been conducted to use modelling approaches to interpret tendon structure–function relationships in combination with experimental data, many issues remain unclear (i.e. the role of minor components such as decorin, aggrecan and elastin), and the integration of mechanical analysis across different length scales has not been well applied to explore stress or strain transfer from macro- to microscale. This review outlines mathematical and computational models that have been used to understand tendon mechanics at different scales of the hierarchical organization. Model representations at the molecular, fibril and tissue levels are discussed, including formulations that follow phenomenological and microstructural approaches (which include evaluations of crimp, helical structure and the interaction between collagen fibrils and proteoglycans). Multiscale modelling approaches incorporating tendon features are suggested to be an advantageous methodology to understand further the physiological mechanical response of tendon and corresponding adaptation of properties owing to unique in vivo loading environments.

The Role of Mechanical Tension in Neurons

2010 ◽  
Vol 1274 ◽  
Author(s):  
Taher Saif ◽  
Jagannathan Rajagopalan ◽  
Alireza Tofangchi
Keyword(s):  
Mechanical Response ◽  
Mechanical Forces ◽  
Active Tension ◽  
Mechanical Tension ◽  
Deformation Response ◽  
Linear Force ◽  
Tension Regulation ◽  
Over Time

AbstractWe used high resolution micromechanical force sensors to study the in vivo mechanical response of embryonic Drosophila neurons. Our experiments show that Drosophila axons have a rest tension of a few nN and respond to mechanical forces in a manner characteristic of viscoelastic solids. In response to fast externally applied stretch they show a linear force-deformation response and when the applied stretch is held constant the force in the axons relaxes to a steady state value over time. More importantly, when the tension in the axons is suddenly reduced by releasing the external force the neurons actively restore the tension, sometimes close to their resting value. Along with the recent findings of Siechen et al (Proc. Natl. Acad. Sci. USA 106, 12611 (2009)) showing a link between mechanical tension and synaptic plasticity, our observation of active tension regulation in neurons suggest an important role for mechanical forces in the functioning of neurons in vivo.

scholarly journals Intracellular and Computational Characterization of the Intracortical Inhibitory Control of Synchronized Thalamic Inputs In Vivo

1997 ◽  
Vol 78 (1) ◽  
pp. 335-350 ◽  
Author(s):  
Diego Contreras ◽  
Alain Destexhe ◽  
Mircea Steriade
Keyword(s):  
Inhibitory Control ◽  
Computational Models ◽  
Pyramidal Cells ◽  
Excitatory Postsynaptic Potential ◽  
Thalamic Stimulation ◽  
Postsynaptic Potential ◽  
Spike Wave

Contreras, Diego, Alain Destexhe, and Mircea Steriade. Intracellular and computational characterization of the intracortical inhibitory control of synchronized thalamic inputs in vivo. J. Neurophysiol. 78: 335–350, 1997. We investigated the presence and role of local inhibitory cortical control over synchronized thalamic inputs during spindle oscillations (7–14 Hz) by combining intracellular recordings of pyramidal cells in barbiturate-anesthetized cats and computational models. The recordings showed that 1) similar excitatory postsynaptic potential (EPSP)/inhibitory postsynaptic potential (IPSP) sequences occurred either during spindles or following thalamic stimulation; 2) reversed IPSPs with chloride-filled pipettes transformed spindle-related EPSP/IPSP sequences into robust bursts with spike inactivation, resembling paroxysmal depolarizing shifts during seizures; and 3) dual simultaneous impalements showed that inhibition associated with synchronized thalamic inputs is local. Computational models were based on reconstructed pyramidal cells constrained by recordings from the same cells. These models showed that the transformation of EPSP/IPSP sequences into fully developed spike bursts critically needs a relatively high density of inhibitory currents in the soma and proximal dendrites. In addition, models predict significant Ca2+ transients in dendrites due to synchronized thalamic inputs. We conclude that synchronized thalamic inputs are subject to strong inhibitory control within the cortex and propose that 1) local impairment of inhibition contributes to the transformation of spindles into spike-wave-type discharges, and 2) spindle-related inputs trigger Ca2+ events in cortical dendrites that may subserve plasticity phenomena during sleep.

scholarly journals In-vivo analysis of thoracic mechanical response under belt loading: The role of body mass index in thorax stiffness

2013 ◽  
Vol 46 (5) ◽  
pp. 883-889 ◽  
Author(s):  
David Poulard ◽  
François Bermond ◽  
Sabine Compigne ◽  
Karine Bruyère
Keyword(s):  
Body Mass Index ◽  
Body Mass ◽  
Mechanical Response ◽  
In Vivo Analysis

3D In Vivo IVUS-Based Anisotropic FSI Models With Cyclic Bending for Human Coronary Atherosclerotic Plaque Mechanical Analysis

2009 ◽  
Author(s):  
Dalin Tang ◽  
Chun Yang ◽  
Jie Zheng ◽  
Pamela K. Woodard ◽  
Kristen Billiar ◽  
...  
Keyword(s):  
Atherosclerotic Plaque ◽  
Computational Models ◽  
Material Model ◽  
3D Models ◽  
Mechanical Analysis ◽  
Intraplaque Hemorrhage ◽  
Plaque Vulnerability ◽  
Cardiovascular Research ◽  
Cyclic Bending

Assessing atherosclerotic plaque vulnerability based on limited in vivo patient data has been a major challenge in cardiovascular research and clinical practice. Considerable advances in medical imaging technology have been made in recent years to identify vulnerable atherosclerotic carotid plaques in vivo with information about plaque components including lipid-rich necrotic pools, calcification, intraplaque hemorrhage, loose matrix, thrombosis, and ulcers, subject to resolution limitations of current technology [1]. Image-based computational models have also been developed which combine mechanical analysis with image technology aiming for more accurate assessment of plaque vulnerability and better diagnostic and treatment decisions [2]. However, 3D models with fluid-structure interactions (FSI), cyclic bending and anisotropic properties based on in vivo IVUS images for human coronary atherosclerotic plaques are lacking in the current literature. In this paper, we introduce 3D FSI models based on in vivo IVUS images to perform mechanical analysis for human coronary plaques. Cyclic bending is included to represent deformation caused by cardiac motion. An anisotropic material model was used for the vessel so that the models would be more realistic for more accurate computational flow and stress/strain predictions.

Quantifying Effects of Artery Shrinkage Using In Vivo MRI-Based 3D FSI Models for Carotid Atherosclerotic Plaques With Bifurcation

2008 ◽  
Author(s):  
Xueying Huang ◽  
Chun Yang ◽  
Chun Yuan ◽  
Thomas Hatsukami ◽  
Fei Liu ◽  
...  
Keyword(s):  
Stress State ◽  
Computational Models ◽  
Initial Conditions ◽  
Plaque Rupture ◽  
Mechanical Analysis ◽  
Western World ◽  
Plaque Morphology ◽  
Atherosclerotic Plaques ◽  
Atherosclerotic Vascular Disease

Atherosclerotic vascular disease leads to changes of the arterial wall and lumen narrowing, and it is the No.1 killer in the western world. Magnetic resonance image (MRI)-based computational models with fluid-structure interactions (FSI) for atherosclerotic plaques have been introduced to perform mechanical analysis to quantify critical flow and stress/strain conditions related to plaque rupture which often leads directly to heart attack or stroke [2]. There are three groups of information needed as model input: plaque morphology, material properties, and flow conditions. Pre shrinkage-stretch process is used to recover the in vivo geometry from zero-stress state with associated initial conditions which are required to achieve building the computational model. An important issue for this process is how to determine zero stress state from in vivo plaque geometry. However, few publications can be found in the current literature about how to quantify human carotid artery shrinkage.

scholarly journals Thalamocortical synchronization during induction and emergence from propofol-induced unconsciousness

2017 ◽  
Vol 114 (32) ◽  
pp. E6660-E6668 ◽  
Author(s):  
Francisco J. Flores ◽  
Katharine E. Hartnack ◽  
Amanda B. Fath ◽  
Seong-Eun Kim ◽  
Matthew A. Wilson ◽  
...  
Keyword(s):  
Prefrontal Cortex ◽  
Medial Prefrontal Cortex ◽  
Computational Models ◽  
The United States ◽  
Self Awareness ◽  
Drug Induced ◽  
Recovery From Anesthesia ◽  
Internal Consciousness

General anesthesia (GA) is a reversible drug-induced state of altered arousal required for more than 60,000 surgical procedures each day in the United States alone. Sedation and unconsciousness under GA are associated with stereotyped electrophysiological oscillations that are thought to reflect profound disruptions of activity in neuronal circuits that mediate awareness and cognition. Computational models make specific predictions about the role of the cortex and thalamus in these oscillations. In this paper, we provide in vivo evidence in rats that alpha oscillations (10–15 Hz) induced by the commonly used anesthetic drug propofol are synchronized between the thalamus and the medial prefrontal cortex. We also show that at deep levels of unconsciousness where movement ceases, coherent thalamocortical delta oscillations (1–5 Hz) develop, distinct from concurrent slow oscillations (0.1–1 Hz). The structure of these oscillations in both cortex and thalamus closely parallel those observed in the human electroencephalogram during propofol-induced unconsciousness. During emergence from GA, this synchronized activity dissipates in a sequence different from that observed during loss of consciousness. A possible explanation is that recovery from anesthesia-induced unconsciousness follows a “boot-up” sequence actively driven by ascending arousal centers. The involvement of medial prefrontal cortex suggests that when these oscillations (alpha, delta, slow) are observed in humans, self-awareness and internal consciousness would be impaired if not abolished. These studies advance our understanding of anesthesia-induced unconsciousness and altered arousal and further establish principled neurophysiological markers of these states.

scholarly journals Experimental and Numerical Characterization of the Mechanical Masseter Muscle Response During Biting

2017 ◽  
Vol 139 (12) ◽  
Author(s):  
J. Weickenmeier ◽  
M. Jabareen ◽  
B. J. D. Le Révérend ◽  
M. Ramaioli ◽  
E. Mazza
Keyword(s):  
Masseter Muscle ◽  
Computational Models ◽  
Mechanical Response ◽  
Force Measurement ◽  
Maxillofacial Surgery ◽  
Numerical Procedure ◽  
Magnetic Resonance Images ◽  
Muscle Response

Predictive simulations of the mastication system would significantly improve our understanding of temporomandibular joint (TMJ) disorders and the planning of cranio-maxillofacial surgery procedures. Respective computational models must be validated by experimental data from in vivo characterization of the mastication system's mechanical response. The present pilot-study demonstrates the feasibility of a combined experimental and numerical procedure to validate a computer model of the masseter muscle. An experimental setup is proposed that provides a simultaneous bite force measurement and ultrasound-based visualization of muscle deformation. The direct comparison of the experimentally observed and numerically predicted muscle response demonstrates the predictive capabilities of such anatomically accurate biting models. Differences between molar and incisor biting are investigated; muscle deformation is recorded for three different bite forces in order to capture the effect of increasing muscle fiber recruitment. The three-dimensional (3D) muscle deformation at each bite position and force-level is approximatively reconstructed from ultrasound measurements in five distinct cross-sectional areas (four horizontal and one vertical cross section). The experimental work is accompanied by numerical simulations to validate the predictive capabilities of a constitutive muscle model previously formulated. An anatomy-based, fully 3D model of the masseter muscle is created from magnetic resonance images (MRI) of the same subject. The direct comparison of experimental and numerical results revealed good agreement for maximum bite forces and masseter deformations in both biting positions. The present work therefore presents a feasible in vivo measurement system to validate numerically predicted masseter muscle contractions during mastication.

scholarly journals Conservation of Structure and Protein-Protein Interactions Mediated by the Secreted Mycobacterial Proteins EsxA, EsxB, and EspA

2009 ◽  
Vol 192 (1) ◽  
pp. 326-335 ◽  
Author(s):  
Brian Callahan ◽  
Kiet Nguyen ◽  
Alissa Collins ◽  
Kayla Valdes ◽  
Michael Caplow ◽  
...  
Keyword(s):  
Protein Interactions ◽  
Helical Structure ◽  
Protein Protein Interactions ◽  
Protein Protein Interaction ◽  
Structures And Properties ◽  
Virulence Protein ◽  
Single Polypeptide ◽  
Specific Association

ABSTRACT Mycobacterium tuberculosis EsxA and EsxB proteins are founding members of the WXG100 (WXG) protein family, characterized by their small size (∼100 amino acids) and conserved WXG amino acid motif. M. tuberculosis contains 11 tandem pairs of WXG genes; each gene pair is thought to be coexpressed to form a heterodimer. The precise role of these proteins in the biology of M. tuberculosis is unknown, but several of the heterodimers are secreted, which is important for virulence. However, WXG proteins are not simply virulence factors, since nonpathogenic mycobacteria also express and secrete these proteins. Here we show that three WXG heterodimers have structures and properties similar to those of the M. tuberculosis EsxBA (MtbEsxBA) heterodimer, regardless of their host species and apparent biological function. Biophysical studies indicate that the WXG proteins from M. tuberculosis (EsxG and EsxH), Mycobacterium smegmatis (EsxA and EsxB), and Corynebacterium diphtheriae (EsxA and EsxB) are heterodimers and fold into a predominately α-helical structure. An in vivo protein-protein interaction assay was modified to identify proteins that interact specifically with the native WXG100 heterodimer. MtbEsxA and MtbEsxB were fused into a single polypeptide, MtbEsxBA, to create a biomimetic bait for the native heterodimer. The MtbEsxBA bait showed specific association with several esx-1-encoded proteins and EspA, a virulence protein secreted by ESX-1. The MtbEsxBA fusion peptide was also utilized to identify residues in both EsxA and EsxB that are important for establishing protein interactions with Rv3871 and EspA. Together, the results are consistent with a model in which WXG proteins perform similar biological roles in virulent and nonvirulent species.

Hydration Effects on the Viscoelastic Properties of Collagen

2005 ◽  
Vol 898 ◽  
Author(s):  
M Ntim ◽  
Amanpreet Bembey ◽  
Virginia Ferguson ◽  
Andrew Bushby
Keyword(s):  
Elastic Modulus ◽  
Dynamic Mechanical Analysis ◽  
Viscoelastic Properties ◽  
Type I Collagen ◽  
Mechanical Analysis ◽  
Hierarchical Organization ◽  
Type I ◽  
Dynamic Mechanical ◽  
Insight Into

AbstractThe manner in which liquid interacts with collagen is unclear, with changes in hydration presenting ambiguity. At present, elastic modulus values for collagen quoted range from MPa to GPa. Dynamic mechanical analysis (DMA) of collagen in isolation provides an insight into the mechanical changes due to altered hydration states.Changes in the viscoelastic properties of collagen were examined as the material was systematically dehydrated in a series of water:solvent mixes to examine effects of dehydration. The effect of solvents with varying polarity was also examined. Tails from 11-week old wild type mice were used. Mouse tail is a tissue with a well-defined, hierarchical organization of type I collagen. The viscoelastic response of collagen was measured using dynamic mechanical analysis (DMA) in fiber extension mode over the frequency range of 1Hz to 10Hz. Samples were sequentially dehydrated in a series of solvent concentrations: 70% ethanol to 100% ethanol to 100% acetone and 70% ethanol to 70% methanol to 100% methanol for at least 1h. Selectively removing and then replacing water from collagen samples provides insight into the role of water in the ultrastructure of the tissue from the corresponding changes in the experimentally determined elastic modulus and viscous energy.

scholarly journals The Relation Between α-Helical Conformation and Amyloidogenicity

2017 ◽  
Author(s):  
B. Haimov ◽  
S. Srebnik
Keyword(s):  
Amyloid Fibrils ◽  
Clinical Importance ◽  
Helical Structure ◽  
Data Bank ◽  
Amino Acid Sequences ◽  
Helical Conformation ◽  
Folded Proteins ◽  
Two Parameters

ABSTRACTAmyloid fibrils are stable aggregates of misfolded proteins and polypeptides that are insoluble and resistant to protease activity. Abnormal formation of amyloid fibrils in vivo may lead to neurodegenerative disorders and other systemic amyloidosis such as Alzheimer’s, Parkinson’s, and atherosclerosis. Because of their clinical importance amyloids are found under intense scientific research. Amyloidogenic sequences of short polypeptide segments within proteins are responsible for the transformation of correctly folded proteins into parts of larger amyloid fibrils. The α-helical secondary structure is believed to host many amyloidogenic sequences and be a key player in different stages of the amyloidogenesis process. Most of the studies on amyloids focus on the role of amyloidogenic sequences. The focus of this study is the relation between amyloidogenicity and the structure of the amyloidogenic α-helical sequence. We have previously shown that the α-helical conformation may be expressed by two parameters (θ and ρ) that form orthogonal coordinates based on the Ramachandran dihedrals (φ and ψ) and provide an illuminating interpretation of the α-helical conformation. By performing statistical analysis on α-helical conformations found in the protein data bank, an apparent relation between α-helical conformation, as expressed by θ and ρ, and amyloidogenicity is revealed. Remarkably, random amino acid sequences, whose helical structure was obtained from the most probably dihedral angles as obtained from PDB data, revealed the same dependency of amyloidogenicity, suggesting the importance of α-helical structure as opposed to sequence.

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