An alternative finite element model for simulation of frictional gap

Hadi Mohammadi,Fereshteh Bahramian,Walter Herzog 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.12

This study is an attempt to modeling a frictional gap in a crack closure process under compressive loading conditions in which the crack surfaces are in touch and the effects of friction between them are significant. An iterative finite element (FE) solution is developed to model a finite crack in an interfacial layer with varying material properties. A mere application of a Lagrange multiplier formulation (node-to-node, NTN, or node-to-segment, NTS) in a developed FE framework to fulfill the contact constraints between contacting surfaces is discussed which improves the penalty formulation used in ANSYS. We then argue that the penalty formulation allows for a certain amount of crack surface interpenetration whereas the Lagrange multiplier formulation fulfils the contact constraints more accurately. This technique is easy to implement and offers higher accuracy than the equivalent FE solution, available in commercial FE software such as ANSYS 9.0, to the same system.

The effect of compressive loading magnitude on in situ chondrocyte calcium signaling

Madden, Ryan M. J.,Han, Sang-Kuy,Herzog, Walter Springer Berlin Heidelberg 2015 Biomechanics and modeling in mechanobiology Vol.14 No.1

<P>Chondrocyte metabolism is stimulated by deformation and is associated with structural changes in the cartilage extracellular matrix (ECM), suggesting that these cells are involved in maintaining tissue health and integrity. Calcium signaling is an initial step in chondrocyte mechanotransduction that has been linked to many cellular processes. Previous studies using isolated chondrocytes proposed loading magnitude as an important factor regulating this response. However, calcium signaling in the intact cartilage differs compared to isolated cells. The purpose of this study was to investigate the effect of loading magnitude on chondrocyte calcium signaling in intact cartilage. We hypothesized that the percentage of cells exhibiting at least one calcium signal increases with increasing load. Fully intact rabbit femoral condyle and patellar bone/cartilage samples were incubated in calcium-sensitive dyes and imaged continuously under compressive loads of 10–40 % strain. Calcium signaling was primarily associated with the dynamic loading phase and greatly increased beyond a threshold deformation of about 10 % nominal tissue strain. There was a trend toward more cells exhibiting calcium signaling as loading magnitude increased ([FORMULA OMISSION] = 0.133). These results provide novel information toward identifying mechanisms underlying calcium-dependent signaling pathways related to cartilage homeostasis and possibly the onset and progression of osteoarthritis.</P>

Three-dimensional micro-scale strain mapping in living biological soft tissues

Moo, Eng Kuan,Sibole, Scott C.,Han, Sang Kuy,Herzog, Walter Elsevier 2018 ACTA BIOMATERIALIA Vol.70 No.-

<P><B>Abstract</B></P> <P>Non-invasive characterization of the mechanical micro-environment surrounding cells in biological tissues at multiple length scales is important for the understanding of the role of mechanics in regulating the biosynthesis and phenotype of cells. However, there is a lack of imaging methods that allow for characterization of the cell micro-environment in three-dimensional (3D) space. The aims of this study were (i) to develop a multi-photon laser microscopy protocol capable of imprinting 3D grid lines onto living tissue at a high spatial resolution, and (ii) to develop image processing software capable of analyzing the resulting microscopic images and performing high resolution 3D strain analyses. Using articular cartilage as the biological tissue of interest, we present a novel two-photon excitation imaging technique for measuring the internal 3D kinematics in intact cartilage at sub-micrometer resolution, spanning length scales from the tissue to the cell level. Using custom image processing software, we provide accurate and robust 3D micro-strain analysis that allows for detailed qualitative and quantitative assessment of the 3D tissue kinematics. This novel technique preserves tissue structural integrity post-scanning, therefore allowing for multiple strain measurements at different time points in the same specimen. The proposed technique is versatile and opens doors for experimental and theoretical investigations on the relationship between tissue deformation and cell biosynthesis. Studies of this nature may enhance our understanding of the mechanisms underlying cell mechano-transduction, and thus, adaptation and degeneration of soft connective tissues.</P> <P><B>Statement of Significance</B></P> <P>We presented a novel two-photon excitation imaging technique for measuring the internal 3D kinematics in intact cartilage at sub-micrometer resolution, spanning from tissue length scale to cellular length scale. Using a custom image processing software (<I>lsmgridtrack</I>), we provide accurate and robust micro-strain analysis that allowed for detailed qualitative and quantitative assessment of the 3D tissue kinematics. The approach presented here can also be applied to other biological tissues such as meniscus and annulus fibrosus, as well as tissue-engineered tissues for the characterization of their mechanical properties. This imaging technique opens doors for experimental and theoretical investigation on the relationship between tissue deformation and cell biosynthesis. Studies of this nature may enhance our understanding of the mechanisms underlying cell mechano-transduction, and thus, adaptation and degeneration of soft connective tissues.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

The Effect of Botox Injections on the Mechanical Properties of Skinned Fibres from Rabbit Paraspinal Muscles

S. K. Han(한상규),Kevin R Boldt,K. J. Chun(전경진),Walter Herzog,Venus Joumaa Korean Society for Precision Engineering 2021 한국정밀공학회 학술발표대회 논문집 Vol.2021 No.11월

Botulinum toxin type A (BTX-A) has been widely used for the treatment of muscle stiffness and hyperactivity, such as spasticity and dystonia in patients post-stroke or children with Cerebral Palsy. However, BTX-A injection has been shown to cause muscle atrophy, fat infiltration, fibrosis, and decreased force output in target muscles, but its potential effects on the contractile machinery and force production on the cellular level remain unknown. The aim of this study was to investigate the effects of BTX-A injections on the mechanical properties of skinned fibres from rabbit paraspinal muscles. Nineteen-month-old rabbits received either saline or BTX-A injections into the paraspinal muscles, equally distributed along the left and right sides of the spine at T12, L1, and L2 for five times during 24 weeks. Fibres were tested for their active and passive force-length relationships, unloaded shortening velocity and myosin heavy chain isoforms. BTX-A injections led to significant fat infiltration within the injected muscles and a greater proportion of IIa to IIx fibres. Single fast fibres from BTX-A injected animals had lower active force and unloaded shortening velocity compared to fibres from saline-injected control animals. Force and velocity properties were not affected by BTX-A injections for the slow fibres.

Consumption of a high-fat-high-sucrose diet partly diminishes mechanical and structural adaptations of cardiac muscle following resistance training

Kevin Boldt,Stela Mattiello,Venus Joumaa,Jeannine Turnbull,Paul W.M. Fedak,Walter Herzog 한국운동영양학회 2021 Physical Activity and Nutrition (Phys Act Nutr) Vol.25 No.2

[Purpose] The purpose of this study was to investigate the effects of a high-fat high-sucrose (HFHS) diet on previously reported adaptations of cardiac morphological and contractile properties to resistance training. [Methods] Twelve-week-old rats participated in 12-weeks of resistance exercise training and consumed an HFHS diet. Echocardiography and skinned cardiac muscle fiber bundle testing were performed to determine the structural and mechanical adaptations. [Results] Compared to chow-fed sedentary animals, both HFHS- and chow-fed resistance-trained animals had thicker left ventricular walls. Isolated trabecular fiber bundles from chow-fed resistance-trained animals had greater force output, shortening velocities, and calcium sensitivities than those of chow-fed sedentary controls. However, trabeculae from the HFHS resistance-trained animals had greater force output but no change in unloaded shortening velocity or calcium sensitivity than those of the chow-fed sedentary group animals. [Conclusion] Resistance exercise training led to positive structural and mechanical adaptations of the heart, which were partly offset by the HFHS diet.

A high-whey-protein diet does not enhance mechanical and structural remodeling of cardiac muscle in response to aerobic exercise in rats

Kevin Boldt,Venus Joumaa,Jeannine Turnbull,Paul W.M. Fedak,Walter Herzog 한국운동영양학회 2022 Physical Activity and Nutrition (Phys Act Nutr) Vol.26 No.1

[Purpose] Aerobic exercise training results in distinct structural and mechanical myocardial adaptations. In skeletal muscle, whey protein supplementation is effective in enhancing muscle adaptation following resistance exercise. However, it is unclear whether cardiac adaptation to aerobic exercise can be enhanced by systematic protein supplementation. [Methods] Twelve-week-old rats were assigned to 12 weeks of either sedentary or aerobic exercise with either a standard (Sed+Standard, Ex+Standard) or high-protein (Sed+Pro, Ex+Pro) diet. Echocardiography was used to measure cardiac structural remodeling and performance. Skinned cardiac fiber bundles were used to determine the active and passive stress properties, maximum shortening velocity, and calcium sensitivity. [Results] Aerobic training was characterized structurally by increases in ventricle volume (Ex+Standard, 19%; Ex+Pro, 29%) and myocardial thickness (Ex+Standard, 26%; Ex+Pro, 12%) compared to that of baseline. Skinned trabecular fiber bundles also had a greater unloaded shortening velocity (Sed+Standard, 1.04±0.05; Sed+Pro, 1.07±0.03; Ex+Standard, 1.16±0.04; Ex+Pro, 1.18±0.05 FL/s) and calcium sensitivity (pCa50: Sed+Standard, 6.04±0.17; Sed+Pro, 6.08±0.19; Ex+Standard, 6.30±0.09; Ex+Pro, 6.36±0.12) in trained hearts compared to that of hearts from sedentary animals. However, the addition of a high-protein diet did not provide additional benefits to either the structural or mechanical adaptations of the myocardium. [Conclusion] Therefore, it seems that a high-whey-protein diet does not significantly enhance adaptations of the heart to aerobic exercise in comparison to that of a standard diet.

초기 관절염 동물모델에서의 연골세포와 주변 조직의 생체역학적 연구

한상규(S. K. Han),Jaana Makitalo,Simo Saarakkala,Lassi Rieppo,Salvatore Federico,Walter Herzog,전경진(K. J. Chun),Rami K Korhonen 한국정밀공학회 2015 한국정밀공학회 학술발표대회 논문집 Vol.2015 No.12월