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Time-dependent and depth-dependent compressive deformation of articular cartilage and chondrocytes
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Oral Presentations
Journal of Biomechanics 2006, Vol. 39 (Suppl 1)
6706 Mo, 12:15-12:30 (P8) Application of DNA technology to signal processing in mechanical
5645
Mo, 14:15-14:30 ( P l l )
systems
Time-dependent and depth-dependent compressive deformation of articular cartilage and chondrocytes
Q.-R Wang. Department of Automation and Computer Aided Engineering,
T. Murakami, N. Sakai, ~ Sawae, M. Okamoto, I. Ishikawa, ~ Kurohara.
The Chinese University of Hong Kong, Hong Kong
Department of Intelligent Machinery and Systems, Kyushu University, Fukueka, Japan
DNA computing has been extremely applied in various fields. In this paper, by constructing DNA algorithm based on new encoding techniques (cf. [1]), signal processing in mechanics systems is completely considered on the DNA domain. The proposed idea consists of five steps. Step 1. Generate DNA series composed by A, T, C, G from the signals, called the signal DNA. Step 2. Encode DNA signals to binary-like words with core relations A = 11, T=00, C=10, G=10. Step 3. Get twin-shuffle Language with universal using Watson-Crick complementarity _A=T, T=A, C=G, G=C. Step 4. Implement bio-information analysis for DNA sequences on DNA domain. Step 5. Search feature to obtained signals based on binary-like words domain. Searching of amplitude feature; Searching of frequency feature; Searching of periodicity; Searching of phase. Experiment demonstration for a practical data in monitoring of an injection molding processing is included. The results show the feasibility and efficient of proposed new DNA technology. Appealing points: Two concepts "DNA domain" and "binary-like domain" are proposed in signal processing. The signals can be easily analyzed by the new DNA encoding technology. DNA domain based signal processing is implemented rapidly, and binary-like domain based fault diagnosis and real time monitoring can be carried out in practical sense. It's also our hope that the new DNA technology will be developed into a usability methodology in bi-mechanics and widely areas.
References [1] Q.R Wang and R. Du. A DNA algorithm for feature selection in condition monitoring of manufacturing processes. In: Proceeding of International Symposium on Intelligent Signal Processing and Communication Systems, Hong Kong, 2005; pp. 773-776. 6283
Mo, 14:00-14:15 (P11)
Interplay between crosslinkers and dynamic molecular motor-induced instabilities in the moderation of biopolymer organization D. Smith 1,2, F. Ziebert3, D. Humphrey2, C. Duggan2, W. Zimmermann 3, J. K~s 1,2. 1Division for Soft Matter Physics, University of Leipzig, D-04103,
Germany, 2Center for Nonlinear Dynamics, University of Texas at Austin, Texas 78712, USA, 3Bayreuth, Germany All eukaryotic cells depend on mechanisms of self-assembly of protein filaments to form a cytoskeleton within the cell. The need for motility and reaction by cells to stimuli additionally requires the existence of pathways which serve to quickly restructure and disassemble cytoskeletal structures. While temperature-driven disordering is, from the viewpoint of physics, the most obvious method for dissolving complex structures, this approach would exceed the physiologically viable temperature range. This motif is exemplified in the de-hybridization of DNA, which is temperature-induced in PCR, but achieved by molecular motors in cells. We report a fundamental mechanism whereby changes in the activity of the actin-specific molecular motor Myosin II induce order-disorder transitions in reconstituted cytoskeletal actin-myosin networks. Bulk activity of the motors, which causes sliding of individual filaments in the presence of ATP, maintains a dynamically disordered network. During depletion of ATP, an increasing fraction of motors becomes inactive, crosslinking actin filaments to small clusters. The remaining active motors combined with continually increasing cross-linking foster further growth of these clusters, resulting in a variety of ordered macro-molecular structures. Modulation of static crosslinker (e.g., streptavidin) concentrations in coordination with molecular motors allows for a wide phase space of order ranging from nematics to compact asters & dense packing of motor-filament clusters. Experiments with photo-activated motors demonstrate a switch-like quick reversible restoration of the disordered state. This ability for rapid, isothermal motor-induced transitions between different degrees of self-organization indicates that molecular motors, in general, may substantially contribute to dynamic cellular organization.
The articular cartilage adapts to changing mechanical environment, but the detailed process controlled by chondroctes has not yet been clarified. To study the mechanism involved, it is important to know the stress-strain state of the cartilage tissue, extracellular matrix around chondrocytes and chondrocytes during cartilage deformation. The articular cartilage has a biphasic viscoelastic property based on high water content up to 80%. Therefore, the timedependent and depth-dependent deformation of compressed articular cartilage was observed in the compressive apparatus located in the stage of confocal laser scanning microscope (CLSM). Some related finite elemnt analysis was conducted. The semi-cylindrical cartilage specimen with 3 mm diamter and about 0.5 mm thickness was prepared from the femoral condyle of porcine knee joints. We observed the changes in local strain in articular cartilage specimens by monitoring the position of stained chondrocyte with calcein-AM in the compression device. On the basis of these visualized images, the timedependent and depth-dependent changes in local strain of articular cartilage were evaluated. In unconfined compression test with constant total deformation of articular cartilage specimen, initial compressive deformation showed depth-dependent strain distribution with small strain near subchondral bone immediately after cpompression. During stress relaxation process, the local deformation of middle zone was clearly recovered. In contrast, the surface zone was largely compressed than average strain during stress relaxation. Chondrocytes are deformed with similar strain to cartilage. Therefore, the chondrocytes in the superficial zone were largely deformed. It was observed that the chondrocytes in the superficial zone have the flattened morphology. For evaluation of these time-dependent and depth-dependent strain behaviors, the finite element analysis based on biphasic theory was conducted. It was shown that the boundary conditions of friction and permeability on the cartilage surface have an important influence on the time-dependent strain. 6158
Mo, 14:30-14:45 ( P l l )
Probing mechanical heterogeneity in chondrocytes using passive microrheology Z. Bomzon 1, M.M. Knight2, D.L. Bader2, E. Kimmel 3. 1Centre for Micro-Photonics, Swinbume University of Technology, Hawthorn, Victoria, Australia, 2Medical Engineering Division, Dept. of Engineering and IRC in Biomedical Materials, Queen Mary University of London, UK, 3Department of Biomedical Engineering, Technion-lsrael Institute of Technology, Haifa, Israel Characterising chondrocytes mechanics is important for understanding mechanotransduction. The bulk viscoelastic response of chondrocytes have been measured. However, their mechanical properties have not been resolved on a subcellular scale. Microrheolgy is a technique in which the mechanical properties of a material are found by analysing the Mean Square Displacement (MSD) [1] of tracerparticles. Microrheology can resolve mechanical properties with subcellular resolution. However, a limitation of microrheology is that large sequences of images of the particles are required for accurate measurements. These are not always available due to particles moving out of focus and photobleaching. This paper presents a microrheology-based study on mechanical heterogeneity in chondrocytes using short sequences of images. Bovine Articular chondrocytes were seeded into agarose constructs [2]. The mitochondria were fluorescently labeled and imaged every 30 seconds for 15 minutes with a confocal microscope. Digital Image Correlation was used to quantify the motion of the mitochondria and their MSDs were calculated. An average MSD was found for every cell and the variability in mitochondrial motion was obtained by comparing the distribution of measured MSDs to the distribution of MSDs obtained from Monte-Carlo simulations of particles embedded within heterogeneous media. Measured mitochondrial motion was consistent with directed diffusion [2]. The diffusion coefficient of the mitochondria varied by about 50% within single cells. Calculations based on statistical mechanics showed that directed diffusion can only occur if the cytoplasm behaves like a fluid on large time-scales. It is probable that this viscous behavior is connected to the non-equilibrium nature of the cytoskeleton [3].
References [1] Tseng Y, et al. Biophys. J 2002; 83: 3162-3176. [2] Bomzon Z, et al. J. Biomech. Eng, in press. [3] Bursac P, et al. Nat. Mater. 2005; 4: 557-561.
Oral Presentations
Journal of Biomechanics 2006, Vol. 39 (Suppl 1)
6706 Mo, 12:15-12:30 (P8) Application of DNA technology to signal processing in mechanical
5645
Mo, 14:15-14:30 ( P l l )
systems
Time-dependent and depth-dependent compressive deformation of articular cartilage and chondrocytes
Q.-R Wang. Department of Automation and Computer Aided Engineering,
T. Murakami, N. Sakai, ~ Sawae, M. Okamoto, I. Ishikawa, ~ Kurohara.
The Chinese University of Hong Kong, Hong Kong
Department of Intelligent Machinery and Systems, Kyushu University, Fukueka, Japan
DNA computing has been extremely applied in various fields. In this paper, by constructing DNA algorithm based on new encoding techniques (cf. [1]), signal processing in mechanics systems is completely considered on the DNA domain. The proposed idea consists of five steps. Step 1. Generate DNA series composed by A, T, C, G from the signals, called the signal DNA. Step 2. Encode DNA signals to binary-like words with core relations A = 11, T=00, C=10, G=10. Step 3. Get twin-shuffle Language with universal using Watson-Crick complementarity _A=T, T=A, C=G, G=C. Step 4. Implement bio-information analysis for DNA sequences on DNA domain. Step 5. Search feature to obtained signals based on binary-like words domain. Searching of amplitude feature; Searching of frequency feature; Searching of periodicity; Searching of phase. Experiment demonstration for a practical data in monitoring of an injection molding processing is included. The results show the feasibility and efficient of proposed new DNA technology. Appealing points: Two concepts "DNA domain" and "binary-like domain" are proposed in signal processing. The signals can be easily analyzed by the new DNA encoding technology. DNA domain based signal processing is implemented rapidly, and binary-like domain based fault diagnosis and real time monitoring can be carried out in practical sense. It's also our hope that the new DNA technology will be developed into a usability methodology in bi-mechanics and widely areas.
References [1] Q.R Wang and R. Du. A DNA algorithm for feature selection in condition monitoring of manufacturing processes. In: Proceeding of International Symposium on Intelligent Signal Processing and Communication Systems, Hong Kong, 2005; pp. 773-776. 6283
Mo, 14:00-14:15 (P11)
Interplay between crosslinkers and dynamic molecular motor-induced instabilities in the moderation of biopolymer organization D. Smith 1,2, F. Ziebert3, D. Humphrey2, C. Duggan2, W. Zimmermann 3, J. K~s 1,2. 1Division for Soft Matter Physics, University of Leipzig, D-04103,
Germany, 2Center for Nonlinear Dynamics, University of Texas at Austin, Texas 78712, USA, 3Bayreuth, Germany All eukaryotic cells depend on mechanisms of self-assembly of protein filaments to form a cytoskeleton within the cell. The need for motility and reaction by cells to stimuli additionally requires the existence of pathways which serve to quickly restructure and disassemble cytoskeletal structures. While temperature-driven disordering is, from the viewpoint of physics, the most obvious method for dissolving complex structures, this approach would exceed the physiologically viable temperature range. This motif is exemplified in the de-hybridization of DNA, which is temperature-induced in PCR, but achieved by molecular motors in cells. We report a fundamental mechanism whereby changes in the activity of the actin-specific molecular motor Myosin II induce order-disorder transitions in reconstituted cytoskeletal actin-myosin networks. Bulk activity of the motors, which causes sliding of individual filaments in the presence of ATP, maintains a dynamically disordered network. During depletion of ATP, an increasing fraction of motors becomes inactive, crosslinking actin filaments to small clusters. The remaining active motors combined with continually increasing cross-linking foster further growth of these clusters, resulting in a variety of ordered macro-molecular structures. Modulation of static crosslinker (e.g., streptavidin) concentrations in coordination with molecular motors allows for a wide phase space of order ranging from nematics to compact asters & dense packing of motor-filament clusters. Experiments with photo-activated motors demonstrate a switch-like quick reversible restoration of the disordered state. This ability for rapid, isothermal motor-induced transitions between different degrees of self-organization indicates that molecular motors, in general, may substantially contribute to dynamic cellular organization.
The articular cartilage adapts to changing mechanical environment, but the detailed process controlled by chondroctes has not yet been clarified. To study the mechanism involved, it is important to know the stress-strain state of the cartilage tissue, extracellular matrix around chondrocytes and chondrocytes during cartilage deformation. The articular cartilage has a biphasic viscoelastic property based on high water content up to 80%. Therefore, the timedependent and depth-dependent deformation of compressed articular cartilage was observed in the compressive apparatus located in the stage of confocal laser scanning microscope (CLSM). Some related finite elemnt analysis was conducted. The semi-cylindrical cartilage specimen with 3 mm diamter and about 0.5 mm thickness was prepared from the femoral condyle of porcine knee joints. We observed the changes in local strain in articular cartilage specimens by monitoring the position of stained chondrocyte with calcein-AM in the compression device. On the basis of these visualized images, the timedependent and depth-dependent changes in local strain of articular cartilage were evaluated. In unconfined compression test with constant total deformation of articular cartilage specimen, initial compressive deformation showed depth-dependent strain distribution with small strain near subchondral bone immediately after cpompression. During stress relaxation process, the local deformation of middle zone was clearly recovered. In contrast, the surface zone was largely compressed than average strain during stress relaxation. Chondrocytes are deformed with similar strain to cartilage. Therefore, the chondrocytes in the superficial zone were largely deformed. It was observed that the chondrocytes in the superficial zone have the flattened morphology. For evaluation of these time-dependent and depth-dependent strain behaviors, the finite element analysis based on biphasic theory was conducted. It was shown that the boundary conditions of friction and permeability on the cartilage surface have an important influence on the time-dependent strain. 6158
Mo, 14:30-14:45 ( P l l )
Probing mechanical heterogeneity in chondrocytes using passive microrheology Z. Bomzon 1, M.M. Knight2, D.L. Bader2, E. Kimmel 3. 1Centre for Micro-Photonics, Swinbume University of Technology, Hawthorn, Victoria, Australia, 2Medical Engineering Division, Dept. of Engineering and IRC in Biomedical Materials, Queen Mary University of London, UK, 3Department of Biomedical Engineering, Technion-lsrael Institute of Technology, Haifa, Israel Characterising chondrocytes mechanics is important for understanding mechanotransduction. The bulk viscoelastic response of chondrocytes have been measured. However, their mechanical properties have not been resolved on a subcellular scale. Microrheolgy is a technique in which the mechanical properties of a material are found by analysing the Mean Square Displacement (MSD) [1] of tracerparticles. Microrheology can resolve mechanical properties with subcellular resolution. However, a limitation of microrheology is that large sequences of images of the particles are required for accurate measurements. These are not always available due to particles moving out of focus and photobleaching. This paper presents a microrheology-based study on mechanical heterogeneity in chondrocytes using short sequences of images. Bovine Articular chondrocytes were seeded into agarose constructs [2]. The mitochondria were fluorescently labeled and imaged every 30 seconds for 15 minutes with a confocal microscope. Digital Image Correlation was used to quantify the motion of the mitochondria and their MSDs were calculated. An average MSD was found for every cell and the variability in mitochondrial motion was obtained by comparing the distribution of measured MSDs to the distribution of MSDs obtained from Monte-Carlo simulations of particles embedded within heterogeneous media. Measured mitochondrial motion was consistent with directed diffusion [2]. The diffusion coefficient of the mitochondria varied by about 50% within single cells. Calculations based on statistical mechanics showed that directed diffusion can only occur if the cytoplasm behaves like a fluid on large time-scales. It is probable that this viscous behavior is connected to the non-equilibrium nature of the cytoskeleton [3].
References [1] Tseng Y, et al. Biophys. J 2002; 83: 3162-3176. [2] Bomzon Z, et al. J. Biomech. Eng, in press. [3] Bursac P, et al. Nat. Mater. 2005; 4: 557-561.