The Experts below are selected from a list of 249 Experts worldwide ranked by ideXlab platform
Michael S. Sacks - One of the best experts on this subject based on the ideXlab platform.
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fiber orientation of the transverse carpal ligament
Clinical Anatomy, 2012Co-Authors: Ryan K Prantil, Michael S. Sacks, Kaihua Xiu, Kwang E Kim, Diana M Gaitan, Savio L C WooAbstract:The transverse carpal ligament is the volar roof of the carpal tunnel. Gross observation shows that the ligament appears to have fibers that roughly orient in the transverse direction. A closer anatomical examination shows that the ligament also has oblique fibers. Knowledge of the fiber orientation of the transverse carpal ligament is valuable for further understanding the ligament's role in regulating the structural function of the carpal tunnel. The purpose of this study is to quantify collagen fiber orientation within the transverse carpal ligament using the small angle Light Scattering technique. Eight transverse carpal ligament samples from cadaver hands were used in this study. Individual 20-μm sections were cut evenly along the thickness of the transverse carpal ligament. Sections of three thickness levels (25%, 50%, and 75% from the volar surface) were collected for each transverse carpal ligament. Fibers were grouped in the following orientation ranges: transverse, longitudinal, oblique in the pisiform-trapezium (PT), and oblique in the scaphoid-hamate (SH) directions. In analyzing the fiber percentages, the orientation types for the different thickness levels of the ligament showed that the transverse fibers were the most prominent (>60.7%) followed by the PT oblique (18.6%), SH oblique (13.0%), and longitudinal (8.6%) fibers.
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functional collagen fiber architecture of the pulmonary heart valve cusp
The Annals of Thoracic Surgery, 2009Co-Authors: Jun Liao, Erinn M Joyce, Frederick J Schoen, John E Mayer, Michael S. SacksAbstract:Background Defects in the pulmonary valve (PV) occur in a variety of forms of congenital heart diseases. Quantitative information on PV collagen fiber architecture, and particularly its response to diastolic forces, is necessary for the design and functional assessment of approaches for PV repair and replacement. This necessity is especially the case for novel tissue-engineered PV, which rely on extensive in-vivo remodeling for long-term function. Methods Porcine PV and aortic valves (AV) were fixed under a 0 to 90 mm Hg transvalvular pressure. After dissection from the root, Small-Angle Light-Scattering measurements were conducted to quantify the collagen fiber architecture and changes with increasing applied transvalvular pressure over the entire cusp. Histomorphologic measurements were also performed to assess changes in cuspal layer thickness with pressure. Results While the PV and AV displayed anticipated structural similarities, they also presented important functionally related differences. In the unloaded state, the AV cusp demonstrated substantial regional variations in fiber alignment, whereas the PV was surprisingly uniform. Further, the AV demonstrated substantially larger changes in collagen fiber alignment with applied transvalvular pressure compared with the PV. Overall, the AV collagen fiber network demonstrated greater ability to respond to applied transvalvular pressure. A decrease in crimp amplitude was the predominant mechanism for improvement in the degree of orientation of the collagen fibers in both valves. Conclusions This study clarified the major similarities and differences between the PV and the AV. While underscoring how the PV can serve as an appropriate replacement of the diseased AV, the observed structural differences may also indicate limits to the ability of the PV to fully duplicate the AV. Moreover, quantitative data from this study on PV functional architecture will benefit development of tissue-engineered PV by defining the critical fiber architectural characteristics.
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Altered structural and mechanical properties in decellularized rabbit carotid arteries
Acta biomaterialia, 2008Co-Authors: Corin Williams, Michael S. Sacks, Erinn M Joyce, Jun Liao, Bo Wang, Jennie B. Leach, Joyce Y. WongAbstract:Recently, major achievements in creating decellularized whole tissue scaffolds have drawn considerable attention to decellularization as a promising approach for tissue engineering. Decellularized tissues are expected to have mechanical strength and structure similar to the native tissues from which they are derived. However, numerous studies have shown that mechanical properties change after decellularization. Often, tissue structure is observed by histology and electron microscopy, but the structural alterations that may have occurred are not always evident. Here, a variety of techniques were used to investigate changes in tissue structure and relate them to altered mechanical behavior in decellularized rabbit carotid arteries. Histology and scanning electron microscopy revealed that major extracellular matrix components were preserved and fibers appeared intact, although collagen appeared looser and less crimped after decellularization. Transmission electron microscopy confirmed the presence of proteoglycans (PG), but there was decreased PG density and increased spacing between collagen fibrils. Mechanical testing and opening angle measurements showed that decellularized arteries had significantly increased stiffness, decreased extensibility and decreased residual stress compared with native arteries. Small-Angle Light Scattering revealed that fibers had increased mobility and that structural integrity was compromised in decellularized arteries. Taken together, these studies revealed structural alterations that could be related to changes in mechanical properties. Further studies are warranted to determine the specific effects of different decellularization methods on the structure and performance of decellularized arteries used as vascular grafts.
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in situ deformation of the aortic valve interstitial cell nucleus under diastolic loading
Journal of Biomechanical Engineering-transactions of The Asme, 2007Co-Authors: Hsiaoying Shadow Huang, Jun Liao, Michael S. SacksAbstract:Within the aortic valve (AV) leaflet resides a population of interstitial cells (AVICs), which serve to maintain tissue structural integrity via protein synthesis and enzymatic degradation. AVICs are typically characterized as myofibroblasts, exhibit phenotypic plasticity, and may play an important role in valve pathophysiology. While it is known that AVICs can respond to mechanical stimuli in vitro, the level of in vivo AVIC deformation and its relation to local collagen fiber reorientation during the cardiac cycle remain unknown. In the present study, the deformation of AVICs was investigated using porcine AV glutaraldehyde fixed under 0–9 0 mm Hgtransvalvular pressures. The resulting change in nuclear aspect ratio (NAR) was used as an index of overall cellular strain, and dependencies on spatial location and pressure loading levels quantified. Local collagen fiber alignment in the same valves was also quantified using small angle Light Scattering. A tissue-level finite element (FE) model of an AVIC embedded in the AV extracellular matrix was also used explore the relation between AV tissue- and cellularlevel deformations. Results indicated large, consistent increases in AVIC NAR with transvalvular pressure (e.g., from mean of 1.8 at 0m m Hgto a mean of 4.8 at 90 mm Hg), as well as pronounced layer specific dependencies. Associated changes in collagen fiber alignment indicated that little AVIC deformation occurs with the large amount of fiber straightening for pressures below 1m m Hg, followed by substantial increases in AVIC NAR from 4m m Hg to 90 mm Hg. While the tissue-level FE model was able to capture the qualitative response, it also underpredicted the extent of AVIC deformation. This result suggested that additional micromechanical and fiber-compaction effects occur at high pressure levels. The results of this study form the basis of understanding transvalvular pressure-mediated mechanotransduction within the native AV and first time quantitative data correlating AVIC nuclei deformation with AV tissue microstructure and deformation. DOI: 10.1115/1.2801670
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effect of length of the engineered tendon construct on its structure function relationships in culture
Journal of Biomechanics, 2007Co-Authors: Victor S Nirmalanandhan, Michael S. Sacks, Balakrishna Haridas, David L ButlerAbstract:Constructs containing autogenous mesenchymal stem cells (MSCs) seeded in collagen gels have been used by our group to repair rabbit central patellar tendon defect injuries. Although these cell–gel composites exhibit improved repair biomechanics compared to natural healing, they can be difficult to handle at surgery and lack the necessary stiffness to resist peak in vivo forces early thereafter. MSCs are typically suspended in collagen gels around two posts in the base of a well in a specially designed silicone dish. The distance between posts is approximately the length of the tendon wound site. MSCs contract the gel around the posts prior to removal of the construct for implantation at surgery. We hypothesized that in vitro construct alignment and stiffness might be enhanced in the midregion of the longer construct where the end effects of the posts on the bulk material (St. Venant effects) could be minimized. Rabbit MSCs were seeded in purified bovine collagen gel at 0.04 M cells/mg collagen. The cell–gel mixture was pipetted into silicone dishes having two post-to-post lengths (short: 11 mm and long: 51 mm) but equivalent well widths and depths and post diameters. After 14 days of incubation, tensile stiffness and modulus of the constructs were measured using equivalent grip-to-grip lengths. Collagen fiber orientation index or OI (which measures angular dispersion of fibers) was quantified using small angle Light Scattering (SALS). Long constructs showed significantly lower angular dispersion vs. short constructs (OI of 41.24°±1.57° vs. 48.43°±1.27°, mean±SEM, p<0.001) with significantly higher linear modulus (0.064±0.009 MPa vs. 0.024±0.004 MPa, p=0.0022) and linear stiffness (0.031±0.005 MPa vs. 0.018±0.004 N/mm, mean±SEM, respectively, p=0.0404). We now plan to use principles of functional tissue engineering to determine if repairs containing central regions of longer MSC-collagen constructs improve defect repair biomechanics after implantation at surgery.
Takeji Hashimoto - One of the best experts on this subject based on the ideXlab platform.
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shear small angle Light Scattering studies of shear induced concentration fluctuations and steady state viscoelastic properties
Journal of Chemical Physics, 2008Co-Authors: Maya K Endoh, Mikihito Takenaka, Tadashi Inoue, Hiroshi Watanabe, Takeji HashimotoAbstract:We aimed at elucidating the influence of shear-induced structures (shear-enhanced concentration fluctuations and/or shear-induced phase separation), as observed by rheo-optical methods with Small-Angle Light Scattering under shear flow (shear-SALS) and shear-microscopy, on viscoelastic properties in semidilute polystyrene (PS) solutions of 6.0wt% concentration using dioctyl phthalate (DOP) as a Θ solvent and tricresyl phosphate (TCP) as a good solvent. In order to quantify the effects of the shear-induced structures, we conducted a numerical analysis of rheological properties in a homogeneous solution based on the constitutive equation developed by Kaye-Bernstein, Kearsley, and Zapas (K-BKZ). In the low-to-intermediate shear rate γ region between τw−1 and τe−1, where τw and τe are, respectively, terminal relaxation time and the relaxation time for chain stretching, the steady state rheological properties, such as shear stress σ and the first normal stress difference N1, for the PS/DOP and PS/TCP solution...
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Light Scattering and small angle neutron Scattering studies of structures in a semidilute polymer solution induced under oscillatory shear flow
Macromolecules, 2000Co-Authors: Shin Saito, Katsuo Matsuzaka, Satoshi Koizumi, Shoji Suehiro, Takeji HashimotoAbstract:Oscillatory-shear-flow-induced structures of a semidilute polymer solution of ultrahigh molecular weight deuterated polystyrene in dioctyl phthalate were investigated by using the Small-Angle Light Scattering (SALS) and the Small-Angle neutron Scattering (SANS). Under a fixed strain amplitude of oscillatory shear flow at 4.8, we observed the shear-induced structures as a function of the angular frequency (ω) and the strain-phase. At low ω, butterfly patterns, which are the Scattering patterns unique to the shear-induced structures formed in semidilute polymer solution, were observed by SALS and isotropic patterns with weak scattered intensities were obtained by SANS. At high ω, on the other hand, SANS showed butterfly patterns and SALS showed almost isotropic patterns. These results indicate that the anisotropic structures developed under oscillatory shear flow become smaller with increasing ω. From the SALS and SANS patterns, we obtained Scattering profiles parallel and perpendicular to the flow directio...
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a rheo optical apparatus for simultaneous detection of rheology small angle Light Scattering and optical microscopy under transient oscillatory and continuous shear flows
Review of Scientific Instruments, 1999Co-Authors: Katsuo Matsuzaka, Takeji HashimotoAbstract:A rheo-optical apparatus is constructed by installing a Small-Angle Light Scattering instrument and an optical microscope in a rheometer to investigate relationships between rheological properties and structures in complex liquids (or soft condensed matters). The apparatus is designed in such a way that it really enables us to measure simultaneously the rheological properties, Light Scattering, and transmission optical micrographs under both steady and dynamic shear field. It covers over a wide range of torque: it is applicable to systems having only the small viscosity of water ∼1 mPa as well as polymer systems in bulk having a high shear modulus G′∼109 Pa. An assembly of lens and a cooled charge coupled device camera allow us quantitative measurements of 2D Light Scattering patterns. For dynamic shear field, both Light Scattering measurements and optical microscopy observations can be synchronized with a given strain phase φ, defined in the text. Preliminary experiments with the apparatus are demonstrat...
Walter Richtering - One of the best experts on this subject based on the ideXlab platform.
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shear induced morphology transition and microphase separation in a lamellar phase doped with clay particles
Langmuir, 2004Co-Authors: Florian Nettesheim, Peter Lindner, Isabelle Grillo, Walter RichteringAbstract:We report on the influence of shear on a nonionic lamellar phase of tetraethyleneglycol monododecyl ether (C 1 2 E 4 ) in D 2 O containing clay particles (Laponite RD). The system was studied by means of Small-Angle Light Scattering (SALS) and Small-Angle neutron Scattering (SANS) under shear. The SANS experiments were conducted using a H 2 O/D 2 O mixture of the respective Scattering length density to selectively match the clay Scattering. The rheological properties show the familiar shear thickening regime associated with the formation of multilamellar vesicles (MLVs) and a shear thinning regime at higher stresses. The variation of viscosity is less pronounced as commonly observed. In the shear thinning regime, depolarized SALS reveals an unexpectedly strong variation of the MLV size. SANS experiments using the samples with lamellar contrast reveal a change in interlamellar spacing of up to 30% at stresses that lead to MLV formation. This change is much more pronounced than the change observed, when shear suppresses thermal bilayer undulations. Microphase separation occurs, and as a consequence, the lamellar spacing decreases drastically. The coincidence of the change in lamellar spacing and the onset of MLV formation is a strong indication for a morphology-driven microphase separation.
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rheo small angle Light Scattering investigation of shear induced structural changes in a lyotropic lamellar phase
Journal of Colloid and Interface Science, 1996Co-Authors: Jörg Läuger, Richard Weigel, Klaus Berger, Karl Hiltrop, Walter RichteringAbstract:The influence of shear on a lamellar phase in the system sodium dodecyl sulfate/decanol/water was investigated by combined rheo-small angle Light Scattering. Three different regions were detected and all could be characterized by different Scattering patterns in depolarized and polarized Light Scattering. Flow alignment of anisotropic domains in flow direction was found at low and high shear rates. A viscosity maximum was observed at intermediate shear rates, and different anisotropic Scattering patterns were detected in polarized and depolarized Scattering. The data are interpreted by a shear-induced formation of vesicles which displayed a characteristic four-lobe pattern in depolarized Scattering. A butterfly pattern observed in polarized Scattering indicated the existence of concentration fluctuations along the flow direction. The transitions between the three regions were reversible, but the formation of vesicles was found only when the sample was sheared for a long time at appropriate shear rates. Complicated rheological properties as, e.g., shear thinning and shear thickening, were found as a consequence of the structural changes.
Gerald G Fuller - One of the best experts on this subject based on the ideXlab platform.
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anisotropy and orientation of the microstructure in viscous emulsions during shear flow
Langmuir, 1998Co-Authors: Jan Vermant, P Van Puyvelde, Paula Moldenaers, Joannes Mewis, Gerald G FullerAbstract:Flow Small-Angle Light Scattering and linear conservative dichroism are used to follow, in situ and time resolved, the flow-induced changes of the microstructure in viscous emulsions such as immisc...
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dynamic response of a near critical polymer blend solution under oscillatory shear flow
Journal of Rheology, 1996Co-Authors: Janet Lai, Gerald G FullerAbstract:External flow is known to induce anisotropic growth of concentration fluctuations in polymer solutions close to the phase boundary. In this article, Scattering dichroism measurements are used to investigate the structural dynamics of flow‐enhanced concentration fluctuations in a near‐critical, semidilute polymer blend solution subjected to small‐amplitude oscillatory shear flow. Our measured frequency response reveals that the behavior of the shear‐induced fluctuations is governed by the relaxation time of the concentration fluctuations. Predictions from a hydrodynamic model, in good agreement with the experimental results, also indicate that the dynamics are dominated by a single relaxation time. In addition, relaxation times of the concentration fluctuations at various temperatures are calculated from dichroism data and are found to agree with those previously obtained from small‐angle Light Scattering experiments.
Didier Roux - One of the best experts on this subject based on the ideXlab platform.
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shear induced states of orientation of the lamellar phase of c12e4 water
Langmuir, 1999Co-Authors: Stefan Muller, Claus Borschig, And Wolfram Gronski, Claudia Schmidt, Didier RouxAbstract:The shear-induced states of orientation of the lamellar lyotropic mesophase of tetraethylene glycol monododecyl ether (C12E4) in water are investigated by polarizing microscopy, viscometry, Small-Angle Light Scattering, and deuteron NMR spectroscopy. The solution containing 40 w/w % surfactant shows a continuous transition from a state of aligned layers, whose normal is parallel to the velocity gradient, to a close packing of multilamellar vesicles (onion state). The size of the vesicles (diameter d) is controlled by the shear rate γ, following the relationship d ∝ γa with a ≈ −0.5.
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structure of a lyotropic lamellar phase under shear
Physical Review Letters, 1997Co-Authors: Philippe Sierro, Didier RouxAbstract:The effect of shear on a lyotropic lamellar phase is studied by the means of Small-Angle Light Scattering and direct microscopic observations. We found a complex behavior that can be described by a shear diagram. This diagram exhibits successively as a function of shear four different steady states. After a transition to a phase of monodisperse multilamellar vesicles with no long-range order there is a transition to the same vesicles exhibiting long-range order. At even higher shear rates, there is a transition between this ordered population of vesicles of size typically $1\ensuremath{\mu}\mathrm{m}$ to another ordered state made of vesicles which are much bigger (from 10 to $50\ensuremath{\mu}\mathrm{m}$).
