The Experts below are selected from a list of 10386 Experts worldwide ranked by ideXlab platform
David G Simpson - One of the best experts on this subject based on the ideXlab platform.
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electrospinning aligned and random polydioxanone polycaprolactone silk fibroin blended scaffolds geometry for a vascular matrix
Biomedical Materials, 2009Co-Authors: Michael J Mcclure, Chantal E Ayres, David G Simpson, Scott A Sell, Gary L BowlinAbstract:Extracellular matrices are arranged with a specific geometry based on tissue type and mechanical stimulus. For blood vessels in the body, preferential Alignment of Fibers is in the direction of repetitive force. Electrospinning is a controllable process which can result in Fiber Alignment and randomization depending on the parameters utilized. In this study, arterial grafts composed of polycaprolactone (PCL), polydioxanone (PDO) and silk fibroin in blends of 100:0 and 50:50 for both PCL:silk and PDO:silk were investigated to determine if Fibers could be controllably aligned using a mandrel rotational speed ranging from 500 to 8000 revolutions per minute (RPM). Results revealed that large- and small-diameter mandrels produced different degrees of Fiber Alignment based on a fast Fourier transform of scanning electron microscope images. Uniaxial tensile testing further demonstrated scaffold anisotropy through changes in peak stress, modulus and strain at break at mandrel rotational speeds of 500 and 8000 RPM, causing peak stress and modulus for PCL to increase 5- and 4.5-fold, respectively, as rotational speed increased. Additional mechanical testing was performed on grafts using dynamic compliance, burst strength and longitudinal strength displaying that grafts electrospun at higher rotational rates produced stiffer conduits which had lower compliance and higher burst strength compared to the lower mandrel rotational rate. Scaffold properties were found to depend on several parameters in the electrospinning process: mandrel rotational rate, polymer type, and mandrel size. Vascular scaffold design under anisotropic conditions provided interesting insights and warrants further investigation.
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measuring Fiber Alignment in electrospun scaffolds a user s guide to the 2d fast fourier transform approach
Journal of Biomaterials Science-polymer Edition, 2008Co-Authors: Chantal E Ayres, Gary L Bowlin, Shekhar B Jha, Hannah R Meredith, James R Bowman, Scott C Henderson, David G SimpsonAbstract:In this study we describe how to use a two-dimensional fast Fourier transform (2D FFT) approach to measure Fiber Alignment in electrospun materials. This image processing function can be coupled with a variety of imaging modalities to assign an objective numerical value to scaffold anisotropy. A data image of an electrospun scaffold is composed of pixels that depict the spatial organization of the constituent Fibers. The 2D FFT function converts this spatial information into a mathematically defined frequency domain that maps the rate at which pixel intensities change across the original data image. This output image also contains quantitative information concerning the orientation of objects in a data image. We discuss the theory and practice of using the frequency plot of the 2D FFT function to measure relative scaffold anisotropy and identify the principal axis of Fiber orientation. We note that specific degrees of scaffold anisotropy may represent a critical design feature in the fabrication of tissue...
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incremental changes in anisotropy induce incremental changes in the material properties of electrospun scaffolds
Acta Biomaterialia, 2007Co-Authors: Chantal E Ayres, Gary L Bowlin, Leander Taylor, Ryan Pizinger, Christopher Keen, David G SimpsonAbstract:Electrospinning can be used to selectively process a variety of natural and synthetic polymers into highly porous scaffolds composed of nano-to-m diameter Fibers. This process shows great potential as a gateway to the development of physiologically relevant tissue engineering scaffolds. In this study, we examine how incremental changes in Fiber Alignment modulate the material properties of a model scaffold. We prepared electrospun scaffolds of gelatin composed of varying Fiber diameters and degrees of anisotropy. The scaffolds were cut into a series of "dog-bone" shaped samples in the longitudinal, perpendicular and transverse orientations and the relative degree of Fiber Alignment, as measured by the fast Fourier transform (FFT) method, was determined for each sample. We measured peak stress, peak strain and the modulus of elasticity as a function of Fiber diameter and scaffold anisotropy. Fiber Alignment was the variable most closely associated with the regulation of peak stress, peak strain and modulus of elasticity. Incremental changes, as judged by the FFT method, in the proportion of Fibers that were aligned along a specific axis induced incremental changes in peak stress in the model scaffolds. These results underscore the critical role that scaffold anisotropy plays in establishing the material properties of an electrospun tissue engineering scaffold and the native extracellular matrix.
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modulation of anisotropy in electrospun tissue engineering scaffolds analysis of Fiber Alignment by the fast fourier transform
Biomaterials, 2006Co-Authors: Chantal E Ayres, Gary L Bowlin, Scott C Henderson, Leander Taylor, Jacqueline C Shultz, John K Alexander, Todd A Telemeco, David G SimpsonAbstract:We describe the use of the fast Fourier transform (FFT) in the measurement of anisotropy in electrospun scaffolds of gelatin as a function of the starting conditions. In electrospinning, Fiber Alignment and overall scaffold anisotropy can be manipulated by controlling the motion of the collecting mandrel with respect to the source electrospinning solution. By using FFT to assign relative Alignment values to an electrospun matrix it is possible to systematically evaluate how different processing variables impact the structure and material properties of a scaffold. Gelatin was suspended at varying concentrations (80, 100, 130, 150 mg/ml) and electrospun from 2,2,2 trifluoroethanol onto rotating mandrels (200–7000 RPM). At each starting concentration, Fiber diameter remained constant over a wide range of mandrel RPM. Scaffold anisotropy developed as a function of Fiber diameter and mandrel RPM. The induction of varying degrees of anisotropy imparted distinctive material properties to the electrospun scaffolds. The FFT is a rapid method for evaluating Fiber Alignment in tissue-engineering materials.
Michael S. Sacks - One of the best experts on this subject based on the ideXlab platform.
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non destructive reflectance mapping of collagen Fiber Alignment in heart valve leaflets
Annals of Biomedical Engineering, 2019Co-Authors: Will Goth, Michael S. Sacks, Samuel Potter, Alicia C B Allen, Janet Zoldan, James W TunnellAbstract:Collagen Fibers are the primary structural elements that define many soft-tissue structure and mechanical function relationships, so that quantification of collagen organization is essential to many disciplines. Current tissue-level collagen Fiber imaging techniques remain limited in their ability to quantify Fiber organization at macroscopic spatial scales and multiple time points, especially in a non-contacting manner, requiring no modifications to the tissue, and in near real-time. Our group has previously developed polarized spatial frequency domain imaging (pSFDI), a reflectance imaging technique that rapidly and non-destructively quantifies planar collagen Fiber orientation in superficial layers of soft tissues over large fields-of-view. In this current work, we extend the light scattering models and image processing techniques to extract a critical measure of the degree of collagen Fiber Alignment, the normalized orientation index (NOI), directly from pSFDI data. Electrospun Fiber samples with architectures similar to many collagenous soft tissues and known NOI were used for validation. An inverse model was then used to extract NOI from pSFDI measurements of aortic heart valve leaflets and clearly demonstrated changes in degree of Fiber Alignment between opposing sides of the sample. These results show that our model was capable of extracting absolute measures of degree of Fiber Alignment in superficial layers of heart valve leaflets with only general a priori knowledge of Fiber properties, providing a novel approach to rapid, non-destructive study of microstructure in heart valve leaflets using a reflectance geometry.
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Fabrication of elastomeric scaffolds with curvilinear fibrous structures for heart valve leaflet engineering
Journal of Biomedical Materials Research Part A, 2015Co-Authors: Christopher M. Hobson, Ethan N. Ungchusri, Nicholas J Amoroso, Antonio D'amore, Rouzbeh Amini, Michael S. Sacks, Yi Hong, William R WagnerAbstract:Native semi-lunar heart valves are composed of a dense fibrous network that generally follows a curvilinear path along the width of the leaflet. Recent models of engineered valve leaflets have predicted that such curvilinear Fiber orientations would homogenize the strain field and reduce stress concentrations at the commissure. In the present work, a method was developed to reproduce this curvilinear Fiber Alignment in electrospun scaffolds by varying the geometry of the collecting mandrel. Elastomeric poly(ester urethane)urea was electrospun onto rotating conical mandrels of varying angles to produce fibrous scaffolds where the angle of Fiber Alignment varied linearly over scaffold length. By matching the radius of the conical mandrel to the radius of curvature for the native pulmonary valve, the electrospun constructs exhibited a curvilinear Fiber structure similar to the native leaflet. Moreover, the constructs had local mechanical properties comparable to conventional scaffolds and native heart valves. In agreement with prior modeling results, it was found under quasi-static loading that curvilinear Fiber microstructures reduced strain concentrations compared to scaffolds generated on a conventional cylindrical mandrels. Thus, this simple technique offers an attractive means for fabricating scaffolds where key microstructural features of the native leaflet are imitated for heart valve tissue engineering.
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elastomeric electrospun polyurethane scaffolds the interrelationship between fabrication conditions Fiber topology and mechanical properties
Advanced Materials, 2011Co-Authors: Nicholas J Amoroso, William R Wagner, Yi Hong, Antonio Damore, Michael S. SacksAbstract:Electrospinning has been gaining increasing popularity in the fabrication of engineered tissue scaffolds due to its ability to produce nano to micro scale fibrous sheets. Many investigators have attempted to apply various degrees of control to this process in order to produce Fiber meshes with more predictable patterns. These attempts have largely been limited to controlling Fiber Alignment and have fallen into two categories: physical manipulation of the Fibers by pulling them into Alignment using a rapidly spinning mandrel[1–3] or manipulation of the electric field during fabrication.[4, 5]
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collagen Fiber Alignment and biaxial mechanical behavior of porcine urinary bladder derived extracellular matrix
Biomaterials, 2008Co-Authors: Thomas W Gilbert, Michael S. Sacks, Silvia Wognum, Erinn M Joyce, Donald O Freytes, Stephen F BadylakAbstract:The collagen Fiber Alignment and biomechanical behavior of naturally occurring extracellular matrix (ECM) scaffolds are important considerations for the design of medical devices from these materials. Both should be considered in order to produce a device to meet tissue specific mechanical requirements (e.g., tendon vs. urinary bladder), and could ultimately affect the remodeling response in vivo. The present study evaluated the collagen Fiber Alignment and biaxial mechanical behavior of ECM scaffold material harvested from porcine urinary bladder tunica mucosa and basement membrane (together referred to as urinary bladder matrix (UBM)) and ECM harvested from urinary bladder submucosa (UBS). Since the preparation of UBM allows for control of the direction of delamination, the effect of the delamination method on the mechanical behavior of UBM was determined by delaminating the submucosa and other abluminal layers by scraping along the longitudinal axis of the bladder (apex to neck) (UBML) or along the circumferential direction (UBMC). The processing of UBS does not allow for similar directional control. UBML and UBS had similar collagen Fiber distributions, with a preferred collagen Fiber Alignment along the longitudinal direction. UBMC showed a more homogenous collagen Fiber orientation. All samples showed a stiffer mechanical behavior in the longitudinal direction. Despite similar collagen Fiber distributions, UBML and UBS showed quite different mechanical behavior for the applied loading patterns with UBS showing a much more pronounced toe region. The mechanical behavior for UBMC in both directions was similar to the mechanical behavior of UBML. There are distinct differences in the mechanical behavior of different layers of ECM from the porcine urinary bladder, and the processing methods can substantially alter the mechanical behavior observed.
Gary L Bowlin - One of the best experts on this subject based on the ideXlab platform.
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electrospinning aligned and random polydioxanone polycaprolactone silk fibroin blended scaffolds geometry for a vascular matrix
Biomedical Materials, 2009Co-Authors: Michael J Mcclure, Chantal E Ayres, David G Simpson, Scott A Sell, Gary L BowlinAbstract:Extracellular matrices are arranged with a specific geometry based on tissue type and mechanical stimulus. For blood vessels in the body, preferential Alignment of Fibers is in the direction of repetitive force. Electrospinning is a controllable process which can result in Fiber Alignment and randomization depending on the parameters utilized. In this study, arterial grafts composed of polycaprolactone (PCL), polydioxanone (PDO) and silk fibroin in blends of 100:0 and 50:50 for both PCL:silk and PDO:silk were investigated to determine if Fibers could be controllably aligned using a mandrel rotational speed ranging from 500 to 8000 revolutions per minute (RPM). Results revealed that large- and small-diameter mandrels produced different degrees of Fiber Alignment based on a fast Fourier transform of scanning electron microscope images. Uniaxial tensile testing further demonstrated scaffold anisotropy through changes in peak stress, modulus and strain at break at mandrel rotational speeds of 500 and 8000 RPM, causing peak stress and modulus for PCL to increase 5- and 4.5-fold, respectively, as rotational speed increased. Additional mechanical testing was performed on grafts using dynamic compliance, burst strength and longitudinal strength displaying that grafts electrospun at higher rotational rates produced stiffer conduits which had lower compliance and higher burst strength compared to the lower mandrel rotational rate. Scaffold properties were found to depend on several parameters in the electrospinning process: mandrel rotational rate, polymer type, and mandrel size. Vascular scaffold design under anisotropic conditions provided interesting insights and warrants further investigation.
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measuring Fiber Alignment in electrospun scaffolds a user s guide to the 2d fast fourier transform approach
Journal of Biomaterials Science-polymer Edition, 2008Co-Authors: Chantal E Ayres, Gary L Bowlin, Shekhar B Jha, Hannah R Meredith, James R Bowman, Scott C Henderson, David G SimpsonAbstract:In this study we describe how to use a two-dimensional fast Fourier transform (2D FFT) approach to measure Fiber Alignment in electrospun materials. This image processing function can be coupled with a variety of imaging modalities to assign an objective numerical value to scaffold anisotropy. A data image of an electrospun scaffold is composed of pixels that depict the spatial organization of the constituent Fibers. The 2D FFT function converts this spatial information into a mathematically defined frequency domain that maps the rate at which pixel intensities change across the original data image. This output image also contains quantitative information concerning the orientation of objects in a data image. We discuss the theory and practice of using the frequency plot of the 2D FFT function to measure relative scaffold anisotropy and identify the principal axis of Fiber orientation. We note that specific degrees of scaffold anisotropy may represent a critical design feature in the fabrication of tissue...
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incremental changes in anisotropy induce incremental changes in the material properties of electrospun scaffolds
Acta Biomaterialia, 2007Co-Authors: Chantal E Ayres, Gary L Bowlin, Leander Taylor, Ryan Pizinger, Christopher Keen, David G SimpsonAbstract:Electrospinning can be used to selectively process a variety of natural and synthetic polymers into highly porous scaffolds composed of nano-to-m diameter Fibers. This process shows great potential as a gateway to the development of physiologically relevant tissue engineering scaffolds. In this study, we examine how incremental changes in Fiber Alignment modulate the material properties of a model scaffold. We prepared electrospun scaffolds of gelatin composed of varying Fiber diameters and degrees of anisotropy. The scaffolds were cut into a series of "dog-bone" shaped samples in the longitudinal, perpendicular and transverse orientations and the relative degree of Fiber Alignment, as measured by the fast Fourier transform (FFT) method, was determined for each sample. We measured peak stress, peak strain and the modulus of elasticity as a function of Fiber diameter and scaffold anisotropy. Fiber Alignment was the variable most closely associated with the regulation of peak stress, peak strain and modulus of elasticity. Incremental changes, as judged by the FFT method, in the proportion of Fibers that were aligned along a specific axis induced incremental changes in peak stress in the model scaffolds. These results underscore the critical role that scaffold anisotropy plays in establishing the material properties of an electrospun tissue engineering scaffold and the native extracellular matrix.
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modulation of anisotropy in electrospun tissue engineering scaffolds analysis of Fiber Alignment by the fast fourier transform
Biomaterials, 2006Co-Authors: Chantal E Ayres, Gary L Bowlin, Scott C Henderson, Leander Taylor, Jacqueline C Shultz, John K Alexander, Todd A Telemeco, David G SimpsonAbstract:We describe the use of the fast Fourier transform (FFT) in the measurement of anisotropy in electrospun scaffolds of gelatin as a function of the starting conditions. In electrospinning, Fiber Alignment and overall scaffold anisotropy can be manipulated by controlling the motion of the collecting mandrel with respect to the source electrospinning solution. By using FFT to assign relative Alignment values to an electrospun matrix it is possible to systematically evaluate how different processing variables impact the structure and material properties of a scaffold. Gelatin was suspended at varying concentrations (80, 100, 130, 150 mg/ml) and electrospun from 2,2,2 trifluoroethanol onto rotating mandrels (200–7000 RPM). At each starting concentration, Fiber diameter remained constant over a wide range of mandrel RPM. Scaffold anisotropy developed as a function of Fiber diameter and mandrel RPM. The induction of varying degrees of anisotropy imparted distinctive material properties to the electrospun scaffolds. The FFT is a rapid method for evaluating Fiber Alignment in tissue-engineering materials.
M Swartz - One of the best experts on this subject based on the ideXlab platform.
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cells in 3d matrices under interstitial flow effects of extracellular matrix Alignment on cell shear stress and drag forces
Journal of Biomechanics, 2010Co-Authors: John A. Pedersen, M Swartz, Seth LichterAbstract:Interstitial flow is an important regulator of various cell behaviors both in vitro and in vivo, yet the forces that fluid flow imposes on cells embedded in a 3D extracellular matrix (ECM), and the effects of matrix architecture on those forces, are not well understood. Here, we demonstrate how Fiber Alignment can affect the shear and pressure forces on the cell and ECM. Using computational fluid dynamics simulations, we show that while the solutions of the Brinkman equation accurately estimate the average fluid shear stress and the drag forces on a cell within a 3D fibrous medium, the distribution of shear stress on the cellular surface as well as the peak shear stresses remain intimately related to the pericellular Fiber architecture and cannot be estimated using bulk-averaged properties. We demonstrate that perpendicular Fiber Alignment of the ECM yields lower shear stress and pressure forces on the cells and higher stresses on the ECM, leading to decreased permeability, while parallel Fiber Alignment leads to higher stresses on cells and increased permeability, as compared to a cubic lattice arrangement. The Spielman-Goren permeability relationships for fibrous media agreed well with CFD simulations of flow with explicitly considered Fibers. These results suggest that the experimentally observed active remodeling of ECM Fibers by fibroblasts under interstitial flow to a perpendicular Alignment could serve to decrease the shear and drag forces on the cell. © 2009 Elsevier Ltd. All rights reserved.
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Cells in 3D matrices under interstitial flow: Effects of extracellular matrix Alignment on cell shear stress and drag forces
Journal of biomechanics, 2009Co-Authors: John A. Pedersen, Seth Lichter, M SwartzAbstract:Interstitial flow is an important regulator of various cell behaviors both in vitro and in vivo, yet the forces that fluid flow imposes on cells embedded in a 3D extracellular matrix (ECM), and the effects of matrix architecture on those forces, are not well understood. Here, we demonstrate how Fiber Alignment can affect the shear and pressure forces on the cell and ECM. Using computational fluid dynamics simulations, we show that while the solutions of the Brinkman equation accurately estimate the average fluid shear stress and the drag forces on a cell within a 3D fibrous medium, the distribution of shear stress on the cellular surface as well as the peak shear stresses remain intimately related to the pericellular Fiber architecture and cannot be estimated using bulk-averaged properties. We demonstrate that perpendicular Fiber Alignment of the ECM yields lower shear stress and pressure forces on the cells and higher stresses on the ECM, leading to decreased permeability, while parallel Fiber Alignment leads to higher stresses on cells and increased permeability, as compared to a cubic lattice arrangement. The Spielman-Goren permeability relationships for fibrous media agreed well with CFD simulations of flow with explicitly considered Fibers. These results suggest that the experimentally observed active remodeling of ECM Fibers by fibroblasts under interstitial flow to a perpendicular Alignment could serve to decrease the shear and drag forces on the cell.
Woodhi Cheng - One of the best experts on this subject based on the ideXlab platform.
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postweld shift induced Fiber Alignment shifts in laser welded laser module packages experiments and simulations
Journal of Lightwave Technology, 2005Co-Authors: Yicheng Hsu, Yingchien Tsai, Jaohwa Kuang, Woodhi ChengAbstract:The Fiber Alignment shifts induced by the postweld shift (PWS) in laser-welded transistor outline (TO)-Can-type laser module packages were studied experimentally and numerically. The PWS-induced Fiber Alignment shifts were quantitatively determined by four geometrical parameters, namely: 1) the lateral shift (r); 2) the position angle (/spl alpha/); 3) the swing angle (/spl theta/); and 4) the tilt angle (/spl psi/). The measured coupling powers in laser module packages before welding, after welding, and after a welding compensation clearly confirmed with the measured Fiber Alignment shifts determined by the dominant parameters of the r and /spl alpha/ that the Fiber shifts due to the PWS could be realigned back closer to their original optimum position after applying a welding compensation, and, hence, the coupling power loss due to the PWS could be regained. A coupled thermal-elastoplasticity model of finite-element-method (FEM) analysis was performed to evaluate the effects of PWS on Fiber Alignment shifts in laser module packages. The measured Fiber Alignment shifts determined by the dominant parameters of the r and /spl alpha/ were in good agreement with the numerical calculation of the FEM analysis. In this study, the combination of the experimental and numerical results have significantly provided a practical design guideline for fabricating reliable laser-welded TO-Can-type laser module packages with a high yield and high performance for use in low-cost lightwave transmission systems.
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a novel Fiber Alignment shift measurement and correction technique in laser welded laser module packaging
Journal of Lightwave Technology, 2005Co-Authors: Yicheng Hsu, Yingchien Tsai, M T Sheen, Jaohwa Kuang, Woodhi ChengAbstract:A novel measurement and correction technique employing an ultra-high-precision laser displacement meter (LDM) with a 20-nm resolution to probe the postweld-shift (PWS)-induced Fiber Alignment shifts in laser-welded laser module packaging is presented. The results show that the direction and magnitude of the Fiber Alignment shifts induced by the PWS in laser-welded laser module packaging can be quantitatively determined by four parameters: the lateral position (r), the position angle (/spl alpha/), the swing angle (/spl theta/), and the tilt angle (/spl psi/). Further studies show that the deformation of the lateral shift and the position angle are the dominant mechanisms that determine the Fiber Alignment shifts induced by the PWS. This clearly indicates that the PWS can be quantitatively corrected timely by applying a single weld spot on the negative lateral shift and the position angle to compensate for the Fiber Alignment shifts. In comparison with previous studies of the PWS correction by a qualitatively estimated technique, this LDM technique has significantly provided an important tool for quantitative measurement and correction to the effect of the PWS on the Fiber Alignment shifts in laser-welded laser module packaging. Therefore, the reliable laser modules with high yield and high performance used in low-cost lightwave transmission systems may be developed and fabricated.