Determining Local Viscoelastic Properties of Collagen Systems Using Optical Tweezers PDF Download
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Author: Marjan Shayegan
Publisher:
ISBN:
Category :
Languages : en
Pages : 160
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Book Description
In this work, I aimed to develop and apply a technique capable of measuring the viscoelastic properties of collagen at different levels of hierarchy. Collagen is the predominant structural protein in vertebrates, and its self-assembly into well-defined structures including fibrils underlies the formation of a wide variety of biological structures with a broad range of functions. Here, in order to understand the correlation between collagen's structure and its mechanical properties, the viscoelastic properties of different collagen systems were characterized, ranging from solutions of molecules to self-assembled forms of fibrillar gels and gelatin. To determine rheological properties, optical tweezers were used to trap and monitor thermal fluctuations of an embedded micron-sized particle, producing measurements of viscoelastic response of collagen systems at a high bandwidth (> 10̂4 Hz). To validate these measurements, I reproduced results on a previously characterized system (polyethylene oxide). The obtained viscoelastic response is affected by the timescales of the interactions between polymers, which play a critical role in conferring elasticity to the system. To provide guidance to the microrheology experiments, the structure of collagen in acidic solution was probed using dynamic light scattering. My microrheology studies of collagen molecules in acidic solution showed that elastic response becomes comparable to viscous response at the highest concentration studied here, 5 mg/ml. Here, the significant elasticity observed at frequencies above ̃200 Hz is due to collagens' intermolecular interactions, which I found were not due to electrostatic interactions. However, elasticity was found to decrease following the removal of collagen's telopeptides, consistent with their role in facilitating fibril formation. At the fibrillar level, unlike in solutions of collagen, I observed spatial heterogeneity in viscoelastic properties. The elastic modulus varies by an order of magnitude at different locations within fibrillar collagen gels. By making measurements over 100-minute timescales as collagen self-assembled into fibrils, I probed the development of microscale heterogeneity and concluded that heterogeneity appears during early phases of fibrillar growth and continues to develop further during this growth phase.
Author: Marjan Shayegan
Publisher:
ISBN:
Category :
Languages : en
Pages : 160
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Book Description
In this work, I aimed to develop and apply a technique capable of measuring the viscoelastic properties of collagen at different levels of hierarchy. Collagen is the predominant structural protein in vertebrates, and its self-assembly into well-defined structures including fibrils underlies the formation of a wide variety of biological structures with a broad range of functions. Here, in order to understand the correlation between collagen's structure and its mechanical properties, the viscoelastic properties of different collagen systems were characterized, ranging from solutions of molecules to self-assembled forms of fibrillar gels and gelatin. To determine rheological properties, optical tweezers were used to trap and monitor thermal fluctuations of an embedded micron-sized particle, producing measurements of viscoelastic response of collagen systems at a high bandwidth (> 10̂4 Hz). To validate these measurements, I reproduced results on a previously characterized system (polyethylene oxide). The obtained viscoelastic response is affected by the timescales of the interactions between polymers, which play a critical role in conferring elasticity to the system. To provide guidance to the microrheology experiments, the structure of collagen in acidic solution was probed using dynamic light scattering. My microrheology studies of collagen molecules in acidic solution showed that elastic response becomes comparable to viscous response at the highest concentration studied here, 5 mg/ml. Here, the significant elasticity observed at frequencies above ̃200 Hz is due to collagens' intermolecular interactions, which I found were not due to electrostatic interactions. However, elasticity was found to decrease following the removal of collagen's telopeptides, consistent with their role in facilitating fibril formation. At the fibrillar level, unlike in solutions of collagen, I observed spatial heterogeneity in viscoelastic properties. The elastic modulus varies by an order of magnitude at different locations within fibrillar collagen gels. By making measurements over 100-minute timescales as collagen self-assembled into fibrils, I probed the development of microscale heterogeneity and concluded that heterogeneity appears during early phases of fibrillar growth and continues to develop further during this growth phase.
Author: F. Henry M. Nestler
Publisher:
ISBN:
Category : Collagen
Languages : en
Pages : 206
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Book Description
Author: Bin Xu
Publisher:
ISBN:
Category :
Languages : en
Pages : 266
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Book Description
Abstract: Collagen is the most abundant protein in the body. It plays critical roles in many supporting and connecting tissues. Collagen matrices prepared from commercially available collagen solution have been broadly used as a biomaterial in tissue engineering, drug delivery, and wound healing for its biocompatibility, low toxicity, and well-documented physical, chemical, and immunological properties. Collagen matrices are also used as three-dimensional model systems of extracellular matrix (ECM) in numerous studies of cell-ECM interactions under physiological and pathological conditions. As a biphasic material, collagen matrices contain a solid phase representing by collagen network and an interstitial fluid phase. This special structure makes collagen a viscoelastic material. The overall research goal of this thesis is to characterize the macroscopic elastic and viscoelastic properties of collagen matrices in both the frequency and time domain and to understand the deformation mechanisms using a coupled experimental and modeling approach. Hydrated collagen gel and dehydrated collagen thin film are exploited as two different hydration levels of collagen matrices. Genipin solution is used to induce crosslinking in collagen matrices.Biaxial tensile stress relaxation results show that the rate of stress relaxation of both hydrated and dehydrated collagen matrices shows a linear initial stress level dependency. Increased crosslinking reduces viscosity in collagen gel, but the effect is negligible for thin film. Relaxation time distribution spectrum was obtained from the stress relaxation data by inverse Laplace transform. For most of the collagen matrices, three peaks at the short (0.3s ∼ 1s), medium (3s ∼ 90s), and long relaxation time (>200s) were observed in the continuous spectrum, which corresponds with relaxation mechanisms involve fiber, inter-fibril, and fibril sliding. The intensity of the long-term peaks increases with higher initial stress levels indicates the engagement of collagen fibrils at higher levels of tissue strain. Splitting of the middle peak was observed at higher initial stress levels suggesting increased structural heterogeneity at the fibril level with mechanical loading. A viscoelastic constitutive model combining hyperelastic and generalized Maxwell model was established with viscous material parameters obtained directly from analysis of the relaxation time spectrum.Rheological shear relaxation and dynamic rheological tests were performed on collagen gel. Crossover of storage and loss modulus was observed from frequency sweep tests. The crossover frequency shows both strain amplitude and crosslinking dependency. Both dynamic moduli and shear relaxation modulus demonstrate strain-softening behavior. Conversion from frequency domain measurements to time domain properties was achieved through relaxation spectrum obtained by Tikhonov regularization method. The relaxation spectrum shows two obvious peaks between 0.01s∼0.1s and between 10s∼40s, which indicate the existence of fast and slow dominant relaxation processes. The peak between 0.01∼0.1s correspond is likely due to the collagen fiber-interstitial fluid sliding. In shear deformation both collagen fiber network and interstitial fluid play important roles, which contribute to the differences in relaxation mechanisms between rheological shear and tensile relaxation tests.
Author: Jiro Nagatomi
Publisher: CRC Press
ISBN: 1420091212
Category : Medical
Languages : en
Pages : 566
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Book Description
Mechanobiology—the study of the effects of mechanical environments on the biological processes of cells—has evolved from traditional biomechanics via the incorporation of strong elements of molecular and cell biology. Currently, a broad range of organ systems are being studied by surgeons, physicians, basic scientists, and engineers. These mechanobiologists aim to create new therapies and further biological understanding by quantifying the mechanical environment of cells and the molecular mechanisms of mechanically induced pathological conditions. To achieve these goals, investigators must be familiar with both the basic concepts of mechanics and the modern tools of cellular/molecular biology. Unfortunately, current literature contains numerous studies that misuse standard mechanical estimations and terminology, or fail to implement appropriate molecular analyses. Therefore, the Mechanobiology Handbook not only presents cutting-edge research findings across various fields and organ systems, but also provides the elementary chapters on mechanics and molecular analysis techniques to encourage cross-field understanding and appropriate planning. Aided by the continuous advancement of research tools in both mechanics and biology, more sophisticated experiments and analyses are possible—thus fueling the growth of the field of mechanobiology. Considering the complexity of the mechanics and the biology of the human body, most of the world of biomechanics remains to be studied. Since the field is still developing, the Mechanobiology Handbook does not force one unified theory, but brings out many different viewpoints and approaches to stimulate further research questions.
Author: Zhilei Liu Shen
Publisher:
ISBN:
Category : Biomedical materials
Languages : en
Pages : 255
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Book Description
Collagenous tissues (e.g. bone and tendon) have well organized hierarchical structures. To improve understanding of the mechanical behavior of collagenous tissues and to guide the development of multiscale models, mechanical testing at different length scales is required. Whole tissues, fascicles, and fibril bundles have been studied extensively, but little is known at the fibrillar level. Using microelectromechanical systems (MEMS) technology, tensile mechanical testing was performed on type I collagen fibril specimens isolated from the dermis of sea cucumbers. In air uniaxial tensile tests showed that the fibrils had a small strain elastic modulus of 860 ± 450 MPa, a yield stress of 220 ± 140 MPa, and a yield strain of 21% ± 13%. In vitro fracture tests showed that the fibrils had an elastic modulus of 470 ± 410 MPa, a fracture strength of 230 ± 160 MPa, and a fracture strain of 80% ± 44%. The fibrils displayed significantly lower elastic modulus in vitro than in air. Both the fracture strength/strain obtained in vitro and in air were significantly larger than those obtained in vacuo, indicating that the difference arises from the lack of intrafibrillar water molecules produced by vacuum drying. Fracture strength/strain of fibril specimens were different from those reported for collagenous structures of higher hierarchical levels, indicating the importance of obtaining these properties at the fibrillar level for multiscale modeling. In vitro coupled creep and stress relaxation tests demonstrated the intrinsic viscoelastic behavior of collagen fibrils. The stress-strain-time data were fitted using a Kelvin model consisting of a spring and a dashpot in parallel. The fibrils showed an elastic modulus of 180 ± 100 MPa, a viscosity of 4.7 ± 3.2 GPa*sec, and a relaxation time of 29 ± 16 sec. The fibrillar relaxation time was smaller than the tissue-level relaxation time, suggesting tissue relaxation is dominated by non-collagenous components (e.g. proteoglycans). To our knowledge, in vitro fracture and viscoelastic properties of isolated collagen fibrils were measured for the first time. The mechanical properties obtained in this work can be used as input parameters for multiscale modeling and help guide the development of synthetic biomaterials.
Author:
Publisher:
ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 862
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Author: Jiro Nagatomi
Publisher: CRC Press
ISBN: 042981674X
Category : Medical
Languages : en
Pages : 705
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Book Description
Mechanobiology—the study of the effects of mechanics on biological events—has evolved to answer numerous research questions. Mechanobiology Handbook 2nd Edition is a reference book for engineers, scientists, and clinicians who are interested in mechanobiology and a textbook for senior undergraduate to graduate level students of this growing field. Readers will gain a comprehensive review of recent research findings as well as elementary chapters on solid mechanics, fluid mechanics, and molecular analysis techniques. The new edition presents, in addition to the chapters of the first edition, homework problem sets that are available online and reviews of research in uncovered areas. Moreover, the new edition includes chapters on statistical analysis, design of experiments and optical imaging. The editors of this book are researchers and educators in mechanobiology. They realized a need for a single volume to assist course instructors as a guide for didactic teaching of mechanobiology to a diverse student body. A mechanobiology course is frequently made up of both undergraduate and graduate students pursuing degrees in engineering, biology, or integrated engineering and biology. Their goal was to present both the elementary and cutting-edge aspects of mechanobiology in a manner that is accessible to students from many different academic levels and from various disciplinary backgrounds. Moreover, it is their hope that the readers of Mechanobiology Handbook 2nd Edition will find study questions at the end of each chapter useful for long-term learning and further discussion. Comprehensive collection of reviews of recent research Introductory materials in mechanics, biology, and statistics Discussion of pioneering and emerging mechanobiology concepts Presentation of cutting-edge mechanobiology research findings across various fields and organ systems End of chapter study questions, available online Considering the complexity of the mechanics and the biology of the human body, most of the world of mechanobiology remains to be studied. Since the field is still developing, the Mechanobiology Handbook raises many different viewpoints and approaches with the intention of stimulating further research endeavours.
Author: Arkadz Fatseyeu
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: A. Fox
Publisher: ASTM International
ISBN:
Category :
Languages : en
Pages : 222
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Book Description
Author: Kenny Breuer
Publisher: Springer Science & Business Media
ISBN: 3540264493
Category : Technology & Engineering
Languages : en
Pages : 268
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Book Description
Microscale Diagnostic Techniques highlights the most innovative and powerful developments in microscale diagnostics. It provides a resource for scientists and researchers interested in learning about the techniques themselves, including their capabilities and limitations. The fields of Micro- and Nanotechnology have emerged over the past decade as a major focus of modern scientific and engineering research and technology. Driven by advances in microfabrication, the investigation, manipulation and engineering of systems characterized by micrometer and, more recently, nanometer scales have become commonplace throughout all technical disciplines. With these developments, an entirely new collection of experimental techniques has been developed to explore and characterize such systems.
