Author: F. Henry M. Nestler
Publisher:
ISBN:
Category : Collagen
Languages : en
Pages : 206

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Author: Marjan Shayegan
Publisher:
ISBN:
Category :
Languages : en
Pages : 160

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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:
Publisher:
ISBN:
Category : Dissertation abstracts
Languages : en
Pages : 552

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Author:
Publisher:
ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 564

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Author: University Microfilms International
Publisher: Ann Arbor, Mich. : University Microfilms International
ISBN:
Category : Reference
Languages : en
Pages : 712

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Author: Bin Xu
Publisher:
ISBN:
Category :
Languages : en
Pages : 266

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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:
Publisher:
ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 714

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Author: Danton Gutierrez-Lemini
Publisher: Springer Science & Business Media
ISBN: 1461481392
Category : Technology & Engineering
Languages : en
Pages : 379

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Book Description
Engineering Viscoelasticity covers all aspects of the thermo- mechanical response of viscoelastic substances that a practitioner in the field of viscoelasticity would need to design experiments, interpret test data, develop stress-strain models, perform stress analyses, design structural components, and carry out research work. The material in each chapter is developed from the elementary to the esoteric, providing the background in mathematics and mechanics that are central to understanding the subject matter being presented. This book also examines how viscoelastic materials respond to the application of loads, and provides practical guidelines to use them in the design of commercial, military and industrial applications.

Author: Stephen C. Cowin
Publisher: Springer Science & Business Media
ISBN: 1402002203
Category : Mathematics
Languages : en
Pages : 252

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Cowin (New York Center for Biomedical Engineering) and Humphrey (biomedical engineering, Texas A&M U.) present seven papers that discuss current research and future directions. Topics concern tissues within the cardiovascular system (arteries, the heart, and biaxial testing of planar tissues such as heart valves). Themes include an emphasis on data on the underlying microstructure, especially collagen; the consideration of the fact that both arteries and the heart contain muscle and that there is, therefore, a need to quantify both the active and passive response; constitutive relations for active behavior; and the growth and remodeling of cardiovascular tissues. Of interest to cardiovascular and biomechanics soft tissue researchers, and bioengineers. Annotation copyrighted by Book News, Inc., Portland, OR.

Author: Van C. Mow
Publisher: Springer
ISBN:
Category : Medical
Languages : en
Pages : 496

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