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Search Results: 1 - 10 of 151172 matches for " Frederick H. Silver "
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Mechanical Analysis of Multi-Component Tissues  [PDF]
Frederick H. Silver, Ruchit G. Shah
World Journal of Mechanics (WJM) , 2017, DOI: 10.4236/wjm.2017.74011
Abstract: Collagen is the major structural fiber found in mammalian tissues. It is a protein in the form of a triple-helix which is found in several subfamilies, the most abundant of which is the fiber forming group containing Types I, II and III. Type I collagen is found in tendons, skin, cornea, bone, lung and vessel walls. This collagen is thought to give rise to the high tensile strengths of collagen fibers in tissues; in addition, it is actively involved in other physiologic processes such mechanotransduction. However, the non-linear mechanical behavior and viscoelasticity of collagen fibers make analysis of the mechanical properties of tissues complicated. Mechanistically, during mechanical loading, a tensional increase in the D period is observed with increasing strain that is associated with: 1) molecular elongation at the triple-helical level of structure; 2) increases in the gap distance between the end of one triple-helix and the start of the next one in the microfibril; and 3) molecular slippage. In this paper, we discuss the relationship between collagen hierarchical structure and its non-linear mechanical properties. Using vibrational analysis and optical coherence tomography, it is hoped that the mechanical properties of collagenous tissues can be studied in vivo in order to better understand tissue mechanics and to be better able to offer early diagnosis and differentiation of different disease states.
Analysis of Mechanical Behavior of Composite Tissues Using Vibrational Optical Coherence Tomography  [PDF]
Frederick H. Silver, Ruchit G. Shah
World Journal of Mechanics (WJM) , 2017, DOI: 10.4236/wjm.2017.710022
Abstract: Extracellular matrices (ECMs) found in vertebrate tissues are fiber reinforced composite materials that prevent premature mechanical failure, store, transmit, and dissipate mechanical energy generated by the musculoskeletal system. We have developed a new method using optical cohesion tomography and vibrational analysis to non-destructively and non-invasively measure the mechanical properties of composite tissues and polymeric materials. In addition, this method can be used to measure the moduli of individual components of composite materials and perform “mechanical spectroscopy” on materials. In addition, we propose that measurement of the resonant frequency of a material minimizes the viscoelastic behavior of a composite material. This approach simplifies the analysis of mechanical behavior of polymers and others materials that demonstrate time-dependence to their properties.
Biochemical, Biophysical and Mechanical Characterization of Decellularized Dermal Implants  [PDF]
Frederick H. Silver, Dale DeVore, Ruchit Shah
Materials Sciences and Applications (MSA) , 2017, DOI: 10.4236/msa.2017.812064
Abstract: Allografts have been used in a variety of applications to augment as well as replace tissues throughout the body. A number of steps are involved in selection, harvesting, processing and testing of dermal allografts. Grafts can be obtained that are: free of antibodies to viruses and low in viral titers. Cellular material can be eliminated from the tissue and the product becomes almost exclusively a collagen fiber network. The purpose of this paper is to examine the changes in collagen structure and properties that occur during processing of decellularized dermis. The results indicate that collagen fiber swelling occurs during processing although the product preserves the native collagen banding pattern at the fibrillar structural level. Fiber swelling and decreased collagen deformability of processed dermis, may lead to stress concentration at the implant-tissue interface and up-regulation of mechanotransduction. This may lead to premature mechanical failure due to creation of a chronic inflammatory condition at the implant-tissue interface. It is suggested that all dermal allografts be oriented such that Langer’s lines of the implant match those of the host tissue, and that wound closure by suturing be done under conditions that preserve the normal tension in skin in order to minimize implant-interfacial failure.
Non-Invasive and Non-Destructive Determination of Corneal and Scleral Biomechanics Using Vibrational Optical Coherence Tomography: Preliminary Observations  [PDF]
Frederick H. Silver, Ruchit G. Shah, Dominick Benedetto
Materials Sciences and Applications (MSA) , 2018, DOI: 10.4236/msa.2018.97047
Abstract: Experimental measurements made in this study on human and porcine eyes suggest that the resonant frequency for both cornea and sclera varies from 130 to 150 Hz and increases slightly with increasing intraocular pressure. The values of the moduli calculated using the experimental values of the thickness are close to 2 MPa. Similar values of the modulus for cornea and sclera suggest that there is very little stress concentration at the cornea-scleral junction and that any stress concentration that occurs probably resides at the scleral attachment laterally and posteriorly. These moduli are close to those measured in vivo on human skin suggesting that the mechanism of tensile deformation of skin, cornea and sclera are similar. Our results suggest that the modulus of cornea and sclera can be measured non-invasively and non-destructively using vibrational OCT. Results of these studies will assist clinicians to better understand the influence of biomechanics on the outcome of corneal refractive surgery as well as the pathogenesis of eye disorders such as glaucoma, myopia and keratoconus.
The Importance of Collagen Fibers in Vertebrate Biology
Frederick H. Silver, Ph.D.
Journal of Engineered Fibers and Fabrics , 2009,
Abstract: Collagen fibers form the basic structural components of extracellular matrix (ECM) of vertebrates that serve to: (1) store elastic energy during muscular deformation, (2) transmit stored energy into joint movement, and (3) transfer excess energy from the joint back to the attached muscles for dissipation. They also act as mechanotransducers by transferring stress borne by the musculoskeleton to the attached cells in order to either up - or down - regulate tissue metabolism as a result of changes in mechanical loading. Finally, they prevent premature mechanical failure of tissues by limiting deformation of most ECMs and organs.
Virtual Biopsy and Physical Characterization of Tissues, Biofilms, Implants and Viscoelastic Liquids Using Vibrational Optical Coherence Tomography  [PDF]
Frederick H. Silver, Ruchit G. Shah, Dominick Benedetto, Abhinav Dulur, Thomas Kirn
World Journal of Mechanics (WJM) , 2019, DOI: 10.4236/wjm.2019.91001
Abstract: Tissue biopsies and implant analysis during animal testing or clinical studies are a requirement for development of new surgical materials and procedures. In this paper we report the use of vibrational OCT (VOCT) to evaluate the viscoelastic behavior of tissues, polymeric materials, biofilms, and viscoelastic solutions of macromolecules. Our results suggest that VOCT is a useful technique to characterize the behavior of cellular tissues and biofilms, polymeric implant materials and viscoelastic solutions used in medicine. It is demonstrated that the modulus and resonant frequency squared per unit thickness is a feature that can be used to characterize a variety of tissues. Further work is needed to understand the generalized behavior of synthetic polymers and viscoelastic solutions.
Viscoelastic Evaluation of Different Hyaluronic Acid Based Fillers Using Vibrational Optical Coherence Tomography  [PDF]
Frederick H. Silver, Ruchit G. Shah, Nikita Kelkar, Dominick Benedetto, Dale DeVore, Justin Cohen
Materials Sciences and Applications (MSA) , 2019, DOI: 10.4236/msa.2019.105031
Abstract: Hylauronic acid (HA) is used as a viscoelastic in Ophthalmology during cataract surgery based on its high viscosity at rest, its ability to shear thin and dissipate energy during phacoemulsification. However, these properties of HA solutions would make them susceptible to migration when used as dermal filler materials. In this study, we apply a new technique termed vibrational optical coherence tomography (VOCT) to compare the physical properties of different HA solutions and fillers used in facial aesthetics. Results presented in this study suggest that HA solutions and HA dermal fillers have markedly different physical properties. HA solutions are highly viscoelastic with high % viscous losses while fillers tend to have lower viscous energy dissipation properties. Clinical observations suggest that the high loss fillers are injected more superficially in the face where tension and internal and external forces are more likely minimized giving tissue of the hands and lips more volume and allowing more natural movement. In contrast, the lower loss gels that are used to lift tissue, generally have a higher G’, and are injected deeper into the face where injection and internal forces are likely to be higher. It is concluded that HA filler gel design can be optimized by use of VOCT to evaluate the % viscous energy loss both in vitro and in vivo.
Calculation of Densities of States and Spectral Functions by Chebyshev Recursion and Maximum Entropy
R. N. Silver,H. Roder
Physics , 1997, DOI: 10.1103/PhysRevE.56.4822
Abstract: We present an efficient algorithm for calculating spectral properties of large sparse Hamiltonian matrices such as densities of states and spectral functions. The combination of Chebyshev recursion and maximum entropy achieves high energy resolution without significant roundoff error, machine precision or numerical instability limitations. If controlled statistical or systematic errors are acceptable, cpu and memory requirements scale linearly in the number of states. The inference of spectral properties from moments is much better conditioned for Chebyshev moments than for power moments. We adapt concepts from the kernel polynomial approximation, a linear Chebyshev approximation with optimized Gibbs damping, to control the accuracy of Fourier integrals of positive non-analytic functions. We compare the performance of kernel polynomial and maximum entropy algorithms for an electronic structure example.
Inferring the developmental basis of the sea star abnormality "double ambulacral groove" (Echinodermata: Asteroidea)
HOTCHKISS,FREDERICK H C;
Revista chilena de historia natural , 2000, DOI: 10.4067/S0716-078X2000000400003
Abstract: very rarely a ray of a sea star is unusually wide and has two parallel ambulacral grooves that extend to a single tip. such a ray has two terminal plates that are coalesced laterally. this abnormality is inferred to develop as a rare result of regeneration because it is recorded from a species with obligate asexual reproduction (fission and regeneration of halves; no gametes). this conclusion is supported also by an example where the abnormality affects only the distal third of a ray
Inferring the developmental basis of the sea star abnormality "double ambulacral groove" (Echinodermata: Asteroidea) Inferencia sobre la base de desarrollo en estrellas de mar de la anormalidad "doble surco ambulacral" (Echinodermata: Asteroidea)
FREDERICK H C HOTCHKISS
Revista chilena de historia natural , 2000,
Abstract: Very rarely a ray of a sea star is unusually wide and has two parallel ambulacral grooves that extend to a single tip. Such a ray has two terminal plates that are coalesced laterally. This abnormality is inferred to develop as a rare result of regeneration because it is recorded from a species with obligate asexual reproduction (fission and regeneration of halves; no gametes). This conclusion is supported also by an example where the abnormality affects only the distal third of a ray Muy raramente un rayo de estrella de mar es desproporcionadamente ancho y tiene dos surcos ambulacrales paralelos que se extienden hasta su único extremo. Dicho rayo tiene dos placas terminales que coalecen lateralmente. Se ha inferido que esta anormalidad se desarrolla como un resultado raro de regeneración, porque se describe de una especie con reproducción asexual obligada (fisión y regeneración de mitades; no gametos). Además, esta conclusión se sostiene por un ejemplo de anormalidad que afecta sólo el tercio distal de un rayo
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