Fiber reinforced anisotropic material abounds in biological world. It has been demonstrated in pr... more Fiber reinforced anisotropic material abounds in biological world. It has been demonstrated in previous theoretical and experimental works that growth of biological soft tubular tissue plays a significant role in morphogenesis and pathology. Here we investigate growth-induced buckling of anisotropic cylindrical tissue, focusing on the effects of type of growth(constraint/unconstraint, isotropic/anisotropic), fiber property(orientation, density and strength), geometry and any interaction between these factors. We studied one-layer and two-layer models and obtained a rich spectrum of results. For one-layer model, we demonstrate that circumferential fiber orientation has a consistent stabilizing effect under various scenarios of growth. Higher fiber density has a destabilizing effect by disabling high-mode buckling. For two-layer model, we found that critical buckling strain at inner boundary is an invariant under same isotropic growth rate ratio between inner/ outer layer(g
ABSTRACT This paper reviews the general biological phenomenon of aging as it applies to cells. Ph... more ABSTRACT This paper reviews the general biological phenomenon of aging as it applies to cells. Philosophical concepts of aging arising from radiation and evolutionary biology are used as a historical context for our understanding of how cells age. The development of multicellularity, and with it, an extracellular matrix is discussed in order to reveal that the biological consequences of aging extend beyond the borders of a cell. The argument is made that an integration of knowledge across levels of biological organization and a unification of theories on aging is needed in order to progress toward a greater understanding of organismal and cellular aging. It is further suggested that complexity theory and a systems level approach provides the means by which that integration can be achieved. The consequences of aging have been observed at virtually every level of biological organization, from molecules to populations. Although explanations of aging are dominated by a few theories (e.g., Kirkwood's (1977) disposable soma theory [1] and Harman's (1956) free radical hypothesis [2]), countless others have been proffered as well (see Rattan (2006) [3] and Weinert and Timiras (2003) [4] for reviews). This proliferation reflects not only the intricacies of aging but also the need for a theory that integrates information across multiple interacting levels of biological organization. Contrary to reductionist expectation, the number of theories increases rather than decreases at progressively lower levels of biological organization. Nowhere is this more evident than at the cellular level. Thus, it is fitting to devote a special issue to the challenges inherent in understanding the dynamics of cellular aging. There are, however, several obstacles that complicate a discussion of cellular aging. Foremost among them is the term “aging” (or “senescence”) itself. What does it mean? How do you distinguish aging from non-aging? When did it arise? Is it universal, or can some organisms escape it? Is it reversible? Is it a monolithic process or a mixture of processes? What is the fundamental unit of aging: a molecule, a cell, a tissue, an organ, the organism, or all of these? Does multicellularity affect the complexity of aging? Did aging evolve? In other words, does it have a genetic basis? Is there a difference between replicative senescence, organismal senescence, and phenotypic plasticity? These are some of the questions that we hope to address in this article.RésuméLes auteurs de cet article proposent une analyse conceptuelle du rôle de la sénescence cellulaire dans le vieillissement de l’organisme et dans les maladies qui l’accompagnent. Ils confrontent certaines des nombreuses théories proposées pour « expliquer » le vieillissement avec les notions essentielles résultant du modèle cellulaire du vieillissement in vitro et de son exploitation expérimentale. Ils commencent par s’interroger sur le sens des concepts « vieillissement » et « sénescence » en essayant d’abord de les définir en suivant l’argumentation de Bernard Strehler qui en a donné une définition valide. Suit ensuite l’interrogation sur la nature même du processus du vieillissement en essayant d’en remonter aux origines. Est-il programmé ou stochastique ? Comme la plupart des auteurs, Carnes et ses collègues acceptent aussi d’attribuer la sénescence aux « négligences de la Nature », l’évolution ne s’étant intéressée qu’à la reproduction efficace en vue de la survie de l’espèce et nullement à sa déchéance. Est-il programmé ou pas programmé, est la question suivante. La réponse découle de l’analyse biologique et historique ci-dessus esquissée. Les gènes ont évolué pour maintenir santé et vigueur et nullement pour accélérer la décrépitude. Pour conclure, en fin de paragraphe, les auteurs s’interrogent : la longévité est-elle souhaitée par l’évolution, contrairement au vieillissement, résultat de sa négligence. Suivent ensuite des paragraphes sur le nombre et la complexité des mécanismes qui contribuent au vieillissement : un ou multiples ? Compliqués ou complexes ? Cette analyse relève de la science de la complexité biologique. Un long chapitre est ensuite consacré au rôle de la multicellularité et de la matrice extracellulaire dans le vieillissement. Les remaniements de cette matrice au cours du vieillissement et son rôle dans les modifications des interactions cellulaires jouent un rôle important dans la perte des fonctions physiologiques de l’organisme. Ces concepts ont été exploités pour la compréhension du vieillissement cutané, largement tributaire des modifications avec l’âge de sa matrice extracellulaire et de la perte progressive de la communication cellule-matrice cutanée. Les mécanismes individuels ci-dessus discutés sont ensuite intégrés au niveau tissulaire, puis au niveau des systèmes physiologiques. Les auteurs insistent sur la nature émergente des propriétés des systèmes vivants, conséquence de l’interaction de leurs composants qui font…
We propose a biomechanical model for investigating wound contraction mechanism and resulting scar... more We propose a biomechanical model for investigating wound contraction mechanism and resulting scarring. Extracellular matrix is modeled as fiber-reinforced anisotropic soft tissue, with its elastic properties dynamically changing with the density and orientation of collagen fibers. Collagen fibers are deposited by fibroblasts infiltrating the wound space, and are dynamically aligned with both migrating fibroblasts and tissue residing tension field. Our new 2D hybrid agent-based model provides a comprehensive platform for examining the mechanobiology in wound contraction and scar formation. Simulation results are consistent with experimental observations and are able to reveal the effects of wound morphology and mechanical environment on contraction patterns. Our model results support the hypothesis that scar formation is the product of collagen fiber synthesis and alignment in the presence of the tensile stress field generated by a wound contraction process.
Abstract This study is the first to examine the experiences and needs of an international sample ... more Abstract This study is the first to examine the experiences and needs of an international sample of current, English-speaking, bisexual, and transgender-identified adults (trans-bisexuals) on a number of later-life and end-of-life (EOL) perceptions, preparations, and concerns. In particular, the author analyzed a subset (n = 147) of the cross-sectional data collected from the online Trans MetLife Survey on Later-Life Preparedness and Perceptions in Transgender-Identified Individuals (N = 1,963). The author assessed perceptions and fears around aging, preparation for later life and end of life, as well as numerous demographic and psychosocial variables. Despite the fact that many respondents feel that they have aged successfully, the respondent trans-bisexual population harbors significant fears around later life challenges. Additionally the author found that this population is ill prepared for the major legalities and events that occur in the later to end-of-life time periods.
Fiber reinforced anisotropic material abounds in biological world. It has been demonstrated in pr... more Fiber reinforced anisotropic material abounds in biological world. It has been demonstrated in previous theoretical and experimental works that growth of biological soft tubular tissue plays a significant role in morphogenesis and pathology. Here we investigate growth-induced buckling of anisotropic cylindrical tissue, focusing on the effects of type of growth(constraint/unconstraint, isotropic/anisotropic), fiber property(orientation, density and strength), geometry and any interaction between these factors. We studied one-layer and two-layer models and obtained a rich spectrum of results. For one-layer model, we demonstrate that circumferential fiber orientation has a consistent stabilizing effect under various scenarios of growth. Higher fiber density has a destabilizing effect by disabling high-mode buckling. For two-layer model, we found that critical buckling strain at inner boundary is an invariant under same isotropic growth rate ratio between inner/ outer layer(g
ABSTRACT This paper reviews the general biological phenomenon of aging as it applies to cells. Ph... more ABSTRACT This paper reviews the general biological phenomenon of aging as it applies to cells. Philosophical concepts of aging arising from radiation and evolutionary biology are used as a historical context for our understanding of how cells age. The development of multicellularity, and with it, an extracellular matrix is discussed in order to reveal that the biological consequences of aging extend beyond the borders of a cell. The argument is made that an integration of knowledge across levels of biological organization and a unification of theories on aging is needed in order to progress toward a greater understanding of organismal and cellular aging. It is further suggested that complexity theory and a systems level approach provides the means by which that integration can be achieved. The consequences of aging have been observed at virtually every level of biological organization, from molecules to populations. Although explanations of aging are dominated by a few theories (e.g., Kirkwood's (1977) disposable soma theory [1] and Harman's (1956) free radical hypothesis [2]), countless others have been proffered as well (see Rattan (2006) [3] and Weinert and Timiras (2003) [4] for reviews). This proliferation reflects not only the intricacies of aging but also the need for a theory that integrates information across multiple interacting levels of biological organization. Contrary to reductionist expectation, the number of theories increases rather than decreases at progressively lower levels of biological organization. Nowhere is this more evident than at the cellular level. Thus, it is fitting to devote a special issue to the challenges inherent in understanding the dynamics of cellular aging. There are, however, several obstacles that complicate a discussion of cellular aging. Foremost among them is the term “aging” (or “senescence”) itself. What does it mean? How do you distinguish aging from non-aging? When did it arise? Is it universal, or can some organisms escape it? Is it reversible? Is it a monolithic process or a mixture of processes? What is the fundamental unit of aging: a molecule, a cell, a tissue, an organ, the organism, or all of these? Does multicellularity affect the complexity of aging? Did aging evolve? In other words, does it have a genetic basis? Is there a difference between replicative senescence, organismal senescence, and phenotypic plasticity? These are some of the questions that we hope to address in this article.RésuméLes auteurs de cet article proposent une analyse conceptuelle du rôle de la sénescence cellulaire dans le vieillissement de l’organisme et dans les maladies qui l’accompagnent. Ils confrontent certaines des nombreuses théories proposées pour « expliquer » le vieillissement avec les notions essentielles résultant du modèle cellulaire du vieillissement in vitro et de son exploitation expérimentale. Ils commencent par s’interroger sur le sens des concepts « vieillissement » et « sénescence » en essayant d’abord de les définir en suivant l’argumentation de Bernard Strehler qui en a donné une définition valide. Suit ensuite l’interrogation sur la nature même du processus du vieillissement en essayant d’en remonter aux origines. Est-il programmé ou stochastique ? Comme la plupart des auteurs, Carnes et ses collègues acceptent aussi d’attribuer la sénescence aux « négligences de la Nature », l’évolution ne s’étant intéressée qu’à la reproduction efficace en vue de la survie de l’espèce et nullement à sa déchéance. Est-il programmé ou pas programmé, est la question suivante. La réponse découle de l’analyse biologique et historique ci-dessus esquissée. Les gènes ont évolué pour maintenir santé et vigueur et nullement pour accélérer la décrépitude. Pour conclure, en fin de paragraphe, les auteurs s’interrogent : la longévité est-elle souhaitée par l’évolution, contrairement au vieillissement, résultat de sa négligence. Suivent ensuite des paragraphes sur le nombre et la complexité des mécanismes qui contribuent au vieillissement : un ou multiples ? Compliqués ou complexes ? Cette analyse relève de la science de la complexité biologique. Un long chapitre est ensuite consacré au rôle de la multicellularité et de la matrice extracellulaire dans le vieillissement. Les remaniements de cette matrice au cours du vieillissement et son rôle dans les modifications des interactions cellulaires jouent un rôle important dans la perte des fonctions physiologiques de l’organisme. Ces concepts ont été exploités pour la compréhension du vieillissement cutané, largement tributaire des modifications avec l’âge de sa matrice extracellulaire et de la perte progressive de la communication cellule-matrice cutanée. Les mécanismes individuels ci-dessus discutés sont ensuite intégrés au niveau tissulaire, puis au niveau des systèmes physiologiques. Les auteurs insistent sur la nature émergente des propriétés des systèmes vivants, conséquence de l’interaction de leurs composants qui font…
We propose a biomechanical model for investigating wound contraction mechanism and resulting scar... more We propose a biomechanical model for investigating wound contraction mechanism and resulting scarring. Extracellular matrix is modeled as fiber-reinforced anisotropic soft tissue, with its elastic properties dynamically changing with the density and orientation of collagen fibers. Collagen fibers are deposited by fibroblasts infiltrating the wound space, and are dynamically aligned with both migrating fibroblasts and tissue residing tension field. Our new 2D hybrid agent-based model provides a comprehensive platform for examining the mechanobiology in wound contraction and scar formation. Simulation results are consistent with experimental observations and are able to reveal the effects of wound morphology and mechanical environment on contraction patterns. Our model results support the hypothesis that scar formation is the product of collagen fiber synthesis and alignment in the presence of the tensile stress field generated by a wound contraction process.
Abstract This study is the first to examine the experiences and needs of an international sample ... more Abstract This study is the first to examine the experiences and needs of an international sample of current, English-speaking, bisexual, and transgender-identified adults (trans-bisexuals) on a number of later-life and end-of-life (EOL) perceptions, preparations, and concerns. In particular, the author analyzed a subset (n = 147) of the cross-sectional data collected from the online Trans MetLife Survey on Later-Life Preparedness and Perceptions in Transgender-Identified Individuals (N = 1,963). The author assessed perceptions and fears around aging, preparation for later life and end of life, as well as numerous demographic and psychosocial variables. Despite the fact that many respondents feel that they have aged successfully, the respondent trans-bisexual population harbors significant fears around later life challenges. Additionally the author found that this population is ill prepared for the major legalities and events that occur in the later to end-of-life time periods.
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Papers by Tarynn M Witten