Volumetric Growth of Thermoelastic Materials and Mixtures

The proteoglycan and collagen constituents of cartilage serve distinct mechanical roles. Changes to the mechanical loading conditions during cartilage growth lead to changes in the concentrations of these molecules and, consequently, the mechanical properties. The main aim of this paper is to present a theory that can describe the mechanical aspects of cartilage growth. The model for cartilage growth is based on a general thermomechanical theory for a mixture of an arbitrary number of growing elastic constituents and an inviscid fluid. Our development of a growth mixture theory is accomplished in two steps. First, the thermodynamics of growing elastic materials are considered. The resulting theory of growing thermoelastic materials is extended to continuum mixture theory. Using this general growth mixture theory, we then propose a cartilage growth model that includes two special types of internal constraints that are relevant to cartilage

A cartilage growth mixture model for infinitesimal strains: solutions of boundary-value problems related to in vitro growth experiments

A cartilage growth mixture (CGM) model is linearized for infinitesimal elastic and growth strains. Parametric studies for equilibrium and nonequilibrium boundary-value problems representing the in vitro growth of cylindrical cartilage constructs are solved. The results show that the CGM model is capable of describing the main biomechanical features of cartilage growth. The solutions to the equilibrium problems reveal that tissue composition, constituent pre-stresses, and geometry depend on collagen remodeling activity, growth symmetry, and differential growth. Also, nonhomogeneous growth leads to nonhomogeneous tissue composition and constituent pre-stresses. The solution to the nonequilibrium problem reveals that the tissue is nearly in equilibrium at all time points. The results suggest that the CGM model may be used in the design of tissue engineered cartilage constructs for the repair of cartilage defects; for example, to predict how dynamic mechanical loading affects the development of nonuniform properties during in vitro growth. Furthermore, the results lay the foundation for future analyses with nonlinear models that are needed to develop realistic models of cartilage growth

Constitutive functions of elastic materials in finite growth and deformation.

Abstract. The constitutive functions of soft biological tissues during growth are studied. A growth, treated as addition (often non-uniform) of material points, results in deformation, residual stresses, and evolution of the constitutive functions. A theory based on the concept of equivalent material points is developed with the current configuration taken as the reference. The residual stresses developed in a spherical shell undergoing spherical growths are studied. Mathematics Subject Classifications (1991): 73B05, 73G05, 73P20, 92C10

Slime-Producing Coagulase-Negative Staphylococci Isolated from Human Eye Infections

Some strains of coagulase-negative staphylococci produce an extracellular material, slime, which mediates adherence to foreign surfaces, such as indwelling biomedical devices. It is not known if slime is involved in adherence to human tissue. Coagulase-negative staphylococci are the most common members of normal ocular flora and cause many ocular infections, although the role of slime in these infections has not been studied

Writing in the discipline of music: Rhetorical parameters in writings about music criticism

Researchers into the writings of a discipline usually seek connections between its disciplinary and discursive practices. This line of rhetorical research has been common in scientific and professional disciplines, but rare in the arts and humanities. Of all the arts, writing in music is perhaps most unlike writing in the sciences because music is an abstract phenomenon, aurally perceived. To examine musicians\u27 discursive practices, this study concentrates on musicians\u27 metacritical statements about writing about music instead of analyzing texts produced in the field. Based on the metacritical analysis, unique discursive practices in music are identified and correlated to the axiomatics of the study of music. The field of music features many written genres, but music criticism has an especially long history of field-specific debates and influences. Musicians apply the label criticism to journalistic accounts of concerts and recordings, theoretical analyses of compositions, and hermeneutic discussions of compositions or issues within the field. This study focuses on approximately seventy-five metacritical statements about what music criticism is and should be. These statements, written by English and American musicians over two centuries, offer numerous insights into musicians\u27 perceptions of what it is to write music criticism in many musical communities. To introduce non-musicians to music criticism and musical communities, one chapter provides a brief history of the genre, introduces the metacritical texts, and summarizes important issues found there. The chapter about audiences and communities analyzes perceptions of audience as self, artist (composer or performer), editor, reader, and public, followed by a discussion of the intricate formulations of community in the field of music and the role of methodology in shaping them. The chapter on objects and language considers ways in which the objects (subject matter) of music are not understood as autonomous, and how such understandings affect musicians\u27 approaches to the language of music criticism. The final chapter pursues ideas of pedagogy for music criticism in the metacritical emphases on of talent, practice, and models as they are understood by musicians. This chapter ends with a larger discussion of field-specific writing pedagogy

A Growth Mixture Theory for Cartilage

In this paper we present a model of growth for cartilaginous tissues in which there exists a saturated solid matrix composed of multiple constituents that may grow and remodel independently of each other. Klisch and Hoger recently developed a general theory of volumetric growth for a mixture of ν-1 growing elastic materials and an inviscid fluid, which included a treatment of two special types of internal constraints that are relevant to cartilage. Here, that theory is specialized to construct a cartilage growth model. This theory allows the constituents of the solid matrix to grow independently of each other, and can model the evolution of the constituent pre-stresses and the tissue’s mechanical properties during developmental growth and degeneration. A simple example is presented which illustrates these features of the theory

On Residual Stress in an Elastic Body

105 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1984.Residual stress is defined as the stress field supported by a body in the absence of external forces. Thus, the residual stress is in equilibrium with zero body force, is symmetric, and gives rise to zero surface traction.An elastic body with a particular material symmetry can admit only those residual stress fields that commute with the elements of the symmetry group of the material. Using this condition, one can obtain the forms for residual stress fields appropriate to specific material symmetries. Here the additional restrictions imposed by equilibrium and the zero traction condition are explored. It is shown that if a body is isotropic it supports no residual stress. For bodies that are transversely isotropic, among other results, it is established that the residual stress must vanish if the axis of symmetry is uniform. Bodies composed of material with rhombic or monoclinic symmetry are also considered. Additional results can be found in the context of particular body geometries. As an example, states of residual stress possible in a transversely isotropic right circular cylinder are discussed.The rest of the thesis is devoted to the construction of a theoretical framework with which to explore the possibility of the nondestructive mechanical determination of residual stress. The body is supposed to support an unknown residual stress field in its reference configuration, and it is assumed that the body responds in a linearly elastic manner to small deformations from the reference configuration. The residual stress appears explicitly in the corresponding constitutive equation, and we treat it as constitutive information which we want to determine.The constitutive equation valid for a linearly elastic body which supports a residual stress is derived and discussed, and the basic equations of the theory are displayed. These equations are then used to construct boundary value problems that allow particular forms of residual stress to be written explicitly in terms of traction boundary data. The uniqueness of the resulting expression for the residual stress is discussed.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD

Shear stress regulates the endothelial Kir2.1 ion channel

Endothelial cells (ECs) line the mammalian vascular system and respond to the hemodynamic stimulus of fluid shear stress, the frictional force produced by blood flow. When ECs are exposed to shear stress, one of the fastest responses is an increase of K(+) conductance, which suggests that ion channels are involved in the early shear stress response. Here we show that an applied shear stress induces a K(+) ion current in cells expressing the endothelial Kir2.1 channel. This ion current shares the properties of the shear-induced current found in ECs. In addition, the shear current induction can be specifically prevented by tyrosine kinase inhibition. Our findings identify the Kir2.1 channel as an early component of the endothelial shear response mechanism

Molecular cloning and expression of a bovine endothelial inward rectifier potassium channel 1The nucleotide sequence data reported in this paper has been submitted to GenBank with Accession Number U95369.1

AbstractA 5.1 kb cDNA encoding an inward rectifier K+ channel (BIK) was isolated from a bovine aortic endothelial cell library. The cDNA codes for a 427-amino-acid protein with two putative transmembrane regions. Sequence analysis reveals that BIK is a member of the Kir2.1 family of inward rectifier K+ channels. Expression in Xenopus oocytes showed that BIK is a K+-specific strong inward rectifier channel that is sensitive to extracellular Ba2+, Cs+, and a variety of anti-arrhythmic agents. Northern analysis revealed that endothelial cells express a 5.5 kb BIK mRNA that is sensitive to shear stress