During the past decades, hydrogels have been introduced suitable as novelmaterials for a variety of applications such as biomedical engineering, sanitaryproducts, agriculture, bioseparation, enhanced oil recovery, etc. They havebeen successfully used as superabsorbent materials and in drug delivery, cellencapsulation and tissue repair due to their high water content and consequentbiocompatibility. Considering the fact that water retention in the hydrogels provides asuitable drug diffusion pathway; many hydrogel-based networks have been designedand fabricated as intelligent carriers of drugs. The rate and degree of hydrogel swellingare the most important parameters which control the release patterns of solvents anddrugs from these polymeric networks. Therefore, the precise account of hydrogelbehaviour as well as mathematical description of equilibrium swelling, dimensionalchanges due to solvent uptake, desorption and drug release profiles were the mainobjectives in many investigations. The objective of this manuscript is to give a briefreview on existing mathematical models and theories in the field of hydrogel swellingas well as the description of the drug release mechanism from swelling-controllednetworks. The most important properties of hydrogels relevant to their swellingbehaviour as well as kinetics and thermodynamic of swelling are also presented.

Theoretical Description of Hydrogel Swelling: A Review

In this chapter, the recent advances in cartilage biomechanics and electromechanics are reviewed and summarized. Our emphasis is on the new experimental techniques in cartilage mechanical testing, new experimental and theoretical findings in cartilage biomechanics and electromechanics, and emerging theories and computational modeling of articular cartilage. The charged nature and depth-dependent inhomogeneity in mechano-electrochemical properties of articular cartilage are examined, and their importance in the normal and/or pathological structure-function relationships with cartilage is discussed, along with their pathophysiological implications. Developments in theoretical and computational models of articular cartilage are summarized, and their application in cartilage biomechanics and biology is reviewed. Future directions in cartilage biomechanics and mechano-biology research are proposed.

Mechano-electrochemical properties of articular cartilage: their inhomogeneities and anisotropies.

Study design A review of the literature on macromechanical factors that accelerate disc degeneration with particular focus on distinguishing the roles of immobilization and overloading. Objective This review examines evidence from the literature in the areas of biomechanics, epidemiology, animal models, and intervertebral disc physiology. The purpose is to examine: 1) what are the degeneration-related alterations in structural, material, and failure properties in the disc; and 2) evidence in the literature for causal relationships between mechanical loading and alterations in those structural and material properties that constitute disc degeneration. Summary of background data It is widely assumed that the mechanical environment of the intervertebral disc at least in part determines its rate of degeneration. However, there are two plausible and contrasting theories as to the mechanical conditions that promote degeneration: 1) mechanical overload; and 2) reduced motion and loading. Results There are a greater number of studies addressing the "wear and tear" theory than the immobilization theory. Evidence is accumulating to support the notion that there is a "safe window" of tissue mechanical conditions in which the discs remain healthy. Conclusions It is concluded that probably any abnormal loading conditions (including overload and immobilization) can produce tissue trauma and/or adaptive changes that may result in disc degeneration. Adverse mechanical conditions can be due to external forces, or may result from impaired neuromuscular control of the paraspinal and abdominal muscles. Future studies will need to evaluate additional unquantified interactions between biomechanics and factors such as genetics and behavioral responses to pain and disability.

/pdf/mechanical-conditions-that-accelerate-intervertebral-disc-599es6ddr5.pdf

Mechanical conditions that accelerate intervertebral disc degeneration: overload versus immobilization.

MECHANO-ELECTROCHEMICAL PROPERTIES OF ARTICULAR CARTILAGE: Their Inhomogeneities

A fibril-reinforced poroviscoelastic swelling model for articular cartilage

An equivalent new expression of the triphasic mechano-electrochemical theory [9] is presented and a mixed finite element formulation is developed using the standard Galerkin weighted residual method. Solid displacement us, modified electrochemical/chemical potentials ϵw, ϵ+and ϵ− (with dimensions of concentration) for water, cation and anion are chosen as the four primary degrees of freedom (DOFs) and are independently interpolated. The modified Newton–Raphson iterative procedure is employed to handle the non-linear terms. The resulting first-order Ordinary Differential Equations (ODEs) with respect to time are solved using the implicit Euler backward scheme which is unconditionally stable. One-dimensional (1-D) linear isoparametric element is developed. The final algebraic equations form a non-symmetric but sparse matrix system. With the current choice of primary DOFs, the formulation has the advantage of small amount of storage, and the jump conditions between elements and across the interface boundary are satisfied automatically. The finite element formulation has been used to investigate a 1-D triphasic stress relaxation problem in the confined compression configuration and a 1-D triphasic free swelling problem. The formulation accuracy and convergence for 1-D cases are examined with independent finite difference methods. The FEM results are in excellent agreement with those obtained from the other methods. Copyright © 1999 John Wiley & Sons, Ltd.

A mixed finite element formulation of triphasic mechano-electrochemical theory for charged, hydrated biological soft tissues


 It has been shown that the triphasic theory [1] is capable of describing many mechano-electrochemical phenomena observed in charged hydrated soft tissues or cells, such as free-swelling, stress-relaxation, streaming potential, diffusion potential, and electro-osmosis [e.g., 1–3]. The theory is useful for the study of signal transduction mechanisms at both tissue and cellular levels. This is important to understanding tissue physiology and pathology. To facilitate applications of the triphasic theory to many practical problems, it is necessary to develop a numerical method for quantitatively investigating tissue behaviors. Thus, the objective of this study is to develop a finite element formulation for the triphasic theory. A free-swelling problem was studied using this finite element method to investigate effects of inhomogeneity of fixed charge density (FCD) on ion concentration, tissue deformation, fluid flow and streaming potential etc.

A mixed finite element formulation of triphasic theory and its application to free swelling problem

Streaming potential of human lumbar anulus fibrosus is anisotropic and affected by disc degeneration.

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A mixed finite element formulation of triphasic mechano-electrochemical theory for charged, hydrated biological soft tissues

A mixed finite element formulation of triphasic theory and its application to free swelling problem

Streaming potential of human lumbar anulus fibrosus is anisotropic and affected by disc degeneration.