Solute transport in hydrogels

In order to design a particular release mechanism, experimental data of statistical significance are compared to a solution of the theoretical model. It is therefore clear that only a combination of accurate and precise data with models accurately depicting the physical situation will provide an insight into the actual mechanism of release. 

The vast majority of theoretical models are based on diffusion equations. The phenomenon of diffusion is intimately connected to the structure of the 

the concentration and mass flux of species i are designated ch and ji, respectively Dip is the diffusion coefficient of species i in the polymer matrix, and x and t stand for the independent variables of position and time, respectively. 

Several important assumptions have been implicitly incorporated in Eqs. (15) and (16). First, these equations describe the release of a drug from a carrier of a thin planar geometry, equivalent equations for release from thick slabs, cylinders, and spheres have been derived (Crank and Park, 1968). It should also be emphasized that in the above written form of Fick s law, the diffusion coefficient is assumed to be independent of concentration. This assumption, while not conceptually correct, has been 

Initial and boundary conditions, which are necessary for solving Eq. (15) and (16), allow for the appropriate description of the experimental conditions imposed upon the drug release device. The solutions of Eqs. (15) and (16) subject to a number of boundary conditions that can be applied to various in vitro and ex vivo experiments have been obtained (Crank and Park, 1968). 

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The implications of the existence of liquid crystals in water-soluble cellulosic gels has not been fully studied in the field of biological applications. In particular, the models developed for water transport in hydrogels do not consider the presence of mesophases. The same is true for solute (drug) release models... 

Polyionic complexes of chitosan and polyacrylic acid were prepared in a wide range of copolymer composition and with two kinds of drugs. Release of amoxicillin trihydrate and sodium amoxicillin from these complexes were studied. The swelling behaviour of and solute transport in swellable hydrogels were investigated. 23 refs. 

Recently, we have examined solute permeation through hydrogel membranes in an effort to develop models which describe in detail the transport phenomena with particular emphasis on the role of water in this process. These studies have utilized p-HEMA and its copolymers, and both hydrophobic and hydrophilic solutes (7., i). It was determined that p-HEMA and its copolymers are permeable to both hydrophobic and hydrophilic solutes. 

Lowman AM, Peppas NA. Solute transport analysis in pH-responsive, complexing hydrogels of poly(methacrylic acid-g-ethylene glycol). J Biomater Sci Polym Ed 1999 10 999-1009. 

The swelling behaviour of polymeric systems has a great importance when they are applied in the biomedical field as their hydration degree influences the surface properties and mobility, the mechanical properties and the type of solute transport mechanism through the hydrogels. ... 

Diffusion in highly swollen matrices such as hydrogels involves a three-component system in which the polymer-solvent matrix constitutes a continuum through which the solute diffuses. The mode and rate of transport through the... 

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