Polyvinyl alcohol as a viable membrane in artificial tissue design and development

Abstract

Polyvinyl alcohol (PVA) membranes have long been used in many applications, most notably in a number of recent biomedical applications. These applications include the encapsulation of hybrid-type artificial organs,1-3 the controlled release of specific molecules,4,5 targeted drug delivery systems,6,7 enhanced wound dressings,8,9 and myriad other applications that utilize the semi-permeability and high biocompatibility of PVA. Nevertheless, prior to its designation for use as the biomaterial of choice in the design and development processes of artificial tissue fabrication applications, the exact nature of PVA's physiological properties needs to be ascertained. In particular, the permeability and the diffusion coefficient are two important parameters that need to be analyzed. The experimental results can subsequently be used to determine the appropriate fabrication technique and design geometry for the design and development of the required tissue engineering applications. This study is based on the following presumption: if a researcher could place a semi-permeable membrane at the interface of two chambers (Chambers 1 and 2) that contain different concentrations of the same solution, then the diffusive parameters of the membrane can be measured simply by continuously measuring the changes in solute concentration in the chamber with the lower concentration. If the researcher waits until equilibrium between the two chambers is reached, both of the chambers would then have the same amount of solute (and, therefore, the same concentration of solute). A complete concentration profile will therefore provide the information that is needed to determine (using Fick's Law) the desired parameters of the membrane. Nevertheless, this procedure is highly impractical, due to the long period of time that is required to record the observations and any related changes. On the other hand, by deriving a model of the underlying diffusion process using Fick's Law, the researcher can predict the diffusive parameters based on the collected data over a relatively short period of time. The derivation of the model begins with constructing materials that are balanced on either side of the membrane. The material balance on the higher-concentration chamber (Chamber 1) can be expressed as where V1 is the chamber volume, P is the permeability, A is the exposed area of the membrane, c1 is the concentration in Chamber 1, and c2 is the concentration in Chamber 2. Similarly, the material balance in the lower-concentration chamber (Chamber 2) can be expressed as Assuming the initial conditions of c1 equals c0, and c2 equals zero, the following mathematical model can be derived and used to determine the permeability, P, and thus the diffusion coefficient, D, of the hydrogel membrane. If the ratio of ct/c0 is sufficiently small (as is the case if the period of the experiment is sufficiently short), then the left-hand side of the equation will be equal to –2ct/c0, according to Taylor's series.5,7 In other words, a linear concentration profile can be expected if the experimental period is sufficiently short, and the permeability and diffusion coefficient can be easily determined thereafter. The aim of this technical report was to study the fundamental parameters in the design and development of an aqueous PVA hydrogel membrane to be used in generic artificial tissue engineering applications; these parameters included the permeability and diffusion coefficient of the membrane and were measured using dextran-fluorescein isothiocyanate (Dextran-FITC) as the solute of choice.