DIMENSIONLESS ANALYSIS OF SOLUTE RELEASE FROM SWELLABLE POLYMER SYSTEMS (CONTROLLED RELEASE DRUG DELIVERY)
Abstract
A theory was developed for use in prediction of release behavior of solutes from swellable systems. Prediction is based on values of the diffusional Deborah number, De(,D), and the swelling interface number, Sw. The Deborah number takes into account the relative importance of polymer relaxation and penetrant diffusion in the penetrant uptake mechanism. The swelling interface number relates the rate of penetrant uptake to the rate of solute diffusion. It is concluded that zero-order (constant rate) release will be observed in cases for which De(,D) is of the order of unity and Sw is very small. Experimental verification of the theory was conducted using copolymers of 2-hydroxyethyl methacrylate (HEMA) and methyl methacrylate (MMA). The monomers were bulk polymerized in polyethylene vials with benzoyl peroxide initiator and the polymers were lathe cut into disks. HEMA mole fractions employed were 1.0, 0.9, 0.8, 0.7, 0.6, and 0.5. Samples were also prepared by bulk polymerization in a casting apparatus for determination of their relaxational behavior. Theophylline was incorporated during polymerization at a loading of 0.5%. Swelling behavior of polymer disks was observed in water at 37(DEGREES)C and the diffusion coefficient of water in the copolymers was determined. Solute release studies were performed on both swollen and glassy copolymers, and the diffusion coefficient of theophylline in the swollen copolymers was determined. The order of release was also determined for theophylline release from glass copolymers. The relaxational behavior of copolymer films at their equilibrium water content and 37(DEGREES)C was observed using tensile stress relaxation experiments. The relaxation behavior was used to determine characteristic relaxation times, the molecular weight between entanglements and other mechanical properties of the copolymers. The experimental results obtained indicate that the new theory can predict release behavior from swellable systems using the results from relatively simple transport and mechanical testing experiments.
Degree
Ph.D.
Subject Area
Chemical engineering
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