Temperature dependence of non-Fickian water transport and swelling in glassy gelatin matrices

Dynamic swelling behaviour of gelatin/poly(acrylic acid) bioadhesive microspheres loaded with oxprenolol

The dynamic swelling of gelatin/poly(acrylic acid) microspheres loaded with oxprenolol has been evaluated. The movement of two distinct and characteristic swelling boundaries was measured directly using an optical microscope. Swelling rate constants associated with the inner moving front and the outer swelling boundary were determined. A polynomial equation incorporating both Fickian diffusion and case II relaxational models was used to fit the kinetics of liquid uptake. The influence of the concentration of the cross-linking agent, the poly(acrylic acid) load, the pH of the swelling medium and the particle size of the microspheres, on the swelling kinetics, was evaluated and discussed.

Effect of water mobility on drug hydrolysis rates in gelatin gels

The stability of drugs incorporated in gelatin gels was studied, with a focus on the water mobility in the gels. Trichlormethiazide hydrolysis and kanamycin-catalyzed flomoxef hydrolysis in gelatin gels were chosen as models for apparent first-order and second-order hydrolysis, respectively. The mobility of water in gelatin gels was determined by NMR, ESR, and dielectric relaxation spectroscopies. The amount of bound water in the gels was determined from dielectric relaxation spectra. Spin-lattice relaxation time of water determined by 17O NMR and rotational correlation time of an ESR probe determined by an ESR probing method were useful in determining the microviscosity of the gels. The hydrolysis rate of trichlormethiazide in the gels was found to depend on the amount of free water available for the reaction, while that of flomoxef depended on the microviscosity of the gels, which reflected the mobility of water molecules. Thus the dependence of hydrolysis rates on the water mobility was influenced by the hydrolysis mechanism.

Consideration of drug load on the swelling kinetics of glassy gelatin matrices

The effect of drug load on water transport into glassy gelatin beads and on the dynamic swelling behavior of the hydrated gel was studied through microscopic measurements of moving boundaries. Isoniazid was found to alter the glassy structure of gelatin, resulting in an increase in water penetration rates with a lowering of the apparent activation energy for water front movement. Differential scanning calorimetry studies revealed a decrease in the glass transition temperature with drug load, further indicating plasticization of the gelatin glass. The presence of drug also accelerated the outer swelling gelatin front, but, in contrast to the water front, the apparent activation energy for matrix expansion rose substantially with higher drug loads for temperatures greater than 20 degrees C. This observation may be rationalized as an increasing osmotic stress on the matrix induced by greater loading with hydrophilic drug. The osmotic stress, in turn, forces the gelatin matrix to expand outward, resulting in a higher apparent activation energy (Eact). Furthermore, the enhanced expansion was especially pronounced at higher temperatures where physical bonds, which are associated with gel structure and needed to resist swelling, are presumably weaker and fewer in number.