Kinetics of the breakdown of cross-linked soy protein films for drug delivery.

The aim of the present work was to investigate the potential of soy protein isolate (SPI) films as controlled release systems for active compounds. Mechanical properties, dissolution and compound release kinetics of SPI films prepared with different concentrations of formaldehyde were measured over time in the absence or presence of digestive enzymes at gastric or intestinal pH. The effect of formaldehyde on tensile strength, elastic modulus, % elongation and swelling suggested that increasing its concentration increased film cross-linking density. Film bulk erosion in the presence of digestive enzymes followed first-order kinetics. Methylene blue or rifampicin release followed variable kinetics depending on compound solubility during a 1-2h initial phase, followed by zero-order release. Cross-linking density appears to provide effective means of regulating the erosion and release rate of SPI films. SPI film networks displayed excellent compound binding capacity, especially for hydrophobic molecules, and hence potential for use in controlled release systems based on matrix erosion.