Compression pressure-induced synergy in xanthan and locust bean gum hydrogels. Effect in drug delivery

Abstract

The study assesses the potential of combining xanthan gum and locust bean gum to create controlled-release hydrogels and also examines how compressing the polysaccharide blends affects their behavior. The research involved evaluating the rheological properties of aqueous dispersion of these gums and their mixtures using a rotational rheometer. Xanthan gum displayed a pseudoplastic Bingham behavior, while locust bean gum exhibited lower viscosity and shear thinning behavior. Gum blends showed an intermediate behavior with varying yield shear stress based on the gum proportions in the mixture. The flow index (n) and the consistency index (K) were calculated using the Power Law model (Ostwald de Waele relationship). The values of n are between 0.6 (Xanthan gum) and 0.1 (locust bean gum), with the blends showing intermediate values. These values are characteristic of shear-thinning systems and show a higher deviation of Xanthan gum from Newtonian behavior than LBG. Additionally, the k values indicate higher consistency for the Xanthan dispersions and similar behavior for the mixtures of the two polysaccharides, regardless of their proportion.

Precompression at 433.6 MPa for 5 min reduced the dispersion viscosity of xanthan gum by 50% at a shear rate of 2s−1, decreasing it from 70 Pa s to 34 Pa s, while having a minimal impact on the rheological behavior of locust bean gum, which changed from 0.18 Pa s to 0.23 Pa s at a shear rate of 2s−1. Temperature also decreased the xanthan gum dispersion viscosity. Oscillatory rheology tests highlighted differences between xanthan gum and locust bean gum dispersions. Xanthan gum formed a durable three-dimensional network with bonds, while locust bean gum exhibited a network with a shorter shelf life. Precompression significantly altered the rheological behavior of the gum blends, increasing the storage and loss moduli.

Drug diffusion tests developed in Franz-Chien cells showed no significant differences in diffusion profiles between gums and gum mixtures at a concentration of 0.5% w/v, indicating similar microviscosity to water at this concentration. Regarding drug release from xerogels prepared by compression, the hydrogels displayed sustained release, with release rates dependent on pH and the specific drug used. Locust bean gum showed consistent release rates at both pH levels, while xanthan gum and xanthan gum-locust bean gum blends exhibited lower release rates at pH 6.8. Triamcinolone acetonide, one of the tested drugs, showed slow release regardless of pH and gel composition.

In conclusion, the study suggests that precompression and temperature can impact the rheological behavior and release properties of gum gels, making them valuable parameters for controlling the release properties of these hydrogels.