Cross-linked chondroitin sulphate: characterization for drug delivery purposes

Chondroitin sulphate was cross-linked with 1,12-diaminododecane to give a series of cross-linked products with reduced water solubility. Since the water solubility of the modified polymers is low, their chemical characterization is complicated. A new method based on the adsorption of the cationic dye, methylene blue, on the cross-linked polymers was developed to characterize the degree of cross-linking. It was found that the values of the adsorptive capacity of the adsorbate, Cp(s), decreased with the extent of cross-linking. However, the values of the adsorptive coefficient, K, and the free energy change of the adsorption reaction, Δμ °, increased with cross-linking. The swelling of films made of the cross-linked polymers was measured in water and an exponential-like dependency between the degree of swelling and extent of cross-linking could be defined. Indomethacin tablets made of two types of cross-linked polymers — very low water soluble and relatively high water soluble — were made and analysed for their water uptake and drug release characteristics. Based on the physicochemical properties, an optimal product with a potential to serve as a colon-specific drug carrier was suggested.