The release of model macromolecules may be controlled by the hydrophobicity of palmitoyl glycol chitosan hydrogels

A non-covalently cross-linked palmitoyl glycol chitosan (GCP) hydrogel has been evaluated as an erodible controlled release system for the delivery of hydrophilic macromolecules. Samples of GCP with hydrophobicity decreasing in the order GCP12>GCP11>GCP21 were synthesised and characterised by 1H NMR. Hydrogels were prepared by freeze-drying an aqueous dispersion of the polymer in the presence or absence of either a model macromolecule fluorescein isothiocyanate-dextran (FITC-dextran, MW 4400), and/or amphiphilic derivatives Gelucire 50/13 or vitamin E d-α-tocopherol polyethylene glycol succinate. Gels were analysed for aqueous hydration, FITC-dextran release, and bioadhesion, and imaged by scanning electron microscopy. The gels were highly porous and could be hydrated to up to 95× their original weight without an appreciable volume change and most gels eventually eroded. Hydration and erosion were governed by the hydrophobicity of the gel and the presence of the amphiphilic additives. GCP gels could be loaded with up to 27.5% (w/w) of FITC-dextran by freeze-drying a dispersion of GCP in a solution of FITC-dextran. The controlled release of FITC-dextran was governed by the hydrophobicity of the gel following the trend GCP21>GCP11>GCP12. GCP gels were bioadhesive but less so than hydroxypropylmethylcellulose, Carbopol 974NF (7:3) tablets.