Controlling the release kinetics of calcein loaded liposomes from chitosan/tannic acid and chitosan/poly(vinyl alcohol)/tannic acid hydrogels
Résumé
The paper describes the preparation of novel hydrogels based on chitosan or chitosan/poly(vinyl alcohol) crosslinked with tannic acid for the inclusion of phosphatidylcholine liposomes loaded with calcein as model fluorescent hydrophilic drug. This procedure ensured the reduction of the “burst effect” or even its elimination. The originality of the paper consists in the utilization of the natural compound tannic acid as crosslinker for the formation of complex hydrogels, which ensures biocompatibility and excellent biological properties. In order to modulate the properties of the hydrogel, the molecular weight of chitosan, the chitosan/tannic acid molar ratio, the molar ratio between the polymers and the crosslinking time have been taken into account as variable parameters. Hydrogels based on medium molecular weight showed a reduced degree of swelling, as compared to those containing high molecular weight chitosan. More tannic acid in the hydrogel composition resulted in a higher crosslinking density in the hydrogels and reduced the swelling degree. As it was expected, the use of the synthetic polymer reduced the hydrophilicity of the materials and, as a consequence, the drug release capacity. Surprisingly, the crosslinking time did not reduce significantly the maximum degree of swelling. In good correlation with the characteristics of the hydrogels, the calcein release from the complex hydrogels could be delayed and better controlled. The release time was prolonged from several days (control hydrogels) to 21 days. The latency parameter showed that more that 40% of the calcein was released in the form of liposomes, which constitutes a second release barrier for the included drug.