Sorption of diclofenac to selectively oxidised cellulose

Abstract

Biologically active fibers as drug carriers have improved characteristics in comparison with conventional medical therapies. Cellulose as a hydrophilic and biocompatible, nontoxic and eco-friendly material, makes a good polymer matrix for obtaining biologically active fibers. Loading drugs on the fiber carrier is accomplished through hydrophobic interactions, which is a prevailing mechanism of drug bonding. These interactions can be achieved by hydrophobic parts of the drug and the fiber carrier or by hydrophobic drugs themselves bonded on the fiber. In this paper, oxidized cellulose (OC) with 0.547, 1.163 and 2.199 mmol/g COOH is produced by using selective oxidation of a cellulose-based bandage. Oxidation has been carried out in mixture of HNO3/H3PO4 2:1 and 1.43 % NaNO2 for 5, 10 and 20 h at 25 ± 1 °C. The OC sample with 2.199 mmol/g COOH showed the lowest sorption capacity as well as weak mechanical properties, so that the sorption experiments were not further pursued. The other two samples of oxidized cellulose with 0.547 and 1.163 mmol/g COOH have been used for chemical bonding of an analgesic, diclofenac, a derivative of potassium salt. Diclofenac in its structure contains two benzene rings which are linked via a secondary amine. The analgesic also contains a carboxyl group, as well as 2 chlorine atoms. As a result of the presence of these functional groups and structures, diclofenac can build multiple chemical bonds with an oxidized cellulose bandage. The chemical bonding of the drug has been performed using three analgesic solutions with concentrations of c = 2.5∙10-3, 3.4∙10-3 and 5.1∙10-3 mol/L, at the temperature of 26 ± 1oC while desorption was performed in physiological saline solution. The amounts of bonded and released antibiotic were determined by UV-VIS spectroscopy at the wavelength of λmax=276 nm. The maximum amount of bonded drug (0.814 mmol/g OC) has been obtained by sorption from the solution of concentration c=5.1∙10-3, while the highest amount of desorbed diclofenac was 0.063 mmol/g OC. The sorption kinetics has been succesfully described by the pseudo-second order model. It was established that the drug bonding was achieved by hydrogen bonds of the drug functional groups with the oxidised cellulose bandage. Low diclofenac relase from the oxsidiesed cellulose (12.5 % in 24 h) is a consequence of formation of multiple bond as well as drug aggregates on fiber surfaces.

Keywords

• oxidised cellulose
• diclofenac-K
• chemism of binding
• biologically active analgetic fiber