Preparation And Release Kinetics Of Avermectin-Loaded Chitosan/Sodium Lignosulphonate Microcapsules Formulated By Layer-By-Layer Polyelectrolyte Self-Assembly

The avermectin-loaded microcapsules were prepared by layer-by-layer polyelectrolytes self-assembly using chitosan and sodium lignosulphonate as shell materials. The dispersion of microcapsules was observed by optical microscope. The morphology of microcapsules was characterized by scanning electron microscopy (SEM). The electrophoretic potentials of microcapsules with different polyelectrolyte layers were determined by using electrophoretic analysis. The technical avermectin, avermectin-loaded microcapsules, chitosan, sodium lignosulphonate and chitosan/sodium lignosulphonate complex were analyzed by FTIR. The effects of preparation conditions on release behaviors of avermectin from microcapsules were investigated and the release mechanism of avermectin from microcapsules was also evaluated by fitting the in-vitro release results into the generalized model.The optical microscope micrographs showed that the avermectin-loaded microcapsules have little aggregation. FTIR spectra indicated no chemical interaction between avermectin and the wall material of microcapsules. The SEM micrographs showed that the avermectin-loaded microcapsules had a rough surface in contrast to the smooth surface of the technical avermectin. The results of electrophoretic potentials showed that electrical charges on the surface of microcapsules were changed inversely after every deposition of polyelectrolytes. The results obtained from SEM and electrophoretic potentials suggested that chitosan and sodium lignosulphonate can alternately deposit on avermectin to obtain avermectin-loaded microcapsules.The effects of the numbers of polyelectrolyte layers,pH of the solutions of polyelectrolytes and the concentrations of NaCl in solutions of polyelectrolytes on release kinetics of the abamectin-loaded microcapsules were investigated in vitro. The results showed that the release rates of avermectin from the microcapsules can be modulated by changing the numbers of polyelectrolyte layers,pH of the solutions of polyelectrolytes and the concentrations of NaCl in the solutions of polyelectrolytes. The release rates of avermectin were considerably decreased with increasing number of the polyelectrolyte multilayers or increasing concentration of NaCl used in the polyelectrolytes solution. The time taken for the cumulative release of 50% (m/m) avermectin, i.e.: t₅₀, could be modulated between 0.20h and 8.57h with increasing number of the polyelectrolyte multilayers (4～12), between 0.86h and 6h with increasing concentration of NaCl (0～1 mol·L^-1) used in the polyelectrolytes solution. The release rates of avermectin were remarkably increased when sodium chloride was incorporated into the individual or both polyelectrolyte solutions. The release rates increased to the greatest extent from the microcapsules obtained from chitosan and sodium lignosulphonate polyeletrolytes solutions which were incorporated simultaneously with increasing amount of sodium chloride. The release rates increased with decreasing pH of the polyelectrolyte solutions without the addition of NaCl.The results obtained from fitting the release data to the generalized model suggested that the release mechanism of avermectin from the layer-by-layer polyelectrolytes self-assembled chitosan/lignosulphonate microcapsules was anomalous.