chitosan and plga microspheres as drug delivery ... - UniCA Eprints

5. RFP Loaded Chitosan Microspheres Prepared by Spray-Drying Method5.2.3. Surface ChargeInvestigation of zeta potential is an important part of microsphere characterization. Thisparameter was investigated by using a solution of KCl 0.1N since phosphate buffer could notbe used due to the effect of the counterions on the positively charged chitosan microspheres.All chitosan formulations were positively charged as can be seen in table 5.2.It was found that the cross-linking with GA led to a decrease of the zeta potential of chitosanmicrospheres as a consequence of diminution of free amino groups in chitosan structure. Infact, GA reacts with chitosan through the formation of covalent bonds mainly with the aminogroups of the polysaccharide.5.2.4. Entrapment Efficiency (E%)Figure 5.4 shows the encapsulation efficiency (E%) of the prepared microspheres. Allformulations showed very good E%, always ranging between 50% for uncross-linkedparticles and 80% for cross-linked microspheres. E% of spray-dried microspheres wasaffected by chitosan concentration: E% decreased as chitosan concentration increased. Theincrease in chitosan concentration led to highly viscous solutions that reduced drug solubilityand therefore the loading capacity.The influence of the cross-linking agent on the RFP entrapment in chitosan microspheres wasalso evaluated.10080E%6040200Form.AForm.BForm.CForm.DForm.EForm.FForm.GForm.HFigure 5.3: Entrapment Efficiency (E%) of Spray-Dried MicrospheresAs can be seen in figure 5.4, cross-linked particles (Formulation A-D) showed the best E%because of their stability during atomization and washing steps.78