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

4. RFP Loaded Chitosan Microspheres Prepared by Precipitation MethodabFigure 4.2: Sem Micrographs of Uncross-Linked Particles (a) and Cross-LinkedParticles (b)4.2.3. Surface ChargeZeta potential has a substantial influence on the stability of suspensions, the interaction ofmicrospheres with charged drugs, and also on the adhesion of drug delivery systems ontobiological surfaces. Consequently, investigation of the zeta potential is an important part ofmicrosphere characterization. Phosphate buffer influenced measurement of zeta potential, dueto the effect of the counterions on the positively charged chitosan microspheres. For thisreason a solution of KCl 0.1N was used for charge surface measurements.Chitosan microspheres were positively charged (Table 4.2), although sulphate ions were usedas precipitant. This indicates that only a part of the amino groups are neutralized duringmicrosphere formation. A different behaviour could be observed between uncross-linked andcross-linked microspheres zeta potential. In fact, while the zeta potential of the uncross-linkedparticles slightly increased as chitosan concentration increased, the contrary was obtainedwith the cross-linked particles formulations. Moreover, the zeta potential of these lastformulations was smaller than the corresponding uncross-linked formulations 1-3 as aconsequence of reduction of amino groups because of interaction with GA.4.2.4. Entrapment Efficiency (E%)Figure 4.4 shows the encapsulation efficiency (E%) of the prepared microspheres. In thepresent work, the influence of chitosan concentration and cross-linking agent on the RFPentrapment in microspheres was evaluated. The highest E% was found in formulationsprepared with the lowest amount of chitosan, that are Form. Ø and Form. ØG obtainedwithout and with GA respectively. Chitosan concentration affected considerably the E: inparticular the loading capacity increased as the chitosan concentration decreased. This isbecause the increase in chitosan concentration led to increased solution viscosity thatdrecreased the loading capacity of the microspheres as a consequence of the reduced drug61