chitosan and plga microspheres as drug delivery ... - UniCA Eprints
chitosan and plga microspheres as drug delivery ... - UniCA Eprints
chitosan and plga microspheres as drug delivery ... - UniCA Eprints
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6. RFP Loaded PLGA Microspheres Prepared by Solvent Evaporation Method6.2.6. Rele<strong>as</strong>e/Stability StudiesIn vitro <strong>drug</strong> rele<strong>as</strong>e profile reveals fundamental information on the structure (e.g., porosity)<strong>and</strong> behavior of a formulation on a molecular level, <strong>as</strong> well <strong>as</strong> possible interactions between<strong>drug</strong> <strong>and</strong> polymer, <strong>and</strong> their influence on the rate <strong>and</strong> mechanism of <strong>drug</strong> rele<strong>as</strong>e <strong>and</strong> modelrele<strong>as</strong>e data.Rele<strong>as</strong>e studies were carried out by using two different rele<strong>as</strong>e medium, phosphate buffer atpH 7.4 <strong>and</strong> acetic acid buffer at pH 4.4, in order to have the same pH values present insidephagosome <strong>and</strong> lysosome <strong>and</strong> to evaluate the effect of pH on RFP rele<strong>as</strong>e from PLGA<strong>microspheres</strong>. In Figure 6.5 <strong>and</strong> 6.6, RFP rele<strong>as</strong>e profiles from PLGA <strong>microspheres</strong> at pH 7.4<strong>and</strong> 4.4 buffer solutions respectively are shown.The rele<strong>as</strong>e profiles were very similar in the two different rele<strong>as</strong>e media. Normally, therele<strong>as</strong>e medium pH is able to affect the <strong>drug</strong> rele<strong>as</strong>e pattern from PLGA-b<strong>as</strong>ed microparticles.In this c<strong>as</strong>e it w<strong>as</strong> found the same behaviour at pH 7.4 <strong>and</strong> at pH 4.4 during the 72 hoursexperiments.The main re<strong>as</strong>on that can explain this behaviour is correlated to the transition temperature(Tg) of the polymer. In fact it is well know that PLGA polymer Tg is commonly above thephysiological temperature of 37 °C, which gives it enough mechanical strength to befabricated into <strong>delivery</strong> devices. Tg incre<strong>as</strong>es with incre<strong>as</strong>e of lactic acid content incopolymer, because the extra methyl group on the lactic acid moiety incre<strong>as</strong>es the rigidity ofthe polymer chain because of the steric hindrance. Moreover, <strong>as</strong> polymer molecular weightincre<strong>as</strong>es a reduced polymer chain mobility is obtained. In fact, incre<strong>as</strong>e in the polymer chainlength enhances the intra- <strong>and</strong> interpolymer chain interactions such <strong>as</strong> chain entanglement <strong>and</strong>packing, which decre<strong>as</strong>e the polymer chain mobility <strong>and</strong> consequently incre<strong>as</strong>e Tg. On theother h<strong>and</strong>, it h<strong>as</strong> been found that the rele<strong>as</strong>e of RFP or other <strong>drug</strong>s from PLGA particles isinfluenced by PLGA monomer composition (lactid acid/glycolic acid).As seen from the results in both c<strong>as</strong>es the PLGA microparticles are able to control RFPrele<strong>as</strong>e rate, <strong>and</strong> the initial burst effect demonstrated for this type of particles (12% of RFPloaded in particles) is significantly low if compared to that obtained from <strong>chitosan</strong> particles.Moreover, after this initial burst, PLGA <strong>microspheres</strong> rele<strong>as</strong>ed RFP at a lower rate (chapter4).96
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