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

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1. General Introductionsphere preparation temperature. The authors found that the highest encapsulation efficienciesoccurred at the lowest and highest formation temperatures tested (about 50% at 4 and 38°C,and about 19% at 22 and 29°C). The non-linear drug loading trend suggested that differentmechanisms governed the encapsulation process at different temperatures. When consideringthe relation of the polymer itself to encapsulation efficiency, Ghaderi et al. (138) found thatincreasing the concentration of polymer in the organic phase increased the encapsulationefficiency. An increase in E% from 1 to 25% was observed depending on the concentration ofthe polymer.Microsphere size can be affected by the polymer concentration, temperature, viscosity, thestirring rate, and the amount of emulsifier employed. Considering the effect of polymerconcentration, it has often been reported that increasing the concentration of polymerincreases sphere size (138, 139, 140, 141, 142). Yang et al. (137) used scanning electronmicroscopy (SEM) to show that sphere size was temperature dependent; lower and highertemperatures produced larger spheres whereas intermediate temperatures produced smallerspheres. Once again, different mechanisms dominated microsphere formation at differenttemperatures. At lower temperatures, the solution’s higher viscosity resulted in the formationof larger spheres; this has also been confirmed by other researchers (143). Larger sphereswere obtained at higher temperatures due to the higher rate of solvent evaporation whichresulted in higher solvent flow pressure moving more material from the sphere center outward(137).Jalil and Nixon (144) studied the variation of sphere size with respect to the stirring rate andthe influence of the emulsifier in the second emulsion step. It was shown that microspheresize decreased with increasing stirring rate since increased stirring results in the formation offiner emulsions. Little change in diameter size was reported by varying emulsifierconcentration.Controlled release is an attainable and desirable characteristic for DDS. The factors affectingthe drug release rate revolve around the structure of the matrix where the drug is containedand the chemical properties associated with both the polymer and the drug. Conventional oraldelivery is not rate controlled. A drug encapsulated in a slowly degrading matrix provides theopportunity for slower release effects, but polymer degradation is not the only mechanism forthe release of a drug. The drug release is also diffusion controlled as the drug can travelthrough the pores formed during sphere hardening. In some cases, drugs containingnucleophilic groups can cause increased chain scission of the polymer matrix, which also28
1. General Introductionincreases the rate of drug expulsion. Polymer molecular weight, drug distribution, polymerblending, crystallinity, and other factors are important in manipulating release profiles. Themost desirable release profile would show a constant release rate with time. However, inmany cases release profiles are more complicated and often contain two main expulsionprocesses: the first being an initial burst of expelled medication from the sphere surface; thesecond, a usually more constant stage with release rates dependent on diffusion anddegradation (145, 146, 147).The release profiles are also dependent on the size of the microspheres; the rate of drugrelease was found to decrease with increasing sphere size (148, 149, 150, 151, 152).Therefore, by mixing microspheres of different sizes it is possible to obtain another degree ofcontrolling release. More importantly, linear, zero-order kinetics are obtainable by combiningthe proper formulation of microsphere sizes.Core-shell microspheres usually refer to spheres formed by making core units through anormal preparative method, followed by the addition of an outer layer by a dipping procedure,mixing procedure, or emulsion procedure (153, 154, 155, 156, 157, 158). Employment of ashell is usually meant to enhance controlled release and possibly reduce the effect of theinitial burst.1.7. Bioadhesive Microspheres as Systems Able to EnhancePulmonary Drug DeliveryThe success of microspheres as DDS is limited due to their short residence time at the site ofabsorption. It would, therefore, be advantageous to have means for providing an intimatecontact of the DDS with the absorbing membranes. It can be achieved by couplingbioadhesion characteristics to microspheres and developing novel delivery systems referred toas “bioadhesive microspheres”.“Bioadhesion” in simple terms can be described as the attachment of a synthetic or biologicalmacromolecule to a biological tissue. An adhesive bond may form with either the epithelialcell layer, the continuous mucus layer or a combination of the two. The term “mucoadhesion”is used specifically when the bond involves mucous coating and an adhesive polymericdevice, while “cytoadhesion” is the cell-specific bioadhesion. Bioadhesive microspheresinclude microparticles and microcapsules (having a core of the drug) of 1–1000 µm indiameter and consisting either entirely of a bioadhesive polymer or having an outer coating of29
Page 1: European Union Ministero dell’Uni
Page 5 and 6: Table Of Contents1. GENERAL INTRODU
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Page 10 and 11: 1. General Introduction1.1. Pulmona
Page 12 and 13: 1. General Introductionmucosa, and
Page 14 and 15: 1. General Introductionis the fact
Page 16 and 17: 1.3. Lung Anatomy1. General Introdu
Page 18 and 19: 1. General Introductionhighly vascu
Page 20 and 21: 201. General Introductionliquid (84
Page 22 and 23: 1. General IntroductionAerosol size
Page 24 and 25: 1. General Introductionof numerous
Page 26 and 27: 1. General Introductionintermittent
Page 30 and 31: 1. General Introductionit, respecti
Page 32 and 33: 1. General Introductionthe subject
Page 34 and 35: 1. General IntroductionA. zahoor et
Page 36 and 37: 2. Chitosan And PLGA2.1. Chitosan a
Page 38 and 39: 2. Chitosan And PLGAfor the prepara
Page 40 and 41: 2. Chitosan And PLGAmainly controll
Page 42 and 43: 2. Chitosan And PLGAAt present, a n
Page 44 and 45: 2. Chitosan And PLGAneed to be a go
Page 46 and 47: 2. Chitosan And PLGAdichloromethane
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Page 51: 3. Aim of the WorkBiodegradable mic
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5. RFP Loaded Chitosan Microspheres
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6. RFP Loaded PLGA Microspheres Pre
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7. RFP Loaded PLGA Coated Chitosan
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8. Final Discussion and Conclusions
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9. References9. References1. Fred S
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9. References40. Wayne L.G., Good R
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1269. References88. Carpenter R.L.
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1289. References135. Fukushima S.;
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9. References173. Zeng X.M., Martin
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9. References219. Berthold A., Crem
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9. Referencesmediates target gene e
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