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

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2. Chitosan And PLGAAt present, a numerous of analytical methodologies are introduced to characterize theseproperties, which then provide the potential clue to understand, predict and eventually modifythe release behavior of the systems.The most commonly used method to analyze the molecular weight of PLGA is the sizeexclusion chromatograph (SEC). Polydispersity reveals the molecular weight distribution.The higher the polydispersity, the wider the molecular weight distribution is (231).Lactic acid contains an asymmetric carbon atom and has two optical isomers. PLA can existin two stereo forms, optically active form (L-PLA) and optically inactive racemic form(D,LPLA). L-PLA is found to be semicrystalline in nature due to high regularity of itspolymer chain while D,L-PLA is an amorphous polymer because of irregularities in itspolymer chain structure. Hence the use of D,L-PLA is preferred over L-PLA as it enablesmore homogeneous dispersion of the drug in an optically inactive polymer matrix.Crystallinity of the PLGA can be determined by DSC or X-ray diffraction. It is directlyrelated to the molecular weight, type, and molar ratio of the copolymer component. PLGAsprepared from L-PLA and PGA are crystalline copolymers while those from D,L-PLA andPGA are amorphous in nature. It was reported that PLGAs containing less than 70% glycolideare amorphous in nature (232).Glass transition temperature (Tg) is the temperature at which the polymers change fromglassy state to rubbery state. At this point, the mechanical behavior of the polymer changesfrom rigid and brittle to tough and leathery (plastic behavior). The Tg of PLGAs is commonlyabove the physiological temperature of 37 °C, which gives them enough mechanical strengthto be fabricated into delivery devices. The Tg of the PLGA decreases with decrease of lacticacid content in copolymer and with decrease in their molecular weight (233).Analysis of copolymer composition of PLGA can be accomplished by magnetic resonancespectroscopy (NMR).The biodegradable profiles of PLGA could be influenced by the physical and chemicalproperties of the polymer and the additives or encapsulated drugs in the polymer matrix. Ingeneral, the degradation rate of the PLGA decreases with the decrease of 1) polymermolecular weight (234); 2) initial crystallinity (235); 3) lactic/glycolic copolymer ratio (236);4) glass transition temperature (237); 5) hydrophilicity of the polymerThe degradation rate increase with incorporation of acidic or basic compounds (238)Microparticles based on biodegradable polymer have been extensively investigated ascontrolled release delivery system over the past three decades. In recent years, a continued42
2. Chitosan And PLGAinterest in PLGA microparticles has been triggered by their application for the controlledrelease of macromolecular drugs. Biodegradable microparticles can be prepared by severalmethods, but the most widely used techniques are phase separation (coacervation), spraydrying, and solvent evaporation.Spray-DryingSolvent EvaporationPhase Separation(Coacervation)CosolventmethodDispersionmethodMultiple EmulsionmethodNon AqueousmethodO/WEmulsionO/WEmulsionW/O/WEmulsionO/OEmulsionFigure 2.4: PLGA Microspheres: Preparation MethodsThe manufacturing method has much influence on the structure and release properties of themicroparticles.General requirements for microparticle preparation include:• Maintain the stability of the encapsulated active ingredient• Obtain optimal drug loading, high encapsulation efficiency and yield• Get desired drug release profiles and low initial release• Involve a simple, reproducible, and scaleable processGenerally PLGA microspheres are prepared by using oil–water emulsions that consist of anorganic phase comprised of a volatile solvent with dissolved polymer and the drug to beencapsulated, emulsified in an aqueous phase containing dissolved surfactant. Two commonexamples of volatile organic solvents used for the organic-phase solvent are dichloromethaneand ethyl acetate. A surfactant is also included in the aqueous phase to prevent the organicdroplets from coalescing once they are formed. Once the droplets are formed via physicalmeans, the organic solvent leaches out of the droplet into the external aqueous phase beforeevaporating at the water–air interface. Emulsions are simply created by using a propeller ormagnetic bar for mixing the organic and aqueous phases. The organic-phase solvent should beable to dissolve the polymer up to reasonably high concentrations but does not necessarily43
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 28 and 29: 1. General Introductionsphere prepa
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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 44 and 45: 2. Chitosan And PLGAneed to be a go
Page 46 and 47: 2. Chitosan And PLGAdichloromethane
Page 49 and 50: 3. Aim of the Work49
Page 51: 3. Aim of the WorkBiodegradable mic
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Page 71 and 72: 5. Rifampicin Loaded ChitosanMicros
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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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