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Viscosity promoters


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  • 1. A SEMINAR ONVISCOSITY PROMOTERS Presented by Sushma.A M.Pharmacy (I sem) Industrial
  • 2. CONTENTS1.Introduction2.Ideal characteristics of viscosity promoters3.Classification  Natural gums  Cellulose derivatives  Microcrystalline cellulose  Chitosan  Synthetic polymers  Clays4. Conclusion References
  • 3. INTRODUCTIONVISCOSITY: Flow property of a simple liquid is expressed in terms of viscosity. Quantitatively, viscosity is an index of resistance of a liquid to flow. A fluid with large viscosity resists motion because its molecular makeup gives it a lot of internal friction. A fluid with low viscosity flows easily because its molecular makeup results in very little friction when it is in motion.
  • 4. VISCOSITY PROMOTERS: These are substances ,which added to anaqueous mixture, increase its viscosity withoutsubstantially modifying its other properties , such as taste.They provide body, increase stability , and improvesuspension of added ingredients. It is desirable to increase the viscosity of liquid toprovide or to improve palatability or pourability
  • 5.  Polymers are used in suspensions, emulsions , and other dispersions ,primarily to minimize or control sedimentation Only small amounts of many polymers(depending on chemistry and molecular weight)are needed to bring the viscosity of an aqueous preparation to almost any desired value Most of the polymer solutions or dispersions are Non-newtonian.
  • 6.  Many polymers of natural origin are attacked directly by microorganisms. Even if the polymer chosen is totally resistant to bacteria and molds , the aqueous medium may allow growth , and a preservative is still necessary. certain inorganic agents are also used as viscosity builders. Examples : veegum (colloidal magnesium aluminium silicate ) and microcrystalline silica
  • 7. Advantages and Disadvantages due to viscosity of medium Advantages:  High viscosity inhibits the crystal growth.  High viscosity enhances the physical stability  High viscosity prevents the transformation of metastable crystal to stable crystal
  • 8. Disadvantages : High viscosity hinders the re-dispersibility of the sediments. High viscosity retards the absorption of the drug. High viscosity creates problems in handling of the material during manufacturing.
  • 9. IDEAL CHARACTERISTICS OF VISCOSITY PROMOTERS:Should produce a structured vehicleShould have high viscosity at negligible shear during storage and low viscosity at high shearing rates during pouring Should exhibit yield stress Should be compatible with other excipientsShould be nontoxicViscosity should not be altered by temperature or on aging
  • 10. CLASSIFICATION: Natural gums Acacia , Tragacanth Alginic acid Karaya , Guar gum etc., Cellulose derivatives Carboxy methyl cellulose Methyl cellulose Ethyl cellulose Hydroxy ethyl cellulose Hydroxy propyl methyl cellulose
  • 11.  Microcrystalline cellulose Chitosan Synthetic polymers carbomer (polyacrylic acid) polyvinyl pyrrolidone polyvinyl alcohol Clays Magnesium aluminium silicate(veegum) Bentonite , Attapulgite
  • 12. 1) NATURAL GUMS Natural gums are polysaccharides of natural origin ,capable of causing a large viscosity increase in solution ,evenat small concentrationsThese polymers may be either nonionic or anionic. Natural gums can be classified according to their origin 1. Natural gums obtained from seaweeds agar alginic acid sodium alginate carrageenan
  • 13. 2.Natural gums obtained from non-marine botanical sources Gum arabic (from the sap of acacia trees) Gum tragacanth(from the sap of astragalus shrubs) Karaya gum(from the sap of sterculia trees) Guar gum(from guar beans) Locust bean gum(from the seeds of carob tress) Dammar gum (from the sap of dipterocarpaceae trees)
  • 14. 3.Natural gums produced by bacterial fermentation gellan gum xanthan gumALGINATES Anionic polysaccharide Derived from brown seaweed in the form of monovalent and divalent salts The most widely used one is sodium alginate Use :thickener and stabilizer
  • 15. GUM ARABIC Anionic polysaccharide It is the dried exudate of trees of the genus acacia Unlike most natural gums,acacia exhibits very low solution viscosities At concentration under 40% ,solutions exhibits newtonian flow;higher concentrations behave in a pseudoplastic manner Use: suspending agent,emulsifier,adhesives and binders in tabletting
  • 16. CARRAGEENAN Anionic polysaccharide derived from seaweed Solutions of carrageenan have a yield point when used in sufficient concentration , and they are also thixotropic Use: emulsifier , thickener , suspension stabilizerGUAR GUM Nonionic polysacccharide derived from seeds It exhibits pseudoplastic flow
  • 17.  Disadvantage of these gels is the presence of insoluble plant residue Use: thickener , suspension stabilizerKARAYA GUM Anionic exudate polysaccharide The viscosity of gum karaya in water increases rapidly with concentrations so that a dispersion with a concentration of 2-3% acts as a gel Use : bulk laxatives , denture adhesives
  • 18. LOCUST BEAN GUM Nonionic seed polysaccharide Solutions of this gum are psuedoplastic It is one of the more efficient thickening natural polymers , along with guar , tragacanth , and karaya gumsTRAGACANTH GUM Anionic polysaccharide It exhibit pseudoplastic flow It is one of the most efficient natural polymer thickeners
  • 19. XANTHAN GUM Anionic polysaccharide Exhibits pseudoplastic rheology Temperature has very little effect on the viscosity of xanthan gum solutions . This temperature independence of viscosity is unique to xanthan gum Use : thickener , suspension stabilizer , suspending agent
  • 20. Properties of Selected Viscosity-Imparting AgentsAgent Structure Ionic pH factors Rheology chargeAlginates Poly anionic Stable at Pseudo saccharide pH 3-10 plastic Gum Poly Viscosity Newtonia arabic saccharide anionic is affected n(<40%), by pH peudoplas tic(>40%)Carragee- Poly anionic Stable at Thixotro-nan saccharide pH 3-10 pic
  • 21. Agent Structure Ionic pH Rheology charge factorsGum Poly anionic Stable at Pseudotragacanth saccharide pH 1.9-8.5 plasticXanthan Poly anionic Good Pseudogum saccharide stability at plastic pH 1-12Locust Poly Pseudobean gum saccharide nonionic --- plasticGuar gum Poly anionic Stable at Pseudo saccharide pH 4-10 plastic
  • 22. Applications of natural gums: Guar gum is a colon- specific drug delivery carrier is based on its degradation by colonic bacteria Gum acacia used in confectionery industry and in baking industry Gum tragacanth is still a preffered ingredient , particularly used in conjunction with gum acacia Xanthan gum is a common suspending agent in suspension for reconstitution
  • 23. 2)CELLULOSE DERIVATIVES Cellulose is one of the most widely used starting material for manufacturing of modified natural polymers. Cellulose ethers with methyl substitution generally form a gel at a elevated temperatures. Gel formation is reversed when temperature is reduced.CARBOXY METHYL CELLULOSE(CMC)Sodium CMC ,an anionic polymer, is available in 3 grades. Food , pharmaceutical and technical
  • 24.  It is also available with a variety of molecular weights and degree of substitution CMC is more resistant to microbial attack than most natural gums. The viscosity of CMC solution decreases reversibly with increasing temperature The rheology of aqueous CMC solution depends on the degree of substitution . Low substituted CMC products exhibit thixotropy;higher substitution leads to pseudoplastic behavior Use : suspending agent , emulsion stabilizer
  • 25. ETHYL CELLULOSE It is a nonionic ether derivative of cellulose It is widely used as tablet binder ,thickening agent , coating material for tablets , microcapsules and microparticlesHYDROXY ETHYL CELLULOSE(HEC) It is a nonionic cellulose ether Solutions of HEC exhibit pseudoplastic flow and have no yield point
  • 26. METHYL CELLULOSE & HYDROXY PROPYL METHYL CELLULOSE (HPMC) Both are interesting examples , as they exhibit a reverse thermal gelation , gelling when heated and melting when cooled These are the nonionic cellulose ether derivatives Rheology of these solutions is pseudoplastic , and there is no yield point Use : suspension stabilizer , thickener
  • 27. Ionic Conc.Agent charge pH Rheology Range factor (%)CMC Anionic Stable at Pseudo 1-2 pH 4-10 plasticEthyl Nonionic Stable at Pseudo 5cellulose pH 4-10 PlasticHydroxy Nonionic Stable at Pseudo 0.3-2propyl pH 4-10 PlasticcelluloseHPMC Nonionic Stable at Pseudo 0.3-2 pH 4-11 PlasticMethyl Nonionic Stable at Pseudo 1-5cellulose pH 4-11 plastic
  • 28. Applications of cellulose derivatives:1.Methyl cellulose: Used in pharmaceutical gels High viscosity grades are used in opthalmic preparations Bulk forming laxative Lubricating jellies for surgical and medical procedures2.HPMC: A 2 % solution is commercially available as an opthalmic surgical aid
  • 29. 3) MICROCRYSTALLINE CELLULOSE (MCC) Dispersions of MCC do not have viscosities that are significantly greater than that of water. However , combinations of CMC,MC or HPMC are used to thicken aqueous solutions The colloidal dispersions of MCC blends exhibit thixotropic rheology , also exhibit a yield point Viscosity is not affected by temperature It is used as stabilizer and thickener in aqueous systems Formulation of dry powder suspension with MCC:alginate complexes(0.5-10%w/w of total dry formulation)
  • 30. 4) CHITOSAN Chitosan is a natural biopolymer derived from the outer shell of crustaceans It is a weak cationic polysaccharide , biocompatible , biodegradable , nontoxic Unlike most gums , chitosan carries a positive charge ( at pH below 6.5 ) and is thus attracted to a variety of biological tissues and surfaces that are negatively charged
  • 31. Uses: As permeation enhancer As mucoadhesive excipient It exhibits favourable biological behaviour , such as bioadhesion and permeabilty enhancing properties , which make it a unique material for the design of ocular drug delivery vehicles Enhanced bone formation by transforming growth factor Solubility increase as well as taste masking
  • 32.  Useful in promoting tissue growth in tissue repair Accelerating wound-healing and bone regeneration Cholesterol lowering effects5) SYNTHETIC POLYMERSCarbomer ( polyacrylic acid ) Solutions of carbomers are very pseudoplastic They exhibit a yield value It is an excellent choice as a thickener in creams and lotions
  • 33.  Carbomer 934P is the official name given to one member of a acrylic polymers . Manufactured under the trade name carbopol 934P , it is used as a thickening agent in a variety of pharmaceutical and cosmetic productsPolyvinylpyrrolidone ( PVP ) Solutions are stable at elevated temperatures , but viscosity drops reversibly with increasing temperature Use : in opthalmic preparations , serving as muco- mimetic agent in arteficial tear formulations
  • 34. 6) CLAYSMagnesium aluminium silicate (veegum ) The gels are formed at about 5% concentration.They exhibit plastic flow It functions well as a suspending agent . It is a superior suspending agent because it prevents caking without affecting pourability or spreadability of suspension
  • 35.  Magnesium aluminium silicate dispersions are influenced by heat , and the viscosity of the dispersion increases on prolonged exposure to elevated temperaturesAttapulgite It is a magnesium aluminium silicate clay of very fine particle size Use : Viscosity building , gelling , thickening agent , protective colloid , suspending agent , adsorbent , emulsion stabilizer
  • 36. Bentonite It is a clay mineral of the smectite group It is an absorbent aluminium phyllosilicate , in general , impure clay consisting of montmorillonite The smectites are a group of minerals that swells as they absorb water or organic molecules within the structural layers It is prescribed as bulk laxative
  • 37. Clays Agent Rheology Conc. Range(%)Magnesium Plastic/ 0.5-5aluminium thixotropysilicateBentonite Plastic/ 1-6 thixotropyAttapulgite Plastic/ 10 thixotropy
  • 38. CONCLUSION In pharmaceutical field , the viscosity promotersplay a vital role , as they stabilize the disperse systems andalso used in various dosage forms Viscosity-inducing polymers should be usedwith caution . They are known to form complexes with avariety of organic and inorganic compounds
  • 39. RECENT ADVANCES Sustained opthalmic delivery of ofloxacin from an ion-activated in-situ gelling system (gelling agent is sodium alginate in combination with hydroxy propyl cellulose) To prolong precorneal residence time and to improve bioavailability attempts were made to increase the viscosity of the formulation using viscosity promoters such as cellulose , poly alcohol and poly acrylic acid Chemically modified chitosan or its derivatives used in delivering the bioactive molecules
  • 40. REFERENCES 1.Herbert A. Lieberman , Martin M. Rieger and Gilbert S.Banker ,Pharmaceutical Dosage Forms : Disperse systemsvolume 1 , 2 & 3 (second Edition , Revised and Expanded )2.James Swarbrick , Encyclopedia of pharmaceuticaltechnology , Third Edition3.S Abraham , S Furtado , S Bharath , BV Basavaraj…pak J Pharm…,