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Suspension & emulsions

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Suspension, interfacial properties of suspended particles, settling in suspensions, formulation of flocculated and deflocculated suspensions. Emulsions and theories of emulsification, microemulsion and multiple emulsions; Stability of emulsions, preservation of emulsions, rheological properties of emulsions.

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Suspension & emulsions

  1. 1. PREPARED BY: K. ARSHAD AHMED KHAN M.Pharm, (Ph.D) Dept. of Pharmaceutics RIPER.
  2. 2. 4.Add Flocculating agent & Structured vehicle FORMULATION OF SUSPENSION: Particles 1.Add Wetting Agent Dispersion Medium Uniform dispersion of Deflocculated Particles 2.Add Structured vehicle 3.Add Flocculating agent Deflocculated Suspension in Structured vehicle Flocculated Suspension Flocculated Suspension in Structured vehicle
  3. 3. Step-1: Dispersion of solids: Water (solvent) + Insoluble solids (Hydrophobic)  Difficult to disperse. Small particles adsorb air and float on solvent surface. Dispersion can be done by 1. Water miscible Co-solvents = Alcohol, Glycerin, PEG Floating particles + Glycerin  removes air on surface, forms a coat  ↑Dispersion. 2. Wetting agents: Surfactants ↓IFT, ↓Contact angle(90-00) ↑Dispersion. (HLB= 7-9)
  4. 4. Step-2: Deflocculated Suspension in Structured vehicle:  Structured vehicles are the vehicles which exhibit pseudo plastic/ plastic rheological behavior.  These also posses thixotropic behavior i.e., gel-sol-gel transformation to improve physical stability of suspension.  Structured vehicles are hydrocolloids, in low Conc. absorb water, swell to give high viscosity.  They act as protective colloid to stabilize charge. Ex: Non-ionic = MC, HPMC Anionic = Sodium CMC, Carbopol. Clays = Bentonite
  5. 5. Concentration of suspending agent depends on: 1. Viscosity of vehicle: Vehicle (low ɳ) + High Conc. suspending agent Vehicle (high ɳ) + low Conc. suspending agent 2. Amount of solid: Oral= high solid content + high Conc. S.A (non-ionic) Parenteral= low solid content + low Conc. S.A (0.5% W/V) If clays are used add preservatives (2-5% W/V) 3. Particle Size: Small size + low Conc. suspending agent Large size + High Conc. suspending agent 4. Density of solids: Structured vehicles + PVP/PEG/Sugars  ↑ viscosity. 5. pH, Ionic strength.
  6. 6. Step-3: Flocculated Suspension: Flocculating agent= electrolytes, surfactants, polymers. 1. Electrolytes: All suspended particles same charge  Repulsive forces Add electrolytes of opposite chargeAttractive forcesFlocs Bismuth sub nitrate(+) + water + WA Deflocculated suspension + Monobasic potassium phosphate(-) electrolyte  Flocculated Suspension. Flocculated Suspension + extra electrolyte all particles (-) charged  repulsions Deflocculated suspension
  7. 7. Zeta potential & Sedimentation: Suspension Charge Sedimentation(Vu/Vo) Deflocculated [+] Low- hard cake flocculated [+][-] = neutral High Deflocculated [-][+][-] = [-] Low-hard cake Other examples: Sulfamerazine (-) and flocculating agent AlCl3 (+)
  8. 8. Controlled floccullation:  Most dispersed particles posses charge depending on pH of the system.  The charge should be adjusted to zero and adjust pH to make flocculated suspension in non-caking zone with optimum zeta potential .
  9. 9. 2. Surfactants:  Reduces IFT, act as wetting agent, deflocculating agent & flocculating agent (Controlled Conc.)  Particles + oppositely charges surfactant  Tails form bridges between particles  Floccules Anionic surfactants – SLS Cationic surfactants – cetyl trimethyl ammonium bromide Nonionic surfactants – tweens
  10. 10. 3. Polymers: Polymers are long hydrocarbon chained molecules. Half chain – adsorbed on particle Other half chain – outside form brides with chains Flocs. Ex: Sulfaguanidine + Xanthan gum Floccules
  11. 11. Protective colloidal action: Hydrophilic polymers form sheath on floccules and improve stability Ex: acidic solution of sulfthiazole  [-] particles  Deflocculated suspension. Sulfthiazole + Polymer (Gelatin)  Protective coat on Floccule.
  12. 12. Step-4: Flocculated Suspension in Structured vehicle:  Flocculated suspension have clear supernatant, undesirable property.  Add structured vehicle/ suspending agent  Good Suspension.  Flocculating agent – uniform sized floccules.  Structured vehicle/ suspending agent – prevent settling of floccules Incompatability: Charges of 1. Particle 2. Flocculating Agent 3. Suspending Agent
  13. 13. Physical stability of suspension:  Physical stability is defined as a condition in which the particles remain uniformly distributed throughout dispersion with out any signs of sedimentation.  Even if particles settle they should be easily redispersed with moderate amount of shaking. SUSPENSION EVALUATIONS: 1. Sedimentation volume (F) 2. Degree of flocculation (β) 3. Redispersibility.
  14. 14. 1. Sedimentation Volume (F): F is dimension less quantity, value ranges from 1-0. F value is proportional to stability If F=1, Vu=Vo, ideal suspension If F=0, Vu=0, total instability. This evaluation is useful for 1. Selection of better suspension 2. Identifying suitable suspending agent 3. Obtaining optimum concentration of suspending agent.
  15. 15. 2. Degree of flocculation (β)  β is dimension less quantity, value ranges from 1-infinity.  β value is proportional to stability  If β =1, F=Fα, minimum value indicating system is defloccuated.  The sedimentation volume of deflocculated system is less than that of flocculated system.
  16. 16. 3. Redispersibility: Mechanical shaker device simulating human motion. Suspension in 100 ml measuring cylinder  stored to sediment  placed in machine, rotated 3600 at 20 RPM sediment redispersed time/no. of rotations NOTED. Less time/ less rotations= disperse stable suspension More time/ more rotations= disperse  unstable suspension.
  17. 17. Rheological considerations:  Important in manufacturing, storage, administration.  Dispersion medium should have thixotropic behavior - plastic/ pseudoplastic (gel-sol-gel) Preformulation studies: Performed to evaluate vehicle for optimum viscosity. Method: 1. Vehicles mixed with various S.A/ various Conc. Of same S.A 2. Shear stress noted form lower to higher rates of shear. 3. Obtained hysteresis loop is compared with standard product graph.
  18. 18. Other Suspending agents: Tragacanth, Sodium alginate, Sodium CMC. Measurement of viscosity: Cup-bob, Cone-plate viscometers not suitable because they break floccules.
  19. 19. Brookfield viscometer:  Best suitable for studying settling in suspensions  Contains helipathic stand with “T” shaped spindle, moves in helix manner up-down.  As suspension exhibits thixotropic behavior Initial GEL show resistance  high dial reading Next SOL  less resistance  low dial reading.  A good suspension has less rate of decrease in dial reading in Gel SOL transformation.
  20. 20. 1. The results indicate how particles settle with respect to time. 2. The technique provides information at which level the floccule network is greater due to aggregation. 3. Effect of aging on storage can be evaluated.
  21. 21. Advanatges/Applications of Suspensions: 1. Stability 2. Choice of solvent 3. Taste masking 4. Prolonged drug action 5. Bioavailability
  22. 22. Advanatges/Applications of Suspensions: 1. Stability: Drug in solution is unstable (hydrolysis) Suspension = insoluble drug  STABLE. Ex: Procaine Penicillin-G 2. Choice of solvent: Drug is insoluble in water, Solvent other than water is not acceptable  prepare Suspension. Ex: Corticosteroid Injection 3. Taste masking: Suspension = (Unpleasant tasted Drug + Flavour/Sweetners) Ex: Chloramphenicol Palmitate.
  23. 23. 4. Prolonged drug action: Insoluble drug  Reservoir  drug released for long period Ex: Procaine Penicillin –G 5. Bioavailability: Suspensions have high bioavailability than Tab, Cap because of large surface area, high dissolution rate. Ex: Antacid Suspension acts faster than antacid tablets.
  24. 24. • DEF: A thermodynamically unstable system consisting of at least two immiscible liquid phases, one of which is dispersed as globules in the other liquid phase. • Emulsion is stabilized by an emulsifying agent. • Globule diameter 0.1- 100µm Ex: Milk, ice cream, paints, lotions of low viscosity to ointments, creams which are semi-solids Classification: 1. Basing on dispersed phase - 2 Types o/w and w/o Medicinal emulsions are mostly o/w type. 2. Basing on globule size – 2 types Microemulsions (0.01µm) Fine emulsions (0.25-25 µm)
  25. 25. EMULSIFYING AGENT Functions: 1. To prevent coalescence of dispersed globules. 2. To reduce IFT between polar and non-polar solvents. Surfactants: HLB (3-8)  W/O emulsifying agent- Spans HLB (8-16)  O/W emulsifying agent- Tweens. Brancrofts Rule: States that though emulsifying agent has affinity towards polar and non-polar liquids, they have preferential solubility in one of the liquid which becomes continuous phase.  Combination of E.A imparts better stability  Ionic type of E.A not preferred for internal use as they interact with biomembranes and effect cell functioning.  Natural E.A show batch-batch variation & microbial growth.
  26. 26. Classification of Emulsifying Agents 1. Natural Emulsifying Agents Animal origin-wool fat. Egg yolk, gelatin, cholesterol, pectin, chondrus. Plant origin- Acacia, Tracaganth. 2. Synthetic Emulsifying Agents Anionic-sodium stearate, sodium lauryl sulphate Cationic- Benzalkonium chloride Non-ionic- Sorbitan Fatty acid esters (Spans), Polyoxyethylene sorbitan fatty acid esters (Tweens) 3. High molecular weight alcohols Stearyl alcohol, cetyl alcohol & glyceryl monostearate. 4. Finely divided solids Bentonite, magnesium hydroxide & aluminium hydroxide.
  27. 27. Mechanisms of emulsion formation Emulsifying agent Forms film on dispersed globules. 1. Monomolecular adsorption film Surfactants- Spans, Tweens. 2. Multimolecular adsorption film  Hydrophilic colloids – Acacia, Gelatin. 3. Solid particle Adsorption  Finely divided solids- Bentonite, Veegum.
  28. 28. 1. Monomolecular adsorption film:  Surfactants form monomolecular film at oil-water interface and cover the globule.  The film should be strong, elastic, flexible to reform when broken.  Emulsion stability depends on physical, chemical, mechanical properties of film.  Oil soluble & water soluble surfactant combination interactions forms complex & strong film.  Ionic surfactants develop repulsive forces between globules to prevent Coalescence.  Nonionic surfactants forms thick film on globule to prevent Coalescence.
  29. 29. 1. Sodium + Cholesterol  strong, strong  Good cetyl sulphate interaction film emulsion 2. Sodium + Oleyl alcohol less  weak film  Poor cetyl sulphate interactions emulsion 3. Sodium + Cetyl alcohol less complex  Poor emulsion oleate film
  30. 30. 2. Multimolecular adsorption film Acacia, Gelatin  multimolecular film  Prevent coalescence.
  31. 31. 3. Solid particle Adsorption:  Finely divided solid particles adsorb at oil-water interface to form rigid film.  Film act as mechanical barrier to prevent coalescence.  o/w  veegum, bentonite  w/o  bentonite  The stability of emulsion depends on the finer state of sub-division of solid particles, irregular surface & charge on surface.
  32. 32. Interfacial properties in emulsion: Surfactants reduce IFT leading to globule formation and increase in surface free energy. ΔG = γ 0/w ΔA γ 0/w = interfacial tension between oil & water ΔA = increase in surface area. With increase in surface free energy system becomes unstable, to stabilize ΔG = 0. 1. Method-A: ΔA =0 means regrouping of particles  phase seperation. 2. Method-B: γ 0/w =0. This is not possible, but γ 0/w can be reduced by adding surfactants.
  33. 33. THEORIES OF EMULSIFICATION: Many theories have been advanced to account for the way or means by which the emulsion is stabilized by the emulsifier. At the present time no theory has been postulated that seems to apply universally to all emulsions. 1) Electric Double Layer Theory. 2) Phase Volume Theory. 3) Hydration Theory of Emulsions 4) Oriented wedge theory. 5) Adsorbed Film and Interfacial tension Theory 6) Surface tension theory.
  34. 34. 1) Electric Double Layer Theory: The oil globules in a O/W emulsion carry a negative charge. The water ionizes so that both hydrogen and hydroxyl ions are present. The negative charge on the oil may come from adsorption of the OH ions. These adsorbed hydroxyl ions form a layer around the oil globules. A second layer of oppositely charged ions forms a layer in the liquid outside the layer of negative ions. These two layers of oppositely charged ions are known as the Helmholtz double layer. They are not confined to emulsions but accompany all boundary phenomena. The electric charge is a factor in all emulsions, even those stabilized with emulsifying agents
  35. 35. 2) Phase Volume Theory: If spheres of the same diameter are packed as closely as possible, one sphere will touch 12 others and the volume the spheres occupy is about 74 per cent of the total volume. Thus if the spheres or drops of the dispersed phase remain rigid it is possible to disperse 74 parts of the dispersed phase in the continuous phase; but if the dispersed phase is increased to more than 74 parts of the total volume, a reversal of the emulsion will occur. However, the dispersed phase does not remain rigid in shape but the drops flatten out where they come in contact with each other.
  36. 36. 3) Hydration Theory of Emulsions: • Fischer and Hooker state that hydrated colloids make the best emulsifiers. • Fischer states the emulsifying agent, by which a permanent emulsion is obtained, invariably "proves to be a hydrophilic colloid when W/O emulsions are concerned (a lyophilic colloid of some sort when other than aqueous mixtures are under consideration). Put another way, oil cannot permanently be beaten into water, but only into a colloid hydrate." • Fischer and Hooker have found albumin, casein, and gelatin to be good emulsifying agents.
  37. 37. 4) Oriented wedge theory: • This theory deals with formation of monomolecular layers of emulsifying agent curved around a droplet of the internal phase of the emulsion. Example: • In a system containing 2 immiscible liquids, emulsifying agent would be preferentially soluble in one of the phases and would be embedded in that phase. • Hence an emulsifying agent having a greater hydrophilic character will promote o/w emulsion and vice-versa. • Sodium oleate is dispersed in water and not oil. It forms a film which is wetted by water than by oil. This leads the film to curve so that it encloses globules of oil in water.
  38. 38. 5) Adsorbed film and interfacial tension theory:  Lowering interfacial tension is one way to decrease the free surface energy associated with the formation of droplets. Assuming the droplets are spherical,  ΔF= 6 γ V D  V= volume of the dispersed phase in ml, d is the mean diameter of the particles.  γ = interfacial tension It is desirable that:  The surface tension be reduced below 10dynes/cm by the emulsifier and Be absorbed quickly.
  39. 39. 6) Surface Tension Theory: • A drop of liquid forms a spherical shape which gives it the smallest surface area per unit volume • When 2 drops come together to form a bigger drop- gives lesser surface area. Also called surface tension at air-liquid interface • Surface Tension- Force that has to be applied parallel to the surface of liquid to counterbalance exactly the internal inward forces that tend to pull the molecule together. • When there are two immiscible liquids-it is called interfacial tension.
  40. 40. Physical instability of Emulsions Oil Water
  41. 41. Instability Factors Prevention 1. FLOCCULATION: Globules come close to each other to form aggregates. 1. Ununiform globule size distribution 2. Opposite charge on globule surface 3. Low viscosity of external medium. 1. Unifrom sized globules 2. Use same charged ionic E.A, electrolytes 3. Viscosity improving agents- hydrocolloids.
  42. 42. Instability Factors Prevention 2. CREAMING: Concentration of globules at top/bottom of emulsion 1. Globule size 2. Viscosity of external medium 3. Differences in density of oil- water (aq>oil) 1. Homogenization - Unifrom sized globules 2. Thickening agents to improve viscosity 3. Reducing density differences (Bromoform + oil) • Creaming is a reversible process/ temporary change and shaking redisperses globules as E.A coating is present • Creaming is detected by differences in colour shades.
  43. 43. Instability Factors Prevention 3. COALESCENCE: Few globules fuse to form bigger globules. Emulsifier film is destroyed. 1. Insufficient amount of E.A 2. Altered partitioning of E.A 3. Incompatability between E.A 4. Phase-volume ratio greater than 74% NO, this is permanent change. 4. BREAKING: Complete separation of oil & aqueous phases. 1. Unnoticed Coalescence. NO, this is permanent change.
  44. 44. Instability Factors 5. PHASE INVERSION: Change in emulsion from o/w to w/o or viceversa 1. Change in chemical nature of E.A: Sodium sterate (water soluble) o/w emul Sodium sterate + CaCl2  Calcium sterate Calcium sterate (oil soluble)  w/o emul 2. Altering phase-volume ratio: o/w emul + oil  w/o emul + water  o/w This method should be properly controlled other wise leads to phase inversion.
  45. 45. Factors to improve physical stability: Brownian motion theory, stokes law provides 9 factors. 1. Globule size 2. Globule size distribution 3. Viscosity 4. Phase-volume ratio 5. Charge on Electrical Double Layer 6. Physical properties of interface 7. Densities of phases 8. Temperature fluctuations 9. Experimental techniques.
  46. 46. 1. Globule size: Globule diameter ↓1/2 then creaming ↓ 4 times. Industrial size reduction = Colloidal mill Maximum stability is by Optimum globule size Globule size (5µ)  Brownian motion = NO Creaming. Micro emulsion (0.01µ) = NO Creaming. 2. Globule size distribution: Uniform, mono size = Stability Ununifrom size = small globule settle in gaps of large globules Coalescence.
  47. 47. 3. Viscosity: High viscosity  NO sedimentation, NO Brownian motion & administration problems. Optimum viscosity  Good stability. Viscosity improving agents o/w= taragacnath CMC w/o= long chain fatty acids, bees wax, alcohols, stearic acid. 4. Phase- volume ratio: This is relative volume of water & oil in emulsion. Medical emulsions (oil: water) = 50:50 In 50% oil globules  48% is porosity & 52% is globules Critical point: is defined as concentration of internal phase above which the E.A can not produce a stable emulsion of desired type. Critical point (74%)+ addition  Coalescence of globules.
  48. 48. 5. Charge of electrical double layer: Ionic E.A form coat on globule  Repulsive forces  NO Flocculation. Charge on EDL depends on pH and important for Ionic E.A 6. Physical properties of interface: Interface of Oil-Water  E.A Film STRONG (NO Coalescence), ELASTIC (reform on breakage) Film strength depends on pH. Optimum pH Stability. 7. Densities of phases: (Aq >Oil) Aq = Oil  prevent Creaming. Oil + Brominated oil  Oil density ↑ (But not practiced)
  49. 49. 8. Temperature fluctuations: High temperature 1. Effect partitioning characteristics of E.A  instability 2. Chemical degradation of drug  instability 3. Water evaporate  instability Low temperature Aq. pahse = Ice Crystals  Rupture E.A film  Coalescence. 9. Experimental techniques: Poor experimental techniques  incomplete emulsification  instability All preparation steps should be carefully followed.
  50. 50. Evaluation of physical stability of emulsions: Stable emulsion should retain initial properties during storage until usage. Chemical instability: Degradation of drug, E.A, preservative etc., Physical instability: Flocculation, creaming, coalescence, phase separation, phase inversion. Evaluation of Emulsions: 1. Extent of phase separation 2. Globule size distribution 3. Centrifugation – Accelerated stability study 4. Microwave irradiation
  51. 51. 1. Extent of phase separation: Suitable for poorly formed, rapidly breaking emulsions. This is quick method, visible after manufacturing. 2. Globule size distribution: Optical microscopy measures globule diameter. Unstable emulsion  Small globules (1st day)  large globules (after few days) Globule size should not be measured immediately after manufacturing, because of active coalescence stage (stress removal).
  52. 52. 3.Centrifugation – Accelerated stability study: Flocculation, creaming, phase separation is slow process. For fast testing stress is induced by centrifugation (2000-3000 rpm)  Phase separation  Depth of oil phase is measured. Induction period- Time required for stable emulsion for oil separation.
  53. 53. 4. Microwave irradiation: Emulsion in beaker  Microwave irradiation (top-bottom) measure temperature on Top & Bottom. Stable emulsion  less difference b/o high transmittance. Unstable emulsion  high difference b/o low transmittance.
  54. 54. PRESERVATION OF EMULSION: Emulsion + Preservative  Oral (No microorganisms), Parenteral (Sterile) Microorganisms  destroy gums, proteins, instability. (fungi, bacteria, yeast) carbohydrates, Presevatives:- benzoic acid, sodium benzoate, methyl paraben, propyl paraben etc., Factors for selection of preservative: 1. Aqueous phase: Bacteria grow in water, interface Water soluble preservative 2. Volume fraction of aqueous phase: o/w emul= high aq. Phase high Conc. Preservative. w/o emul= low aq. Phase  low conc. Preservative. 3. pH of aqueous phase: Adjust pH  Preservative undissociated form kill M.O easy
  55. 55. Preservative should be used in optimum concentration for maximum effect. [HA]w = concentration of undissociated acid in aq. phase C = total concentration of acid K = partition coefficient of acid q = volume ratio of oil to aq. Phase Ka = dissociation constant of acid [H30+] = concentration of [H30+] ions in acid
  56. 56. Rheological properties of emulsion: 1. Removal of emulsion from bottle/tube 2. Flow of emulsion through hypodermic needle 3. Spreadability of an emulsion on skin 4. Stress induced flow changes during manufacturing.  Optimum viscosity gives maximum stability. Phase-volume ratio Type of flow Viscosity measurement Dilute emul- 5% Newtonian Single point viscometer Concentrated emul- 50% Pseudoplastic Multiple point viscometer- Cone & plate, Cup & bobConcentrated emul- 74% Plastic
  57. 57. Preparation of emulsion: 1. Selection of oil phase Fixed, mineral, volatile oils oxidation  Add Anti-Oxidants If oil is dispersed phase  phase volume ↓ 25% 2. Selection of aqueous phase: Adjust pH, Add preservatives, organoleptic additives. 3. Selection of Emulsifying agent: Selected basing on type of emulsion (o/w, w/o), HLB, Use (internal, external). Optimum concentration is 2%. 4. Emulsion preparation: Small scale:- Mortar & pestle 1. Wet gum method (English method) 2. Dry gum method (Continental method) 3. Bottle method. Large scale:- Colloidal mill
  58. 58. Advantages of emulsions: 1. Mask the unpleasant taste 2. Economical 3. Improved bioavailability 4. Sustained release medication 5. Nutritional supplement 6. Diagnostic purpose 7. Topical use.
  59. 59. 1.Mask the unpleasant taste: Unpleasant tasted drug  globules in emulsion Ex: laxatives, vitamin-A 2. Economical: Expensive solvents are used to dissolve lipids. In emulsion lipids are dispersed in water (cheaper). 3. Improved bioavailability: Absorption of drugs is faster & better in emulsion Ex: griseofulvin corn oil-water emulsion > griseofulvin tablets 4. Sustained release medication: Water soluble antigen dispersed in oil  o/w emul Injected in body  Depots in muscle slow drug release Multiple emulsions (o/w/o) (w/o/w) give sustained release
  60. 60. 5. Nutritional supplement: Terminally ill patients are given nutrition parenterally. Emulsion  oil phase (fats) ,Aq. phase (nutrients) 6. Diagnostic purpose: radio-opaque emulsions are used in X-ray exam 7. Topical use: Concentrated emulsion semi-solids. Ex: cold cream, vanishing cream, benzyl benzoate etc.,
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Suspension, interfacial properties of suspended particles, settling in suspensions, formulation of flocculated and deflocculated suspensions. Emulsions and theories of emulsification, microemulsion and multiple emulsions; Stability of emulsions, preservation of emulsions, rheological properties of emulsions.


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