Colloid An Introduction Kausar Ahmad Kulliyyah of Pharmacy http://staff.iiu.edu.my/akausar

Contents Lecture 1: Types of colloids Classification based on size Types of dispersions ------------------------------------------------------ Lecture 2: Types of emulsions Emulsification factors Properties of colloids PHM2213 2008/9

Colloidal System Discrete particles dispersed in a different medium Particle size below 1 mm High specific surface area Discrete particles dispersed in a different medium In pharmaceutical emulsions or suspensions, particle size ranges from colloidal to visible or coarse.

Types of Colloids Type Disperse phase Continuous phase Emulsion: o/w Oil Water Emulsion: w/o Suspension Solid Water or oil Aerosol Solid or liquid air Others Multiple emulsion: w/o/w, o/w/o PHM2213 2008/9

Classification Based on Size Examples Molecular dispersion < 1.0 nm Oxygen gas, ordinary ions, glucose Colloidal dispersion 1.0 nm to 0.5 mm Silver sols, natural and synthetic polymer latices Coarse dispersion > 0.5 mm Sand, pharmaceutical emulsions & dispersions, red blood cells PHM2213 2008/9

Classification of dispersed systems hydrophilic colloidal dispersion (in water) surfactant micelles and phospholipid vesicles, also known as association colloids. lyophilic colloids (lyo=solvent) colloidal systems are proteins, rubber, gelatin and gums. lyophobic colloids gold, silver and sulfur. PHM2213 2008/9

…..or Sols….another definition Sol – refers to any colloidal system in which the dispersion medium is a liquid. Lyophilic sol – a sol consisting of a dispersed phase which has an affinity for the continuous phase. This means that the colloid is readily formed e.g. starch in water. Lyophobic sol – a sol which is solvent-repelling, such that the disperse phase has little or no attraction for the dispersion medium e.g. gold in water. PHM2213 2008/9

Use of Colloidal Phenomena Detergency Dewatering of sludges via coagulation Emulsion polymerisation Natural phenomena i.e. milk (casein) Demulsification example? PHM2213 2008/9

Detergency Main component is surfactant Most important products using surfactants Main component is surfactant Involves in adsorption, wetting, emulsification and dispersion Wetting of substrate ->soil-removing process ->preventing soil redeposition (PEG) PHM2213 2008/9

Pharmaceutical suspensions Coarse dispersions lyophobic colloids (lyo=solvent) Suspension: solid in liquid prepared from water-insoluble drugs for delivery orally or by injection (intra-muscular) in liquid vehicle. E.g. Oral suspensions, topical applications, Injectables: intra-muscular Surfactant/Dispersant to wet the particles Stabilisation by electric repulsive force and steric hindrance effect PHM2213 2008/9

Pharmaceutical Emulsions Emulsion: liquid drug in liquid vehicle: o/w or w/o Main function of emulsion is to provide vehicles for drug delivery and parenteral nutrition. The drug is dissolved in the water or oil phase. E.g. Parenterals, creams, lotions Surfactant/Emulsifier reduces the interfacial energy and the emulsion becomes thermodynamically stable PHM2213 2008/9

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Preparing a Dispersion Particle size reduction aggregates may require considerable mechanical energy to break them down completely - to the point when the surface of each primary particle is available to the wetting liquid. Wetting of the powder this is necessary not to wet external surfaces but also for displacing air between the internal clusters. Dispersing by using charged bulky surfactants e.g. sodium oleate, sodium or ammonium caseinate Modifying the viscosity to minimise sedimentation (see Stoke’s Law) Dry powders usually consist of aggregates and agglomerates which need to be dispersed in the liquid to produce "individual" units which may be further subdivided into smaller particles. This requires understanding of various phenomena such as powder wetting, dispersion of aggregates and agglomerates and comminution of the primary particles into smaller units. HOW? Once a powder is dispersed into a liquid, it is essential to prevent aggregation of the particles and their sedimentation. Powder wetting, dispersion and subsequent stabilization requires in most cases the use of a dispersing agent, usually a surfactant, a polymer or polyelectrolyte. PHM2213 2008/9

Properties of dispersing agents Adsorption of surfactants at the solid/liquid interface. Highly charged Can provide steric hindrance END OF LECTURE 1 OF 2 PHM2213 2008/9

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Types of Emulsions Macroemulsion Nanoemulsion Microemulsion Multiple emulsion PHM2213 2008/9

Nanoemulsion and Microemulsion Nanoemulsions cover the size range of 50-200 nm Microemulsions usually in the size range of 5-50 nm long term physical stability against creaming, flocculation and coalescence Due to their small size they enhance penetration, spreading and will give uniform distribution on the substrate on which they are applied. application in personal care products and cosmetics, agrochemicals, pharmaceuticals, household products etc. PHM2213 2008/9

Methods of Preparation Nanoemulsions are easily formulated using high-pressure homogenizers with proper choice of surfactants and/or polymers. The production of microemulsions may employ the Phase Inversion Temperature (PIT) principle. These emulsions are stabilised through steric stabilization and by the thickness of the adsorbed layer. PHM2213 2008/9

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Emulsification Factors Concentration of dispersed/oil phase Types and concentrations of surfactants Emulsifying temperature especially for non-ionic surfactants Type of homogeniser/emulsifying equipment PHM2213 2008/9

Multiple Emulsion Disperse phase contains droplets of another phase. Exist as o/w/o or w/o/w. Prepared through a double homogenization process or a one step procedure using the PIT. Both are important for drug delivery. PHM2213 2008/9

Example of w/o/w emulsion for drug delivery by intra-muscular route advantage: slow-release because drug has to diffuse through oil disadvantage: viscosity of medium is high solution: to disperse the w/o in aqueous medium. On injection, the aqueous phase dissipates rapidly leaving behind the w/o. PHM2213 2008/9

Multiple emulsion An example from research Evaluation of process factors in oil-water-oil multiple emulsion method for flavor encapsulation Y. H. CHO and J. Park. Dept. of Biotechnology, Yonsei University, 134, Shinchon-dong, Seodaemoon-gu, Seoul, 120-749, South Korea Multiple emulsion method is proposed for the encapsulation of sensitive ingredients since it is carried out in mild conditions and without any toxic compounds. This method has been applied in pharmaceutics and chemical industry, while it is relatively new to flavor and food industry. Research on multiple emulsion, especially O/W/O type is limited because of the practical difficulty in preparing a stable emulsion. PHM2213 2008/9

Exercise: What are the factors involved for preparing stable O/W/O multiple emulsion? gum arabic to maltodextrin (0:10-5:5) Homogeniser microfluidizer (34-83 MPa) piston-type homogenizer (20 MPa) This O/W emulsion was emulsified in molten hydrogenated palm kernel oil containing 5% emulsifier at 13,500 rpm using Ultra-TurraxTM. Selected emulsifiers were Span 80, Tween 80, polyglycerin polylysinoleate (PGPR) and glycerin monostearate (ES-95®). O/W/O multiple emulsion was solidified in ethanol:water (9:1) solution. Solid microcapsules were collected by filtration and freeze-dried. The physical properties and morphology of microspheres were determined. PHM2213 2008/9

OBSERVATIONS Microfluidizer (at 70 MPa) produced more stable emulsion, as it produced small uniform droplet. Increasing gum arabic content created highly viscous emulsion, which subsequently resulted in stable O/W emulsion. The stability of O/W/O multiple emulsion was highly affected by the type of emulsifiers and the most stable emulsion was prepared using the blend of Span 80 and PGPR. Microcapsules were 273.5 m in mean diameter, spherical in shape, and had a porous structure. PHM2213 2008/9

Multiple Emulsion for Pharmaceuticals Examples Sandostatin LARTM Depot – Novartis (hypothalamic hormones analogue) Control of hypersecretion at the site of the tumor where hormone overproduction starts Human NutropinTM Depot – Alkermes/Genentech (human insulin suspension) somatropin (rDNA origin) for injectable suspension - long-acting dosage form of recombinant human growth hormone (rhGH). PHM2213 2008/9

Multiple emulsion Pharmaceutical Problems Rapid release during the first day typically accounts for 10-80% of the total drug loading. This ‘initial burst’ poses a toxicity threat and is a major hurdle for the development of microspheres. Very slow (close to zero) release period after the initial burst period. This can last for weeks and is referred to as the ’lag-time’. During this induction period, the patient is not effectively treated due to lack of drug release. PHM2213 2008/9

Properties of System Colloidal Particles not resolved by ordinary microscope visible in electron microscope Particles diffuse very slowly Coarse Particles visible under microscope Do not pass through filter paper Particles do not diffuse PHM2213 2008/9

Optical Properties of Colloids Faraday-Tyndall effect – when a strong beam of light is passed through a colloidal sol, a visible cone, resulting from the scattering of light by the colloidal particles is formed. Turbidity – as a result of light scattering caused by fine particles obstructing the path of light Based on this property, the investigation on molecular weight of the colloid is possible via light scattering studies. Results from a suspension of fine particles that obscures light rays - requires many days for sedimentation because of the small particle size. In industries: 1. light-interference method is classified as nephelometric. Unit of measurement is nephelometric turbidity unit, NTU. 2. When formazin is used to prepare turbidity standards for comparator tube determinations, the unit is formazin turbidity unit, FTU. Turbidity, t, is the fractional decrease in intensity of the incident light, which passes through 1 cm of solution. It is expressed as the intensity of light scattered in all direction (Is) divided by the intensity of the incident light, I. t = Is / I At a given concentration of a dispersed phase, turbidity is proportional to the molecular weight of the lyophilic colloid:   M PHM2213 2008/9

Kinetic Properties of Colloids Brownian motion – arises from bombardment of dispersed particles by molecules of dispersion medium. Diffusion – particles diffuse spontaneously from region of high to low concentration Osmotic pressure: allows the calculation of molecular weight of colloid Sedimentation: as given by Stoke’s law Viscosity – resistance to flow under applied stress. Brownian motion – arises from bombardment of dispersed particles by molecules of dispersion medium. Diffusion – particles diffuse spontaneously from region of high to low concentration, according to Fick’s law the amount of substance dq diffusing in time dt across a plane with surface area S: dq = -DS(dc/dx)dt where D is the diffusion coefficient and dc/dx is the concentration gradient. Osmotic pressure: allows the calculation of molecular weight of colloid Sedimentation: as given by Stoke’s law Viscosity – resistance to flow under applied stress Brownian motion – arises from bombardment of dispersed particles by molecules of dispersion medium. Viscosity – resistance to flow under applied stress PHM2213 2008/9

References PC Hiemenz & Raj Rajagopalan, Principles of Colloid and Surface Chemistry, Marcel Dekker, New York (1997) HA Lieberman, MM Rieger & GS Banker, Pharmaceutical Dosage Forms: Disperse Systems Volume 1, Marcel Dekker, New York (1996) F Nielloud & G Marti-Mestres, Pharmaceutical Emulsions and Suspensions, Marcel Dekker, New York (2000) J Kreuter (ed.), Colloidal Drug Delivery Systems, Marcel Dekker, New York (1994) PHM2213 2008/9