Sodium Alginate and Polymer Drug Delivery Systems
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Published: Wed, 23 May 2018
Sodium alginate is a hygroscopic material, although, stable at low humidities and at cool temperatures. Aqueous solutions of sodium alginate are most stable at ph 4-10. Below ph3, alginic acid is precipitated. Sodium alginate solutions are susceptible to microbial spoilage during storage, which may effect on solution viscosity. Subsequent loss of viscosity due to depolarization was observed when sodium alginate was heated above 70°c. Preparations containing sodium alginate for external use may be preserved by the addition of 0. 1% chlorocresol, chloroxylenol, or parabens and if the medium is acidic, benzoic acid may be used. Bulk material should be stored in an airtight container in a cool and dry place.
Sodium alginate is incompatible with acridine derivatives, crystal violet, phenyl mercuric acetate and nitrate, heavy metals and ethanol in concentrations greater than 5%w/v. Low concentrations of electrolytes cause an increase in viscosity but high electrolyte concentrations causing salting out of sodium alginate; salting out occurs if more than 4% of sodium chloride is present.
Sodium alginate is used in variety of oral and pharmaceutical formulations. In tablet formulations, sodium alginate may be used as both a binder and disintegrant. It has also been used as a diluents in capsule formulations and also been used in the preparation of sustained release oral formulations, since it can delay the dissolution of a drug from tablets, capsules and aqueous suspensions.
Recently, sodium alginate has been used for the aqueous microencapsulation of drugs in contrast with the more conventional microencapsulation techniques which use organic solvent systems. It has also been used in the formation of nanoparticles.
The adhesive nature of hydrogels prepared from sodium alginate has been investigated and the drug release from oral mucosal adhesive tablets based in sodium alginate has been reported. Hydrogel systems containing alginates have also been investigated for delivery of proteins and peptides.
Therapeutically sodium alginate has been used in the combination with an h2 receptor antagonist in the management of gastroesophageal reflux and as a haemostatic agent in surgical dressings. Alginate dressings, used to treat exuding wounds often contain significant amounts of sodium alginate as this improves the gelling properties. Sodium alginate is also used in cosmetics and food products at concentrations given in table 4
Sodium alginate is widely used in cosmetics, food products, and pharmaceutical formulations, such as topical products, including wound dressings. It is generally regarded as a nontoxic and non-irritant material, although excessive oral consumption may be harmful. The WHO has not specified an acceptable daily intake for alginic acid and alginate salts as the levels used in foods do not represent a hazard to health.
Sodium alginate may be irritant to eye or respiratory system if inhaled as dust;eye protection, gloves, dust respirator are needed while handling. Sodium alginate should be handled in a well ventilated environment.
The various substances related to sodium alginate include alginic acid, potassium alginate, calcium alginate, propylene glycol alginate.
Chitosan is a derivative of chitin and it is a unique polysaccharide and hydrophilic polymer.
Non Proprietary Names
BP: Chitosan hydrochloride
Ph Eur : Chitosan hydrochloridum
The principle derivative of chitin, namely Chitosan (C6H11O4N)n is a unique polysaccharide and hydrophilic polymer which is taken from the chitin, a polysaccharide found in exoskeletons of crustaceans. it is processed by removing the shells from shellfish such as shrimp, lobusters and crabs. The shells are then ground into a pulverous powder. This powder is then deacetylated. This involves boiling chitin in concentrated alkali (50%) for several hours. This will yield chitosan with a degree of acetylation between 20-30%, the most popular commercial form of Chitosan. In such a chitosan, the acetyl groups are uniformly distributed along the polymer chain. This is in contrast with the Chitosan of similar degree of acetylation, but isolated from fungal cell walls in which the acetylresidues are grouped into clusters. Special chemical treatments are required to obtain completely de-acetylated forms of chitosan.
It is used as a coating agent; disintegrant; film forming agent; mucoadhesive, tablet binder; viscosity increasing agent etc.
Chitosan is a cationic polyamine with a high charge density at ph<6. 5 so adheres to negatively charged surface and chelates metal ions. It is a linear polyelectrolyte with reactive hydroxyl and amino groups so available for chemical reaction and salt formation. Chitosan is a linear polysaccharide composed of randomly distributed î²-(1-4)-linked d-glucosamine (deacetylated unit;d) and n-acetyle-d-glucosamine(acetyl unit;a). The perentage degree of deacetylation (%da) of chitin can be determined by nmr spectroscopy, and the %da in commercial chitosan is in the range 60-100%. The viscosity of a chitosan solution primarily depend on the average molecular weight of the polymer, which can be determined by size exclusion chromatography combined with light scattering detection.
The amino group in chitosan has a pka value of approximately 6. 5, thus chitosan is positively charged and soluble in acidic to neutral solution with a charge density depend on ph and the %da. Numerous studies have demonstrated that the salt form, molecular weight, and degree of deacetylation as well as ph at which chitosan is used all influence how this polymer is utilized in pharmaceutical application. Chitosan is incompatible with strong oxidising agent.
Chitosan is a cationic polyamine with a high charge density at ph<6. 5. It is linear poly electrolyte with reactive hydroxyl and amino groups. The properties of chitosan relate to its poly electrolyte and polymeric carbohydrate character. The presence of a number of amino groups allows chitosan to react chemically with anionic systems, which results in alteration of physicochemical characteristics of such combinations.
Acidity / alkalinity
pH=4-6(1%w/v aqueous solution)
1. 35-1. 49g/cm3
Particle size distribution
Stability and storage conditions
Chitosan is a stable material at room temperature although it is hygroscopic after drying. Chitosan should be stored in a tigjtly closed container in a cool and dry place.
Chitosan is incompatible with strong oxidizing agents.
Chitosan is being investigated widely for use as an excipient in oral and other pharmaceutical formulations. It is also used in cosmetics. chitosan is generally regarded as biodegradable, nontoxic and non irritant material. it is biocompatible with both healthy and infected skin.
Chitosan is found useful in many fields like sustained drug delivery, components of mucoadhesive dosage forms, rapid release dosage forms, improved peptide delivery, colonic drug delivery systems and use for gene delivery. Chitosan is processed into several pharmaceutical forms including gels, beads, films, microspheres tablets and coatings for liposomes.
(Î²-adrenergic blocking agents)
Adrenergic nonselective Î²-receptor antagonist. (antihypertensive, antianginal and antiarrhythmic. )
Chemical name (Â±)-1-isopropylamino-3-(1-naphthyloxy) propan-2-ol
Molecular formula C16H21NO2. HCl
Molecular weight 295. 8
Description: A white powder, odourless and bitter in taste
Solubility: Soluble Soluble 1 in 2 of water and ethanol
Slightly soluble in chloroform
I . PHARMACOLOGICAL ACTIONS
a. Cardiovascular-Propranolol diminishes cardiac output, heart rate, and force of contraction. These effects are useful in the treatment of angina.
b. Peripheral vasoconstriction-Blockade of Î²-receptors prevents Î²2-mediated vasodilation. The reduction in cardiac output leads to decreased blood pressure.
c. Bronchoconstriction-Blocking Î²2 receptors in the lungs of susceptible patients causes contraction of the bronchiolar smooth muscle. Î’-blockers are thus contradicted in patients with asthma.
d. increased Na+ retention-reduced blood pressure causes a decrease in renal perfusion, resulting in an increase in Na+ and plasma volume. in some cases this compensatory response tends to elevate the BP. For these patients, Î²-blockers are often combined with a diuretic to prevent Na+ retention.
II. THERAPEUTIC EFFECTS
a. Hypertension-propranolol lowers BP in hypertension by decreasing cardiac output.
b. glaucoma-propranolo is effective in diminishing intraocular pressure in glaucoma.
c. migraine-propranolol is also effective in reducing migraine episodes by blocking the catecholamine induced vasodilation in the brain vasculature.
d. angina pectoris-propranolol decreases the oxygen requirement of heart muscle and therefore effective in reducing the chest pain in angina.
e. myocardial infarction-propranolol and other Î²-blockers have a protective effect on the myocardium. thus, patient who have had one myocardial infarction appear to be protected against a second heart attack by prophylactic use of Î²-blockers.
III. ADVERSE EFFECTS
a. broncho constriction-when propranolol is administered to an asthmatic patient, an immediate contraction of the bronchiolar smooth muscle prevents air from entering the lungs. Therefore, propranolol must never be used in treating any individual with obstructive pulmonary disease.
b. arrhythmias-treatment with the Î²-blockers must never be stopped quickly because of the risk of precipitating cardiac arrhythmias.
c. disturbances in metabolism- Î² bloackade leads to decreased glycogenolysis and decreased glucagon secretion.
d. drug interaction-drugs that interfere with the metabolism of propranolol, such as cimetidine, furosemide and chlorpromazine may potentiate its antihypertensive effects. conversely those that stimulate is metabolism, such as barbiturates, phenytoin and rifampicin can mitigate its effects.
Propranolol is well absorbed after oral administration but has low bioavailability due to high first pass metabolism in liver. it is highly bound to plasma proteins.
Metabolism of propranolol is dependent on hepatic blood flow.
Oral – 10mg BD to 10mg QID (average 40-60mg/day)
I. V – 2-8mg injected over 10min with with constant monitoring. it is not injected S. C or I. M because of irritant property.
NAME OF THE MATERIALS
NAME OF THE COMPANY
Sodium alginate AR
Hi-Media biosciences Ltd, Mumbai.
Calcium chloride AR
S. D Fine chemicals Ltd, Mumbai
Barium chloride AR
Qualigens Fine Chemicals Ltd, Mumbai
Fluca Biochemicals Ltd, Switzerland. (Viscosity 200-400 mPa. s)
Name of equipment
Name of company
Jasco-FT-IR 8201 PC
Differential scanning calorimeter
DSC-60 (Shimadzu, Tokyo, Japan)
Optical Microscope and Stage Micrometer
Scanning Electron Microscope
Bruker AXS D8
Electrolab TDT-08L, USP XXIV Type I Apparatus. Chennai
Remi Hi-speed motor
Universal motors. Mumbai
A process in which very thin coatings of polymeric materials are deposited around particles of solids or droplets of liquid.
Different terms for solid particle systems are employed in drug delivery among them pellets, beads, microcapsules, microspheres, millispheres are few. The terminologies of most relevant multiparticulate systems are provided here.
Pellets can be defined as “Small, free flowing spherical particles manufactured by agglomeration of fine powders or granules of drug substances and excipients using appropriate processing equipment. ” The size of these particles rae usually between 0. 5 and 1. 5mm. sphericity and intra granular porosity are the two important quality attributes of pellets. The terms ‘spherical granules’ and ‘beads’ have been applied interchangeably to pellet system.
Microspheres are solids approximately spherical particles ranging in size from 1 to 1000Âµm. They are made of polymeric, waxy, or other protective materials, that are biodegradable synthetic polymers and modified natural products such as gums, proteins, waxes etc.
Microsphere: the enbtrapped substance is dispersed throughout the microsphere matrix.
Microcapsule: the entrapped substance is completely surrounded by distinct capsule wall.
The similiarities between microsphers and microcapsules are clear and illustrations of these particles are shown in Fig:
Two major classes of encapsulation methods have evolved, viz chemical and physical. The first class of encapsulation involves polymerisation during the process of preparing the microcapsules. examples of this class are usually known by the name of interfacial polymerisation or in situ polymerisation. The second type involves controlled precipitation of a polymeric solution where in physical changes usually occur.
The precipitation and or gelation listed in table cover many techniques. one example isthe precipitation of water soluble polymers such as gelatin with water miscible solvents such as isopropranol. other examples include the precipitation of ethyl cellulose from cyclohexane agin by cooling, and gelation of sodium alginate with aqueous calcium salt solutions. in all cases the objective is to precipitate a performed polymer around the core (sometimes a multi-particulate) to cause encapsulation.
- Coating material
- Suspended medium
- Interfacial polymerization
- Water soluble and insoluble monomers
- Aqueous/organic solvents
- Complex coacervation
- Water soluble polyelectrolyte
- Simple coacervation
- Hydrophobic polymers
- Organic solvents
- Thermal denaturation
- Organic solvents
- Salting out
- Water-soluble polymer
- Solvent evaporation
- Hydrophilic or hydrophobic polymer
- Organic or Water
- Hot melt
- Hydrophilic or hydrophobic polymer
- Aqueous/organic solvents
- Solvent removal
- Hydrophilic or hydrophobic polymer
- Organic solvents
- Spray drying
- Hydrophilic or hydrophobic polymer
- Air, nitrogen
- Phase separation
- Hydrophilic or hydrophobic polymer
- Aqueous/organic solvents
POLYMER BASED DRUG DELIVERY SYSTEM
There has been growing interest in polymer based bioadhesive drug delivery systems. one of the goals of such systems is to prolong the residence time of a drug carrier in the Gastro Intestinal tract(GIT). The bioadhesive bond can be of a covalent, electrostatic, hydrophobicor hydrogen bond nature. ionic polymers are reported to be more adhesive than neutral polymers, and an increased charge density will also give better adhesion suggesting that the electrostatic interactions are of great importance. except for the oesophagus, the entire GI tract including the stomach is covered with a continous layer of insoluble mucus gel. The mucus gel mainly consists of glycolproteins and due to their content of ester sulphate and sialic acid groups, the mucus layer has an overall strong net negative charge. The mucus layer has been considered as a possible site for bioadhesion and drug delivery by several groups.
Recently, the use of natural polymers in the design of drug delivery formulation has received much attention due to their excellent biocompatibility, biodegradability, non toxicity and easy in availability.
Polymers as carriers used in drug delivery system
The different types of polymers for extended release preparations are given below.
The biodegradable polymers comprised of monomers linked to one another through functional groups and have unstable linkages in the backbone. They are biologically degraded or eroded by enzymes or generated by living cells.
Albumin, alginate, collagen, starch, chitosan, dextran, casein, gelatine, fibrinogen etc.
Polyalklyl-cyanoacrylate, poly ethyl cyano acrylate, poly amino acids, poly amides, poly acryl amides etc.
Poly(maleicacid), poly (glycolic acid), poly(hydroxyl butyrate), poly (lactic acid), poly vinyl alcohol(PVA) etc.
Poly ethylene vinyl acetate(EVA), poly ether urethane(PEU), cellulose acetate, poly vinyl chloride(PVC), ethyl cellulose etc.
In recent years a lrge number of biodegradable polymers have been investigated for their potential use as drug delivery systems. among them, sodium alginate and chitosan are very promising and have been widely exploited in pharmaceutical industry for sustained drug release. polysaccharides such as alginic acid, agar, chitin and chitosan have been used to agglomerate drugs for controlled drug delivery systems.
Chitosan is a anaturally occurring polysaccharide comprosing of glucosamine and N-Acetyl glucosamine with unique poly cation characteristics. The polycationic nature of chitosan leads to a strong interaction with negatively charged alginate. when alginate is dropped into chitosan solution, the electrostatic interaction of carboxylic groups of alginate with the amino groups of chitosan results in the formation of a membarane on the surface of sodium alginate and improves the stability and drug content. This process has been widely used in the preparation of alginate chitosan membaranes with a solid calcium-alginate gel core. There are many advantages of the chitosan coating, such as the improvement of drug loading and bioadhesive property, as well as the prolonged drug release properties etc.
Alginate(ionic, hydrophilic polymer) is a negatively charged polysachharide with high charge density and has been reported to be bioadhesive. among polyanionic polymers, alginate has been widely studied and applied for its possibility to modulate the release according to the properties of its carboxyl groups as well as its biodegradability and absence of its toxicity. alginate is a naturally derived anionic polysaccharide mainly from algae belonging to the family of phaeophyceae. Alginic acid is an algal polysaccharide and a species of poly carboxylic acid. alginate consists of two sugar moieties Î²-D mannuronic acid and Î±-L guluronic acid which exist either in blocks or random sequences and their relative proportions determines the biofunctional properties of alginc acid. alginate is known to form complexes with divalent cations, such as Ca2+, Ba2+, and Sr2+ in aqueous solution. depending upon the composition of two sugar residues and sequential distribution within the molecules, the complexes form either precipitates or hydrogels. guluronic acid blocks are known to form a rigid buckled structure, the so called “egg box” array, in which chelating calcium ions are nestled in the aqueous environment of the ordered gel structure due to the spatial arrangements of guluronic block oxygen atoms of carboxyl and hydroxyl groups.
Alginate has been widely used as food additive, a tablet disintegrator or gelation agent, and the mechanism of its gelation have been extensively investigated. when an aqueous solution of sodium alginate(SA) is added dropwise to an aqueous solution of calcium chloride, spherical alginate beads with regular shape and size are produced, since an insoluble calcium alginate matrix is formed by the cation exchange between sodium and calcium ions. alginates are known to form reticulated structure when in contact with calcium chloride ions and this characteristic has been used to produce SR particulate systems for a variety of drugs.
GEL FORMATION (GENERAL MECHANISM)
A gel in classical colloidal terminology, is defined as a system which owes its characteristic properties to a cross linked network of polymeric chains which form at the gel point. a considerable amount of research has been carried out in recent years to elucidate the nature of the crosslinks and determine the structure of alginate gels. alginate beads can be prepared by extruding a solution of sodium alginate containing the desired drug or protein, as droplets, into a divalent crosslinking solution such as Ca2+, Ba2+, and Sr2+ . monovalent cations do not induce gelation while Ba2+, and Sr2+ ions produce stronger alginate gels than Ca2+. other divalent cations such as Pb2+, Cu2+, Cd2+, CO2+, Ni2+, Zn2+, Mn2+ will also cross link alginate gels but their use is limited due to their toxicity. The gelation and cross linking of the polymers are mainly achieved by the exchange of divalent cations and stacking of these guluronic acids with the divalent cations, and the stacking of these guluronic groups to form the characteristic egg-box structure shown in fig
LARGE BEAD PREPARATION
In general, beads greater than 1. 0mm in diameter which can be produced by using a syringe, with a needle or a pipette. sodium alginate solution that contains the solubilised drug or protein is transferred dropwise into a gently agitated divalent cross linking solution. The diameter of the beads formed is dependant on the size of the needle used and the viscosity of the alginate solution . a larger diameter needle and higher viscosity solutions will produce larger diameter beads. The viscosity of SA can also influence the shape of the microbeads produced. The beads become more spherical as the concentration of SA increased. however, in general SA solutions of greater than 5% are difficult to prepare.
Since, gelation occurs in an aqueous environment, alginate is a promising material as a food additive, drug formulation and useful even for encapsulation of living cells to protect them from immune responses. utilizing this stable complex formation with divalent cations, alginate gels have been utilized for investigation of cells are considered to be the ultimate system for the pulsatile release of biologically active compounds.
Formulation of delivery devices for protein and peptide drugs under aqueous conditions are desirable to avoid the undesirable decrease of bioactivities which may occur when using organic solvents or heat during formulations. since relatively stable alginate gels can be formed in aqueous environments through chelation or complexation, which are promising delivery of matrices for bioactive compounds.
It has been suggested that the crosslinks were caused either by ionic bridging of 2 carboxyl groups on adjacent polymer chains via calcium ions or by chelation of single calcium ions by hydroxyl and carboxyl groups on each of a pair of polymer chains. although these bonds may play a role in the gelation mechanism which are not sufficiently energetically favourable to account for the gelation of alginate. it has been shown on thebasis of fibre diffraction data and model-building calculations that the shape of both poly-mannuronic acid segments and the polygulutended, and that these extended ribbons can stack together in sheets. on the basis of these data and the properties of gels it has been suggested that the cooperative association of either polymannuronic acid segments or polyguluronic acid segments are involved in the formation of the crosslinked network of polymer chain.
This technique has shown attractive applications in different fields, including cell immobilisation, owing to its mild operating conditions. as the encapsulation method is mild, and done at room temperature in aqueous medium, several sensitive drugs, proteins, living cells, enzymes, spermatozoa etc have been successfully encapsulated through alginate beads.
The primary structure of alginate depends on the producing species and for the marine species, seasonal and geographical changes might result in variations in alginates extracted from the same species. The polymer is nown to form a physical gel by hydrogen bonding at low pH(acid gel)and by ionic interactions with polyvalent cations such as calcium, the cation acting as a cross linker between the polymer chains. The viscosity and primary structure of polymer are important features determining it swelling and gelling properties.
At neutral pH, sodium alginate is soluble and hydrates to form viscous solutions, but below pH3, alginic acid, water swellable but insoluble, which is rapidly formed. since the hydration characteristics of the polymer and the subsequent physical properties of the hydrated gel layer may critically influence drug release.
When CA beads are treated with 0. 1M HCl, alginate gels hydrolysed to lower molecular weight fractions of alginic acid. due to conversion of COO- groups into unionised carboxylic groups, the electrostatic attraction between Ca2+ ions and COO- ions in the egg-box junction almost disappears. moreover, there may occur in ion-exchange between H+ ion(presence in the external HCl solution) and free Ca2+ ions inside the beads. thus a reduced Ca2+ ions concentration within the beads results in a weaker Ca2+ cross linked beads when put in phosphate buffer at pH 6. 8. Therefore, the acid-treated beads are loosely crosslinked structure more soluble alginate as constituent. when such beads are put in the phosphate buffer pH6. 8, the beads swell at a faster rate but do not attain a higher water uptake value due to loosely bound structure of the beads which is unable to retain large amount of water within the beads. moreover, there is possibility of ion-exchange between H+ ions produced due to ionisation of carboxylic groups in the buffer at pH.
A group of scientists developed a method of enclosing viable cells, tissues, and other labile biological substances within a semipermeable membrane. preliminary in-vitro studies of several types of microencapsulated cells and tissues(redblood cells, sperm cells, hepatica cells, hepatocytes, pancreatic endocrine tissues, and islets) were described by them. essentially, the process involves suspending the living cells or tissues in sodium alginate solution. The cell or tissue suspension is extruded through a device producing micro-droplets which fall into a calcium chloride solution and form gelled microbeads with the cells or tissues entrapped. These cell containing gel microbeads are next treated with polysine which displaces the surface layer of calcium ions and forms a permanent polysalt shell or membrane. finally, the interior calcium alginate is “liquefied”, either to stay in or to cum out(depending on molecular weight and size of the starting alginate) of the capsule with a calcium sequestrant such as buffered citrate solution.
Gohel et al ., prepared diclofenac sodium microspeheres by using sodium alginate as a polymer and CaCl2 as a cross linking agent. in this investigation stirring speed, concentration of crosslinking agent and heavy liquid paraffin were studied, on the time required for 80% of drug dissolution. a statistical model with significant interaction terms was derived to predict t80 and drug was released by diffusion of anomalous type. The results of multiple regression analysis and F value statistics revealed that, obtaining of controlled drug release and microspheres were to be prepared using relatively lower stirring speed.
Literature reports indicate wide spread use of sodium alginate for achieving sustained release of drugs, targeting gastric mucosa and increasing the bioavailability of drugs because of sodium alginate’s ability to form a stable and bioadhesive gel with calcium ions.
Alginate also has several unique properties that have enabled it to be used as a matrix for the entrapment or delivery of a variety of proteins, macromolecules and cells.
USES Of Alginate Beads
- A relatively inert aqueous environment within the matrix.
- A mild room temperature encapsulation process free of organic solvent
- A high gel porosity which allows for high diffusion rate of macromolecules
- The ability to control this porosity with simple coating procedures.
- Dissolution and biodegradation of the system under normal physiological conditions.
Standard graph for propranolol hydrochloride
A stock solution of propranolol hydrochloride was prepared by dissolving 100mg of the drug in 100ml of the phosphate buffer of pH6. 8 to give 1mg/ml solution. ten millilitres of stock solution was diluted to 100ml using phosphate buffer f pH6. 8 to produce 100Âµg/ml working stock solution. from this working solution, dilutions were made with phosphate buffer of pH6. 8 to produce 10, 20, 30, 40 and 50 Âµg/ml. The Î» max of the drug was determined by scanning the dilutions between 400 and 200nm using a Shimadzu 1400 UV visible spectrophotometer. At this wavelength, the absorbances of all the other solutions were measured against a blank. Standard curve between concentration and absorbance was plotted.
One of the requirements for the selection of suitable polymers or carriers for pharmaceutical formulation is its compatibility. Therefore in the present work a compatibility study was done by using Infra Red spectroscopy (IR) and Differential Scanning Calorimetry (DSC) to find out if there is any possible chemical interaction between propranolol hydrochloride and the polymers.
DIFFERENTIAL SCANNING CALORIMETRY (DSC)
Differential Scanning calorimetric analysis was used to characterize the thermal behaviour of the drug substances. It was performed by using DSC-60(Shimadzu, Tokyo, Japan) calorimeter to study the thermal behaviour of selected formulations. The instrument comprised of calorimeter (DSC60), flow controller (FCL60), thermal analyzer (TA60) and operating software(TA 60). The samples were heated in hermetically sealed aluminium pans under nitrogen flow (30ml/min)at a scanning rate of 5°C/min from 24 + 1°C to 300°C. An empty aluminium pan, sealed in the same way as the sample was used as a reference.
SCANNING ELECTRON MICROSCOPY
Scanning electron microscopy is used to obtain the surface topographical characterization of beads. SEM photographs of prepared formulations were taken with (Instrument JSM-6390)at different magnification ranging from 30 to 5000x at room temperature. The samples were mounted on double sided adhesive tape that has previously been secured on copper stubs. The acceleratio
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