gels - pharmaceutics

8/18/2019 Gels - Pharmaceutics

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Gels


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• Characteristics of Gels

A) Swelling

When a gelling agent is kept in contactwith

a liquid that solvates it, then an

appreciable amount of liquid is takenup by the agent

and the volume increases !his process

isreferred to as swelling


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") Syneresis

#any gels often contract spontaneously

on standing and e$ude some %uidmedium !his e&ect is known assyneresis !he degree to whichsyneresis occurs, increases as theconcentration of gelling agentdecreases !he occurrence of syneresisindicates that the original gel was

thermodynamically unstable


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C) Ageing

Colloidal systems usually e$hibit slow

spontaneous aggregation !his processis referred to as ageing 'n gels, ageingresults in gradual formation of adenser network of the gelling agent


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() Structure

!he rigidity of a gel arises from thepresence of a network formed by theinterlinking of particles of the gellingagents !he nature of the particle andthe type of force that is responsible for

thelinkages determine the structure of the

network and the properties of the gel


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) *heology

Solutions of the gelling agents and

dispersion of %occulated solid arepseudo

plastic ie e$hibiting +on+ewtonian

%owbehaviour, characteri-ed by adecrease in

viscosity with increase in shear rate


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• Gel forming substances

.olymers are used to give the structural networkwhich is essential for the preparation of gels Gelforming polymers are classi/ed as follows0

1 Natural polymer

a .roteins

i Gelatin ii Collagen

b .olysaccharides

i Alginic acid ii Agar iii !ragacanth iv

Sodium or .otassium carrageenan v .ectinvi Gellum Gum vii 2anthin viii Cassia tora

i$ Guar Gum


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3 Semisynthetic polymers

a Cellulose derivatives

i 4ydro$yethyl cellulose ii #ethylcellulose

iii 4ydro$ypropyl methyl cellulose iv4ydro$ypropyl cellulose v Carbo$ymethyl

cellulose

3. Synthetic polymersa Carbomer

i Carbopol 561 ii Carbopol 567 iii

Carbopol 586

b .olo$amer

c .olyvinyl alcohol

d .olyacrylamide

e .olyethylene and its copolymers


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4. Inorganic substances

a "entonite

b Aluminium hydro$ide5. Surfactants

a "ri95:

b Cetostearyl alcohol


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.reparation of gels

• ;usion method

'n this method various wa$y materialare employed as gelling agents in nonpolar media (rug was added whenwa$es melted due to fusion Stirred tilluniform gel is formed


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• (ispersion method

Gelling agent was dispersed in waterwith constant stirring at 1377 rpm for87mins (rug was dissolved in non aqsolution and added to above gel withconstant stirring


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valuation of Gels

• Measurement of pH

!he p4 of various gel formulations wasdetermined by using digital p4 meter


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• Drug Content

1 g of the prepared gel was mi$ed with177ml of suitable solvent Aliquots of

di&erent concentration were prepared bysuitable dilutions after /ltering the stocksolution and absorbance was measured

(rug content was calculated using theequation, which was obtained by linearregression analysis of calibration curve


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• Viscosity Stuy

!he measurement of viscosity of theprepared gel was done with a"rook/eld =iscometer !he gels wererotated at 78, 7: and 1> rotationsper minute At each speed, the

corresponding dial reading was noted


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• Spreabability

•


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• 't is calculated by using the

formula0

S # @ B ! where,# wt tied to upper slide

@ length of glass slides

! time taken to separate the slides


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• !"truability Stuy

!he formulations were /lled in thecollapsible tubes after the gels wereset in the container !he e$trudabilityof the formulation was determined interms of weight in grams required to

e$trude a 7> cm ribbon of gel in 17second

ki i i i d


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• Skin irritation study

Guinea pigs 677>77 g) of either se$ wereused for testing of skin irritation !he

animals were maintained on standardanimal feed and had free access to water

!he animals were kept under standardconditions 4air was shaved from back ofguinea pigs and area of 6 sq cm wasmarked on both the sides, one side servedas control while the other side was test Gel

was applied >77 mg B guinea pig) twice aday for D days and the site was observedfor

any sensitivity and the reaction if any


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#rae $eaction

7 +o reaction

1 slight patchy erythema,

3 slight but con%uent or

moderate but patchy erythema8 severe erythema with or without

edema


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• 'n vitro (i&usion studies

!he di&usion studies of the prepared gels canbe carrying out in ;ran- di&usion cell for

studying the dissolution release of gels througha cellophane membrane Gel sample 7>g) wastaken in cellophane membrane and the di&usionstudies were carried out at 8D E 1F using 3>7 ml

of phosphate bu&er p4 D6) as the dissolutionmedium

;ive milliliters of each sample was withdrawnperiodically at 1, 3, 8, 6, >, :, D and h and

each sample was replaced with equal volume offresh dissolution medium !hen the sampleswere analy-ed for the drug content by usingphosphate bu&er as blank


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• 4omogeneity

After the gels have been set in the

container, all developed gels weretested

for homogeneity by visual inspection !hey

were tested for their appearance andpresence of any aggregates


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• Grittiness

All the formulations were evaluated

microscopically for the presence of any

appreciable particulate matter which was

seen under light microscope 4ence

obviously the gel preparation ful/ls the

requirement of freedom from particularmatter and from grittiness as desired forany topical preparation


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.astes

• !hick sti& ointment that do notordinarily

%ow t body temperature and thereforeserve as protective covering over thearea where they are applied

• H37I of solid

• (ilatant %ow


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Jellies

• Jellies are water soluble basesprepared from natural gums such astragacanth, pectin etc

gels - pharmaceutics

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