Suspensions in pharmacy

 Dear readers, I am Sarang Morea former pharmacy student. Here is my first blog. It is a knowledgeable ride of one of the important topic i. e. Suspension. 

Here we go....... 

               A pharmaceutical suspension is a coarse dispersion in which internal phase is dispersed uniformly through the external phase. The internal phase consisting of insoluble solid particles having a specific range of size which is maintained uniformly throughout the suspending vehicle with the aid if single or combination of suspending agent. 

Classification :-

 𝘽𝙖𝙨𝙚𝙙 𝙤𝙣 𝙜𝙚𝙣𝙚𝙧𝙖𝙡 𝙘𝙡𝙖𝙨𝙨𝙚𝙨:-

Eg- Oral suspension

Externally applied suspension

Parental suspension

𝘽𝙖𝙨𝙚𝙙 𝙤𝙣 𝙜𝙚𝙣𝙚𝙧𝙖𝙡 𝙥𝙧𝙤𝙥𝙤𝙧𝙩𝙞𝙤𝙣 𝙤𝙛 𝙨𝙤𝙡𝙞𝙙 𝙥𝙖𝙧𝙩𝙞𝙘𝙡𝙚𝙨:-

Eg- Dilute (2-10%v/w) suspension

Concentrated (50% v/w) suspension

𝗯𝗮𝘀𝗲𝗱 𝗼𝗻 𝗲𝗹𝗲𝗰𝘁𝗿𝗼𝗸𝗶𝗻𝗲𝘁𝗶𝗰 𝗻𝗮𝘁𝘂𝗿𝗲 𝗼𝗳 𝘀𝗼𝗹𝗶𝗱 𝗽𝗮𝗿𝘁𝗶𝗰𝗹𝗲𝘀:-

Eg:-particles suspension

Flocculated suspension

Deflocculated suspension

𝗯𝗮𝘀𝗲𝗱 𝗼𝗻 𝘀𝗶𝘇𝗲 𝗼𝗳 𝗽𝗮𝗿𝘁𝗶𝗰𝗹𝗲:-

Eg:colloidal suspension

Coarse suspension

Nano 𝘀𝘂𝘀𝗽𝗲𝗻𝘀𝗶𝗼𝗻

𝘁𝗵𝗲𝗼𝗿𝘆 𝗼𝗳 𝗽𝗵𝗮𝗿𝗺𝗮𝗰𝗲𝘂𝘁𝗶𝗰𝗮𝗹 𝘀𝘂𝘀𝗽𝗲𝗻𝘀𝗶𝗼𝗻:-

Sedimentation behaviour:-

In simple word, sedimentation behaviour can be explained as the floccules settle under the influence of gravitational force, After possessing  the stability for longer time.

According to thermodynamics, In large system the influence of gravity as correspondence to mass is negligible but due to change in medium and thermodynamically small system the influence of gravity play the huge role. 

Lets derive a small derivation For simple understanding and for your convenience. 

Let this sedimentation be “S” and surface area of floccules be “A” and viscosity be “V”.

Then,

 

         S=𝗞𝗔

Where K is proportionality constant. 

𝗦𝘁𝗼𝗸𝗲'𝘀 𝗹𝗮𝘄:-

Velocity of sedimentation is expressed as, 

Vsed= d2 (ps-p0) g/18n

         =2[(ps-p0) g/9n]

Where, 

V= sedimentation velocity

d=diameter of particle

r= radius

Ps= density of disperse phase

Po= density of disperse medium

g= acceleration due to gravity

no= viscosity in disperse medium in poise. 

𝗳𝗮𝗰𝘁𝗼𝗿𝘀 𝗮𝗳𝗳𝗲𝗰𝘁𝗶𝗻𝗴 𝘀𝗲𝗱𝗶𝗺𝗲𝗻𝘁𝗮𝘁𝗶𝗼𝗻:-

𝟭. Particle size diameter. 

𝟮. Density difference between disperse phase and disperse media

𝟯. Viscosity of dispersion medium. 

𝟰 Sedimentation volume flocculated suspension :-

Sedimentation volume can be explained in the simple word is the difference in the formation of the cake in its active mode as well as a stable mode. 

Sedimentation volume is the ratio of final volume of sediment to original volume of sediment. 

F= Vu/Vo.

Sedimentation velocity:-

The velocity dx/dtof the particle in the unit centrifugal force can be expressed in the terms of svedberg coefficients ‘S'.

Sedimentation behaviour of flocculated and deflocculated suspension:-

Flocculated suspension-

The flocc will cause increase in sedimentation rate due to increase size of sediment in particle. 

Sedimentation depends on size of flock and porosity of flock. 

Due to formation of loose structure it entraps up appreciable amount of liquid it can be easily redispersed by agitation. 

Deflocculated suspension-

In this suspension the individual particles settle slowly as they are whole entity the sedimentation rate is low. 

The force of attraction between individual particle is high so it forms a cake at the bottom known as claying. 

The large particles settle down forming cake but small particles remain dispersed at the Superatent liquid  so it appears to be cloudy. 

As in case of flocculated suspension due to viods between big particles the small particles settle over there and super Nant liquid appears clear. 

The density and porosity of dispersed phase also plays important role.

 

𝗯𝗿𝗼𝘄𝗻𝗶𝗮𝗻 𝗺𝗼𝘃𝗲𝗺𝗲𝗻𝘁 (𝗱𝗿𝘂𝗻𝗸𝗲𝗻 𝘄𝗮𝗹𝗸) :-

Let us recall the kinetic theory of gas that we had studied earlier. 

According to kinetic theory of gas , a gas molecule remains in constant motion in its surrounding spontaneously in multi direction.

In that, the gas molecule will either bombard with another same gas molecule or the boundary between the system and surrounding.

Take that idea and apply it in the case of suspension. 

In the suspension the particle will bombard either with another gas  molecule or container which will always recharge up it’s kinetic energy. 

Hence the particle will never sediment to form a cake if particle size is between 2 to 5 mm density of particles and viscosity of medium. 

The equation for brownian movement is, 

Di2= RTt/N3πnr

Where, 

R= gas constant

T= temperatures in kelvin

N= Avogadro number

n=viscosity of medium

t= time

r= radius of particle. 

Here we can explain the NSD i. e. No sedimentation diameter. It refers to diameter of suspended particle where no sedimentation occurs in suspending system. The NSD values depend upon density and viscosity of system. 

It's my first blog . Please forgive me for any mistake. Thank you very much for giving your most precious time.