Liposome Size : Type and Factors Affecting

Liposome can be produced in the form of multi-compartment with vesicles sizes ranging from 100 nm to 1000 nm and each vesicle usually composed of five or more concentric lamellae. In the process of its formation, the resulting liposomes with various sizes which will be the basis of classification:

a. Unilamellar Small vesicles (SUV)
SUV has the smallest size variation. Size SUV based on the strength of ionization liquid medium and fat composition of frontier membrane vesicle size ± 15 nm for the liposomes derived from pure egg lecithin in normal saline and ± 25 nm for DPPC liposome

Liposomes In Vivo Properties: Benefits of Preclinical and Clinical Research

The exact mechanism of in vivo biodistribution and disposition is vary depending on the fat composition, size, charge and degree of surface / steric hydration. Route of administration will also affect the properties of liposomes in vivo. Immediately after intravenous administration, liposomes are usually wrapped with serum proteins and taken by RES cells and finallyeliminated.

SELECTION OF PLASTICIZERS USED FOR FILM COATING TABLET

Selection of the plasticizer is very critical in coating tablet.
Plasticizer selection depends upon two major criteria :
  1. Glass transition temperature
  2. solubility parameter
For a controlled release dosage form the polymer plasticizer interaction in the latex emulsion must be considered as affecting primarily the drug and substrate and nature of rate limiting system
The type and the concentration of plasticizers actually controls the desired flexibility and permeability in the finished film.

PROPERTIES OF COMMONLY USED PLASTICIZERS FOR COATING TABLET

PEG (Polyethylene Glycol)
  • These are hydrophilic substances and soluble in water
  • PEGs are used alone as hydrophilic plasticizers in film coating
  • Rate of release of water soluble drugs decreases with increase in the molecular weight of PEGs.
  • The PEG with molecular weight of 6000 and above decreases plasticizing effect and increases lubricants effect
  • Migration of PEG can occur from the tablet film coating leading to interactions with core compounds.
DBS (Di-Butyl Sebacate)
  • These are esters of n-butanol and saturated dibasic acids.
  • Principally used as plasticizers in film coating.
  • For film coating as a plasticizer, DBS is used in 10-30% concentration by weight of polymer.
  • Solubility : Insoluble in water but soluble in ethanol, mineral oil, etc
  • Quite suitable for solvent based coating dispersion.

Function of Plasticizers in Film Coating Tablet

What is Plasticizers? Plasticizer or also known as dispersants are additives that increase the plasticity or fluidity of the material to which they are added. Plasticizers are relatively low molecular weight materials which have a capacity to alter the physical properties of a polymer to render it more useful as film forming agents.

Polymers are widely used as film forming material as they :
  • Produce transparent films
  • Produce intact films
  • They have lower values for water vapor permeability rate
  • They have lower values for oxygen transmission rates.
The polymers cellulose (derivates or cellulose related compounds like HPMC, MC, EC, HPMCP) used as film forming agents are relatively brittle in nature at room temperature and pressure do to their complex structure. When such a material is applied as a film coat on to tablet a smooth film is not be obtained. This condition necessitated the addition of plasticizers to the coating dispersions. That’s why we add plasticizer to film coating. The function of plasticizer is to make the polymer more liable and soft and thereby enhancing the flexibility and plasticity to the films.