POLYELECTROLYTES: AS A DRUG DELIVERY SYSTEM

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ABOUT AUTHORS:
Surya Pratap Singh*, Meenakshi Sahetya1, Mahaveer Prasad khichi1*, Yogesh Yaduwanshi2
1Department of pharmaceutics, Kota college of pharmacy
2Department of pharmacology, Kota college of pharmacy,
Rajasthan, India
*sp.kota91@gmail.com

ABSTRACT
The purpose of this paper is to focus on drug delivery system developing by such polyelectrolytes and most focused on targeting of  drugs to specific sites have aroused as revolution in pharmaceutical  field, thereby, giving rise to drug  delivery systems. Polymers have gained much importance indrug delivery especially those which respond in some desired way to change in pH, temperature, electric or magnetic field. For this reason they are very frequently and extensively used as excipients in design and advancement of controlled and/or sustained release products. The scope of polymers used in dosage form design can be increased by several approaches such as modification of their chemical structure, by combining different polymers in physical mixtures or by formation of polymer-polymer associations such as polyelectrolyte complexes.

REFERENCE ID: PHARMATUTOR-ART-2079

PharmaTutor (ISSN: 2347 - 7881)

Volume 2, Issue 2

Received On: 11/012/2014; Accepted On: 13/01/2014; Published On: 10/02/2014

How to cite this article: SP Singh, M Sahetya, MP Khichi, Y Yaduwansi, Polyelectrolytes: as a Drug Delivery System, PharmaTutor, 2014, 2(2), 44-51

INTRODUCTION
The  term  polyelectrolyte  can  be  more  precisely defined under class of macromolecules, as the polymers that contain a net negative or positive charge at near neutral pH. Above all, the polyelectrolyte belongs either to the group of cationic or to the group of anionic polyelectrolytes depending whether the polyelectrolyte carries  positive or negative charges. Mixed architectures with both negative and positive monomeric units belong therefore to the class of polyampholytes. A special case of polyampholytes is given by polybetaines (positive and negative charges on  eachrepeating unit). Irrespective to the sign of charge it can be distinguished between two other types of polyelectrolytes: strong (quenched) or weak (annealed) polyelectrolytes. The number of nominal charges is irrespective to changes in pH for strong polyelectrolytes, where as the number of nominal charges can be easily adjusted by pH for weak electrolyte.[1]

CLASSIFICATION OF POLYELECTROLYTES
Polyelectrolytes are both inorganic and organic exhibiting both flocculation and deflocculation properties. Inorganic polyelectrolytes exhibitingsedi­mentation properly are coagulants rather than flocculants, whereas organic polyele­ctrolytes, exhibiting sedimentation, property, are invariably high molecular weight synthetic polymers. Inorganic flocculants are salts of multivalent metals like aluminium and iron. The process of sedimentation these salts exhibit is totally different from the organic types.

The polyelectrolytes are classified into various types.

1. Based on origin:
a)   Natural  polyelectrolytes: Nucleic Acids, Carrageenan, Alginates.
b) Chemically modified polymers: Pectin, Chitin, Cellulose based, Dextran based.
c) Synthetic polyelectrolytes: Poly (vinyl benzene tri alkyl ammonium, Poly (vinyl sulfonic acid), Poly (acrylic or methaacrylic  acid), Poly( styrene sulfonic acid), Poly(acryl amido alkyl trialkyl ammonium).

2.  Based on the charge:

a)   Anionic (negatively charged):
The acrylic acid unit of a polymer ionised to produce a negatively charged polymer backbone. Since the charge carried by the active portion of polymer is negative all such polyelectrolytes are known as anionics.The common anionic polyelectrolytes are homo polymers and co polymers of NaSalt of acrylic acid with acrylamide which are generally termed as polyacrylamides.

b)  Cationic(positively charged):
In the case of cationics the positive charge carrying nitrogen is a part of the polymer. In the case of nonionics there is no charge on the base polymer as there are no ionisable groups present in these.Cationic polyelectrolytes are homopolymers or Co­polymers with Acrylamide of three major cationic monomers.A wide range of cationic polyelectrolytes are hence available depending on the cationic monomer present, the charge density and the molecular weight. Poly(dimethyl diallyl ammoniam chloride) and copolymers with acrylamide are type of cationic.

c)  Nonionic (no charge):
The nonionic polyelectrolytes are by and large homopolymers of acrylamide with a wide range of molecular weights. Though countless polyelectrolytes are theoretically possible depending upon the charge density and molecular weight a few of them have found commercial application. This limits the usage of polyacrylamides of a specific pattern for a specific application irrespective of the source of supply. [1]

MECHANISM OF POLYELECTROLYTES
There are two possible mechanisms given for the phenomena of polyelectrolyte induced coagulation and flocculation.Polyelectrolyte flocculants can be generally divided into two groups, depending on their molecular character and mode of operation:
i.   Primary coagulants (eg., polyamine types)
ii.   Coagulation aids/flocculants (eg., polyacrylamides)

i.      Primary coagulants (eg., polyamine types):
Have high cationic charge density; satisfy the 'cationic demand' of the negatively charged suspended particles and initiate coagulation and formation of flocs. Have low to medium molecular weight which allows a slow building of flocs (provided there is an adequately long contact time between the forming floc and the suspended matter) which gives a maximum removal of suspended solids (maximum turbidity reduction).

ii.      Coagulation aids/flocculants (eg., polyacrylamides):
Have low charge density; are used only for building the size of floc by bridging the primary flocs ­­do not satisfy the 'charge demand'. Have very high molecular weight ; this is need to produce large, fast settling flocs by bridging many small primary flocs. [3,4,5]

FACTORS  AFFECT  MECHANISM:
POLYELECTROLYTES are water soluble polymer carrying ionic charge along the polymer chain. Depending upon the charge, these polymers are anionic or cationic. Polyelectrolytes are available in a wide range of molecular weights and charge densities. Homo polymers of acrylamide are also included in the family of polyelectrolytes though they do not carry any charge. These are called nonionic. Polyelectrolytes have got a wide range of applications right from water purification, oil recovery, colour removal, paper making, mineral processing,etc.

The factors affecting the selection of the appropriate polyelectrolyte(s) for a given process are:

A.    The nature of the suspended particles (substrate) :
a) Organic/inorganic content
b) Net surface charge density
c) Solids content of substrate
d) pH of the substrate
e) Temperature of the system (Brownian motion)

B.     The end result to be achieved :­
a) Rapid separation of the solid matter from the fluid.
b) Clarity of the separated fluid.

C.    Dynamic and shear effects ­:
a) Mixing /conditioning of polymer and substrate
b) Nature of the shear forces associated with the dewatering equipment used. [1,3,4]

APPLICATIONSOF POLYELECTROLYTES
Major applications of flocculants are their inherent solid liquid separating efficiency. This makes polyelectrolytes a unique class of polymers which find extensive application. Some of the major areas of applications of polyelectrolytes[8] are in the following industries:

a)   Potable water treatment

b)   Waste water treatment

c)Municipal Sewage treatment

d)  Paper making

e)   Mineral Processing

f)    Oil field applications

g)   Drilling muds

h)   Anticalants and Despersants

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