Drug Delivery using Alginate and chitosan beads: An Overview
About Authors: Rajan Sharma Bhattarai*, D.Nagasamy Venkatesh**, Ayush Shrestha
*Final Year B.Pharmacy Student.
Department of Pharmaceutics
JSS College of Pharmacy, (A constituent college of JSS University, Mysore)
Ooty – 643 001, Tamil Nadu.
Reference ID: PHARMATUTOR-ART-1065
Alginate and chitosan are commonly used polymers in modifying the drug release. These two polymers can be used together or separately to form drug loaded modified release beads. The ionotropic gelation method and a slight modification in various ways are used to prepare these beads of different characteristics. The bead characteristics like morphology, buoyancy, swelling nature, drug entrapment efficiency, adsorption, release behavior are of importance. Also the therapeutic uses of the different modifications of the beads can be immense for the drugs which have low water solubility, short biological half life, require organ specific targeting and are proteineous in nature.
Alginate is a naturally occurring biopolymer that finds increasing applications in various fields. It has been used successfully for many years in the food and beverage industry as a thickening agent, a gelling agent and a colloidal stabilizer. Alginate also has several unique properties that have enabled it to be used as a matrix for the entrapment and/or delivery of a variety of proteins, drugs and cells.
These properties include:
(i) a relatively inert aqueous environment within the matrix;
(ii) a mild room temperature encapsulation process free of organic solvents; (iii) a high gel porosity which allows for high diffusion rates of macromolecules;
(iv) the ability to control this porosity with simple coating procedures and (v) dissolution and biodegradation of the system under normal physiological conditions. 
Alginate is a water-soluble linear, polyanionic, polysaccharide extracted from brown seaweed and is composed of alternating blocks of 1–4 linked α-L-guluronic and β-D-mannuronic acid residues. The gel beads are prepared through the sol-gel transformation of alginate, which is brought about by cross-linking the alginate with divalent cations like Ca2+, Zn2+. Guluronic acid is responsible for the formation of gel by the alginate with the cations. The alginate matrix which consists of an open lattice structure forms porous beads. They have low retention capacity for encapsulating low molecular weight and water soluble drugs. 
Chitosan is a biocompatible, biodegradable, nontoxic, linear co-polymer polysaccharide consisting of β (1–4)-linked 2-amino-2-deoxy-D-glucose (D-glucosamine) and 2-acetamido-2-deoxy-D-glucose (N-acetyl-D-glucosamine) units. The structure of chitosan is very similar to that of cellulose (made up of β (1–4)-linked D-glucose units). Chitosan is the N-deacetylated derivative of chitin, although this N-deacetylation is never complete, exposing a number of amino groups making it polycationic polysaccharide. Different grades of chitosan are found depending on the amount of deacetylation of the compounds. Due to its gel-forming property it has been used in the design of drug delivery system. 
The interaction between alginate and chitosan has been systematically investigated. Their polyelectrolyte complex has been widely used to obtain devices for the controlled release of drugs.  The interaction between the alginate and the chitosan forms the polyelectrolyte complex via the ionic interaction between the carboxyl residue of alginate and the amino residue of chitosan. The complexation of alginate with chitosan decreases the leakage of the encapsulated drug from the beads. Due to this reason the previously used chitosan-tripolyphosphate beads which had low mechanical strengths and the alginate beads are replaced by the alginate chitosan beads which can be prepared by various methods.
Methods of Preparation of beads:
Modification in Preparation of the beads (alginate and alginate chitosan) by Ionotropic gelation. 
i. Syringe or Dropper Method
ii. Extrusion Method
iii. Laminar jet break-up or Prilling method