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MICROSPHERES: FORMULATION & EVALUATION


About Authors:
Piyush Gupta*
Department of Pharmaceutics,
Regional College of Pharmacy,
Jaipur, Rajasthan

ABSTRACT:-
The term MICROSPHERE is defined as a spherical particle with size varying from 50nm to 2µm, containing a core substance. Microspheres are, in strict sense, spherical empty particles.However, the terms microspheres and microencapsulationare used synonymously. In addition, some related terms are “beads” are used alternatively. Spheres and spherical particles are also usedfor a large size and rigid morphology. The microspheres are characteristically free flowing powders consisting of proteins orsynthetic polymers, which are biodegradable in nature, andideally having a particle size less than 200 micrometer. Novel Drug Delivery Systems are developed to address the challengesof drug development such as Bioavailability, Permeability & Poor solubility. These demand changes in the conventional use of Excipients, the growth of the Biotechnology industry,including Stem cell therapy,Vaccines & Genetic products, also necessitates different drug delivery requirements, there by demonstrating the acceptance of these excipients by the US food & drug administration or other agencies in the major markets.For materials in which Toxicity is a possible concern, formulators can give information about the excipients regulatory acceptance& allowable amount by consulting with excipients manufactures& toxicology experts.

REFERENCE ID: PHARMATUTOR-ART-1266

INTRODUCTION
Between 1940s and 1960s, the concept of Micro encapsulation technology began as an alternative means of delivering drugs. In continued quest for the more refined system, in 1980s Polymer/Membrane technology came to be known at forefront. Further, the process of targeting and site specific delivery with absolute accuracy can be achieved by attaching bioactive molecule to liposome, bioerodable polymer, implants, monoclonal antibodies and various  particulate carriers (e.g. Nano particles and Microspheres etc).The term Microsphere is defined as a spherical particle with size varying with diameters in the micrometer range (typically 1μm to 1000μm (1mm), containing a core substance.The microspheres are characteristically free flowing powders consisting of proteins or synthetic polymers, which are biodegradable in nature, and ideally having a particle size less than 200 micrometer. Microsphere have been extensively studied for use as drug delivery systems, where they have been shown to protect sensitive macromolecules from enzymatic and acid degradation, and allow controlled release and tissue targeting of the formulated drug.

Drug carriers one can name soluble polymers, microparticles made of insoluble or biodegradable natural and synthetic polymers, microcapsules, cells, cell ghosts, lipoproteins, liposomes, and micelles. The carriers can be made slowly degradable, stimuli-reactive (e.g. pH or temperature-sensitive), and even targeted (e.g. by conjugating them with specific antibodies against certain characteristic components of the area of interest).[18]

Figure 1:-Pharmaceutical carriers[18]

The Novel Drug Delivery System started the alternative means of delivering the drug in the form of microspheres. A unique pharmaceutical delivery system comprising a physiologically acceptable nonaqueous liquid such as an edible oil and a thickening agent such as colloidal silicon dioxide which together form a semi-solid having the consistency of a pudding is provided. Microspheres prepared with gelatin as the polymer have been found to be highly mucoadhesive and have been used for the controlled release of many drugs. Microspheres prepared from admixtures of gelatin and crosslinked chitosan  demonstrated some advantage over that prepared from gelatin alone in terms of better controlled release rate of cemetidine. Nanoparticles (including nanospheres and nanocapsules of size 10-200nm) are in the solid state and are either amorphous or crystalline. They are able to absorb and/or encapsulate a drug, thus protecting it against chemical and enzymatic degradation. Novel drug delivery system development is largely based on promoting the therapeutic effects of a drug and minimizing its toxic effects by increasing the amount and persistence of a drug in the vicinity of a target cell and reducing the drug exposure of nontarget cells.[18]

CLASSIFICATION

There are different types of Microspheres.

1. Glass microspheres

· Hollow glass microspheres

· Solid glass microspheres

2.Polymer microspheres

· Polyethylene microspheres
· Polystyrene microspheres
·  Fluorescent microspheres

3.Starch microspheres

· Cross-linked starch microspheres

4.Ceramic microspheres
5.
Albumin microspheres
6.
Gelatin microspheres
7.
Dextran microspheres
8.
Poly lactide and polyglycolide microspheres
9.
Poly anhydride microspheres
10.
Poly phosphane microspheres
11.
Chitosan microspheres
12.
Lipid cross linked chitosan microspheres
13.
Carrageenan microspheres
14.
Alginate microspheres
15.
Poly (alkyl cynoacrylate) microspheres
16.
Poly acrolein microspheres

ADVANTAGES
(1)
  Improved antigenicity by adjuvant action.
(2)
  Modulation of antigen release.
(3)
  Stabilization of antigen.
(4)
  Microspheres are very small particles that can be loaded easily.

PREREQUISITES
The material utilized for the preparation of microspheres should ideally fulfill the following prerequisites:-
(1)
   Longer duration of action
(2)
   Control of content release
(3)
   Increase of content of therapeutic efficiency
(4)
   Protection of drug
(5)
   Reduction of toxicity
(6)
   Biocompatibility
(7)
   Sterilizability
(8)
   Relative stability
(9)
   Water solubility or dispersability
(10)
Bioresorbability
(11)
Targetability
(12)
Polyvalent

GOVERNING FACTORS
In the preparation of microspheres ,the governing factors are:-
1.
The particle size requirements
2.
The drug or protein should not be affected by the process.
3.
Reproducibility of the release profile and the method.
4.
No stability problems.
5.
No toxic products produced as the final product.

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