INTRODUCTION:

Chitosan is a naturally occurring polymer obtained from the alkaline deacetylation of chitin. Chitosan is the abundant polymer infact next to the cellulose. Chitin is the principle component of protective cuticles of crustaceans such as crabs, shrimps, prawns, lobsters and cell walls of some fungi such as asperigillus and mucor. Among several sources, the exoskeleton of crustaceans consists of 15% to 20% chitin by dry weight. Chitin found in nature is a renewable bioresource. Chitosan is the only pseudonatural cationic polymer and thus, it finds many applications that follow from its unique character (flocculants for protein recovery, depollution, etc.). Being soluble in aqueous solutions, it is largely used in different applications as solutions, gels, or films and fibers. Chitosan is a unique polymer having compatible properties which can be used as a carrier. The basic properties of the chitosan include its biocompatibility, biodegradability and non toxic nature. It also consists of mucoadhesiveness which can retain the drug in the intestine for long time.

Structure of Chitosan:

Chitin is a straight homopolymer composed of β-(1, 4)-linked N-acetyl-glucosamine units and chitosan consists of copolymers of glucosamine and N-acetyl-glucosamine.

Figure 1: Structure of Chitosan

Chitosan has one primary amine group at the C₂ position and two free hydroxyl groups for each C₆ unit. Chitosan always carries a positive charge because of the presence of free amino groups and thus reacts with many negatively charged surfaces/polymers and also undergoes chelation with metal ions¹. The structure of chitosan is shown in Figure 1. Preparation of chitin and chitosan was depicted in Figure 2. The crude chitosan is dissolved in aqueous 2 % w/v acetic acid. Then the insoluble material is removed giving a clear supernatant solution, which is neutralized with NaOH solution resulting in a purified sample of chitosan as a white precipitate. Further purification may be necessary to prepare medical and pharmaceutical-grade chitosan.

Figure 2: Preparation of Chitin and Chitosan

Characterization of Chitosan:

· Degree of N-acetylation – Chitosan is characterized by either degree of acetylation (DA), which corresponds to N-acetylamine units or degree of deacetylation (DDA), corresponds to the D-glucosamine units. The degree of acetylation has an influence on all the physicochemical properties (molecular weight, viscosity, solubility) of the chitosan. The degree of acetylation can be characterized using IR spectroscopy.

· Solubility – The solubility is a very difficult parameter to control; it is related to the Degree of acetylation, ionic concentration, pH, nature of the acid used for protonation, and the distribution of acetyl groups along the chain, as well as the conditions of isolation, drying of the polysaccharide and the intra-chain H-bonds involving the hydroxyl groups. The solubility of chitosan is usually tested in acetic acid by dissolving it in 1% or 0.1M acetic acid. The amount of acid needed depends on the quantity of chitosan to be dissolved. The concentration of protons needed is at least equal to the concentration of NH2 units involved for protonation. Chitosan is soluble below pH 6. Solubility of chitosan in HCl give a homogenous solution but, at high concentrations salting out can occur. It is precipitated in alkaline solution or with polyanions and form gels at low pH.

· Molecular weight – The average molecular weight of polysaccharides and the relation with physicochemical properties are creating a real problem. The primary structure of chitosan is a backbone of (1, 4)-β-D-glucosamine units randomly acetylated to various extents. The properties of chitosan differ with altering molecular weight of chitosan. Methods generally based on viscometric measurements by Mark–Houwink equation.

[η] = K x M^a

Where, ‘K’ and ‘a’ are the constants for the solvents used, for instance a and K values for 0.3M AcOH/0.2NaCl solvent are 0.93 and 1.81x10^-3 respectively².

Methods of Characterization:

Chitosan is available in both crystalline and amorphous forms. Depending on its physical state and based on the extraction from raw resources, the residual crystallinity varies. The main parameters affecting the polymer properties are degree of deacetylation (DD), molecular weight (Mw), polydispersity and crystallinity. It has been reported that DD is one of the most important chemical characteristics that can influence performance of chitosan in many applications including microspheres. The influence of average Mw on the viscosity development of aqueous solutions plays a significant role in the biochemical and biopharmacological significance of chitosan. Various methods reported for the determination of chitosan characteristics. Degree of acetylation, average degree of polymerization, ash content and the polydispersity index are the foremost characteristics to be determined for a marketed product. The physicochemical characteristics are shown in Table 1. The effect of DD and molecular weight of chitosan on micosphere properties are shown in Table 2.

Biological Properties of Chitosan

· Biodegradability – Chitin and chitosan are absent in mammals but they can be degraded in vivo by several proteases (lysozyme, papain, pepsin). Their biodegradation leads to the release of non-toxic oligosaccharides of variable length which can be subsequently incorporated to glycosaminoglycans and glycoproteins, to metabolic pathways or be excreted¹⁵. Lysozyme, a non-specific protease present in all mammalian tissues, seems to play a degradation role on chitin and chitosan. The degradation kinetics seems to be inversely related to the degree of crystallinity which is controlled mainly by the Degree of deacetylation and the distribution of acetyl groups also affects biodegradability since the absence of acetyl groups or their homogeneous distribution (random rather than block) results in very low rates of enzymatic degradation¹⁶. The degradation rate also affects the biocompatibility since very fast rates of degradation will produce an accumulation of the amino sugars and produce an inflammatory response. Chitosan samples with low DD induce an acute inflammatory response while chitosan samples with high DD induce a minimal response due to the low degradation rate. The degradation rate cannot be decided using DD value ¹⁷.

· Biocompatibility – The compatibility of chitosan depends on the characteristics of the sample (natural source, method of preparation, Mw and DD). Chitosan shows better cytocompatability and has been proved in vitro with myocardial, endothelial and epithelial cells, fibroblast, hepatocytes, condrocytes and keratinocytes¹⁸. This property seems to be related to the DD of the samples. When the positive charge of the polymer increases, the interactions between chitosan and the cells increase too, due to the presence of free amino groups. The adhesion and proliferation of keratinocytes and fibroblasts on several chitosan films with different DDs depend on both, DD and cell type. In both cells, the percentage of cell adhesion was strongly dependent of the DD, increasing with this parameter. The type of cell was a factor that also affected the adhesion, being more favorable for fibroblasts which exhibit a more negative charge surface than for keratinocytes. On the other hand, the proliferation decreased considerably by increasing the DD.

· Permeation Enhancing Effect - It has been reported that chitosan acts as a permeation enhancer by opening epithelial tight junctions¹⁹. The mechanism underlying this behavior is based on the interaction of positively charged chitosan and the cell membrane resulting in a reorganization of the tight junction-associated proteins. This property varies with the type of chitosan and its characteristics (DD, Mw).

· Mucoadhesion – Several factors affect chitosan mucoadhesion, such as physiological variables and the physicochemical properties of chitosan. The mucus is composed of a glycoprotein called mucin, which is rich in negative charges since it has sialic acid residues. In the stomach, chitosan is positively charged due to the acidic environment and, therefore, it can interact with mucin by electrostatic forces. The extent of this union depends on the amount of sialic acid present in the mucin and on the Mw and DD of chitosan. It has been found that when the Mw of chitosan increases, the penetration in the mucin layer also increases and hence the mucoadhesion is stronger²⁰. On the other hand, a higher DD leads to an increase in charge density of the molecule and the adhesive properties become more relevant. Mucoadhesivity of chitosan and cationic derivatives is recognized and has been proved to enhance the adsorption of drugs especially at neutral pH.

· Analgesic Effect – Many authors have reported that chitosan show analgesic effect. The Inflammatory pain due to intraperitoneal administration of acetic acid was studied by Okamoto et al. and has proposed a mechanism for this analgesic effect²¹. Due to its polycationic nature, the free primary amino groups of chitosan can protonate in the presence of proton ions and the reduction in the pH is the main cause of the analgesic effect. From the experimental data, it was concluded that the analgesic effect was due to the absorption of bradykinin.

· Haemostatic – The anticoagulant activity of chitosan seems to be related to its positive charge since ‘red blood cells’ membranes are negatively charged. It has been reported that chitosan, as well as sulphated chitosan oligomers, presents anticoagulant activity tested in vitro ²². Solid-state chitosan with a high DD bound more platelets and was more haemostatic than chitosan solutions.

Preparation of Chitosan Microspheres

The main objective of any dosage form is to achieve a desired concentration of drug in blood or tissue, which is therapeutically effective and non toxic for an extended period of time. There has been considerable interest in recent years in developing controlled or sustained drug delivery systems by using bio polymers. Chitosan can be used as a potential drug carrier and using its stable properties microspheres can be formulated as follows

Interactions with ions

· Ionotropic Gelation - The counter ions used for ionotropic gelation can be divided into three categories such as low molecular weight counter ions (e.g. pyrophosphate, tripolyphosphate, tetrapolyphosphate, octapolyphosphate, and hexametaphosphate), hydrophobic counterions (e.g. alginate, carragenan, poly-1-hydroxy-1-sulphonate-propene-2, and olyaldehydro-carbonic acid), high molecular weight ions (e.g. octyl sulphate, lauryl sulphate, hexadecyl sulphate, cetylstearyl sulphate). The chitosan solution in acetic acid was extruded drop wise through a needle into different concentrations of aqueous solutions of magnetically stirred tri polyphosphate or some other anion. The beads were removed from the counter ion solution by filtration, washed with distilled water and dried. Chitosan microparticles produced by ionic cross linking with tri polyphosphate (TPP) increased the drug loading efficiency and prolonged the drug release period.

· Emulsification Ionic Gelation – In this method, the dispersed phase, which consists of an aqueous solution of chitosan, is added to a non-aqueous continuous phase (iso-octane and emulsifier) to form w/o emulsion. Sodium hydroxide (1 N) solution is then added at different intervals leading to ionotropic gelation. The microspheres thus formed are removed by filtration, washed and dried.

· Wet Phase Inversion – In this method of preparation, chitosan solution in acetic acid was dropped into an aqueous solution of a counter ion sodium tri polyphosphate through a nozzle. Microspheres formed were allowed to stand for 1 h, washed and cross linked with 5% ethylene glycol diglycidyl ether. Finally, the microspheres were washed and freeze-dried to form porous chitosan microspheres.

· Coacervation – In this process, the polymer is solubilized to form a solution, it is followed by addition of a solute, which forms insoluble polymer derivative and precipitates the polymer. This process avoids the use of toxic organic solvents and glutaraldehyde used in the other methods of preparation of chitosan microspheres.

· Complex-coacervation – Chitosan microparticles can also be prepared by complex coacervation. Sodium alginate, sodium carboxymethylcellulose, carregeenan and sodium polyacrylic acid can be used for complex coacervation with chitosan to form microspheres. These microparticles are formed by interionic interaction between oppositely charged polymers. The obtained capsules were hardened in the counterion solution and the formed capsules were washed and dried.

Cross linking with other chemicals

· Emulsion cross linking method – In this process chitosan solution (in acetic acid) is added to liquid paraffin containing a surfactant resulting in formation of w/o emulsion. A cross linking agent of varying amount is added depending upon the cross linking density required. The microspheres formed are filtered, washed with suitable solvents and dried. It has also been reported that glutaraldehyde cross linking leads to the formation of microspheres with rough surface which can be overcome by using toluene saturated glutaraldehyde, the cross-linking process was shown in Figure 3.

· Multiple Emulsion Method – Water insoluble drugs are simply dispersed in chitosan solution and entrapped by emulsion cross linking process. In case, where the drug gets partitioned more into the oily phase, multiple emulsions are the way to increase the entrapment efficiency. This method involves formation of (o/w) primary emulsion (non-aqueous drug solution in chitosan solution) and then addition of primary emulsion to external oily phase to form o/w/o emulsion followed by either addition of glutaraldehyde (crosslinking agent) and evaporation of organic solvent. Chitosan microspheres prepared by multiple emulsion method, loaded with hydrophobic drug (ketoprofen) were found to have good morphological character and satisfactory production yield when prepared using this method.

· Cross linking with Naturally Occurring Agent – The chitosan microspheres with small particle size, low crystallinity and good sphericity were prepared by a spray-drying method followed by cross linking with a naturally occurring cross linking agent (genipin). The results of the study demonstrated that the genipin cross linked chitosan microspheres had a superior biocompatibility and a slower degradation rate than the glutaraldehyde-cross linked chitosan microspheres.

Miscellaneous methods

· Thermal Cross linking – Chitosan solutions of varying concentrations were prepared maintaining a constant molar ratio between chitosan and citric acid. The above chitosan cross linker solution was then cooled at 0◦C and added to corn oil followed by thermal cross linking at 120◦C.

· Solvent Evaporation Method – The drug solution (in acetone) was dispersed in chitosan solution and this mixture was emulsified in liquid paraffin and stirred. The suspension of microspheres was filtered, washed and dried. In a modified method called “Dry-in-oil”, chitosan solution in acetic acid was dropped into oil and the temperature of the system was raised and pressure reduced, resulting in evaporation of the solvent and formation of microspheres.

· Spray Drying – In Spray drying, the polymer is first dissolved in a suitable volatile organic solvent such as dichloromethane, Acetone, etc. The drug in the solid form is then dispersed in the polymer solution under high-speed homogenization. This dispersion is then atomized in a stream of hot air. The atomization leads to the formation of the small droplets or the fine mist from which the solvent evaporate instantaneously leading the formation of the microspheres in a size range 1-100μm. Microparticles are separated from the hot air by means of the cyclone separator while the trace of solvent is removed by vacuum drying. One of the major advantages of process is feasibility of operation under aseptic conditions. This process is rapid and this leads to the formation of porous micro particles.

Table 2: Influence of Chitosan DD and Molecular weight on Microspheres Properties ^[14]

Physico-Chemical Property

Effect on Microsphere Properties

↑DD

↑Covalent crosslinking

↓Size

↓Surface roughness

↓Swelling

↑Compactness and hydrophobicity

↓Loading capacity

↓Burst release

↑Molecular Weight

↑Sphericity

↑Morphology Homogeneity

↑Crosslinkig

↓Swelling

↓Release rate

↓Diffusion Coeffecient

Parameters affecting entrapment efficiency of drugs:

Entrapment efficiency of the drugs can be affected by many factors like nature of the drug, chitosan concentration, drug polymer ratio, stirring speed etc. A number of reports have shown that entrapment efficiency increases with an increase in chitosan concentration. This may be explained on the basis that an increase in chitosan concentration prevents drug crystals from leaving the droplet. Ketoprofen microspheres made with a mixture of high molecular weight/low molecular weight chitosan (1:2 w/w) showed good drug content and encapsulation efficiency and these were independent of polymer/drug ratio²³. Entrapment efficiency of Nifedipine was increased in the microspheres with increasing stirring rate during preparation and Scanning electron microscopy indicated that the roughness on the surface of the microsphere increased with increase in loading.

Various classes of drugs microencapsulated with chitosan

Numbers of drugs are incorporated in chitosan microparticles by using various procedures and by using different cross-linking agents.

Anti-inflammatory drugs

· Indomethacin – The drug can be given as sustained release formulation for its prolonged activity. Chitosan gel beads composed of chitosan hydrolysate produces good correlation between molecular weight of chitosan and dissolution rate constant or the mean absorption time or area under the plasma concentration-time curve. Beads were prepared by dispersing the drug in solutions of the ionic polysaccharides chitosan or sodium alginate. These dispersions were then dropped into solutions of the respective counterions tripolyphosphate or calcium chloride (CaCl₂). Strong spherical beads with a narrow particle size distribution and low friability could be prepared with high yield and a drug content approaching 98%²⁴. Orienti et.al,²⁵ prepared indomethacin loaded microspheres using cross linking agent citric acid. The release behavior of the drug depending on the concentration of chitosan and the pH of the medium were explained. The variations induced by these parameters on drug diffusion and solubility in the matrix undergoing erosion were reported.

· Diclofenac sodium– Chitosan microspheres of diclofenac were prepared by the coacervation phase separation method and the in vivo bioavailability study was carried out in rabbits. The microspheres exhibited good spherical geometry and release kinetics of the drug was according to the Higuchi model²⁶. In order to exploit the colon specific biodegradation of chitosan, diclofenac sodium microcores with chitosan were prepared. These were further entrapped in acrylic polymeric coatings using different enteric coating polymers. So, this method combined colon specific biodegradability and pH-dependent release of the drug. The method involved entrapment of the drug within chitosan microspheres by spray-drying method, which was then microencapsulated into Eudragit L-100 and Eudragit S-100 using an o/o solvent evaporation method. A continuous release for a variable time (8–12 h) was achieved by this system due to the dissolution of the Eudragit coating along with swelling of the Chitosan microcore²⁷.

· Ketoprofen – Effect of molecular weight of chitosan on drug loading and drug release was studied using ketoprofen as a model drug. Chitosans with molecular weight between 70,000 and 2,000,000 were found to be suitable carriers for ketoprofen that could modulate drug release within 48 h²⁸. Chitosan-coated ketoprofen microparticles were prepared by the precipitation of droplets of chitosan solution containing microspheres. The adhesion of chitosan-coated ketoprofen microparticles was tested using rat small intestinal mucosa. It was observed that chitosan-coated ketoprofen microparticles showed a good mucoadhesion. The maximum plasma concentration of ketoprofen for chitosan-coated ketoprofen microparticles was less than one-third of that for ketoprofen powder suspension. Chitosan-coated ketoprofen microparticles tended to show higher and steadier plasma level than microspheres^{29, 30}. Ketoprofen and ketoprofen lysinate were encapsulated into alginate microspheres prepared by prilling. The effect of polymer concentration, viscosity, and drug/polymer ratio on bead micromeritics and drug release rate was reported. Alginate solutions with concentration higher than 0.50% (w/w) were suitable to prepare ketoprofen gastro-resistant formulation, while for ketoprofen lysinate alginate, concentration should be increased to 1.50% (w/w) in order to retain the drug in gastric environment. Total release of the drugs in intestinal medium was dependent on the solubility of the drug and was achieved between 4 and 6 h³¹.

· Ibuprofen– Spherical pellets were prepared by dispersing the drug in solutions of the ionic polysaccharides chitosan or sodium alginate, and then dropping these dispersions into solutions of the respective counterions tripolyphosphate (TPP) or calcium chloride. The droplets instantaneously formed gelled spheres by ionotropic gelation. Strong spherical beads with a narrow particle size distribution and low friability could be prepared with high yield and a drug content approaching 98%.

· Aceclofenac - Aceclofenac microspheres were prepared by ionotropic gelation method using tripolyphosphate as cross linking agent. As the cross-linking time and concentration of TPP increased, the release behavior of aceclofenac decreased significantly, whereas decrease in pH increased in the release of aceclofenac. It was reported that the drug release showed slight burst effect in the pH 7.4 phosphate buffer followed by a prolong release for 8hrs.

· Celecoxib – Hetal Paresh Thakkar et.al,³² reported the preparation of celecoxib loaded chitosan microspheres with high entrapment efficiency using chemical cross linking method. Microspheres were prepared using formaldehyde and glutaraldehyde as crosslinking agents. Heat cross linking gives the microspheres with low entrapment efficiency and low particle size. The glutaraldehyde cross linked microspheres retains the drug release compared to formaldehyde cross linked microspheres.

Anticancer drugs

· Fluorouracil- 5-flurouracil loaded chitosan microspheres prepared by dry-in-oil method show good sustained release of the drug. Chitosan-coated PLA (polylactic acid)/PLGA (polylactic-co-glycolic acid) microspheres for the targeted delivery of 5-FU to treat cerebral tumors. The amount of drug release was much higher initially (approximately 25%), followed by a constant slow release profile for a 30-day period of study, thus exhibiting biphasic pattern³³.

· Cisplatin - Albumin coated chitosan microspheres possess sustained release characteristics and also been used in hepatic artery embolization. The rate of cisplatin release reduced with increasing concentration of chitosan. The time taken for 50% cisplatin release from microspheres prepared with 1.0% of chitosan was less (0.5 h) compared to microspheres prepared using 5.0% of chitosan (4.5 h), indicating about nine-fold prolongation. The addition of chitin further resulted in retardation of the rate of release of cisplatin. Chitosan microspheres were shown to undergo enzymatic degradation by lysozymes ³⁴.

· Mitoxantrone - Microspheres of mitoxantrone were prepared by crosslinking technique using glutaraldehyde-saturated toluene. Implantation of placebo chitosan microspheres in skeletal muscle of rats showed biocompatibility and biodegradability of the microspheres for long duration. The anti tumor activity of the spheres were observed to be much higher demonstrating the potential of these microspheres for sustained drug delivery to minimize drug toxicity and maximize therapeutic efficacy³⁵.

Calcium channel blockers

· Dilitiazem hydrochloride - Casein–chitosan microspheres containing diltiazem hydrochloride were prepared by colloidal coacervation technique. The interaction between chitosan solution in acetic acid (5%, v/v) and casein solution in 0.5M sodium hydroxide formed the basis of formation of microspheres. Formaldehyde was used as the crosslinking agent. The concentration of casein, chitosan, drug and stirring speed affected the properties and performance of the microspheres. Drug release was retarded by increasing the concentration of casein and the stirring time while fast drug release was obtained upon increasing the concentration of chitosan and a high initial drug loading. The entrapment efficiency of the microspheres varied between 14.5 and 53.7% ³⁶.

· Nifedipine - Nifedipine and nifedipine–cyclodextrin complexes were encapsulated in chitosan microspheres. Varying the cross linking density, particle size and initial drug loading in the microspheres modified drug release profile. More than 70% of drug entrapment efficiency was achieved. The drug release from cyclodextrin complex was reduced significantly though the solubility of the drug was enhanced by the complexation³⁷.

Anti-diabetic drugs:

· Gliclizide- The blood glucose lowering effect of the gliclizide can be sustained by incorporating the drug in the core of the chitosan microspheres. Gliclizide microspheres were prepared by dispersion technique. Beads prepared by 2% low-molecular-weight chitosan that were cross-linked by 5% TPP at pH 2 with a curing time of 10 min could decrease blood glucose level in normal rats for 24 h compared to powder of gliclazide that lasted for just 10 h ³⁸.

· Insulin - SK.Jain et.al,³⁹ proposed a novel invasive method for the administration of insulin by nasal pathway. The mucoadhesive chitosan microspheres were prepared by emulsification method using both glutaraldehyde and citric acid as cross linkers. It was observed that the glutaraldehyde cross linked microspheres showed better reduction of blood glucose level than citric acid cross linked microspheres. After administration, the maximum blood glucose reduction (66.78±3.33%) was observed in 7 hrs with glutaraldehyde cross linked microspheres whereas with citric acid cross linked microspheres exhibited 69.37±3.46% of the initial blood glucose level after 7 hrs. U. Ubaidulla et.al,⁴⁰ synthesized chitosan phthalate and produce microspheres for the acid resistant insulin delivery. Microspheres were prepared by emulsion phase separation technique and the in vitro release behavior of the microspheres was investigated under different pH conditions (pH 2.0 and pH 7.4). The drug release in pH 2 was very less compared to pH 7.4 buffers.

Antibiotics

· Clarithromycin - R.Kotadiya et.al,⁴¹attempted to modify the release of clarithromycin by altering the conventional dosage form. Chitosan mucoadhesive microspheres with small particle size and good spherecity were prepared by an emulsification cross linking technique using glutaraldehyde as cross linking agent. A high entrapment efficiency of 45% was reported and a percentage mucoadhesion after 5 hours was reported as 15%. The drug release was sustained for 12 hours with initial burst effect

· Ciprofloxacin - A.Srinatha et.al,⁴² fabricated extended release ciprofloxacin loaded chitosan microspheres by ionic cross linking method with tri polyphosphate. Drug release was high in pH 1.2 medium than in pH 7.4. Drug release was increased with increasing in concentration of ciprofloxacin and decreasing proportion of chitosan. Drug release was reported as both first order and higuchi root time kinetics with non fickian release mechanism.

Pharmaceutical Applications of chitosan

Chitosan has been considered as a superior pharmaceutical excipient due to its wide range of applications. Chitosan can be used in conventional formulations as a directly compressible vehicle in tablets, as a binder in wet granulation and also as a novel carrier of drugs (carrier for mucosal delivery of antigens in connection with oral vaccination). The biocompatible, low toxicity properties of chitosan and moreover the abundant availability from the natural origin makes it a superior over other excipients. The main interest of chitosan in controlled formulations is its ability to become hydrated and form gel in acidic aqueous environments. Chitosan has been evaluated in vitro as a drug carrier in hydrocolloids and gels; and as a hydrophilic matrix retarding drug release in tablets, granules and microparticles. The hydrophilic nature of chitosan has also aroused interest in its use in immediate-release formulations as a disintegrant in small amounts in tablets, where it has been found to have effects similar to or better than those of microcrystalline cellulose, and as an excipient to increase the rate of dissolution of poorly soluble drug substances. It has also been suggested that chitosan might be valuable for delivery of drugs to specific regions of the gastrointestinal tract, e.g. the stomach, small intestine, and buccal mucosa. Delivery to other mucosal surfaces, e.g. delivery of peptide drugs on to the nasal epithelia has also been studied. Colon targeting of chitosan has been studied by many authors for the local infections, 5-Flurouracil for the treatment of colon cancer. Chitosan can be used in gastro retentive formulations. Chitosan granules prepared by deacidification process are used for the controlled release of prednisolone and mucoadhesive microspheres of metoclopromide and glipizide tends to retain in the stomach for more than 10 hours⁵⁵. The pharmaceutical applications of chitosan were given in Table 3.

Applications of Chitosan in Food Industry

Chitosan offers a wide range of unique applications in the food industry, including preservation of foods from microbial deterioration, formation of biodegradable films, and recovery of material from food processing discards. Moreover, it can act as a dietary fiber and as a functional food ingredient. Chitosan can be used as food preservative, food emulsions, and as a dietary ingredient. The various applications of chitosan were shown in Table 4.

Chitosan Safety

Chitosan is not only very useful, it is also very safe. Chitosan has been used extensively in numerous industrial, health, and food applications. Chitosan has been found to have an LD₅₀ of over 16 grams/day/kg body weight in mice⁵⁶. Chitosan is a fiber which expands to form a gel in the acidic environment of the stomach. The problems encountered with extremely high doses of chitosan were caused by gastric dehydration and impaction due to the expansion of the fiber. As with any fiber, a person is well advised to drink plenty of water. Changing our diets affects our colon function. Constipation or diarrhea may occur in some persons depending on their individual constitutions and on how well the Chitosan supplement was originally formulated. The breakdown of chitosan by our colon microflora would release D-glucosamine which is itself a wonderfully beneficial nutrient for osteoarthritis sufferers. Because Chitosan can bind lipids and certain minerals, it is best to take essential fatty acid supplements, fat soluble vitamins and mineral supplements separate from Chitosan. Taking Chitosan with D- or L-ascorbic acid helps increase the amount of fat bound and decrease the loss of minerals. Chitosan was contraindicated in patients having shellfish allergy, as chitosan was extracted from the wastes of shellfishes. It was not fully reported safe in pregnancy women.

CONCLUSION:

Chitosan is a versatile polymer whose applications range from weight supplement in the market to a drug carrier in formulation research. Chitosan can be easily molded to various forms and their derivatives are digested in vivo by lysozomal enzymes. Chitosan has been shown to improve the dissolution rate of poorly soluble drugs and thus can be exploited for bioavailability enhancement of such drugs. The transdermal absorption promoting characteristics of chitosan have been exploited, especially for nasal and oral delivery of polar drugs to include peptides and proteins and for vaccine delivery. Reacting chitosan with controlled amounts of multivalent anion results in cross linking between chitosan molecules. This cross linking has been used extensively for the preparation of chitosan microspheres. Release of drug from chitosan microspheres is dependent upon the molecular weight of chitosan, concentration of chitosan, drug content and density of cross-linking. Various therapeutic agents such as anticancer, anti inflammatory, antibiotics, antithrombotic, steroids, proteins, amino acids, antidiabetic and diuretics have been incorporated in chitosan microspheres to achieve controlled release.

ACKNOWLEDGEMENTS:

The authors are thankful to Chalapathi Educational Society, Guntur for providing the necessary facilities.

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Received on 10.07.2010 Modified on 23.07.2010

Research J. Pharm. and Tech.4 (5): May 2011; Page 667-676

Physicochemical Properties	Methods
Degree of Deacetylation (DD)	Infrared spectroscopy^[3] First derivative UV-spectrophotometry^[4] Nuclear magnetic resonance spectroscopy (¹HNMR) and (¹³CNMR)^[5] Conductometric titration^[5] Potentiometric titration^[6] Differential scanning calorimetry^[7]
Average Molecular weight (Mw) and/or Mw distribution	Viscosimetry ^[8] Gel Permeation chromatography ^[9] Light scattering ^[10]
Crystallinity	X-ray Diffraction^[11]
Moisture content	Gravimetric analysis^[12]
Ash content	Gravimetric analysis^[12]
Protein	Bradford method^[13]

Applications	Examples
Water and waste treatment	Flocculent to clarify water (drinking water, pools), Removal of metal ions, Ecological polymer (eliminate synthetic polymers), Reduce odors
Pulp and paper	Surface treatment, photographic paper, carbonless copy paper
Medical	Bandages, artificial skin, tumor inhibition membranes, blood cholesterol control, dental/plaque inhibition, eye humor fluid, contact lens, controlled release of drugs, bone disease treatment
Cosmetics	Make-up powder, nail polish, moisturizers, fixtures, bath lotion, tooth paste, foam enhancing
Biotechnology	Enzyme immobilization, protein separation, chromatography, cell recovery, cell immobilization, glucose electrode
Agriculture	Defensive mechanism in plants, Stimulation of plant growth Seed coating, Frost protection, Time release of fertilizers and nutrients into the soil
Food	Not digestible by human (dietary fiber), Bind lipids (reduce cholesterol), Preservative, Thickener and stabilizer for sauces, Protective, fungistatic, antibacterial, coating for fruit
Membranes	Reverse osmosis, Permeability control, Solvent separation
Biopharmaceutics	Immunologic, antitumoral, Hemostatic and anticoagulant Healing, bacteriostatic