Cellulose coated chitosan hollow beads for controlled drug delivery

Cellulose-Coated Chitosan Hollow Beads for Controlled Drug Delivery... Cellulose-Coated Chitosan Hollow Beads for Controlled Drug Delivery... Cellulose-Coated Chitosan Hollow Beads for

Cellulose-Coated Chitosan Hollow Beads for

Controlled Drug Delivery

Cellulose-Coated Chitosan Hollow Beads for

Controlled Drug Delivery

Cellulose-Coated Chitosan Hollow Beads for

Controlled Drug Delivery

Chapter 1 Orientation and Objectives 1

Chapter 4 Ionic liquids assisted preparation of 58

cellulose coated hydrogels

LIST OF FIGURES

Fig 2.2 Schematic representation of preparation of chitosan 8

particulate system by emulsion cross-linking method

Fig 2.3 Schematic representation of preparation of chitosan 13

particulate system by spray drying method

Fig 2.4 Schematic representation of preparation of chitosan 17

particulate system by emulsion-droplet coalescence method

Fig 2.5 Schematic representation of preparation of chitosan 19

particulate systems by ionic gelation method

Fig 2.6. Schematic representation of preparation of chitosan 22

particulate system by reverse micellar method

Fig 2.7. Schematic representation of preparation of chitosan 24

particulate system by sieving method

Fig 3.1. Time course of alkaline deacetylation of chitin 46

under 120oC and 60% NaOH

Fig 3.2. Hollow hydrogels with different thickness of shell 50

observed under optical microscope (A) and their corresponding cross-sections prepared by paraffin section (B)

Fig 3.3. Mechanical properties of the prepared chitosan 51

Fig 3.6. Schematic representation of hypothesized mechanisms 56

of hollow chitosan hydrogels formation

Fig 3.7. Drug loading efficiency of hydrogels prepared from 57

chitosan with different degree of deacetylation

Fig 4.1. Structure of 1-ethyl-3-methylimidazolium acetate 64 Fig 4.2. Optical microscopy examination of cellulose-coated 67

and uncoated chitosan hydrogels

Fig 4.3 Schematic representation of hypothesized mechanisms of 68

cellulose coating

Fig 4.4. Release patterns of insulin in SIF from cellulose-coated 70

and uncoated chitosan hydrogels

Fig 4.5. Release patterns of insulin in SGF and SIF from 72

cellulose-coated and uncoated chitosan hydrogels

Fig 4.6. Release patterns of metronidazole in SGF from 73

cellulose-coated and uncoated chitosan hydrogels

Fig 4.7. Morphological observation of chitosan beads, bubbles 74

and coated bubbles during incubation in SGF at

37oC, 120 rpm

LIST OF TABLES

Table 3.1 Physicochemical characteristics of chitosan samples 47

prepared under deacetylation conditions of 60% NaOH,

120oC, and reaction time ranges from 45 to 180 min

Cellulose-Coated Chitosan Hollow Beads for

Controlled Drug Delivery

Pham, Thi Phuong ThuyDepartment of Bioprocess Engineering

The Graduate School

Chonbuk National University

Abstract

Chitosan is a biodegradable natural polymer with great potential for pharmaceutical applications due to its biocompatibility, high charge density, low toxicity and mucoadhesion It has been shown that it not only improves the dissolution of poorly soluble drugs but also exerts a significant effect on fat metabolism in the body Chitosan can be readily processed into various forms of materials that can be used as delivery vesicles for drugs, dyes and inks, or as microcapsules of artificial cells Whether in the form of microspheres, multilayer films or scaffolds, their polyelectrolytic and hydrophilic properties make them excellent protective matrices for small bioactive molecules such as bovine serum albumin, insulin or other growth factors as well as cells Therefore, controlled processing of these polymeric materials is of great importance, aiming at fabrication of specifically designed surfaces or interior structures Of particular interest are microspheres with hollow interiors, in part due to their low density, which

facilitates floating property when they are applied as drug carriers Hollow spheres could be obtained by different approaches, such as emulsion polymerization, the use of core-shell micelles made of block copolymers, noncovalently connected micelles, or a template method Among these, template-assisted synthesis, which requires a template, such as colloids, surfactant vesicles or emulsion droplets, is most commonly used to prepare hollow particles In this method, the target material is coated or polymerized

on the surface of the template, following by selective removal of the template to form a cavity, leading to a hollow structure However, this fabrication technique is laborious and involves the use of organic solvents under harsh reaction conditions, which in turn influences the biocompatibility of the microspheres Accordingly, a novel synthesis technique for the preparation of chitosan hollow scaffolds is practically valuable

In this thesis, we present a simple single-step fabrication process for the preparation of chitosan hollow scaffolds without the use of toxic covalent crosslinking agents and any sophisticate equipment The ionic interactions between the positively charged amino groups of chitosan and negatively charged counterion, tripolyphosphate, were successfully used to prepare chitosan hollow spheres through either intermolecular or intramolecular

prepared chitosan hollow microspheres was observed to be controlled by the degree of deacetylation of chitosan This finding provides critical information for controllable preparation of hollow hydrogel-based devices in biomedical applications.

In an attempt to improve material properties used for oral administration, which is restricted by fast dissolution in the stomach, chitosan hollow spheres were coated with cellulose dissolved in ionic liquid Using insulin and metronidazole as model compounds, the properties of these cellulose-coated microparticles for the controlled release of drug were investigated These microparticles were stable at low pH and thus, suitable for oral delivery without requiring any harmful cross-linkage treatment

Chapter 1.

ORIENTATION AND OBJECTIVES

Chitosan is a biodegradable natural polymer with great potential for pharmaceutical applications due to its biocompatibility, high charge density, low toxicity and mucoadhesion It has been shown that it not only improves the dissolution of poorly soluble drugs but also exerts a significant effect on fat metabolism in the body (Sinha et al., 2004) Chitosan can be readily processed into various forms of materials that can be used as delivery vesicles for drugs, dyes and inks, or as microcapsules of artificial cells (Borchard, 2001; Prabaharan and Mano, 2005) Whether in the form of microspheres, multilayer films or scaffolds, their polyelectrolytic and hydrophilic properties make them excellent protective matrices for small bioactive molecules such as bovine serum albumin, insulin or other growth factors as well as cells (Kumar, 2001) Therefore, controlled processing of these polymeric materials is of great importance, aiming at fabrication of specifically designed surfaces or interior structures Of particular interest are microspheres with hollow interiors, in part due to their low density, which facilitates floating property when they are applied as drug carriers (Huang et

emulsion polymerization, the use of core-shell micelles made of block copolymers, noncovalently connected micelles, or a template method (Hu et al., 2004; Shi et al., 2006; Breitenkamp and Emrick, 2003; Sanji et al., 2000; Wang et al., 2002; Dou et al., 2003; Wang and Jiang, 2006; Baidu et al., 2009; Caruso et al., 1998; Xu and Asher, 2004) Among these, template-assisted synthesis, which requires a template, such as colloids (Caruso et al., 2001), surfactant vesicles (Hubert et al., 2000) or emulsion droplets (Zhang

et al., 2012), is most commonly used to prepare hollow particles In this method, the target material is coated or polymerized on the surface of the template, following by selective removal of the template to form a cavity, leading to a hollow structure However, this fabrication technique is laborious and involves the use of organic solvents under harsh reaction conditions, which in turn influences the biocompatibility of the microspheres Accordingly, a novel synthesis technique for the preparation

of chitosan hollow scaffolds is practically valuable

In this thesis, we present a simple single-step fabrication process for the preparation of chitosan hollow scaffolds without the use of toxic covalent crosslinking agents and any sophisticate equipment The ionic interactions between the positively charged amino groups of chitosan and negatively charged counterion, tripolyphosphate, were successfully used to prepare chitosan hollow spheres through either intermolecular or intramolecular

linkages of the anionic counterions Interestingly, the shell thickness of the prepared chitosan hollow microspheres was observed to be controlled by the degree of deacetylation of chitosan This finding provides critical information for controllable preparation of hollow hydrogel-based devices in biomedical applications.

In an attempt to improve material properties used for oral administration, which is restricted by fast dissolution in the stomach, chitosan hollow spheres were coated with cellulose dissolved in ionic liquid Using insulin and metronidazole as model compounds, the properties of these cellulose-coated microparticles for the controlled release of drug were investigated These microparticles were stable at low pH and thus, suitable for oral delivery without requiring any harmful cross-linkage treatment

The final goal of this thesis is to propose a simple, fast and friendly but effective preparation process of chitosan hollow scaffolds for biomedical applications Towards an enhancement in controlled release of drug in gastric cavity, ionic liquid-mediated cellulose coating of microspheres is also developed

environmental-To support these purposes, following studies have been completed.

1 Preparation of chitosan hollow microspheres by ionotropic gelation of chitosan and sodium tripolyphosphate

2 Mechanistic aspects of hollow formation

3 Control of morphology and hollow size of the prepared chitosan scaffolds

4 Coating of chitosan hollow spheres by cellulose dissolved in ionic liquid for applications in drug delivery

cell wall of fungi, mushrooms such as Enoki mushroom (Flammulina

velutipes) and Shiitake mushrooms (Lentinus edodes) and bacteria (Kumar,

2000; Hejazi and Amiji, 2003; Rinaudo, 2006) The percentage of chitin content varies with the source of supply (Felt et al., 1998) Industrially, the isolation of chitin from crustacean shells mainly involves removal of protein

concentrations (Kumar, 2000) The resulting chitin is deacetylated in 40% sodium hydroxide at 120 oC for 1 to 3 h giving rise to 70% deacetylated chitosan The degree of deacetylation of chitosan varies with the source of chitin and processing method.

Fig 2.1 Structures of chitin and chitosan

2.2 Methods of preparation of chitosan microspheres

2.2.1 Emulsion cross-linking

This method utilizes the reactive functional amine group of chitosan to link with aldehyde groups of the cross-linking agent In this method, a water-in-oil (w/o) emulsion is prepared by emulsifying the chitosan aqueous solution in the oil phase Aqueous droplets are stabilized using a suitable surfactant The stable emulsion is cross-linked by using an appropriate cross-linking agent such as glutaraldehyde to harden the droplets Microspheres are filtered and washed repeatedly with n-hexane followed by alcohol and then dried (Akbuğa and Durmaz, 1994) By this method, size of the particles can

cross-be controlled by varying the size of aqueous droplets However, the particle size of final product depends upon the extent of cross-linking agent used while hardening in addition to speed of stirring during the formation of emulsion This method is schematically represented in Fig 2.2 The emulsion cross-linking method has few drawbacks since it involves tedious procedures as well as use of harsh cross-linking agents, which might possibly induce chemical reactions with the active agent However, complete removal

of the un-reacted cross-linking agent may be difficult in this process

Fig 2.2 Schematic representation of preparation of chitosan particulate system by emulsion cross-linking method

2.2.2 Coacervation/precipitation

Coacervation techniques involve the separation of a polymer solution into two coexisting phases: a dense coacervate phase, which is rich in colloids and a diluted equilibrium phase or supernatant, which is poor in colloids (Okhamafe et al., 1996; Mooren et al., 1998) Coacervation in aqueous system is subdivided into simple and complex coacervation

In simple coacervation, the hydrophilic colloid is deprived of the solvent by the addition of a competing hydrophilic substance, such as salt or alcohol (“salting out”) An example of this method has been described recently by Çelik and Akbuğa (2007), who prepared superoxide dismutase loaded microspheres, by adding a sodium sulfate solution while stirring into a chitosan solution containing dissolved protein and the microspheres obtained

in this way were separated by ultracentrifugation The addition of polyethylene glycol (PEG) to the protein solution and the acidification lead

to a higher protein encapsulation

Hejazi and Amiji (2002) prepared chitosan microspheres by precipitation with sodium sulfate loaded with tetracycline for the treatment of

Helicobacter pylori infection They observed that when the drug was

incorporated into the chitosan solution before precipitation with the salt, the

with the pre-formed microspheres, the drug loading was much higher (68%) Berthold and colleagues (1996a) described the preparation of prednisolone sodium phosphate loaded microspheres by precipitation of chitosan, of different molecular weights, also with sodium sulfate The drug loading ranged between 24–79% and the incorporation of an adequate surfactant (polysorbate 80) was essential to avoid agglomerates They found no differences on surface charge of the microparticles prepared with different molecular weights, since the deacetylation degree is not dependent on the length of the polysaccharide chain Further studies with these microspheres demonstrated that they can improve the transport of prednisolone sodium phosphate across the epithelial monolayer of HT-29B6 cells, since chitosan microspheres are capable of opening the tight junctions of the epithelial cells This is possible because chitosan can interact with cytoskeletal F-actin, which is associated with the proteins of the tight junctions (Mooren et al., 1998).

In all cases, the encapsulation efficiency using the coacervation-precipitation method was quite low; for that reason, it is not one of the most widely used methods for encapsulation with chitosan, although it is simple and mild

Complex coacervation is one of the few methods which can be applied to natural polymers, one of the most important prerequisites for the processing

of food supplements (Lamprecht et al., 2000) It can be defined as the spontaneous liquid/liquid phase separation that occurs when oppositely charged colloids are mixed as a result of electrostatic attractions It is a well established method for the microencapsulation of oils or solids; in the food industry, especially, this method is used to mask a potentially bad taste or to

avoid oxidation of the incorporated material, e.g certain vitamins and/or

unsaturated fatty acids The coacervation process occurs under mild conditions, and consequently has great potential for the microencapsulation

of living cells and labile molecules, which are unable to withstand harsh conditions (heat, organic solvents) involved in other microencapsulation processes As coacervation can be induced in systems containing both cationic and anionic hydrophilic colloids, Remuñán-López and Bodmeier (1996a) described the complex coacervation between chitosan, and type B gelatin They observed that the coacervation was influenced by the temperature, since gelatin is soluble above 40oC The coacervation yield decreased with an increase of temperature (up to 70oC) The pH of the solution was another important aspect, since complex coacervation involves both polymers having opposite charges, and gelatin is a protein that is only negatively charged at pH values above its isoelectric point For that reason, the pH range of work was narrow and they found that the optimum pH was

5.25.The mixing ratio of polymers was also studied and above 50:1 ratio coacervation was completely suppressed.

2.2.3 Spray-drying

Spray-drying is a relatively simple process that has been industrially used since 1927 The technique is based on spraying a solution of the polymer, in which the drug is dissolved or dispersed, inside a chamber at high temperature (Fig 2.3)

When the liquid is fed into the nozzle through a peristaltic pump, atomization occurs by the force of the compressed air, disrupting the liquid into small droplets, from which solvent evaporates instantaneously leading to the formation of free flowing particles (He et al., 1999a) The microparticles formed this way are separated in a cyclone and collected in a collection bottle

Fig 2.3 Schematic representation of preparation of chitosan particulate system by spray drying method

The particles thus isolated usually show a shrunken shape, due to the rapid evaporation of the solvent and the formation of an external crust during the first stages of drying After this external crust is formed, the solvent present

in the inner parts of the droplet evaporates, leading to partial shrinkage of the particle (Martinac et al., 2005)

He et al (1999a, b) prepared chitosan microparticles cross-linked with glutaraldehyde and formaldehyde by spray drying The release properties of the model drugs, cimetidine, famotidine and nizatidine, from the microparticles were compared with spray-dried ethylcellulose microparticles They observed that the size of the particles was influenced by various process parameters such as size of the nozzle, rate of feeding, and inlet air temperature, as some other authors also described (Agnihotri et al., 2004) However, the zeta potential was not affected by these manufacturing aspects Microspheres with different zeta potential could be prepared by varying the cross-linking level The release of the drug was very fast, because of the high hydrophilicity of the drug Pavanetto et al (1994) described that the release

of less soluble drugs, such as dexamethasone, was also fast when employing this system It is believed that it is necessary to use a lipophilic drug and polymer to prepare a slow release by spray drying Shi and Tan (2002) prepared chitosan/ethylcellulose microparticles by spray drying a chitosan solution with vitamin D2 and then microencapsulating the chitosan micro-

cores in an ethylcellulose solution Another modification of the spray-drying technique is the use of this method to prepare microencapsulated nanoparticles (Grenha et al., 2005) Lorenzo-Lamosa et al (1998) described the microencapsulation of chitosan spray-dried microspheres into Eudragit L-100 and Eudragit S-100 using a solvent evaporation method An interaction between amino groups of chitosan and carboxyl groups of Eudragit provided the system a new controlled release element

Spray drying can be combined with some other microencapsulation methods For example, in a recently published study, chitosan-Ca-alginate microparticles for the colon-specific delivery of 5-aminosalicylic acid (5-ASA) prepared by a spray drying method followed by inotropic gelation/polyelectrolyte complexation were evaluated A solution of sodium alginate with the model drug was spray dried into a solution of chitosan and CaCl2 in acetic acid A dispersion of microparticles of less than 10 µm was achieved This dispersion was allowed to harden for few hours, and then the microparticles were separated by centrifugation, washed and freeze dried These microparticles released the 5-ASA at the colon due to the increased deprotonization of chitosan at pH 6.4–7.0 that provokes a lower interaction between carboxyl groups of alginate, the drug and the chitosan that have inter and intramolecular hydrogen bonds at lower pH (Mladenovska et al.,

2.2.4 Emulsion-droplet coalescence method

The novel emulsion-droplet coalescence method was developed by Tokumitsu et al (1999), which utilizes the principles of both emulsion cross-linking and precipitation However, in this method, instead of cross-linking the stable droplets, precipitation is induced by allowing coalescence of chitosan droplets with NaOH droplets First, a stable emulsion containing aqueous solution of chitosan along with drug is produced in liquid paraffin oil and then, another stable emulsion containing chitosan aqueous solution of NaOH is produced in the same manner When both emulsions are mixed under high-speed stirring, droplets of each emulsion would collide at random and coalesce, thereby precipitating chitosan droplets to give small size particles The method is schematically shown in Fig 2.4 Gadopentetic acid-loaded chitosan nanoparticles have been prepared by this method for gadolinium neutron-capture therapy Particle size depends upon the type of

chitosan, i.e., as the deacetylation degree of chitosan decreased, particle size

increased, but drug content decreased Particles produced using 100% deacetylated chitosan had the mean particle size of 452 nm with 45% drug loading Nanoparticles were obtained within the emulsion-droplet Size of the nanoparticle did not reflect the droplet size Since gadopentetic acid is a bivalent anionic compound, it interacts electrostatically with the amino groups of chitosan, which would not have occurred if a cross-linking agent is

used that blocks the free amino groups of chitosan Thus, it was possible to achieve higher gadopentetic acid loading by using the emulsion-droplet coalescence method compared to the simple emulsion cross-linking method.

Fig 2.4 Schematic representation of preparation of chitosan particulate system by emulsion-droplet coalescence method

2.2.5 Ionotropic gelation

The use of complexation between oppositively charged macromolecules to prepare chitosan microspheres has attracted much attention because the process is very simple and mild (Polk et al., 1994; Liu et al., 1997) In addition, reversible physical cross-linking by electrostatic interaction, instead

of chemical cross-linking, has been applied to avoid the possible toxicity of reagents and other undesirable effects Tripolyphosphate (TPP) is a polyanion, which can interact with the cationic chitosan by electrostatic forces (Kawashima et al., 1985a, b) After Bodmeier et al (1989) reported the preparation of TPP-chitosan complex by dropping chitosan droplets into

a TPP solution; many researchers have explored its potential pharmaceutical usage (Shiraishi et al., 1993; Sezer and Akbuğa, 1995; Aydin and Akbuğa, 1996; Calvo et al., 1997a, b; Shu and Zhu, 2000) In the ionotropic gelation method, chitosan is dissolved in aqueous acidic solution to obtain the cationic chitosan This solution is then added dropwise under constant stirring to polyanionic TPP solution Due to the complexation between oppositely charged species, chitosan undergoes ionic gelation and precipitates to form spherical particles The method is schematically represented in Fig 2.5 However, TPP/chitosan microparticles formed have poor mechanical strength thus, limiting their usage in drug delivery

Fig 2.5 Schematic representation of preparation of chitosan particulate systems by ionic gelation method

2.2.6 Reverse micellar method

Reverse micelles are thermodynamically stable liquid mixtures of water, oil and surfactant Macroscopically, they are homogeneous and isotropic, structured on a microscopic scale into aqueous and oil microdomains separated by surfactant-rich films One of the most important aspects of reverse micelle hosted systems is their dynamic behavior Nanoparticles prepared by conventional emulsion polymerization methods are not only large (>200 nm), but also have a broad size range Preparation of ultrafine polymeric nanoparticles with narrow size distribution could be achieved by using reverse micellar medium (Leong and Candau, 1982) Aqueous core of the reverse micellar droplets can be used as a nanoreactor to prepare such particles Since the size of the reverse micellar droplets usually lies between

1 and 10 nm (Maitra, 1984), and these droplets are highly nondispersed, preparation of drug-loaded nanoparticles in reverse micelles will produce extremely fine particles with a narrow size distribution Since micellar droplets are in Brownian motion, they undergo continuous coalescence followed by re-separation on a time-scale that varies between millisecond and microsecond (Luisi et al., 1988) The size, polydispersity and thermodynamic stability of these droplets are maintained in the system by a rapid dynamic equilibrium

In this method, the surfactant is dissolved in an organic solvent to prepare reverse micelles To this, aqueous solution of chitosan and drug are added with constant vortexing to avoid any turbidity The aqueous phase is regulated in such a way as to keep the entire mixture in an optically transparent microemulsion phase Additional amount of water may be added

to obtain nanoparticles of larger size To this transparent solution, a linking agent is added with constant stirring, and cross-linking is achieved by stirring overnight The maximum amount of drug that can be dissolved in reverse micelles varies from drug to drug and has to be determined by gradually increasing the amount of drug until the clear microemulsion is transformed into a translucent solution The organic solvent is then evaporated to obtain the transparent dry mass The material is dispersed in water and then adding a suitable salt precipitates the surfactant out The mixture is then subjected to centrifugation The supernatant solution is decanted, which contains the drug-loaded nanoparticles The aqueous dispersion is immediately dialyzed through dialysis membrane for about 1 h and the liquid is lyophilized to dry powder The method is schematically represented in Fig 2.6

cross-Fig 2.6 Schematic representation of preparation of chitosan particulate system by reverse micellar method

2.2.7 Sieving method

Recently, Agnihotri and Aminabhavi (2004) have developed a simple, yet novel method to produce chitosan microparticles In this method, microparticles were prepared by cross-linking chitosan to obtain a non-sticky glassy hydrogel followed by passing through a sieve as shown in Fig 2.7 A suitable quantity of chitosan was dissolved in 4% acetic acid solution to form

a thick jelly mass that was cross-linked by adding glutaraldehyde The sticky cross-linked mass was passed through a sieve with a suitable mesh size to get microparticles The microparticles were washed with 0.1 N NaOH solution to remove the un-reacted excess glutaldehyde and dried overnight in

non-an oven at 40 oC Clozapine was incorporated into chitosan before linking with entrapment efficiency up to 98.9% This method is devoid of tedious procedures, and can be scaled up easily Microparticles were irregular in shape, with the average particle sizes in the range of 543–698

cross-µm The in vitro release was extended up to 12 h, while the in vivo studies

indicated a slow release of clozapine

Fig 2.7 Schematic representation of preparation of chitosan particulate system by sieving method

2.3 Pharmaceutical applications of chitosan microspheres

2.3.1 Drug delivery to colon

The colon is a site for the administration of protein and peptides that are degraded by digestive enzymes in the upper gastrointestinal tract Along with many applications in local and systemic delivery of drugs, the colon-specific drug delivery systems can delay the absorption for the treatment of diseases that exhibit circadian rhythm, such as nocturnal asthma, angina and rheumatoid arthritis Chitosan for the oral administration to human has been recognized as safe by scientists (Lee et al., 2002), hence can be used as an absorption enhancer in solid oral dosage forms delivery of drugs that are either poorly absorbed or destroyed in gastrointestinal tract These may be introduced to the systemic circulation through the colonic absorption mod (Hejazi and Amiji, 2003) As chitosan is biodegradable by the colonic bacterial flora (Zhang et al., 2002), it is a promising polymer for colon drug delivery The effect of chitosan tripolyphosphate beads on the absorption of insulin was studied by measuring the decrease of the plasma glucose concentration and the relative pharmacological availability (Tozaki et al., 2002) Chitosan tripolyphosphate showed excellent association with insulin and improved the intestinal absorption of insulin to a great extent Chitosan succinate and chitosan phthalate loaded with sodium diclofenac (Aiedeh and

Taha, 1999) have been found to resist dissolution under acidic conditions and showed improved dissolution under basic conditions, suggesting their suitability for colon-specific drug delivery systems Chitosan-pectin complexes (Feranandez-Hervas and Fell, 1998) were also found to be suitable for colon-specific delivery of indomethacin and paracetamol Chitosan-alginate beads loaded with a model protein, bovine serum albumin, were investigated to explore the temporary protection of protein against acidic and enzymatic degradation during gastric passage During incubation

in gastric fluid (pH 1.2) and subsequently in intestinal fluid (pH 7.5), the beads were found to erode, burst, and release the protein (Anal et al., 2003) 5-Aminosalicylic acid, a cyclo-oxygenase inhibitor and an anti-inflammatory drug effective in Crohn’s disease and ulcerative-colitis, is rapidly absorbed from the small intestine Eudragit-coated chitosan microspheres (200 µm) have been developed by an emulsion-solvent evaporation technique based on

a multiple water/oil/water emulsion to deliver it specifically to the colon (Varshosaz et al., 2006) Also, for colon-specific delivery, mucoadhesive alginate-chitosan microspheres containing prednisolone have been prepared Depending on the preparation method, the particles displayed varying mucoadhesiveness (Wittaya-Areekul et al., 2006) Albendazole was also delivered specifically into the colon, in another study, by microspheres of chitosan hydrochloride, and drug release in 24 h was 48.9% and 76.5% in