Effect of Concentration of Gellan Gum and Calcium Chloride Solution on Entrapment Efficiency and Drug Release from Calcium Gellan Beads.

 

Patil SV*, Lade PD, Janugade BU, Babar SA and Ghewade YB

Department of Pharmaceutics, Shree Santkrupa College of Pharmacy, A/P Ghogaon, Tal. Karad, Dist. Satara. Maharashtra, 415111

*Corresponding Author E-mail: sachinpatil79@rediffmail.com.

ABSTRACT

Gellan gum has wide variety of applications, mainly concentrated in ophthalmic drug delivery and oral sustained release preparations. Due to the characteristic property of cation induced gelation, it has been widely used in the formulation at in situ gelling ophthalmic preparations. The objective of this study was to evaluate concentration dependant effect of gellan gum and calcium chloride solution on entrapment efficiency and drug release of diclofenac sodium through calcium-gellan beads by ionotropic gelation. Prepared beads were evaluated for percentage yield, percentage entrapment efficiency and drug release. It was found that as concentration of gellan gum increases entrapment efficiency increases and as concentration of calcium chloride increases entrapment efficiency decreases. Also as concentration of gellan gum increases drug release decreases and as concentration of calcium increases drug release increases.

 

KEYWORDS: Calcium-gellan beads, Deacetylated gellan gum, Ionotropic gelation.

 


INTRODUCTION:

Gellan gum is linear anionic polysaccharide produced by the microorganism pseudomanous elodea. 1, 2 There are two chemical forms of gellan gum, natural (high acyl) and deacetylated (low acyl) form. β-D-glucose, β-D-glucuronic acid and α-L-rhamnose residues in the molar ratio of 2:1:1. The native form contains two acyl substituents, namely acetate and glycerate, both of which are located on the same glucose residue and on average there is one glycerate, and a half acetate group per every tetrasaccharide repeating unit (Fig. 1a.).

 

In commercial gellan gum (deacetylated form) the acetyl groups are removed by alkaline treatment (Fig. 1b.). This difference in substitutions leads to a difference in the gelling potential and, therefore, microencapsulation efficiency of native and deacetylated forms. The native form produce soft, elastic and non-brittle gels, whereas the low acyl form produce strong, non-elastic and brittle gels under optimal gelling conditions.3 The presence of acetyl group or glycerate group does not interfere with double helix formation but does alter its ion binding ability. Gellan gum forms gels in presence of mono and divalent cations; However, its affinity for divalent cations such as Na++ and Mg++ is much stronger than monovalents such as Na+ and K+.4

 

Gellan gum has wide variety of applications, mainly concentrated in ophthalmic drug delivery and oral sustained release preparations.5, 6 Due to the characteristic property of cation induced gelation, it has been widely used in the formulation at in situ gelling ophthalmic preparations.7, 8 Gellan gum beads of propranolol were developed and it was found that drug release was rapid. However the ionotropic gelation of gellan gum offers new opportunities in the field of bioencapsulation.9 Also cross-linked calcium-gellan beads containing diclofenac sodium as model drug, using full 33 factorial design were studied. It showed that, drug: polymer ratio, pH of cross-linking solution and speed of agitation also influence the formation and properties of calcium-gellan beads.10 The objective of this study was to evaluate concentration dependant effect of gellan gum and calcium chloride solution on entrapment efficiency and drug release of diclofenac sodium as model drug from gellan gum beads by ionotropic gelation.

 

MATERIALS AND METHODS:

Materials:

Deacetylated Gellan gum, Kelcogel®, was obtained as gift sample from CP Kelco (Burzin and Leons, Pvt. Ltd.), Mumbai (India). Diclofenac sodium was obtained as gift sample from Emcure Pharmaceuticals Pvt. Ltd., Pune (India). Calcium chloride and potassium dihydrogen phosphate was purchased from Rajesh Chemicals, Mumbai (India). All other chemicals used were of analytical grade.

 

Methods:

Preparation of Beads

The beads were prepared by the method of ionotropic gelation and the quantities were as given in Table 1. Diclofenac sodium was dissolved in deionised water at 55°C. Gellan gum was added to this stirred solution at the same temperature until a uniform dispersion was obtained. The resultant homogeneous bubble-free slurry was added in calcium chloride solution using a disposable glass syringe as given in Fig. 1 and the mixture was stirred continuously for 15 min. The beads obtained were separated by filtration and washed with deionized water. Beads were dried at room temperature. All batches were prepared in triplicate. Bead size was determined manually by the method of microscopy.

 

Fig. 1a: Structure of native form of gellan gum.

 

Fig. 1b: Structure of deacetylated form of gellan gum.

 

Table 1: Formulation codes with quantities. GG: Gellan gum, DCL-Na: Diclofenac sodium.


GG                   

Dispersion

DCL- Na 

Calcium Chloride Solution

2 %

4 %

6 %

2 %

2 %

A1

A2

A3

2.5 %

2 %

B1

B2

B3

3 %

2 %

C1

C2

C3

 

Evaluation of Beads

Yield and Entrapment Efficiency

Beads prepared were weighed after drying, and percent yield was calculated using formula (1).            

 

Percentage Yield = (Actual weight x 100)/ Expected Weight        (1)

 

The entrapment efficiency within the beads was determined indirectly by determining the amount of nonencapsulated drug, by measuring concentration of diclofenac sodium in the preparation medium and in the washing solutions. The entrapment efficiency in preparation medium of calcium chloride was determined by analyzing spectrophotometrically (JASCO-V530, Japan) at 275 nm after suitable dilution of samples with respective bulk preparation medium. The entrapment efficiency (EE) was calculated according to the formula given below. EE = 1 - (Quantity of nonencapsulated drug / Quantity of added drug) × 100   (2)

 

Fig. 2: Schematic representation of beads preparation, GG: Gellan gum.

 

In-Vitro dissolution studies

In-Vitro dissolution studies were performed by using USP 26 type II dissolution test apparatus (Dolphin Mumbai, India). Dissolution medium used were phosphate buffer (pH 7.4), each 900 ml, temperature was maintained at 37 ± 2°C and 100 rpm stirring was provided for each dissolution study. Drug-loaded gellan gum beads equivalent to 100 mg of pure drug were used for each dissolution study. Samples were collected periodically and replaced with a fresh dissolution medium. After filtration through Whatman filter paper 41, concentration of diclofenac sodium was determined spectrophotometrically at 275 nm.

 

RESULTS AND DISCUSSION:

Preparation of beads:

Gellan gum beads were prepared by ionotropic gelation method. The gellan gum contains carbohydrate side groups in glucupyronosyl residues and hence it can be crosslinked by inducing ion gelation with cations.11 The ion interaction between the negatively charged gellan polymer and the positively charged divalent calcium was responsible for formation of beads. Commercially available deacetylated gellan gum is insoluble in cold water also the low level of divalent ions are present in it which inhibited the hydration2 so that during drop wise addition of the gellan gum dispersion in calcium chloride solution gellan gum solutions were preheated to 55°C for complete hydration.  . 

Determination of bead size:

Diameters of the dried beads were measured by optical microscopy. Dried calcium-gellan beads were spherical with rough surface as given in Fig. 3. Sizes of beads were as given in Table 2. Batch C2 was having highest size of 1.71 mm and batch A1 was having lowest size of 1.20 mm. It showed that as concentration of gellan gum increases bead size also increases. Concentration of calcium chloride solution has not been shown any effect on bead size.

 

Table 2: Bead size, percentage yield and percentage entrapment efficiency (EE) of Diclofenac sodium in Calcium-Gellan beads.

 

Formulation Code

Bead Size (mm)

Yield (%)

EE (%)

A1

1.20 ± 0.81

92 ± 2

80 ± 2.8

A2

1.21 ± 0.71

91 ± 1

76 ± 1.6

A3

1.22 ± 0.62

93 ± 1.5

72 ± 2.3

B1

1.42 ± 0.53

93 ± 2.5

86 ± 2.5

B2

1.41 ± 0.62

94 ± 1.5

78 ± 1.9

B3

1.41 ± 0.39

92 ± 2

74 ± 3.1

C1

1.69 ± 0.42

90 ± 1

92 ± 2.9

C2

1.71 ± 0.53

93 ± 1.5

86 ± 2.2

C3

1.69 ± 0.51

92 ± 1.5

78 ± 2.6

 

Fig 3: Photograph of calcium gellan beads with diclofenac sodium. (Batch A3)

 

Determination of Yield and Entrapment Efficiency:

The percentage yield and percentage entrapment efficiency of calcium gellan beads were as given in Table 2. Batch C1 was having highest and batch A3 was having lowest entrapment efficiency. It was found that entrapment efficiency was higher for 3% concentration of gellan gum and as concentration of gellan gum increases entrapment efficiency also increases. It may be due to increase in gel strength with gellan concentration.4 As concentration of calcium chloride increases entrapment efficiency decreases. It may be due to the reason that the gel strength decreases with linearly with increasing calcium ion concentration12 and excess calcium ion concentration has been shown to weaken the gel strength of gellan gum.13 Excess calcium ions might occupy anionic bonding site at gellan gum molecules thus preventing the formation of linkage between adjacent polymer chain. As a result repulsive forces in the junction zones may reduce the formation of linkages between aggregated helices leading to weaken gel structure.14 It has been also suggested that higher concentration at divalent calcium tends to prevent hydration of gellan gum and consequently increase hydration temperature. Thus calcium ion concentration increase gel strength decrease which leads to decrease in entrapment efficiency of diclofenac sodium in calcium-gellan beads.          

 

In-Vitro dissolution studies:

Drug release of diclofenac sodium through calcium-gellan beads were as given in Fig. 4. As concentration of gellan gum increases drug release decreases. It may be due to the reasons that gel strength increases with in concentration of gellan gum. Also at higher concentration of gellan, crosslinking increases, free volume of matrix was less which leads to decreases in early transport of drug through calcium-gellan beads. As concentration of calcium increases drug release increases. As already explained this may be due to decrease in gel strength of beads with increase in concentration of calcium ion which also leads to decrease in mechanical strength. Also as calcium ion concentration increases hydration temperature also increases so that hydration was incomplete which results in decrease in crosslinking of gellan.

 

Fig. 4: Percentage drug release of diclofenac sodium through calcium-gellan beads.

 

 


CONCLUSION:

Gellan gum beads were prepared by ionotropic gelation method. The ion interaction between the negatively charged gellan polymer and the positively charged divalent calcium was responsible for formation of beads. Prepared calcium-gellan beads were spherical with rough surface. It was found that concentration of gellan gum is directly proportional entrapment efficiency and inversely proportional to drug release. But concentration of calcium chloride is inversely proportional entrapment efficiency and directly proportional to drug release.

 

ACKNOWLEDGMENT:

The authors are thankful to CP Kelco (Burzin and Leons, Pvt. Ltd.) Mumbai (India) and Emcure Pharmaceuticals Pvt. Ltd., Pune (India) for providing free gift sample of Kelcogel® and diclofenac sodium, respectively. The authors are also thankful to Jadge D. R., I/C Principal, Shree Santkrupa College of pharmacy, Ghogaon for providing research facility.

 

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Received on 10.01.2009       Modified on 13.03.2009

Accepted on 18.04.2009      © RJPT All right reserved

Research J. Pharm. and Tech.2 (4): Oct.-Dec. 2009; Page 842-845