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International Journal of Biological Macromolecules journal homepage: www.elsevier.com/locate/ijbiomac
Alginate beads of Captopril using galactomannan containing Senna tora gum, guar gum and locust bean gum
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Harshal A. Pawar a,∗ , K.G. Lalitha b,1 , K. Ruckmani c,2 a b c
Ultra College of Pharmacy, 4/235 College Road, Thasildar Nagar, Madurai 625020, Tamil Nadu, India Department of Pharmaceutical Chemistry, Ultra College of Pharmacy, 4/235 College Road, Thasildar Nagar, Madurai 625020, Tamil Nadu, India Department of Pharmaceutical Technology, Bharathidasan Institute of Technology, Anna University, Tiruchirapalli 620024, Tamil Nadu, India
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Article history: Received 3 November 2014 Received in revised form 16 February 2015 Accepted 17 February 2015 Available online xxx
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Keywords: Galactomannan Guar gum Locust bean gum
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1. Introduction
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Gastro-retentive Captopril loaded alginate beads were prepared by an ionotropic gelation method using sodium alginate in combination with natural gums containing galactomannans (Senna tora seed gum, guar gum and locust bean gum) in the presence of calcium chloride. The process variables such as concentration of sodium alginate/natural polymer, concentration of calcium chloride, curing time, stirring speed and drying condition were optimized. Prepared beads were evaluated for various parameters such as flow property, drug content and entrapment efficiency, size and shape, and swelling index. Surface morphology of the beads was studied using scanning electron microscopy. In vitro mucoadhesion and in vitro drug release studies were carried out on the prepared beads. From the entrapment efficiency and dissolution study, it was concluded that galactomannans in combination with sodium alginate show sustained release property. The bead formulation F4 prepared using combination of sodium alginate and guar gums in the ratio 2:1 showed satisfactory sustained release for 12 h. The release of Captopril from the prepared beads was found to be controlled by the swelling of the polymer followed by drug diffusion through the swelled polymer and slow erosion of the beads. © 2015 Published by Elsevier B.V.
Gastro-retentive drug delivery system (GRDDS) is a new approach for the drugs that are degraded by the alkaline pH or that are less soluble in the gastrointestinal tract (GIT) or are absorbed from the proximal part of the GIT [1,2]. GRDDS is thus advantageous for such drugs by improving their bioavailability, therapeutic efficacy and by possible reduction of dose [3]. Bioadhesive polymers have been extensively used in the last decade to improve the performance of GRDDS [4]. Mucoadhesive drug delivery system is a type of gastro-retentive system that has achieved substantial attention now a day due to their capability to adhere the mucus layer and release the drug in a sustained manner. By using these dosage forms, the intimate contact time at the mucus surface would increase, thus resulting in an improved drug retention time and drug concentration in the local sites. This would lead to an improved
∗ Corresponding author. Tel.: +91 8097148638. E-mail addresses: [email protected] (H.A. Pawar), [email protected] (K.G. Lalitha), [email protected] (K. Ruckmani). 1 Tel.: +91 9894893301. 2 Tel.: +91 9842484568.
therapeutic effect for the local diseases [5,6]. Mucoadhesive drug delivery systems offer several advantages over other oral sustained release drug delivery systems by virtue of prolongation of residence time of drug in GIT, and targeting and localization of the dosage form at a specific site [7]. Mucoadhesive polymers are able to interact with mucus glycoproteins (mucins), which are responsible for gel-type characteristics of the mucus and thereby increases the contact time with the mucosal tissue and also drug permeability across epithelial barriers [8,9]. Captopril belongs to the class angiotensin converting enzyme inhibitor (ACE inhibitor). The drug is freely soluble and has elimination half life after an oral dose of 1.7–2 h. It is stable at pH 1.2 and as pH increases, the drug becomes unstable and undergoes a degradation reaction [10]. It affects the renin angiotensin system and inhibits the conversion of relatively inactive angiotensin-I to active angiotensin-II [11]. Captopril, an antihypertensive agent, has been used widely for the treatment of hypertension and congestive heart failure. However, the duration of anti-hypertensive action after a single oral dose of Captopril is only 6–8 h, so clinical use requires a daily dose of 37.5–75 mg to be taken three times. Thus a sustained and control release dosage form of Captopril is desirable [12]. Captopril belongs to the class III of BCS (biopharmaceutical classification of system), exhibiting high solubility and low
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permeability. Hence, enhanced gastric retention time of Captopril sustained release dosage form will increase its absorption. Captopril has site specific absorption from GIT and also it is unstable in the alkaline pH of the intestine, where as stable in acidic pH and specifically absorbed from stomach. Based on the above reasons there is a clear need to localize the developed formulation at the target area of the GIT. Therefore, Captopril was selected as suitable drugs for designing gastroretentive/sustained drug delivery system with a view to improve its oral bioavailability. Seed galactomannans are vegetable, heterogeneous polysaccharides widely distributed in nature. Galactomannans are polysaccharides built up of a -(1-4)-d-mannan backbone with single d-galactose branches linked ␣-(1-6). Because of their water absorption, swelling and gel forming ability, galactomannas are ideal polymeric matrix for mucoadhesive sustained release formulations. The present research work was aimed at developing and evaluating oral mucoadhesive multiparticulate drug delivery system of Captopril using galactomannans [Senna tora seed gum, guar gum and locust bean gum]. Mucoadhesive beads were prepared by ionotropic gelation technique using sodium alginate. The mixing of alginate with other polymers has an influence on the pore size and network complexity. It has also been reported that alginates when mixed with neutral gums improve its performance as drug carrier system. Considering this, galactomannans, a group of neutral polysaccharides (gum) obtained from seeds of S. tora, Cyamopsis tetragonoloba (guar gum) and Ceratonia siliqua (locust bean gum) have been selected in the present study [13].
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2. Materials and methods
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2.1. Materials
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The dried pods of S. tora were collected from Kalyan taluka (district – Thane, Maharashtra) and the seeds were manually separated. Plant was authenticated by Dr. Rajendra D. Shinde, Associate Professor, Blatter Herbarium; St. Xavier’s College, Mumbai and was identified as S. tora (L.) Roxb (Herbarium Specimen No. 8361). Captopril was obtained as a gift sample from Kwality Pharmaceuticals, Amritsar (India). Sodium alginate was obtained from Signet Chemicals, Japan. Guar gum SD Fine Chemicals Limited, Mumbai, India. Locust bean gum was purchased from Research Lab Fine Chem Industries, Mumbai, India. All chemicals and reagents used were of analytical grade.
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2.2. Isolation and purification of S. tora seed gum
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The dried seeds were subjected to mechanical treatment to separate endosperm from husk and germs followed by milling and screening of the endosperm. The gum was isolated from endosperm using method reported in literature. The obtained crude gum was dissolved in warm water, re-precipitated using ethanol (1:1), dried at 40 ◦ C, powdered and stored in airtight container at room temperature. The process of dissolution in water and precipitation with alcohol was repeated until an almost white precipitate was obtained. The dried polysaccharide was milled and sifted with a 60 mesh for further use [13]. 2.3. Formulation and evaluation of sustained release alginate bead 2.3.1. Preformulation study by Fourier transforms infrared (FTIR) spectroscopy FTIT studies were performed on the drug, physical mixture of drug with individual natural polymer at 1:1 ratio (S. tora gum, guar gum, locust bean gum and sodium alginate) and optimized
formulation using FTIR (FT-IR spectrophotometer Affinity 1, Shimadzu, Japan). The samples were analyzed in the region of 4000 and 400 cm−1 . The procedure consisted of dispersing a sample in excess of potassium bromide (KBr) nearly at the ratio 1:100, mixed well and pellets were prepared for IR analysis. 2.3.2. Preparation of alginate beads An orifice ionic gelation process was used to prepare large sized alginate beads [14]. Sodium alginate and polymers were dissolved in distilled water (30 mL) to form a homogeneous polymer solution; core material (Captopril) was added to the polymer solution and mixed thoroughly to form a smooth viscous dispersion. The resulting dispersion was then added drop wise via an 18-gauge hypodermic needle fitted with a 10 mL glass-syringe into a 40 mL of calcium chloride solution contained in a beaker with stirring at 400 RPM using a mechanical stirrer. Stirring was continued for 30 min to complete the curing reaction and to produce spherical beads. Mixture was then filtered and the product thus separated was washed repeatedly with water and dried at 50 ◦ C for 24 h. The prepared beads were stored in a desiccator until further use. The yields of prepared beads of various formulations were calculated using the weight of final product after drying with respect to the initial total weight of the drug and polymer used for preparation of beads, and percent production yields were calculated as per the formula mentioned below: Production yield (%) =
amount of dried beads amount of drug + amount of polymer
Trial batches (F1–F3) were prepared using sodium alginate alone to optimize the process parameters and concentration of sodium alginate for formation of beads. Various batches of alginate beads containing Captopril (F4–F12) were prepared, by employing sodium alginate in combination with individual galactomannan (S. tora gum, guar gum and locust bean gum) at different concentrations. The composition of various batches (F1–F12) of alginate beads prepared is shown in Table 1. 2.3.3. Optimization of process parameters The following process variables were investigated, centration of sodium alginate, concentration of calcium curing time, stirring speed and drying condition. The batches produced were analyzed for size, shape, ease of tion, drug content and drug release.
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i.e. conchloride, different prepara-
2.3.3.1. Concentration of sodium alginate. To find out the optimum concentration of sodium alginate required for the formation of beads, the different batches of beads were prepared using 1–4% concentration of sodium alginate (polymer concentration). The concentration of calcium chloride, stirring time and speed of the stirrer was kept constant. The formed beads were evaluated for their actual drug content, entrapment efficiency and in vitro dissolution studies. 2.3.3.2. Concentration of calcium chloride. In order to study the effect of concentration of calcium chloride (CaCl2 ) on the beads, different concentrations of CaCl2 (5%, 10% and 15%, w/v) were used to prepare beads. The parameters such as concentration of drug, polymer (sodium alginate), stirring time and speed of the stirrer were kept constant. The formed beads were evaluated for their actual drug content, entrapment efficiency and in vitro dissolution studies. 2.3.3.3. Stirring speed and stirring time. To fix stirring speed, various trials were taken at 200, 300, 400, 500 and 600 revolutions per minute (RPM). Resultant beads were examined visually. To
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Table 1 Composition of different formulations of Captopril alginate beads. Formulation code
Drug (mg)
Polymer concentration (%)
Sodium alginate
Senna tora gum
Locust bean gum
Guar gum
Quantity in mg per batch Beads using sodium alginate alone (trial batches) 600 2 F1 600 3 F2 600 4 F3 Beads using sodium alginate and individual galactomannan in combination F4 600 3 600 3 F5 600 3 F6 600 3 F7 600 3 F8 F9 600 3 F10 600 3 F11 600 3 600 3 F12
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optimize stirring time the trial batches were taken with different stirring times – 15 min, 30 min, 45 min and 1 h. It was found that the optimum concentration of sodium alginate [2–3%], calcium chloride [10%], cross-linking time [30 min], and stirring speed – 400 RPM could influence the beads size, average diameter, recovery, entrapment efficiency, size distribution swelling behavior and the release characteristics. Different batches [F4–F12] of alginate beads were then prepared by using the optimized process variables. The total polymer concentration was kept constant and the ratio of sodium alginate:polymer (S. tora gum, guar gum and locust bean gum) was varied. The final formulations were subjected to several characterization studies. 2.3.4. Evaluation of beads The developed sustained release mucoadhesive beads were evaluated for various parameters like size and shape analysis, drug content, entrapment efficiency, drug release, in vitro wash off test for mucoadhesion, swelling and micrometric properties. The shape and surface characteristics were determined by scanning electron microscopy.
600 900 1200
– – –
– – –
– – –
600 700 800 600 700 800 600 700 800
– – – – – – 300 200 100
– – – 300 200 100 – – –
300 200 100 – – – – – –
2.3.4.3. Bulk density and tapped density. To calculate the bulk density and tapped density, the beads were weighed, and transferred to a measuring cylinder. The volume occupied by beads was noted as bulk volume and the cylinder was tapped until the constant volume was achieved, and this was noted as tapped volume. The values of bulk density and tapped density were calculated by using following equations: Bulk density =
weight of powder volume of the packing
Tapped density =
2.3.4.4. Hausner’s ratio and Carr’s compressibility index. The Hausner’s ratio and Carr’s compressibility index were determined from the value of bulk density and tapped density using following formulae. Hausne’s ratio =
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2.3.4.1. Flow properties of beads. Following parameters were evaluated to study the flow properties and compressibility of beads [15,16]. 2.3.4.2. Angle of repose. Angle of repose is a measure to determine the flow ability of the powder or granules. The fixed funnel free standing cone method was used to determine angle of repose. Beads were passed through fixed funnel to make a heap of the predetermined height. The angle made by heap with that of base was determined. The angle of repose of the beads was determined by fixed funnel free standing cone method using the following formula. = tan−1
h r
where “h” is height between the lower tip of funnel and the base of heap of beads, and “r” is radius of the base of heap formed. Relationship between angle of repose () and flow ability is represented in Table 2. Table 2 Relationship between angle of repose () and flow ability. Angle of repose ()
Flow ability
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Excellent Good Passable Very poor
weight of powder volume of the packing
tapped density bulk density
Car’s compressibility index =
tapped density − bulk density × 100 bulk density
The values within range 5–15% of Carr’s index and values less than 1.25 of Hausner’s ratio showed good compressibility of the sample. 2.3.4.5. Actual drug content and entrapment efficiency. Drug content estimation was done by stirring 20 mg beads in sodium citrate solution (1%, w/v) until complete dissolution occurs. Methanol was added to the sodium citrate solution to gel the dissolved calcium alginate and further solubilize Captopril. This solution was then filtered to get the drug solution. The filtrate was then suitably diluted with 0.01 N hydrochloric acid, and absorbance was taken at 205 nm [17]. All the measurements were done in triplicate. The actual drug content and entrapment efficiency were calact × culated using following formulae.Actual drug content (%) = M Mms 100 Entrapment efficiency (%) =
Mact × 100 Mthe
where Mact is the actual drug content in weighed quantity of beads, Mms is the weighed quantity of dried beads and Mthe is the theoretical amount of drug in beads calculated from the quantity added in the process.
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Fig. 1. FTIR spectrum of Captopril.
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2.3.4.6. Size and shape of the bead. The diameter of the bead was determined by screw gauge. For this purpose, ten dried beads were randomly selected from each batch, and the mean diameter was determined by screw gauge. The least count of screw gauge was 0.005 mm. The sphericity was observed by the microscope. 2.3.5. Swelling index Beads were studied for swelling characteristics. Samples from drug-loaded beads were taken, weighed and placed in the wire basket of USP dissolution apparatus-I. The basket containing beads was put in a beaker containing 100 mL of 0.01 N HCl maintained at 37 ◦ C. The beads were periodically removed at predetermined intervals and weighed. Then the swelling ratio was calculated as per the following formula [18–20]. Swelling ratio =
weight of wet beads weight of dried bead
2.3.6. In vitro test for mucoadhesion Mucoadhesion of the beads was evaluated by an in vitro adhesion testing method, known as wash off method. The pieces of goat intestinal mucosa (2 cm × 2 cm) were tied on glass slides (3 inch × 1 inch) by rubber band. About 50 beads were counted and spread over the wet rinsed tissue specimen and wait for 10 min and immediately thereafter, the supports were hung on the arm of a USP tablet disintegrating test machine. By operating the disintegration machine, the tissue specimen was given slow regular up and down movement in the 1 L vessel containing 0.01 N HCl at 37 ± 2 ◦ C. At the end of each hour, the machine was stopped and number of beads still adhering on the tissue were counted [21,22]. This procedure was carried out for 12 h. From the unbound beads, the numbers of adhered beads were calculated and adhering % was calculated after each interval of time. number of adhered bead % Mucoadhesion = × 100 total number of applied beads
2.3.7. Scanning electron microscopy (SEM) Scanning electron microscopy (SEM) is an electron optical imaging technique that provides photographic images and elemental information. SEM is useful for characterizing the morphology and size of microscopic specimens with particle size as low as nanometer. It is used to determine particle size distribution, surface topography, texture and examine the morphology of fractured or sectioned surface. Prepared beads were coated with gold–palladium under an argon atmosphere at room temperature and then beads were examined with SEM operating at 15 kV. 2.3.8. In vitro drug release studies The drug-loaded beads equivalent to 50 mg of Captopril were filled in the empty hard gelatin capsule shells. A calibrated dissolution apparatus (USP I) was used with baskets at 50 RPM and bath temperature maintained at 37 ± 0.5 ◦ C. Nine hundred milliliter freshly prepared and degassed 0.01 N HCl solution was used as the dissolution medium. Dissolution samples were collected immediately at the end of 1 h, 2 h, 4 h, 6 h, 8 h, 10 h and 12 h. At each time point; a 5 mL sample was removed from each vessel and filtered through a nylon filter (0.45 m, 25 mm) into labeled glass tubes and analyzed spectrophotometrically at 205 nm after appropriate dilutions. Drug concentrations in the sample were determined from the standard calibration curve [23,24]. 2.3.9. Mathematical modeling of kinetic release The in vitro release data was subjected to zero order, first order, Higuchi, Korsemeyer–Peppas and Hixson Crowell mathematical model in order to establish the drug release mechanism and kinetics of drug release from beads [25–29]. 2.3.10. Accelerated stability studies The optimized formulation was weighed in two sets and wrapped in a butter paper and placed in petri-dishes. These containers were stored at room temperature (27 ± 2 ◦ C) and at an elevated temperature (40 ± 2 ◦ C) for a period of six months according to ICH guidelines. Then beads were withdrawn at the different time intervals of one month, two month, three months and at the
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Fig. 2. FTIR spectrum of physical mixture of Captopril and sodium alginate (1:1).
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end of six months and analyzed for physical changes (such as color and texture), size, actual drug content and in vitro drug release.
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3. Result and discussion
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3.1. Isolation and purification of S. tora seed gum
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The isolated gum from S. tora seeds was an amorphous free flowing powder with dull brown color. 3.2. Preformulation study by Fourier transforms infrared (FTIR) spectroscopy The identification of drug was confirmed by comparing IR spectrum of drug with reported spectrum of Captopril. The FTIR spectrum of Captopril (Fig. 1) showed characteristic bands similar to that of reported in literature [30]. FTIR of Captopril, its physical mixture with natural polymer and optimized formulation exhibited the peak for Captopril at similar places (Figs. 2–6). This indicated that there was no interaction between the Captopril and excipient. 3.3. Formulation development and optimization of process parameter’s Formulations of Captopril sustained release mucoadhesive bead were prepared by using sodium alginate as core coating polymer, as alginate is easily gelled by the addition of Ca2+ . An aqueous insoluble calcium alginate gel was formed by cation exchange between Na+ and Ca2+ . The gelation and cross linking was due to the stacking of the guluronic acid-G blocks of alginate chains with the formation of egg-box junction. Literature survey revealed that seed polysaccharides such as guar gum, locust bean gum, tamarind seed polysaccharide, fenugreek seed mucilage, etc. have been used as a drug delivery carrier along with sodium alginate in the development of mucoadhesive hydrogel beads, which modifies the network complexity and drug release performance [31–39]. An orifice-ionic gelation process was used to prepare Captopril encapsulated beads, employing sodium alginate in combination
with three individual galactomannan containing natural polysaccharides (S. tora gum, guar gum and locust bean gum) in the different ratios. Stirring speed of more than or equal to 500 RPM causes formation of threading or oval shaped beads. At stirring speed of less than 300 RPM, sticking of beads was observed. At 400 RPM spherical and uniform sized beads were obtained. Thus 400 RPM was decided as the optimum speed in this study. The curing time was optimized to 30 min to avoid surface deposition of leached drug. At low curing time, the beads obtained were soft. The slow release from beads prepared at medium curing time confirms the drug release by diffusion from a strong and thick hydrated gel. It was observed that actual drug content and entrapment efficiency (%) was improved with increasing CaCl2 concentration in cross-linking solutions, due to the high degree of cross-linking by the concentrated calcium ions. The beads prepared using lower CaCl2 concentration might have larger pores due to insufficient cross-linking, and drug leaching may occur through the pores that may result in lower drug encapsulation. However, the higher calcium chloride concentration influenced the formation of smaller beads because of shrinkage and showed an increased angle of repose. The drug entrapment efficiency was improved progressively with increasing concentration of sodium alginate resulting in entrapping the greater amount of the drug. This may be attributed to the greater availability of active calcium binding sites in the polymeric chains and, consequently, the greater degree of cross-linking as the amount of sodium alginate increased. On the other hands, further increase in the concentration of calcium chloride above (10%, w/v) did not enhance the drug loading. This could be due to possible saturation of calcium binding sites in the guluronic acid chain, preventing further Ca2+ ions entrapment and, hence, cross-linking was not altered with higher concentration of calcium chloride solution. Optimized process variables are represented in Table 3. Different batches [F4–F12] of alginate beads and individual galactomannan combinations were then prepared by using the optimized process variables. The total polymer concentration was kept constant and the ratio of sodium alginate:polymer (S. tora
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Fig. 3. FTIR spectrum of physical mixture of Captopril and locust bean gum (1:1).
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gum, guar gum and locust bean gum) was varied. The final formulations were subjected to several characterization studies. The representative photograph of wet and dry beads is shown in Fig. 7.
high viscous polymer dispersion which may be lost during manufacturing process. Further observation, while increasing in the concentration of calcium chloride and long curing time slightly increased the percent of yield.
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3.4. Determination of production yield (%) 3.5. Evaluation of beads
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In the preparation of the beads the production yields of the batches are ranging from 79.78 ± 0.95 to 92.11 ± 0.89 as shown in Table 4. It was observed that increasing the concentration of S. tora gum, guar gum and locust bean gum in the formulation significantly lowers the product yield, due to the formation of
3.5.1. Bead size and shape analysis The average diameters of different batches of bead are reported in Table 5. Results indicated that the bead size increases with increase in the concentration of polymer. The color of the beads
Fig. 4. FTIR spectrum of physical mixture of Captopril and guar gum (1:1).
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Fig. 5. FTIR spectrum of physical mixture of Captopril and Senna tora gum (1:1).
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was varied with gum used. All beads obtained per batch were found to be uniform in size. Beads were found to be discrete, large, and spherical, free flowing, monolithic matrix with smooth surfaces. 3.5.2. Flow properties The micrometric parameters like angle of repose, bulk density and tapped density confirms better flow and packaging properties of the beads. All the formulations showed excellent flow ability in terms of angle of repose. The sodium alginate concentration has a significant positive effect on the angle of repose. Particle size increased with increase in the concentration of S. tora gum, guar gum and locust bean gum which in turn resulted in decreased
angle of repose. Bulk and tapped density of the beads were in acceptable range indicated that the beads have good pack ability. The density of the beads increases as the concentration of the S. tora gum, guar gum and locust bean gum increases which suggests that the beads formed at high polymer concentration are more compact and less porous than those prepared with sodium alginate alone. Carr’s index and Hausner’s ratio of the formulated beads showed excellent compressibility and good flow properties suggesting that the beads can be easily handled during processing. The result of rheological parameters like angle of repose, bulk density and tapped density of all the prepared beads is shown in Table 6.
Fig. 6. FTIR spectrum of Captopril beads (optimized formulation).
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Fig. 7. Photographs of (A) beads before drying and (B) beads after drying.
Table 3 Optimized process variables.
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Process variable parameters
Optimized data
Concentration of sodium alginate Calcium chloride concentration Bore diameter of the needle Stirring speed Stirring time Drying time and temperature
2–3% 10%, w/v, solution 18 gauge 400 RPM 30 min after addition 50 ◦ C for 24 h
From the various parameters studied for the flow ability and compressibility of the beads, values for angle of repose indicated good flow properties of beads and this was further supported by compressibility index and Hausner’s ratio.
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3.5.3. Determination of actual drug content and entrapment efficiency The drug entrapment efficiencies increased progressively with increasing the concentration of sodium alginate resulting in entrapping the greater amount of the drug. This may be attributed to the greater availability of active calcium binding sites in the polymeric chains and, consequently, the greater degree of cross-linking as the amount of sodium alginate increased. Addition of co-polymer (galactomannans) to sodium alginate also showed positive effect on entrapment. As the co-polymer concentration increased, entrapment efficiency was increased due to increase in viscosity of solution. The results of actual drug content and entrapment efficiency of all formulations are shown in Table 7. From the below reported table, formulation batch F4 showed maximum actual drug content (18.64 mg) and maximum entrapment efficiency (93.2%).
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3.6. Swelling studies
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The swelling behavior indicates the rate at which the formulation absorbs water from dissolution medium and swells. Swelling behavior of the prepared formulations is summarized in Fig. 8.
Fig. 8. (A) Swelling study of Captopril beads [F1–F6] and (B) swelling study of Captopril beads [F7–F12].
Swelling index was increased with increase in co-polymer concentration. The maximum swelling up to 1.85 w/w was observed within 5 h in 0.01 N HCl followed by gradual reduction in weight in the next hours as shown in Fig. 8. This effect might be owing to
Table 4 Production yield of different batches of beads. Sr. no.
Batch code
Production yielda (%)
1 2 3 4 5 6
F1 F2 F3 F4 F5 F6
92.11 86.26 79.78 82.48 85.67 89.94
a
± ± ± ± ± ±
0.89 0.71 0.95 0.49 0.88 0.93
Sr. no.
Batch code
Production yielda (%)
7 8 9 10 11 12
F7 F8 F9 F10 F11 F12
80.29 83.33 88.02 81.72 84.61 88.55
± ± ± ± ± ±
0.76 0.45 0.94 0.82 0.69 0.81
Each value is average of three separate determinations ± standard deviation (SD).
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Table 5 Bead size analysis of beads batches F1–F12. Sr. no.
Batch code
Mean bead size (mm)a
1 2 3 4 5 6
F1 F2 F3 F4 F5 F6
1.03 1.28 1.72 1.51 1.42 1.36
a
± ± ± ± ± ±
0.01 0.01 0.02 0.03 0.01 0.03
Sr. no.
Batch code
Mean bead size (mm)a
7 8 9 10 11 12
F7 F8 F9 F10 F11 F12
1.29 1.20 1.12 1.37 1.31 1.24
± ± ± ± ± ±
0.02 0.01 0.01 0.02 0.04 0.03
Each value is average of ten separate determinations ± SD.
Table 6 Various parameters showing flow properties of different batches of beads (F1–F12). Batch code
Bulk densitya
F1 F2 F3 F4 F5 F6 F7 F8 F9 F10 F11 F12
0.487 0.499 0.541 0.573 0.566 0.548 0.592 0.581 0.553 0.585 0.561 0.556
a
450 451 452 453 454 455 456
457
± ± ± ± ± ± ± ± ± ± ± ±
Tapped densitya
0.034 0.030 0.028 0.021 0.017 0.032 0.022 0.011 0.031 0.027 0.036 0.014
0.545 0.572 0.642 0.642 0.648 0.656 0.655 0.675 0.687 0.651 0.641 0.666
± ± ± ± ± ± ± ± ± ± ± ±
0.018 0.027 0.015 0.021 0.029 0.013 0.023 0.033 0.027 0.017 0.011 0.035
Hausner’s ratio
Carr’s index
Angle of repose ()
1.12 1.15 1.19 1.12 1.14 1.20 1.11 1.16 1.24 1.11 1.14 1.20
10.64 12.76 15.73 10.75 12.65 16.46 9.62 13.93 19.51 10.14 12.48 16.52
18.97 15.74 11.86 12.37 14.23 17.29 12.12 14.22 16.32 11.05 13.51 16.77
Each value is average of three separate determinations ± SD.
the acid solubility of drug that might have influenced the swelling behavior of the beads; otherwise the acid gels of sodium alginate are resistance to erosion. Maximum swelling was observed in the bead formulation F4 containing sodium alginate and guar gum in the ratio 2:1. This indicated that the swelling of the beads will help to retard release the drug successfully in the suitable environment of the stomach.
3.8. Scanning electron microscopy (SEM)
471
The SEM photomicrographs of beads prepared using sodium alginate alone and in combination with different galactomannan are depicted in Fig. 10. Beads showed morphological regularity due with dense good spherical geometry. The formation of thick coat on outer surface of the sodium alginate beads indicated complete entrapment of drug into interior polymer network.
459 460 461 462 463 464 465 466 467 468 469 470
473 474 475 476 477
3.7. In vitro test for mucoadhesion 3.9. In vitro release of beads
458
472
Mucoadhesive property was evaluated for all the formulated beads. It was observed that as the concentration of polymer decreased, mucoadhesion of beads also decreased. It is graphically presented in Fig. 9. All the galactomannan containing formulations showed good mucoadhesion as compared to plain sodium alginate beads. Mucoadhesion of alginate–guar gum combination was found to be moderately high; this may be due to significant mucus gel strengthening, which results in formation of stable mucoadhesive joint. Hence the large force was required to detach the beads from the mucosal surface. Mucoadhesion of locust bean gum loaded alginate beads was found to be poor when compared to alginate–guar gum and alginate–S. tora gum, this may due to their low viscosity and swelling capacity.
478
The % cumulative drug release from batches F1–F12 is represented in Fig. 11. The results clearly indicated that the rate of drug release decreased with the increase in thickness, because the drug cannot diffuse through the pore of the alginate gel matrix, which has not been swollen. In the dissolution study, burst effect was observed for all the batches. The drug release from all the formulations shows a biphasic release profile i.e. the initial rapid release (burst effect) was followed by sustained release as all the formulations deals with hydrophilic polymer and water soluble drug. This sustained release was due to the shrinkage property of alginate in the acid
Table 7 Actual drug content and entrapment efficiency of beads batches (F1–F12). Batch code
Actual drug contenta (mg)
F1 F2 F3 F4 F5 F6 F7 F8 F9 F10 F11 F12
13.27 15.62 17.11 18.64 17.12 16.42 16.98 14.36 13.88 17.85 16.57 14.13
a
± ± ± ± ± ± ± ± ± ± ± ±
0.05 0.08 0.10 0.31 0.16 0.19 0.47 0.27 0.11 0.24 0.14 0.08
Theoretical drug content (mg)
Entrapment efficiency (%)
20 20 20 20 20 20 20 20 20 20 20 20
66.35 78.1 85.55 93.2 85.6 82.1 84.9 71.8 69.4 89.25 82.85 70.65
Each value is average of three separate determinations ± SD.
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Fig. 9. (A) Mucoadhesion study of Captopril beads [F1–F6] and (B) mucoadhesion study of Captopril beads [F7–F12].
Fig. 11. (A) In vitro drug release profile of beads F1–F6 and (B) in vitro drug release profile of beads F7–F12.
media as well as due to the combination of sodium alginate and co-polymer in these formulations which swells in the acidic pH and forms a thick viscous layer through which drug diffuses resulting in slow release of drug. Formulation F1–F3 containing only sodium
alginate showed the complete release of drug in 4–8 h with more than 30% drug release in first hour. The addition of co-polymer controls initial rapid release and further control drug release in sustained manner. In acidic medium, the swelling and drug
Fig. 10. SEM photograph of drug-loaded beads prepared using (A) sodium alginate alone, (B) sodium alginate and guar gum, (C) sodium alginate and Senna tora gum and (D) sodium alginate and locust bean gum.
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Fig. 12. (A) Zero order release profile, (B) first order release profile, (C) Higuchi release profile and (D) Korsmeyer–Peppa’s release profile and (E) Hixson Crowell release profile of optimized formulation of Captopril beads (F4).
499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519
release properties were influenced by drug solubility and not by gel properties of calcium alginate. Calcium alginate is insensitive to acidic solution; it does swell to some extent and thus provides slow release of the embedded drug. The batch F7 containing sodium alginate and locust bean gum in the ratio 2:1 showed the complete drug release in 8 h. The batch F10 containing sodium alginate and S. tora gum in the ratio 2:1 showed the complete drug release in 10 h. From the entrapment and dissolution study, it was concluded that almost all the polymers shown sustained release property but the bead formulation F4 prepared using combination of sodium alginate and guar gums in the ratio 2:1 showed the satisfactory sustained release for 12 h. The alginate–guar gum beads showed the better sustained release as compared to all other alginate polymer combinations. Thus, the drug release followed the rank order of using alone sodium alginate and in combination with co-polymers as sodium alginate > sodium alginate–locust bean gum > sodium alginate–S. tora gum > sodium alginate–guar gum. The regression coefficient values of different release kinetic equations evaluated from the dissolution profile of developed formulations for Captopril beads are compared.
Among all the prepared formulations, formulation F4 showed satisfactory release of 12 h with highest correlation value (r2 ) of 0.9912 for the zero order kinetic model. The value of n as estimated by linear regression of log Mt/M∞ versus log t of formulation F4 was 0.5626 which indicates the drug release mechanism from matrix tablets involving a combination of both diffusion and chain relaxation mechanisms. Therefore, the release of Captopril from the prepared bead is controlled by the swelling of the polymer followed by drug diffusion through the swelled polymer and slow erosion of the beads. The kinetic release of optimized formulation (F4) using the different kinetic models is depicted in Fig. 12.
3.10. Accelerated stability data The results of stability study are summarized in Table 8. The physical appearance, size, actual drug content and dissolution profile of beads was not affected significantly during stability study. The results indicated that the optimized formulations F4 is stable for 6 months at 40 ± 2 ◦ C and 75 ± 5% RH.
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520 521 522 523 524 525 526 527 528 529 530 531
532
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Pale yellow, spherical 1.48 ± 0.03 18.04 ± 0.72 89.90 Pale yellow, spherical 1.48 ± 0.05 18.32 ± 0.28 91.39
Pale yellow, spherical 1.51 ± 0.05 18.45 ± 0.47 92.99
The development of sustained release beads with acceptable physicochemical and in vitro drug release justifies the application of used technique in the development of multiparticulate sustained drug delivery. The objective of the present work was achieved i.e. successful formulation development of gastro-retentive mucoadhesive alginate beads of Captopril with galactomannan. Certainly these findings can be applied for sustained delivery of drugs with mucoadhesion. Further these findings help the industry to scale up the commercial production. S. tora gum, guar gum and locust bean gum (natural polymers) were found to be significantly affects mechanical properties, decreases porosity and sustained drug release due to its swelling properties. Therefore, one can assume that the galactomannans (such as S. tora gum, guar gum and locust bean gum) are promising natural biopolymers used in pharmaceutical dosage forms by providing sustained release drug delivery systems and avoiding the dose related side effects. In combination with sodium alginate, guar gum shows better sustaining property as compared to other two galactomannan containing gums i.e. S. tora gum and locust bean gum.
Pale yellow, spherical 1.50 ± 0.03 18.61 ± 0.41 93.85
Controla Controla
3 Month
Acceleratedb
6 Month
Acceleratedb
4. Conclusion
Conflict of interest
Pale yellow, spherical 1.49 ± 0.03 18.40 ± 0.39 93.81
Acknowledgement
Pale yellow, spherical 1.49 ± 0.02 18.70 ± 0.19 94.79
The authors are thankful to Ultra College of Pharmacy, Madurai, for providing the laboratory facilities to carry out the present investigation. References
c
a
b
Bead size (mm) Actual drug content (mg) F2 valuec (similarity factor)
Samples were stored 27 ± 2 ◦ C and 45 ± 5% RH. Samples were stored 40 ± 2 ◦ C and 75 ± 5% RH. F2 values of 50–100 indicate similarity between the dissolution profiles.
Pale yellow, spherical 1.50 ± 0.04 18.49 ± 0.29 95.01 Pale yellow, spherical 1.50 ± 0.06 18.55 ± 0.34 95.72 Pale yellow, spherical 1.51 ± 0.03 18.64 ± 0.51 – Physical appearance
Controla Acceleratedb Controla
1 Month Initials Parameter
Table 8 Tablet properties of the developed Captopril beads (F4) after storage in stability studies.
2 Month
Acceleratedb
The authors declare that there is no conflict of interests regarding the publication of this article.
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International Journal of Biological Macromolecules journal homepage: www.elsevier.com/locate/ijbiomac
Alginate beads of Captopril using galactomannan containing Senna tora gum, guar gum and locust bean gum
1
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3
Q1
4 5 6
Harshal A. Pawar a,∗ , K.G. Lalitha b,1 , K. Ruckmani c,2 a b c
Ultra College of Pharmacy, 4/235 College Road, Thasildar Nagar, Madurai 625020, Tamil Nadu, India Department of Pharmaceutical Chemistry, Ultra College of Pharmacy, 4/235 College Road, Thasildar Nagar, Madurai 625020, Tamil Nadu, India Department of Pharmaceutical Technology, Bharathidasan Institute of Technology, Anna University, Tiruchirapalli 620024, Tamil Nadu, India
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a r t i c l e
i n f o
a b s t r a c t
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Article history: Received 3 November 2014 Received in revised form 16 February 2015 Accepted 17 February 2015 Available online xxx
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Keywords: Galactomannan Guar gum Locust bean gum
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1. Introduction
16 17 18
22Q2 23 24 25 26 27 28 29 30 31 32 33 34 35
Gastro-retentive Captopril loaded alginate beads were prepared by an ionotropic gelation method using sodium alginate in combination with natural gums containing galactomannans (Senna tora seed gum, guar gum and locust bean gum) in the presence of calcium chloride. The process variables such as concentration of sodium alginate/natural polymer, concentration of calcium chloride, curing time, stirring speed and drying condition were optimized. Prepared beads were evaluated for various parameters such as flow property, drug content and entrapment efficiency, size and shape, and swelling index. Surface morphology of the beads was studied using scanning electron microscopy. In vitro mucoadhesion and in vitro drug release studies were carried out on the prepared beads. From the entrapment efficiency and dissolution study, it was concluded that galactomannans in combination with sodium alginate show sustained release property. The bead formulation F4 prepared using combination of sodium alginate and guar gums in the ratio 2:1 showed satisfactory sustained release for 12 h. The release of Captopril from the prepared beads was found to be controlled by the swelling of the polymer followed by drug diffusion through the swelled polymer and slow erosion of the beads. © 2015 Published by Elsevier B.V.
Gastro-retentive drug delivery system (GRDDS) is a new approach for the drugs that are degraded by the alkaline pH or that are less soluble in the gastrointestinal tract (GIT) or are absorbed from the proximal part of the GIT [1,2]. GRDDS is thus advantageous for such drugs by improving their bioavailability, therapeutic efficacy and by possible reduction of dose [3]. Bioadhesive polymers have been extensively used in the last decade to improve the performance of GRDDS [4]. Mucoadhesive drug delivery system is a type of gastro-retentive system that has achieved substantial attention now a day due to their capability to adhere the mucus layer and release the drug in a sustained manner. By using these dosage forms, the intimate contact time at the mucus surface would increase, thus resulting in an improved drug retention time and drug concentration in the local sites. This would lead to an improved
∗ Corresponding author. Tel.: +91 8097148638. E-mail addresses: [email protected] (H.A. Pawar), [email protected] (K.G. Lalitha), [email protected] (K. Ruckmani). 1 Tel.: +91 9894893301. 2 Tel.: +91 9842484568.
therapeutic effect for the local diseases [5,6]. Mucoadhesive drug delivery systems offer several advantages over other oral sustained release drug delivery systems by virtue of prolongation of residence time of drug in GIT, and targeting and localization of the dosage form at a specific site [7]. Mucoadhesive polymers are able to interact with mucus glycoproteins (mucins), which are responsible for gel-type characteristics of the mucus and thereby increases the contact time with the mucosal tissue and also drug permeability across epithelial barriers [8,9]. Captopril belongs to the class angiotensin converting enzyme inhibitor (ACE inhibitor). The drug is freely soluble and has elimination half life after an oral dose of 1.7–2 h. It is stable at pH 1.2 and as pH increases, the drug becomes unstable and undergoes a degradation reaction [10]. It affects the renin angiotensin system and inhibits the conversion of relatively inactive angiotensin-I to active angiotensin-II [11]. Captopril, an antihypertensive agent, has been used widely for the treatment of hypertension and congestive heart failure. However, the duration of anti-hypertensive action after a single oral dose of Captopril is only 6–8 h, so clinical use requires a daily dose of 37.5–75 mg to be taken three times. Thus a sustained and control release dosage form of Captopril is desirable [12]. Captopril belongs to the class III of BCS (biopharmaceutical classification of system), exhibiting high solubility and low
http://dx.doi.org/10.1016/j.ijbiomac.2015.02.026 0141-8130/© 2015 Published by Elsevier B.V.
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permeability. Hence, enhanced gastric retention time of Captopril sustained release dosage form will increase its absorption. Captopril has site specific absorption from GIT and also it is unstable in the alkaline pH of the intestine, where as stable in acidic pH and specifically absorbed from stomach. Based on the above reasons there is a clear need to localize the developed formulation at the target area of the GIT. Therefore, Captopril was selected as suitable drugs for designing gastroretentive/sustained drug delivery system with a view to improve its oral bioavailability. Seed galactomannans are vegetable, heterogeneous polysaccharides widely distributed in nature. Galactomannans are polysaccharides built up of a -(1-4)-d-mannan backbone with single d-galactose branches linked ␣-(1-6). Because of their water absorption, swelling and gel forming ability, galactomannas are ideal polymeric matrix for mucoadhesive sustained release formulations. The present research work was aimed at developing and evaluating oral mucoadhesive multiparticulate drug delivery system of Captopril using galactomannans [Senna tora seed gum, guar gum and locust bean gum]. Mucoadhesive beads were prepared by ionotropic gelation technique using sodium alginate. The mixing of alginate with other polymers has an influence on the pore size and network complexity. It has also been reported that alginates when mixed with neutral gums improve its performance as drug carrier system. Considering this, galactomannans, a group of neutral polysaccharides (gum) obtained from seeds of S. tora, Cyamopsis tetragonoloba (guar gum) and Ceratonia siliqua (locust bean gum) have been selected in the present study [13].
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2. Materials and methods
88
2.1. Materials
59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85
99
The dried pods of S. tora were collected from Kalyan taluka (district – Thane, Maharashtra) and the seeds were manually separated. Plant was authenticated by Dr. Rajendra D. Shinde, Associate Professor, Blatter Herbarium; St. Xavier’s College, Mumbai and was identified as S. tora (L.) Roxb (Herbarium Specimen No. 8361). Captopril was obtained as a gift sample from Kwality Pharmaceuticals, Amritsar (India). Sodium alginate was obtained from Signet Chemicals, Japan. Guar gum SD Fine Chemicals Limited, Mumbai, India. Locust bean gum was purchased from Research Lab Fine Chem Industries, Mumbai, India. All chemicals and reagents used were of analytical grade.
100
2.2. Isolation and purification of S. tora seed gum
89 90 91 92 93 94 95 96 97 98
101 102 103 104 105 106 107 108 109 110
111 112
113 114 115 116 117
The dried seeds were subjected to mechanical treatment to separate endosperm from husk and germs followed by milling and screening of the endosperm. The gum was isolated from endosperm using method reported in literature. The obtained crude gum was dissolved in warm water, re-precipitated using ethanol (1:1), dried at 40 ◦ C, powdered and stored in airtight container at room temperature. The process of dissolution in water and precipitation with alcohol was repeated until an almost white precipitate was obtained. The dried polysaccharide was milled and sifted with a 60 mesh for further use [13]. 2.3. Formulation and evaluation of sustained release alginate bead 2.3.1. Preformulation study by Fourier transforms infrared (FTIR) spectroscopy FTIT studies were performed on the drug, physical mixture of drug with individual natural polymer at 1:1 ratio (S. tora gum, guar gum, locust bean gum and sodium alginate) and optimized
formulation using FTIR (FT-IR spectrophotometer Affinity 1, Shimadzu, Japan). The samples were analyzed in the region of 4000 and 400 cm−1 . The procedure consisted of dispersing a sample in excess of potassium bromide (KBr) nearly at the ratio 1:100, mixed well and pellets were prepared for IR analysis. 2.3.2. Preparation of alginate beads An orifice ionic gelation process was used to prepare large sized alginate beads [14]. Sodium alginate and polymers were dissolved in distilled water (30 mL) to form a homogeneous polymer solution; core material (Captopril) was added to the polymer solution and mixed thoroughly to form a smooth viscous dispersion. The resulting dispersion was then added drop wise via an 18-gauge hypodermic needle fitted with a 10 mL glass-syringe into a 40 mL of calcium chloride solution contained in a beaker with stirring at 400 RPM using a mechanical stirrer. Stirring was continued for 30 min to complete the curing reaction and to produce spherical beads. Mixture was then filtered and the product thus separated was washed repeatedly with water and dried at 50 ◦ C for 24 h. The prepared beads were stored in a desiccator until further use. The yields of prepared beads of various formulations were calculated using the weight of final product after drying with respect to the initial total weight of the drug and polymer used for preparation of beads, and percent production yields were calculated as per the formula mentioned below: Production yield (%) =
amount of dried beads amount of drug + amount of polymer
Trial batches (F1–F3) were prepared using sodium alginate alone to optimize the process parameters and concentration of sodium alginate for formation of beads. Various batches of alginate beads containing Captopril (F4–F12) were prepared, by employing sodium alginate in combination with individual galactomannan (S. tora gum, guar gum and locust bean gum) at different concentrations. The composition of various batches (F1–F12) of alginate beads prepared is shown in Table 1. 2.3.3. Optimization of process parameters The following process variables were investigated, centration of sodium alginate, concentration of calcium curing time, stirring speed and drying condition. The batches produced were analyzed for size, shape, ease of tion, drug content and drug release.
118 119 120 121 122
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143 144 145 146 147 148 149 150
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i.e. conchloride, different prepara-
2.3.3.1. Concentration of sodium alginate. To find out the optimum concentration of sodium alginate required for the formation of beads, the different batches of beads were prepared using 1–4% concentration of sodium alginate (polymer concentration). The concentration of calcium chloride, stirring time and speed of the stirrer was kept constant. The formed beads were evaluated for their actual drug content, entrapment efficiency and in vitro dissolution studies. 2.3.3.2. Concentration of calcium chloride. In order to study the effect of concentration of calcium chloride (CaCl2 ) on the beads, different concentrations of CaCl2 (5%, 10% and 15%, w/v) were used to prepare beads. The parameters such as concentration of drug, polymer (sodium alginate), stirring time and speed of the stirrer were kept constant. The formed beads were evaluated for their actual drug content, entrapment efficiency and in vitro dissolution studies. 2.3.3.3. Stirring speed and stirring time. To fix stirring speed, various trials were taken at 200, 300, 400, 500 and 600 revolutions per minute (RPM). Resultant beads were examined visually. To
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Table 1 Composition of different formulations of Captopril alginate beads. Formulation code
Drug (mg)
Polymer concentration (%)
Sodium alginate
Senna tora gum
Locust bean gum
Guar gum
Quantity in mg per batch Beads using sodium alginate alone (trial batches) 600 2 F1 600 3 F2 600 4 F3 Beads using sodium alginate and individual galactomannan in combination F4 600 3 600 3 F5 600 3 F6 600 3 F7 600 3 F8 F9 600 3 F10 600 3 F11 600 3 600 3 F12
176 177 178 179 180 181 182 183 184 185 186 187
188 189 190 191 192 193 194
optimize stirring time the trial batches were taken with different stirring times – 15 min, 30 min, 45 min and 1 h. It was found that the optimum concentration of sodium alginate [2–3%], calcium chloride [10%], cross-linking time [30 min], and stirring speed – 400 RPM could influence the beads size, average diameter, recovery, entrapment efficiency, size distribution swelling behavior and the release characteristics. Different batches [F4–F12] of alginate beads were then prepared by using the optimized process variables. The total polymer concentration was kept constant and the ratio of sodium alginate:polymer (S. tora gum, guar gum and locust bean gum) was varied. The final formulations were subjected to several characterization studies. 2.3.4. Evaluation of beads The developed sustained release mucoadhesive beads were evaluated for various parameters like size and shape analysis, drug content, entrapment efficiency, drug release, in vitro wash off test for mucoadhesion, swelling and micrometric properties. The shape and surface characteristics were determined by scanning electron microscopy.
600 900 1200
– – –
– – –
– – –
600 700 800 600 700 800 600 700 800
– – – – – – 300 200 100
– – – 300 200 100 – – –
300 200 100 – – – – – –
2.3.4.3. Bulk density and tapped density. To calculate the bulk density and tapped density, the beads were weighed, and transferred to a measuring cylinder. The volume occupied by beads was noted as bulk volume and the cylinder was tapped until the constant volume was achieved, and this was noted as tapped volume. The values of bulk density and tapped density were calculated by using following equations: Bulk density =
weight of powder volume of the packing
Tapped density =
2.3.4.4. Hausner’s ratio and Carr’s compressibility index. The Hausner’s ratio and Carr’s compressibility index were determined from the value of bulk density and tapped density using following formulae. Hausne’s ratio =
195 196 197
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207 208 209 210
2.3.4.1. Flow properties of beads. Following parameters were evaluated to study the flow properties and compressibility of beads [15,16]. 2.3.4.2. Angle of repose. Angle of repose is a measure to determine the flow ability of the powder or granules. The fixed funnel free standing cone method was used to determine angle of repose. Beads were passed through fixed funnel to make a heap of the predetermined height. The angle made by heap with that of base was determined. The angle of repose of the beads was determined by fixed funnel free standing cone method using the following formula. = tan−1
h r
where “h” is height between the lower tip of funnel and the base of heap of beads, and “r” is radius of the base of heap formed. Relationship between angle of repose () and flow ability is represented in Table 2. Table 2 Relationship between angle of repose () and flow ability. Angle of repose ()
Flow ability
40
Excellent Good Passable Very poor
weight of powder volume of the packing
tapped density bulk density
Car’s compressibility index =
tapped density − bulk density × 100 bulk density
The values within range 5–15% of Carr’s index and values less than 1.25 of Hausner’s ratio showed good compressibility of the sample. 2.3.4.5. Actual drug content and entrapment efficiency. Drug content estimation was done by stirring 20 mg beads in sodium citrate solution (1%, w/v) until complete dissolution occurs. Methanol was added to the sodium citrate solution to gel the dissolved calcium alginate and further solubilize Captopril. This solution was then filtered to get the drug solution. The filtrate was then suitably diluted with 0.01 N hydrochloric acid, and absorbance was taken at 205 nm [17]. All the measurements were done in triplicate. The actual drug content and entrapment efficiency were calact × culated using following formulae.Actual drug content (%) = M Mms 100 Entrapment efficiency (%) =
Mact × 100 Mthe
where Mact is the actual drug content in weighed quantity of beads, Mms is the weighed quantity of dried beads and Mthe is the theoretical amount of drug in beads calculated from the quantity added in the process.
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Fig. 1. FTIR spectrum of Captopril.
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2.3.4.6. Size and shape of the bead. The diameter of the bead was determined by screw gauge. For this purpose, ten dried beads were randomly selected from each batch, and the mean diameter was determined by screw gauge. The least count of screw gauge was 0.005 mm. The sphericity was observed by the microscope. 2.3.5. Swelling index Beads were studied for swelling characteristics. Samples from drug-loaded beads were taken, weighed and placed in the wire basket of USP dissolution apparatus-I. The basket containing beads was put in a beaker containing 100 mL of 0.01 N HCl maintained at 37 ◦ C. The beads were periodically removed at predetermined intervals and weighed. Then the swelling ratio was calculated as per the following formula [18–20]. Swelling ratio =
weight of wet beads weight of dried bead
2.3.6. In vitro test for mucoadhesion Mucoadhesion of the beads was evaluated by an in vitro adhesion testing method, known as wash off method. The pieces of goat intestinal mucosa (2 cm × 2 cm) were tied on glass slides (3 inch × 1 inch) by rubber band. About 50 beads were counted and spread over the wet rinsed tissue specimen and wait for 10 min and immediately thereafter, the supports were hung on the arm of a USP tablet disintegrating test machine. By operating the disintegration machine, the tissue specimen was given slow regular up and down movement in the 1 L vessel containing 0.01 N HCl at 37 ± 2 ◦ C. At the end of each hour, the machine was stopped and number of beads still adhering on the tissue were counted [21,22]. This procedure was carried out for 12 h. From the unbound beads, the numbers of adhered beads were calculated and adhering % was calculated after each interval of time. number of adhered bead % Mucoadhesion = × 100 total number of applied beads
2.3.7. Scanning electron microscopy (SEM) Scanning electron microscopy (SEM) is an electron optical imaging technique that provides photographic images and elemental information. SEM is useful for characterizing the morphology and size of microscopic specimens with particle size as low as nanometer. It is used to determine particle size distribution, surface topography, texture and examine the morphology of fractured or sectioned surface. Prepared beads were coated with gold–palladium under an argon atmosphere at room temperature and then beads were examined with SEM operating at 15 kV. 2.3.8. In vitro drug release studies The drug-loaded beads equivalent to 50 mg of Captopril were filled in the empty hard gelatin capsule shells. A calibrated dissolution apparatus (USP I) was used with baskets at 50 RPM and bath temperature maintained at 37 ± 0.5 ◦ C. Nine hundred milliliter freshly prepared and degassed 0.01 N HCl solution was used as the dissolution medium. Dissolution samples were collected immediately at the end of 1 h, 2 h, 4 h, 6 h, 8 h, 10 h and 12 h. At each time point; a 5 mL sample was removed from each vessel and filtered through a nylon filter (0.45 m, 25 mm) into labeled glass tubes and analyzed spectrophotometrically at 205 nm after appropriate dilutions. Drug concentrations in the sample were determined from the standard calibration curve [23,24]. 2.3.9. Mathematical modeling of kinetic release The in vitro release data was subjected to zero order, first order, Higuchi, Korsemeyer–Peppas and Hixson Crowell mathematical model in order to establish the drug release mechanism and kinetics of drug release from beads [25–29]. 2.3.10. Accelerated stability studies The optimized formulation was weighed in two sets and wrapped in a butter paper and placed in petri-dishes. These containers were stored at room temperature (27 ± 2 ◦ C) and at an elevated temperature (40 ± 2 ◦ C) for a period of six months according to ICH guidelines. Then beads were withdrawn at the different time intervals of one month, two month, three months and at the
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Fig. 2. FTIR spectrum of physical mixture of Captopril and sodium alginate (1:1).
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end of six months and analyzed for physical changes (such as color and texture), size, actual drug content and in vitro drug release.
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3. Result and discussion
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3.1. Isolation and purification of S. tora seed gum
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The isolated gum from S. tora seeds was an amorphous free flowing powder with dull brown color. 3.2. Preformulation study by Fourier transforms infrared (FTIR) spectroscopy The identification of drug was confirmed by comparing IR spectrum of drug with reported spectrum of Captopril. The FTIR spectrum of Captopril (Fig. 1) showed characteristic bands similar to that of reported in literature [30]. FTIR of Captopril, its physical mixture with natural polymer and optimized formulation exhibited the peak for Captopril at similar places (Figs. 2–6). This indicated that there was no interaction between the Captopril and excipient. 3.3. Formulation development and optimization of process parameter’s Formulations of Captopril sustained release mucoadhesive bead were prepared by using sodium alginate as core coating polymer, as alginate is easily gelled by the addition of Ca2+ . An aqueous insoluble calcium alginate gel was formed by cation exchange between Na+ and Ca2+ . The gelation and cross linking was due to the stacking of the guluronic acid-G blocks of alginate chains with the formation of egg-box junction. Literature survey revealed that seed polysaccharides such as guar gum, locust bean gum, tamarind seed polysaccharide, fenugreek seed mucilage, etc. have been used as a drug delivery carrier along with sodium alginate in the development of mucoadhesive hydrogel beads, which modifies the network complexity and drug release performance [31–39]. An orifice-ionic gelation process was used to prepare Captopril encapsulated beads, employing sodium alginate in combination
with three individual galactomannan containing natural polysaccharides (S. tora gum, guar gum and locust bean gum) in the different ratios. Stirring speed of more than or equal to 500 RPM causes formation of threading or oval shaped beads. At stirring speed of less than 300 RPM, sticking of beads was observed. At 400 RPM spherical and uniform sized beads were obtained. Thus 400 RPM was decided as the optimum speed in this study. The curing time was optimized to 30 min to avoid surface deposition of leached drug. At low curing time, the beads obtained were soft. The slow release from beads prepared at medium curing time confirms the drug release by diffusion from a strong and thick hydrated gel. It was observed that actual drug content and entrapment efficiency (%) was improved with increasing CaCl2 concentration in cross-linking solutions, due to the high degree of cross-linking by the concentrated calcium ions. The beads prepared using lower CaCl2 concentration might have larger pores due to insufficient cross-linking, and drug leaching may occur through the pores that may result in lower drug encapsulation. However, the higher calcium chloride concentration influenced the formation of smaller beads because of shrinkage and showed an increased angle of repose. The drug entrapment efficiency was improved progressively with increasing concentration of sodium alginate resulting in entrapping the greater amount of the drug. This may be attributed to the greater availability of active calcium binding sites in the polymeric chains and, consequently, the greater degree of cross-linking as the amount of sodium alginate increased. On the other hands, further increase in the concentration of calcium chloride above (10%, w/v) did not enhance the drug loading. This could be due to possible saturation of calcium binding sites in the guluronic acid chain, preventing further Ca2+ ions entrapment and, hence, cross-linking was not altered with higher concentration of calcium chloride solution. Optimized process variables are represented in Table 3. Different batches [F4–F12] of alginate beads and individual galactomannan combinations were then prepared by using the optimized process variables. The total polymer concentration was kept constant and the ratio of sodium alginate:polymer (S. tora
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Fig. 3. FTIR spectrum of physical mixture of Captopril and locust bean gum (1:1).
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gum, guar gum and locust bean gum) was varied. The final formulations were subjected to several characterization studies. The representative photograph of wet and dry beads is shown in Fig. 7.
high viscous polymer dispersion which may be lost during manufacturing process. Further observation, while increasing in the concentration of calcium chloride and long curing time slightly increased the percent of yield.
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3.4. Determination of production yield (%) 3.5. Evaluation of beads
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In the preparation of the beads the production yields of the batches are ranging from 79.78 ± 0.95 to 92.11 ± 0.89 as shown in Table 4. It was observed that increasing the concentration of S. tora gum, guar gum and locust bean gum in the formulation significantly lowers the product yield, due to the formation of
3.5.1. Bead size and shape analysis The average diameters of different batches of bead are reported in Table 5. Results indicated that the bead size increases with increase in the concentration of polymer. The color of the beads
Fig. 4. FTIR spectrum of physical mixture of Captopril and guar gum (1:1).
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Fig. 5. FTIR spectrum of physical mixture of Captopril and Senna tora gum (1:1).
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was varied with gum used. All beads obtained per batch were found to be uniform in size. Beads were found to be discrete, large, and spherical, free flowing, monolithic matrix with smooth surfaces. 3.5.2. Flow properties The micrometric parameters like angle of repose, bulk density and tapped density confirms better flow and packaging properties of the beads. All the formulations showed excellent flow ability in terms of angle of repose. The sodium alginate concentration has a significant positive effect on the angle of repose. Particle size increased with increase in the concentration of S. tora gum, guar gum and locust bean gum which in turn resulted in decreased
angle of repose. Bulk and tapped density of the beads were in acceptable range indicated that the beads have good pack ability. The density of the beads increases as the concentration of the S. tora gum, guar gum and locust bean gum increases which suggests that the beads formed at high polymer concentration are more compact and less porous than those prepared with sodium alginate alone. Carr’s index and Hausner’s ratio of the formulated beads showed excellent compressibility and good flow properties suggesting that the beads can be easily handled during processing. The result of rheological parameters like angle of repose, bulk density and tapped density of all the prepared beads is shown in Table 6.
Fig. 6. FTIR spectrum of Captopril beads (optimized formulation).
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Fig. 7. Photographs of (A) beads before drying and (B) beads after drying.
Table 3 Optimized process variables.
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Process variable parameters
Optimized data
Concentration of sodium alginate Calcium chloride concentration Bore diameter of the needle Stirring speed Stirring time Drying time and temperature
2–3% 10%, w/v, solution 18 gauge 400 RPM 30 min after addition 50 ◦ C for 24 h
From the various parameters studied for the flow ability and compressibility of the beads, values for angle of repose indicated good flow properties of beads and this was further supported by compressibility index and Hausner’s ratio.
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3.5.3. Determination of actual drug content and entrapment efficiency The drug entrapment efficiencies increased progressively with increasing the concentration of sodium alginate resulting in entrapping the greater amount of the drug. This may be attributed to the greater availability of active calcium binding sites in the polymeric chains and, consequently, the greater degree of cross-linking as the amount of sodium alginate increased. Addition of co-polymer (galactomannans) to sodium alginate also showed positive effect on entrapment. As the co-polymer concentration increased, entrapment efficiency was increased due to increase in viscosity of solution. The results of actual drug content and entrapment efficiency of all formulations are shown in Table 7. From the below reported table, formulation batch F4 showed maximum actual drug content (18.64 mg) and maximum entrapment efficiency (93.2%).
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3.6. Swelling studies
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The swelling behavior indicates the rate at which the formulation absorbs water from dissolution medium and swells. Swelling behavior of the prepared formulations is summarized in Fig. 8.
Fig. 8. (A) Swelling study of Captopril beads [F1–F6] and (B) swelling study of Captopril beads [F7–F12].
Swelling index was increased with increase in co-polymer concentration. The maximum swelling up to 1.85 w/w was observed within 5 h in 0.01 N HCl followed by gradual reduction in weight in the next hours as shown in Fig. 8. This effect might be owing to
Table 4 Production yield of different batches of beads. Sr. no.
Batch code
Production yielda (%)
1 2 3 4 5 6
F1 F2 F3 F4 F5 F6
92.11 86.26 79.78 82.48 85.67 89.94
a
± ± ± ± ± ±
0.89 0.71 0.95 0.49 0.88 0.93
Sr. no.
Batch code
Production yielda (%)
7 8 9 10 11 12
F7 F8 F9 F10 F11 F12
80.29 83.33 88.02 81.72 84.61 88.55
± ± ± ± ± ±
0.76 0.45 0.94 0.82 0.69 0.81
Each value is average of three separate determinations ± standard deviation (SD).
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Table 5 Bead size analysis of beads batches F1–F12. Sr. no.
Batch code
Mean bead size (mm)a
1 2 3 4 5 6
F1 F2 F3 F4 F5 F6
1.03 1.28 1.72 1.51 1.42 1.36
a
± ± ± ± ± ±
0.01 0.01 0.02 0.03 0.01 0.03
Sr. no.
Batch code
Mean bead size (mm)a
7 8 9 10 11 12
F7 F8 F9 F10 F11 F12
1.29 1.20 1.12 1.37 1.31 1.24
± ± ± ± ± ±
0.02 0.01 0.01 0.02 0.04 0.03
Each value is average of ten separate determinations ± SD.
Table 6 Various parameters showing flow properties of different batches of beads (F1–F12). Batch code
Bulk densitya
F1 F2 F3 F4 F5 F6 F7 F8 F9 F10 F11 F12
0.487 0.499 0.541 0.573 0.566 0.548 0.592 0.581 0.553 0.585 0.561 0.556
a
450 451 452 453 454 455 456
457
± ± ± ± ± ± ± ± ± ± ± ±
Tapped densitya
0.034 0.030 0.028 0.021 0.017 0.032 0.022 0.011 0.031 0.027 0.036 0.014
0.545 0.572 0.642 0.642 0.648 0.656 0.655 0.675 0.687 0.651 0.641 0.666
± ± ± ± ± ± ± ± ± ± ± ±
0.018 0.027 0.015 0.021 0.029 0.013 0.023 0.033 0.027 0.017 0.011 0.035
Hausner’s ratio
Carr’s index
Angle of repose ()
1.12 1.15 1.19 1.12 1.14 1.20 1.11 1.16 1.24 1.11 1.14 1.20
10.64 12.76 15.73 10.75 12.65 16.46 9.62 13.93 19.51 10.14 12.48 16.52
18.97 15.74 11.86 12.37 14.23 17.29 12.12 14.22 16.32 11.05 13.51 16.77
Each value is average of three separate determinations ± SD.
the acid solubility of drug that might have influenced the swelling behavior of the beads; otherwise the acid gels of sodium alginate are resistance to erosion. Maximum swelling was observed in the bead formulation F4 containing sodium alginate and guar gum in the ratio 2:1. This indicated that the swelling of the beads will help to retard release the drug successfully in the suitable environment of the stomach.
3.8. Scanning electron microscopy (SEM)
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The SEM photomicrographs of beads prepared using sodium alginate alone and in combination with different galactomannan are depicted in Fig. 10. Beads showed morphological regularity due with dense good spherical geometry. The formation of thick coat on outer surface of the sodium alginate beads indicated complete entrapment of drug into interior polymer network.
459 460 461 462 463 464 465 466 467 468 469 470
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3.7. In vitro test for mucoadhesion 3.9. In vitro release of beads
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Mucoadhesive property was evaluated for all the formulated beads. It was observed that as the concentration of polymer decreased, mucoadhesion of beads also decreased. It is graphically presented in Fig. 9. All the galactomannan containing formulations showed good mucoadhesion as compared to plain sodium alginate beads. Mucoadhesion of alginate–guar gum combination was found to be moderately high; this may be due to significant mucus gel strengthening, which results in formation of stable mucoadhesive joint. Hence the large force was required to detach the beads from the mucosal surface. Mucoadhesion of locust bean gum loaded alginate beads was found to be poor when compared to alginate–guar gum and alginate–S. tora gum, this may due to their low viscosity and swelling capacity.
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The % cumulative drug release from batches F1–F12 is represented in Fig. 11. The results clearly indicated that the rate of drug release decreased with the increase in thickness, because the drug cannot diffuse through the pore of the alginate gel matrix, which has not been swollen. In the dissolution study, burst effect was observed for all the batches. The drug release from all the formulations shows a biphasic release profile i.e. the initial rapid release (burst effect) was followed by sustained release as all the formulations deals with hydrophilic polymer and water soluble drug. This sustained release was due to the shrinkage property of alginate in the acid
Table 7 Actual drug content and entrapment efficiency of beads batches (F1–F12). Batch code
Actual drug contenta (mg)
F1 F2 F3 F4 F5 F6 F7 F8 F9 F10 F11 F12
13.27 15.62 17.11 18.64 17.12 16.42 16.98 14.36 13.88 17.85 16.57 14.13
a
± ± ± ± ± ± ± ± ± ± ± ±
0.05 0.08 0.10 0.31 0.16 0.19 0.47 0.27 0.11 0.24 0.14 0.08
Theoretical drug content (mg)
Entrapment efficiency (%)
20 20 20 20 20 20 20 20 20 20 20 20
66.35 78.1 85.55 93.2 85.6 82.1 84.9 71.8 69.4 89.25 82.85 70.65
Each value is average of three separate determinations ± SD.
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Fig. 9. (A) Mucoadhesion study of Captopril beads [F1–F6] and (B) mucoadhesion study of Captopril beads [F7–F12].
Fig. 11. (A) In vitro drug release profile of beads F1–F6 and (B) in vitro drug release profile of beads F7–F12.
media as well as due to the combination of sodium alginate and co-polymer in these formulations which swells in the acidic pH and forms a thick viscous layer through which drug diffuses resulting in slow release of drug. Formulation F1–F3 containing only sodium
alginate showed the complete release of drug in 4–8 h with more than 30% drug release in first hour. The addition of co-polymer controls initial rapid release and further control drug release in sustained manner. In acidic medium, the swelling and drug
Fig. 10. SEM photograph of drug-loaded beads prepared using (A) sodium alginate alone, (B) sodium alginate and guar gum, (C) sodium alginate and Senna tora gum and (D) sodium alginate and locust bean gum.
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Fig. 12. (A) Zero order release profile, (B) first order release profile, (C) Higuchi release profile and (D) Korsmeyer–Peppa’s release profile and (E) Hixson Crowell release profile of optimized formulation of Captopril beads (F4).
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release properties were influenced by drug solubility and not by gel properties of calcium alginate. Calcium alginate is insensitive to acidic solution; it does swell to some extent and thus provides slow release of the embedded drug. The batch F7 containing sodium alginate and locust bean gum in the ratio 2:1 showed the complete drug release in 8 h. The batch F10 containing sodium alginate and S. tora gum in the ratio 2:1 showed the complete drug release in 10 h. From the entrapment and dissolution study, it was concluded that almost all the polymers shown sustained release property but the bead formulation F4 prepared using combination of sodium alginate and guar gums in the ratio 2:1 showed the satisfactory sustained release for 12 h. The alginate–guar gum beads showed the better sustained release as compared to all other alginate polymer combinations. Thus, the drug release followed the rank order of using alone sodium alginate and in combination with co-polymers as sodium alginate > sodium alginate–locust bean gum > sodium alginate–S. tora gum > sodium alginate–guar gum. The regression coefficient values of different release kinetic equations evaluated from the dissolution profile of developed formulations for Captopril beads are compared.
Among all the prepared formulations, formulation F4 showed satisfactory release of 12 h with highest correlation value (r2 ) of 0.9912 for the zero order kinetic model. The value of n as estimated by linear regression of log Mt/M∞ versus log t of formulation F4 was 0.5626 which indicates the drug release mechanism from matrix tablets involving a combination of both diffusion and chain relaxation mechanisms. Therefore, the release of Captopril from the prepared bead is controlled by the swelling of the polymer followed by drug diffusion through the swelled polymer and slow erosion of the beads. The kinetic release of optimized formulation (F4) using the different kinetic models is depicted in Fig. 12.
3.10. Accelerated stability data The results of stability study are summarized in Table 8. The physical appearance, size, actual drug content and dissolution profile of beads was not affected significantly during stability study. The results indicated that the optimized formulations F4 is stable for 6 months at 40 ± 2 ◦ C and 75 ± 5% RH.
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Pale yellow, spherical 1.48 ± 0.03 18.04 ± 0.72 89.90 Pale yellow, spherical 1.48 ± 0.05 18.32 ± 0.28 91.39
Pale yellow, spherical 1.51 ± 0.05 18.45 ± 0.47 92.99
The development of sustained release beads with acceptable physicochemical and in vitro drug release justifies the application of used technique in the development of multiparticulate sustained drug delivery. The objective of the present work was achieved i.e. successful formulation development of gastro-retentive mucoadhesive alginate beads of Captopril with galactomannan. Certainly these findings can be applied for sustained delivery of drugs with mucoadhesion. Further these findings help the industry to scale up the commercial production. S. tora gum, guar gum and locust bean gum (natural polymers) were found to be significantly affects mechanical properties, decreases porosity and sustained drug release due to its swelling properties. Therefore, one can assume that the galactomannans (such as S. tora gum, guar gum and locust bean gum) are promising natural biopolymers used in pharmaceutical dosage forms by providing sustained release drug delivery systems and avoiding the dose related side effects. In combination with sodium alginate, guar gum shows better sustaining property as compared to other two galactomannan containing gums i.e. S. tora gum and locust bean gum.
Pale yellow, spherical 1.50 ± 0.03 18.61 ± 0.41 93.85
Controla Controla
3 Month
Acceleratedb
6 Month
Acceleratedb
4. Conclusion
Conflict of interest
Pale yellow, spherical 1.49 ± 0.03 18.40 ± 0.39 93.81
Acknowledgement
Pale yellow, spherical 1.49 ± 0.02 18.70 ± 0.19 94.79
The authors are thankful to Ultra College of Pharmacy, Madurai, for providing the laboratory facilities to carry out the present investigation. References
c
a
b
Bead size (mm) Actual drug content (mg) F2 valuec (similarity factor)
Samples were stored 27 ± 2 ◦ C and 45 ± 5% RH. Samples were stored 40 ± 2 ◦ C and 75 ± 5% RH. F2 values of 50–100 indicate similarity between the dissolution profiles.
Pale yellow, spherical 1.50 ± 0.04 18.49 ± 0.29 95.01 Pale yellow, spherical 1.50 ± 0.06 18.55 ± 0.34 95.72 Pale yellow, spherical 1.51 ± 0.03 18.64 ± 0.51 – Physical appearance
Controla Acceleratedb Controla
1 Month Initials Parameter
Table 8 Tablet properties of the developed Captopril beads (F4) after storage in stability studies.
2 Month
Acceleratedb
The authors declare that there is no conflict of interests regarding the publication of this article.
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