Disintegration Properties of Films Prepared with Sodium Alginate: A Colorimetric Quantification Method

Research Article

Disintegration Properties of Films Prepared with Sodium Alginate: A Colorimetric Quantification Method

Corresponding author: Dr. Yoshifumi Murata, Ho-3, Kanagawa-machi, Kanazawa 920-1181, Japan, Tel: +81-76-229-6184; Fax: +81-76-229-2781; Email: y-murata@hokuriku-u.ac.jp


Films containing active therapeutic agents are considered a useful mode of oral drug administration. A hydroxamic acid deri- vatization of sodium alginate (Alg-Na) in an aqueous solution and its application in the colorimetry-based quantification of the compound were the subject of this study, in which the disintegration properties of films prepared with Alg-Na species and additives were investigated colorimetrically. Hydroxamic acid formation was shown to progress quantitatively in the presence of a water-soluble carbodiimide; calibration curves for Alg-Na exhibited good linearity in the range of 0.1 mg to 1.0 mg. Films prepared with Alg-Na swelled rapidly and disintegrated in physiological saline, into which the Alg-Na then dissolved. The dis- integration profile of film differed markedly depending on the Alg-Na species used as the film base. The regulation of initial disintegration rates of the films by modification of the film base with additives such as alginic acid was demonstrated. Based on these findings, films prepared with Alg-Na are considered fast-dissolving dosage forms suitable for limited media environments.

Keywords: Sodium Alginate; Film Disintegration; Colorimetric Quantification; Hydroxamic Acid; Alginic Acid


ALG: Alginic Acid;

Alg-Na: Sodium Alginate;

BPS: A Polysaccharide produced by Bifidobacterium longum JBL05;

CMEC: 1-Cyclohexyl-3-(2-morpholinoethyl)Carbodimide metho-p-Toluenesulfonate; FD: Film Dosage Form;

G: α-L-Guluronic Acid;

HX: Hydroxylamine;

HXA: Hydroxamic Acid;

M:β-D-Mannuronic Acid


Films incorporating active compounds have been studied as a functional dosage form. Film dosage forms (FDs) prepared with water-soluble polymers are of particular interest because of their safety for oral administration [1-4]. Alginic acid (ALG), which consists of α-L-guluronic acid (G) and β-D-mannuronic acid (M), is widely used as a food additive [5]. The sodium salt

of ALG, Alg-Na, is a water-soluble polysaccharide and high mo- lecular weight Alg-Na forms a thin film by evaporation of the solvent from the solution. An FD can be simply prepared from Alg-Na using the casting method without the need for dissolu- tion in organic solvents or heating [6-8].

Cite this article: Yoshifumi Murata. Disintegration Properties of Films Prepared with Sodium Alginate: A Colorimetric Quantification Method. J J Materl Sci. 2016. 1(1): 001.

In bodily fluids such as saliva, FDs swell rapidly before dissolv- ing and thus releasing the drug contained within the FD. Such FDs may be useful for patients who have difficulty swallowing regular oral dosage forms [9,10] and are a useful tool by which drugs can be delivered to the local disease site in, for example, the oral cavity for diseases such as Candida [11,12]. Disintegra- tion rate of a film matrix is an important property in character- izing drug-carrying potential, and films prepared with Alg-Na are known to immediately disintegrate in aqueous media. The degree of disintegration is, however, difficult to quantify, since the disintegration of FDs is gauged visually.

We previously reported on a colorimetric method by which gel disintegration can be determined using pectin, polygalac- turonic acid, and the ester resulting from the derivatization of the carboxyl group to hydroxamic acid (HXA) [13]. The for- mation of HXA occurs upon the reaction between the carboxyl groups on other polysaccharides and hydroxylamine (HX). In this study, the HXA derivatization of Alg-Na using water-solu- ble carbodiimide and the subsequent application of this deri- vatization to colorimetry-based quantification the compound were investigated. Next, this simple colorimetric method was used to generate and assess disintegration profiles of films prepared with Alg-Na and additives in the limited medium.

Materials and Methods


As a film base, six species of high molecular weight Alg-Na, Alg-A (300 cps, Nacali Tesque Inc., Kyoto, Japan), Alg-B (1000 cps, Nacali Tesque Inc.), Alg-C (150M, Kibun Food Chemifa Co., Tokyo, Japan), Alg-D (IL-1, Kimica Co., Tokyo, Japan), Alg-E (IL- 6, Kimica Co.) and Alg-F (IL-6G, Kimica Co.) were used. Two ALGs (ALG-S, ALG-NS) and HX were purchased from Wako (Osaka, Japan). Two species of low molecular weight Alg-Na (ULV-L3, ULV-L5) were supplied by Kimica Co.. 1-Cyclohex- yl-3-(2-morpholinoethyl) carbodiimide metho-p-toluenesul- fonate (CMEC) was purchased from Aldrich Chem Co. (Mil- waukee, WI). A polysaccharide produced by Bifidobacterium longum JBL05 (BPS) was supplied by Morishita Jintan (Osaka, Japan). All other chemicals were of reagent grade and were ob- tained from commercial sources.

Preparation of low molecular weight ALG

The ALG of ULV-L3, ALG-L3, was prepared as follows: 2M HCl was gradually added to 100 g ULV-L3 solution (4%; w/w) while stirring (MAG-MIXER M-41, Yamato Scientific Co., Tokyo, Japan). The solution changed into a white suspension when the pH was lowered. At pH 3, the suspension was centrifuged at 1900 × g (2100 model, Kubota Co., Tokyo, Japan) for 5 min. The pellet was washed twice with 0.1 M HCl, three times with ethanol, and was then dried. The resulting ALGs, obtained as white powders, were sieved (mesh size: 75 µm) before

being used as additives in subsequent experiments. The ALG of ULV-L5, ALG-L5, was prepared in the same manner described here for ALG-L3.

Preparation of alginate hydrolysate (G-block) and the so- dium salt

Alg-A was partially hydrolyzed (0.2 M HCl, 2 h, 100°C), and G-block was separated using the methods described by Haug, et al. [14] The sodium salt of G-block was obtained as follows: G-block was suspended in ion-exchanged water, after which

0.2 M NaOH was added to the suspension with stirring. The pH of the solution was then raised to ~7 to produce the sodi- um salt of G-block. The addition of ethanol resulted in the for- mation of a white precipitate in the solution, which was then centrifuged at 1900 × g for 5 min. The pellet was washed three times with ethanol before being dried.

FD preparation

Using the casting method, 1.5–2.0% (w/w) Alg-Na containing an additive was prepared in deionized water as the film base solution. The mixture was thoroughly mixed by sonication (BRANSON 8200, Kanagawa, Japan), after which 3.0 g of each solution was poured into individual plastic Petri dishes (diam- eter, 54 mm, KORD-Valmark, USA). After 24 h at 37°C, the circu- lar films formed on each dish were transferred to a desiccator.

Colorimetric quantification

Two solutions were prepared: 20 mM HX in ion exchanged-wa- ter and 0.1 M CMEC in 2% pyridine-HCl buffer (pH 5.0). The HX and CMEC solutions (1 mL each) were added to a sample solution (1 mL), which was then mixed by vortex mixer (S-10, TAITEC Co., Saitama, Japan). Each mixture was incubated at 40°C for 20 min, after which 20 mM FeCl3 in 0.1 M HCl (3 mL) was added. Absorbance at 480 nm was measured in a quartz cell with (1 cm light path) using a spectrophotometer (UV- 1200, Shimadzu Co., Kyoto, Japan). Absorbance values were normalized using a reagent blank.

Film disintegration test

A film was placed in a plastic dish and 10 mL dissolution me- dium (physiological saline preheated to 37°C) was added. The dish was shaken (300 rpm) in an incubator (SI-300; As One Co., Osaka, Japan) set to 37°C. After 1, 3, 5, 10, 15, 20, 30, 45, and 60 min, 0.3 mL of the medium was removed using a plas- tic syringe and was filtered through a syringe-driven filter unit (pore size: 0.45 µm). An equal volume (0.3 mL) of physiological saline (37°C) was added to the dish in the incubator to main- tain a constant volume. Aliquots (0.2 mL) of the filtered solu- tion were combined with ion exchanged-water (0.8 mL) in test tubes before being mixed well by a vortex mixer. The amounts of Alg-Na in each sample solution (1 mL) were measured us- ing the method described in Colorimetric quantification. For each disintegration test, a calibration curve was constructed using a fresh set of Alg-Na standards. All tests were performed in triplicate.


Colorimetric quantification of Alg-Na in this study was based on HXA formation between HX and the carboxyl group of uron- ic acid containing polysaccharides. The reaction progressed quantitatively in an aqueous solution in the presence of the coupling reagent CMEC, and the HXA formed in the solution yielded a red color when dilute HCl containing FeCl3 was add- ed. Calibration curves for Alg-A exhibited good agreement in the range of 0.1–1.0 mg (Figure 1). The coefficient of variation for the quantification of 1 mg Alg-A was 1.9% (n = 8). These parameters were applicable to the other Alg-Na species and similar calibration curves were obtained in all cases (Figure 1).

Figure 1. Calibration curves for six Alg-Na species.

Calibration curves equation

(Y: Absorbance at 480 nm, X: Amount of Alg-Na (mg), R: Correlation


Alg-A: Y = 0.246 X – 0.0056 (R2 = 0.9999) Alg-B: Y = 0.249 X – 0.0037 (R2 = 0.9999) Alg-C: Y = 0.235X – 0.0013 (R2 = 1.000) Alg-D: Y = 0.267 X – 0.0046 (R2 = 1.000) Alg-E: Y = 0.258 X – 0.0064 (R2 = 0.9999) Alg-F: Y = 0.256 X – 0.0068 (R2 = 0.9999)

The FDs prepared with Alg-Na species quickly swelled and dis-

integrated in the aqueous physiological saline medium. Upon FD disintegration, Alg-Na dissolved in the test solution. In the case of FD prepared with 1.5% Alg-A, for example, 40 ± 2% of the Alg-Na had dissolved after 10 min (Figure 2).

As shown in Figure 2, the disintegration profiles of FDs dif- fered markedly depending on the Alg-Na species used as the film base in the FD preparation. In all cases except for Alg-A,

>65% of the Alg-Na had dissolved within 10 min. In the case of FD prepared with 2% Alg-D, dissolution was particularly fast: the FD disintegrated immediately and ~90% of the Alg-Na had dissolved from the FD by 5 min.

Figure 2. Dissolution profiles of Alg-Na from FDs.

Modification of the FDs using an additive was shown to affect the disintegration profile of the form (Figure 3): initial disso- lution rates increased following the addition of ALG to the film base. In the case of FD prepared with 1.5% Alg-A containing 0.1% ALG-S, for example, >80% of the Alg-Na had dissolved after 5 min. This phenomenon was also observed for the FD modified with ALG-NS.

Figure 3. Dissolution profiles of Alg-Na from FDs prepared with 1.5%

Alg-A containing ALG.

Cite this article: Yoshifumi Murata. Disintegration Properties of Films Prepared with Sodium Alginate: A Colorimetric Quantification Method. J J Materl Sci. 2016. 1(1): 001.

Alg-Na (%)
Additive 1 min 3 min 5 min
None 5 ± 3 18 ± 8 29 ± 6
0.1% ALG-L3 15 ± 10 68 ± 16 72 ± 7
0.1% ULV-L3 6 ± 3 13 ± 3 25 ± 10
0.1% ALG-L5 4 ± 0 78 ± 6 74 ± 4
0.1% ULV-L5 6 ± 5 25 ± 12 37 ± 3
0.1% G-block 12 ± 6 76 ± 8 82 ± 16
0.1% sodium salt of G-block 3 ± 1 11 ± 3 19 ± 2

Table 1. Effects of additives on Alg-Na dissolution from FDs prepared with 1.5% Alg-A.

The dissolution rates of Alg-Na from FDs containing ALG-L3, ALG-L5, or G-block are shown in Table 1. The FD prepared with 1.5% Alg-A containing 0.1% ALG-L3 immediately disintegrat- ed, and 68% of the Alg-Na dissolved into the test solution with- in 3 min. The disintegration of the FD was accelerated when another low-molecular weight ALG was added to the film base solution; however, the initial dissolution rate of Alg-Na from FD did not increase in the case of FD modified with the sodium salt of each ALG, i.e., with low-molecular-weight Alg-Na spe- cies.

Figure 4. Dissolution profiles of Alg-Na from FDs prepared with Alg- Na containing BPS.

On the other hand, the disintegration rate of FD decreased with the addition of BPS to the film base. In the case of FD prepared with 1.5% Alg-A containing 0.5% BPS, for example, Alg-Na gradually dissolved and only 40 ± 2% of Alg-Na had dissolved into the test solution after 10 min. The initial dissolution rate of Alg-Na decreased following the addition of BPS to the film base, as shown in Figure 4. These results suggest that the ini- tial disintegration rate of FDs can be regulated by modification of the film base with additives.


FDs prepared with Alg-Na are considered useful for oral drug administration. In the present study, a simple colorimetric as- say was developed to quantify Alg-Na. This method was sub- sequently used to generate disintegration profiles for various FDs, which demonstrated that FDs prepared with Alg-Na disin- tegrate in limited solutions and that initial disintegration rates can be regulated by modification of the FD with additives. Fur- ther studies will assess the relationship between FD erosion and drug release from the form using the newly developed col- orimetric method of quantification.

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