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Journal of Chemistry
Volume 2013 (2013), Article ID 576370, 9 pages
http://dx.doi.org/10.1155/2013/576370
Research Article

Modified Chitosan-Clay Nanocomposite as a Drug Delivery System Intercalation and In Vitro Release of Ibuprofen

1Biology Department, King Khalid University, Saudi Arabia
2Department of Chemistry, Polymer Research Group, Faculty of Science, Tanta University, Egypt

Received 3 April 2013; Accepted 6 September 2013

Academic Editor: Ali Nokhodchi

Copyright © 2013 Rehab Abdeen and Nehal Salahuddin. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The present paper focused on the intercalation of ibuprofen into sodium montmorillonite, chitosan, and chitosan montmorillonite nanocomposites as a sustained release drug carrier. The compounds were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). The basal spacing of montmorillonite increased from 9.6 Å to 19.6 Å indicating the intercalation of modified chitosan and ibuprofen between lamellar layers. UV spectroscopy was employed to monitor the in vitro drug release processes in both pH 5.4 and 7.8 solutions. The results revealed that ibuprofen was released from MMT, CS, and Mod-CS/MMT steadily and was pH dependent.

1. Introduction

The need for safe, therapeutically effective, and patient compliant drug delivery systems continuously leads researchers to design novel tools and strategies. Clay minerals play a very crucial role in modulating drug delivery [1].

Ibuprofen (2-(p-isobutylphenyl) propionic acid) is a well-known hydrophobic oral nonsteroidal anti-inflammatory drug (NSAID) [2]. Ibyprofen has analgesic (pain-relieving) and antipyretic (fever-reducing) properties. It is particularly known for its use in pain relief from arthritis. However, it has a wide spectrum of gastrointestinal side effects ranging from mild dyspepsia to gastric bleeding. The gastric irritation is mainly due to the free carboxylic acid group in the chemical formula [3]. Due to its short plasma half life of 1–3 h following oral dosing and the gastric irritation, ibuprofen is an ideal candidate for preparing prolonged or controlled release drug products [311]. Since the property of reswelling is susceptible to the environmental pH, the incorporation of acid-sensitive drugs into the beads protects them from the gastric juice [12]. Therefore, drug-loaded alginate beads might provide these advantages for NSAIDs such as ibuprofen, which lead to gastric irritation. The formulation of ibuprofen as a controlled release dosage form of beads seems to be an important approach to overcome the potential problems in the gastrointestinal (GI) tract so as to achieve a reduction of the NSAID’s adverse effects [13, 14].

Chitosan is a biocompatible, biodegradable, nontoxic, linear copolymer polysaccharide consisting of β (1-4)-linked 2-amino-2-deoxy-D-glucose (D-glucosamine) and 2-acetamido-2-deoxy-D-glucose (N-acetyl-D-glucosamine) units and has the structural similarity to cellulose (made up of β (1-4)-linked D-glucose units) [15]. Chitosan is the N-deacetylated derivative of chitin, although this N-deacetylation is never complete, which has a number of exposed amino groups making it polycationic polysaccharide. Depending on the amount/extent of deacetylation, different grades of chitosan are found. Due to its gel-forming property, it has been used in the designing of drug delivery system [15].

Montmorillonite (MMT) clay is one of the smectite groups, composed of silica tetrahedral sheets layered between alumina octahedral sheets. The imperfection of the crystal lattice and the isomorphous substitution induce a net negative charge that leads to the adsorption of alkaline earthmetal ions in the interlayer space. Such imperfection is responsible for the activity and exchange reactions with organic compounds. MMT also contains dangling hydroxyl end groups on the surfaces [16]. MMT has large specific surface area and exhibits good adsorption ability, cation exchange capacity, standout adhesive ability, and drug-carrying capability. Thus, MMT is a common ingredient as both the excipient and active substance in pharmaceutical products [17]. The intercalation of organic species into layered inorganic solids provides a useful and convenient route to prepare organic-inorganic hybrids that contain properties of both the inorganic host and organic guest in a single material [18].

In recent years, smectite clays intercalated by drug molecules have attracted great interest from researchers since they exhibit novel physical and chemical properties [19].

In the present work, we successfully intercalate chitosan into layered silicate to prepare nanocomposite drug carrier that would alleviate some of the disadvantages of using clay. The cationic exchange mechanism involves interaction between Ph3P+ groups of modified CS and negatively charged sites in the clay structure. The resulting materials were characterized by IR, XRD, and TEM. The release rate of ibuprofen from the nanocomposites, Na-MMT, and CS was investigated.

2. Characterization of Organoclay/Drug

2.1. XRD Spectra

The XRD patterns of Ibuprofen, Na-MMT, chitosan, mod-CS/MMT (1 : 1), mod-CS/MMT (1 : 1)/ibuprofen, Na-MMT/ibuprofen, and CS/ibuprofen are shown in Figures 1(a)1(c). Pure ibuprofen exhibits typical reflection at , , and . Na-MMT exhibits typical reflection at corresponding to is 9.6  . CS shows the characteristic crystalline peaks around , 20, and . The peaks around 10 and 20 are related to crystal (1) and crystal (2) in chitosan, respectively. The unit cell of crystal (1) is characterized by , ,  Å, and and it is larger than that of crystal (2) whose unit cell is characterized by , ,  Å, and [2022]. After modification of chitosan, mod-CS showed two sharp peaks at and and a broad peak at 22°. This indicates that mod-CS formed a new crystallite. In mod-CS/MMT (1 : 1) the peak of the clay has disappeared and a broad peak at appeared corresponding to an increase in -spacing. This increase in basal spacing is attributable to the intercalation of polymer chain inside the clay layers. The low peak intensity in the nanocomposite is because of the decrease in the coherent layer scattering.

fig1
Figure 1: X-ray diffraction pattern of (a) Na-MMT, CS, mod-CS, mod-CS/MMT (1 : 1), ibuprofen, mod-CS/MMT—ibuprofen on cold. (b) Na-MMT, CS, mod-CS, and mod-CS/MMT (1 : 1), Ibuprofen, mod-CS/MMT—ibuprofen on hot. (c) ibuprofen, CS, and CS/ibuprofen after release at pH = 5.4 and 7.8.

The XRD of the nanocomposite formed after loading ibuprofen on Na-MMT, chitosan, mod-CS/MMT (1 : 1) showed peaks characteristic for both ibuprofen and support. the intensity of the (001) reflection the intercalation of ibuprofen.

2.2. TEM Result

TEM of a thin film of mod-CS/MMT (1 : 1) ibuprofen (solvent method on cold) and mod-CS/MMT (1 : 1) ibuprofen (solvent method on cold) are shown in Figures 2(a) and 2(b), respectively. Figure 2(a) shows that silicate layers remain in exfoliated structure in mod-CS/MMT (1 : 1) ibuprofen on cold. However, it is observed that few layers remain in intercalated structure in mod-CS/MMT (1 : 1) ibuprofen prepared by solvent method on hot. This is consistent with the conclusion drawn from XRD.

fig2
Figure 2: TEM micrographs of (a) M. chitosan-MMT/ibuprofen (1 : 1) on cold and (b) M. chitosan-MMT/ibuprofen (1 : 1) on hot.
2.3. IR Spectrum

The IR spectrum in Figures 3(a)3(c) of ibuprofen the strong carbonyl absorption band at 1721 cm−1, the bands between 3700 and 3100 cm−1 are related to the aromatic ring. The bands between 3000 and 2800 cm−1 are the alkyl stretching vibration of ibuprofen. For Na-MMT, the characteristic absorption band at 3632 cm−1 [ (O–H)] is assigned to the stretching vibration of Al–OH. The symmetrical Si–O–Si band [ (Si–O–Si)] is characterized by the stretching band at 1160 cm−1. Other characteristic adsorption bands of pure clay mineral are at 914 [ (Al–Al–O)], 886 [ (Al–Fe–O)], and 848 cm−1 [ (Al–Mg–O)]. IR spectrum of CS shows a broad band at 3462 cm−1 corresponding to the stretching vibration of N–H. The peaks at 2937 and 2857 cm−1 are typical of C–H stretching vibration, while peaks at 1660, 1551, and 1309 cm−1 are characteristic of amides I, II, and III, respectively. The sharp peaks at 1442 and 1374 cm−1 are assigned to the CH3 symmetrical deformation mode and 1036 cm−1 is indicative of C–O stretching vibration [ν (C–O–C)]. The small peak at 798 cm−1 corresponds to wagging of the saccharide structure of CS. The IR spectrum of mod-CS shows bands at 1740 and 1615 cm−1 corresponding to C=O stretching vibration and NH–, respectively. The bands at 1421 (m), 1164 (m), and 1063 cm−1 (w) correspond to phosphonium salt attached to Ph group. Not all characteristic bands belonging to MMT and ibuprofen appear in the spectrum of ibuprofen/MMT; several new absorption bands at 2390 and 1558 cm−1 are also recognized. This also indicates that ibuprofen interacts strongly with the montmorillonite layers.

fig3
Figure 3: IR spectra in the region 4000–400 cm−1 of (a). Na-MMT, CS, mod-CS, mod-CS/MMT (1 : 1), ibuprofen, mod-CS/MMT—ibuprofen on cold. (b) Na-MMT, CS, mod-CS, mod-CS/MMT (1 : 1), Ibuprofen, mod-CS/MMT—Ibuprofen on hot. (c). Ibuprofen, CS, CS/ibuprofen and after release at pH = 5.4 and 7.8.
2.4. Thermal Stability

Montmorillonite shows two distinct steps. The first one of about 7% at 48–120°C is due to the free water evaporation. The second weight loss at 550–720°C is due to the structural dehydration [23]. In TGA curves (Figure 4) of mod-CS, mod-CS-MMT, and mod-CS-MMT ibuprofen, weight loss at 100 to 400°C corresponds to the decomposition of ibuprofen. Other weight losses are the same as those of MMT. The TGA curve of mod-CS-MMT ibuprofen on cold with an initial concentration of 0.3 mmol/g (drug-loaded amount 36.09 wt.%) while mod-CS-MMT Ibuprofen on hot with the same initial concentration (drug-loaded amount 15.12 wt.%) shows a sharp weight loss at around 471°C due to the decomposition of intercalated ibuprofen.

fig4
Figure 4: TGA of mod-CS, mod-CS/MMT (1 : 1), and mod-CS/MMT—ibuprofen prepared by solvent method (a) on cold and (b) on hot.
2.5. Drug Release Response

The drug release response from mod-CS/MMT nanocomposite in buffer solution with two different pH values, 5.4 as example for stomach pH and 7.4 for colon, was studied at the physiological temperature of 37°C (Figures 5(a)5(c)). The swellability of the carrier in the buffer solution The swelling ratio for mod-CS/MMT (1 : 1) in table indicate that the great swellability the greater the release is shown in Table 1.

tab1
Table 1: Swellability of the carriers in different pH buffer solutions. Swellability wt%.
fig5
Figure 5: In vitro ibuprofen release in phosphate buffer solution at (a) pH = 7.8, and (b) pH = 5.4 at 37°C. ((a)-(b)) Mod-CS/MMT—ibuprofen (1 : 1) by different method. (c) CS/ibuprofen.

Ibuprofen, a relatively weak acidic drug, was intercalated into mod-CS/MMT and CS. The in vitro release experiment showed that the release of ibuprofen from mod-CS/MMT ibuprofen and CS ibuprofen was affected by the pH value of the dispersion. The release rate in simulated intestinal fluid (pH = 7.4) was noticeably higher than that in simulated gastric (pH = 5.4). The release of ibuprofen from ibuprofen/MMT was affected by the pH value of the dispersion. The release rate in simulated intestinal fluid (pH = 7.4) was noticeably higher than that in simulated gastric (pH = 1.2). The results indicate that MMT can be used as the sustained-release carrier of IBU in oral administration. The results indicate that mod-CS/MMT can be used as the sustained-release carrier of ibuprofen in oral administration which allows minimum effective dose to be delivered locally and prolongs the duration of drug activity, thus improving the therapeutic efficacy and decreasing side effects by minimizing the transportation of the drug to the systemic circulation against inflammation [24] which minimizes the adverse effect of oral administration and avoids contact between the drug and the gastric mucosa [25].

2.6. Characterization of the Support after Release

The drug carrier nanocomposites were further subjected to examination by IR and XRD after drug release. The IR spectra of mod-CS/MMT/ibuprofen after release Figure 3 indicates that the peaks characteristic to mod-CS, Ibuprofen disappeared and bands characteristic to Na-MMT is observed. These observations suggest that the drug release occurred by degradation of the nanocomposites. XRD of samples after release has no visible diffraction peak within the measured range. The peak at appearing in all the diffraction patterns corresponding to the crystallographic plans (110) and (020) of the clay layers disappeared after release and an amorphous structure is obtained as in Figure 6 especially after immersion of the carrier at pH 7.8.

576370.fig.006
Figure 6: X-ray diffraction pattern of mod-CS, mod-CS/MMT (1 : 1), ibuprofen, and mod-CS/MMT—ibuprofen on cold after release.

3. Experimental

3.1. Materials

Chitosan from a shell of Chionoecetes opilio has 70% degree of deacetylation with average molecular weight of 400.000 and was purchased from Aldrich chemicals. Ibuprofen, triphenyl phosphine, and chloroacetyl chloride were provided from Aldrich chemicals. The clay mineral used in this study was sodium montmorillonite (Colloid BP) from Southern Clay Products Inc. (Gonzales, TX, USA) with cation exchange capacity (CEC) of 114.8 meq/100 g. The structure of CS and ibuprofen is shown in Figure 7.

576370.fig.007
Figure 7: Structure of CS and ibuprofen.
3.2. Chloroacetylation of Chitosan

75.2 mL (99.6 mmol) of pyridine was added to 1 g of chitosan. The mixture was cooled in an ice-salt bath and chloroacetyl chloride (7.965 mL, 99.6 mmol) was added dropwise with stirring. The reaction mixture was stirred overnight at 40°C for three days. The chloroacetylated chitosan was precipitated by addition of diluted HCl (1 N), filtered off, and washed with distilled water several times and the product was dried to give 0.95 g.

3.3. Synthesis of Triphenyl-Chloro Acetylated Chitosan Phosphonium Salt (mod-CS)

2 g of chloroacetylated chitosan was dissolved in 20 mL of dry DMF followed by addition of 5.33 g (20 mmol) of triphenyl phosphine. The reaction mixture was stirred for four days at 80°C in an oil bath. The product was filtered off and washed with DMF to give 1.5 g.

3.4. Preparation of Triphenyl-(Chloroacetylated Chitosan) Phosphonium Salt-Montmorillonite Intercalates (mod-CS/MMT)

1 g of Na-MMT was swelled in 30 mL of water by stirring overnight at 40°C. After swelling of clay, 1 g mod-CS dissolved in 10 mL DMF was added and stirred for 24 hr. The product (mod-CS/MMT (1 : 1)) was filtered, washed several times with water, and collected by a filter press, and dried at 80°C in vacuum oven for 10 hr.

3.5. Loading of Ibuprofen by Solvent Method
3.5.1. Loading of Ibuprofen on Modified Chitosan

0.3 g ibuprofen in 10 mL DMF was added to 0.5 g of mod-CS/MMT (1 : 1) and was swelled in 30 mL DMF with stirring for 24 hr. The product was filtered, washed several times with water, collected by a filter press, and dried at 80°C in vacuum oven for 10 hr. The same procedure was done by applying temperature (80°C) to improve the absorption between the drug and Mod-CS.

3.5.2. Loading of Ibuprofen on Na-MMT

1 g of Na-MMT was swelled for 48 hrs at 40°C in DMF. Then, 5 g of ibuprofen dissolved in DMF was added. The reaction mixture was further stirred for another 24 h at 40°C. The product (Na-MMT/ibuprofen) was collected by filtration and washed with ethanol (three times) to remove the excess of unloaded drug and dried under vacuum at 40°C overnight.

3.5.3. Loading of Ibuprofen on CS

1 g of CS was dissolved in 2% acetic acid. Then, 0.3 g of ibuprofen dissolved in 10 mL DMF was added. The reaction mixture was further stirred for another 24 h at 40°C. The product (CS-ibuprofen) was collected by filtration and washed with ethanol (three times) to remove the excess of unloaded drug and dried under vacuum at 40°C overnight.

3.6. Drug Release
3.6.1. Preparation of Phosphate Buffer (PB) Solution

Phosphate buffer solution (PB) was prepared by dissolving sodium phosphate dibasic (21.7 g) and potassium phosphate monobasic (2.6 g) in 1 L deionized water and the pH was adjusted to 5.4 and 7.8 using 0.1 N sodium hydroxide or 0.1 N hydrochloric acid, respectively.

3.6.2. In Vitro Drug Release

The drug release responses of CS, Na-MMT, and mod-CS/MMT drug carriers were studied at the physiological temperature of °C and pH 5.4 and 7.8. The pH values of 5.4 and 7.8 were selected to closely mimic the pH gradient from the stomach to the intestine. In each experiment, 10 mg of the drug carriers was submerged in 50 mL of buffer solution. An aliquot of the release medium (3 mL) was withdrawn at regular time for 72 h. The content of ibuprofen in buffer solution was quantified using UV-VIS spectrophotometry at  nm. After each measurement, the withdrawn was put back into the system. Given that the measurement time was very short, while the predetermined drug release time interval was significantly larger, the influence of the returned medium on drug release during the measurement time was insignificant. All the drug release experiments were repeated three times and the average was calculated.

3.6.3. Swelling Measurements

The samples were weighed in a sintered glass, , and immersed in buffer solution (pH = 5.4 and 7.8) at 37°C. The samples were centrifuged to remove the surface buffer solution and reweighed immediately, . The process was repeated at the same time intervals used in the measurement of in vitro drug release. The swellability percentage was calculated using the formula .

4. Conclusions

Modified chitosan/MMT nanocomposite was successfully synthesized. It entails two steps: modification of chitosan by chloroacetylation and formation of phosphonium salt, which is then chemically intercalated to MMT through an ion exchange process. The resulting nanocomposite was used as support for ibuprofen. The release of ibuprofen from the support is affected by the drug loading capacity, the percentage of CS in the nanocomposite, the pH of the medium, and the morphology of the nanocomposites, which is affected by the method of preparation. The drug loaded chitosan and mod-chitosan can be of immense importance in the drug delivery through the oral rout as well as the other routes as sustained and controlled release dosage forms. The desired effects in the drug release and the therapeutic value can be obtained by intercalated ibuprofen at different temperature. As chitosan is nontoxic, biodegradable, and biocompatible, it can be used for the delivery of the ibuprofen in controlled and sustained release manners.

Acknowledgment

The authors wish to thank King Khalid University for supporting this research.

References

  1. G. V. Joshi, B. D. Kevadiya, H. A. Patel, H. C. Bajaj, and R. V. Jasra, “Montmorillonite as a drug delivery system: intercalation and in vitro release of timolol maleate,” International Journal of Pharmaceutics, vol. 374, no. 1-2, pp. 53–57, 2009. View at Publisher · View at Google Scholar · View at Scopus
  2. C. G. Wilson, N. Washington, J. L. Greaves et al., “Bimodal release of ibuprofen in a sustained-release formulation: a scintigraphic and pharmacokinetic open study in healthy volunteers under different conditions of food intake,” International Journal of Pharmaceutics, vol. 50, no. 2, pp. 155–161, 1989. View at Scopus
  3. A. G. G. Gilman, L. S. Goodman, T. W. Rall, and F. Murad, The Pharmacological Basis of Therapeutics, Macmillan, New York, NY, USA, 7th edition, 1985.
  4. W. Diamantis, J. Melton, R. D. Sofia, and V. B. Ciofalo, “Comparative gastric ulcerogenic effects of meseclazone, 5-chlorosalicylic acid and other nonsteroidal anti-inflammatory drugs following acute and repeated oral administration to rats,” Toxicology and Applied Pharmacology, vol. 52, no. 3, pp. 454–461, 1980. View at Scopus
  5. R. Bodmeier and H. Chen, “Preparation and characterization of microspheres containing the anti-inflammatory agents, indomethacin, ibuprofen, and ketoprofen,” Journal of Controlled Release, vol. 10, no. 2, pp. 167–175, 1989. View at Scopus
  6. J. A. Bakan, T. C. Powell, and P. S. Szotac, “Recent advances imicroencapsulation of drugs to obtain reduced gastric irritation,” in Microcapsules and Nanocapsules in Medicine and Pharmacy, M. Donbrow, Ed., pp. 183–192, CRC Press, Boca Raton, Fla, USA, 1992.
  7. E. Leo, F. Forni, and M. T. Bernabei, “Surface drug removal from ibuprofen-loaded PLA microspheres,” International Journal of Pharmaceutics, vol. 196, no. 1, pp. 1–9, 2000. View at Publisher · View at Google Scholar · View at Scopus
  8. O. Sipahigil and B. Dortunç, “Preparation and in vitro evaluation of verapamil HCl and ibuprofen containing carrageenan beads,” International Journal of Pharmaceutics, vol. 228, no. 1-2, pp. 119–128, 2001. View at Publisher · View at Google Scholar · View at Scopus
  9. B. C. Arica, S. alis, H. S. Kas, and A. A. Hincal, “Chitosan microspheres of ibuprofen: evaluation and in vitro characterization,” in Chitosan in Pharmacy and Chemistry, R. A. A. Muzzarelli and C. Muzzarelli, Eds., pp. 71–76, Atec, Italy, 2002.
  10. S. L. De Guevara-Fernández, C. V. Ragel, and M. Vallet-Regí, “Bioactive glass-polymer materials for controlled release of ibuprofen,” Biomaterials, vol. 24, no. 22, pp. 4037–4043, 2003. View at Publisher · View at Google Scholar · View at Scopus
  11. M. Saravanan, K. Bhaskar, G. Srinivasa Rao, and M. D. Dhanaraju, “Ibuprofen-loaded ethylcellulose/polystyrene microspheres: an approach to get prolonged drug release with reduced burst effect and low ethylcellulose content,” Journal of Microencapsulation, vol. 20, no. 3, pp. 289–302, 2003. View at Publisher · View at Google Scholar · View at Scopus
  12. N. Segi, T. Yotsuyanagi, and K. Ikeda, “Interaction of calcium-induced gelation of alginic acid and pH-sensitive reswelling of dried gels,” Chemical Pharmaceutical Bulletin, vol. 37, pp. 3092–3095, 1989.
  13. S. Çalis, B. Arica, P. Atilla, T. Durlu, N. Çakar, and A. A. Hincal, “Effect of ibuprofen and ibuprofen incorporated biodegradable alginate beads on gastric and duodenal mucosa (a comparative histological study),” in Proceedings of the 30th Annual Meeting of Controlled Release Society, pp. 495–501, Glasgow, UK, July, 2003.
  14. B. J. Lee, J. H. Cui, T. W. Kim, M. Y. Heo, and C. K. Kim, “Biphasic release characteristics of dual drug-loaded alginate beads,” Archives of Pharmacal Research, vol. 21, no. 6, pp. 645–650, 1998. View at Scopus
  15. T. W. Wong, L. W. Chan, S. B. Kho, and P. W. Sia Heng, “Design of controlled-release solid dosage forms of alginate and chitosan using microwave,” Journal of Controlled Release, vol. 84, no. 3, pp. 99–114, 2002. View at Publisher · View at Google Scholar · View at Scopus
  16. M. Kong, X. G. Chen, K. Xing, and H. J. Park, “Antimicrobial properties of chitosan and mode of action: a state of the art review,” International Journal of Food Microbiology, vol. 144, no. 1, pp. 51–63, 2010. View at Publisher · View at Google Scholar · View at Scopus
  17. H. Khalil, D. Mahajan, and M. Rafailovich, “Polymer-montmorillonite clay nanocomposites. Part 1: complexation of montmorillonite clay with a vinyl monomer,” Polymer International, vol. 54, no. 2, pp. 423–427, 2005. View at Publisher · View at Google Scholar · View at Scopus
  18. X. Wang, Y. Du, and J. Luo, “Biopolymer/montmorillonite nanocomposite: preparation, drug-controlled release property and cytotoxicity,” Nanotechnology, vol. 19, no. 6, Article ID 065707, 2008. View at Publisher · View at Google Scholar · View at Scopus
  19. L. Mohanambe and S. Vasudevan, “Anionic clays containing anti-inflammatory drug molecules: comparison of molecular dynamics simulation and measurements,” Journal of Physical Chemistry B, vol. 109, no. 32, pp. 15651–15658, 2005. View at Publisher · View at Google Scholar · View at Scopus
  20. J. P. Zheng, L. Luan, H. Y. Wang, L. F. Xi, and K. D. Yao, “Study on ibuprofen/montmorillonite intercalationcomposites as drug release system,” Applied Clay Science, vol. 36, no. 4, pp. 297–301, 2007. View at Publisher · View at Google Scholar · View at Scopus
  21. R. J. Samuels, “Solid state characterization of the structure of chitosan film,” Polymer Science, vol. 19, no. 7, pp. 1081–1105, 1981. View at Publisher · View at Google Scholar
  22. K. Ogawa, T. Yui, and M. Miya, “Dependence on the preparation procedure of the polymorphism and crystallinity of chitosan membranes,” Bioscience, Biotechnology, and Biochemistry, vol. 56, no. 6, pp. 858–862, 1992.
  23. C. S. Hutchison, Laboratory Hand Book of Pertrographic Techniques, Wiley, New York, NY, USA, 1974.
  24. K. Kofuji, H. Akamine, C. J. Qian et al., “Therapeutic efficacy of sustained drug release from chitosan gel on local inflammation,” International Journal of Pharmaceutics, vol. 272, no. 1-2, pp. 65–78, 2004. View at Publisher · View at Google Scholar · View at Scopus
  25. M. L. González-Rodríguez, M. A. Holgado, C. Sánchez-Lafuente, A. M. Rabasco, and A. Fini, “Alginate/chitosan particulate systems for sodium diclofenac release,” International Journal of Pharmaceutics, vol. 232, no. 1-2, pp. 225–234, 2002. View at Publisher · View at Google Scholar · View at Scopus